A polyester film and a method for producing the same

Abstract

The application discloses a polyester film and a preparation method thereof, and relates to the technical field of polymer optical film materials, and the polyester film is prepared from a PETG resin as a base body, compounded with 3,5-isoxazole dicarboxylic acid, triethoxy-2-pyridine silane, a multi-component nucleating agent and other functional additives, and is prepared by means of a segmented bidirectional stretching and gradient annealing and shaping process. The application optimizes the crystalline structure and interface compatibility of the film by means of synergistic modification of the functional components, and effectively improves the optical, mechanical and weather resistance of the film. The polyester film has low haze, high bidirectional stretching and tearing strength, small high-temperature dimensional change rate and slight long-term aging and yellowing degree.

Description

Technical Field

[0001] This invention relates to the field of polymer optical thin film materials technology, and in particular to a polyester film and its preparation method. Background Technology

[0002] Polyester film, especially biaxially oriented polyester film, is widely used in packaging, electronics, electrical, optics, and new energy fields due to its excellent mechanical strength, optical properties, electrical insulation, and dimensional stability. However, with the continuous expansion of application areas, more comprehensive and stringent requirements are being placed on the performance of polyester film, and the performance shortcomings of traditional polyester film are gradually becoming apparent.

[0003] Existing conventional polyester films generally suffer from uncontrollable crystallization rates and uneven grain sizes during their preparation. Traditional processes rely solely on a single stretching and shaping process to control the film structure, resulting in highly disordered melt crystallization and numerous microcrystalline defects and internal stresses within the film. This leads to insufficient toughness and poor tear resistance, making the film prone to cracking and brittle fracture under bending and stretching conditions. Simultaneously, the film surface has poor smoothness, high haze, and insufficient light transmittance, failing to meet the high-definition light transmission requirements of optical-grade materials and severely limiting its application in high-end optical fields such as liquid crystal displays and touch screen coatings.

[0004] To improve the performance of polyester films, existing technologies often optimize film properties by adding single antioxidants, slip agents, or nucleating agents. However, this modification approach is simplistic and has significant drawbacks. Modification with a single additive is prone to uneven dispersion and agglomeration, failing to simultaneously improve the film's mechanical and optical properties. Furthermore, it leads to a substantial decrease in the film's aging resistance, resulting in yellowing, reduced light transmittance, and decreased mechanical strength after long-term use. In addition, existing preparation processes suffer from poor matching of temperature, stretching rate, and annealing parameters, resulting in high residual internal stress and poor dimensional stability after film formation. The films are susceptible to warping and deformation under high temperature and humidity conditions, making them unsuitable for long-term outdoor use and the applications of precision electronic devices.

[0005] To address the aforementioned problems, invention patent document CN111086306A discloses a high-stiffness polyester film. This polyester film is a three-layer A / B / A co-extruded biaxially oriented polyester film. The B layer contains polyester modified with magnesium oxide whiskers and silicon carbide whiskers. The magnesium oxide whiskers have a diameter of 0.05μm–0.3μm and a length of 0.7μm–1.5μm, while the silicon carbide whiskers have a diameter of 0.15μm–0.6μm and a length of 1μm–2.5μm. Both the magnesium oxide and silicon carbide whiskers are surface-modified with an aluminate coupling agent. This invention's polyester film exhibits high stiffness, excellent optical and mechanical properties, and superior surface quality, significantly improving the polyester film's resistance to deformation, effectively simplifying the product manufacturing process, substantially reducing production costs, and increasing product yield. It can be widely used in release molding, protection, explosion-proof applications, liquid crystal displays, and new energy photovoltaic fields. However, this patent only uses inorganic whiskers to physically fill and modify the polyester matrix, relying on the multilayer co-extrusion structure to improve the stiffness of the film. It does not modify the structure at the molecular chain level, and cannot fundamentally improve the heat resistance and durability performance. It is difficult to meet the stringent application requirements of ultra-low haze, ultra-high dimensional stability and long-term yellowing resistance of high-end optical films. Summary of the Invention

[0006] To overcome the problems and defects in the above-mentioned technologies, the present invention provides a polyester film and its preparation method. The polyester film has good tensile properties, excellent optical properties, high tear strength, good dimensional stability, sufficient aging resistance, and long service life.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a polyester film, comprising the following raw materials in parts by weight: 80-90 parts of PETG resin, 0.5-1 parts of 3,5-isoxazole dicarboxylic acid, 0.001-0.003 parts of tetrabutyl titanate, 1.2-2.5 parts of composite nucleating agent, 0.05-0.15 parts of triethoxy-2-pyridinesilane, 0.8-1.5 parts of composite antioxidant stabilizer, 0.3-0.6 parts of slip modifier, 1-2 parts of toughening agent, 0.2-0.4 parts of dispersant, and 0.1-0.3 parts of hexamethyldisilazane hydrophobically modified fumed silica.

[0008] Preferably, the PETG resin is Liaoyang Petrochemical PETG LH300.

[0009] Preferably, the composite nucleating agent is a mixture of an organophosphate nucleating agent, talc, nano-calcium carbonate, and nucleating agent 3988 in a mass ratio of (1-2):1:(0.8-1.2):1.

[0010] Preferably, the organophosphate nucleating agent is organophosphate nucleating agent NP-508; the average particle size of the talc is 500-800 nm, and the average particle size of the nano-calcium carbonate is 80-100 nm.

[0011] Preferably, the composite antioxidant stabilizer is composed of antioxidant 1010, antioxidant 168 and ultraviolet absorber UV-531 in a mass ratio of 1:(1-1.5):(0.8-1).

[0012] Preferably, the slip modifier is glyceryl monostearate.

[0013] Preferably, the toughening agent is a compound of PBAT and polyethylene glycol in a mass ratio of (4-6):1; the polyethylene glycol is PEG-4000; and the PBAT is of the brand name BK900.

[0014] Preferably, the dispersant is a mixture of polyethylene wax micro powder and zinc stearate in a mass ratio of (2-4):1; the grade of the polyethylene wax micro powder is PEW-0200.

[0015] Preferably, the grade of the hexamethyldisilazane hydrophobically modified fumed silica nanoparticles is HB-630.

[0016] Another object of the present invention is to provide a method for preparing the polyester film, comprising the following steps: Step S1, High-speed premixing treatment: Put the dried raw materials into a high-speed mixer, with a mixing speed of 800-1000 r / min, a mixing temperature of 60-70℃, and a mixing time of 15-20 min to obtain a mixture. Step S2, High-speed premixing treatment: The mixture is fed into a twin-screw extruder for melt plasticization and in-situ copolymerization. The melt is filtered through a double-layer filter screen of 200 mesh and 300 mesh to remove impurities and trace agglomerates, ensuring high purity of the melt. Then it is uniformly extruded. Step S3, Casting: The extruded melt is uniformly cast onto the surface of a cooling casting roller at a temperature of 25-32℃, and then cooled and shaped into an amorphous PETG sheet at a low temperature. The cooling air velocity is kept constant at 3-5m / s. Step S4, Segmented biaxial stretching: adopts step-by-step biaxial stretching first in the longitudinal direction and then in the transverse direction, with gradual orientation through gradient heating; Step S5, Stress gradient slow-release annealing and shaping: The stretched film enters the annealing and shaping zone and is annealed and shaped using a three-stage gradient temperature control + low-speed air circulation heat preservation annealing process. Step S6, Cooling and winding: After annealing and setting, the film is naturally cooled to room temperature. After electrostatic dust removal, thickness detection, and edge trimming, it is wound up at a uniform speed of 15-20m / min to finally obtain the polyester film.

[0017] Preferably, the temperatures of each section of the twin-screw extruder in step S2 are set as follows: Zone 1 230-240℃, Zone 2 240-250℃, Zone 3 245-255℃, Die head temperature 250-260℃, and screw speed 200-250 r / min.

[0018] Preferably, the segmented biaxial stretching parameters in step S4 are as follows: longitudinal stretching is divided into two segments, with the first segment at 100°C, a magnification ratio of 1.8, and a speed of 60 mm / s, and the second segment at 110°C, a magnification ratio of 2.0, and a speed of 90 mm / s; transverse stretching is divided into two segments, with the first segment at 115°C, a magnification ratio of 2.0, and a speed of 80 mm / s, and the second segment at 128°C, a magnification ratio of 1.9, and a speed of 110 mm / s.

[0019] Preferably, the three-stage gradient temperature control + air circulation heat preservation annealing process parameters in step S5 are as follows: the first stage is 135-140℃ with no wind for 30s, the second stage is 120-125℃ with a wind speed of 2m / s constant temperature slow release for 40s, and the third stage is 95-100℃ natural cooling and curing for 50s.

[0020] Due to the application of the above technical solution, the present invention has the following beneficial effects: (1) The polyester film and its preparation method disclosed in this invention can participate in the in-situ copolymerization of PETG matrix, and be incorporated into the molecular chain segment to regulate the regularity of molecular chain and crystallization kinetics, thereby solving the problems of uncontrolled crystallization rate and uneven grain size of traditional polyester; when combined with triethoxy-2-pyridinesilane, its silane group can form chemical bonds with resin molecules and inorganic fillers, and the two work together to constrain the disordered movement of molecular chains, refine grains, reduce crystal defects, significantly reduce residual internal stress inside the film, effectively improve the cracking and brittle fracture problems during bending and stretching, and significantly improve tear resistance and toughness.

[0021] (2) The polyester film and its preparation method disclosed in this invention, with the bonding effect of hexamethyldisilazane modified nano-silica and composite nucleating agents, avoids agglomeration and precipitation. Combined with precise filtration and segmented stretching processes, the surface smoothness of the film is significantly improved, the haze is reduced, and the light transmittance is enhanced. At the same time, it avoids the problem of optical index degradation caused by single additive modification, and can meet the high-definition light transmittance requirements of high-end optical fields.

[0022] (3) The polyester film and its preparation method disclosed in this invention have excellent UV blocking and antioxidant capabilities due to the heterocyclic structure of 3,5-isoxazole dicarboxylic acid, and triethoxy-2-pyridinesilane can form a protective network on the surface and inside of the film. The two, together with the composite antioxidant stabilizer, form a multi-protective system. Compared with the existing single-agent modification scheme, it can effectively suppress problems such as yellowing, light transmittance decay, and mechanical strength reduction during long-term use, and significantly improve the film's weather resistance and thermo-oxidative aging performance.

[0023] (4) The polyester film and its preparation method disclosed in this invention combine raw material system modification and three-stage gradient annealing process, and are further supplemented with two functional additives to fix the molecular chain, so that the internal stress is fully released after the film is formed. It is not easy to warp or deform in high temperature and high humidity environment, which overcomes the shortcomings of poor dimensional stability of traditional polyester film, and can be stably applied to outdoor scenes and precision electronic devices.

[0024] (5) The polyester film and its preparation method disclosed in this invention are made from the following raw materials in parts by weight: 80-90 parts of PETG resin, 0.5-1 parts of 3,5-isoxazole dicarboxylic acid, 0.001-0.003 parts of tetrabutyl titanate, 1.2-2.5 parts of composite nucleating agent, 0.05-0.15 parts of triethoxy-2-pyridinesilane, 0.8-1.5 parts of composite antioxidant stabilizer, 0.3-0.6 parts of slip modifier, 1-2 parts of toughening agent, 0.2-0.4 parts of dispersant, and 0.1-0.3 parts of hexamethyldisilazane hydrophobically modified fumed silica. Through the interaction between the raw materials, the resulting film exhibits good tensile properties, excellent optical properties, high tear strength, good dimensional stability, sufficient aging resistance, and long service life. Detailed Implementation

[0025] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0026] Example 1

[0027] A polyester film is made from the following raw materials in parts by weight: 80 parts PETG resin, 0.5 parts 3,5-isoxazole dicarboxylic acid, 0.001 parts tetrabutyl titanate, 1.2 parts composite nucleating agent, 0.05 parts triethoxy-2-pyridinesilane, 0.8 parts composite antioxidant stabilizer, 0.3 parts slip modifier, 1 part toughening agent, 0.2 parts dispersant, and 0.1 parts hexamethyldisilazane hydrophobically modified fumed silica.

[0028] The PETG resin is Liaoyang Petrochemical PETG LH300; the composite nucleating agent is a mixture of organophosphate nucleating agent, talc, nano-calcium carbonate, and nucleating agent 3988 in a mass ratio of 1:1:0.8:1; the organophosphate nucleating agent is organophosphate nucleating agent NP-508; the average particle size of the talc is 500 nm, and the average particle size of the nano-calcium carbonate is 80 nm; the composite antioxidant stabilizer is composed of antioxidant 1010, antioxidant 168, and ultraviolet absorber UV-531 in a mass ratio of 1:1: The mixture consists of 0.8% compounded components; the slip modifier is glyceryl monostearate; the toughening agent is PBAT and polyethylene glycol compounded in a mass ratio of 4:1; the polyethylene glycol is PEG-4000; the PBAT is grade BK900; the dispersant is polyethylene wax micropowder and zinc stearate compounded in a mass ratio of 2:1; the polyethylene wax micropowder is grade PEW-0200; and the hexamethyldisilazane hydrophobically modified fumed silica is grade HB-630.

[0029] A method for preparing the polyester film includes the following steps: Step S1, High-speed premixing treatment: Put the dried raw materials into a high-speed mixer, mix at 800 r / min, mix at 60℃, and mix for 15 min to obtain a mixture. Step S2, High-speed premixing treatment: The mixture is fed into a twin-screw extruder for melt plasticization and in-situ copolymerization. The melt is filtered through a double-layer filter screen of 200 mesh and 300 mesh to remove impurities and trace agglomerates, ensuring high purity of the melt. Then it is uniformly extruded. Step S3, Casting: The extruded melt is uniformly cast onto the surface of a cooling casting roller at 25°C, and then cooled and shaped into an amorphous PETG sheet at a low temperature. The cooling air velocity is constant at 3m / s. Step S4, Segmented biaxial stretching: adopts step-by-step biaxial stretching first in the longitudinal direction and then in the transverse direction, with gradual orientation through gradient heating; Step S5, Stress gradient slow-release annealing and shaping: The stretched film enters the annealing and shaping zone and is annealed and shaped using a three-stage gradient temperature control + low-speed air circulation heat preservation annealing process. Step S6, Cooling and winding: After annealing and setting, the film is naturally cooled to room temperature. After electrostatic dust removal, thickness detection, and edge trimming, it is wound up at a uniform speed of 15m / min to finally obtain the polyester film.

[0030] In step S2, the temperatures of each section of the twin-screw extruder are set as follows: Zone 1 230℃, Zone 2 240℃, Zone 3 245℃, Die head temperature 250℃, and screw speed 200r / min.

[0031] The segmented biaxial stretching parameters mentioned in step S4 are as follows: longitudinal stretching is divided into two segments, with the first segment at 100°C, a magnification ratio of 1.8, and a speed of 60 mm / s, and the second segment at 110°C, a magnification ratio of 2.0, and a speed of 90 mm / s; transverse stretching is divided into two segments, with the first segment at 115°C, a magnification ratio of 2.0, and a speed of 80 mm / s, and the second segment at 128°C, a magnification ratio of 1.9, and a speed of 110 mm / s.

[0032] The three-stage gradient temperature control + air circulation heat preservation annealing process parameters in step S5 are as follows: the first stage is 135℃ with no wind for 30s, the second stage is 120℃ with a wind speed of 2m / s constant temperature slow release for 40s, and the third stage is 95℃ natural cooling and curing for 50s.

[0033] Example 2

[0034] A polyester film is made from the following raw materials in parts by weight: 83 parts PETG resin, 0.6 parts 3,5-isoxazole dicarboxylic acid, 0.0015 parts tetrabutyl titanate, 1.5 parts composite nucleating agent, 0.08 parts triethoxy-2-pyridinesilane, 1 part composite antioxidant stabilizer, 0.4 parts slip modifier, 1.2 parts toughening agent, 0.25 parts dispersant, and 0.15 parts hexamethyldisilazane hydrophobically modified fumed silica nanoparticles.

[0035] The PETG resin is Liaoyang Petrochemical PETG LH300; the composite nucleating agent is a mixture of organophosphate nucleating agent, talc, nano-calcium carbonate, and nucleating agent 3988 in a mass ratio of 1.3:1:0.9:1; the organophosphate nucleating agent is organophosphate nucleating agent NP-508; the average particle size of the talc is 600 nm, and the average particle size of the nano-calcium carbonate is 85 nm; the composite antioxidant stabilizer is composed of antioxidant 1010, antioxidant 168, and ultraviolet absorber UV-531 in a mass ratio of 1:1.3:0. The mixture is composed of 0.85 compounds; the slip modifier is glyceryl monostearate; the toughening agent is PBAT and polyethylene glycol in a mass ratio of 4.5:1; the polyethylene glycol is PEG-4000; the PBAT is grade BK900; the dispersant is polyethylene wax micro powder and zinc stearate in a mass ratio of 2.5:1; the polyethylene wax micro powder is grade PEW-0200; and the hexamethyldisilazane hydrophobically modified fumed silica is grade HB-630.

[0036] A method for preparing the polyester film includes the following steps: Step S1, High-speed premixing: The dried raw materials are put into a high-speed mixer, the mixing speed is 850 r / min, the mixing temperature is 63℃, and the mixing time is 17 min to obtain a mixture. Step S2, High-speed premixing treatment: The mixture is fed into a twin-screw extruder for melt plasticization and in-situ copolymerization. The melt is filtered through a double-layer filter screen of 200 mesh and 300 mesh to remove impurities and trace agglomerates, ensuring high purity of the melt. Then it is uniformly extruded. Step S3, Casting: The extruded melt is uniformly cast onto the surface of a cooling casting roller at 27°C, and then cooled and shaped into an amorphous PETG sheet at a low temperature. The cooling air velocity is kept constant at 3.5 m / s. Step S4, Segmented biaxial stretching: adopts step-by-step biaxial stretching first in the longitudinal direction and then in the transverse direction, with gradual orientation through gradient heating; Step S5, Stress gradient slow-release annealing and shaping: The stretched film enters the annealing and shaping zone and is annealed and shaped using a three-stage gradient temperature control + low-speed air circulation heat preservation annealing process. Step S6, Cooling and winding: After annealing and setting, the film is naturally cooled to room temperature. After electrostatic dust removal, thickness detection, and edge trimming, it is wound up at a uniform speed of 17m / min to finally obtain the polyester film.

[0037] The temperatures of each section of the twin-screw extruder in step S2 are set as follows: Zone 1 233℃, Zone 2 242℃, Zone 3 247℃, Die head temperature 253℃, and screw speed 220r / min.

[0038] The segmented biaxial stretching parameters mentioned in step S4 are as follows: longitudinal stretching is divided into two segments, with the first segment at 100°C, a magnification ratio of 1.8, and a speed of 60 mm / s, and the second segment at 110°C, a magnification ratio of 2.0, and a speed of 90 mm / s; transverse stretching is divided into two segments, with the first segment at 115°C, a magnification ratio of 2.0, and a speed of 80 mm / s, and the second segment at 128°C, a magnification ratio of 1.9, and a speed of 110 mm / s.

[0039] The three-stage gradient temperature control + air circulation heat preservation annealing process parameters in step S5 are as follows: the first stage is 137℃ with no wind for 30s, the second stage is 122℃ with a wind speed of 2m / s constant temperature slow release for 40s, and the third stage is 96℃ natural cooling and curing for 50s.

[0040] Example 3

[0041] A polyester film is made from the following raw materials in parts by weight: 85 parts PETG resin, 0.8 parts 3,5-isoxazole dicarboxylic acid, 0.002 parts tetrabutyl titanate, 1.8 parts composite nucleating agent, 0.1 parts triethoxy-2-pyridinesilane, 1.2 parts composite antioxidant stabilizer, 0.45 parts slip modifier, 1.5 parts toughening agent, 0.3 parts dispersant, and 0.2 parts hexamethyldisilazane hydrophobically modified fumed silica.

[0042] The PETG resin is Liaoyang Petrochemical PETG LH300; the composite nucleating agent is a mixture of organophosphate nucleating agent, talc, nano-calcium carbonate, and nucleating agent 3988 in a mass ratio of 1.5:1:1:1; the organophosphate nucleating agent is organophosphate nucleating agent NP-508; the average particle size of the talc is 650 nm, and the average particle size of the nano-calcium carbonate is 90 nm; the composite antioxidant stabilizer is composed of antioxidant 1010, antioxidant 168, and ultraviolet absorber UV-531 in a mass ratio of 1:1.3:0. The mixture is composed of .9 compounds; the slip modifier is glyceryl monostearate; the toughening agent is PBAT and polyethylene glycol compounded in a mass ratio of (4-6):1; the polyethylene glycol is PEG-4000; the PBAT is grade BK900; the dispersant is polyethylene wax micro powder and zinc stearate compounded in a mass ratio of 3:1; the polyethylene wax micro powder is grade PEW-0200; and the hexamethyldisilazane hydrophobically modified fumed silica is grade HB-630.

[0043] A method for preparing the polyester film includes the following steps: Step S1, High-speed premixing treatment: Put the dried raw materials into a high-speed mixer, with a mixing speed of 900 r / min, a mixing temperature of 65℃, and a mixing time of 18 min to obtain a mixture. Step S2, High-speed premixing treatment: The mixture is fed into a twin-screw extruder for melt plasticization and in-situ copolymerization. The melt is filtered through a double-layer filter screen of 200 mesh and 300 mesh to remove impurities and trace agglomerates, ensuring high purity of the melt. Then it is uniformly extruded. Step S3, Casting: The extruded melt is uniformly cast onto the surface of a cooling casting roller at 29°C, and then cooled and shaped into an amorphous PETG sheet at a low temperature. The cooling air velocity is constant at 4 m / s. Step S4, Segmented biaxial stretching: adopts step-by-step biaxial stretching first in the longitudinal direction and then in the transverse direction, with gradual orientation through gradient heating; Step S5, Stress gradient slow-release annealing and shaping: The stretched film enters the annealing and shaping zone and is annealed and shaped using a three-stage gradient temperature control + low-speed air circulation heat preservation annealing process. Step S6, Cooling and winding: After annealing and setting, the film is naturally cooled to room temperature. After electrostatic dust removal, thickness detection, and edge trimming, it is wound up at a uniform speed of 17m / min to finally obtain the polyester film.

[0044] In step S2, the temperatures of each section of the twin-screw extruder are set as follows: Zone 1 235℃, Zone 2 245℃, Zone 3 250℃, Die head temperature 255℃, and screw speed 230r / min.

[0045] The segmented biaxial stretching parameters mentioned in step S4 are as follows: longitudinal stretching is divided into two segments, with the first segment at 100°C, a magnification ratio of 1.8, and a speed of 60 mm / s, and the second segment at 110°C, a magnification ratio of 2.0, and a speed of 90 mm / s; transverse stretching is divided into two segments, with the first segment at 115°C, a magnification ratio of 2.0, and a speed of 80 mm / s, and the second segment at 128°C, a magnification ratio of 1.9, and a speed of 110 mm / s.

[0046] The three-stage gradient temperature control + air circulation heat preservation annealing process parameters in step S5 are as follows: the first stage is 138℃ with no wind for 30s, the second stage is 123℃ with a wind speed of 2m / s constant temperature slow release for 40s, and the third stage is 98℃ natural cooling and curing for 50s.

[0047] Example 4

[0048] A polyester film is made from the following raw materials in parts by weight: 88 parts PETG resin, 0.9 parts 3,5-isoxazole dicarboxylic acid, 0.0025 parts tetrabutyl titanate, 2.3 parts composite nucleating agent, 0.13 parts triethoxy-2-pyridinesilane, 1.4 parts composite antioxidant stabilizer, 0.55 parts slip modifier, 1.8 parts toughening agent, 0.35 parts dispersant, and 0.25 parts hexamethyldisilazane hydrophobically modified fumed silica nanoparticles.

[0049] The PETG resin is Liaoyang Petrochemical PETG LH300; the composite nucleating agent is a mixture of organophosphate nucleating agent, talc, nano-calcium carbonate, and nucleating agent 3988 in a mass ratio of 1.8:1:1.1:1; the organophosphate nucleating agent is organophosphate nucleating agent NP-508; the average particle size of the talc is 750 nm, and the average particle size of the nano-calcium carbonate is 95 nm; the composite antioxidant stabilizer is composed of antioxidant 1010, antioxidant 168, and ultraviolet absorber UV-531 in a mass ratio of 1:1.4:0. The mixture is composed of .95% compound; the slip modifier is glyceryl monostearate; the toughening agent is PBAT and polyethylene glycol compounded in a mass ratio of 5.5:1; the polyethylene glycol is PEG-4000; the PBAT grade is BK900; the dispersant is polyethylene wax micro powder and zinc stearate compounded in a mass ratio of 3.5:1; the polyethylene wax micro powder grade is PEW-0200; and the hexamethyldisilazane hydrophobically modified fumed silica grade is HB-630.

[0050] A method for preparing the polyester film includes the following steps: Step S1, High-speed premixing: The dried raw materials are put into a high-speed mixer, the mixing speed is 950 r / min, the mixing temperature is 68℃, and the mixing time is 19 min to obtain a mixture. Step S2, High-speed premixing treatment: The mixture is fed into a twin-screw extruder for melt plasticization and in-situ copolymerization. The melt is filtered through a double-layer filter screen of 200 mesh and 300 mesh to remove impurities and trace agglomerates, ensuring high purity of the melt. Then it is uniformly extruded. Step S3, Casting: The extruded melt is uniformly cast onto the surface of a cooling casting roller at 31°C, and then cooled and shaped into an amorphous PETG sheet at a low temperature. The cooling air velocity is constant at 4.5 m / s. Step S4, Segmented biaxial stretching: adopts step-by-step biaxial stretching first in the longitudinal direction and then in the transverse direction, with gradual orientation through gradient heating; Step S5, Stress gradient slow-release annealing and shaping: The stretched film enters the annealing and shaping zone and is annealed and shaped using a three-stage gradient temperature control + low-speed air circulation heat preservation annealing process. Step S6, Cooling and winding: After annealing and setting, the film is naturally cooled to room temperature. After electrostatic dust removal, thickness detection, and edge trimming, it is wound up at a uniform speed of 19m / min to finally obtain the polyester film.

[0051] In step S2, the temperatures of each section of the twin-screw extruder are set as follows: Zone 1 238℃, Zone 2 248℃, Zone 3 253℃, Die head temperature 258℃, and screw speed 240r / min.

[0052] The segmented biaxial stretching parameters mentioned in step S4 are as follows: longitudinal stretching is divided into two segments, with the first segment at 100°C, a magnification ratio of 1.8, and a speed of 60 mm / s, and the second segment at 110°C, a magnification ratio of 2.0, and a speed of 90 mm / s; transverse stretching is divided into two segments, with the first segment at 115°C, a magnification ratio of 2.0, and a speed of 80 mm / s, and the second segment at 128°C, a magnification ratio of 1.9, and a speed of 110 mm / s.

[0053] The three-stage gradient temperature control + air circulation heat preservation annealing process parameters in step S5 are as follows: the first stage is 139℃ with no wind for 30s, the second stage is 124℃ with a wind speed of 2m / s constant temperature slow release for 40s, and the third stage is 99℃ natural cooling and curing for 50s.

[0054] Example 5

[0055] A polyester film is made from the following raw materials in parts by weight: 90 parts PETG resin, 1 part 3,5-isoxazole dicarboxylic acid, 0.003 parts tetrabutyl titanate, 2.5 parts composite nucleating agent, 0.15 parts triethoxy-2-pyridinesilane, 1.5 parts composite antioxidant stabilizer, 0.6 parts slip modifier, 2 parts toughening agent, 0.4 parts dispersant, and 0.3 parts hexamethyldisilazane hydrophobically modified fumed silica.

[0056] The PETG resin is Liaoyang Petrochemical PETG LH300; the composite nucleating agent is a mixture of organophosphate nucleating agent, talc, nano-calcium carbonate, and nucleating agent 3988 in a mass ratio of 2:1:1.2:1; the organophosphate nucleating agent is organophosphate nucleating agent NP-508; the average particle size of the talc is 800 nm, and the average particle size of the nano-calcium carbonate is 100 nm; the composite antioxidant stabilizer is composed of antioxidant 1010, antioxidant 168, and ultraviolet absorber UV-531 in a mass ratio of 1:1. The mixture is composed of a 5:1 compound; the slip modifier is glyceryl monostearate; the toughening agent is PBAT and polyethylene glycol compounded in a 6:1 mass ratio; the polyethylene glycol is PEG-4000; the PBAT is grade BK900; the dispersant is polyethylene wax micro powder and zinc stearate compounded in a 4:1 mass ratio; the polyethylene wax micro powder is grade PEW-0200; and the hexamethyldisilazane hydrophobically modified fumed silica is grade HB-630.

[0057] A method for preparing the polyester film includes the following steps: Step S1, High-speed premixing treatment: Put the dried raw materials into a high-speed mixer, mix at 1000 r / min, mix at 70℃, and mix for 20 min to obtain a mixture. Step S2, High-speed premixing treatment: The mixture is fed into a twin-screw extruder for melt plasticization and in-situ copolymerization. The melt is filtered through a double-layer filter screen of 200 mesh and 300 mesh to remove impurities and trace agglomerates, ensuring high purity of the melt. Then it is uniformly extruded. Step S3, Casting: The extruded melt is uniformly cast onto the surface of a cooling casting roller at 32°C, and then cooled and shaped into an amorphous PETG sheet at a low temperature. The cooling air velocity is kept constant at 5m / s. Step S4, Segmented biaxial stretching: adopts step-by-step biaxial stretching first in the longitudinal direction and then in the transverse direction, with gradual orientation through gradient heating; Step S5, Stress gradient slow-release annealing and shaping: The stretched film enters the annealing and shaping zone and is annealed and shaped using a three-stage gradient temperature control + low-speed air circulation heat preservation annealing process. Step S6, Cooling and winding: After annealing and setting, the film is naturally cooled to room temperature. After electrostatic dust removal, thickness detection, and edge trimming, it is wound up at a uniform speed of 20m / min to finally obtain the polyester film.

[0058] In step S2, the temperatures of each section of the twin-screw extruder are set as follows: Zone 1 240℃, Zone 2 250℃, Zone 3 255℃, Die head temperature 260℃, and screw speed 250r / min.

[0059] The segmented biaxial stretching parameters mentioned in step S4 are as follows: longitudinal stretching is divided into two segments, with the first segment at 100°C, a magnification ratio of 1.8, and a speed of 60 mm / s, and the second segment at 110°C, a magnification ratio of 2.0, and a speed of 90 mm / s; transverse stretching is divided into two segments, with the first segment at 115°C, a magnification ratio of 2.0, and a speed of 80 mm / s, and the second segment at 128°C, a magnification ratio of 1.9, and a speed of 110 mm / s.

[0060] The three-stage gradient temperature control + air circulation heat preservation annealing process parameters in step S5 are as follows: the first stage is 140℃ with no wind for 30s, the second stage is 125℃ with a wind speed of 2m / s constant temperature slow release for 40s, and the third stage is 100℃ natural cooling and curing for 50s.

[0061] Comparative Example 1 A polyester film and its preparation method are basically the same as those in Example 5, except that an equal amount of terephthalic acid is used instead of 3,5-isoxazole dicarboxylic acid.

[0062] Comparative Example 2 A polyester film and its preparation method are basically the same as those in Example 5, except that an equal amount of silane coupling agent KH550 is used instead of triethoxy-2-pyridinesilane.

[0063] Comparative Example 3 A polyester film and its preparation method are basically the same as those in Example 5, except that an equal amount of organic phosphate nucleating agent is used instead of nucleating agent 3988.

[0064] Comparative Example 4 A polyester film and its preparation method are basically the same as those in Example 5, except that an equal amount of nucleating agent 3988 is used instead of the organophosphate nucleating agent.

[0065] Experimental data verification The experimental method is as follows: the film thickness (total thickness of the finished product) was controlled at 20 μm. (1) Haze test: Refer to GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics", use a transmittance haze tester, test sample size 50mm×50mm, test 5 samples in each group, and take the average value.

[0066] (2) Tensile strength test: Referring to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", an electronic universal testing machine was used to sample and test the film in the longitudinal and transverse directions respectively. The tensile rate was 50 mm / min, the sample width was 15 mm, the gauge length was 50 mm, and 10 samples were tested in each group. The average value was taken and the longitudinal and transverse tensile strength data were recorded.

[0067] (3) Tear strength test: Refer to GB / T 16578.2-2009 "Determination of tear resistance of plastic films and sheets - Part 2: Elmendorf method" to test the longitudinal and transverse tear strength of the film.

[0068] (4) Dimensional stability test: Refer to GB / T 12027-2004 "Test method for dimensional change rate of plastic film and sheet under heating", cut standard samples (100mm×100mm) in the longitudinal and transverse directions of the film respectively, place the samples in a 120℃ forced air oven for 30min at a constant temperature, take them out and cool them to room temperature, accurately measure the dimensional change, calculate the longitudinal and transverse thermal dimensional change rate respectively, take the average value of 5 samples in each group, and evaluate the high temperature dimensional stability of the film.

[0069] (5) Aging resistance test: Referring to GB / T 16422.2-2014 "Laboratory Light Source Exposure Test Methods for Plastics Part 2: Xenon Arc Lamp", a 500-hour xenon lamp aging test was conducted to test the yellowing index (Δb) of the film and evaluate the long-term yellowing resistance and weather resistance of the film. The test results are shown in Table 1.

[0070] Table 1. Performance test results of polyester film

[0071] As shown in Table 1, the polyester film of Example 5, prepared using 3,5-isoxazole dicarboxylic acid, triethoxy-2-pyridinesilane, and a multi-component nucleating agent, exhibits lower haze and yellowing index, higher longitudinal and transverse tensile and tear strength, and smaller thermal dimensional change rate compared to Comparative Examples 1, 2, 3, and 4, which replaced the core functional components. It also demonstrates the best overall optical performance, mechanical properties, high-temperature dimensional stability, and resistance to aging and yellowing. This proves that the synergistic modification effect of 3,5-isoxazole dicarboxylic acid, triethoxy-2-pyridinesilane, and the multi-component nucleating system is crucial for improving the overall performance of PETG polyester film.

[0072] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A polyester film, characterized in that, It is made from the following raw materials in parts by weight: 80-90 parts PETG resin, 0.5-1 part 3,5-isoxazole dicarboxylic acid, 0.001-0.003 parts tetrabutyl titanate, 1.2-2.5 parts composite nucleating agent, 0.05-0.15 parts triethoxy-2-pyridinesilane, 0.8-1.5 parts composite antioxidant stabilizer, 0.3-0.6 parts slip modifier, 1-2 parts toughening agent, 0.2-0.4 parts dispersant, and 0.1-0.3 parts hexamethyldisilazane hydrophobically modified fumed silica.

2. The polyester film according to claim 1, characterized in that, The PETG resin is Liaoyang Petrochemical PETGLH300; the composite nucleating agent is a mixture of organophosphate nucleating agent, talc, nano-calcium carbonate, and nucleating agent 3988 in a mass ratio of (1-2):1:(0.8-1.2):

1.

3. The polyester film according to claim 2, characterized in that, The organophosphate nucleating agent is organophosphate nucleating agent NP-508; the average particle size of the talc is 500-800 nm, and the average particle size of the nano-calcium carbonate is 80-100 nm.

4. The polyester film according to claim 1, characterized in that, The composite antioxidant stabilizer is composed of antioxidant 1010, antioxidant 168, and ultraviolet absorber UV-531 in a mass ratio of 1:(1-1.5):(0.8-1).

5. The polyester film according to claim 1, characterized in that, The smoothing modifier is glyceryl monostearate; the toughening agent is a mixture of PBAT and polyethylene glycol in a mass ratio of (4-6):1; the polyethylene glycol is PEG-4000; and the PBAT is grade BK900.

6. The polyester film according to claim 1, characterized in that, The dispersant is a compound of polyethylene wax micro powder and zinc stearate in a mass ratio of (2-4):1; the grade of the polyethylene wax micro powder is PEW-0200; and the grade of the hexamethyldisilazane hydrophobically modified fumed silica is HB-630.

7. A method for preparing a polyester film according to any one of claims 1-6, characterized in that, Includes the following steps: Step S1, High-speed premixing treatment: Put the dried raw materials into a high-speed mixer, with a mixing speed of 800-1000 r / min, a mixing temperature of 60-70℃, and a mixing time of 15-20 min to obtain a mixture. Step S2, High-speed premixing treatment: The mixture is fed into a twin-screw extruder for melt plasticization and in-situ copolymerization. The melt is filtered through a double-layer filter screen of 200 mesh and 300 mesh to remove impurities and trace agglomerates, ensuring high purity of the melt. Then it is uniformly extruded. Step S3, Casting: The extruded melt is uniformly cast onto the surface of a cooling casting roller at a temperature of 25-32℃, and then cooled and shaped into an amorphous PETG sheet at a low temperature. The cooling air velocity is kept constant at 3-5m / s. Step S4, Segmented biaxial stretching: adopts step-by-step biaxial stretching first in the longitudinal direction and then in the transverse direction, with gradual orientation through gradient heating; Step S5, Stress gradient slow-release annealing and shaping: The stretched film enters the annealing and shaping zone and is annealed and shaped using a three-stage gradient temperature control + low-speed air circulation heat preservation annealing process. Step S6, Cooling and winding: After annealing and setting, the film is naturally cooled to room temperature. After electrostatic dust removal, thickness detection, and edge trimming, it is wound up at a uniform speed of 15-20m / min to finally obtain the polyester film.

8. The method for preparing polyester film according to claim 7, characterized in that, In step S2, the temperatures of each section of the twin-screw extruder are set as follows: Zone 1 230-240℃, Zone 2 240-250℃, Zone 3 245-255℃, Die head temperature 250-260℃, and screw speed 200-250 r / min.

9. The method for preparing polyester film according to claim 7, characterized in that, The segmented biaxial stretching parameters mentioned in step S4 are as follows: longitudinal stretching is divided into two segments, with the first segment at 100°C, a magnification ratio of 1.8, and a speed of 60 mm / s, and the second segment at 110°C, a magnification ratio of 2.0, and a speed of 90 mm / s; transverse stretching is divided into two segments, with the first segment at 115°C, a magnification ratio of 2.0, and a speed of 80 mm / s, and the second segment at 128°C, a magnification ratio of 1.9, and a speed of 110 mm / s.

10. The method for preparing polyester film according to claim 7, characterized in that, The three-stage gradient temperature control + air circulation heat preservation annealing process parameters in step S5 are as follows: the first stage is 135-140℃ with no wind for 30s, the second stage is 120-125℃ with a wind speed of 2m / s constant temperature slow release for 40s, and the third stage is 95-100℃ natural cooling and curing for 50s.

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