CN110791247A - Solar cell backboard adhesive resin and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of organic synthesis and relates to a technology of polymer polymerization, in particular to a solar cell back sheet adhesive resin and a preparation method thereof. The solar cell back sheet adhesive resin is a solvent-based two-component adhesive resin, which is composed of epoxy chain-extended high-molecular-weight polyester with hydroxyl groups as component A, and polyisocyanate as component B; wherein the components A and component B are mixed in a mass ratio of 3:4‑20:1. The adhesive prepared by the invention has good initial peeling strength for PET film, PVF film and EVA film, good weather resistance, and after 3000 hours under double 85 conditions, the peeling strength is still greater than 6N/cm (180° peeling). It can fully meet the application performance requirements of solar back sheet adhesive.

Description

A kind of solar cell back sheet adhesive resin and preparation method thereof

technical field

The invention belongs to the field of organic synthesis and relates to a technology of polymer polymerization, in particular to a solar cell back sheet adhesive resin and a preparation method thereof.

Background technique

The solar cell backsheet mostly adopts a three-layer film structure, and each layer is bonded with an adhesive. The adhesive is directly related to the performance and service life of the backsheet.

At present, solar cells are mostly made of TPT and TPE backsheets. The higher the fluorine content of the outer film, the better the weather resistance, but the adhesion performance also deteriorates, resulting in problems such as low interlayer peeling force. The main manufacturers of backplane adhesives are foreign companies. A few domestic companies have low-end adhesive production lines, and the production technology is backward, and the product quality is significantly different from that of foreign products. Therefore, some companies use the coating method to produce backplanes. Since the raw materials used in the coated backsheet are imported from abroad, the price is high and the supply is unstable, which is severely restricted by foreign fluorine chemical companies. my country's photovoltaic industry is mainly concentrated in the Yangtze River, Pearl River Delta and other regions. There are very few enterprises involved in the photovoltaic industry in our province, and the existing production technology foundation of adhesives for solar panel backsheets is weak, and there is a big gap with the technical level of the photovoltaic industry. In order to change the unfavorable current situation such as weak application performance and low market share of domestic solar cell back sheet adhesives, it is very necessary to carry out the research on this project. Through the development of the new structure and composition of the adhesive, the application performance and service life of the product are improved, so as to realize the localization of the preparation process of the high-quality backplane adhesive.

CN102250577A discloses a two-component polyurethane solar back sheet adhesive, the main agent is obtained by polycondensation of terephthalic acid, phthalic acid, 1,6-hexanediol, cyclohexanedimethanol and ethylene glycol, The curing agent adopts one or more of HDI trimer, IPDI trimer, TDI-HDI mixed trimer, hydrogenated TDI and hydrogenated MDI. The compounded adhesive has higher Tg, and can compound the solar back sheet of fluorine-containing material.

CN104017531A discloses a hydrolysis-resistant photovoltaic backplane adhesive and a preparation method thereof. Component A is a new type of polyester polyol and added light stabilizer, etc., and component B is a diisocyanate curing agent. Under the premise of retaining good mechanical properties, it improves the adhesiveness of polyurethane adhesives prepared by using traditional polyester polyols. At the same time, a certain proportion of light stabilizer is added to the adhesive, which improves the hydrolysis resistance and aging resistance of the polyurethane adhesive used in photovoltaic back sheets to a certain extent.

CN106244081A discloses an adhesive composition for solar cell back sheets and a preparation method thereof. The composition is composed of a prepolymer component and a curing agent component, wherein the prepolymer component includes a fluorine-modified resin , polyester resin, antioxidant, ultraviolet light absorber, anti-hydrolysis agent and ethyl acetate; curing agent component is hexamethylene diisocyanate trimer. The components are physically mixed in a certain proportion to obtain an adhesive used as a solar back sheet adhesive, which makes the double "85" test more than 3000 hours.

It can be seen from the above documents that the existing solar back sheet adhesives are more commonly used two-component polyurethane adhesives, namely polyester resins and polyisocyanates. Polyester resins are mostly linear long-chain polymers. After sizing, the terminal hydroxyl groups of polyester react with isocyanate groups in the trimer of HDI, TDI and MDI to cure and bond to the backing material. Because the linear long-chain polyester only has terminal hydroxyl groups, there are few anchor points with the polyisocyanate curing agent and the backing material, and the ester bond of the polyester can undergo hydrolysis reaction in a long-term atmospheric environment, resulting in poor weather resistance of the adhesive. Furthermore, it is more necessary to obtain adhesives with new structures under different components, so as to improve the application performance and service life of products.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a solar cell back sheet adhesive resin and a preparation method thereof.

To achieve the above object, the present invention adopts the technical scheme as follows:

A solar cell back sheet adhesive resin, the solar cell back sheet adhesive resin is a solvent-type two-component adhesive resin, and the epoxy chain-extended high-molecular-weight polyester with a hydroxyl group is used as the component A, Polyisocyanate is used as component B; wherein, component A and component B are mixed in a mass ratio of 3:4-20:1.

The epoxy chain-extended macromolecule polyester with hydroxyl group is a carboxyl-terminated polyester with a Mn of 5000-20000 and an epoxy chain extender through chain extension and viscosity increase to obtain a hydroxyl group with a molecular weight of Mn of 40000-120000. The epoxy chain-extended macromolecule polyester; wherein, the added amount of the epoxy chain extender is 1-20% of the mass of the carboxyl-terminated polyester.

The epoxy chain extender is 1,4-cyclohexanedimethanol glycidyl ether, 1,4-butanediol diglycidyl ether, bisphenol A-diglycidyl ether, glycidyl ether, isocyanuric acid Triglycidyl ester, N,N,N',N'-tetraglycidyl ester-4,4'diaminodiphenylmethane, bisphenol A polyglycidyl ether, bisphenol A epoxy resin, bisphenol F One or both of epoxy resins.

The epoxy chain-extended macromolecule polyester with hydroxyl group is esterified by mixing aromatic dibasic acid, long-chain aliphatic dibasic acid, dihydric alcohol and trihydric alcohol under normal pressure and 240-270°C. Then, the esterified product is polycondensed through a polycondensation catalyst under high temperature and high vacuum conditions to obtain a carboxyl-terminated polyester with Mn of 5000-20000; High molecular polyester with Mn of 40000-120000.

The carboxyl-terminated polyester is obtained by mixing aliphatic diol, aliphatic dibasic acid and aromatic dibasic acid, stirring under nitrogen protection, and heating up to 240-270°C within 1 hour for esterification reaction , heat preservation reaction for 2-3h, until the condenser anhydrous distillation, then add polycondensation catalyst, continue to heat up to 260-280℃, 100-40Pa absolute pressure for polycondensation reaction for 1-4h, obtain the target molecular weight 5000～20000 carboxyl end capping Polyester; add the polyester and epoxy chain extender into the extruder, extend the chain and increase the viscosity until the molecular weight reaches 40000-120000. Wherein, the molar ratio of aromatic dibasic acid, aliphatic dibasic alcohol, and aliphatic dibasic acid is 1-6:1-6:1.

The aliphatic diols are two or three kinds of C ₂ -C ₁₂ straight-chain or branched-chain diols; specifically, ethylene glycol, 1.2-propanediol, 1.3-propanediol, butanediol, new Pentanediol, 3-methyl-1,5-pentanediol, 1.6-hexanediol, 1.2-heptanediol, 1.7-heptanediol, 1.2-octanediol, 1.8-octanediol, 1.2-nonanediol One, two or three of diol, 1.9-nonanediol, 1.2-decanediol, 1.10-decanediol, 1,11-undecanediol, 1,12-dodecanediol . Preferred are ethylene glycol, 1.2-propanediol, butanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1.6-hexanediol, 1.7-heptanediol, 1.8-octanediol, 1.10 - One or both of decanediol and 1,12-dodecanediol.

Aliphatic dibasic acid is C ₃ -C ₁₈ aliphatic dibasic acid; aromatic dibasic acid is phthalic acid, terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid or naphthalene-1 , two or three kinds of 4-dicarboxylic acid. Specifically, it can be malonic acid, succinic acid, adipic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid , one, two or three kinds of tridecanedioic acid, tetradecanedioic acid, hexadecanedioic acid and octadecanedioic acid. One or both of glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid are preferred.

The aliphatic polyol used for preparing the carboxyl-terminated polyester is one or two of glycerol, trimethylolpropane and pentaerythritol.

The above-mentioned aromatic dibasic acid for preparing the carboxyl-terminated polyester is phthalic acid or naphthalene diacid. Specifically, it may be two or three kinds of phthalic acid, terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid or naphthalene-1,4-dicarboxylic acid.

The polyisocyanate is an adduct of TDI, pentaerythritol and trimethylolpropane.

An application of adhesive resin for solar battery back sheet, the adhesive resin is used as adhesive resin in solar back sheet adhesive.

The epoxy chain-extended polymer polyester with hydroxyl groups prepared above is dissolved in a solvent, and the solvent can be ethyl acetate, methyl ethyl ketone, or toluene. A solution with a solid content of 30% is obtained as component A.

For the solvent-based two-component adhesive resin for solar back sheets, the polyisocyanate is an adduct of TDI, pentaerythritol and trimethylolpropane. The obtained adduct is dissolved in ethyl acetate or butanone to obtain component B with a solid content of 70-75%.

In the application of the solvent-based two-component adhesive resin for solar back sheets, the adhesive resin components A and B are mixed uniformly in proportion, and then the catalyst, ultraviolet absorber, light stabilizer, Oxygen agent, after mixing uniformly, the solar cell back sheet adhesive is obtained.

The adhesive resin and the catalyst, the ultraviolet absorber, the light stabilizer and the antioxidant are uniformly mixed to obtain the solar cell back sheet adhesive.

A solar cell back sheet, the solar back sheet adhesive of the adhesive resin is coated on the PET layer of the back sheet support layer, dried at 70-100 DEG C for 3 minutes, and the obtained adhesive film and the back sheet support layer PVF The layer is hot-pressed and compounded at a temperature of 70-90° C. and a pressure of 0.5 MPa, and aged at 60° C. for 72 hours to obtain a solar cell back sheet.

The advantages of the present invention:

The adhesive resin for the solar cell back sheet of the invention is obtained by compounding the epoxy chain-extended polyester polyol and the polyisocyanate curing agent in a certain proportion respectively. The use of aromatic dibasic acid to improve the adhesive performance, long carbon chain aliphatic dibasic acid to improve the flexibility of the adhesive, and adjusting the ratio of each monomer, the prepared polyester can improve the toughening, hydrolysis resistance, and resistance of the adhesive. High temperature and high bonding strength performance; after polyester epoxy chain extension, the obtained component A has the characteristics of high molecular weight and high hydroxyl content. After compounding it with component B into an adhesive, the polyester adhesion material is realized. The advantage of many bonding anchor points; at the same time, branched diols are added during the molecular synthesis process. The combination of the two gives the adhesive excellent resistance to "Double 85" and still has high glass strength after 3000 hours.

Detailed ways

The present invention is further described in detail through the following examples. But the present invention is by no means limited to this.

The adhesive resin for the solar cell back sheet of the present invention, component A is epoxy chain-extended polyester, and component B is polyisocyanate. As an adhesive resin for PVF and PET, it is used as a bonding material between solar back sheets. The molecule of component A contains polyhydroxy active groups and the molecular weight is 40,000-120,000. Component B contains TDI polymers or adducts of 3-5 isocyanate groups. The preparation method of the adhesive composition is as follows: aliphatic dihydric alcohol, long-chain aliphatic dibasic acid and aromatic dibasic acid are esterified in an inert gas under normal pressure; and then a catalyst is added at high temperature and high temperature. The polycondensation reaction is carried out under vacuum conditions, and the polymer obtained after chain extension of the obtained carboxyl-terminated polyester diol with an epoxy compound is added to a solvent to dissolve, thereby obtaining component A. Component B is TDI polymer or adduct with pentaerythritol and trimethylolpropane. The adhesive prepared by the invention has good initial peeling strength for PET film, PVF film and EVA film, good weather resistance, and after 3000 hours under double 85 conditions, the peeling strength is still greater than 6N/cm (180° peeling). It can fully meet the application performance requirements of solar back sheet adhesive.

Example 1

Add 580.5 grams of terephthalic acid, 720.6 grams of isophthalic acid, 317.0 grams of sebacic acid, 496 grams of ethylene glycol, 128.1 grams of 1,6-hexanediol, 6.5 grams of trimethylolpropane to the 3L polymerization reactor , 1.0 g of antimony acetate, heat up to 240 ° C in about one hour, adjust the water distillation rate generated, keep the pressure in the kettle at 0.25-0.3 MPa, and the water distillation column top temperature is lower than 120 ° C, until the amount of distilled water reaches 170 grams to complete the esterification reaction. Turn on the vacuum system, adjust the vacuum degree in the kettle to about 80Pa for about half an hour, while the temperature rises to 275°C, start the polycondensation reaction, react under this condition for 2.5 hours, and discharge the material to obtain the carboxyl-terminated polyester.

The polyester obtained above has a molecular weight of Mn 19800, an acid value of 5.36 mgKOH/g, and a hydroxyl value of 0.45 mgKOH/g as measured by GPC.

1250 grams of the above-obtained carboxyl-terminated polyester, 183.1 grams of bisphenol A epoxy resin E20, and 0.5 grams of antimony trioxide were added to the extruder, and the temperature was raised to 240 ° C, and the extrusion speed was controlled to be 10 g/min to obtain Granulated product. The acid value is 0.89mgKOH/g, the hydroxyl value is 65.2mgKOH/g, and the molecular weight is Mn78000 by GPC. It was refluxed in ethyl acetate to prepare a hydroxyl-containing epoxy chain-extended polyester with a solid content of 30%.

Example 2

824.0 g of isophthalic acid, 317.0 g of adipic acid, 378.2 g of ethylene glycol, 98.4 g of 3-methyl 1,5-pentanediol, 4.5 g of trimethylolpropane, 1.0 g of trimethylolide were added to the 3L polymerization reactor. Antimony oxide, heat up to 250°C in about one hour, adjust the water distilling speed, keep the pressure in the kettle at 0.25-0.3MPa, and the temperature at the top of the distillation column is lower than 120°C, until the amount of distilled water reaches 90 grams, and the ester is completed. chemical reaction. Turn on the vacuum system, adjust the vacuum degree in the kettle to about 60Pa for about half an hour, while the temperature rises to 280°C, start the polycondensation reaction, react under this condition for 3 hours, and discharge the material to obtain the carboxyl-terminated polyester.

The above-obtained polyester has a molecular weight of Mn 8600, an acid value of 12.80 mgKOH/g, and a hydroxyl value of 0.28 mgKOH/g as measured by GPC.

1200 grams of carboxyl-terminated polyester, 338 grams of 1,4-butanediol diglycidyl ether, 0.5 grams of antimony trioxide were added to the extruder, the temperature was raised to 240 ° C, and the extrusion speed was controlled to 10 g/min. Get a granulated product. Test acid value 0.52mgKOH/g, hydroxyl value 61.1mgKOH/g, GPC test molecular weight Mn105000. It was refluxed in ethyl acetate to prepare a hydroxyl-containing epoxy chain-extended polyester with a solid content of 30%.

Example 3

Add 580.5 grams of phthalic acid, 720.6 grams of isophthalic acid, 217.0 grams of adipic acid, 612.4 grams of 1,2-propanediol, 128.1 grams of 1,4-butanediol, 6.5 grams of trimethylol to a 3L polymerization reactor Propane and 1.0 g of antimony acetate, heat up to 260°C in about one hour, adjust the distillation rate of the generated water, keep the pressure in the kettle at 0.25-0.3MPa, and the temperature at the top of the distillation column is lower than 120°C until the amount of distilled water reaches 165 g to complete the esterification reaction. Turn on the vacuum system, adjust the vacuum degree in the kettle to about 45Pa for about half an hour, while the temperature rises to 275°C, start the polycondensation reaction, react under this condition for 2.5 hours, and discharge the material to obtain the carboxyl-terminated polyester.

The polyester obtained above has a molecular weight of Mn 15200, an acid value of 6.00 mgKOH/g, and a hydroxyl value of 0.38 mgKOH/g as measured by GPC.

1200 grams of carboxyl-terminated polyester, 84 grams of bisphenol A polyglycidyl ether, and 0.5 grams of antimony trioxide were added to the extruder, and the temperature was raised to 240 ° C, and the extrusion speed was controlled to be 10 g/min to obtain pelletized products. . The acid value is 0.47mgKOH/g, the hydroxyl value is 18.2mgKOH/g, and the molecular weight is Mn64000 by GPC. It was refluxed in ethyl acetate to prepare a hydroxyl-containing epoxy chain-extended polyester with a solid content of 30%.

Example 4

880.0 grams of terephthalic acid, 217.0 grams of azelaic acid, 280.4 grams of ethylene glycol, 160.5 grams of neopentyl glycol, 0.8 grams of antimony acetate were added to the 3L polymerization reactor, and the temperature was raised to 260°C in about one hour to adjust the resulting The speed of water distilling, keeping the pressure in the kettle at 0.25-0.3MPa, and the temperature at the top of the distillation column is lower than 120°C, until the amount of distilled water reaches 160 grams, and the esterification reaction is completed. Turn on the vacuum system, adjust the vacuum degree in the kettle to about 45Pa for about half an hour, while the temperature rises to 270°C, start the polycondensation reaction, react under this condition for 2.5 hours, and discharge the material to obtain the carboxyl-terminated polyester.

The above-obtained polyester has a molecular weight of Mn 13800, an acid value of 7.50 mgKOH/g and a hydroxyl value of 0.63 mgKOH/g as measured by GPC.

1200 grams of carboxyl-terminated polyester, 302.3 grams of bisphenol A epoxy resin E44, and 0.6 grams of antimony trioxide were added to the extruder, and the temperature was raised to 240° C. The extrusion speed was controlled to be 10 g/min to obtain pellets. product. The tested acid value is 1.89 mgKOH/g, the hydroxyl value is 54.0 mgKOH/g, and the GPC test molecular weight is Mn105000. It was refluxed in ethyl acetate to prepare a hydroxyl-containing epoxy chain-extended polyester with a solid content of 30%.

Comparative Example 1

Add 580.5 g of terephthalic acid, 720.6 g of isophthalic acid, 317.0 g of sebacic acid, 746 g of ethylene glycol, 128.1 g of 1,6-hexanediol, 6.5 g of trimethylolpropane into a 3L polymerization reactor , 1.0 g of antimony acetate, heat up to 240 ° C in about one hour, adjust the distillation rate of the generated water, keep the pressure in the kettle at 0.25-0.3 MPa, and the temperature at the top of the distillation tower is lower than 120 ° C, until the amount of distilled water reaches 170 g, The esterification reaction is completed. Turn on the vacuum system, adjust the vacuum degree in the kettle to about 80Pa for about half an hour, and at the same time the temperature rises to 275°C, start the polycondensation reaction, and react for 4-5 hours under this condition, the power increases slowly, and the polycondensation distillate is 256 grams , discharging to obtain hydroxyl-terminated polyester.

GPC test molecular weight Mn 34000, hydroxyl value 2.61mgKOH/g, acid value 0.5mgKOH/g.

Comparative Example 2

320.6 grams of isophthalic acid, 617.0 grams of adipic acid, 296.0 grams of ethylene glycol, 160.5 grams of 3-methylpentanediol, 6.5 grams of trimethylolpropane, 1.0 grams of antimony trioxide were added to the 3L polymerization reactor, The temperature was raised to 240°C in about one hour, the water distillation rate was adjusted, the pressure in the kettle was maintained at 0.25-0.3MPa, and the temperature at the top of the distillation column was lower than 120°C, until the amount of distilled water reached 110 grams, and the esterification reaction was completed. Turn on the vacuum system, adjust the vacuum degree in the kettle to about 80Pa for about half an hour, while the temperature rises to 275°C, start the polycondensation reaction, react under this condition for 2.5 hours, and discharge the material to obtain the carboxyl-terminated polyester.

GPC test molecular weight Mn 14000, acid value 7.38mgKOH/g, hydroxyl value 0.60mgKOH/g.

1200 grams of carboxyl-terminated polyester, 111.3 grams of bisphenol A epoxy resin E44, and 0.6 grams of antimony trioxide were added to the extruder, and the temperature was raised to 240 ° C, and the extrusion speed was controlled to be 10 g/min to obtain pellets product. The acid value is 1.49 mgKOH/g, the hydroxyl value is 22.1 mgKOH/g, and the molecular weight is Mn45000 by GPC. It was refluxed in ethyl acetate to prepare a hydroxyl-containing epoxy chain-extended polyester with a solid content of 30%.

Application test:

*With glue:

After the embodiment and comparative example products and TDI pentaerythritol adduct (TDI and pentaerythritol mol ratio are 1:4 in solvent toluene, 90 DEG C of reaction for 4 hours) are mixed according to the hydroxyl value of the solute and the NCO mol ratio 1:1.15, Add 0.3% antioxidant, 06% ultraviolet absorber and 1% hydrolysis stabilizer, mix well and set aside.

*Sample Preparation:

Apply the prepared adhesive to the PET sheet, the sizing amount is 10g/m ² (folded), dry at 80°C for 10 minutes, and place the pretreated PVD film on the surface of the PET sheet. On the agent, compound on a flat press with a pressure of 1.0 MPa, the temperature is 50 °C, and the pressing is for 40 minutes. The composite sheet was aged at 40°C for 48 hours.

*Evaluation method:

1. Peel strength test: Cut the composite sheet into a 15mm wide sample, and perform a 180° peel test on a universal testing machine at a speed of 50mm/min. Reference standard: National standard GB/T2790 "Test method for 180° peel strength of adhesives for flexible materials to rigid materials".

2. Constant humidity and heat aging resistance: 3000h at 85℃, 85% relative humidity. Before and after the test, the strips (15*200mm) were tested for peel strength according to the national standard. Reference standard: National standard GB/T2790 "Test method for 180° peel strength of adhesives for flexible materials to rigid materials".

3. PCT aging resistance

In a pressure cooker at 121°C and one atmosphere for 72 hours, the strips (15*200mm) before and after the test were tested for peel strength according to standard methods. Reference standard: National standard GB/T2790 "Test method for 180° peel strength of adhesives for flexible materials to rigid materials".

4. Weather resistance

The spline (50*150mm) was placed in a xenon lamp weathering tester to carry out an accelerated aging test, and the appearance after light irradiation was observed. Reference standard ASTM G155.

The test data is shown in the following table:

Table 1 Sample application performance evaluation table

It can be seen from the test results that the adhesive prepared by the polyester adhesive resin prepared by the method of the present invention is applied to the multi-layer bonding of solar cell back sheets, and its weather resistance, initial peel strength, double "85" after 3000 hours The peel strengths all have high values, which can meet the application performance requirements of solar cell backsheet adhesives.

Claims (10)

1. a solar cell back sheet adhesive resin, it is characterized in that: the solar cell back sheet adhesive resin is a solvent-based two-component adhesive resin, and it is made up of the epoxy chain-extended high molecular weight polymer with hydroxyl. The ester is used as component A, and the polyisocyanate is used as component B; wherein, component A and component B are mixed in a mass ratio of 3:4-20:1. 2. The solar cell back sheet adhesive resin according to claim 1, wherein the epoxy chain-extended macromolecule polyester with hydroxyl group is a carboxyl-terminated polyester with Mn of 5000-20000 and a The epoxy chain extender is chain-extended and viscosified to obtain an epoxy chain-extended macromolecule polyester with a hydroxyl group with a molecular weight of Mn of 40,000-120,000; wherein, the added amount of the epoxy chain extender is the quality of the carboxyl-terminated polyester 1 to 20% of . 3. The solar cell back sheet adhesive resin according to claim 2, wherein the epoxy chain extender is 1,4-cyclohexanedimethanol glycidyl ether, 1,4-butanediol Diglycidyl ether, bisphenol A-diglycidyl ether, glycidyl ether, triglycidyl isocyanurate, N,N,N',N'-tetraglycidyl ether-4,4'diaminodiphenyl One or both of methane, bisphenol A polyglycidyl ether, bisphenol A epoxy resin, and bisphenol F epoxy resin. 4. The solar cell back sheet adhesive resin according to claim 2 or 3, wherein the epoxy chain-extended macromolecule polyester with hydroxyl group is made of aromatic dibasic acid, long-chain aliphatic dibasic After the acid, diol and triol are mixed, the esterification reaction is carried out under normal pressure and 240-270 ° C; then the esterification product is polycondensed through a polycondensation catalyst under high temperature and high vacuum conditions to obtain a carboxyl group with Mn of 5000-20000 End-capped polyester; the polyester and epoxy chain extender are chain-extended and viscosified to obtain a high molecular polyester with a molecular weight of Mn of 40000-120000. 5. The solar cell back sheet adhesive resin according to claim 4, wherein the carboxyl-terminated polyester is a mixture of aliphatic diol, aliphatic dibasic acid and aromatic dibasic acid. , stir under nitrogen protection, heat up to 240-270 ℃ within 1 hour to carry out esterification reaction, keep the temperature for 2-3 hours, until the condenser has no water to distill, then add polycondensation catalyst, continue to heat up to 260-280 ℃, After the polycondensation reaction is carried out at an absolute pressure of 100-40Pa for 1-4h, a polymer with a target molecular weight of 5000-20000 is obtained; wherein, the molar ratio of aromatic dibasic acid, aliphatic dibasic alcohol, and aliphatic dibasic acid is 1-6: 1-6:1. 6. The solar cell back sheet adhesive resin according to claim 5, wherein the aliphatic diol is two or three of C ₂ -C ₁₂ linear or branched diols Species; aliphatic dibasic acid is C ₃ -C ₁₈ aliphatic dibasic acid; aromatic dibasic acid is phthalic acid, terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid or naphthalene - Two or three of the 1,4-dicarboxylic acids. 7 . The solar cell back sheet adhesive resin according to claim 1 , wherein the polyisocyanate is an adduct of TDI, pentaerythritol and trimethylolpropane. 8 . 8 . The application of the adhesive resin for solar cell backsheets according to claim 1 , wherein the adhesive resin is used as an adhesive resin for solar backsheet adhesives. 9 . 9. The application of the solar cell back sheet adhesive resin according to claim 8, characterized in that: the adhesive resin of claim 1 and catalyst, ultraviolet absorber, light stabilizer, anti- Oxygen agent, after mixing uniformly, the solar cell back sheet adhesive is obtained. 10. A solar cell back sheet, characterized in that: the solar back sheet adhesive containing the adhesive resin of claim 1 is coated on the PET layer of the back sheet support layer, and dried at 70-100° C. for 3 minutes, the obtained adhesive film and the PVF layer of the back sheet support layer are hot-pressed and compounded at a temperature of 70-90° C. and a pressure of 0.5 MPa, and aged at 60° C. for 72 hours to obtain a solar cell back sheet.