Optical polyester film and method for producing the same

Abstract

An optical polyester film, the polyester film comprising a core layer and at least one surface layer, the core layer and surface layer being prepared by melt extrusion and biaxial stretching with a co-extrusion die, the core layer comprising 30wt%-90wt% of a conventional polyester and 10wt%-70wt% of semi-crystalline polyethylene naphthalate; the surface layer comprising 5wt%-55wt% of a modified polyester, 35wt%-94.9wt% of a conventional polyester and 0.1wt%-10wt% of a functional masterbatch; the functional masterbatch containing slip particles; the modified polyester being obtained by melt extrusion of 30wt%-90wt% of a conventional polyester and 10wt%-70wt% of a modified methacrylic resin, the modified polyester having an intrinsic viscosity of 0.70dL / g-0.85dL / g. The optical polyester film has the characteristics of low exudation, excellent barrier property and good optical performance.

Description

Technical Field

[0001] This invention relates to an optical polyester film and its preparation method, belonging to the field of polyester film technology. Background Technology

[0002] With the rapid development of the flat panel display industry, especially the liquid crystal display (LCD) industry, high-end optical-grade polyester films are widely used in products such as LCD TVs, tablet computers, and mobile phones. Meanwhile, the development of flexible displays is receiving increasing attention. Because water vapor in the air can easily damage the photoelectric layer in these flexible optoelectronic devices, high-barrier materials are needed to encapsulate them, thereby improving the reliability and lifespan of the components. However, during the production process and subsequent processing and use, oligomers can precipitate on the surface of the optical polyester film used in various electronic product displays, causing the film to whiten, reducing visibility, lowering its optical performance, affecting subsequent use, contaminating internal components, and failing to meet the requirements of high-end optical films.

[0003] Currently, in order to meet the requirements of subsequent high-temperature and high-humidity processing, a coating layer is usually applied to suppress the precipitation of oligomers. For example, Chinese patent CN202111576765.6 states that coating at least one layer of polyurethane-containing crosslinking agent on a multilayer co-extruded longitudinally stretched film can effectively prevent the precipitation of oligomers. However, this coating method has the following disadvantages: (1) it requires high heat resistance and thickness of the coating, which complicates the process and increases production costs; (2) the coating can cause the film surface to develop spots and streaks, increasing the risk of defects and affecting downstream use.

[0004] To fundamentally reduce the precipitation of oligomers in polyester, solid-state polymerization was proposed to increase the intrinsic viscosity of polyester chips. By using multilayer co-extrusion, the intrinsic viscosity of the surface polyester is above 0.7 dL / g, which can block the precipitation of oligomers in the core layer. However, in this method, the intrinsic viscosity of the surface polyester is too high. When preparing the film, the load of the extrusion process increases, the shear stress increases accordingly, and the polymer may undergo thermal degradation, thereby affecting the appearance and internal quality of the film. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides an optical polyester film and its preparation method, which features low exudation, excellent barrier properties, and good optical performance.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] An optical polyester film comprising a core layer and at least one surface layer, wherein the core layer and the surface layer are obtained by melt extrusion and biaxial stretching using a co-extrusion die; the core layer comprises 30wt%-90wt% conventional polyester and 10wt%-70wt% semi-crystalline polyethylene naphthalate; the surface layer comprises 5wt%-55wt% modified polyester, 35wt%-94.9wt% conventional polyester, and 0.1wt%-10wt% functional masterbatch; the functional masterbatch contains slip particles.

[0008] The modified polyester is obtained by melt extrusion of 30wt%-90wt% conventional polyester and 10wt%-70wt% modified methacrylic resin, and the intrinsic viscosity of the modified polyester is 0.70dL / g-0.85dL / g.

[0009] The aforementioned optical polyester film, wherein the intrinsic viscosity of the semi-crystalline polyethylene naphthalate is 0.5 dL / g-0.7 dL / g.

[0010] The modified methacrylate resin in the aforementioned optical polyester film is prepared from methyl methacrylate, butyl acrylate, acrylic acid, ammonium persulfate, and sulfonate emulsifier.

[0011] The above-mentioned modified methacrylate resin preparation steps are as follows: In a three-necked flask containing 15wt%-25wt% methyl methacrylate, 20wt%-25wt% butyl acrylate, 30wt%-38wt% acrylic acid, and 1wt%-10wt% glyceryl methacrylate, add 1wt%-3wt% sulfonate emulsifier and 5wt%-10wt% deionized water. Stir at 220 rpm for 20 min, add 0.1%-0.5% acrylic acid and continue stirring for 30 min. Reduce the stirring speed to 160 rpm, heat to 75°C, add 1-3 mL ammonium persulfate and continue stirring for 30 min, heat to 85°C, add 1-3 mL ammonium persulfate and continue stirring. Add 0.5-2 mL ammonium persulfate every 15 min. After 6 hours, cool to 40°C and filter to obtain the final product.

[0012] The aforementioned optical polyester film has a conventional polyester intrinsic viscosity of 0.65 dL / g to 0.85 dL / g.

[0013] In the aforementioned optical polyester film, the slip particles are one or more of silicon dioxide, organosilicon, barium sulfate, or calcium carbonate, and the particle size of the slip particles is 0.6μm-3.5μm, with an addition amount of 1wt%-10wt% of the masterbatch weight.

[0014] A method for preparing an optical polyester film, the method comprising the following steps:

[0015] a. Mix conventional polyester and semi-crystalline polyethylene naphthalate evenly and melt them through a single screw extrusion. Mix conventional polyester, modified polyester and functional masterbatch containing slip particles evenly and melt them through a twin screw extrusion. The melt is extruded through a co-extrusion die.

[0016] b. Casting: The melt is cast and then formed into an amorphous polyester sheet on a cooling casting roller;

[0017] c. Biaxial stretching and shaping: After preheating, the cooling roller casting is stretched longitudinally by 2.9-4.6 times and transversely by 3.0-5.1 times after preheating, and then crystallized and shaped.

[0018] d. Rewinding and Packaging: Cool and rewind the biaxially stretched polyester film to obtain an optical polyester film.

[0019] The beneficial effects of this invention are:

[0020] After heat treatment at 180°C for 60 minutes, the amount of oligomers precipitated onto the surface of the optical polyester film prepared by this invention is less than 7.05 × 10⁻⁶. -4 mg / cm 2 .

[0021] The modified formic acid acrylate resin selected in this invention is prepared from methyl methacrylate, butyl acrylate, acrylic acid, glyceryl methacrylate, ammonium persulfate, etc. Compared with conventional polyester melt extrusion, the modified polyester exhibits better thermal stability. By adding it to the surface layer of the polyester film through melt extrusion, it effectively inhibits the precipitation of oligomers on the film surface during high-temperature preparation. Furthermore, due to its higher intrinsic viscosity than the core layer, the sufficient crystallinity of both the surface layer and the core layer during preparation allows oligomers precipitated from the core layer to remain on the surface.

[0022] The low-viscosity semi-crystalline polyethylene naphthalate used in this invention is a homologue of PET, possessing superior properties compared to PET, such as better heat resistance, dimensional stability, and moisture barrier properties. While its chemical structure is similar to PET, the difference lies in the replacement of the benzene rings in PET with more rigid naphthalene rings in the molecular chain. This structure gives it higher physical and mechanical properties, gas barrier properties, chemical stability, and thermal stability. Its intrinsic viscosity is significantly lower than that of conventional polyesters used in production. When preparing multilayer co-extruded films, it is added to the intermediate core layer along with conventional polyesters. The viscosity of the surface polyester is much higher than that of the intermediate core layer, causing oligomers precipitated from the intermediate core layer to remain on the surface, effectively preventing oligomer precipitation on the film surface. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0024] The present invention will be further described below with reference to the embodiments.

[0025] Example 1

[0026] a) In a three-necked flask containing 21 wt% methyl methacrylate, 24 wt% butyl acrylate, 36 wt% acrylic acid, and 9 wt% glyceryl methacrylate, add 2.5 wt% sulfonate emulsifier and 7.5 wt% deionized water. Stir at 220 rpm for 20 min, add 0.25% acrylic acid and continue stirring for 30 min. Reduce the stirring speed to 160 rpm, heat to 75°C, add 2 mL of ammonium persulfate and continue stirring for 30 min. Heat to 85°C, add 2 mL of ammonium persulfate and continue stirring. Add 1 mL of ammonium persulfate every 15 min. After 6 hours, cool to 40°C and filter to obtain the final product.

[0027] b. Conventional polyester and modified methacrylic resin are melt-synthesized and extruded at a weight ratio of 99%:1% to obtain modified polyester with an intrinsic viscosity of 0.74 dL / g. Modified polyester is then melt-extruded with conventional polyester with an intrinsic viscosity of 0.75 dL / g and calcium carbonate masterbatch with a particle size of 0.6 μm at a weight ratio of 55%:43%:2%. The mixture is then melt-extruded at 275°C using a twin-screw extruder.

[0028] c. Mix conventional polyester with an intrinsic viscosity of 0.68 dL / g and semi-crystalline polyethylene naphthalate with an intrinsic viscosity of 0.62 dL / g at a weight ratio of 30%:70% until homogeneous, and then melt-extrude the mixture using a single-screw extruder at 288°C.

[0029] d. The two molten materials mentioned above are passed through a co-extrusion die and cast onto a cooling casting roller to form an amorphous A / B / A three-layer casting sheet.

[0030] e. After preheating the film casting, it is stretched longitudinally by 2.9 times and then stretched transversely by 5.1 times. The biaxially stretched polyester film is heat-set at 230°C and finally cooled and wound up to obtain an optical polyester film.

[0031] f. Cut the optical polyester film into A4 samples, heat-treat it at 180℃ for 60 minutes, and measure the amount of oligomer precipitation on its surface.

[0032] Example 2

[0033] a) In a three-necked flask containing 21 wt% methyl methacrylate, 24 wt% butyl acrylate, 36 wt% acrylic acid, and 9 wt% glyceryl methacrylate, add 2.5 wt% sulfonate emulsifier and 7.5 wt% deionized water. Stir at 220 rpm for 20 min, add 0.25% acrylic acid and continue stirring for 30 min. Reduce the stirring speed to 160 rpm, heat to 75°C, add 2 mL of ammonium persulfate and continue stirring for 30 min. Heat to 85°C, add 2 mL of ammonium persulfate and continue stirring. Add 1 mL of ammonium persulfate every 15 min. After 6 hours, cool to 40°C and filter to obtain the final product.

[0034] b. Conventional polyester and modified methacrylic resin are melt-synthesized and extruded at a weight ratio of 98.5%:1.5% to obtain modified polyester with an intrinsic viscosity of 0.76 dL / g. This modified polyester is then melt-extruded with conventional polyester with an intrinsic viscosity of 0.75 dL / g and calcium carbonate masterbatch with a particle size of 0.6 μm at a weight ratio of 50%:48%:2%. The mixture is then melt-extruded at 275°C using a twin-screw extruder.

[0035] c. Mix conventional polyester with an intrinsic viscosity of 0.68 dL / g and semi-crystalline polyethylene naphthalate with an intrinsic viscosity of 0.62 dL / g at a weight ratio of 50%:50% until homogeneous, and then melt-extrude the mixture using a single-screw extruder at 285°C.

[0036] d. The two molten materials mentioned above are passed through a co-extrusion die and cast onto a cooling casting roller to form an amorphous A / B / A three-layer casting sheet.

[0037] e. After preheating the film casting, it is stretched longitudinally by 4.6 times and then stretched transversely by 3.2 times. The biaxially stretched polyester film is heat-set at 230°C and finally cooled and wound up to obtain an optical polyester film.

[0038] f. Cut the optical polyester film into A4 samples, heat-treat it at 180℃ for 60 minutes, and measure the amount of oligomer precipitation on its surface.

[0039] Example 3

[0040] a) In a three-necked flask containing 21 wt% methyl methacrylate, 24 wt% butyl acrylate, 36 wt% acrylic acid, and 9 wt% glyceryl methacrylate, add 2.5 wt% sulfonate emulsifier and 7.5 wt% deionized water. Stir at 220 rpm for 20 min, add 0.25% acrylic acid and continue stirring for 30 min. Reduce the stirring speed to 160 rpm, heat to 75°C, add 2 mL of ammonium persulfate and continue stirring for 30 min. Heat to 85°C, add 2 mL of ammonium persulfate and continue stirring. Add 1 mL of ammonium persulfate every 15 min. After 6 hours, cool to 40°C and filter to obtain the final product.

[0041] b. Conventional polyester and modified methacrylic resin are melt-synthesized and extruded at a weight ratio of 95%:5% to obtain modified polyester with a intrinsic viscosity of 0.78 dL / g. This modified polyester is then mixed with conventional polyester with an intrinsic viscosity of 0.75 dL / g and silicone masterbatch with a particle size of 1 μm at a weight ratio of 40%:50%:10% and melt-extruded at 275°C using a twin-screw extruder.

[0042] c. Mix conventional polyester with an intrinsic viscosity of 0.68 dL / g and semi-crystalline polyethylene naphthalate with an intrinsic viscosity of 0.62 dL / g at a weight ratio of 60%:40% until homogeneous, and then melt-extrude the mixture using a single-screw extruder at 283°C.

[0043] d. The two molten materials mentioned above are passed through a co-extrusion die and cast onto a cooling casting roller to form an amorphous A / B / A three-layer casting sheet.

[0044] e. After preheating the film casting, it is stretched longitudinally by 3.0 times and then stretched transversely by 4.9 times. The biaxially stretched polyester film is heat-set at 230°C and finally cooled and wound up to obtain an optical polyester film.

[0045] f. Cut the optical polyester film into A4 samples, heat-treat it at 180℃ for 60 minutes, and measure the amount of oligomer precipitation on its surface.

[0046] Example 4

[0047] a) In a three-necked flask containing 21 wt% methyl methacrylate, 24 wt% butyl acrylate, 36 wt% acrylic acid, and 9 wt% glyceryl methacrylate, add 2.5 wt% sulfonate emulsifier and 7.5 wt% deionized water. Stir at 220 rpm for 20 min, add 0.25% acrylic acid and continue stirring for 30 min. Reduce the stirring speed to 160 rpm, heat to 75°C, add 2 mL of ammonium persulfate and continue stirring for 30 min. Heat to 85°C, add 2 mL of ammonium persulfate and continue stirring. Add 1 mL of ammonium persulfate every 15 min. After 6 hours, cool to 40°C and filter to obtain the final product.

[0048] b. Conventional polyester and modified methacrylic resin are melt-synthesized and extruded at a weight ratio of 85%:15% to obtain modified polyester with an intrinsic viscosity of 0.8 dL / g. This modified polyester is then mixed with conventional polyester with an intrinsic viscosity of 0.75 dL / g and barium sulfate masterbatch with a particle size of 3 μm at a weight ratio of 15%:79%:6% and melt-extruded at 275°C using a twin-screw extruder.

[0049] c. Mix conventional polyester with an intrinsic viscosity of 0.68 dL / g and semi-crystalline polyethylene naphthalate with an intrinsic viscosity of 0.62 dL / g at a weight ratio of 70%:30% until homogeneous, and then melt-extrude the mixture using a single-screw extruder at 280°C.

[0050] d. The two molten materials mentioned above are passed through a co-extrusion die and cast onto a cooling casting roller to form an amorphous A / B / A three-layer casting sheet.

[0051] e. After preheating the film casting, it is stretched longitudinally by 3.5 times and then stretched transversely by 4.2 times. The biaxially stretched polyester film is heat-set at 230°C and finally cooled and wound up to obtain an optical polyester film.

[0052] f. Cut the optical polyester film into A4 samples, heat-treat it at 180℃ for 60 minutes, and measure the amount of oligomer precipitation on its surface.

[0053] Example 5

[0054] a) In a three-necked flask containing 21 wt% methyl methacrylate, 24 wt% butyl acrylate, 36 wt% acrylic acid, and 9 wt% glyceryl methacrylate, add 2.5 wt% sulfonate emulsifier and 7.5 wt% deionized water. Stir at 220 rpm for 20 min, add 0.25% acrylic acid and continue stirring for 30 min. Reduce the stirring speed to 160 rpm, heat to 75°C, add 2 mL of ammonium persulfate and continue stirring for 30 min. Heat to 85°C, add 2 mL of ammonium persulfate and continue stirring. Add 1 mL of ammonium persulfate every 15 min. After 6 hours, cool to 40°C and filter to obtain the final product.

[0055] b. Conventional polyester and modified methacrylic resin are melt-synthesized and extruded at a weight ratio of 70%:30% to obtain modified polyester with an intrinsic viscosity of 0.82 dL / g. This modified polyester is then mixed with conventional polyester with an intrinsic viscosity of 0.75 dL / g and silica masterbatch with a particle size of 2 μm at a weight ratio of 5%:92%:3% and melt-extruded at 275°C using a twin-screw extruder.

[0056] c. Mix conventional polyester with an intrinsic viscosity of 0.68 dL / g and semi-crystalline polyethylene naphthalate with an intrinsic viscosity of 0.62 dL / g at a weight ratio of 90%:10% until homogeneous, and then melt-extrude the mixture using a single-screw extruder at 280°C.

[0057] d. The two molten materials mentioned above are passed through a co-extrusion die and cast onto a cooling casting roller to form an amorphous A / B / A three-layer casting sheet.

[0058] e. After preheating the film casting, it is stretched longitudinally by 3.3 times and then stretched transversely by 4.5 times. The biaxially stretched polyester film is heat-set at 230°C and finally cooled and wound up to obtain an optical polyester film.

[0059] f. Cut the optical polyester film into A4 samples, heat-treat it at 180℃ for 60 minutes, and measure the amount of oligomer precipitation on its surface.

[0060] Comparative Example 1

[0061] a) In a three-necked flask containing 21 wt% methyl methacrylate, 24 wt% butyl acrylate, 36 wt% acrylic acid, and 9 wt% glyceryl methacrylate, add 2.5 wt% sulfonate emulsifier and 7.5 wt% deionized water. Stir at 220 rpm for 20 min, add 0.25% acrylic acid and continue stirring for 30 min. Reduce the stirring speed to 160 rpm, heat to 75°C, add 2 mL of ammonium persulfate and continue stirring for 30 min. Heat to 85°C, add 2 mL of ammonium persulfate and continue stirring. Add 1 mL of ammonium persulfate every 15 min. After 6 hours, cool to 40°C and filter to obtain the final product.

[0062] b. Conventional polyester and modified methacrylic resin are melt-synthesized and extruded in a weight ratio of 70%:30%. The intrinsic viscosity of the modified polyester is increased to 0.85 dL / g by solid-phase polymerization. It is then mixed with conventional polyester with an intrinsic viscosity of 0.75 dL / g and silica masterbatch with a particle size of 1 μm in a weight ratio of 5%:92%:3%, and melt-extruded at 275°C using a twin-screw extruder.

[0063] c. Conventional polyester with an intrinsic viscosity of 0.68 dL / g is melt-extruded at 280°C using a single-screw extruder.

[0064] d. The two molten materials mentioned above are passed through a co-extrusion die and cast onto a cooling casting roller to form an amorphous A / B / A three-layer casting sheet.

[0065] e. After preheating the film casting, it is stretched longitudinally by 3.2 times and then stretched transversely by 4.6 times. The biaxially stretched polyester film is heat-set at 230°C and finally cooled and wound up to obtain an optical polyester film.

[0066] f. Cut the optical polyester film into A4 samples, heat-treat it at 180℃ for 60 minutes, and measure the amount of oligomer precipitation on its surface.

[0067] Comparative Example 2

[0068] a. A conventional polyester with an intrinsic viscosity of 0.75 dL / g and a silica masterbatch with a particle size of 1 μm are mixed evenly at a weight ratio of 97%:3% and then melt-extruded at 275°C using a twin-screw extruder.

[0069] b. Mix conventional polyester with an intrinsic viscosity of 0.68 dL / g and semi-crystalline polyethylene naphthalate with an intrinsic viscosity of 0.62 dL / g at a weight ratio of 60%:40% until homogeneous, and then melt-extrude the mixture using a single-screw extruder at 283°C.

[0070] c. The two molten materials mentioned above are passed through a co-extrusion die and cast onto a cooling casting roller to form an amorphous A / B / A three-layer casting sheet.

[0071] d. After preheating the film casting, it is stretched longitudinally by 3.2 times and then stretched transversely by 4.6 times. The biaxially stretched polyester film is heat-set at 230°C and finally cooled and wound up to obtain an optical polyester film.

[0072] e. Cut the optical polyester film into A4 samples, heat-treat it at 180°C for 60 minutes, and measure the amount of oligomers precipitated on its surface.

[0073] Comparative Example 3

[0074] a. A conventional polyester with an intrinsic viscosity of 0.75 dL / g and a silica masterbatch with a particle size of 1 μm are mixed evenly at a weight ratio of 97%:3% and then melt-extruded at 275°C using a twin-screw extruder.

[0075] b. Conventional polyester with an intrinsic viscosity of 0.68 dL / g is melt-extruded at 280°C using a single-screw extruder.

[0076] c. The two molten materials mentioned above are passed through a co-extrusion die and cast onto a cooling casting roller to form an amorphous A / B / A three-layer casting sheet.

[0077] d. After preheating the film casting, it is stretched longitudinally by 3.2 times and then stretched transversely by 4.6 times. The biaxially stretched polyester film is heat-set at 230°C and finally cooled and wound up to obtain an optical polyester film.

[0078] e. Cut the optical polyester film into A4 samples, heat-treat it at 180°C for 60 minutes, and measure the amount of oligomers precipitated on its surface.

[0079] The polyester films prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to performance tests, and the test results are shown in Table 1.

[0080] Table 1 Comparison of Optical Polyester Film Properties

[0081]

[0082] The test methods for each performance item are as follows in Table 1:

[0083] Light transmittance, haze, and clarity were tested using a BYK AT-4725 haze meter.

[0084] Oligomer precipitation determination: The membrane was heat-treated at 180℃ for 60 min, and oligomers were precipitated on the membrane surface. The membrane surface was then immersed in DMF to dissolve the oligomers, and the oligomer content was determined by high performance liquid chromatography (HPLC).

[0085] The water vapor transmission rate was determined according to GB / T 26253-2010 standard using a C303H water vapor transmission rate test system.

[0086] As can be seen from Table 1, the optical polyester film prepared by this invention not only has less surface oligomer precipitation, but also has good optical and barrier properties, meeting the high-end optical film requirements of display optical components.

Claims

1. An optical polyester film, characterized in that: The polyester film comprises a core layer and at least one surface layer, wherein the core layer and the surface layer are obtained by melt extrusion and biaxial stretching using a co-extrusion die. The core layer comprises 30wt%-90wt% conventional polyester and 10wt%-70wt% semi-crystalline polyethylene naphthalate. The surface layer comprises 5wt%-55wt% modified polyester, 35wt%-94.9wt% conventional polyester, and 0.1wt%-10wt% functional masterbatch. The functional masterbatch contains slip particles. The modified polyester is obtained by melt extrusion of 30wt%-90wt% conventional polyester and 10wt%-70wt% modified methacrylic acid resin, and the intrinsic viscosity of the modified polyester is 0.70dL / g-0.85dL / g. The modified methacrylate resin is prepared from methyl methacrylate, butyl acrylate, acrylic acid, glyceryl methacrylate, ammonium persulfate, and sulfonate emulsifier. The preparation process is as follows: 1 wt%-3 wt% sulfonate emulsifier and 5 wt%-10 wt% deionized water are added to a three-necked flask containing 15 wt%-25 wt% methyl methacrylate, 20 wt%-25 wt% butyl acrylate, 30 wt%-38 wt% acrylic acid, and 1 wt%-10 wt% glyceryl methacrylate. The mixture is stirred at 220 r / min for 20 min, then 0.1%-0.5% acrylic acid is added and stirring continues for 30 min. The stirring speed is reduced to 160 r / min, and the mixture is heated to 75°C. 1-3 mL of ammonium persulfate is added and stirring continues for 30 min. The mixture is heated to 85°C, then 1-3 mL of ammonium persulfate is added and stirring continues. Every 15 min, 0.5-2 mL of ammonium persulfate is added. After 6 hours, the mixture is cooled to 40°C and filtered to obtain the final product. The intrinsic viscosity of the semi-crystalline polyethylene naphthalate is 0.5 dL / g-0.62 dL / g; The intrinsic viscosity of the conventional polyester is 0.65 dL / g to 0.85 dL / g.

2. The optical polyester film according to claim 1, characterized in that: The slip particles are one or more of silicon dioxide, organosilicon, barium sulfate, or calcium carbonate, and the particle size of the slip particles is 0.6μm-3.5μm. The amount added is 1wt%-10wt% of the weight of the masterbatch.

3. A method for preparing an optical polyester film according to any one of claims 1-2, characterized in that: The preparation method includes the following steps: a. Mix conventional polyester and semi-crystalline polyethylene naphthalate evenly and melt them through a single screw extrusion. Mix conventional polyester, modified polyester and functional masterbatch containing slip particles evenly and melt them through a twin screw extrusion. The melt is extruded through a co-extrusion die. b. Casting: The melt is cast and formed into an amorphous polyester sheet on a cooling casting roller; c. Biaxial stretching and shaping: The cooling roller casting is preheated, stretched longitudinally by 2.9-4.6 times, then preheated and stretched transversely by 3.0-5.1 times, and then crystallized and shaped. d. Rewinding and Packaging: Cool and rewind the biaxially stretched polyester film to obtain an optical polyester film.

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