A biaxially oriented optical polyester film

Abstract

The application relates to a biaxial orientation film, in particular a biaxial orientation optical polyester film, which adopts A / B / A or A / B / C three-layer structure co-extrusion, the A layer and the C layer contain modified polyesters; the modified polyesters are obtained by copolymerization of diacids and diols; the diacids are 4-(3,5-dicarboxyphenoxy) phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propane diyl dioxy dibenzoic acid and terephthalic acid. The optical polyester film has the advantages of not affecting the PPF self-repairing surface water contact angle before and after peeling, no orange peel, easy peeling, simple process, low cost and the like.

Description

Technical Field

[0001] The present invention relates to a biaxially oriented film, in particular to a biaxially oriented optical polyester film. Background Art

[0002] In the field of polymer materials, polyethylene terephthalate (PET), formed by the esterification and polycondensation of terephthalic acid and ethylene glycol, possesses numerous excellent properties and can be used in diverse applications, such as spinning, engineering plastics, and thin films. BOPET film, produced by melt coextrusion and biaxial stretching of PET, is widely used in packaging, industrial, electrical, electronic, display, and protective applications due to its excellent mechanical, thermal, electrical, and optical properties.

[0003] The automotive industry has developed rapidly, especially in recent years, with significant advancements in new energy vehicles. Cars have become a fundamental means of transportation. How to better protect car paint has become a key concern for car owners. Car covers (PPF, paint protection film) play a crucial role in protecting car paint. The original main material for car covers was PVC, or polyvinyl chloride. While low-cost, it is prone to yellowing and cracking over time. With technological advancements, TPU is now the most common material for invisible car covers, due to its high and low temperature resistance, mildew resistance, and excellent elasticity.

[0004] The overall structure of the car cover includes a white matte release film, an acrylic adhesive layer, a TPU carrier, a self-repairing layer, and an optical polyester film for self-repairing surface protection.

[0005] There are currently two mainstream types of car covers, differentiated primarily by their self-repairing properties: hydrophobic and hydrophilic. The primary difference between the two lies in their water contact angle. Specifically, hydrophobic covers are designed to form balls when raindrops fall onto them, while hydrophilic covers tend to spread out and slide down in parallel planes. Hydrophobic covers easily bead up, which has two main drawbacks: first, they act as convex lenses when exposed to sunlight, potentially damaging the car's paint; and second, they dry, leaving stains on the car's exterior. Hydrophilic covers, on the other hand, do not have these drawbacks and are therefore widely popular with car owners.

[0006] The optical polyester film used to protect the PPF self-repairing surface has the following main requirements: first, it does not affect the water contact angle of the PPF self-repairing surface before and after peeling; second, it does not affect the brightness of the PPF self-repairing surface before and after peeling; third, it is easy to peel and there should be no jamming problems during the peeling process.

[0007] To meet the requirements of optical polyester film for PPF self-healing surface protection, current technical solutions in the polyester film field include: 1. Treating the polyester film surface with silicone oil or a non-silicone release layer to achieve easy peeling. 2. Treating the polyester film surface with a scratch-resistant coating to achieve a smooth surface. 3. Using an untreated optical polyester film substrate for lower cost.

[0008] Although technicians have conducted extensive research on polyester film, the existing technical solutions to the polyester film problem still have many shortcomings: 1. Silicone oil or non-silicone release layer processing on the polyester film surface can achieve the purpose of minimizing the impact on the water contact angle before and after peeling; however, due to the release force on its surface, after being bonded to the PPF self-repairing surface, bubbles are easily generated during placement, causing it to peel off by itself, affecting the appearance of the PPF; at the same time, when the silicone oil is released, the silicon in the release layer easily migrates to the self-repairing layer, affecting the effect of the self-repairing layer. 2. Although the polyester film surface is treated with an anti-scratch coating to make the film surface smooth and not affect the brightness of the PPF surface after peeling, its surface is too flat, which easily causes peeling jams and high manufacturing costs. 3. Using an optical polyester film substrate with an untreated surface is low cost, but the unevenness of the substrate surface (such as orange peel texture) is easily transferred to the PPF self-repairing surface. After peeling, the water contact angle of the hydrophilic self-repairing surface increases, the hydrophilic performance deteriorates, and the brightness of the PPF surface is also affected. Summary of the Invention

[0009] The present invention provides a biaxially oriented optical polyester film, which has the advantages of not affecting the water contact angle of the PPF self-repairing surface before and after peeling, having no orange peel texture, being easy to peel, having a simple process and low cost.

[0010] To achieve the above technical objectives, the technical solution adopted in this application is as follows: a biaxially oriented optical polyester film, co-extruded with a three-layer structure of A / B / A or A / B / C, wherein the A layer and the C layer contain modified polyester;

[0011] The modified polyester is obtained by copolymerizing a dibasic acid and a diol;

[0012] Wherein, the dibasic acid is 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid and terephthalic acid;

[0013] Definition: X1 is the content of 4-(3,5-dicarboxyphenoxy)phthalic acid component relative to the total dicarboxylic acid components in the modified polyester;

[0014] X2 is the content of 2-(carboxymethoxy)-4-fluorobenzoic acid component relative to the total dicarboxylic acid components in the modified polyester;

[0015] X3 is the content of 4,4-propanediyldioxydibenzoic acid component relative to the total dicarboxylic acid components in the modified polyester;

[0016] X4 is the content of terephthalic acid components relative to the total dicarboxylic acid components in the modified polyester;

[0017] Among them, X1, X2, X3, and X4 satisfy the following relationship:

[0018] 5 mol%≤X1≤15 mol%

[0019] 2 mol%≤X2≤10 mol%

[0020] 3 mol%≤X3≤25 mol%

[0021] 50 mol%≤X4≤90 mol%

[0022] X1+X2+X3+X4=100 mol%.

[0023] As an improved technical solution of the present application, the content of 4-(3,5-dicarboxyphenoxy)phthalic acid component in the modified polyester relative to the total dicarboxylic acid components is 7 mol %≤X1≤12 mol %.

[0024] As an improved technical solution of the present application, the content of 2-(carboxymethoxy)-4-fluorobenzoic acid component in the modified polyester relative to the total dicarboxylic acid components is 3 mol %≤X2≤9 mol %.

[0025] As an improved technical solution of the present application, the content of 4,4-propanediyldioxydibenzoic acid component in the modified polyester relative to the total dicarboxylic acid components is 5 mol %≤X3≤20 mol %.

[0026] As an improved technical solution of the present application, the diol is selected from one of ethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, hexanediol, and polyethylene oxide glycol, or multiple thereof in any molar ratio; the molar ratio of the dibasic acid to the diol is 1:1.21 to 1:1.46.

[0027] As an improved technical solution of the present application, the dibasic acid and the diol are copolymerized under a catalyst, and the catalyst is selected from antimony, iron, aluminum, germanium or titanium catalysts, and the addition amount is 80ppm to 300ppm.

[0028] As an improved technical solution of the present application, the dibasic acid and the diol are copolymerized in the presence of a stabilizer, the stabilizer being selected from trimethyl phosphate, triethyl phosphate, triphenyl phosphate, tri-n-butyl phosphate, tetrabutyl titanate, or tetraethyl titanate; the addition amount is 25 ppm to 130 ppm.

[0029] As an improved technical solution of the present application, the thickness of the optical polyester film is 19 μm to 150 μm.

[0030] As an improved technical solution of the present application, the biaxially oriented optical polyester film structure is a three-layer A / B / A, and the thickness ratio of the A layer to the B layer is 1:16 to 1:5.

[0031] As an improved technical solution of the present application, the optical polyester film structure is a three-layer A / B / C, the thickness ratio of layer A to layer B is 1:35 to 1:10, the thickness ratio of layer C to layer B is 1:35 to 1:10, and the thickness of layer A and layer C can be the same or different.

[0032] Beneficial effects

[0033] 1. The present invention utilizes the acid modification principle and, from a microscopic perspective, copolymerizes and modifies the polyester polymer chain segments (by introducing characteristic functional groups in the new monomers, such as phenoxy, methoxy, phenylfluoro, and dioxy groups, into the modified polyester), giving the polyester polymer material new properties and enhancing the added value of its deep-processing products.

[0034] 2. The present invention designs polyester polymer chain segments (second and third monomers such as 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, and 4,4-propanediyldioxydibenzoic acid directly participate in the polyester synthesis reaction to form a stable block polymer) to achieve polyester modification, avoid the compatibility problems caused by doping modification, and make the polyester film performance more uniform and stable.

[0035] 3. The present invention directly melt-extrudes and stretches the modified polyester into a film, which has a simple process and low cost.

[0036] 4. The optical polyester film of the present invention does not require deep processing of release layer and anti-scratch layer, and is environmentally friendly and pollution-free. DETAILED DESCRIPTION

[0037] To facilitate understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0039] Definition: In this application, dicarboxylic acid is a dibasic acid.

[0040] The invention discloses a biaxially oriented optical polyester film, which is co-extruded using an A / B / A or A / B / C three-layer structure, wherein the A layer and the C layer contain modified polyester.

[0041] The modified polyester is obtained by copolymerizing a dibasic acid and a diol;

[0042] Specifically, the dibasic acids used are 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid.

[0043] The content of 4-(3,5-dicarboxyphenoxy)phthalic acid relative to the total dicarboxylic acid components in the modified polyester is X1; the content of 2-(carboxymethoxy)-4-fluorobenzoic acid relative to the total dicarboxylic acid components is X2; the content of 4,4-propanediyldioxydibenzoic acid relative to the total dicarboxylic acid components is X3; and the content of terephthalic acid relative to the total dicarboxylic acid components is X4. X1, X2, X3, and X4 satisfy the following relationship:

[0044] 5 mol%≤X1≤15 mol%

[0045] 2 mol%≤X2≤10 mol%

[0046] 3 mol%≤X3≤25 mol%

[0047] 50 mol%≤X4≤90 mol%

[0048] X1+X2+X3+X4=100 mol%.

[0049] Among them, 4-(3,5-dicarboxyphenoxy)phthalic acid, whether the dicarboxyl groups on the same benzene ring or on two benzene rings participate in the reaction, can ensure that the two carboxyl groups are left outside. Carboxyl groups are polar groups. When used in the production of polyester films, they exist on the surface of polyester films. When bonded to a hydrophilic self-repairing surface, they can "induce" the hydrophilic groups in the self-repairing surface to face outward, so after bonding, the water contact angle of the self-repairing surface will not be affected, and the hydrophilicity of the self-repairing surface may even be increased. At the same time, the carboxyl group is highly active, which increases the instability of the modified polyester. The presence of the phenoxy group has a good stabilizing effect on the polymer material, which can effectively prevent the oxidation and decomposition reactions of the polymer material, and effectively compensate for the instability of the modified polyester caused by the vacant carboxyl groups.

[0050] The content ratio of 4-(3,5-dicarboxyphenoxy) phthalic acid component in the modified polyester relative to the total dicarboxylic acid component is 5 mol%≤X1≤15 mol%, preferably 7 mol%≤X1≤12 mol%. The content ratio less than 5 mol% cannot play the role of the modified monomer, and the content ratio greater than 15 mol% affects the hydrophilic effect in the self-repairing surface.

[0051] The methoxy group in the 2-(carboxymethoxy)-4-fluorobenzoic acid is a group with high electronegativity and has strong electron-donating properties. Due to the expansion of the electron cloud of the oxygen atom in the methoxy group and the pushing effect of the electron pair, the methoxy group can increase the steric hindrance of atoms or molecules, change the electron distribution and charge density, and increase the steric hindrance. The methoxy group can also form hydrogen bonds to affect the interaction between molecules, ensuring the stability and transparency of the modified polyester. The fluorine group has strong polarity, which can also make the hydrophilic group in the self-repairing surface face outward.

[0052] The content ratio of 2-(carboxymethoxy)-4-fluorobenzoic acid component in the modified polyester relative to the total dicarboxylic acid component is 2 mol%≤X2≤10 mol%, preferably 3 mol%≤X2≤9 mol%. The content ratio less than 2 mol% cannot play the role of the modified monomer, and the content ratio greater than 10 mol% affects the fitting effect of the self-repairing surface.

[0053] The presence of the diphenyloxy group in the 4,4-propanediyl dioxy dibenzoic acid further ensures the stability of the modified polyester with strong polarity. The content ratio of 4,4-propanediyl dioxy dibenzoic acid component in the modified polyester relative to the total dicarboxylic acid component is 3 mol%≤X3≤25 mol%, preferably 5 mol%≤X3≤20 mol%. The content ratio less than 3 mol% cannot play the role of the modified monomer, and the content ratio greater than 25 mol% affects the modified polyester, causing changes in the main structure of polyethylene terephthalate.

[0054] For the direction perpendicular to the polymer chain segment, the hydrogen bonds between the three dicarboxylic acid molecules are formed, providing a carrier and increasing the intermolecular forces, making it difficult for the polymer chain segment to creep, effectively inhibiting the generation of orange peel patterns on the surface of the polyester film.

[0055] The presence of terephthalic acid ensures that the entire polyester system remains unchanged.

[0056] In the present application, several acid monomers interact with and coordinate with each other, and are indispensable. At the same time, 4-(3,5-dicarboxyphenoxy) phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyl dioxy dibenzoic acid, and terephthalic acid can make the polyester film have the advantages of not affecting the water contact angle of the PPF self-repairing surface before and after peeling, no orange peel pattern, easy peeling, simple process, low cost, etc. by designing the total dicarboxylic acid component content ratio.

[0057] The modified polyester of the present invention can be prepared by the following method:

[0058] 1. Add the required dibasic acid, diol, catalyst and stabilizer into the polyester reactor in sequence and beat for 15 minutes; introduce nitrogen protection and carry out esterification at 235℃~260℃ and 260KPa for 2.5h~4h.

[0059] The dibasic acid is selected from 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid. The content of 4-(3,5-dicarboxyphenoxy)phthalic acid component relative to the total dicarboxylic acid components in the modified polyester is 5 mol%≤X1≤15 mol%, preferably 7 mol%≤X1≤12 mol%; the content of 2-(carboxymethoxy)-4-fluorobenzoic acid component relative to the total dicarboxylic acid components is 2 mol%≤X2≤10 mol%, preferably 3 mol%≤X2≤9 mol%; the content of 4,4-propanediyldioxydibenzoic acid component relative to the total dicarboxylic acid components is 3 mol%≤X3≤25 mol%, preferably 5 mol%≤X3≤20 mol%, and X1+X2+X3+X4=100 mol%.

[0060] The diol is selected from ethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, hexanediol, polyethylene oxide glycol, etc., preferably ethylene glycol.

[0061] The molar ratio of dibasic acid to diol is 1:1.21 to 1:1.46.

[0062] The catalyst is selected from antimony, iron, aluminum, germanium, titanium and the like, and the addition amount of ethylene glycol antimony is preferably 80 ppm to 300 ppm.

[0063] The stabilizer is selected from trimethyl phosphate, triethyl phosphate, triphenyl phosphate, tri-n-butyl phosphate, tetrabutyl titanate, tetraethyl titanate, etc., preferably triphenyl phosphate, and the addition amount is 25ppm to 130ppm.

[0064] 2. The esterification endpoint is determined based on the water output. After the esterification is complete, vacuum is applied and the polycondensation reaction is carried out at 262° C. to 280° C. and 25 Pa to 70 Pa for 3 to 5 hours. The modified polyester of the present invention is obtained through spinning, cooling, pelletizing, and drying. The intrinsic viscosity of the modified polyester is 0.58 dl / g to 0.68 dl / g.

[0065] The optical polyester film of the present invention has a thickness of 19 μm to 150 μm.

[0066] The optical polyester film structure is three layers A / B / A, and the thickness ratio of the A layer to the B layer is 1:16 to 1:5.

[0067] The optical polyester film structure is three layers A / B / C, the thickness ratio of layer A to layer B is 1:35-1:10, the thickness ratio of layer C to layer B is 1:35-1:10, and the thickness of layer A and layer C can be the same or different.

[0068] The optical polyester film structure is a three-layer structure of A / B / C, and the components of the A layer and the C layer can be the same or different.

[0069] Generally, in the prior art, in order to increase the smoothness of polyester film and improve the winding and slitting performance of polyester film, a polyester masterbatch containing micron-sized smooth particles is often added to the surface layer. The viscosity of the polyester masterbatch is 0.62 dl / g, the concentration of the micron-sized smooth particles in the polyester masterbatch is 0.3%, and the particle size is 1.5 μm; the micron-sized smooth particles are selected from silicon dioxide, calcium carbonate, kaolin, barium sulfate, etc., preferably silicon dioxide.

[0070] The optical polyester film is prepared by co-extrusion through a die head, sheet casting, longitudinal stretching, transverse stretching, shaping, pulling and winding.

[0071] The optical polyester film of the present invention can be prepared by the following method:

[0072] 1. The prepared modified polyester is added to the A layer and C layer of the polyester film, and a polyester masterbatch containing micron-sized smooth particles is added to the surface layer. A pure polyester resin with an intrinsic viscosity of 0.66 dl / g (usually refers to polyethylene terephthalate without any modification) is added to the B layer and melt extruded. The viscosity of the polyester masterbatch is 0.62 dl / g, the concentration of the silica particles in the polyester masterbatch is 0.3%, and the particle size is 1.5 μm.

[0073] 2. The melt is co-extruded through the die head and cast onto the casting roll to form a three-layer co-extruded casting sheet.

[0074] 3. The cast sheet is longitudinally stretched with a longitudinal stretching ratio of 2.7 to 3.8.

[0075] 4. The longitudinal sheet is stretched transversely with a transverse stretching ratio of 3.3 to 5.6.

[0076] 5. The stretched film is heat-set at a temperature of 220°C to 243°C.

[0077] 6. Then cool, pull and reel.

[0078] The present invention will be further described below with reference to the following examples, but the implementation and protection scope of the present invention are not limited to these examples.

[0079] Example 1

[0080] Preparation of modified polyester:

[0081] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.21, the addition amount of ethylene glycol antimony is 80ppm, and the addition amount of triphenyl phosphate is 25ppm. Among them, the content rate of each component of the dibasic acid relative to the total dicarboxylic acid component, 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid, are as follows: X1=5 mol%, X2=2 mol%, X3 =3 mol %, X4 = 90 mol %, and after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C to 262°C and 265 kPa for 2.5 hours; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C to 282°C and 25 Pa for 3 hours. After silk making, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.58 dl / g is obtained.

[0082] The modified polyester of the present invention in layer A and a smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the silica particles with an average particle size of 1.5 μm are present in a surface layer of the polyester film at a content of 350 ppm, and a pure polyester resin with an intrinsic viscosity of 0.66 dl / g in layer B are added to a corresponding extrusion system, melted at 260°C, co-extruded through a die, and cast onto a casting roll to form a three-layer A / B / A extruded cast sheet; the cast sheet is longitudinally stretched at a longitudinal stretching temperature of 75°C to 87°C and a longitudinal stretching ratio of 3.8; the longitudinally stretched sheet is transversely stretched at a transverse stretching temperature of 108°C to 130°C and a transverse stretching ratio of 5.6; the stretched film is shaped and cooled at a shaped temperature of 220°C; the film is then cooled, pulled, and rolled to produce an optical polyester film with a thickness of 19 μm, wherein the thickness ratio of layer A to layer B is 1:5.

[0083] Example 2

[0084] Preparation of modified polyester:

[0085] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.3, the addition amount of titanium dioxide is 100ppm, and the addition amount of triphenyl phosphate is 35ppm. Among them, the content rate of each component of the dibasic acid relative to the total dicarboxylic acid component, 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid, are as follows: X1=7 mol%, X2=3 mol%, X3= 5 mol%, X4 = 85 mol%, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C ~ 262°C, 265KPa for 2.5h; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C ~ 282°C, 35Pa for 3.5h. After silk making, cooling, pelletizing and drying, a modified polyester with an intrinsic viscosity of 0.60dl / g is obtained.

[0086] The modified polyester of the present invention in layer A and a smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the silica particles with an average particle size of 1.5 μm are present in a surface layer of the polyester film at a content of 400 ppm, and a pure polyester resin with an intrinsic viscosity of 0.66 dl / g in layer B are added to a corresponding extrusion system, melted at 265°C, co-extruded through a die, and cast onto a casting roll to form a three-layer A / B / A extruded cast sheet; the cast sheet is longitudinally stretched at a longitudinal stretching temperature of 75°C to 87°C and a longitudinal stretching ratio of 3.5; the longitudinally stretched sheet is transversely stretched at a transverse stretching temperature of 108°C to 130°C and a transverse stretching ratio of 5.2; the stretched film is shaped and cooled at a shaped temperature of 225°C; the film is then cooled, pulled, and rolled to produce an optical polyester film with a thickness of 23 μm, wherein the thickness ratio of layer A to layer B is 3:20.

[0087] Example 3

[0088] Preparation of modified polyester:

[0089] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.33, the addition amount of ethylene glycol antimony is 150ppm, and the addition amount of triphenyl phosphate is 50ppm. Among them, the content rate of each component of the dibasic acid relative to the total dicarboxylic acid component, 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid, are as follows: X1=7 mol%, X2=5 mol%, X3 =8 mol %, X4 =80 mol %, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C to 262°C, 265KPa for 3h; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C to 282°C, 35Pa for 3.5h. After silk making, cooling, pelletizing and drying, a modified polyester with an intrinsic viscosity of 0.61dl / g is obtained.

[0090] The modified polyester of the present invention in layer A and a smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the silica particles with an average particle size of 1.5 μm are present in a surface layer of the polyester film at a content of 400 ppm, and a pure polyester resin with an intrinsic viscosity of 0.66 dl / g in layer B are added to a corresponding extrusion system, melted at a temperature of 265°C, co-extruded through a die, and cast onto a casting roll to form a three-layer A / B / A extruded cast sheet; the cast sheet is longitudinally stretched at a longitudinal stretching temperature of 75°C to 87°C and a longitudinal stretching ratio of 3.5; the longitudinally stretched sheet is transversely stretched at a transverse stretching temperature of 108°C to 130°C and a transverse stretching ratio of 5.0; the stretched film is shaped and cooled at a shaped temperature of 230°C; the film is then cooled, pulled, and rolled to produce an optical polyester film with a thickness of 38 μm, wherein the thickness ratio of layer A to layer B is 3:25.

[0091] Example 4

[0092] Preparation of modified polyester:

[0093] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.35, the addition amount of ethylene glycol antimony is 180ppm, and the addition amount of triphenyl phosphate is 65ppm. Among them, the content rate of 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid in the dibasic acid relative to the total dicarboxylic acid components is as follows: X1=9 mol%, X2=4 mol%, X 3 = 12 mol%, X4 = 75 mol%, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C ~ 262°C, 265KPa for 3h; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C ~ 282°C, 50Pa for 4h. After silk making, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.64dl / g is obtained.

[0094] The modified polyester of the present invention in layer A and a smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the silica particles with an average particle size of 1.5 μm are present in a surface layer of the polyester film at a content of 500 ppm, and a pure polyester resin with an intrinsic viscosity of 0.66 dl / g in layer B are added to a corresponding extrusion system, melted at a temperature of 265°C, co-extruded through a die, and cast onto a casting roll to form a three-layer A / B / A extruded cast sheet; the cast sheet is longitudinally stretched at a longitudinal stretching temperature of 75°C to 87°C and a longitudinal stretching ratio of 3.3; the longitudinally stretched sheet is transversely stretched at a transverse stretching temperature of 108°C to 130°C and a transverse stretching ratio of 4.9; the stretched film is shaped and cooled at a shaped temperature of 232°C; the film is then cooled, pulled, and rolled to produce an optical polyester film with a thickness of 50 μm, wherein the thickness ratio of layer A to layer B is 1:5.

[0095] Example 5

[0096] Preparation of modified polyester layer A:

[0097] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.35, the addition amount of ethylene glycol antimony is 180ppm, and the addition amount of triethyl phosphate is 65ppm. Among them, the content rate of 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid in the dibasic acid relative to the total dicarboxylic acid components is as follows: X1=9 mol%, X2=4 mol%, X 3 = 12 mol%, X4 = 75 mol%, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C ~ 262°C, 265KPa for 3h; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C ~ 282°C, 50Pa for 4h. After silk making, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.64dl / g is obtained.

[0098] Preparation of modified polyester layer C:

[0099] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.35, the addition amount of ethylene glycol antimony is 180ppm, and the addition amount of triphenyl phosphate is 65ppm. Among them, the content rate of each component of the dibasic acid relative to the total dicarboxylic acid component, 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid, is as follows: X1=8 mol%, X2=6 mol%, X 3 = 10 mol%, X4 = 76 mol%, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C ~ 262°C, 265KPa for 3h; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C ~ 282°C, 55Pa for 4h. After silk making, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.63dl / g is obtained.

[0100] The modified polyester of the present invention in layer A and a smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the silica particles with an average particle size of 1.5 μm are contained in a content of 500 ppm in layer A of the polyester film; the modified polyester of the present invention in layer C and a smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the silica particles with an average particle size of 1.5 μm are contained in a content of 500 ppm in layer C of the polyester film; and the pure A polyester resin is added to a corresponding extrusion system, melted at a temperature of 270°C, co-extruded through a die head, and cast onto a casting roller to form a three-layer A / B / C extruded casting sheet; the casting sheet is longitudinally stretched at a longitudinal stretching temperature of 75°C to 87°C and a longitudinal stretching ratio of 3.3; the longitudinally stretched sheet is transversely stretched at a transverse stretching temperature of 108°C to 130°C and a transverse stretching ratio of 4.9; the stretched film is shaped and cooled at a shaping temperature of 232°C; the film is then cooled, pulled, and rolled to obtain an optical polyester film with a thickness of 50 μm, wherein the thickness ratio of layer A to layer B is 1:10, and the thickness ratio of layer C to layer B is 1:10.

[0101] Example 6

[0102] Preparation of modified polyester:

[0103] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.4, the addition amount of ethylene glycol antimony is 200ppm, and the addition amount of triphenyl phosphate is 90ppm. Among them, the content rate of each component of the dibasic acid relative to the total dicarboxylic acid component, 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid, are as follows: X1=10 mol%, X2=7 mol%, X3=10 mol%, X4=10 mol%, X5=10 mol%, X6=10 mol%, X7=10 mol%, X8=10 mol%, X9=10 mol%, X10=10 mol%, X110=10 mol%, X120=10 mol%, X130=10 mol%, X140=10 mol%, X150=10 mol%, X160=10 mol%, X170=10 mol%, X180=10 mol%, X190=10 mol%, X21 ... =13 mol %, X4=70 mol %, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C to 262°C, 265KPa for 3 hours; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C to 282°C, 65Pa for 4.5 hours. After silk making, cooling, pelletizing and drying, a modified polyester with an intrinsic viscosity of 0.66dl / g is obtained.

[0104] The modified polyester of the present invention in layer A and a slippery polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the content of silica particles with an average particle size of 1.5 μm in the surface layer of the polyester film is 500 ppm, and a pure polyester resin with an intrinsic viscosity of 0.66 dl / g in layer B are added to the corresponding extrusion system, melted at a temperature of 275°C, co-extruded through a die, and cast onto a casting sheet. On the roller, a three-layer A / B / A extruded cast sheet is formed; the cast sheet is longitudinally stretched, the longitudinal stretching temperature is 75°C to 87°C, and the longitudinal stretching ratio is 3.3; the longitudinally stretched sheet is transversely stretched, the transverse stretching temperature is 108°C to 130°C, and the transverse stretching ratio is 4.6; the stretched film is shaped and cooled, and the shaping temperature is 235°C; then the film is cooled, pulled, and rolled to obtain an optical polyester film with a thickness of 75μm, wherein the thickness ratio of layer A to layer B is 9:100.

[0105] Example 7

[0106] Preparation of modified polyester:

[0107] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.4, the addition amount of ethylene glycol antimony is 200ppm, and the addition amount of triphenyl phosphate is 100ppm. Among them, the content rate of each component of the dibasic acid relative to the total dicarboxylic acid component, 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid, are as follows: X1=10 mol%, X2=8 mol%, X3= 14 mol%, X4 = 68 mol%, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C ~ 262°C, 265KPa for 3.5 hours; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C ~ 282°C, 60Pa for 4.5 hours. After silk making, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.66dl / g is obtained.

[0108] The modified polyester of the present invention in layer A and a slippery polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the content of silica particles with an average particle size of 1.5 μm in the surface layer of the polyester film is 580 ppm, and a pure polyester resin with an intrinsic viscosity of 0.66 dl / g in layer B are added to the corresponding extrusion system, melted at a temperature of 275°C, co-extruded through a die, and cast onto a casting sheet. On the roller, a three-layer A / B / A extruded cast sheet is formed; the cast sheet is longitudinally stretched, the longitudinal stretching temperature is 75°C to 87°C, and the longitudinal stretching ratio is 3.2; the longitudinally stretched sheet is transversely stretched, the transverse stretching temperature is 108°C to 130°C, and the transverse stretching ratio is 4.3; the stretched film is shaped and cooled, and the shaping temperature is 235°C; then the film is cooled, pulled, and rolled to obtain an optical polyester film with a thickness of 100 μm, wherein the thickness ratio of layer A to layer B is 1:10.

[0109] Example 8

[0110] Preparation of modified polyester:

[0111] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.4, the addition amount of ethylene glycol antimony is 200ppm, and the addition amount of triphenyl phosphate is 100ppm. Among them, the content rate of each component of the dibasic acid relative to the total dicarboxylic acid component, 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid, are as follows: X1=8 mol%, X2=10 mol%, X3= 16 mol%, X4 = 66 mol%, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C ~ 262°C, 265KPa for 3.5h; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C ~ 282°C, 60Pa for 4.5h. After silk making, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.66dl / g is obtained.

[0112] The modified polyester of the present application of layer A, layer C, and a pure polyester resin of layer B with intrinsic viscosity of 0.66 dl / g were added into the corresponding extrusion system, melted at 275°C, co-extruded through the die, cast onto the casting roll to form a three-layer A / B / C extruded casting sheet; the casting sheet was longitudinally stretched, the longitudinal stretching temperature was 75°C to 87°C, and the longitudinal stretching ratio was 3.2; the longitudinally stretched sheet was transversely stretched, the transverse stretching temperature was 108°C to 130°C, and the transverse stretching ratio was 4.3; the stretched film was set and cooled, the setting temperature was 235°C; then the film was cooled, drawn, and wound to obtain an optical polyester film with thickness of 100 μm, wherein the thickness ratio of layer A to layer B was 1:16, and the thickness ratio of layer C to layer B was 1:25.

[0113] Example 9

[0114] Preparation of modified polyester:

[0115] According to the molar ratio of diacid to ethylene glycol of 1:1.43, the addition amount of ethylene glycol antimony was 250 ppm, and the addition amount of triphenyl phosphate was 110 ppm, wherein the content of 4-(3,5-dicarboxyphenoxy) phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propane diyl dioxy dibenzoic acid, and terephthalic acid in the diacid was X1=12 mol%, X2=7 mol%, X3=18 mol%, and X4=63 mol%, respectively. After mixing the above uniformly, they were added into a polyester synthesis reactor, beaten for 15 minutes, and protected by nitrogen. Esterification was carried out at 236°C to 262°C and 265 KPa for 3 hours. After the esterification was completed, vacuum was applied, and polycondensation reaction was carried out at 265°C to 282°C and 55 Pa for 4 hours. After spinning, cooling, granulation, and drying, a modified polyester with intrinsic viscosity of 0.67 dl / g was obtained.

[0116] The modified polyester of the present invention in layer A and a slippery polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the content of silica particles with an average particle size of 1.5 μm in the surface layer of the polyester film is 650 ppm, and the pure polyester resin with an intrinsic viscosity of 0.66 dl / g in layer B are added to the corresponding extrusion system, melted at a temperature of 280°C, co-extruded through a die, and cast onto a casting sheet. On the roller, a three-layer A / B / A extruded cast sheet is formed; the cast sheet is longitudinally stretched, the longitudinal stretching temperature is 75°C to 87°C, and the longitudinal stretching ratio is 3.0; the longitudinally stretched sheet is transversely stretched, the transverse stretching temperature is 108°C to 130°C, and the transverse stretching ratio is 3.8; the stretched film is shaped and cooled, and the shaping temperature is 240°C; then the film is cooled, pulled, and rolled to obtain an optical polyester film with a thickness of 100 μm, wherein the thickness ratio of layer A to layer B is 3:25.

[0117] Example 10

[0118] Preparation of modified polyester:

[0119] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.46, the addition amount of ethylene glycol antimony is 300ppm, and the addition amount of triphenyl phosphate is 130ppm. Among them, the content rate of each component of the dibasic acid relative to the total dicarboxylic acid component, 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid, is as follows: X1=12 mol%, X2=9 mol%, X3 = 20 mol%, X4 = 59 mol%, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C to 262°C and 265 kPa for 4 hours; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C to 282°C and 55 Pa for 5 hours. After silk making, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.68 dl / g is obtained.

[0120] The modified polyester of the present invention in layer A and a slippery polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the content of silica particles with an average particle size of 1.5 μm in the surface layer of the polyester film is 750 ppm, and the pure polyester resin with an intrinsic viscosity of 0.66 dl / g in layer B are added to the corresponding extrusion system, melted at a temperature of 280°C, co-extruded through a die, and cast onto a casting sheet. On the roller, a three-layer A / B / A extruded cast sheet is formed; the cast sheet is longitudinally stretched, the longitudinal stretching temperature is 75°C to 87°C, and the longitudinal stretching ratio is 2.7; the longitudinally stretched sheet is transversely stretched, the transverse stretching temperature is 108°C to 130°C, and the transverse stretching ratio is 3.3; the stretched film is shaped and cooled, and the shaping temperature is 243°C; then the film is cooled, pulled, and rolled to obtain an optical polyester film with a thickness of 125 μm, wherein the thickness ratio of layer A to layer B is 1:16.

[0121] Example 11

[0122] Preparation of modified polyester:

[0123] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.46, the addition amount of ethylene glycol antimony is 300ppm, and the addition amount of triphenyl phosphate is 130ppm. Among them, the content rate of each component of the dibasic acid relative to the total dicarboxylic acid component, 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid, is as follows: X1=15 mol%, X2=10 mol%, X3 = 25 mol%, X4 = 50 mol%, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C to 262°C and 265 kPa for 4 hours; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C to 282°C and 50 Pa for 5 hours. After silk making, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.68 dl / g is obtained.

[0124] The modified polyester of the present application of layer A, layer C, and a pure polyester resin of layer B with intrinsic viscosity of 0.66 dl / g were added into the corresponding extrusion system, melted at 280°C, co-extruded through the die, cast onto the casting roll to form a three-layer A / B / C extruded casting sheet; the casting sheet was longitudinally stretched, the longitudinal stretching temperature was 75°C to 87°C, and the longitudinal stretching ratio was 2.7; the longitudinally stretched sheet was transversely stretched, the transverse stretching temperature was 108°C to 130°C, and the transverse stretching ratio was 3.3; the stretched film was set, cooled, and the setting temperature was 243°C; then the film was cooled, drawn, and wound to obtain an optical polyester film with thickness of 150 μm, wherein the thickness ratio of layer A to layer B was 1:35, and the thickness ratio of layer C to layer B was 1:35.

[0125] Example 12

[0126] Preparation of the modified polyester of layer A:

[0127] According to the molar ratio of diacid to ethylene glycol of 1:1.46, the addition amount of ethylene glycol antimony was 300 ppm, and the addition amount of triphenyl phosphate was 130 ppm, wherein the content of 4-(3,5-dicarboxyphenoxy) phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propane diyl dioxy dibenzoic acid, and terephthalic acid in the diacid was X1=15 mol%, X2=10 mol%, X3=25 mol%, and X4=50 mol%, respectively, the above was uniformly mixed, then added into a polyester synthesis reactor, beaten for 15 minutes, and protected by nitrogen, esterification was carried out at 236°C to 262°C and 265 KPa for 4 h; after the esterification was completed, vacuum was extracted, and polycondensation reaction was carried out at 265°C to 282°C and 50 Pa for 5 h, then spinning, cooling, granulation, and drying were carried out to obtain a modified polyester with intrinsic viscosity of 0.68 dl / g.

[0128] Preparation of the modified polyester of layer C:

[0129] According to the molar ratio of dibasic acid to ethylene glycol of 1:1.46, the addition amount of ethylene glycol antimony is 300ppm, and the addition amount of triphenyl phosphate is 130ppm. Among them, the content rate of each component of the dibasic acid relative to the total dicarboxylic acid component, 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid, and terephthalic acid, is as follows: X1=15 mol%, X2=8 mol%, X3 = 17 mol%, X4 = 60 mol%, after the above are evenly mixed, added to a polyester synthesis reactor, beaten for 15 minutes, and nitrogen protection is introduced, and esterification is carried out at 236°C to 262°C and 265 kPa for 4 hours; after the esterification is completed, vacuum is turned on, and the polycondensation reaction is carried out at 265°C to 282°C and 50 Pa for 5 hours. After silk making, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.68 dl / g is obtained.

[0130] The modified polyester of the present invention in layer A and a smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the silica particles with an average particle size of 1.5 μm are contained in a content of 650 ppm in layer A of the polyester film; the modified polyester of the present invention in layer C and a smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the silica particles with an average particle size of 1.5 μm are contained in a content of 650 ppm in layer C of the polyester film; and the pure A polyester resin is added to a corresponding extrusion system, melted at a temperature of 275°C, co-extruded through a die head, and cast onto a casting roller to form a three-layer A / B / C extruded casting sheet; the casting sheet is longitudinally stretched at a longitudinal stretching temperature of 75°C to 87°C and a longitudinal stretching ratio of 2.7; the longitudinally stretched sheet is transversely stretched at a transverse stretching temperature of 108°C to 130°C and a transverse stretching ratio of 3.3; the stretched film is shaped and cooled at a shaping temperature of 240°C; the film is then cooled, pulled, and rolled to obtain an optical polyester film with a thickness of 50 μm, wherein the thickness ratio of layer A to layer B is 1:25, and the thickness ratio of layer C to layer B is 1:35.

[0131] Comparative Example 1

[0132] The pure polyester resin with an intrinsic viscosity of 0.641 dl / g for layer A and a smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the content of silica particles with an average particle size of 1.5 μm in the surface layer of the polyester film is 400 ppm, and the pure polyester resin with an intrinsic viscosity of 0.66 dl / g for layer B were added to the corresponding extrusion system, melted at a temperature of 265°C, and passed through a die. The film is co-extruded and cast onto a casting roll to form a three-layer A / B / A extruded cast sheet; the cast sheet is longitudinally stretched at a temperature of 75°C to 87°C and a longitudinal stretch ratio of 3.5; the longitudinally stretched sheet is transversely stretched at a temperature of 108°C to 130°C and a transverse stretch ratio of 5.0; the stretched film is shaped and cooled at a shaping temperature of 230°C; the film is then cooled, pulled, and rolled to obtain an optical polyester film with a thickness of 38 μm, wherein the thickness ratio of layer A to layer B is 3:25.

[0133] Comparative Example 2

[0134] The A layer of pure polyester resin with an intrinsic viscosity of 0.64 dl / g and a smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the content of silica particles with an average particle size of 1.5 μm in the polyester film surface layer is 500 ppm, and the B layer of pure polyester resin with an intrinsic viscosity of 0.66 dl / g were added to the corresponding extrusion system, melted at a temperature of 265°C, and passed through a die. The film is co-extruded and cast onto a casting roll to form a three-layer A / B / A extruded casting sheet; the casting sheet is longitudinally stretched at a longitudinal stretching temperature of 75°C to 87°C and a longitudinal stretching ratio of 3.3; the longitudinally stretched sheet is transversely stretched at a transverse stretching temperature of 108°C to 130°C and a transverse stretching ratio of 4.9; the stretched film is shaped and cooled at a shaping temperature of 232°C; the film is then cooled, pulled and rolled to obtain an optical polyester film with a thickness of 50 μm, wherein the thickness ratio of layer A to layer B is 1:5.

[0135] Comparative Example 3

[0136] The pure polyester resin with an intrinsic viscosity of 0.646 dl / g of layer A and layer C, the smooth polyester masterbatch containing silica with an average particle size of 1.5 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.62 dl / g, wherein the content of the silica particles with an average particle size of 1.5 μm in the surface layer of the polyester film is 580 ppm, and the pure polyester resin with an intrinsic viscosity of 0.66 dl / g of layer B are added into the corresponding extrusion system, melted at a temperature of 275°C, co-extruded through a die, and cast onto a casting roll to form a three-layer A / B / C extrusion casting sheet; the casting sheet is longitudinally stretched at a longitudinal stretching temperature of 75°C to 87°C and a longitudinal stretching ratio of 3.2; the longitudinally stretched sheet is transversely stretched at a transverse stretching temperature of 108°C to 130°C and a transverse stretching ratio of 4.3; the stretched film is shaped and cooled at a shaping temperature of 235°C; and then the film is cooled, drawn, and wound to obtain an optical polyester film with a thickness of 100 μm, wherein the thickness ratio of layer A to layer B is 1:16, and the thickness ratio of layer C to layer B is 1:25.

[0137] Table 1 Specific implementation effects

[0138]

[0139] Note: When the optical polyester film of the present application has a layer structure of A / B / C, the A surface is included when the self-repairing surface is attached, but is not limited to the A surface.

[0140] Thickness test method: GB / T 33399-2016.

[0141] Water contact angle test method: GB / T 30693-2014. Using the same hydrophilic self-repairing layer formula and the same production process, the self-repairing layer is cured and crosslinked in an oven, and then the sample without film attachment is taken from the self-repairing surface and is aged in an environment at 40°C for 72 hours, and then the water contact angle of the self-repairing surface before peeling is tested and recorded as the water contact angle of the self-repairing surface before peeling. Using the same formula and process as described above, the self-repairing layer is cured and crosslinked in an oven, and then the self-repairing surface is cold-attached to the optical polyester film using a 0.3 kg attachment pressure, and then the sample is aged in an environment at 40°C for 72 hours, and then the optical polyester film is removed, and then the water contact angle of the self-repairing surface is tested and recorded as the water contact angle of the self-repairing surface after peeling.

[0142] Orange peel evaluation method:

[0143] An optical polyester film with a width of 1 meter and a length of 1 meter is taken, a daylight lamp or a strong light lamp is used, the angle between the light and the film surface is about 45°, the distance between the eye and the light spot of the film is about 30 cm, the reflection mode is observed, and the film surface is observed by eye. If the film surface is bright and flat, mark “◎”; if the film surface has a “orange peel”-like roughness, mark “×”.

[0144] By comparing example 3 with comparative example 1, example 4 with comparative example 2, example 8 with comparative example 3 respectively, it can be seen that under the same polyester film thickness, film forming process, surface layer silica adding concentration and other conditions, the optical polyester film of the application has no influence on the self-repairing surface water contact angle before and after peeling, and the orange peel is obviously better than the ordinary polyester film.

[0145] Although embodiments of the application have been shown and described, it is to be understood that various modifications, substitutions, combinations and variations can be made to these embodiments without departing from the spirit and scope of the application, which is defined by the appended claims and their equivalents.

[0146] While the application has been described by way of example and in terms of the preferred embodiment, it is to be understood that certain modifications can be made to the disclosed apparatus without departing from the spirit and scope of the application, which is defined by the appended claims.

Claims

1. A biaxially oriented optical polyester film, co-extruded with an A / B / A or A / B / C three-layer structure, characterized in that: Layers A and C contain modified polyester; The modified polyester is obtained by copolymerizing a dibasic acid and a diol; Wherein, the dibasic acid is 4-(3,5-dicarboxyphenoxy)phthalic acid, 2-(carboxymethoxy)-4-fluorobenzoic acid, 4,4-propanediyldioxydibenzoic acid and terephthalic acid; Definition: X1 is the content of 4-(3,5-dicarboxyphenoxy)phthalic acid component relative to the total dicarboxylic acid components in the modified polyester; X2 is the content of 2-(carboxymethoxy)-4-fluorobenzoic acid component relative to the total dicarboxylic acid components in the modified polyester; X3 is the content of 4,4-propanediyldioxydibenzoic acid component relative to the total dicarboxylic acid components in the modified polyester; X4 is the content of terephthalic acid components relative to the total dicarboxylic acid components in the modified polyester; Among them, X1, X2, X3, and X4 satisfy the following relationship: 5 mol%≤X1≤15 mol% 2 mol%≤X2≤10 mol% 3 mol%≤X3≤25 mol% 50 mol%≤X4≤90 mol% X1+X2+X3+X4=100 mol%.

2. The biaxially oriented optical polyester film according to claim 1, characterized in that: The content of the 4-(3,5-dicarboxyphenoxy)phthalic acid component in the modified polyester relative to the total dicarboxylic acid components is 7 mol % ≤ X1 ≤ 12 mol %.

3. The biaxially oriented optical polyester film according to claim 1, characterized in that: The content of the 2-(carboxymethoxy)-4-fluorobenzoic acid component in the modified polyester relative to the total dicarboxylic acid components is 3 mol % ≤ X2 ≤ 9 mol %.

4. The biaxially oriented optical polyester film according to claim 1, characterized in that: The content of the 4,4-propanediyldioxydibenzoic acid component in the modified polyester relative to the total dicarboxylic acid components is 5 mol % ≤ X3 ≤ 20 mol %.

5. The biaxially oriented optical polyester film according to claim 1, characterized in that: The diol is selected from one of ethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, hexanediol, and polyethylene oxide glycol, or multiple thereof in any molar ratio; the molar ratio of the dibasic acid to the diol is 1:1.21 to 1:1.

46.

6. The biaxially oriented optical polyester film according to claim 1, characterized in that: The dibasic acid and the diol are copolymerized in the presence of a catalyst, the catalyst is selected from antimony, iron, aluminum, germanium or titanium catalysts, and the addition amount is 80ppm to 300ppm.

7. The biaxially oriented optical polyester film according to claim 1, characterized in that: The dibasic acid and the diol are copolymerized in the presence of a stabilizer selected from trimethyl phosphate, triethyl phosphate, triphenyl phosphate, tri-n-butyl phosphate, tetrabutyl titanate, or tetraethyl titanate; the added amount of the stabilizer is 25 ppm to 130 ppm.

8. The biaxially oriented optical polyester film according to claim 1, characterized in that: The optical polyester film has a thickness of 19 μm to 150 μm.

9. The biaxially oriented optical polyester film according to claim 1, characterized in that: The biaxially oriented optical polyester film has a three-layer structure of A / B / A, and the thickness ratio of the A layer to the B layer is 1:16 to 1:

5.

10. The biaxially oriented optical polyester film according to claim 1, characterized in that The optical polyester film structure is three layers A / B / C, the thickness ratio of layer A to layer B is 1:35-1:10, the thickness ratio of layer C to layer B is 1:35-1:10, and the thickness of layer A and layer C can be the same or different.

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