A polyester resin for fluorocarbon coatings of a photovoltaic backsheet, its preparation method and applications

Abstract

The present invention belongs to the technical field of polyester resin preparation, and provides a polyester resin for fluorocarbon coatings of photovoltaic backsheets, a preparation method thereof, and an application thereof. The preparation method includes: formulating and melting a quantitative A component and a B component; the A component includes a quantitative 1,2-cyclohexanedicarboxylic acid or its anhydride and other acids or anhydrides (at least one of maleic acid, maleic anhydride, succinic acid, fumaric acid, fumaric anhydride); the B component includes a quantitative 1,6-hexanediol and other alcohols (which includes a quantitative neopentyl glycol and 2-ethyl-2-(hydroxymethyl)-1,3-propanediol); adding a catalyst, raising the temperature, and carrying out an esterification reaction; then reducing the pressure, raising the temperature, and carrying out a polycondensation reaction to obtain the polyester resin. When the polyester resin is added to the fluorocarbon coating for photovoltaic backsheets, the fluorocarbon coating can have better aging resistance adhesion performance, aging resistance peel strength, aging resistance yellowing performance, acid and alkali resistance performance, and solvent resistance performance.

Description

Technical Field

[0001] The present invention relates to the technical field of polyester resin preparation, and particularly to a polyester resin for fluorocarbon coatings on photovoltaic backsheets, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the improvement of environmental awareness and the increasing importance of renewable energy, solar photovoltaic power generation has received extensive attention and application. As is well known, a solar photovoltaic module is prepared through a photovoltaic front plate, a photovoltaic cell, an encapsulation adhesive film, a photovoltaic backsheet, and a photovoltaic frame. Among them, the photovoltaic backsheet is bonded to the back of the photovoltaic cell through the encapsulation adhesive film, and the photovoltaic backsheet is connected to a connector, which is used to insulate and protect the photovoltaic cell. With the continuous improvement of the market's requirements for the power generation efficiency of batteries, it has gradually become a trend to use excellent photovoltaic backsheets to improve the power generation efficiency on the back of photovoltaic cells. Fluorocarbon coatings are coatings with fluorocarbon resins as the main film-forming substances, and are widely used in fields such as construction, chemical industry, aerospace industry, and household products. Compared with silicone coatings, polyurethane coatings, etc., fluorocarbon coatings have excellent properties such as corrosion resistance, weather resistance, and stain resistance. Therefore, fluorocarbon coatings are widely used in photovoltaic backsheets.

[0003] In the fluorocarbon coatings applied in photovoltaic backsheets disclosed in the prior art (such as CN116218296A, CN116333274A), polyester resins are usually added in combination. Although the proportion of polyester resins in the fluorocarbon coatings for photovoltaic backsheets is not high, they play a crucial role in their adhesion, bonding strength, and other properties. However, the aging-resistant bonding strength between the coatings formed by the fluorocarbon coatings added with polyester resins disclosed in the prior art (such as CN116218296A, CN116333274A) and photovoltaic backsheets (such as PET photovoltaic backsheets), encapsulation adhesive films (such as EVA adhesive films) is low; and the diluents of solvent-based fluorocarbon coatings will swell the plastic substrates for photovoltaic backsheets (such as PVC base films, TPU base films), resulting in poor aging-resistant adhesion between the coatings and the substrates for photovoltaic backsheets. Therefore, it will have an adverse impact on the comprehensive performance of photovoltaic backsheets. In addition, in order to further improve the comprehensive performance of photovoltaic backsheets, the aging-resistant yellowing performance, acid and alkali resistance, and solvent resistance of the existing fluorocarbon coatings added with polyester resins still need to be further improved. Therefore, it is necessary to prepare a high-performance polyester resin suitable for fluorocarbon coatings on photovoltaic backsheets. Summary of the Invention

[0004] The object of the present invention is to provide a polyester resin for fluorocarbon coatings on photovoltaic backsheets, a preparation method thereof, and an application thereof, aiming at the deficiencies of the prior art.

[0005] Based on this, the present invention discloses a preparation method of a polyester resin for fluorocarbon coatings on photovoltaic backsheets, including the following steps:

[0006] Step 1: Melt the reaction raw materials prepared by mixing Component A and Component B in a molar ratio of 0.8 - 1:1 until the solution becomes clear and transparent.

[0007] Among them, Component A, in terms of mole percentage, includes 80 - 90%mol of 1,2 - cyclohexanedicarboxylic acid or its anhydride and 10 - 20%mol of other acids or acid anhydrides; the other acids or acid anhydrides include at least one of maleic acid, maleic anhydride, succinic acid, fumaric acid, and fumaric anhydride.

[0008] Among them, Component B, in terms of mole percentage, includes 60 - 70%mol of 1,6 - hexanediol and 30 - 40%mol of other alcohols; the other alcohols include neopentyl glycol and 2 - ethyl - 2 - (hydroxymethyl)-1,3 - propanediol in a molar ratio of 3:1 - 2.

[0009] Step 2: Add a catalyst to the solution in Step 1, heat up to 170 - 190 °C for an esterification reaction until the yield of by - product water reaches more than 95%.

[0010] Step 3: Reduce the pressure of the reaction system in Step 2 to - 0.03 - 0.01 MPa, heat up to 200 - 230 °C for a polycondensation reaction to obtain the polyester resin for the fluorocarbon coating of the photovoltaic backplane.

[0011] Preferably, in Step 1, the reaction raw materials, in terms of mole parts, include: 0.30 - 0.33 parts of 1,2 - cyclohexanedicarboxylic anhydride, 0.04 - 0.07 parts of maleic acid, 0.23 - 0.26 parts of 1,6 - hexanediol, 0.09 parts of neopentyl glycol, and 0.03 - 0.06 parts of 2 - ethyl - 2 - (hydroxymethyl)-1,3 - propanediol.

[0012] Further preferably, in Step 1, the molar ratio of Component A to Component B is 0.37:0.38.

[0013] The polyester resin in the present invention is mainly used in the fluorocarbon coating for the photovoltaic backplane. The reaction principle of the polyester resin for the fluorocarbon coating of the photovoltaic backplane in the present invention is as follows:

[0014]

[0015] During the experiment, it was found that compared with the linear - structured dibasic acid and diol, when using the dibasic acid and diol containing a benzene ring to react and synthesize the polyester resin, the benzene ring structure can endow the resin with rigidity and chemical resistance, greatly improving the hardness of the polyester resin; adding this polyester resin to the fluorocarbon coating for the photovoltaic backplane can significantly increase the adhesion between the fluorocarbon coating and the photovoltaic backplane; however, the polyester resin containing a benzene ring often has a relatively large dry - heat yellowing, so a cycloalkane such as 1,2 - cyclohexanedicarboxylic anhydride is used for substitution.

[0016] Among them, 1. By introducing 1,2-cyclohexanedicarboxylic anhydride, the ring structure is increased, endowing the polyester resin with rigidity and chemical resistance, and greatly improving the hardness of the polyester resin. Moreover, as a saturated anhydride, 1,2-cyclohexanedicarboxylic anhydride can effectively adjust the double bond density, improve the elongation rate of the cured polyester resin, play a plasticizing role, reduce the number of unsaturated bonds in the polyester resin, and reduce aging and yellowing. 2. As saturated diols, 1,6-hexanediol and neopentyl glycol can effectively reduce the double bond density of the polyester resin, improve the elongation rate of the cured polyester resin, play a plasticizing role, and help reduce yellowing. 3. By selecting 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, due to its structural asymmetry, an amorphous polyester resin can be obtained. The remaining hydroxyl groups after the reaction can increase the hydroxyl value of the polyester resin. When applied in the fluorocarbon coating for photovoltaic backsheets, it can effectively improve the aging resistance adhesion between the fluorocarbon coating and the photovoltaic backsheet, as well as between the fluorocarbon coating and the encapsulation adhesive film. 4. When synthesizing the polyester resin for the fluorocarbon coating of photovoltaic backsheets, maleic acid and fumaric acid are commonly used unsaturated acids, which can provide unsaturated double bonds. The introduction of unsaturated bonds can improve the adhesion to the encapsulation adhesive film.

[0017] Preferably, in step 1, in an inert atmosphere (such as a nitrogen atmosphere), the reaction raw materials are melted at 90-120°C for 0.5-1.5 h (preferably 0.5-1.0 h) to make the solution clear and transparent. Groups such as ester groups, hydroxyl groups, carboxyl groups, double bonds, and hydrogenated aromatic rings in the molecular chain of the polyester resin can cause thermal oxidative degradation in an oxygen atmosphere, turning the color of the polyester resin yellow. Therefore, nitrogen or other inert gases need to be introduced during the synthesis process to prevent oxidation and discoloration.

[0018] Preferably, in step 2, the catalyst is at least one of tetrabutyl titanate, tetraisopropyl titanate, monobutyltin oxide, dibutyltin oxide, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dichloride, titanium glycolate, lithium acetate, potassium acetate, calcium acetate, magnesium acetate, barium acetate, and toluenesulfonic acid;

[0019] The dosage of the catalyst is 0.1-0.3 wt% of the total mass of component A and component B.

[0020] More preferably, the catalyst is tetrabutyl titanate, and the dosage of the catalyst is 0.2 wt% of the total mass of component A and component B.

[0021] Preferably, in step 2, the reaction temperature of the esterification reaction is 180 - 190°C, the reaction time is 1.0 - 3.0 h (preferably 1.5 - 2.5 h), until the yield of by-product water reaches more than 95%. In step 2, in order to ensure that the esterification reaction is basically completed, the yield of by-product water needs to reach more than 95%. The degree of esterification reaction in polyester synthesis is usually estimated by the percentage of by-product water collected in the theoretical generated water volume.

[0022] Preferably, in step 3, the reaction temperature of the polycondensation reaction is 220 - 230°C, the reaction time is 2.0 - 3.0 h (preferably 1.5 - 2.5 h), until the acid value is less than or equal to 8 mg KOH / g, then cool down, add propylene glycol methyl ether acetate to dilute to a solid content of 60 - 68% (preferably 65%) to obtain the polyester resin for the fluorocarbon coating of the photovoltaic backplane.

[0023] The present invention also discloses a polyester resin for the fluorocarbon coating of the photovoltaic backplane, which is prepared by using the preparation method of a polyester resin for the fluorocarbon coating of the photovoltaic backplane described above in the present invention content;

[0024] The polyester resin for the fluorocarbon coating of the photovoltaic backplane is an unsaturated polyester resin, its acid value is less than or equal to 8 mg KOH / g (preferably 5 - 8 mg KOH / g), its hydroxyl value is 50 - 80 mg KOH / g (preferably 55 - 70 mg KOH / g), and its weight average molecular weight is 5000 - 30000 (preferably 8600 - 9500).

[0025] The present invention also discloses an application of the polyester resin for the fluorocarbon coating of the photovoltaic backplane, adding the polyester resin for the fluorocarbon coating of the photovoltaic backplane described above in the present invention content to the fluorocarbon coating for the photovoltaic backplane;

[0026] The fluorocarbon coating includes component C and component D; by weight, component C includes 0.5 - 30 parts of curing agent, and component D includes 10 - 70 parts of fluorocarbon resin, 0.1 - 10 parts of polyester resin (a polyester resin for the fluorocarbon coating of the photovoltaic backplane described above in the present invention content), 0.5 - 25 parts of acrylic oligomer with a molecular weight of 500 - 1500, 0.1 - 40 parts of additives, and 20 - 70 parts of diluent.

[0027] Preferably, the curing agent is preferably N3390 of Covestro; the fluorocarbon resin is preferably GK570 of Daikin; the acrylic oligomer is preferably 6145 - 100 of Changxing Co., Ltd. in Taiwan, China; the additives include an ultraviolet absorber and a leveling agent added in a ratio of 1:1. The ultraviolet absorber is preferably UV400 of BASF, and the leveling agent is preferably BYK333 of BYK Chemie; the diluent is preferably propylene glycol methyl ether acetate.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] In the process of preparing the polyester resin of the present invention, the structure of the polyester resin is adjusted by regulating the molar content of each reaction raw material. After adding this polyester resin to the fluorocarbon coating, it helps to improve the aging-resistant adhesion between the fluorocarbon coating and the photovoltaic backsheet (such as PET photovoltaic backsheet), and between the fluorocarbon coating and the encapsulation film (such as EVA film); meanwhile, in the fluorocarbon coating, only a small amount of this polyester resin needs to be added to improve the aging-resistant adhesion between the fluorocarbon coating and the photovoltaic backsheet, and can improve the aging-resistant yellowing performance, acid and alkali resistance performance and solvent resistance performance of the fluorocarbon coating for photovoltaic backsheet, and can reduce the production cost. This polyester resin can be applied to a variety of fluorocarbon coating formulation systems for photovoltaic backsheets, which helps to improve the comprehensive performance of photovoltaic backsheets. Detailed implementation manners

[0030] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the specific implementation manners.

[0031] Example 1

[0032] A preparation method of a polyester resin for a fluorocarbon coating of a photovoltaic backsheet in this example includes the following preparation steps:

[0033] Step S1: Add the following reaction raw materials into a reaction system connected with a heating device, a stirring device, a water separation and condensation device, and a nitrogen protection device: 0.33 mol of 1,2-cyclohexanedicarboxylic anhydride, 0.04 mol of maleic acid, 0.26 mol of 1,6-hexanediol, 0.09 mol of neopentyl glycol, and 0.03 mol of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol.

[0034] Step S2: Under the atmosphere of high-purity nitrogen, raise the temperature of the reaction system to 90 °C to completely dissolve the reaction raw materials until it becomes clear and transparent, and keep it for 0.5 h.

[0035] Step S3: Add tetrabutyl titanate accounting for 0.2% of the total mass of the reaction raw materials, slowly raise the temperature of the reaction system to 190 °C for esterification reaction, keep it for 2.0 h under normal pressure, and the amount of by-product water collected by the water separator accounts for 95% of the theoretically generated water amount.

[0036] Step S4: Evacuate to reduce the pressure of the reaction system to -0.01 MPa, gradually raise the temperature to 230 °C and keep it for 2.0 h for polycondensation reaction. When the acid value of the reaction system is not more than 8 mgKOH / g, end the reaction; that is, when the temperature of the reaction system drops to 180 °C, discharge the material, and add propylene glycol methyl ether acetate to dilute to a solid content of 65% to obtain the polyester resin for the fluorocarbon coating of the photovoltaic backsheet in this example.

[0037] Example 2

[0038] A preparation method of a polyester resin for a fluorocarbon coating on a photovoltaic backsheet in this example includes the following preparation steps:

[0039] Step S1: Add the following reaction raw materials into a reaction system connected with a heating device, a stirring device, a water separation and condensation device, and a nitrogen protection device: 0.30 mol of 1,2-cyclohexanedicarboxylic anhydride, 0.07 mol of maleic acid, 0.26 mol of 1,6-hexanediol, 0.09 mol of neopentyl glycol, and 0.03 mol of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol.

[0040] The subsequent preparation steps of this example all refer to steps S2 - S4 of Example 1 to obtain the polyester resin for the fluorocarbon coating on the photovoltaic backsheet of this example.

[0041] Example 3

[0042] A preparation method of a polyester resin for a fluorocarbon coating on a photovoltaic backsheet in this example includes the following preparation steps:

[0043] Step S1: Add the following reaction raw materials into a reaction system connected with a heating device, a stirring device, a water separation and condensation device, and a nitrogen protection device: 0.33 mol of 1,2-cyclohexanedicarboxylic anhydride, 0.04 mol of maleic acid, 0.23 mol of 1,6-hexanediol, 0.09 mol of neopentyl glycol, and 0.06 mol of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol.

[0044] The subsequent preparation steps of this example all refer to steps S2 - S4 of Example 1 to obtain the polyester resin for the fluorocarbon coating on the photovoltaic backsheet of this example.

[0045] Comparative Example 1

[0046] A preparation method of a polyester resin for a fluorocarbon coating on a photovoltaic backsheet in this comparative example includes the following preparation steps:

[0047] Step S1: Add the following reaction raw materials into a reaction system connected with a heating device, a stirring device, a water separation and condensation device, and a nitrogen protection device: 0.23 mol of 1,2-cyclohexanedicarboxylic anhydride, 0.14 mol of maleic acid, 0.26 mol of 1,6-hexanediol, 0.09 mol of neopentyl glycol, and 0.03 mol of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol.

[0048] The subsequent preparation steps of this comparative example all refer to steps S2 - S4 of Example 1 to obtain the polyester resin for the fluorocarbon coating on the photovoltaic backsheet of this comparative example.

[0049] Comparative Example 2

[0050] The preparation method of the polyester resin for the fluorocarbon coating of the photovoltaic backplane in this comparative example includes the following preparation steps:

[0051] Step S1: Add the following reaction raw materials into the reaction system connected with a heating device, a stirring device, a water separation and condensation device, and a nitrogen protection device: 0.33 mol of 1,2-cyclohexanedicarboxylic anhydride, 0.04 mol of maleic acid, 0.20 mol of 1,6-hexanediol, 0.09 mol of neopentyl glycol, and 0.09 mol of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol.

[0052] The subsequent preparation steps of this comparative example all refer to the steps S2 - S4 of Example 1 to obtain the polyester resin for the fluorocarbon coating of the photovoltaic backplane in this comparative example.

[0053] Comparative Example 3

[0054] The preparation method of the polyester resin for the fluorocarbon coating of the photovoltaic backplane in this comparative example includes the following preparation steps:

[0055] Step S1: Add the following reaction raw materials into the reaction system connected with a heating device, a stirring device, a water separation and condensation device, and a nitrogen protection device: 0.37 mol of 1,2-cyclohexanedicarboxylic anhydride, 0.26 mol of 1,6-hexanediol, 0.09 mol of neopentyl glycol, and 0.03 mol of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol.

[0056] The subsequent preparation steps of this comparative example all refer to the steps S2 - S4 of Example 1 to obtain the polyester resin for the fluorocarbon coating of the photovoltaic backplane in this comparative example.

[0057] Comparative Example 4

[0058] The preparation method of the polyester resin for the fluorocarbon coating of the photovoltaic backplane in this comparative example includes the following preparation steps:

[0059] Step S1: Add the following reaction raw materials into the reaction system connected with a heating device, a stirring device, a water separation and condensation device, and a nitrogen protection device: 0.33 mol of 1,2-cyclohexanedicarboxylic anhydride, 0.04 mol of maleic acid, 0.29 mol of 1,6-hexanediol, and 0.09 mol of neopentyl glycol.

[0060] The subsequent preparation steps of this comparative example all refer to the steps S2 - S4 of Example 1 to obtain the polyester resin for the fluorocarbon coating of the photovoltaic backplane in this comparative example.

[0061] Performance Test

[0062] 1. The polyester resins for fluorocarbon coatings of the photovoltaic backsheets prepared in Examples 1-3 and Comparative Examples 1-4 were respectively subjected to performance tests, and the test results are shown in Table 1 below.

[0063] Table 1

[0064]

[0065] 2. To test the performance of the fluorocarbon coatings for photovoltaic backsheets added with polyester resins, the polyester resins of Examples 1-3 and Comparative Examples 1-4 were respectively added to a fluorocarbon coating for photovoltaic backsheets. The raw materials of this fluorocarbon coating are divided into Component C and Component D. By weight, Component C is 10 parts of curing agent; Component D is 40 parts of fluorocarbon resin, 8 parts of polyester resin, 10 parts of acrylic oligomer, 4 parts of additives, and 28 parts of diluent. Among them, the curing agent is N3390 of Covestro; the fluorocarbon resin is GK570 of Daikin; the acrylic oligomer is 6145-100 of Changxing Co., Ltd. in Taiwan, China; the additives include an ultraviolet absorber and a leveling agent added in a ratio of 1:1. The ultraviolet absorber is UV400 of BASF, and the leveling agent is BYK333 of BYK Chemie; the diluent is propylene glycol methyl ether acetate. The performance tests were carried out on the fluorocarbon coatings respectively added with the polyester resins of Examples 1-3 and Comparative Examples 1-4, and the performance test was also carried out on the fluorocarbon coating without adding polyester resin. The test results are shown in Table 2 below (the thickness of the fluorocarbon coating used in the test of Table 2 is 8 microns).

[0066] The test methods are as follows:

[0067] (1) Adhesion: Referring to the standard GB / T 9286-2021, 10*10 small grids of 1mm*1mm were scratched on the surface of the sample, and the adhesion between the fluorocarbon coating added with polyester resin and the PET photovoltaic backsheet was tested.

[0068] (2) Aging resistance (high-pressure accelerated aging test): Referring to the standard JESD 22-A102-C, the temperature is 121°C, the pressure is 205 KPa, the humidity is 100%, the test time is 48 h, and the aging resistance of the fluorocarbon coating is tested.

[0069] (3) Interlayer peel strength: Referring to the standard GB / T 2790-1995, the sample size is 200 mm in length and 10±1 mm in width, and the peel speed is 100 mm / min. The peel strength between the fluorocarbon coating added with polyester resin and the EVA film was tested.

[0070] (4) Coating solvent resistance (resistance to methyl ethyl ketone): Referring to the standard GB / T 17748-2016, the sample is 100*430 mm, the wiping solvent is methyl ethyl ketone, the load is 10 N, and the wiping frequency is 100 times / min. The solvent resistance (resistance to methyl ethyl ketone) of the fluorocarbon coating added with polyester resin was tested.

[0071] (5)Hydrochloric acid / alkali resistance: Referring to the standard GB / T 17748-2016, use 5% HCl (volume fraction) and 5% NaOH (mass fraction), with a liquid level height of 20 mm ± 2 mm and a test time of 24 h to test the hydrochloric acid / alkali resistance of the fluorocarbon coating added with polyester resin.

[0072] Table 2

[0073]

[0074] Combined with Tables 1-2, it can be seen that:

[0075] (1) Compared with the fluorocarbon coating without polyester resin, the aging resistance adhesion performance between the fluorocarbon coating added with polyester resin in Examples 1-3 and the PET photovoltaic backsheet has been significantly improved. Also, the peel strength between the fluorocarbon coating added with polyester resin in Examples 1-3 and the EVA film has been significantly improved. At the same time, the polyester resin in Examples 1-3 also promotes the formation of a fluorocarbon coating with better hardness. The fluorocarbon coating in Examples 1-3 has good acid and alkali resistance, and the solvent resistance (resistance to methyl ethyl ketone) of the fluorocarbon coating in Examples 1-3 has also been greatly improved.

[0076] (2) Among them, compared with Example 1 (in the process of preparing polyester resin in Example 1, the molar content of maleic acid is 0.04 mol and the molar content of 1,2-cyclohexanedicarboxylic anhydride is 0.33 mol), the aging resistance peel strength between the fluorocarbon coating added with the polyester resin of Comparative Example 3 (in the process of preparing polyester resin in Comparative Example 3, maleic acid is not added and the molar content of 1,2-cyclohexanedicarboxylic anhydride is increased by 0.37 mol) and the EVA film has significantly decreased, and the solvent resistance has also significantly decreased.

[0077] Compared with Example 1, the aging resistance peel strength between the fluorocarbon coating added with the polyester resin of Example 2 (in the process of preparing polyester resin in Example 2, the molar content of maleic acid is increased to 0.07 mol and the molar content of 1,2-cyclohexanedicarboxylic anhydride is decreased to 0.30 mol) and the EVA film has increased, but its aging resistance yellowing performance and solvent resistance are both poor.

[0078] Compared with Example 1, the weathering peel strength between the fluorocarbon coating added with the polyester resin of Comparative Example 1 (in the process of preparing the polyester resin of Comparative Example 1, the molar content of maleic acid was increased to 0.14 mol and the molar content of 1,2-cyclohexanedicarboxylic anhydride was decreased to 0.23 mol) and the EVA film was further improved. However, the weathering peel strength between the fluorocarbon coating and the EVA film is not necessarily the better the greater it is. If the weathering peel strength between the fluorocarbon coating and the EVA film is too large, it will instead have an adverse effect on the adhesion performance between the fluorocarbon coating and the PET photovoltaic backsheet. Moreover, the weathering yellowing resistance and solvent resistance of the fluorocarbon coating of Comparative Example 1 are significantly worse. Furthermore, it is difficult for the fluorocarbon coating added with the polyester resin of Comparative Example 1 to extend the service life of the photovoltaic backsheet in long-term outdoor use, so it is not suitable for application in photovoltaic backsheets.

[0079] Therefore, to ensure that the fluorocarbon coating for photovoltaic backsheets has good weathering peel strength, weathering yellowing resistance and solvent resistance, in the process of preparing the polyester resin for the fluorocarbon coating of photovoltaic backsheets, the molar content of maleic acid should not be too much or too little, and the molar ratio of maleic acid to 1,2-cyclohexanedicarboxylic anhydride should be moderate.

[0080] (3) Among them, compared with Example 1 (in the process of preparing the polyester resin of Example 1, the molar content of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol was 0.03 mol and the molar content of 1,6-hexanediol was 0.26 mol), the weathering adhesion performance, weathering peel strength, acid and alkali resistance and solvent resistance of the fluorocarbon coating added with the polyester resin of Comparative Example 4 (in the process of preparing the polyester resin of Comparative Example 4, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol was not added and the molar content of 1,6-hexanediol was increased to 0.29 mol) decreased significantly.

[0081] Compared with Example 1, the fluorocarbon coating added with the polyester resin of Example 3 (in the process of preparing the polyester resin of Example 3, the molar content of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol was increased to 0.06 mol and the molar content of 1,6-hexanediol was decreased to 0.23 mol) helps to improve the weathering adhesion between its coating and the PET photovoltaic backsheet. However, in the process of preparing the polyester resin, if the molar content of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol is relatively high, it is easy to rapidly polycondense and crosslink, which will in turn lead to a decrease in the weathering peel strength between the fluorocarbon coating added with this polyester resin and the EVA film.

[0082] Compared with Example 1, the intrinsic viscosity of the polyester resin in Comparative Example 2 (in the process of preparing the polyester resin in Comparative Example 2, the molar content of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol was increased to 0.09 mol and the molar content of 1,6-hexanediol was decreased to 0.20 mol) was too high, and it was prone to explosive polymerization; moreover, the aging resistance adhesion performance, aging resistance peel strength, acid and alkali resistance performance, and solvent resistance performance of the fluorocarbon coating containing the polyester resin of Comparative Example 2 all deteriorated.

[0083] Therefore, when preparing the polyester resin for the fluorocarbon coating of the PV backplane, the molar content of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol should not be too much or too little, and the molar ratio of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol to 1,6-hexanediol should be appropriate, so as to avoid explosive polymerization and affect the aging resistance adhesion performance, aging resistance peel strength, acid and alkali resistance performance, and solvent resistance performance of the fluorocarbon coating.

[0084] In summary, compared with Comparative Examples 1-4, in the process of preparing the polyester resin in Examples 1-3, the structure of the polyester resin was adjusted by adjusting the molar content of each reaction raw material in step S1, and the prepared polyester resin was synergistically combined with the effective components in the fluorocarbon coating, which helped to improve the crosslinking strength of the fluorocarbon coating system for the PV backplane, further promoted the fluorocarbon coating to bind more firmly on the surface of the PET PV backplane, so that the fluorocarbon coating containing the polyester resin of Examples 1-3 had better aging resistance adhesion performance, aging resistance peel strength, aging resistance yellowing performance, acid and alkali resistance performance, and solvent resistance performance. Therefore, a fluorocarbon coating with better aging resistance adhesion, stronger aging resistance bonding force, higher hardness, better thermal aging resistance, less aging resistance yellowing, better acid and alkali resistance performance, and better solvent resistance performance could be obtained, which further helped to improve the comprehensive performance of the PV backplane.

[0085] Although the preferred embodiments of the embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they know the basic creative concepts. Therefore, the appended claims are intended to be construed to include the preferred embodiments and all changes and modifications falling within the scope of the embodiments of the present invention.

[0086] The technical solutions provided by the present invention have been introduced in detail above. Specific examples are used in this article to elaborate on the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for preparing a polyester resin for photovoltaic backplane fluorocarbon coating, characterized in that: The steps include: Step 1, melt the reaction raw materials prepared with component A and component B in a molar ratio of 0.8-1:1 until the solution is clear and transparent; Wherein, the component A comprises, by mole percentage, 80-90% mol of 1,2-cyclohexanedicarboxylic anhydride and 10-20% mol of other acids or anhydrides; the other acids or anhydrides comprise maleic acid; Wherein, the B component, in terms of molar percentage, includes 60-70% mol of 1,6-hexanediol and 30-40% mol of other alcohols; the other alcohols include neopentyl glycol and 2-ethyl-2-(hydroxymethyl)-1,3-propanediol in a molar ratio of 3:1-2; In step 1, the reaction raw materials, by mole, include: 0.30-0.33 parts of 1,2-cyclohexanedicarboxylic anhydride, 0.04-0.07 parts of maleic acid, 0.23-0.26 parts of 1,6-hexanediol, 0.09 parts of neopentyl glycol and 0.03-0.06 parts of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol; Step 2, adding a catalyst to the solution of step 1, heating to 170-190° C. to carry out esterification reaction until the yield of byproduct water reaches more than 95%; Step 3: reduce the pressure of the reaction system in step 2 to minus 0.03-0.01 MPa, raise the temperature to 200-230° C. to carry out polycondensation reaction, and obtain the polyester resin for photovoltaic backplane fluorocarbon coating.

2. The method for preparing a polyester resin for photovoltaic backsheet fluorocarbon coating according to claim 1, characterized in that: In step 1, the molar ratio of component A to component B is 0.37:0.

38.

3. The method for preparing a polyester resin for photovoltaic backsheet fluorocarbon coating according to claim 1, characterized in that: In step 1, in an inert atmosphere, the reaction raw materials are melted at 90-120° C. for 0.5-1.5 h to make the solution clear and transparent.

4. The method for preparing a polyester resin for photovoltaic backsheet fluorocarbon coating according to claim 1, characterized in that: In step 2, the catalyst is at least one of tetrabutyl titanate, tetraisopropyl titanate, monobutyl tin oxide, dibutyl tin oxide, dibutyl tin dilaurate, dibutyl tin diacetate, dibutyl tin dichloride, ethylene glycol titanium, lithium acetate, potassium acetate, calcium acetate, magnesium acetate, barium acetate, and toluenesulfonic acid; The amount of the catalyst used is 0.1-0.3 wt % of the total mass of the A component and the B component.

5. The method for preparing a polyester resin for photovoltaic backsheet fluorocarbon coating according to claim 4, characterized in that: The catalyst is tetrabutyl titanate, and the amount of the catalyst used is 0.2 wt % of the total mass of the A component and the B component.

6. The method for preparing a polyester resin for photovoltaic backsheet fluorocarbon coating according to claim 1, characterized in that: In step 2, the reaction temperature of the esterification reaction is 180-190° C., and the reaction time is 1.0-3.0 h, until the yield of the by-product water reaches more than 95%.

7. The method for preparing a polyester resin for photovoltaic backsheet fluorocarbon coating according to claim 1, characterized in that: In step 3, the reaction temperature of the polycondensation reaction is 220-230° C., the reaction time is 2.0-3.0 h, until the acid value is less than or equal to 8 mgKOH / g, the temperature is lowered, and propylene glycol methyl ether acetate is added to dilute to a solid content of 60-68% to obtain the polyester resin for photovoltaic backplane fluorocarbon coating.

8. A polyester resin for photovoltaic backsheet fluorocarbon coating, characterized in that: It is prepared by the method for preparing a polyester resin for photovoltaic backplane fluorocarbon coating according to any one of claims 1 to 7; The polyester resin for photovoltaic backplane fluorocarbon coating is an unsaturated polyester resin, the acid value of which is less than or equal to 8 mgKOH / g, the hydroxyl value of which is 50-80 mgKOH / g, and the weight average molecular weight of which is 5000-30000.

9. An application of polyester resin for photovoltaic backplane fluorocarbon coating, characterized in that: Adding the polyester resin for photovoltaic backsheet fluorocarbon coating according to claim 8 to the fluorocarbon coating for photovoltaic backsheet; The fluorocarbon coating comprises a component C and a component D; in parts by weight, the component C comprises 0.5 to 30 parts of a curing agent, and the component D comprises 10 to 70 parts of a fluorocarbon resin, 0.1 to 10 parts of a polyester resin, 0.5 to 25 parts of an acrylic oligomer with a molecular weight of 500 to 1500, 0.1 to 40 parts of an auxiliary agent, and 20 to 70 parts of a diluent.

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