Ultrathin high-smoothness polyester film and preparation method thereof

Abstract

The invention belongs to the technical field of macromolecules, and particularly relates to an ultrathin high-smoothness polyester film which is prepared from the following raw materials in parts by weight: 100 parts of polyester chips, 1-10 parts of maleic anhydride compatilizer modified silicon oxide and 5-20 parts of cycloolefin copolymer. The polyester film provided by the invention has excellent optical performance, good surface smoothness and good toughness.

Description

Ultrathin, highly smooth polyester film and its preparation method Technical Field

[0001] This invention belongs to the field of polymer technology, specifically relating to an ultrathin, highly smooth polyester film and its preparation method. Background Technology

[0002] Polyester film, with its excellent mechanical properties, chemical stability, transparency, and processability, is widely used in packaging, electronics, optics, medical, and industrial fields. Especially in fields such as optical displays, flexible electronics, and high-end packaging, where extremely high requirements are placed on material surface smoothness and optical performance, the performance of polyester film directly determines the quality and lifespan of the final product.

[0003] During the preparation of polyester films, due to factors such as unstable melt flow and crystallization behavior, micron- or even submicron-sized defects such as protrusions, depressions, or fisheyes are easily formed on the film surface, reducing its smoothness. Furthermore, in existing processes, high-ratio stretching is usually used to improve the strength of the film, but this leads to a decrease in material toughness. To address these issues, existing processes often improve the performance of polyester by adding inorganic nanoparticles. However, the aggregation of nanoparticles in the polyester system increases the surface roughness of the polyester, and the poor compatibility between nanoparticles and polyester chips may lead to migration after long-term use, affecting the stability of the film. Alternatively, polyester can be blended with other polymers to adjust crystallization behavior and mechanical properties, but blended systems often experience a decrease in optical uniformity due to phase separation.

[0004] In summary, existing polyester films still have significant shortcomings in terms of surface smoothness, optical properties, and mechanical toughness. Summary of the Invention

[0005] The first aspect of the present invention provides an ultrathin, highly smooth polyester film, wherein the raw materials for preparing the polyester film, by weight, include: 100 parts of polyester chips, 1-10 parts of maleic anhydride-modified silica, and 5-20 parts of cyclic olefin copolymer.

[0006] The polyester film prepared using the above-mentioned raw materials in this invention achieves excellent results in terms of light transmittance, toughness, and surface smoothness. The reason for this is that the maleic anhydride-based compatibilizer-modified silica has excellent dispersibility in the polyester system, reducing light scattering caused by inorganic particle agglomeration. At the same time, the cyclic olefin copolymer and polyester have similar refractive indices, reducing interfacial light reflection and further reducing interfacial optical defects. Furthermore, the maleic anhydride-based compatibilizer-modified silica can form an energy dissipation network on the film surface. Meanwhile, a specific amount of cyclic olefin copolymer forms physical entanglement or a partial eutectic structure with the polyester molecular chain, absorbing impact energy and inhibiting crack propagation, significantly improving the toughness of the film. More importantly, the interaction between the cyclic olefin copolymer and polyester can improve the processing fluidity of the blend system, reduce surface ripple defects during extrusion or casting, and obtain a surface morphology with lower roughness.

[0007] In this invention, in order to make the polyester film have better overall performance, as a preferred technical solution of this invention, the raw materials for preparing the polyester film include, by weight, 100 parts of polyester chips, 5-6 parts of maleic anhydride compatibilizer modified silica, and 10-12 parts of cyclic olefin copolymer.

[0008] In this invention, the content of the raw materials for preparing the polyester film is controlled within the above-mentioned range, so that the raw materials can better cooperate with each other to increase the performance of the prepared polyester film, especially its smoothness.

[0009] As a preferred embodiment of the present invention, the intrinsic viscosity of the polyester chips is 0.6-0.9 dL / g, and more specifically, the intrinsic viscosity of the polyester chips is 0.7-0.8 dL / g.

[0010] As a preferred embodiment of the present invention, the polyester chips are selected from at least one of polybutylene terephthalate (PBT), polyethylene terephthalate (PET), and poly(1,3-propylene terephthalate) (PTT), preferably polyethylene terephthalate (PET).

[0011] The polyethylene terephthalate (PET) in this invention can be obtained commercially, for example, it can be polyethylene terephthalate chips with the grade FG720 provided by Yizheng Chemical Co., Ltd. of China Petroleum & Chemical Corporation, with an intrinsic viscosity of 0.74±0.02dl / g.

[0012] As a preferred technical solution of the present invention, the preparation method of maleic anhydride-based compatibilizer modified silica includes: S1 plasma treatment of silica to obtain modified silica; S2 adding maleic anhydride-based compatibilizer to toluene, stirring at 70-80℃ for 30-60 min, then adding modified silica and dicumyl peroxide, replacing the air in the system with nitrogen, heating to 95-105℃ and reacting for 2-4 hours, and finally filtering, washing and drying to obtain maleic anhydride-based compatibilizer modified silica.

[0013] As a preferred embodiment of the present invention, the average particle size of the silicon oxide is 10-100 nm, for example, 20 nm.

[0014] The silicon dioxide obtained in this invention can be obtained commercially, for example, purchased from Nanjing Baoket New Materials Co., Ltd., model PST-P10.

[0015] As a preferred technical solution of the present invention, the maleic anhydride compatibilizer is selected from at least one of POE-g-MAH, SEBS-g-MAH and PP-g-MAH, preferably POE-g-MAH.

[0016] The POE-g-MAH in this invention is commercially available, for example, FUSABOND™ N416 Dow POE-G-MAH.

[0017] As a preferred embodiment of the present invention, the mass ratio of the maleic anhydride compatibilizer to the modified silica is (10-20):100, preferably (15-18):100.

[0018] As a preferred embodiment of the present invention, the mass ratio of toluene to modified silicon oxide is (10-20):1.

[0019] As a preferred embodiment of the present invention, the mass ratio of the maleic anhydride compatibilizer to the modified silica is (0.1-0.5):100, preferably (0.2-0.3):100.

[0020] As a preferred technical solution of the present invention, the specific steps of plasma treatment in step S1 include: spreading silicon oxide on a silicon wafer substrate and placing it into a plasma chamber, closing the chamber door, and then introducing a mixed gas of argon and oxygen with a volume ratio of (3-5):1 at atmospheric pressure and 40-50°C, with a flow rate of 20-30L / min, a power of 50-60W, and a nozzle-to-substrate distance of 3-4mm, and treating the silicon oxide for 3-4 minutes to obtain modified silicon oxide.

[0021] The washing and drying in step S2 of the present invention can be conventional techniques in the art, such as washing with ethanol 3-5 times; or vacuum drying at 50-60°C for 8-24 hours.

[0022] In this invention, it was found that silicon dioxide treated with plasma and then modified with a compatibilizer can better improve the optical properties and smoothness of polyester films. It is speculated that this is because the treatment method can form a gradient refractive index transition layer, reduce interface reflection, and avoid removing organic contaminants on the surface of silicon dioxide, thus avoiding light absorption or scattering caused by impurities, or avoiding defects such as film roughness caused by organic matter.

[0023] As a preferred embodiment of the present invention, the melt flow rate of the cyclic olefin copolymer at 260°C and 2.16 kg is 20-40 g / 10 min, preferably 25-35 g / 10 min, and more preferably 29 g / 10 min.

[0024] In this invention, by controlling the melt flow rate of the cyclic olefin copolymer within the above-mentioned range, the polyester film prepared has better toughness and smoothness.

[0025] The cyclic olefin copolymers in this invention are commercially available, for example, the German TOPAS® 8007X10.

[0026] The second aspect of the present invention provides a method for preparing the ultrathin, highly smooth polyester film described in the first aspect of the present invention. The method includes: (1) drying: drying polyester chips, maleic anhydride-modified silica, and cyclic olefin copolymer respectively; (2) melt extrusion: mixing the dried polyester chips, dried maleic anhydride-modified silica, and dried cyclic olefin copolymer and adding them to an extruder, controlling the temperature of the preheating section of the extruder to be 280°C and the temperature of the melting section to be 290±10°C, and extruding the melt through a metering pump, a filter, and a melt line from a die head at an extrusion speed of 20-25 r / min; (3) casting: casting the melt through a die head at a surface temperature of 1 (3) Cooling the casting sheet at 0-15℃ to obtain a thick sheet, and controlling the speed of the casting roller at 10-15m / min; (4) Longitudinal stretching: The thick sheet is fed into the far-infrared heating zone at 70-80℃ and stretched longitudinally at a stretching ratio of 3.8-4.8. After longitudinal stretching, it is cooled by a cooling roller at a temperature of 40-50℃; (5) Transverse stretching: The casting sheet after longitudinal stretching is stretched transversely at a stretching temperature of 150±10℃ and a stretching ratio of 5-5.6 times; (6) Heat setting: The stretched film is heat set at 235-245℃ for 5-10s, and after cooling, it is wound up to obtain the ultra-thin high-smooth polyester film.

[0027] As a preferred technical solution of the present invention, the drying temperature in step (1) is 120-150℃, and the drying endpoint is that the water content of the polyester chips, maleic anhydride compatibilizer modified silica and cyclic olefin copolymer is below 20ppm.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects: the polyester film of the present invention has excellent optical properties, low surface roughness, and is smoother, which meets the high smoothness application requirements of the magnetic tape product processing technology. Detailed Implementation

[0029] 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.

[0030] Preparation of modified silica A: S1 10 kg of silica (Nanjing Baoket New Materials Co., Ltd., model PST-P10, average particle size 20 nm) was spread on a silicon wafer substrate and placed in a plasma chamber. The chamber door was closed, and then a mixture of argon and oxygen with a volume ratio of 4:1 was introduced at atmospheric pressure and 45°C. The flow rate was 25 L / min, the power was 54 W, and the distance from the nozzle to the substrate was 3.8 mm. The silica was treated for 3 minutes to obtain modified silica A.

[0031] Preparation of modified silica B: S1 10 kg of silica (Nanjing Baoket New Material Co., Ltd., model PST-P10, average particle size of 20 nm) was spread on a silicon wafer substrate and placed in a plasma chamber. The chamber door was closed, and then a mixture of argon and oxygen with a volume ratio of 3:1 was introduced at atmospheric pressure and 50 °C. The flow rate was 30 L / min, the power was 60 W, and the distance from the nozzle to the substrate was 3 mm. The silica was treated for 4 minutes to obtain modified silica B.

[0032] Preparation of maleic anhydride-based compatibilizer modified silica A: 180g of FUSABOND™ N416 Dow POE-G-MAH was added to 18kg of toluene and stirred at 80℃ for 50min. Then, 1kg of modified silica A and 3g of dicumyl peroxide were added. The air in the system was replaced with nitrogen, and the temperature was raised to 100℃ and reacted for 3 hours. Finally, the mixture was filtered, washed 5 times with ethanol, and dried under vacuum at 55℃ for 12 hours to obtain maleic anhydride-based compatibilizer modified silica A.

[0033] Preparation of maleic anhydride-based compatibilizer modified silica B: 150g of FUSABOND™ N416 Dow POE-G-MAH was added to 15kg of toluene and stirred at 75℃ for 40min. Then, 1kg of modified silica B and 2g of dicumyl peroxide were added. The air in the system was replaced with nitrogen, and the temperature was raised to 105℃ and reacted for 2 hours. Finally, the mixture was filtered, washed 5 times with ethanol, and dried under vacuum at 55℃ for 12 hours to obtain maleic anhydride-based compatibilizer modified silica B.

[0034] Preparation of maleic anhydride-based compatibilizer modified silica C: 180g of FUSABOND™ N416 (Dow POE-G-MAH) was added to 18kg of toluene and stirred at 80℃ for 50min. Then, 1kg of silica (Nanjing Baoket New Materials Co., Ltd., model PST-P10, average particle size 20nm) and 3g of dicumyl peroxide were added. The air in the system was replaced with nitrogen, and the temperature was raised to 100℃ for 3 hours. Finally, the mixture was filtered, washed 5 times with ethanol, and vacuum dried at 55℃ for 12 hours to obtain maleic anhydride-based compatibilizer modified silica A. Examples

[0035] Preparation of polyester film: (1) Drying: 1 kg of polyester chips (polyethylene terephthalate chips of grade FG720 provided by Yizheng Chemical Co., Ltd. of China Petroleum & Chemical Corporation), 50 g of maleic anhydride compatibilizer modified silica A and 120 g of cyclic olefin copolymer (model TOPAS® 8007X10 of Germany, melt flow rate of 29 g / 10 min at 260℃ and 2.16 kg) were dried at 135℃ until the water content of each was less than 20 ppm; (2) Melt extrusion: the dried polyester chips, dried maleic anhydride compatibilizer modified silica A and dried cyclic olefin copolymer were mixed and added to the extruder. The temperature of the preheating section of the extruder was controlled at 280℃ and the temperature of the melting section was controlled at 290±10℃. The melt was extruded from the die through the metering pump, filter and melt line. The extrusion speed was 23 r / min; (3) Casting: the melt was heated by surface temperature (3) Cooling the casting sheet at 10°C to obtain a thick sheet, with the casting roller speed controlled at 12 m / min; (4) Longitudinal stretching: The thick sheet is fed into a far-infrared heating zone at 75°C and stretched longitudinally at a stretching ratio of 4.2. After longitudinal stretching, it is cooled by a cooling roller at a temperature of 45°C; (5) Transverse stretching: The casting sheet after longitudinal stretching is stretched transversely at a stretching temperature of 150±10°C and a stretching ratio of 5.2; (6) Heat setting: The stretched film is heat-set at 240°C for 8 seconds, cooled, and then wound up to obtain a polyester film with a thickness of 6 micrometers. Example

[0036] Preparation of polyester film: (1) Drying: 1 kg of polyester chips (polyethylene terephthalate chips of grade FG720 provided by Yizheng Chemical Co., Ltd. of China Petroleum & Chemical Corporation), 60 g of maleic anhydride compatibilizer modified silica A and 100 g of cyclic olefin copolymer (model TOPAS® 8007X10 of Germany, melt flow rate of 29 g / 10 min at 260℃ and 2.16 kg) were dried at 135℃ until the water content of each was less than 20 ppm; (2) Melt extrusion: the dried polyester chips, dried maleic anhydride compatibilizer modified silica A and dried cyclic olefin copolymer were mixed and added to the extruder. The temperature of the preheating section of the extruder was controlled at 280℃ and the temperature of the melting section was controlled at 290±10℃. The melt was extruded from the die through the metering pump, filter and melt line. The extrusion speed was 23 r / min; (3) Casting: the melt was cast into sheets at a surface temperature of 1 (3) Cooling the casting sheet at 0℃ to obtain a thick sheet, with the casting roller speed controlled at 12m / min; (4) Longitudinal stretching: The thick sheet is fed into the far-infrared heating zone at 75℃ and stretched longitudinally at a stretching ratio of 4.6. After longitudinal stretching, it is cooled by a cooling roller at a temperature of 45℃; (5) Transverse stretching: The casting sheet after longitudinal stretching is stretched transversely at a stretching temperature of 150±10℃ and a stretching ratio of 5.4; (6) Heat setting: The stretched film is heat set at 235℃ for 10s. After cooling, it is wound up to obtain a polyester film with a thickness of 4.5 micrometers. Example

[0037] Preparation of polyester film: (1) Drying: 1 kg of polyester chips (polyethylene terephthalate chips of grade FG720 provided by Yizheng Chemical Co., Ltd. of China Petroleum & Chemical Corporation), 50 g of maleic anhydride compatibilizer modified silica A and 120 g of cyclic olefin copolymer (model TOPAS® 5013L-10 of Germany, melt flow rate of 44 g / 10 min at 260℃ and 2.16 kg) were dried at 135℃ until the water content of each was less than 20 ppm; (2) Melt extrusion: the dried polyester chips, dried maleic anhydride compatibilizer modified silica A and dried cyclic olefin copolymer were mixed and added to the extruder. The temperature of the preheating section of the extruder was controlled at 280℃ and the temperature of the melting section was controlled at 290±10℃. The melt was extruded from the die through the metering pump, filter and melt line. The extrusion speed was 23 r / min; (3) Casting: the melt was cast from the die through the surface temperature of the film. (3) Cooling the casting sheet at 10℃ to obtain a thick sheet, with the casting roller speed controlled at 12m / min; (4) Longitudinal stretching: The thick sheet is fed into the far-infrared heating zone at 75℃ and stretched longitudinally at a stretching ratio of 4.2. After longitudinal stretching, it is cooled by a cooling roller at a temperature of 45℃; (5) Transverse stretching: The casting sheet after longitudinal stretching is stretched transversely at a stretching temperature of 150±10℃ and a stretching ratio of 5.2; (6) Heat setting: The stretched film is heat-set at 240℃ for 8s. After cooling, it is wound up to obtain a polyester film with a thickness of 5.8 micrometers. Example

[0038] Preparation of polyester film: (1) Drying: 1 kg of polyester chips (polyethylene terephthalate chips of grade FG720 provided by Yizheng Chemical Co., Ltd. of China Petroleum & Chemical Corporation), 50 g of maleic anhydride compatibilizer modified silica A and 120 g of cyclic olefin copolymer (model TOPAS® 6015S-04 of Germany, melt flow rate of 4 g / 10 min at 260℃ and 2.16 kg) were dried at 135℃ until the water content of each was less than 20 ppm; (2) Melt extrusion: the dried polyester chips, dried maleic anhydride compatibilizer modified silica A and dried cyclic olefin copolymer were mixed and added to the extruder. The temperature of the preheating section of the extruder was controlled at 280℃ and the temperature of the melting section was controlled at 290±10℃. The melt was extruded from the die through the metering pump, filter and melt line. The extrusion speed was 23 r / min; (3) Casting: the melt was cast into sheets by passing through the die through the surface temperature of the sheet. (3) Cooling the casting sheet at 10°C to obtain a thick sheet, with the casting roller speed controlled at 12 m / min; (4) Longitudinal stretching: The thick sheet is fed into a far-infrared heating zone at 75°C and stretched longitudinally at a stretching ratio of 4.2. After longitudinal stretching, it is cooled by a cooling roller at a temperature of 45°C; (5) Transverse stretching: The casting sheet after longitudinal stretching is stretched transversely at a stretching temperature of 150±10°C and a stretching ratio of 5.2; (6) Heat setting: The stretched film is heat-set at 240°C for 8 seconds. After cooling, it is wound up to obtain a polyester film with a thickness of 6.5 micrometers. Example

[0039] Preparation of polyester film: (1) Drying: 1 kg of polyester chips (polyethylene terephthalate chips of grade FG720 provided by Yizheng Chemical Co., Ltd. of China Petroleum & Chemical Corporation), 50 g of maleic anhydride compatibilizer modified silica A and 120 g of cyclic olefin copolymer (model TOPAS® 8007X10 of Germany, melt flow rate of 29 g / 10 min at 260℃ and 2.16 kg) were dried at 135℃ until the water content of each was less than 20 ppm; (2) Melt extrusion: the dried polyester chips, dried maleic anhydride compatibilizer modified silica C and dried cyclic olefin copolymer were mixed and added to the extruder. The temperature of the preheating section of the extruder was controlled at 280℃ and the temperature of the melting section was controlled at 290±10℃. The melt was extruded from the die through the metering pump, filter and melt line. The extrusion speed was 23 r / min; (3) Casting: the melt was cast into sheets by passing through the die through the surface temperature of the sheet. (3) Cooling the casting sheet at 10℃ to obtain a thick sheet, the casting roll speed is controlled at 12m / min; (4) Longitudinal stretching: The thick sheet is fed into the far-infrared heating zone at 75℃ and longitudinally stretched at a stretching ratio of 4.2. After longitudinal stretching, it is cooled by a cooling roll at 45℃; (5) Transverse stretching: The casting sheet after longitudinal stretching is stretched laterally at 150±10℃ and the stretching ratio is 5.2; (6) Heat setting: The stretched film is heat set at 240℃ for 8s. After cooling, it is wound up to obtain a polyester film with a thickness of 6.2 micrometers.

[0040] Comparative Example 1: Preparation of polyester film: (1) Drying: 1 kg of polyester chips (polyethylene terephthalate chips of grade FG720 provided by Yizheng Chemical Co., Ltd. of China Petroleum & Chemical Corporation) and 170 g of maleic anhydride compatibilizer modified silica A were dried at 135°C until the water content of each was less than 20 ppm; (2) Melt extrusion: The dried polyester chips, dried maleic anhydride compatibilizer modified silica C and dried cyclic olefin copolymer were mixed and added to the extruder. The temperature of the preheating section of the extruder was controlled at 280°C and the temperature of the melting section was controlled at 290±10°C. The melt was extruded from the die through a metering pump, filter and melt line. The speed is 23 r / min; (3) Casting: The melt is cooled by a cold drum with a surface temperature of 10°C to obtain a thick sheet. The speed of the casting roller is controlled at 12 m / min; (4) Longitudinal stretching: The thick sheet is fed into a far-infrared heating zone at 75°C and stretched longitudinally at a longitudinal stretching ratio of 4.2. After longitudinal stretching, it is cooled by a cooling roller at a temperature of 45°C; (5) Transverse stretching: The cast sheet after longitudinal stretching is stretched transversely. The stretching temperature is controlled at 150±10°C and the stretching ratio is 5.2 times; (6) Heat setting: The stretched film is heat set at 240°C for 8s. After cooling, it is wound up to obtain a polyester film with a thickness of 6.8 micrometers. Performance testing: The transmittance, roughness Ra and elongation at break of the polyester films prepared in Examples 1-5 and Comparative Example 1 are tested.

[0041] 1. Light transmittance test: Tested according to ASTM D 1003-2013 standard; 2. Roughness Ra test: Select 5 different locations on the surface of the polyester film and use the tapping mode of AFM atomic force microscope to detect the surface roughness of the surface layer of the polyester film and calculate the average value; 3. Elongation at break test: Tested according to GB / T 1040.3 standard.

[0042] The test results of light transmittance, roughness Ra and elongation at break of the polyester films in Examples 1-5 and Comparative Example 1 are shown in Table 1.

[0043] Table 1. Test results of transmittance, roughness Ra, and elongation at break of polyester films. Ra (nm) Transmittance TD Elongation at break MD Elongation at break Example 1 7.894% 173% 155% Example 2 7.393% 175% 162% Example 3 16.791% 166% 149% Example 4 14.687% 141% 127% Example 5 19.185% 168% 152% Comparative Example 122.383% 106% 89% As can be seen from the test results in Table 1, the polyester film of the present invention has excellent optical properties, good surface smoothness, and good toughness.

[0044] 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. An ultrathin, highly smooth polyester film, characterized in that, The raw materials for preparing the polyester film, by weight, include: 100 parts polyester chips, 1-10 parts maleic anhydride-modified silica, and 5-20 parts cyclic olefin copolymer.

2. The polyester film according to claim 1, characterized in that, The raw materials for preparing the polyester film, by weight, include: 100 parts polyester chips, 5-6 parts maleic anhydride-modified silica, and 10-12 parts cyclic olefin copolymer.

3. The polyester film according to claim 1 or 2, characterized in that, The intrinsic viscosity of the polyester chips is 0.6-0.9 dL / g.

4. The polyester film according to claim 1 or 2, characterized in that, The preparation method of maleic anhydride-based compatibilizer modified silica includes: S1 Plasma treatment of silica to obtain modified silica; S2 Adding maleic anhydride-based compatibilizer to toluene, stirring at 70-80℃ for 30-60 min, then adding modified silica and dicumyl peroxide, replacing the air in the system with nitrogen, heating to 95-105℃ and reacting for 2-4 hours, and finally filtering, washing and drying to obtain maleic anhydride-based compatibilizer modified silica.

5. The polyester film according to claim 4, characterized in that, The maleic anhydride compatibilizer is selected from at least one of POE-g-MAH, SEBS-g-MAH, and PP-g-MAH.

6. The polyester film according to claim 4, characterized in that, The mass ratio of toluene to modified silica is (10-20):1; the mass ratio of maleic anhydride compatibilizer to modified silica is (10-20):100; the mass ratio of maleic anhydride compatibilizer to modified silica is (0.1-0.5):

100.

7. The polyester film according to claim 4, characterized in that, The specific steps of plasma treatment in step S1 include: after spreading silicon oxide on a silicon wafer substrate, placing it into a plasma chamber, closing the chamber door, and then introducing a mixed gas of argon and oxygen with a volume ratio of (3-5):1 at atmospheric pressure and 40-50℃, with a flow rate of 20-30L / min, a power of 50-60W, and a nozzle-to-substrate distance of 3-4mm, treating the silicon oxide for 3-4 minutes to obtain modified silicon oxide.

8. The polyester film according to claim 4, characterized in that, The cyclic olefin copolymer has a melt flow rate of 20-40 g / 10 min at 260 °C and 2.16 kg.

9. A method for preparing an ultrathin, highly smooth polyester film according to any one of claims 1-8, the method comprising: (1) Drying: The polyester chips, maleic anhydride compatibilizer-modified silica and cyclic olefin copolymer were dried separately; (2) Melt extrusion: The dried polyester chips, dried maleic anhydride compatibilizer modified silica and dried cyclic olefin copolymer are mixed and added to the extruder. The temperature of the preheating section of the extruder is controlled at 280℃ and the temperature of the melting section is controlled at 290±10℃. The melt is extruded from the die through a metering pump, filter and melt line. The extrusion speed is 20-25r / min; (3) Casting: The melt is cooled and cast into thick sheets through a cold drum with a surface temperature of 10-15℃. The speed of the casting roller is controlled at 10-15m / min; (4) Longitudinal stretching: The thick sheet is fed into the far-infrared heating zone at 70-80℃ and stretched longitudinally at a stretching ratio of 3.8-4.

8. After longitudinal stretching, it is cooled by a cooling roller at a temperature of 40-50℃. (5) Transverse stretching: The cast sheet after longitudinal stretching is stretched transversely at a stretching temperature of 150±10℃ and a stretching ratio of 5-5.6 times. (6) Heat setting: The stretched film is heat set at 235-245℃ for 5-10s. After cooling, it is wound up to obtain the ultra-thin high-smooth polyester film.

10. The preparation method according to claim 9, characterized in that, The drying temperature in step (1) is 120-150℃, and the drying endpoint is when the water content of the polyester chips, maleic anhydride compatibilizer modified silica and cyclic olefin copolymer is below 20ppm.