A 1.5μm polyester film, its preparation method and application

Abstract

This invention relates to a 1.5μm polyester film, its preparation method, and its applications. Specifically, it relates to a polyester film made from PET polyester chips and functional masterbatch, wherein the functional masterbatch includes an opening agent, an antioxidant, and a lubricant. The thickness of the polyester film is 1.0~2.0μm, and the elongation at break is 60%~150%. This invention achieves a balance between flexibility and dimensional stability by controlling the heat shrinkage rate within a reasonable range while ensuring high elongation at break, thus meeting the heat resistance requirements in the processing of electronic devices.

Description

Technical Field

[0001] This invention relates to the field of polyester film technology, specifically to a 1.5μm polyester film, its preparation method, and its applications. Background Technology

[0002] Polyethylene terephthalate (PET) is one of the most important synthetic materials, widely used in textile fibers, films, electronics, and engineering plastics. Flexible printed circuit boards (FPCBs), also known as flexible printed circuit boards, are printed circuits made with polyester film or polyimide film as the substrate, offering high assembly reliability and excellent flexibility. Due to their small size, light weight, and excellent electrical properties, FPCBs are particularly suitable for the miniaturization and thinning requirements of digital products, making them popular in the electronics industry and widely used in various portable electronic products such as tablets and smartphones. The electronics manufacturing industry has led to the widespread application of high-performance circuit board protective tapes, with the flexible circuit board assembly industry accounting for a significant proportion of the demand. This market continues to grow with economic development. Currently, PET-based masking protective tapes are widely used in the flexible circuit board assembly industry.

[0003] Ultra-thin tapes are evolving towards thinner, higher-performance, and more environmentally friendly designs. For example, the demand for tapes with a thickness of less than 10 micrometers is increasing, while also requiring higher adhesion and anti-aging properties. In terms of environmental protection, the application of water-based and solvent-free adhesives is gradually increasing, replacing traditional solvent-based adhesives to reduce VOC emissions. However, existing ultra-thin PET tape base films suffer from problems such as easy sticking and insufficient dimensional stability at high temperatures, making it difficult to meet the requirements of flexible electronics processing. Specifically, the ultra-thin film has a dramatically increased specific surface area, resulting in tight interlayer bonding during winding, which easily leads to sticking and poor slitting. Simultaneously, ultra-thin films are prone to thermal shrinkage and deformation during high-temperature processing, affecting mounting accuracy.

[0004] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a polyester film, its preparation method, and its application. The resulting polyester film has a thickness of approximately 1.5 μm, a smooth surface, stable temperature resistance, and stable production.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention provides a polyester film, characterized in that it is made of PET polyester chips and functional masterbatch, wherein the functional masterbatch includes an opening agent, an antioxidant and a lubricant; the thickness of the polyester film is 1.0~2.0μm and the elongation at break of the polyester film is 60%~150%.

[0007] Preferably, the mass ratio of the PET polyester chips to the functional masterbatch is (90~95):(5~10).

[0008] Preferably, the number-average molecular weight of the PET polyester chips is in the range of 25,000 to 35,000, and the intrinsic viscosity is 0.60 to 0.68 dl / g.

[0009] Preferably, the PET polyester chips are dried and then mixed for use, with a moisture content of 20-35 ppm.

[0010] Preferably, the opening agent is selected from one or more of silica, talc, and fatty acid amide, and is preferably silica.

[0011] Preferably, the particle size of the opening agent is 1~2.5μm.

[0012] Preferably, the antioxidant is selected from one or more of phosphite antioxidants and phenolic antioxidants, and is preferably triisodecyl phosphite.

[0013] Preferably, the lubricant is selected from one or more of erucamide, oleamide, and stearic acid, and is preferably erucamide.

[0014] Preferably, by mass fraction, the functional masterbatch comprises 3-8 parts of opening agent, 0.5-2 parts of antioxidant, 0.5-2 parts of lubricant, and 88-96 parts of PET carrier resin.

[0015] Preferably, the polyester film satisfies one or more of the following characteristics (1) to (6); (1) The thickness of the polyester film is 1.4~1.6μm; (2) The tensile strength of the polyester film is 200~260MPa; (3) The thermal shrinkage rate of the polyester film in the MD direction after standing at 150°C for 30 minutes is 0.1%~4.5%; (4) The thermal shrinkage rate of the polyester film in the TD direction after standing at 150°C for 30 minutes is 0.1%~3.0%; (5) The surface roughness Ra of the polyester film is 0.02 to 0.1 μm; (6) The haze of the polyester film is 4% to 15%.

[0016] The present invention also provides a method for preparing the polyester film according to any one of the above claims, the method comprising the steps of: S1: After uniformly mixing PET polyester chips and functional masterbatch, crystallize, dry, melt-plasticize, and extrude them; S2: A low-pressure air knife is used to attach the melt to a cooling drum for cooling and to form a thick film; S3: Simultaneously biaxially stretch, shape, cool, and wind up the thick film to obtain a polyester film.

[0017] Preferably, in step S1, the pre-crystallization temperature of the crystallization drying is 160~175℃, the drying temperature is 150~165℃, the dehumidification temperature of the crystallization drying is 135~145℃, and the crystallinity after crystallization drying is 30~35%.

[0018] Preferably, the temperature of the melting feeding section is 260~270℃.

[0019] Preferably, the temperature of the melting and plasticizing section is 275~285℃.

[0020] Preferably, the temperature of the melt extrusion nozzle is 270~280℃.

[0021] Preferably, in step S2, the cooling temperature is 15~25℃.

[0022] Preferably, the crystallinity of the thick film is less than 3%.

[0023] Preferably, in step S3, the synchronous biaxial stretching temperature is 90~110℃.

[0024] Preferably, the stretching ratio of the synchronous bidirectional stretching is 3.5×3.5~4.5×4.5, and the ratio of the transverse stretching ratio to the longitudinal stretching ratio is 1:1; preferably 4×4.

[0025] Preferably, the shaping temperature is 210~230℃.

[0026] Preferably, the setting time is 8 to 15 seconds.

[0027] Preferably, in step S3, the cooling process further includes corona treatment, with a corona treatment power of 6~10 W·min / m².

[0028] Preferably, the winding process further includes slitting.

[0029] The present invention also provides the application of the polyester film described in any of the above claims or the polyester film prepared by the above preparation method in flexible electronic products, semiconductor packaging or optical display products.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention, by adding functional masterbatch containing opening agent, antioxidant and lubricant, and controlling the synchronous biaxial stretching temperature at 90~110℃ and the setting temperature at 210~230℃, enables a 1.5μm ultrathin PET base film to simultaneously possess high elongation at break (≥60%) and high tensile strength (≥200MPa). The lubricant in the functional masterbatch reduces intermolecular friction, which is beneficial for stretching and orientation; the antioxidant inhibits thermal degradation during high-temperature processing. The two work synergistically with the process parameters to achieve a balance between flexibility and strength. Comparative Example 1 shows that, under the same process conditions without the addition of functional masterbatch, the elongation at break is only 55%, which is less than 60%. (2) By adding functional masterbatch containing opening agent, antioxidant and lubricant, the surface roughness Ra of the film is controlled at 0.02~0.1μm, which effectively prevents the ultra-thin film from sticking during winding and ensures the slitting yield. Comparative Example 1 shows that the surface roughness is only 0.01μm without the addition of functional masterbatch, and serious sticking occurs; (3) Under the premise of ensuring high elongation at break, the present invention controls the thermal shrinkage rate within a reasonable range, achieving a balance between flexibility and dimensional stability, and can meet the heat resistance requirements in the processing of electronic devices. Detailed Implementation

[0031] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below by listing specific embodiments. Unless otherwise defined, the technical and scientific terms used herein have the same meanings as those in the technical field to which this application pertains.

[0032] The present invention provides a polyester film, characterized in that it is made of PET polyester chips and functional masterbatch, wherein the functional masterbatch includes an opening agent, an antioxidant and a lubricant; the thickness of the polyester film is 1.0~2.0μm and the elongation at break of the polyester film is 60%~150%.

[0033] In some embodiments, the elongation at break of the polyester film is 60% to 150%, for example, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, etc.

[0034] In some embodiments, the polyester film has a single-layer structure.

[0035] In some embodiments, the mass ratio of the PET polyester chips to the functional masterbatch is (90~95):(5~10).

[0036] In some embodiments, the PET polyester chips have a number-average molecular weight range of 25,000 to 35,000 and an intrinsic viscosity of 0.60 to 0.68 dl / g.

[0037] In some embodiments, the PET polyester chips are dried and then mixed for use, with a moisture content of 20-35 ppm.

[0038] In some embodiments, the opening agent is selected from one or more of silica, talc, and fatty acid amides.

[0039] In some embodiments, the opening agent is selected from silicon dioxide.

[0040] In some embodiments, the particle size of the opening agent is 1~2.5 μm.

[0041] In some embodiments, the antioxidant is selected from one or more of phosphite antioxidants and phenolic antioxidants.

[0042] In some embodiments, the antioxidant is selected from triisodecyl phosphite.

[0043] In some embodiments, the lubricant is selected from one or more of erucamide, oleamide, and stearic acid.

[0044] In some embodiments, the lubricant is selected from erucamide.

[0045] In some embodiments, the functional masterbatch comprises, by mass fraction, 3 to 8 parts of opening agent, 0.5 to 2 parts of antioxidant, 0.5 to 2 parts of lubricant, and 88 to 96 parts of PET carrier resin.

[0046] In some embodiments, the polyester film satisfies one or more of the following characteristics (1) to (6); (1) The thickness of the polyester film is 1.4~1.6μm; (2) The tensile strength of the polyester film is 200~260MPa; (3) The thermal shrinkage rate of the polyester film in the MD direction after standing at 150°C for 30 minutes is 0.1%~4.5%; (4) The thermal shrinkage rate of the polyester film in the TD direction after standing at 150°C for 30 minutes is 0.1%~3.0%; (5) The surface roughness Ra of the polyester film is 0.02 to 0.1 μm; (6) The haze of the polyester film is 4% to 15%.

[0047] In some embodiments, the polyester film satisfies two or more of the features (1) to (6).

[0048] In some embodiments, the polyester film satisfies three or more of the features (1) to (6).

[0049] In some embodiments, the polyester film satisfies four or more of the features (1) to (6).

[0050] In some embodiments, the polyester film satisfies five or more of the features (1) to (6).

[0051] In some embodiments, the thickness of the polyester film is 1.4 to 1.6 μm, for example, 1.41 μm, 1.42 μm, 1.43 μm, 1.44 μm, 1.45 μm, 1.46 μm, 1.47 μm, 1.48 μm, 1.49 μm, 1.5 μm, 1.51 μm, 1.52 μm, 1.53 μm, 1.54 μm, 1.55 μm, 1.56 μm, 1.57 μm, 1.58 μm, 1.59 μm, 1.6 μm, etc.

[0052] In some embodiments, the tensile strength of the polyester film is 200~260MPa, such as 200MPa, 205MPa, 210MPa, 215MPa, 220MPa, 222MPa, 225MPa, 228MPa, 230MPa, 235MPa, 239MPa, 240MPa, 245MPa, 250MPa, 252MPa, 255MPa, 260MPa, etc.

[0053] In some embodiments, the thermal shrinkage rate of the polyester film in the MD direction after standing at 150°C for 30 minutes is 0.1% to 4.5%, for example, 0.1%, 0.5%, 1.0%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, etc.

[0054] In some embodiments, the thermal shrinkage rate of the polyester film in the MD direction after standing at 150°C for 30 minutes is 1.5% to 4.0%.

[0055] In some embodiments, the polyester film has a thermal shrinkage rate in the TD direction of 0.1% to 3.0% after standing at 150°C for 30 minutes, for example, 0.1%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, etc.

[0056] In some embodiments, the polyester film has a thermal shrinkage rate of 0.5% to 2.2% in the TD direction after being left to stand at 150°C for 30 minutes.

[0057] In some embodiments, the surface roughness Ra of the polyester film is 0.02 to 0.1 μm, for example, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, etc.

[0058] In some embodiments, the haze of the polyester film is 4% to 15%, for example, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc.

[0059] The present invention also provides a method for preparing the polyester film according to any one of the above claims, the method comprising the steps of: S1: After uniformly mixing PET polyester chips and functional masterbatch, crystallize, dry, melt-plasticize, and extrude them; S2: A low-pressure air knife is used to attach the melt to a cooling drum for cooling and to form a thick film; S3: Simultaneously biaxially stretch, shape, cool, and wind up the thick film to obtain a polyester film.

[0060] In some embodiments, in step S1, the pre-crystallization temperature of the crystallization drying is 160~175℃, the drying temperature is 150~165℃, the dehumidification temperature of the crystallization drying is 135~145℃, and the crystallinity after crystallization drying is 30~35%.

[0061] In some embodiments, the temperature of the molten feeding section is 260~270°C.

[0062] In some embodiments, the temperature of the melting and plasticizing section is 275~285°C.

[0063] In some embodiments, the temperature of the melt extrusion nozzle is 270~280°C.

[0064] In some embodiments, the cooling temperature in step S2 is 15~25°C.

[0065] In some embodiments, the crystallinity of the thick film is less than 3%.

[0066] In some embodiments, in step S3, the synchronous biaxial stretching temperature is 90~110℃.

[0067] In some embodiments, the stretching ratio of the synchronous bidirectional stretching is 3.5×3.5 to 4.5×4.5, and the ratio of the transverse stretching ratio to the longitudinal stretching ratio is 1:1; preferably 4×4.

[0068] In some embodiments, the shaping temperature is 210~230°C.

[0069] In some implementations, the setting time is 8 to 15 seconds.

[0070] In some embodiments, step S3 further includes a corona treatment after cooling, with a corona treatment power of 6~10 W·min / m².

[0071] In some implementations, the winding process may also include slitting.

[0072] The present invention also provides the application of the polyester film described in any of the above claims or the polyester film prepared by the above preparation method in flexible electronic products, semiconductor packaging or optical display products.

[0073] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. All materials used are commercially available conventional products, including but not limited to the materials used in the embodiments of this invention.

[0074] The method of the present invention will be described below through specific embodiments. It should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0075] Example 1 A method for preparing a polyester film includes the following steps: S1: Raw material preparation, crystallization drying, melt plasticizing and extrusion

[0076] Take 93 kg of film-grade PET polyester chips (number average molecular weight Mn=28000, intrinsic viscosity IV=0.65dL / g) and 7 kg of functional masterbatch, and mix them evenly in a high-speed mixer.

[0077] The functional masterbatch comprises, by weight, 5 parts fumed silica opening agent (particle size D50 = 1.5 μm), 1 part triisodecyl phosphite antioxidant, 1 part erucamide lubricant, and 93 parts PET carrier resin. The functional masterbatch is prepared by melt extrusion of each component at 275°C using a twin-screw extruder, followed by stranding, cooling, water tank pelletizing, and drying.

[0078] The uniformly mixed raw materials are fed into the crystallization and drying system. The pre-crystallization temperature is 165℃, the drying temperature is 158℃, the dehumidification temperature is 140℃, and the crystallization and drying time is 4 hours. After drying, the moisture content of the raw materials is controlled at 25ppm and the crystallinity is 32%.

[0079] The dried raw material is fed into a single-screw extruder for melt plasticizing and extrusion. The feeding section temperature is 265℃, the plasticizing section temperature is 280℃, and the extrusion nozzle (die) temperature is 275℃. A T-type die is used with a die lip opening of 0.8mm, and the extrusion speed is 40r / min. The melt is then extruded through the die after passing through a metering pump and a filter (15μm pore size).

[0080] S2: Cooling of low-pressure air knife castings A low-pressure air knife system is used to attach the extruded melt to the surface of a cooling drum for cooling. The surface temperature of the cooling drum is controlled at 20°C, and the air knife pressure is 0.02 MPa, forming a thick film with a crystallinity of less than 2%.

[0081] S3: Synchronous bidirectional stretching, shaping, cooling, and winding. The thick film is fed into a synchronous biaxial stretching device and subjected to synchronous biaxial stretching at 100°C. The longitudinal (MD) stretching ratio and the transverse (TD) stretching ratio are both 4 times (i.e., 4×4), and the stretching rate is 500% / s.

[0082] The stretched film was heat-set at 220°C for 10 seconds.

[0083] After the film is shaped, it is cooled to room temperature by cooling rollers and then subjected to corona treatment with a power of 8 W·min / m².

[0084] The corona-treated film is wound up with a winding tension of 15 N / m. After winding, it is slit according to product requirements to obtain a polyester film with a thickness of about 1.5 μm.

[0085] Example 2 A method for preparing a polyester film is basically the same as that in Example 1, except that in step S3, the synchronous biaxial stretching temperature is 110°C, and the remaining steps are the same as in Example 1, to obtain a polyester film with a thickness of about 1.5 μm.

[0086] Example 3 A method for preparing a polyester film is basically the same as that in Example 1, except that in step S3, the setting temperature is 230°C and the setting time is 15 seconds. The remaining steps are the same as in Example 1, and a polyester film with a thickness of about 1.5 μm is obtained.

[0087] Example 4 A method for preparing a polyester film is basically the same as that in Example 1, except that: (1) Different raw material ratios: 90kg of PET polyester chips and 10kg of functional masterbatch (i.e., the mass ratio of PET polyester chips to functional masterbatch is 90:10). (2) Different opening agent content in functional masterbatch: The composition of the functional masterbatch by mass parts includes: 8 parts fumed silica opening agent (particle size D50=2.0μm), 1 part triisodecyl phosphite antioxidant, 1 part erucamide lubricant, and 90 parts PET carrier resin. (3) The bidirectional stretching ratios are different: the longitudinal (MD) stretching ratio and the transverse (TD) stretching ratio are both 3.5 times (i.e., 3.5 × 3.5). The remaining steps are the same as in Example 1, and a polyester film with a thickness of about 1.5 μm is obtained.

[0088] Comparative Example 1 A method for preparing a polyester film is basically the same as in Example 1, except that no functional masterbatch is added; that is, the raw material is only 100 kg of PET polyester chips, and no opening agent, antioxidant, or lubricant is added. The remaining steps are the same as in Example 1, and a polyester film with a thickness of approximately 1.5 μm is obtained.

[0089] Comparative Example 2 A method for preparing a polyester film is basically the same as in Example 1, except that in step S3, the simultaneous biaxial stretching temperature is 130°C. The remaining steps are the same as in Example 1, resulting in a polyester film with a thickness of approximately 1.5 μm.

[0090] Comparative Example 3 A method for preparing a polyester film is basically the same as in Example 1, except that in step S3, the setting temperature is 250°C. The remaining steps are the same as in Example 1, resulting in a polyester film with a thickness of approximately 1.5 μm.

[0091] Experimental Example 1 The performance of the films prepared in Examples 1-4 and Comparative Examples 1-3 was tested using the following standards and methods: 1. Thickness test: Tested in accordance with GB / T13542.2-2021 standard.

[0092] Wherein, average thickness deviation = (measured average thickness − nominal thickness) / nominal thickness × 100%; In the formula, the nominal thickness is 1.5 μm.

[0093] 2. Tensile strength and elongation at break test: The test was conducted in accordance with GB / T1040.3-2006 "Determination of tensile properties of plastics" standard, with sample type 2 and tensile speed of 50 mm / min.

[0094] 3. Heat shrinkage rate test (150℃×30min): The test was conducted according to GB / T13542.2-2021 standard. After the film sample was placed in an oven at 150℃ for 30 minutes, the dimensional change rate in the MD direction and TD direction was measured respectively.

[0095] 4. Surface roughness Ra: Tested using a contact surface roughness tester in accordance with GB / T1031-2009 standard.

[0096] 5. Haze: Tested in accordance with GB / T2410-2008 "Determination of light transmittance and haze of transparent plastics".

[0097] The test results are shown in Table 1.

[0098] Table 1 Test Results

[0099] Analysis of the test results of Examples 1-4 and Comparative Examples 1-3 shows that this invention, by controlling the synchronous biaxial stretching temperature at 90-110℃ and the setting temperature at 210-230℃, and adding functional masterbatch containing opening agents, antioxidants, and lubricants, enables the 1.5μm ultrathin PET base film to simultaneously possess high elongation at break and high tensile strength, meeting the dual requirements of polyester film for flexibility and strength. Simultaneously, the surface roughness Ra is controlled at 0.02-0.1μm, effectively preventing the ultrathin film from sticking during winding and ensuring a high slitting yield. While ensuring high elongation at break, this invention controls the heat shrinkage rate within a reasonable range, achieving a balance between flexibility and dimensional stability, and meeting the heat resistance requirements during electronic device processing. In comparison, Comparative Example 1, which did not contain functional masterbatch, had excessively low surface roughness, resulting in severe sticking and poor slitting, and its elongation at break did not reach 60%. In Comparative Example 2, the stretching temperature was 130℃, which entered the PET cold crystallization range, leading to severe deterioration of the elongation, haze rising to 18.50%, and uneven film thickness. In Comparative Example 3, the setting temperature was 250℃, which caused excessive crystallization and embrittlement, with an elongation of only MD28%. Although it had the highest strength, it lost its toughness.

[0100] It should be understood that the above embodiments are exemplary and are not intended to encompass all possible implementations included in the claims. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. A polyester film, characterized in that, Made from PET polyester chips and functional masterbatch, the functional masterbatch includes an opening agent, antioxidant and lubricant, the polyester film has a thickness of 1.0~2.0μm and an elongation at break of 60%~150%.

2. The polyester film according to claim 1, characterized in that, The mass ratio of the PET polyester chips to the functional masterbatch is (90~95):(5~10); Preferably, the number-average molecular weight of the PET polyester chips is in the range of 25,000 to 35,000, and the intrinsic viscosity is 0.60 to 0.68 dl / g; Preferably, the PET polyester chips are dried and then mixed for use, with a moisture content of 20-35 ppm; Preferably, the opening agent is selected from silica, talc, and fatty acid amide, and more preferably silica; Preferably, the particle size of the opening agent is 1~2.5μm.

3. The polyester film according to claim 1, characterized in that, The antioxidant is selected from one or more of phosphite antioxidants and phenolic antioxidants, preferably triisodecyl phosphite; Preferably, the lubricant is selected from one or more of erucamide, oleamide, and stearic acid, and is preferably erucamide; Preferably, by mass fraction, the functional masterbatch comprises 3-8 parts of opening agent, 0.5-2 parts of antioxidant, 0.5-2 parts of lubricant, and 88-96 parts of PET carrier resin.

4. The polyester film according to claim 1, characterized in that, The polyester film satisfies one or more of the following characteristics (1) to (6); (1) The thickness of the polyester film is 1.4~1.6μm; (2) The tensile strength of the polyester film is 200~260MPa; (3) The thermal shrinkage rate of the polyester film in the MD direction after standing at 150°C for 30 minutes is 0.1%~4.5%; (4) The thermal shrinkage rate of the polyester film in the TD direction after standing at 150°C for 30 minutes is 0.1%~3.0%; (5) The surface roughness Ra of the polyester film is 0.02 to 0.1 μm; (6) The haze of the polyester film is 4% to 15%.

5. A method for preparing a polyester film according to any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: S1: After uniformly mixing PET polyester chips and functional masterbatch, crystallize, dry, melt-plasticize, and extrude them; S2: A low-pressure air knife is used to attach the melt to a cooling drum for cooling and to form a thick film; S3: Simultaneously biaxially stretch, shape, cool, and wind up the thick film to obtain a polyester film.

6. The preparation method according to claim 5, characterized in that, In step S1, the pre-crystallization temperature for crystallization drying is 160~175℃, the drying temperature is 150~165℃, the dehumidification temperature for crystallization drying is 135~145℃, and the crystallinity after crystallization drying is 30~35%. Preferably, the temperature of the melting and feeding section is 260~270℃; Preferably, the temperature of the melting and plasticizing section is 275~285℃; Preferably, the temperature of the melt extrusion nozzle is 270~280℃.

7. The preparation method according to claim 5, characterized in that, In step S2, the cooling temperature is 15~25℃; Preferably, the crystallinity of the thick film is less than 3%.

8. The preparation method according to claim 5, characterized in that, In step S3, the synchronous biaxial stretching temperature is 90~110℃; Preferably, the stretching ratio of the synchronous bidirectional stretching is 3.5×3.5~4.5×4.5, and the ratio of the transverse stretching ratio to the longitudinal stretching ratio is 1:1; preferably 4×4. Preferably, the shaping temperature is 210~230℃; Preferably, the setting time is 8 to 15 seconds.

9. The preparation method according to claim 5, characterized in that, In step S3, the cooling process further includes corona treatment, with a corona treatment power of 6~10 W·min / m². Preferably, the winding process further includes slitting.

10. The application of a polyester film according to any one of claims 1–4 or a polyester film prepared by the preparation method according to any one of claims 5–9 in flexible electronic products, semiconductor packaging or optical display products.

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