Polyester film for transparent back plate and preparation method of polyester film

Abstract

The invention belongs to the technical field of macromolecules, and particularly relates to a polyester film for a transparent back plate and a preparation method thereof. The polyester film comprises a base film and a coating attached to the outer surface of the base film. The base film comprises the following raw materials in parts by weight: 100 parts of PET slices and 12-15 parts of polyester copolymerized master batch; in parts by weight, the coating is obtained by coating and curing paint; the coating is prepared from the following raw materials in parts by weight: 8 to 15 parts of epoxidized hydroxyl-terminated liquid polybutadiene, 25 to 32 parts of glycidyl methacrylate, 10 to 15 parts of coupling agent modified hydroxyl aluminum oxide, 10 to 20 parts of water, 4 to 5 parts of hexamethylene diisocyanate tripolymer, 0.2 to 0.3 part of catalyst, 20 to 30 parts of urethane acrylate, 8 to 15 parts of styrene-acrylic emulsion, 1.5 to 2.5 parts of photoinitiator and 2.5 to 3.5 parts of polydimethylsiloxane. The polyester film for the transparent back plate is good in transparency and excellent in high-temperature and high-humidity resistance.

Description

A transparent backsheet polyester film and its preparation method Technical Field

[0001] This invention belongs to the field of polymer technology, specifically relating to a transparent backing polyester film and its preparation method. Background Technology

[0002] Solar backsheet films serve to support, block, and regulate chemical properties. PET polyester film, with its excellent mechanical properties and electrical insulation, has gradually become the core substrate for photovoltaic backsheets. However, the ester bonds in ordinary PET polyester film are prone to hydrolysis under high temperature and humidity conditions, which leads to a decrease in its mechanical properties. Furthermore, ordinary PET polyester film has poor dimensional stability.

[0003] To improve the above defects, copolyesters such as isophthalic acid or 1,4-cyclohexanediethanol can be used to prepare modified PET polyester films. Although this method can increase the hydrolysis resistance of the film to a certain extent, it will reduce the light transmittance of the film. There are also existing processes that use inorganic coatings to increase the hydrolysis resistance of polyester films. Similarly, this process can also reduce the light transmittance of the film and reduce the toughness of the film, making it easy to crack after aging. Summary of the Invention

[0004] To address the aforementioned problems, the first aspect of this invention provides a polyester film for a transparent backsheet. The polyester film comprises a base film and a coating layer adhered to the outer surface of the base film. By weight, the base film comprises 100 parts PET chips and 12-15 parts polyester copolymer masterbatch. By weight, the coating layer is obtained by applying and curing a paint, wherein the paint comprises 8-15 parts epoxidized hydroxyl-terminated liquid polybutadiene, 25-32 parts glycidyl methacrylate, 10-15 parts coupling agent-modified alumina hydroxyl, 10-20 parts water, 4-5 parts hexamethylene diisocyanate trimer, 0.2-0.3 parts catalyst, 20-30 parts polyurethane acrylate, 8-15 parts styrene-acrylic emulsion, 1.5-2.5 parts photoinitiator, and 2.5-3.5 parts polydimethylsiloxane.

[0005] As a more preferred technical solution of the present invention, the raw materials of the coating include: 12 parts of epoxidized hydroxyl-terminated liquid polybutadiene, 28 parts of glycidyl methacrylate, 12 parts of coupling agent modified hydroxyl aluminum oxide, 15 parts of water, 4.5 parts of hexamethylene diisocyanate trimer, 0.25 parts of catalyst, 23 parts of polyurethane acrylate, 11 parts of styrene-acrylic emulsion, 2 parts of photoinitiator, and 2.7 parts of polydimethylsiloxane.

[0006] In this invention, the outer surface of the base film refers to the side of the base film that is in contact with air.

[0007] The PET chips in this invention refer to sheet materials made of polyethylene terephthalate, which can be any type of PET chip in the art capable of preparing films. This invention does not have any special limitation on their source. For example, FG600 type PET chips provided by Yizheng Chemical Fiber can be used.

[0008] The method for preparing the polyester copolymer masterbatch includes:

[0009] (1) In the presence of a catalyst, terephthalic acid, isophthalic acid, tricyclodecanediethanol and neopentyl glycol are added to a reaction vessel for esterification and the by-product water is removed. When the total esterification rate reaches more than 95%, the esterification reaction ends.

[0010] (2) In the presence of a stabilizer, the pressure of the reactor is continuously reduced to a vacuum of 10-200 Pa within 40 minutes. During this process, the byproducts tricyclodecanediethanol and neopentyl glycol are continuously distilled out. When the vacuum is reached, the reaction temperature is controlled at 220-245℃ for vacuum polycondensation for 2-3 hours. Then, the reactor is restored to normal pressure with an inert gas to obtain a polymer melt. The polymer melt is then pelletized by a melt pump to obtain polyester copolymer masterbatch.

[0011] As a preferred embodiment of the present invention, in step (1), the conditions for the esterification reaction include: carrying out the esterification reaction under an inert gas protective atmosphere, and the reaction temperature being 180-230°C. The aforementioned inert gas can be any inert gas in the art, such as nitrogen.

[0012] As a preferred technical solution of the present invention, in step (1), the catalyst is selected from at least one of tetraethyl titanate, tetraisopropyl titanate and tetrabutyl titanate, preferably tetrabutyl titanate.

[0013] As a preferred technical solution of the present invention, in step (1), the molar ratio of phthalic acid to isophthalic acid is 1:(0.08-0.1).

[0014] As a preferred technical solution of the present invention, in step (1), the mass ratio of tricyclodecanediethanol to neopentyl glycol is (0.08-0.1):1.

[0015] As a preferred technical solution of the present invention, in step (1), the ratio of the sum of the moles of terephthalic acid and isophthalic acid to the sum of the moles of tricyclodecanediethanol and neopentyl glycol is 1:(1.2-1.5).

[0016] As a preferred technical solution of the present invention, in step (1), the amount of catalyst used is 0.4-0.8% of the total mass of terephthalic acid, isophthalic acid, tricyclodecanediethanol and neopentyl glycol.

[0017] As a preferred technical solution of the present invention, in step (2), the stabilizer is selected from at least one of triphenyl phosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, tri(nonylphenyl) phosphite and dimethyl methylphosphonate, preferably triphenyl phosphite.

[0018] As a preferred technical solution of the present invention, in step (2), the amount of stabilizer is 0.05-0.08% of the total mass of terephthalic acid, isophthalic acid, tricyclodecanediethanol and neopentyl glycol.

[0019] As a preferred embodiment of the present invention, the method for preparing the polyester copolymer masterbatch includes:

[0020] (1) Add terephthalic acid, isophthalic acid, tricyclodecanediethanol and neopentyl glycol to a reaction vessel, replace the air in the reaction vessel with nitrogen, and then raise the temperature. When the temperature reaches 180-230℃, add tetrabutyl titanate (equivalent to 0.4-0.8% of the total mass of terephthalic acid, isophthalic acid, tricyclodecanediethanol and neopentyl glycol) to carry out esterification reaction and remove the by-product water. When the total esterification rate reaches more than 95%, the esterification reaction ends. The molar ratio of terephthalic acid to isophthalic acid is 1:(0.08-0.1), the mass ratio of tricyclodecanediethanol to neopentyl glycol is (0.08-0.1):1, and the ratio of the sum of the moles of terephthalic acid and isophthalic acid to the sum of the moles of tricyclodecanediethanol and neopentyl glycol is 1:(1.2-1.5).

[0021] (2) Continue to add triphenyl phosphite (equivalent to 0.05-0.08% of the total mass of terephthalic acid, isophthalic acid, tricyclodecanediethanol and neopentyl glycol), and then continuously reduce the pressure of the reactor to a vacuum of 10-200 Pa within 40 minutes. During this process, the byproducts tricyclodecanediethanol and neopentyl glycol are continuously distilled off. When the vacuum of 10-200 Pa is reached, control the reaction temperature at 220-245℃ for vacuum polycondensation for 2-3 hours. Then, use nitrogen to restore the reactor to normal pressure to obtain polymer melt. After passing the polymer melt through a melt pump, it is pelletized to obtain polyester copolymer masterbatch.

[0022] As a preferred embodiment of the present invention, the epoxy value of the epoxidized hydroxyl-terminated liquid polybutadiene is 1.7-2 mmol / g.

[0023] As a preferred embodiment of the present invention, the epoxidized hydroxyl-terminated liquid polybutadiene was purchased from Zibo Qilong Chemical Co., Ltd., with an average epoxy value of 1.85 mmol / g.

[0024] As a preferred embodiment of the present invention, the preparation method of the coupling agent modified aluminum hydroxyaluminate includes:

[0025] (1) Disperse aluminum hydroxide with anhydrous ethanol to obtain a suspension;

[0026] (2) Mix the coupling agent with a mixture of ethanol and water, then adjust the pH to 4-5 with acetic acid, and finally hydrolyze to obtain a coupling agent hydrolysate.

[0027] (3) The coupling agent hydrolysate is added dropwise to the suspension to carry out the modification reaction, and then filtered, washed and dried to obtain coupling agent modified aluminum hydroxide.

[0028] As a preferred technical solution of the present invention, in step (1), the average particle size of the aluminum hydroxyaluminate is 10-30 nm, preferably 20 nm.

[0029] As a preferred technical solution of the present invention, in step (1), the amount of aluminum hydroxide and anhydrous ethanol used is such that the concentration of the suspension is 5-20 wt%, preferably 10 wt%.

[0030] In this invention, there are no special restrictions on the dispersion conditions in step (1), as long as the dispersion can be uniform. As a preferred technical solution of this invention, in step (1), ultrasonic dispersion is performed for 10-60 minutes.

[0031] As a preferred technical solution of the present invention, in step (2), the volume ratio of ethanol to water is 1:(0.5-2), preferably 1:1.

[0032] As a preferred technical solution of the present invention, in step (2), the mass ratio of the coupling agent to the mixture of ethanol and water is (0.5-1.5):10, preferably 1:10.

[0033] As a preferred embodiment of the present invention, the mass of the coupling agent is 3-6 wt% of the mass of the aluminum hydroxide.

[0034] As a preferred technical solution of the present invention, the coupling agent is selected from at least one of coupling agent KH-550, coupling agent KH-560, coupling agent KH-792 and coupling agent KH-570, preferably coupling agent KH-560.

[0035] As a preferred technical solution of the present invention, in step (2), the hydrolysis conditions include: stirring the reaction at 45-60℃ for 20-60 min.

[0036] As a preferred technical solution of the present invention, in step (3), the conditions for the modification reaction include: constant temperature stirring at 60-75℃ for 1-4 hours.

[0037] The filtration, washing, and drying in step (3) of this invention are conventional operating methods in the field.

[0038] As a more preferred technical solution of the present invention, the preparation method of the coupling agent modified aluminum hydroxyaluminate includes:

[0039] (1) Add aluminum hydroxide with an average particle size of 20 nm to anhydrous ethanol and ultrasonically disperse for 30 min to obtain a suspension with a concentration of 10 wt%.

[0040] (2) The coupling agent KH-560 with a mass ratio of 1:10 was mixed with a mixture of ethanol and water with a volume ratio of 1:1. Then, the pH was adjusted to 5 with acetic acid. The mixture was stirred at 50°C for 30 min to obtain a coupling agent hydrolysate. The mass of the coupling agent KH-560 was 4.5 wt% of the mass of aluminum hydroxide.

[0041] (3) The coupling agent hydrolysate was added dropwise to the suspension, and then stirred at 70°C for 2 hours. After filtration, the filter cake was washed three times with anhydrous ethanol, and finally dried under vacuum at 60°C for 12 hours to obtain coupling agent modified aluminum hydroxyalumina.

[0042] As a preferred embodiment of the present invention, the catalyst is selected from at least one of dibutyltin dilaurate, stannous octoate, and tetrabutyl titanate, preferably dibutyltin dilaurate.

[0043] As a preferred technical solution of the present invention, the polyurethane acrylate is EBECRIL 4738 aliphatic polyurethane acrylate, a UV-curable resin from Zhanxin.

[0044] As a preferred technical solution of the present invention, the styrene-acrylic emulsion is BASF Acronal 7588 styrene-acrylic emulsion.

[0045] As a preferred technical solution of the present invention, the photoinitiator is selected from at least one of photoinitiator 1173, photoinitiator 184 and photoinitiator 1104.

[0046] As a preferred embodiment of the present invention, the polydimethylsiloxane is of the type Dow Corning DC1785.

[0047] As a preferred embodiment of the present invention, the method for preparing the coating includes:

[0048] a. Epoxidized hydroxyl-terminated liquid polybutadiene, glycidyl methacrylate, and coupling agent-modified aluminum hydroxyaluminate are mixed with water in the first step, and then hexamethylene diisocyanate trimer is added to carry out the first reaction to obtain emulsion A.

[0049] b. Polyurethane acrylate, styrene-acrylic emulsion, photoinitiator and polydimethylsiloxane are mixed in a second mixture to obtain emulsion B;

[0050] c. Under the protection of an inert gas, emulsion A is added dropwise to emulsion B. After the addition is complete, a second reaction is carried out to obtain the coating.

[0051] As a preferred technical solution of the present invention, in step a, the conditions for the first mixing include: ultrasonic dispersion at 50-70℃ for 20-60 min.

[0052] As a preferred technical solution of the present invention, in step a, the conditions of the first reaction include: a reaction temperature of 80-90℃ and a reaction time of 1-3h.

[0053] As a preferred technical solution of the present invention, in step b, the conditions for the second mixing include: shearing at a shear rate of 4000-6000 s⁻¹ for 10-60 min.

[0054] As a preferred technical solution of the present invention, in step c, the inert gas is selected from nitrogen and / or argon.

[0055] As a preferred technical solution of the present invention, in step c, the conditions for the second reaction include: a reaction temperature of 40-60℃ and a reaction time of 3-8h.

[0056] As a more preferred technical solution of the present invention, the method for preparing the coating includes:

[0057] a. After ultrasonically dispersing epoxidized hydroxyl-terminated liquid polybutadiene, glycidyl methacrylate, and coupling agent-modified aluminum hydroxide with water at 60°C for 30 min, hexamethylene diisocyanate trimer and catalyst were added and reacted at 85°C for 2 h to obtain emulsion A.

[0058] b. Polyurethane acrylate, styrene-acrylic emulsion, photoinitiator and polydimethylsiloxane were subjected to shearing at a shear rate of 5000 s⁻¹ for 30 min to obtain emulsion B.

[0059] c. Under nitrogen protection, emulsion A is added dropwise to emulsion B. After the addition is complete, the mixture is reacted at 50°C for 5 hours to obtain the coating.

[0060] As a preferred embodiment of the present invention, the thickness of the coating is 5-20 micrometers.

[0061] As a preferred embodiment of the present invention, the thickness of the base film is 30-100 micrometers.

[0062] The second aspect of the present invention provides a method for preparing the polyester film for the transparent backing plate described in the first aspect of the present invention.

[0063] S1. The raw materials for the base film are stirred and mixed at a speed of 1200-1500 rpm for 10-30 min to obtain a premix. The premix is ​​then sent to a granulation extruder and extruded and granulated at 270-280℃ to prepare the composite.

[0064] S2 sends the prepared composite to an extruder, where it is melt-extruded, cooled, biaxially stretched, heat-set, and wound up to obtain a base film.

[0065] S3 applies the coating to one surface of the base film, followed by pre-baking, UV curing, and heat curing.

[0066] The melting extrusion followed by cooling, biaxial stretching, heat setting, and winding in step S2 of this invention are conventional techniques in the field. As long as a base film of the corresponding thickness can be prepared, it is acceptable. This invention will not elaborate further on these techniques.

[0067] As a preferred technical solution of the present invention, in step S3, the pre-drying conditions include: pre-drying at 70-80℃ for 2-3 minutes.

[0068] As a preferred embodiment of the present invention, in step S3, the UV curing conditions include: a power of 90-150 W / m 2 Energy 600-800mJ / m 2 .

[0069] In step S3 of this invention, there is no special limitation on the amount of coating applied, as long as the coating obtained subsequently has the corresponding thickness.

[0070] Compared with the prior art, the present invention has at least the following beneficial effects:

[0071] The transparent backsheet polyester film of this invention is produced by blending polyester chips and polyester copolymer masterbatch in different proportions, followed by extrusion, stretching, and coating processes. It exhibits excellent transparency, with a light transmittance exceeding 90%, superior resistance to high temperature and humidity, and a break elongation retention rate of over 50% after aging. The product also boasts excellent flatness, with a shrinkage rate below 0.5%, facilitating subsequent processing and reducing bumps and deformation. Furthermore, it demonstrates good barrier properties, with a water vapor barrier performance below 1.0, overcoming the shortcomings of ordinary polyester films and enabling its application in the photovoltaic new energy field, meeting the requirements for solar cell backsheet modules. Detailed Implementation

[0072] The embodiments given below are intended to further illustrate the present invention, but should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0073] The following preparation examples and embodiments illustrate the preparation of coupling agent-modified aluminum hydroxyalumina:

[0074] (1) Add aluminum hydroxide with an average particle size of 20 nm to anhydrous ethanol and ultrasonically disperse for 30 min to obtain a suspension with a concentration of 10 wt%.

[0075] (2) The coupling agent KH-560 with a mass ratio of 1:10 was mixed with a mixture of ethanol and water with a volume ratio of 1:1. Then, the pH was adjusted to 5 with acetic acid. The mixture was stirred at 50°C for 30 min to obtain a coupling agent hydrolysate. The mass of the coupling agent KH-560 was 4.5 wt% of the mass of aluminum hydroxide.

[0076] (3) The coupling agent hydrolysate was added dropwise to the suspension, and then stirred at 70°C for 2 hours. After filtration, the filter cake was washed three times with anhydrous ethanol, and finally dried under vacuum at 60°C for 12 hours to obtain coupling agent modified aluminum hydroxyalumina.

[0077] In the following preparation examples and embodiments, the preparation method of polyester copolymer masterbatch A includes:

[0078] (1) Terephthalic acid, isophthalic acid, tricyclodecanediethanol and neopentyl glycol are added to a reaction vessel. The air in the reaction vessel is replaced with nitrogen. Then the temperature is raised. When the temperature reaches 225°C, tetrabutyl titanate (equivalent to 0.7% of the total mass of terephthalic acid, isophthalic acid, tricyclodecanediethanol and neopentyl glycol) is added to carry out the esterification reaction and remove the by-product water. When the total esterification rate reaches more than 95%, the esterification reaction ends. The molar ratio of terephthalic acid to isophthalic acid is 1:0.09, the mass ratio of tricyclodecanediethanol to neopentyl glycol is 0.092:1, and the ratio of the sum of the moles of terephthalic acid and isophthalic acid to the sum of the moles of tricyclodecanediethanol and neopentyl glycol is 1:1.35.

[0079] (2) Continue to add triphenyl phosphite (equivalent to 0.06% of the total mass of terephthalic acid, isophthalic acid, tricyclodecanediethanol and neopentyl glycol), and then continuously reduce the pressure of the reactor to a vacuum of 50 Pa within 40 minutes. During this process, the byproducts tricyclodecanediethanol and neopentyl glycol are continuously distilled off. When the vacuum of 50 Pa is reached, control the reaction temperature at 235 °C for vacuum polycondensation for 3 hours. Then, use nitrogen to restore the reactor to normal pressure to obtain polymer melt. After passing the polymer melt through a melt pump, it is pelletized to obtain polyester copolymer masterbatch A.

[0080] In the following preparation examples and embodiments, the preparation method of polyester copolymer masterbatch B includes:

[0081] (1) Add terephthalic acid, isophthalic acid and neopentyl glycol to a reaction vessel, replace the air in the reaction vessel with nitrogen, and then raise the temperature. When the temperature reaches 225°C, add tetrabutyl titanate (equivalent to 0.7% of the total mass of terephthalic acid, isophthalic acid and neopentyl glycol) to carry out esterification reaction and remove the by-product water. When the total esterification rate reaches more than 95%, the esterification reaction ends. The molar ratio of terephthalic acid to isophthalic acid is 1:0.09, and the ratio of the sum of the moles of terephthalic acid and isophthalic acid to the moles of neopentyl glycol is 1:1.35.

[0082] (2) Continue to add triphenyl phosphite (equivalent to 0.06% of the total mass of terephthalic acid, isophthalic acid and neopentyl glycol), and then continuously reduce the pressure of the reactor to a vacuum of 50 Pa within 40 minutes. During this process, the by-product neopentyl glycol is continuously distilled off. When the vacuum reaches 50 Pa, control the reaction temperature at 235 °C for vacuum polycondensation for 3 hours. Then, use nitrogen to restore the reactor to normal pressure to obtain polymer melt. After passing the polymer melt through a melt pump, it is pelletized to obtain polyester copolymer masterbatch B.

[0083] In the following preparation examples and embodiments, the preparation method of polyester copolymer masterbatch C includes:

[0084] (1) Add terephthalic acid, isophthalic acid and tricyclodecanediethanol to a reaction vessel, replace the air in the reaction vessel with nitrogen, and then raise the temperature. When the temperature reaches 225°C, add tetrabutyl titanate (equivalent to 0.7% of the total mass of terephthalic acid, isophthalic acid and tricyclodecanediethanol) to carry out esterification reaction and remove the by-product water. When the total esterification rate reaches more than 95%, the esterification reaction ends. The molar ratio of terephthalic acid to isophthalic acid is 1:0.09, and the ratio of the sum of the moles of terephthalic acid and isophthalic acid to the sum of the moles of tricyclodecanediethanol is 1:1.35.

[0085] (2) Continue to add triphenyl phosphite (equivalent to 0.06% of the total mass of terephthalic acid, isophthalic acid and tricyclodecanediethanol), and then continuously reduce the pressure of the reactor to a vacuum of 50 Pa within 40 minutes. During this process, the byproduct tricyclodecanediethanol is continuously distilled off. When the vacuum of 50 Pa is reached, control the reaction temperature at 235 °C for vacuum polycondensation for 3 hours. Then, use nitrogen to restore the reactor to normal pressure to obtain polymer melt. After passing the polymer melt through a melt pump, it is pelletized to obtain polyester copolymer masterbatch C.

[0086] In the following preparation examples and embodiments, the epoxidized hydroxyl-terminated liquid polybutadiene was purchased from Zibo Qilong Chemical Co., Ltd., with an average epoxy value of 1.85 mmol / g.

[0087] In the following preparation examples and embodiments, the polyurethane acrylate is Zhanxin UV-curable resin EBECRYL4738 aliphatic polyurethane acrylate.

[0088] In the following preparation examples and embodiments, the styrene-acrylic emulsion is BASF Acronal 7588 styrene-acrylic emulsion.

[0089] In the following preparation examples and embodiments, the polydimethylsiloxane is Dow Corning DC1785.

[0090] Preparation Example

[0091] Preparation Example 1

[0092] Raw material preparation for coating: By weight, prepare 12 parts of epoxidized hydroxyl-terminated liquid polybutadiene, 28 parts of glycidyl methacrylate, 12 parts of coupling agent modified hydroxyl aluminum oxide, 15 parts of water, 4.5 parts of hexamethylene diisocyanate trimer, 0.25 parts of catalyst, 23 parts of polyurethane acrylate, 11 parts of styrene-acrylic emulsion, 2 parts of photoinitiator, and 2.7 parts of polydimethylsiloxane.

[0093] Preparation of coatings:

[0094] a. After ultrasonically dispersing epoxidized hydroxyl-terminated liquid polybutadiene, glycidyl methacrylate, and coupling agent-modified aluminum hydroxide with water at 60°C for 30 min, hexamethylene diisocyanate trimer and dibutyltin dilaurate were added and reacted at 85°C for 2 h to obtain emulsion A.

[0095] b. Polyurethane acrylate, styrene-acrylic emulsion, photoinitiator 184 and polydimethylsiloxane were subjected to shearing at a shear rate of 5000 s⁻¹ for 30 min to obtain emulsion B.

[0096] c. Under nitrogen protection, emulsion A is added dropwise to emulsion B. After the addition is complete, the mixture is reacted at 50°C for 5 hours to obtain a coating, which is denoted as coating A.

[0097] Preparation Example 2

[0098] Raw material preparation for coating: By weight, prepare 15 parts of epoxidized hydroxyl-terminated liquid polybutadiene, 25 parts of glycidyl methacrylate, 15 parts of coupling agent modified aluminum hydroxyalumina, 10 parts of water, 5 parts of hexamethylene diisocyanate trimer, 0.3 parts of dibutyltin dilaurate, 30 parts of polyurethane acrylate, 12 parts of styrene-acrylic emulsion, 2 parts of photoinitiator 184, and 3.5 parts of polydimethylsiloxane.

[0099] Preparation of coating: Same as in preparation example 1, the final coating is prepared and denoted as coating B.

[0100] Preparation Example 3

[0101] Raw material preparation for coating: By weight, prepare 40 parts glycidyl methacrylate, 12 parts coupling agent modified aluminum hydroxyaluminate, 15 parts water, 4.5 parts hexamethylene diisocyanate trimer, 0.25 parts catalyst, 23 parts polyurethane acrylate, 11 parts styrene-acrylic emulsion, 2 parts photoinitiator, and 2.7 parts polydimethylsiloxane.

[0102] Preparation of coatings:

[0103] a. Glycidyl methacrylate and coupling agent-modified aluminum hydroxide were ultrasonically dispersed with water at 60°C for 30 min, and then hexamethylene diisocyanate trimer and dibutyltin dilaurate were added and reacted at 85°C for 2 h to obtain emulsion A.

[0104] b. Polyurethane acrylate, styrene-acrylic emulsion, photoinitiator 184 and polydimethylsiloxane were subjected to shearing at a shear rate of 5000 s⁻¹ for 30 min to obtain emulsion B.

[0105] c. Under nitrogen protection, emulsion A is added dropwise to emulsion B. After the addition is complete, the mixture is reacted at 50°C for 5 hours to obtain a coating, which is denoted as coating C.

[0106] Example

[0107] Example 1

[0108] S1. PET chips with a weight ratio of 100:14 and polyester copolymer masterbatch are stirred and mixed at 1200 rpm for 25 min to obtain a premix. The premix is ​​then sent to a granulation extruder and extruded and granulated at 275°C to prepare the composite.

[0109] S2 sends the prepared composite to an extruder, and after melt extrusion, it is cooled, biaxially stretched, heat-set, and wound up to obtain a base film with a thickness of 80 micrometers.

[0110] S3 involves applying coating A onto one surface of the base film, pre-baking at 75°C for 2 minutes, and finally UV curing (power 120W / m). 2 Energy 750mJ / m 2 A transparent backing film with a coating thickness of 20 micrometers, formed by thermosetting.

[0111] Example 2

[0112] S1. PET chips with a weight ratio of 100:12 and polyester copolymer masterbatch A are stirred and mixed at 1200 rpm for 15 min to obtain a premix. The premix is ​​then sent to a granulation extruder and extruded and granulated at 275°C to prepare the composite.

[0113] S2 sends the prepared composite to an extruder, and after melt extrusion, it is cooled, biaxially stretched, heat-set, and wound up to obtain a base film with a thickness of 80 micrometers.

[0114] S3 involves applying coating B onto one surface of the base film, pre-baking at 75°C for 2 minutes, and finally UV curing (power 100W / m). 2 Energy 750mJ / m 2 A transparent backing film with a coating thickness of 20 micrometers, formed by thermosetting.

[0115] Example 3

[0116] The method is the same as in Example 1, except that paint A is replaced with paint C;

[0117] Finally, a transparent polyester film for the backing plate was prepared.

[0118] Example 4

[0119] The method is the same as in Example 1, except that polyester copolymer masterbatch A is replaced with polyester copolymer masterbatch B.

[0120] Finally, a transparent polyester film for the backing plate was prepared.

[0121] Example 5

[0122] The method is the same as in Example 1, except that polyester copolymer masterbatch A is replaced with polyester copolymer masterbatch C.

[0123] Finally, a transparent polyester film for the backing plate was prepared.

[0124] Comparative Example 1

[0125] S1 feeds PET chips to an extruder, where they are melt-extruded, cooled, biaxially stretched, heat-set, and wound to obtain a base film with a thickness of 80 micrometers.

[0126] S2 involves applying coating A onto one surface of the base film, pre-baking at 75°C for 2 minutes, and finally UV curing (power 120W / m). 2 Energy 750mJ / m 2 A transparent backing film with a coating thickness of 20 micrometers, formed by thermosetting.

[0127] Performance testing

[0128] The following tests were conducted on the polyester film used for the transparent backsheets in Examples 1-5 and Comparative Example 1, respectively:

[0129] 1. Light transmittance test: The test was conducted in accordance with ASTM D 1003-2013 standard.

[0130] 2. Water vapor transmission rate (WVTR) test: The test was conducted using a Mocon water vapor transmission rate tester (USA).

[0131] 3. Observe whether there are bumps on the surface of the polyester film used for the transparent back panel.

[0132] 4. After heat-treating the transparent backing sheet with polyester film at 121℃ and 100%RH for 100h, test and calculate its elongation at break retention rate.

[0133] The test results of the polyester film used for the transparent backsheet in Examples 1-5 and Comparative Example 1 are shown in Table 1.

[0134] Table 1. Test results of the polyester film for the transparent backsheet in Examples 1-5 and Comparative Example 1.

[0135]

[0136] As can be seen from the test results of the examples and comparative examples, the polyester film for the transparent backing plate of the present invention has good transparency, excellent high temperature and high humidity resistance, a high elongation at break retention rate of 50% after aging, and excellent product flatness.

[0137] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0138] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A polyester film for a transparent backing plate, characterized in that, The polyester film includes a base film and a coating that is adhered to the outer surface of the base film; By weight, the raw materials of the base film include: 100 parts PET chips and 12-15 parts polyester copolymer masterbatch; by weight, the coating is obtained by applying and curing a paint, and the raw materials of the paint include: 8-15 parts epoxidized hydroxyl-terminated liquid polybutadiene, 25-32 parts glycidyl methacrylate, 10-15 parts coupling agent modified aluminum hydroxyalumina, 10-20 parts water, 4-5 parts hexamethylene diisocyanate trimer, 0.2-0.3 parts catalyst, 20-30 parts polyurethane acrylate, 8-15 parts styrene-acrylic emulsion, 1.5-2.5 parts photoinitiator, and 2.5-3.5 parts polydimethylsiloxane.

2. The polyester film for a transparent backing plate according to claim 1, characterized in that, The preparation method of the polyester copolymer masterbatch includes: (1) in the presence of a catalyst, terephthalic acid, isophthalic acid, tricyclodecanediethanol and neopentyl glycol are added to a reactor for esterification reaction and water by-product is removed. When the total esterification rate reaches more than 95%, the esterification reaction ends; (2) in the presence of a stabilizer, the reactor is continuously depressurized to a vacuum degree of 10-200 Pa within 40 minutes. During this process, the by-products tricyclodecanediethanol and neopentyl glycol are continuously distilled out. When the vacuum degree is reached, the reaction temperature is controlled at 220-245℃ for vacuum polycondensation for 2-3 hours. Then, the reactor is restored to normal pressure with an inert gas to obtain a polymer melt. The polymer melt is then pelletized by a melt pump to obtain polyester copolymer masterbatch.

3. The polyester film for a transparent backing plate according to claim 2, characterized in that, In step (1), the molar ratio of terephthalic acid to isophthalic acid is 1:(0.08-0.1); in step (1), the mass ratio of tricyclodecanediethanol to neopentyl glycol is (0.08-0.1):1; in step (1), the ratio of the sum of the moles of terephthalic acid and isophthalic acid to the sum of the moles of tricyclodecanediethanol and neopentyl glycol is 1:(1.2-1.5).

4. The polyester film for a transparent backing plate according to claim 1, characterized in that, The epoxy value of the epoxidized hydroxyl-terminated liquid polybutadiene is 1.7-2 mmol / g; the catalyst is selected from at least one of dibutyltin dilaurate, stannous octoate, and tetrabutyl titanate, preferably dibutyltin dilaurate; the photoinitiator is selected from at least one of photoinitiator 1173, photoinitiator 184, and photoinitiator 1104.

5. The polyester film for a transparent backing plate according to claim 1, characterized in that, The preparation method of the coupling agent modified aluminum hydroxyaluminum includes: (1) dispersing aluminum hydroxyaluminum with anhydrous ethanol to obtain a suspension; (2) mixing the coupling agent with a mixture of ethanol and water, then adjusting the pH to 4-5 with acetic acid, and finally hydrolyzing to obtain a coupling agent hydrolysate; (3) adding the coupling agent hydrolysate dropwise to the suspension for modification reaction, and then filtering, washing and drying to obtain coupling agent modified aluminum hydroxyaluminum.

6. The polyester film for a transparent backing plate according to claim 1, characterized in that, The preparation method of the coating includes: a) mixing epoxidized hydroxyl-terminated liquid polybutadiene, glycidyl methacrylate, and coupling agent-modified aluminum hydroxyaluminate with water, followed by adding hexamethylene diisocyanate trimer to carry out a first reaction to obtain emulsion A; b) mixing polyurethane acrylate, styrene-acrylic emulsion, photoinitiator, and polydimethylsiloxane to obtain emulsion B; c) under inert gas protection, adding emulsion A dropwise to emulsion B, and after the addition is complete, carrying out a second reaction to obtain the coating.

7. The polyester film for a transparent backing plate according to claim 6, characterized in that, In step a, the conditions for the first mixing include: ultrasonic dispersion at 50-70℃ for 20-60 min; in step a, the conditions for the first reaction include: reaction temperature of 80-90℃ and reaction time of 1-3 h.

8. The polyester film for a transparent backing plate according to claim 6, characterized in that, In step b, the conditions for the second mixing include: shearing at a shear rate of 4000-6000 s⁻¹ for 10-60 min; in step c, the inert gas is selected from nitrogen and / or argon; in step c, the conditions for the second reaction include: a reaction temperature of 40-60 °C and a reaction time of 3-8 h.

9. The polyester film for a transparent backing plate according to claim 1, characterized in that, The coating has a thickness of 5-20 micrometers; the base film has a thickness of 30-100 micrometers.

10. A method for preparing a polyester film for a transparent backing plate according to any one of claims 1-9, characterized in that, The preparation method includes: S1, stirring and mixing the raw materials of the base film at a speed of 1200-1500 rpm for 10-30 min to obtain a premix, and then sending the premix to a granulation extruder for extrusion granulation at 270-280℃ to prepare a composite; S2 sending the prepared composite to an extruder, and after melt extrusion, cooling, biaxial stretching, heat setting, and winding to obtain a base film; S3 coating a coating on one surface of the base film, and then pre-baking, UV curing, and heat curing.

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