A high-barrier anti-ultraviolet polyester film and preparation method thereof

Abstract

The present invention relates to the technical field of polyester films, and specifically to a high-barrier anti-ultraviolet polyester film and a preparation method thereof. Conventional photovoltaic back panels available on the market have a high water permeability and cannot meet the technical requirements of N-type batteries. In view of the above problems, the present invention provides a high-barrier anti-ultraviolet polyester film, in which exfoliation-modified mica sheets are added during the in-situ polymerization of PET polyester. The modified mica sheets utilize quaternary ammonium salts to replace the sodium ions between the mica sheets, so that the mica sheets are exfoliated. The modified mica sheets are uniformly dispersed in the polyester film in the form of nano-thin sheets. The layered structure of the mica sheets causes the path for water vapor molecules to penetrate tortuously, which significantly improves the water vapor barrier performance of the polyester film.

Description

Technical Field

[0001] The invention relates to the technical field of polyester films, and in particular to a high-barrier anti-ultraviolet polyester film and a preparation method thereof. Background Art

[0002] The development of photovoltaics revolves around two hot topics: low electricity cost and low carbon. The conversion efficiency of N-type batteries continues to break world records, and N-type batteries have ushered in a new era. High-efficiency batteries are the development trend in the next 5-10 years, and Topcon and HJT technologies of N-type batteries will become mainstream. However, Topcon and HJT technologies are very sensitive to water vapor. How to reduce the water vapor permeability of photovoltaic backplanes is the technical key for N-type batteries to occupy the future market.

[0003] The water permeability of conventional photovoltaic backsheets currently on the market is about (1.8-2.3) g / m 2 ·day (infrared method: 38℃, 90%RH). The water vapor barrier property of commercially available photovoltaic backsheets is relatively weak and cannot meet the technical requirements of N-type batteries. Therefore, how to improve the water vapor barrier property of photovoltaic backsheets becomes particularly important. The backsheet is located on the back of the solar cell and supports and protects the cell. It generally has a three-layer structure. The polyester film serves as an insulating and water-blocking middle layer. Therefore, improving the water vapor barrier property of the polyester film plays a vital role in the water vapor barrier property of the photovoltaic backsheet.

[0004] In order to solve the above problems, Chinese invention patent CN112373169A discloses a method for preparing a high barrier aluminum oxide film, which deposits aluminum oxide on a polyester film to reduce the water vapor permeability of the polyester film. However, this technology has high manufacturing costs and high requirements on the appearance of the polyester film. The deposited inorganic coating is prone to vacuum, cracks and other defects due to the rough, uneven and loose surface of the polyester film, resulting in a decrease in the barrier properties of the inorganic coating. Another Chinese invention patent CN104943301B discloses an ultra-high barrier optical polyester film, which uses polyvinyl alcohol to prepare an emulsion and coats it on a polyester film substrate. This coating liquid can play a good role in water vapor barrier, but the coating is not resistant to hydrolysis. When the coating is in a high humidity environment, its water vapor barrier performance will fail.

[0005] In order to solve the above problems, the present invention modifies and peels off the mica sheet, adds the modified mica sheet with high aspect ratio to the PET polyester raw material, and obtains polyester slices through esterification and polycondensation reaction, and then obtains polyester film by biaxial stretching the polyester slices. The modified mica sheet itself has good water vapor barrier performance, and as an added component of the polyester film, it can significantly improve the water vapor permeability of the polyester film. The surface of the modified mica sheet is also loaded with silicon dioxide nanoparticles. Nano silicon dioxide has strong hydrophobicity, which can not only hinder the adsorption of water molecules on the surface of the mica sheet, but also increase the roughness of the surface of the modified mica sheet, making the penetration and diffusion of water vapor in the polyester film more tortuous and difficult, thereby achieving the purpose of greatly improving the water vapor barrier performance of the polyester film. Summary of the invention

[0006] The problem in the prior art is how to improve the water vapor barrier performance of the polyester film for photovoltaic backsheets. In view of the above problem, the present invention provides a high barrier anti-ultraviolet polyester film, which is prepared by direct esterification and polycondensation of terephthalic acid, ethylene glycol and modified mica sheets under the action of a catalyst to obtain polyester chips, and then the obtained polyester chips are melt-extruded through a twin-screw extruder, and then cast, biaxially stretched, shaped, cooled and rolled to obtain a film.

[0007] Specifically, the molar ratio of terephthalic acid to ethylene glycol is 1:(1.1-1.4).

[0008] Specifically, the added amount of the modified mica flakes is 1-5% of the weight of terephthalic acid.

[0009] Specifically, the preparation method of the modified mica sheet comprises the following steps:

[0010] (1) Modification and exfoliation of mica sheets by quaternary ammonium salts

[0011] 10 g of mica flakes were added to 250 mL of DMF, and ultrasonically dispersed for 1 h. After adding quaternary ammonium salt, the mixture was stirred in a water bath at 80° C. for 24 h, and then centrifuged and dried with anhydrous ethanol for multiple times to obtain quaternary ammonium salt-modified mica flakes, wherein the amount of the quaternary ammonium salt added was 1-10% of the mass of the mica flakes;

[0012] (2) The quaternary ammonium salt-modified mica flakes, dodecylamine, and ethyl orthosilicate were mixed uniformly in a mass ratio of 1:1:2, stirred and reacted at room temperature for 3-5 hours, washed and dried, and then calcined in a muffle furnace at 300°C for 2 hours to obtain nano-SiO 2 Loaded mica sheets.

[0013] Specifically, the average particle size of the mica flakes is 3-10 μm.

[0014] Specifically, the quaternary ammonium salt includes at least one of epoxytrimethylammonium bromide, dodecyltrimethylammonium bromide, choline, and betaine.

[0015] Specifically, the added amount of the catalyst accounts for 0.02-0.05% by weight of terephthalic acid.

[0016] Specifically, the catalyst includes at least one of antimony acetate, antimony trioxide, titanium glycol, and tetrabutyl titanate.

[0017] Specifically, the temperature of the esterification reaction is 220-260° C., the pressure of the esterification reaction is 0-0.3 MPa, and the reaction time is 2-5 h.

[0018] Specifically, the temperature of the polycondensation reaction is 270-285° C., the vacuum degree is 0-80 Pa, and the reaction time is 2-5 hours.

[0019] Specifically, the temperature of the polyester chips during melt extrusion is 260-280°C, the biaxial stretching ratio is 3-4 times, and the shaping temperature is 200-250°C.

[0020] Beneficial Effects

[0021] (1) The present invention adds exfoliated modified mica sheets during the in-situ polymerization of PET polyester, and the modified mica sheets have a high aspect ratio, and their sheet structure is not easily destroyed during the processing;

[0022] (2) Compared with other sheet silicate materials, mica is a non-expanding clay without interlayer water, which will not cause the agglomeration and shrinkage of nanoparticles and can give full play to its water vapor barrier stability;

[0023] (3) The present invention utilizes quaternary ammonium salt to replace sodium ions between mica sheets, so that the mica sheets are peeled off, and the mica sheets are evenly dispersed in the polyester film in the form of nano-thin sheets. The layered structure of the mica sheets causes the path for water vapor molecules to penetrate tortuously, thereby improving the water vapor barrier performance of the polyester film.

[0024] (4) Mica flakes also have excellent UV shielding and aging resistance. Their two-dimensional flake structure can produce polarization and interference effects, which can greatly improve the anti-UV aging performance of polyester film and effectively prevent the problem of water vapor barrier performance of polyester film being reduced due to UV aging;

[0025] (5) The modified mica layer structure of the present invention also carries nano-silicon dioxide particles. 2 It is hydrophobic, which can prevent water molecules from adsorbing on the surface of modified mica sheets. On the other hand, nano-SiO 2The presence of increases the roughness of the surface of the modified mica sheet, further hindering the penetration and diffusion of water vapor in the polyester film, thereby greatly improving the water vapor barrier performance of the polyester film. DETAILED DESCRIPTION

[0026] Example 1

[0027] A high barrier UV-resistant polyester film is prepared according to the following steps:

[0028] (1) adding terephthalic acid, ethylene glycol, modified mica flakes, and antimony trioxide into a reaction kettle, stirring and mixing evenly, then raising the temperature of the reaction system to 220° C., adjusting the pressure to 0.3 MPa, stirring and esterifying for 5 hours, wherein the molar ratio of terephthalic acid to ethylene glycol is 1:1.1, the amount of the modified mica flakes added is 2% of the weight of terephthalic acid, and the amount of antimony trioxide added is 0.03% of the weight of terephthalic acid. After the reaction is completed, the vacuum degree of the reaction system is adjusted to 80 Pa, the temperature is adjusted to 270° C., and the polycondensation reaction is stirred for 2 hours to obtain polyester chips;

[0029] (2) The polyester chips obtained in step (1) are added into a twin-screw extruder for melt extrusion, the temperature of the twin-screw extruder is 265° C., and after casting, biaxial stretching, shaping, cooling and winding, a high-barrier anti-ultraviolet polyester film with a thickness of 250 μm is obtained, wherein the biaxial stretching ratio is 3 times and the shaping temperature is 220° C.

[0030] The preparation method of modified mica flakes is as follows:

[0031] (1) 10 g of mica flakes were added to 250 mL of DMF, and ultrasonically dispersed for 1 h, and then 0.2 g of epoxytrimethylammonium bromide was added, and the mixture was stirred and reacted in a water bath at 80° C. for 24 h, and then centrifuged and washed with anhydrous ethanol for multiple times and dried to obtain quaternary ammonium salt-modified mica flakes;

[0032] (2) Quaternary ammonium salt-modified mica flakes, dodecylamine, and ethyl orthosilicate were mixed uniformly in a mass ratio of 1:1:2, stirred and reacted at room temperature for 3 h, washed and dried, and then calcined in a muffle furnace at 300 °C for 2 h to obtain nano-SiO 2 Loaded mica sheets.

[0033] The mica flakes used for modification are synthetic mica with an average particle size of 8 μm, purchased from Lingshou Huajing Mica Co., Ltd.

[0034] Example 2

[0035] A high barrier UV-resistant polyester film is prepared according to the following steps:

[0036] (1) adding terephthalic acid, ethylene glycol, modified mica flakes, and antimony acetate into a reaction kettle, stirring and mixing evenly, then raising the temperature of the reaction system to 240° C., adjusting the pressure to 0.2 MPa, and stirring for esterification for 3 hours, wherein the molar ratio of terephthalic acid to ethylene glycol is 1:1.3, the amount of the modified mica flakes added is 3% of the weight of terephthalic acid, and the amount of antimony acetate added is 0.03% of the weight of terephthalic acid. After the reaction is completed, the vacuum degree of the reaction system is adjusted to 60 Pa, the temperature is adjusted to 280° C., and the polycondensation reaction is stirred for 3 hours to obtain polyester chips;

[0037] (2) The polyester chips obtained in step (1) are added into a twin-screw extruder for melt extrusion. The temperature of the twin-screw extruder is 275° C. After casting, biaxial stretching, shaping, cooling and winding, a high-barrier anti-ultraviolet polyester film with a thickness of 280 μm is obtained. The biaxial stretching ratio is 3.5 times and the shaping temperature is 230° C.

[0038] The preparation method of modified mica flakes is as follows:

[0039] (1) 10 g of mica flakes were added to 250 mL of DMF, ultrasonically dispersed for 1 h, 0.3 g of choline was added, and the mixture was stirred in a water bath at 80° C. for 24 h. The mica flakes were then washed with anhydrous ethanol by centrifugation and dried several times to obtain quaternary ammonium salt-modified mica flakes;

[0040] (2) The quaternary ammonium salt-modified mica flakes, dodecylamine, and ethyl orthosilicate were mixed uniformly in a mass ratio of 1:1:2, stirred and reacted at room temperature for 3-5 hours, washed and dried, and then calcined in a muffle furnace at 300°C for 2 hours to obtain nano-SiO 2 Loaded mica sheets.

[0041] The mica flakes used for modification are synthetic mica with an average particle size of 6 μm, purchased from Lingshou Huajing Mica Co., Ltd.

[0042] Example 3

[0043] A high barrier UV-resistant polyester film is prepared according to the following steps:

[0044] (1) Add terephthalic acid, ethylene glycol, modified mica flakes, and titanium glycol to a reaction kettle, stir and mix evenly, then raise the temperature of the reaction system to 250° C., adjust the pressure to 0.2 MPa, and stir for esterification for 2 hours. The molar ratio of terephthalic acid to ethylene glycol is 1:1.3, the amount of the modified mica flakes added is 1% by weight of terephthalic acid, and the amount of the titanium glycol added is 0.02% by weight of terephthalic acid. After the reaction is completed, adjust the vacuum degree of the reaction system to 40 Pa, adjust the temperature to 285° C., stir and polycondense for 3 hours, and obtain polyester chips;

[0045] (2) The polyester chips obtained in step (1) are added into a twin-screw extruder for melt extrusion, the temperature of the twin-screw extruder is 270° C., and after casting, biaxial stretching, shaping, cooling and winding, a high-barrier anti-ultraviolet polyester film with a thickness of 250 μm is obtained, wherein the biaxial stretching ratio is 4 times and the shaping temperature is 240° C.

[0046] The preparation method of the modified mica sheet is as follows:

[0047] (1) 10 g of mica flakes were added to 250 mL of DMF, ultrasonically dispersed for 1 h, 0.3 g of betaine was added, and the mixture was stirred in a water bath at 80° C. for 24 h. The mixture was then centrifuged and washed with anhydrous ethanol for multiple times and dried to obtain modified quaternary ammonium salt mica flakes;

[0048] (2) The quaternary ammonium salt-modified mica flakes, dodecylamine, and ethyl orthosilicate were mixed uniformly in a mass ratio of 1:1:2, stirred and reacted at room temperature for 3-5 hours, washed and dried, and then calcined in a muffle furnace at 300°C for 2 hours to obtain nano-SiO 2 Loaded mica sheets.

[0049] The mica flakes used for modification are synthetic mica with an average particle size of 5 μm, purchased from Lingshou Huajing Mica Co., Ltd.

[0050] Example 4

[0051] A high barrier UV-resistant polyester film is prepared according to the following steps:

[0052] (1) Add terephthalic acid, ethylene glycol, modified mica flakes, and tetrabutyl titanate into a reaction kettle, stir and mix evenly, then raise the temperature of the reaction system to 260° C., adjust the pressure to 0.2 MPa, and stir for esterification for 2 hours. The molar ratio of terephthalic acid to ethylene glycol is 1:1.2, the amount of the modified mica flakes added is 5% by weight of terephthalic acid, and the amount of the tetrabutyl titanate added is 0.04% by weight of terephthalic acid. After the reaction is completed, adjust the vacuum degree of the reaction system to 50 Pa, adjust the temperature to 285° C., stir and polycondense for 4 hours, and obtain polyester chips;

[0053] (2) adding the polyester chips obtained in step (1) into a twin-screw extruder for melt extrusion, the temperature of the twin-screw extruder is 280° C., and after casting, biaxial stretching, shaping, cooling and winding, a high-barrier anti-ultraviolet polyester film with a thickness of 300 μm is obtained, wherein the biaxial stretching ratio is 3 times and the shaping temperature is 250° C.

[0054] The preparation method of modified mica flakes is as follows:

[0055] (1) 10 g of mica flakes were added to 250 mL of DMF, ultrasonically dispersed for 1 h, 0.6 g of hexadecyltrimethylammonium bromide was added, and the mixture was stirred in a water bath at 80° C. for 24 h. The mixture was then centrifugally washed and dried with anhydrous ethanol for multiple times to obtain quaternary ammonium salt-modified mica flakes;

[0056] (2) The quaternary ammonium salt-modified mica flakes, dodecylamine, and ethyl orthosilicate were mixed uniformly in a mass ratio of 1:1:2, stirred and reacted at room temperature for 3-5 hours, washed and dried, and then calcined in a muffle furnace at 300°C for 2 hours to obtain nano-SiO 2 Loaded mica sheets.

[0057] The mica flakes used for modification are synthetic mica with an average particle size of 3 μm, purchased from Lingshou Huajing Mica Co., Ltd.

[0058] Comparative Example 1 is the same as Example 1, except that unmodified mica sheets are used in Comparative Example 1 to replace the modified mica sheets in Example 1. The mica sheets used in Comparative Example 1 are synthetic mica with an average particle size of 8 μm, purchased from Lingshou Huajing Mica Co., Ltd.

[0059] Comparative Example 2 is the same as Example 1, except that the modified mica sheet in Comparative Example 2 is not loaded with nano-SiO 2 , and its preparation method is as follows:

[0060] 10 g of mica flakes were added to 50 mL of DMF, ultrasonically dispersed for 1 h, 0.2 g of epoxytrimethylammonium bromide was added, and the mixture was stirred in a water bath at 80° C. for 24 h. The mica flakes were then washed and dried by centrifugation with anhydrous ethanol for multiple times to obtain quaternary ammonium salt-modified mica flakes.

[0061] Comparative Example 3 is the same as Example 1, except that the nano-SiO 2 and quaternary ammonium salt modified mica flakes to replace the modified mica flakes in Example 1, the nano-SiO 2 The mass ratio of the quaternary ammonium salt modified mica sheet is 1:1, and the quaternary ammonium salt modified mica sheet is prepared according to the following steps:

[0062] 10 g of mica flakes were added to 250 mL of DMF, ultrasonically dispersed for 1 h, and then 0.2 g of epoxytrimethylammonium bromide was added. The mixture was stirred and reacted in a water bath at 80° C. for 24 h. After that, the mica flakes were washed by centrifugation and dried with anhydrous ethanol for multiple times to obtain quaternary ammonium salt-modified mica flakes.

[0063] Performance Testing

[0064] The polyester films obtained in Examples 1-4 and Comparative Examples 1-3 were subjected to relevant performance tests, and the specific test results are shown in Table 1.

[0065] Water vapor barrier performance: tested in accordance with standard GB / T 21529-2008.

[0066] Anti-ultraviolet performance: The ultraviolet blocking rate at 280-380nm was tested using a UV-visible spectrophotometer and the ultraviolet aging performance of the polyester film was tested in accordance with IEC61215. The specific test results are shown in Table 1.

[0067] Table 1

[0068]

[0069] Note: △b in Table 1 refers to the yellowing index of polyester film after ultraviolet irradiation.

[0070] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A high barrier UV resistant polyester film, It is characterized in that The film is prepared by direct esterification and polycondensation of terephthalic acid, ethylene glycol and modified mica in the presence of a catalyst, and then the obtained polyester chips are melt-extruded through a twin-screw extruder, and then cast, biaxially stretched, shaped, cooled and rolled to obtain a film. The preparation method of the modified mica sheet comprises the following steps: (1) Exfoliation and modification of mica sheets by quaternary ammonium salts 10 g of mica flakes were added to 250 mL of DMF, and ultrasonically dispersed for 1 h. After adding quaternary ammonium salt, the mixture was stirred in a water bath at 80° C. for 24 h, and then centrifuged and dried with anhydrous ethanol for multiple times to obtain quaternary ammonium salt-modified mica flakes, wherein the amount of the quaternary ammonium salt added was 1-10% of the mass of the mica flakes; (2) The quaternary ammonium salt-modified mica flakes obtained in step (1), dodecylamine, and ethyl orthosilicate were mixed uniformly in a mass ratio of 1:1:2, stirred and reacted at room temperature for 3-5 hours, washed and dried, and calcined in a muffle furnace at 300° C. for 2 hours to obtain nano-SiO 2 Loaded mica sheets.

2. A high barrier anti-ultraviolet polyester film according to claim 1, It is characterized in that The molar ratio of terephthalic acid to ethylene glycol is 1:(1.1-1.4).

3. A high barrier anti-ultraviolet polyester film according to claim 1, It is characterized in that The added amount of the modified mica flakes is 1-5% of the weight of terephthalic acid.

4. The high barrier anti-ultraviolet polyester film according to claim 1, It is characterized in that The average particle size of the mica flakes is 3-10 μm.

5. The high barrier anti-ultraviolet polyester film according to claim 1, It is characterized in that The quaternary ammonium salt includes at least one of epoxytrimethylammonium bromide, dodecyltrimethylammonium bromide, choline and betaine.

6. The high barrier anti-ultraviolet polyester film according to claim 1, It is characterized in that The added amount of the catalyst is 0.02-0.05% by weight of terephthalic acid.

7. The high barrier anti-ultraviolet polyester film according to claim 1, It is characterized in that The temperature of the esterification reaction is 220-260° C., the pressure of the esterification reaction is 0-0.3 MPa, and the reaction time is 2-5 hours.

8. The high barrier anti-ultraviolet polyester film according to claim 1, It is characterized in that The temperature of the polycondensation reaction is 270-285° C., the vacuum degree is 0-80 Pa, and the reaction time is 2-5 hours.

9. The high barrier anti-ultraviolet polyester film according to claim 1, It is characterized in that The temperature of melt extrusion of polyester chips is 260-280°C, the biaxial stretching ratio is 3-4 times, and the shaping temperature is 200-250°C.

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