Optical polyester film for flexible display

Abstract

The present application belongs to the field of polyester film, and relates to an optical polyester film for flexible display, which has a single-layer A, double-layer A / B, three-layer A / B / A or A / B / C structure; wherein the A layer, the C layer or / and the B layer contains a modified polyester; and then the single-layer A, double-layer A / B, three-layer A / B / A or A / B / C structure is made through bidirectional stretching. The optical polyester film has the characteristics of bending resistance, sufficient flexibility, strong bending resistance and the like, and the product can be widely applied to flexible display, especially the folding screen display field.

Description

TECHNICAL FIELD

[0001] The present application belongs to polyester film, and relates to an optical polyester film for flexible display. BACKGROUND

[0002] Polyethylene terephthalate (PET) is a high molecular material obtained by esterification and polycondensation reaction of terephthalic acid and ethylene glycol. The polyester film is prepared by melt co-extrusion and two-way stretching of PET material. The polyester film is widely used in packaging, industry, electricity, electronics, display, protection, explosion-proof and other fields due to its good mechanical properties, thermal properties, electrical insulation and optical properties.

[0003] With the continuous improvement of people's living standards and the continuous progress of science and technology, people's demand for the quality of life is increasingly obvious. Traditional display (LCD) technology can meet people's needs in terms of thinness, brightness and response speed, and flexible display (OLED) technology emerges as the times require. OLED (Organic Light Emitting Display) refers to the phenomenon that organic semiconductor materials and light-emitting materials emit light under the driving of an electric field by injecting and recombining carriers. Its principle is that ITO transparent electrode and metal electrode are used as anode and cathode of the device respectively. Under the driving of a certain voltage, electrons and holes are injected into the electron and hole transport layers from the cathode and anode respectively. The electrons and holes migrate through the electron and hole transport layers to the light-emitting layer, and meet in the light-emitting layer to form excitons and excite the light-emitting molecules. The latter emits visible light by radiative relaxation. The radiation light can be observed from the ITO side, and the metal electrode film also acts as a reflecting layer. The display made according to this light-emitting principle is called organic light-emitting display, also called OLED display, which can realize flexible display. OLED has a series of advantages such as active light-emitting, no viewing angle problem, light weight, small thickness, high brightness, high light-emitting efficiency, rich light-emitting materials, easy realization of color display, fast response speed, high dynamic picture quality, wide temperature range, flexible display, simple process, low cost, strong anti-shock ability and the like.

[0004] OLED is a self-luminous flexible display technology, and does not need a traditional display backlight module. At present, the thin film material for flexible display generally includes two types. One type is for process, which mainly protects the display device from scratches and wear during the manufacturing process and is removed before assembly. The other type is integrated with flexible display and finally applied to mobile phones, notebooks and the like. The most commonly used types are organic light-emitting material support and OLED display screen protection.

[0005] Process film material, because it is mainly made process protection, and will not be used in mobile phones, notebook display, so the performance requirements are relatively low, generally polyester film can meet its use requirements.

[0006] And as the life-long follow electronic products, especially folding screen display application of film material, its bending resistance, flexibility and resistance to bending, etc. have high requirements, generally polyester film is difficult to meet its use requirements. For flexible display, especially the folding screen display field of film material many high performance requirements, the existing polyester film field problem solving technical scheme is: 1, using polyethylene naphthalate and polyethylene terephthalate blend modification, improve the bending resistance of polyester film. 2, the different thickness of polyester film multilayer stacking composite, through the overall thickness to improve the strength of the composite film material, using the elastic body between the composite layers to provide flexibility. 3, application of transparent polyimide (Colorless Polyimide) film, as a support and screen protection.

[0007] Although the technical staff has carried on a lot of research to polyester film, but the existing polyester film problem solving technical scheme still has many deficiencies: 1, polyethylene naphthalate and polyethylene terephthalate blend modification, improve the bending resistance of polyester film, naphthalene ring in polyethylene naphthalate, can improve the rigidity of polyester film to a certain extent, to improve the bending resistance, but does not consider the flexibility, easy to cause the modified polyester film in the bending position produces fold. 2, through the effective combination of polyester film and elastic glue, the flexibility and toughness of the laminated body can be considered, but the glue resistance to heat, aging resistance, yellowing resistance and other aspects are worse than polyester film, "barrel principle" makes the actual application effect of laminated body worse. 3, at present, ordinary polyimide film (yellow) has been mass produced in China, but due to its color, it is difficult to be used in folding mobile phones and other flexible displays. Transparent polyimide film bending resistance, flexibility and other can meet the requirements of flexible display, especially folding display, but its manufacturing technology is still monopolized by Japan and South Korea, the manufacturing difficulty is big, the application cost is high. SUMMARY

[0008] The present application provides a kind of optical polyester film for flexible display.The optical polyester film has bending resistance, flexibility and resistance to bending, etc., simplifies production process, reduces production cost, and expands the application range of polyester film.

[0009] To overcome the deficiencies in the prior art, the technical scheme adopted by the present application is as follows: an optical polyester film for flexible display, the optical polyester film is made by bidirectional stretching and has a single-layer A, a double-layer A / B, a three-layer A / B / A or a three-layer A / B / C structure.

[0010] Wherein, A layer, C layer or / and B layer contains modified polyester; the modified polyester is obtained by esterification of diacid and diol in a molar ratio of 1:(1.2-1.43);

[0011] The diol includes the following molar fractions of each substance:

[0012] 1,1'-bis(4-hydroxy-3-methylphenyl)cyclohexane 3-25%

[0013] trans-1-methyl-1,2-cyclopentanediol 2-15%

[0014] neopentyl glycol 1-10%

[0015] Ethylene glycol 50-94%.

[0016] As the improved technical solution of the present application, the diacid is selected from one or any molar ratio of multiple combinations of terephthalic acid, isophthalic acid, phthalic acid, adipic acid, dodecanedioic acid, etc.

[0017] As the improved technical solution of the present application, the esterification process further includes the action of 100ppm-300ppm catalyst; the catalyst is selected from one or any weight ratio of multiple combinations of antimony, aluminum, germanium, titanium, zinc, magnesium.

[0018] As the improved technical solution of the present application, the esterification process further includes the action of 25ppm-80ppm stabilizer; the stabilizer is selected from one or any weight ratio of multiple combinations of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, tetrabutyl titanate, tetraethyl titanate, tri-n-butyl phosphate

[0019] As the improved technical solution of the present application, the optical polyester film thickness is 6μm-125μm.

[0020] As the improved technical solution of the present application, the optical polyester film structure is single layer A, and the thickness of A layer is 6μm-125μm.

[0021] As the improved technical solution of the present application, the optical polyester film structure is double layer A / B, and the relationship between the thickness Ma of A layer and the thickness Mb of B layer is 3≤Mb / Ma≤14.

[0022] As the improved technical solution of the present application, the optical polyester film structure is three layers A / B / A, and the relationship between the thickness Ma of A layer and the thickness Mb of B layer is 6≤Mb / Ma≤19.

[0023] As the improved technical solution of the present application, the optical polyester film structure is three layers of A / B / C, the relationship between the thickness Ma of the A layer and the thickness Mb of the B layer is 3≤Mb / Ma≤29, the relationship between the thickness Mc of the C layer and the thickness Mb of the B layer is 3≤Mb / Ma≤29, and the thickness Ma of the A layer and the thickness Mc of the C layer can be the same or different.

[0024] The beneficial effects obtained by the present application are embodied in:

[0025] 1. The present application redesigns the polyester molecular chain structure from the microstructure, introduces new dihydric alcohol monomers, and gives the modified polyester new properties, which is simple in process and low in cost.

[0026] 2. The A layer, the C layer or / and the B layer of the present application contains modified polyester, which improves the overall performance of the polyester film, so that the polyester film has the characteristics of bending resistance, sufficient flexibility, strong bending resistance and the like, and expands the new application field of the polyester film.

[0027] 3. The polyester film of the present application is integrally formed by melt extrusion and stretching, which is simple in process, uniform in performance and long in service period. DETAILED DESCRIPTION

[0028] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to specific embodiments. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application herein are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0030] The present application is a kind of optical polyester film for flexible display, which is made by bidirectional stretching and has single-layer A, double-layer A / B, three-layer A / B / A or three-layer A / B / C structure.

[0031] The A layer, the C layer or / and the B layer contains modified polyester. The modified polyester of the present application is obtained by esterification of diacid and dihydric alcohol at a use ratio of 1:(1.2-1.43) mole ratio.

[0032] The diacid is selected from one or any mole ratio of a plurality of combinations of terephthalic acid, isophthalic acid, phthalic acid, adipic acid, dodecanedioic acid, etc.

[0033] The dihydric alcohol includes the following mole fractions of each substance:

[0034] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 3-25%

[0035] Trans-1-methyl-1,2-cyclopentanediol 2-15%

[0036] Neopentyl glycol 1-10%

[0037] Ethylene glycol 50-94%.

[0038] The base diol ethylene glycol is replaced by 1,1'-bis(4-hydroxy-3-methylphenyl)cyclohexane, trans-1-methyl-1,2-cyclopentanediol, neopentyl glycol, new monomers are introduced, and the molecular chain structure is micro-designed. 1,1'-bis(4-hydroxy-3-methylphenyl)cyclohexane exists in a chair conformation, the C-C-C bond angle is 109.5°, the carbon-carbon bond rotates in the ring without breaking the carbon-carbon bond, which provides flexibility to the molecular chain, and the existence of the dimethylphenyl group on the e bond further ensures the stability of the molecular chain; at the same time, the biphenyl effectively provides the rigidity required in the alcohol chain, the chair conformation distribution of the six-membered carbon ring provides elastic support to the polyester macromolecular segment, makes it rigid and tough, and effectively improves the overall flexibility, toughness and rigidity. Trans-1-methyl-1,2-cyclopentanediol also has the performance characteristics of the chair conformation, and this conformation has very small carbon-carbon bond tension and is very stable. The trans functional group is more easily rotated than the cis functional group, and the activity resistance is smaller, and the half-chair conformation distribution of the five-membered carbon ring cooperates with the six-membered carbon ring, which is beneficial to the improvement of the flexibility of the whole molecular chain segment. Neopentyl glycol has the flexibility of aliphatic carbon chains, but the pure straight carbon chain has poor rigidity and insufficient temperature resistance, and the existence of dimethyl in neopentyl glycol plays a fixing support role on the straight carbon chain in the spatial position. The existence of ethylene glycol ensures that the entire polyethylene terephthalate system remains unchanged, and only the molecular structure design is chemically modified. In the present application, the several monomers interact with and coordinate with each other, and are indispensable, and 1,1'-bis(4-hydroxy-3-methylphenyl)cyclohexane, trans-1-methyl-1,2-cyclopentanediol, neopentyl glycol and ethylene glycol can make the technical effect of the present application reach the best through the design of the appropriate molar fraction in the present application.

[0039] The esterification process also includes the action of 100ppm-300ppm of a catalyst; the catalyst is selected from one or any weight ratio combination of antimony, aluminum, germanium, titanium, zinc, and magnesium.

[0040] The modified polyester described in the present application can be prepared by the following method:

[0041] 1. In polyester reactor, sequentially add required diacid, diol, catalyst, stabilizer, beat for 15 minutes, and protect with nitrogen, esterification at 230-265℃, 260KPa for 3-5h.

[0042] 2. Determine esterification end point according to water output, after esterification, open vacuum, condensation polymerization at 265-280℃, 25-65Pa for 2.5-4.5h, after spinning, cooling, pelletizing, drying, obtain modified polyester with intrinsic viscosity of 0.56-0.66dl / g.

[0043] The optical polyester film has a thickness of 6-125μm.

[0044] The optical polyester film has a single-layer A structure, and the thickness of the A layer is 6-125μm. The single-layer is a polyester film structure, which is mainly related to the structure design of the film manufacturing equipment, and the thickness range is a conventional thickness range in the application field.

[0045] The optical polyester film has a double-layer A / B structure, and the relationship between the thickness Ma of the A layer and the thickness Mb of the B layer is 3≤Mb / Ma≤14. The double-layer is a polyester film structure, which is mainly related to the structure design of the film manufacturing equipment, and the interlayer thickness ratio is designed to ensure the over-machine property of one side. If the thickness is too thick, it is not conducive to the surface protrusion of the smooth particle, and affects the over-machine property.

[0046] The optical polyester film has a three-layer A / B / A structure, and the relationship between the thickness Ma of the A layer and the thickness Mb of the B layer is 6≤Mb / Ma≤19. The three-layer is a polyester film structure, which is mainly related to the structure design of the film manufacturing equipment, and the interlayer thickness ratio is designed to ensure the protrusion of the smooth particle on the surface layer, and improve the over-machine property of the film.

[0047] The optical polyester film has a three-layer A / B / C structure, and the relationship between the thickness Ma of the A layer and the thickness Mb of the B layer is 3≤Mb / Ma≤29, the relationship between the thickness Mc of the C layer and the thickness Mb of the B layer is 3≤Mb / Ma≤29, and the thickness Ma of the A layer and the thickness Mc of the C layer can be the same or different. The modified polyester structure contained in the A layer and the C layer of the optical polyester film can be the same or different. The three-layer is a polyester film structure, which is mainly related to the structure design of the film manufacturing equipment, and the interlayer thickness ratio is designed to ensure the protrusion of the smooth particle on the surface layer, and improve the over-machine property of the film. The A layer and the C layer can be designed with different thicknesses and compositions according to customer requirements.

[0048] Generally, in order to increase the smoothness of the polyester film, improve the winding and slitting performance of the polyester film, the polyester masterbatch containing micron-level smooth particles is added in the surface layer in the prior art, the viscosity of the polyester masterbatch is 0.60 dl / g, the concentration of the micron-level smooth particles in the polyester masterbatch is 0.3%, and the particle size of the particles is 2.0 μm; the micron-level smooth particles are selected from silica, calcium carbonate, kaolin, barium sulfate and the like, preferably silica and calcium carbonate, and further preferably silica.

[0049] The optical polyester film is prepared by melt extrusion, casting, longitudinal stretching, transverse stretching, traction and winding.

[0050] The optical polyester film can be prepared by the following method.

[0051] Step 1, the prepared modified polyester is added to the A layer, C layer or / and B layer of the polyester film, and the polyester masterbatch containing micron-level smooth particles is added in the surface layer, and melt extrusion is carried out, the viscosity of the polyester masterbatch is 0.60 dl / g, the concentration of the silica particles in the polyester masterbatch is 0.3%, and the particle size is 2.0 μm.

[0052] Step 2, the melt is co-extruded through a die head and cast onto a casting roller to form a single-layer or multi-layer co-extruded casting sheet.

[0053] Step 3, the casting sheet is longitudinally stretched, and the longitudinal stretching ratio is 2.8-3.8.

[0054] Step 4, the longitudinally stretched sheet is transversely stretched, and the transverse stretching ratio is 3.5-5.1.

[0055] Step 5, the stretched film is heat set, and the heat setting temperature is 225-240°C.

[0056] Step 6, then cooling, traction and winding are carried out.

[0057] It should be noted that, without affecting the technical effects of the present application, the single side or double side of the polyester film can be subjected to corona pretreatment, or the thickness of the primer pretreatment is 0.01-0.20 μm.

[0058] The present application is further described below in conjunction with examples, but the implementation and protection scope of the present application is not limited to these examples.

[0059] Example 1

[0060] Preparation of the modified polyester:

[0061] The modified polyester of the present application and a silica smooth polyester masterbatch containing silica particles having an average particle size of 2.0 μm, a concentration of 0.3%, and a specific viscosity of 0.60 dl / g, wherein the content of the silica particles having an average particle size of 2.0 μm in the total polyester film is 500 ppm, are added to a corresponding extrusion system, melted at a temperature of 260°C, extruded through a die, and cast onto a casting roll to form a single-layer A extrusion cast sheet. The cast sheet is longitudinally stretched at a longitudinal stretching temperature of 70°C to 85°C and a longitudinal stretching ratio of 3.8. The longitudinally stretched sheet is transversely stretched at a transverse stretching temperature of 105°C to 128°C and a transverse stretching ratio of 5.1. The stretched film is set and cooled at a setting temperature of 240°C. Then the film is cooled, drawn, and wound to produce an optical polyester film having a thickness of 9 μm.

[0062] wherein the diol composition is (in mole fraction):

[0063] 1,1'-bis(4-hydroxy-3-methylphenyl)cyclohexane 3%

[0064] trans-1-methyl-1,2-cyclopentanediol 2%

[0065] neopentyl glycol 1%

[0066] ethylene glycol 94%.

[0067] wherein the diacid composition is (in mole fraction):

[0068] terephthalic acid 96.5%

[0069] isophthalic acid 3.5%

[0070] wherein the catalyst composition is (in weight fraction):

[0071] ethyltin bis(ethylhexanoate) 85%

[0072] ethylaluminum sesquichloride 15%

[0073] wherein the stabilizer composition is (in weight fraction):

[0074] triphenyl phosphate 78%

[0075] trimethyl phosphate 22%

[0076] The modified polyester of the present application and a silica smooth polyester masterbatch containing silica particles having an average particle size of 2.0 μm, a concentration of 0.3%, and a specific viscosity of 0.60 dl / g, wherein the content of the silica particles having an average particle size of 2.0 μm in the total polyester film is 500 ppm, are added to a corresponding extrusion system, melted at a temperature of 260°C, extruded through a die, and cast onto a casting roll to form a single-layer A extrusion cast sheet. The cast sheet is longitudinally stretched at a longitudinal stretching temperature of 70°C to 85°C and a longitudinal stretching ratio of 3.8. The longitudinally stretched sheet is transversely stretched at a transverse stretching temperature of 105°C to 128°C and a transverse stretching ratio of 5.1. The stretched film is set and cooled at a setting temperature of 240°C. Then the film is cooled, drawn, and wound to produce an optical polyester film having a thickness of 9 μm.

[0077] Example 2

[0078] Preparation of modified polyester:

[0079] According to the terephthalic acid and dihydric alcohol molar ratio 1:1.3, the addition amount of ethylene glycol antimony is 150 ppm, the addition amount of triphenyl phosphate is 25 ppm, the above is uniformly mixed, then added into the polyester synthesis reaction kettle, the pulp is beaten for 15 min, and the nitrogen protection is carried out, the esterification is carried out at 230-265℃, 260KPa for 3h; after the esterification is finished, the vacuum is opened, the polycondensation reaction is carried out at 265-280℃, 30Pa for 3h, the spinning, cooling, granulation and drying are carried out, and the modified polyester with the intrinsic viscosity of 0.58dl / g is prepared.

[0080] The dihydric alcohol composition is (molar fraction):

[0081] 1,1'-bis(4-hydroxy-3-methylphenyl)cyclohexane 5%

[0082] trans-1-methyl-1,2-cyclopentanediol 5%

[0083] neopentyl glycol 3%

[0084] Ethylene glycol 87%.

[0085] The modified polyester of the application and the silica smooth polyester masterbatch containing the silica particles with the average particle size of 2.0μm, the concentration of 0.3% and the intrinsic viscosity of 0.60dl / g, wherein the content of the silica particles with the average particle size of 2.0μm in the total polyester film is 500ppm, are added into the corresponding extrusion system, melted at 265℃, extruded through the die, cast onto the casting roll to form the single-layer A extrusion casting sheet; the casting sheet is longitudinally stretched, the longitudinal stretching temperature is 70-85℃, and the longitudinal stretching ratio is 3.8; the longitudinally stretched sheet is transversely stretched, the transverse stretching temperature is 105-128℃, and the transverse stretching ratio is 5.0; the stretched film is shaped, cooled, and the shaping temperature is 240℃; then the film is cooled, pulled and wound to prepare the optical polyester film with the thickness of 19μm.

[0086] Example 3

[0087] Preparation of modified polyester:

[0088] The modified polyester was prepared by mixing terephthalic acid and diol in a molar ratio of 1:1.3, adding 150 ppm of antimony glycol and 35 ppm of triphenyl phosphate, and then adding the mixture into a polyester synthesis reactor. The mixture was pulped for 15 minutes and protected with nitrogen gas. Esterification was carried out for 3.5 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied and polycondensation was carried out for 3 hours at 265℃~280℃ and 30Pa. The resulting product was then filamentized, cooled, pelletized, and dried to obtain a modified polyester with an intrinsic viscosity of 0.58 dl / g.

[0089] The composition of the diol is as follows (in mole fraction):

[0090] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 9%

[0091] trans-1-methyl-1,2-cyclopentanediol 6%

[0092] Neopentyl glycol 3%

[0093] Ethylene glycol 82%.

[0094] The modified polyester in layer A and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g, wherein the silica particles with an average particle size of 2.0 μm contain 500 ppm of silica in the total polyester film, and the conventional polyester in layer B with an intrinsic viscosity of 0.65 dl / g and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g, wherein the silica particles with an average particle size of 2.0 μm contain 500 ppm of silica in the total polyester film, are added... The material is fed into the corresponding extrusion system, melted at 265℃, extruded through a die, and cast onto a casting roller to form a double-layer A / B extruded casting. The casting is then longitudinally stretched at a temperature of 70℃~85℃ with a longitudinal stretch ratio of 3.8. The longitudinally stretched film is then transversely stretched at a temperature of 105℃~128℃ with a transverse stretch ratio of 4.9. The stretched film is then shaped and cooled at a shaped temperature of 235℃. Finally, the film is cooled, drawn, and wound to obtain a 23μm thick optical polyester film, wherein the relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma=3.

[0095] Example 4

[0096] Preparation of modified polyester:

[0097] The modified polyester was prepared by mixing terephthalic acid and diol in a molar ratio of 1:1.3, adding 150 ppm of antimony glycol and 30 ppm of triphenyl phosphate, and then adding the mixture into a polyester synthesis reactor. The mixture was pulped for 15 minutes and protected with nitrogen gas. Esterification was carried out for 3.5 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied and polycondensation was carried out for 3 hours at 265℃~280℃ and 35Pa. The resulting product was then filamentized, cooled, pelletized, and dried to obtain a modified polyester with an intrinsic viscosity of 0.58 dl / g.

[0098] The composition of the diol is as follows (in mole fraction):

[0099] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 10%

[0100] 5% trans-1-methyl-1,2-cyclopentanediol

[0101] Neopentyl glycol 5%

[0102] Ethylene glycol 80%.

[0103] The modified polyester of layer A and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm in the total polyester film content is 500 ppm) and the modified polyester of layer B and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm in the total polyester film content is 500 ppm) are added to the corresponding extrusion process. The system melts at 265℃, extrudes through a die, and casts onto a casting roller to form a double-layer A / B extruded casting. The casting is then longitudinally stretched at a temperature of 70℃~85℃ with a longitudinal stretch ratio of 3.7. The longitudinally stretched film is then transversely stretched at a temperature of 105℃~128℃ with a transverse stretch ratio of 4.9. The stretched film is then shaped and cooled at a shaped temperature of 235℃. Finally, the film is cooled, drawn, and wound to obtain a 23μm thick optical polyester film, wherein the relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma=9.

[0104] Example 5

[0105] Preparation of modified polyester:

[0106] The mixture of terephthalic acid and diol in a molar ratio of 1:1.35, ethylene glycol antimony added at 160 ppm, and triphenyl phosphate added at 35 ppm was added and then added to a polyester synthesis reactor. The mixture was pulped for 15 minutes and protected with nitrogen gas. Esterification was carried out for 3 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied and polycondensation was carried out for 3.5 hours at 265℃~280℃ and 40Pa. After fiber formation, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.59 dl / g was obtained.

[0107] The composition of the diol is as follows (in mole fraction):

[0108] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 15%

[0109] 5% trans-1-methyl-1,2-cyclopentanediol

[0110] Neopentyl glycol 3%

[0111] Ethylene glycol 77%.

[0112] The modified polyester of layer A and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm in the total polyester film content is 500 ppm) and the modified polyester of layer B and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm in the total polyester film content is 500 ppm) are added to the corresponding extrusion system. The film is melted at 265℃, extruded through a die, and cast onto a casting roller to form a double-layer A / B extruded film. The film is then longitudinally stretched at a temperature of 70℃~85℃ with a longitudinal stretch ratio of 3.6. The longitudinally stretched film is then transversely stretched at a temperature of 105℃~128℃ with a transverse stretch ratio of 5.0. The stretched film is then shaped and cooled at a shaped temperature of 235℃. Finally, the film is cooled, drawn, and wound to obtain a 23μm thick optical polyester film, wherein the relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma=14.

[0113] Example 6

[0114] Preparation of modified polyester:

[0115] The mixture of terephthalic acid and diol in a molar ratio of 1:1.35, ethylene glycol antimony added at 180 ppm, and triphenyl phosphate added at 50 ppm was added and then added to a polyester synthesis reactor. The mixture was pulped for 15 minutes and protected with nitrogen gas. Esterification was carried out for 4 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied and polycondensation was carried out for 4 hours at 265℃~280℃ and 50Pa. After fiber formation, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.62 dl / g was obtained.

[0116] The composition of the diol is as follows (in mole fraction):

[0117] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 15%

[0118] trans-1-methyl-1,2-cyclopentanediol 7%

[0119] Neopentyl glycol 6%

[0120] Ethylene glycol 72%.

[0121] Modified polyester (layer A) and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm constitute 650 ppm of the total polyester film), along with modified polyester (layer B), are added to a corresponding extrusion system. The mixture is melted at 268°C, extruded through a die, and cast onto a casting roller to form a three-layer A / B / A extruded casting. The casting is then longitudinally stretched at a temperature of 70°C–85°C with a longitudinal stretch ratio of 3.6. The longitudinally stretched film is then transversely stretched at a temperature of 105°C–128°C with a transverse stretch ratio of 4.6. The stretched film is then shaped and cooled at a shaped temperature of 235°C. Finally, the film is cooled, drawn, and wound to obtain a 50 μm thick optical polyester film. The relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma = 6.

[0122] Example 7

[0123] Preparation of modified polyester:

[0124] The mixture of terephthalic acid and diol in a molar ratio of 1:1.35, 200 ppm of antimony glycol, and 50 ppm of triphenyl phosphate was thoroughly mixed and added to a polyester synthesis reactor. The mixture was pulped for 15 minutes under nitrogen protection and esterified for 3.5 hours at 230℃–265℃ and 260 kPa. After esterification, a vacuum was applied, and the mixture underwent polycondensation for 3.5 hours at 265℃–280℃ and 35 Pa. The resulting product was then filamentized, cooled, pelletized, and dried to obtain a modified polyester with an intrinsic viscosity of 0.63 dl / g.

[0125] The composition of the diol is as follows (in mole fraction):

[0126] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 17%

[0127] 9% trans-1-methyl-1,2-cyclopentanediol

[0128] Neopentyl glycol 3%

[0129] Ethylene glycol 71%.

[0130] Modified polyester (layer A) and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm constitute 650 ppm of the total polyester film), along with modified polyester (layer B), are added to a corresponding extrusion system. The mixture is melted at 270°C, extruded through a die, and cast onto a casting roller to form a three-layer A / B / A extruded casting. The casting is then longitudinally stretched at a temperature of 70°C–85°C with a longitudinal stretch ratio of 3.5. The longitudinally stretched film is then transversely stretched at a temperature of 105°C–128°C with a transverse stretch ratio of 4.4. The stretched film is then shaped and cooled at a shaped temperature of 235°C. Finally, the film is cooled, drawn, and wound to obtain a 75 μm thick optical polyester film. The relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma = 9.

[0131] Example 8

[0132] Preparation of modified polyester:

[0133] The modified polyester was prepared by mixing terephthalic acid and diol in a molar ratio of 1:1.4, adding 250 ppm of antimony glycol and 60 ppm of triphenyl phosphate, and then adding the mixture into a polyester synthesis reactor. The mixture was pulped for 15 minutes and protected with nitrogen gas. Esterification was carried out for 3.5 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied and polycondensation was carried out for 4 hours at 265℃~280℃ and 55Pa. The resulting product was then filamentized, cooled, pelletized, and dried to obtain a modified polyester with an intrinsic viscosity of 0.65 dl / g.

[0134] The composition of the diol is as follows (in mole fraction):

[0135] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 20%

[0136] trans-1-methyl-1,2-cyclopentanediol 3%

[0137] Neopentyl glycol 4%

[0138] Ethylene glycol 73%.

[0139] Modified polyester (layer A) and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm constitute 800 ppm of the total polyester film), along with modified polyester (layer B), are added to a corresponding extrusion system. The mixture is melted at 270°C, extruded through a die, and cast onto a casting roller to form a three-layer A / B / A extruded casting. The casting is then longitudinally stretched at a temperature of 70°C–85°C with a longitudinal stretch ratio of 3.3. The longitudinally stretched film is then transversely stretched at a temperature of 105°C–128°C with a transverse stretch ratio of 4.6. The stretched film is then shaped and cooled at a shaped temperature of 230°C. Finally, the film is cooled, drawn, and wound to obtain a 100 μm thick optical polyester film. The relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma = 13.

[0140] Example 9

[0141] Preparation of modified polyester:

[0142] The mixture of terephthalic acid and diol in a molar ratio of 1:1.3, with 250 ppm of antimony glycol and 65 ppm of triphenyl phosphate, was thoroughly mixed and added to a polyester synthesis reactor. The mixture was pulped for 15 minutes under nitrogen protection and esterified for 4 hours at 230℃–265℃ and 260 kPa. After esterification, a vacuum was applied, and the polycondensation reaction was carried out for 3.5 hours at 265℃–280℃ and 60 Pa. The resulting product was then filamentized, cooled, pelletized, and dried to obtain a modified polyester with an intrinsic viscosity of 0.61 dl / g.

[0143] The composition of the diol is as follows (in mole fraction):

[0144] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 7%

[0145] trans-1-methyl-1,2-cyclopentanediol 6%

[0146] Neopentyl glycol 5%

[0147] Ethylene glycol 82%.

[0148] Modified polyester (layer A) and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm constitute 800 ppm of the total polyester film), along with modified polyester (layer B), are added to a corresponding extrusion system. The mixture is melted at 275°C, extruded through a die, and cast onto a casting roller to form a three-layer A / B / A extruded sheet. The casting sheet is then longitudinally stretched at a temperature of 70°C–85°C with a longitudinal stretch ratio of 3.4. The longitudinally stretched sheet is then transversely stretched at a temperature of 105°C–128°C with a transverse stretch ratio of 4.5. The stretched film is then shaped and cooled at a shaped temperature of 235°C. Finally, the film is cooled, drawn, and wound to obtain a 100 μm thick optical polyester film. The relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma = 19.

[0149] Example 10

[0150] Preparation of modified polyester:

[0151] The mixture of terephthalic acid and diol in a molar ratio of 1:1.43, ethylene glycol antimony at 300 ppm, and triphenyl phosphate at 80 ppm was thoroughly mixed and added to a polyester synthesis reactor. The mixture was pulped for 15 minutes under nitrogen protection and esterified for 5 hours at 230℃–265℃ and 260 kPa. After esterification, a vacuum was applied, and the polycondensation reaction was carried out for 4.5 hours at 265℃–280℃ and 65 Pa. The resulting product was then filamentized, cooled, pelletized, and dried to obtain a modified polyester with an intrinsic viscosity of 0.66 dl / g.

[0152] The composition of the diol is as follows (in mole fraction):

[0153] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 25%

[0154] trans-1-methyl-1,2-cyclopentanediol 15%

[0155] Neopentyl glycol 10%

[0156] 50% ethylene glycol.

[0157] Modified polyester (layer A) and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm in the total polyester film content is 800 ppm), modified polyester (layers B and C) and the silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm in the total polyester film content is 800 ppm), are added to the corresponding extrusion system and extruded at 275°C. The film is melted, extruded through a die, and cast onto a casting roller to form a three-layer A / B / C extruded film. The film is then longitudinally stretched at a temperature of 70℃~85℃ with a longitudinal stretch ratio of 2.8. The longitudinally stretched film is then transversely stretched at a temperature of 105℃~128℃ with a transverse stretch ratio of 3.5. The stretched film is then shaped and cooled at a shaped temperature of 225℃. Finally, the film is cooled, drawn, and wound to obtain a 125μm thick optical polyester film. The thicknesses of the A layer (Ma) and B layer (Mb) are related by Mb / Ma = 3, and the thicknesses of the C layer (Mc) and B layer (Mb) are related by Mb / Mc = 11.

[0158] Example 11

[0159] Preparation of modified polyester:

[0160] The modified polyester was prepared by mixing terephthalic acid and diol in a molar ratio of 1:1.4, adding 200 ppm of antimony glycol and 40 ppm of triphenyl phosphate, and then adding the mixture into a polyester synthesis reactor. The mixture was pulped for 15 minutes and protected with nitrogen gas. Esterification was carried out for 3.5 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied and polycondensation was carried out for 4 hours at 265℃~280℃ and 50Pa. The resulting product was then filamentized, cooled, pelletized, and dried to obtain a modified polyester with an intrinsic viscosity of 0.65 dl / g.

[0161] The composition of the diol is as follows (in mole fraction):

[0162] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 18%

[0163] trans-1-methyl-1,2-cyclopentanediol 11%

[0164] Neopentyl glycol 3%

[0165] Ethylene glycol 68%.

[0166] The modified polyester of layer A and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g, wherein the silica particles with an average particle size of 2.0 μm in the total polyester film content is 800 ppm, along with the modified polyester of layer B and the conventional polyester of layer C with an intrinsic viscosity of 0.65 dl / g and silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g, wherein the silica particles with an average particle size of 2.0 μm in the total polyester film content is 800 ppm, are added to the corresponding extrusion system and extruded at 27°C. The film is melted at 5℃, extruded through a die, and cast onto a casting roller to form a three-layer A / B / C extruded film. The film is then stretched longitudinally at a temperature of 70℃~85℃ with a longitudinal stretch ratio of 3.0. The longitudinally stretched film is then stretched transversely at a temperature of 105℃~128℃ with a transverse stretch ratio of 3.9. The stretched film is then shaped and cooled at a shaped temperature of 230℃. Finally, the film is cooled, drawn, and wound to obtain a 100μm thick optical polyester film. The relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma=15, and the relationship between the thickness Mc of layer C and the thickness Mb of layer B is Mb / Mc=15.

[0167] Example 12

[0168] Preparation of modified polyester:

[0169] The modified polyester was prepared by mixing terephthalic acid and diol in a molar ratio of 1:1.35, adding 180 ppm of antimony glycol and 35 ppm of triphenyl phosphate, and then adding the mixture into a polyester synthesis reactor. The mixture was pulped for 15 minutes and protected with nitrogen gas. Esterification was carried out for 4 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied and polycondensation was carried out for 4 hours at 265℃~280℃ and 35Pa. The resulting product was then filamentized, cooled, pelletized, and dried to obtain a modified polyester with an intrinsic viscosity of 0.63 dl / g.

[0170] The composition of the diol is as follows (in mole fraction):

[0171] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 13%

[0172] trans-1-methyl-1,2-cyclopentanediol 7%

[0173] Neopentyl glycol 8%

[0174] Ethylene glycol 72%.

[0175] A conventional polyester with an intrinsic viscosity of 0.65 dl / g (layer A) and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm in the total polyester film content is 800 ppm) were added to the corresponding extrusion system. The modified polyester (layers B and C) and the modified polyester (layers C) also contained silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm in the total polyester film content is 800 ppm). The film is melted at 70℃, extruded through a die, and cast onto a casting roller to form a three-layer A / B / C extruded film. The film is then stretched longitudinally at a temperature of 70℃~85℃ with a longitudinal stretch ratio of 3.6. The longitudinally stretched film is then stretched transversely at a temperature of 105℃~128℃ with a transverse stretch ratio of 4.3. The stretched film is then shaped and cooled at a shaped temperature of 230℃. Finally, the film is cooled, drawn, and wound to obtain a 75μm thick optical polyester film. The relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma=18, and the relationship between the thickness Mc of layer C and the thickness Mb of layer B is Mb / Mc=3.

[0176] Example 13

[0177] Preparation of modified polyester:

[0178] The mixture of terephthalic acid and diol in a molar ratio of 1:1.3, with 150 ppm of antimony glycol and 30 ppm of triphenyl phosphate, was thoroughly mixed and added to a polyester synthesis reactor. The mixture was pulped for 15 minutes under nitrogen protection and esterified for 3.5 hours at 230℃–265℃ and 260 kPa. After esterification, a vacuum was applied, and the mixture underwent polycondensation for 4 hours at 265℃–280℃ and 30 Pa. The resulting product was then filamentized, cooled, pelletized, and dried to obtain a modified polyester with an intrinsic viscosity of 0.64 dl / g.

[0179] The composition of the diol is as follows (in mole fraction):

[0180] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 22%

[0181] 9% trans-1-methyl-1,2-cyclopentanediol

[0182] Neopentyl glycol 6%

[0183] Ethylene glycol 63%.

[0184] Modified polyester (layer A) and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm constitute 800 ppm of total polyester film), modified polyester (layers B and C) and silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm constitute 800 ppm of total polyester film) were added to the corresponding extrusion system and extruded at 270°C. The material is melted, extruded through a die, and cast onto a casting roller to form a three-layer A / B / C extruded film. The film is then longitudinally stretched at a temperature of 70℃~85℃ with a longitudinal stretch ratio of 3.3. The longitudinally stretched film is then transversely stretched at a temperature of 105℃~128℃ with a transverse stretch ratio of 4.1. The stretched film is then shaped and cooled at a shaped temperature of 235℃. Finally, the film is cooled, drawn, and wound to obtain a 125μm thick optical polyester film. The relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma=29, and the relationship between the thickness Mc of layer C and the thickness Mb of layer B is Mb / Mc=29.

[0185] Comparative Example 1

[0186] Layer A consists of a conventional polyester with an intrinsic viscosity of 0.65 dl / g and a silica-based slip polyester masterbatch containing 0.3% silica particles with an average particle size of 2.0 μm and an intrinsic viscosity of 0.60 dl / g, wherein the silica particles with an average particle size of 2.0 μm constitute 500 ppm of the total polyester film. Layer B consists of a conventional polyester with an intrinsic viscosity of 0.65 dl / g and a silica-based slip polyester masterbatch containing 0.3% silica particles with an average particle size of 2.0 μm and an intrinsic viscosity of 0.60 dl / g, wherein the silica particles with an average particle size of 2.0 μm constitute 500 ppm of the total polyester film. 00ppm is added to the corresponding extrusion system and melted at 265℃. The melt is then extruded through a die and cast onto a casting roller to form a double-layer A / B extruded casting. The casting is then longitudinally stretched at a temperature of 70℃~85℃ with a longitudinal stretching ratio of 3.7. The longitudinally stretched film is then transversely stretched at a temperature of 105℃~128℃ with a transverse stretching ratio of 4.9. The stretched film is then shaped and cooled at a shaped temperature of 235℃. Finally, the film is cooled, drawn, and wound to obtain an optical polyester film with a thickness of 23μm. The relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma=9.

[0187] Comparative Example 2

[0188] A conventional polyester with an intrinsic viscosity of 0.65 dl / g (layer A) and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g (where the silica particles with an average particle size of 2.0 μm constitute 650 ppm of the total polyester film) and a conventional polyester with an intrinsic viscosity of 0.65 dl / g (layer B) are added to a corresponding extrusion system, melted at 270°C, extruded through a die, and cast onto a casting roller. A three-layer A / B / A extruded film is formed; the film is longitudinally stretched at a temperature of 70℃~85℃ with a longitudinal stretching ratio of 3.5; the longitudinally stretched film is transversely stretched at a temperature of 105℃~128℃ with a transverse stretching ratio of 4.4; the stretched film is shaped and cooled at a temperature of 235℃; then the film is cooled, drawn, and wound to obtain an optical polyester film with a thickness of 75μm, wherein the relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma=9.

[0189] Comparative Example 3

[0190] The film consists of two layers: Layer A, a conventional polyester with an intrinsic viscosity of 0.65 dl / g, and Layer C, a conventional polyester with an intrinsic viscosity of 0.65 dl / g and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g, wherein the silica particles with an average particle size of 2.0 μm constitute 800 ppm of the total polyester film; and Layer B, a conventional polyester with an intrinsic viscosity of 0.65 dl / g, and Layer C, a conventional polyester with an intrinsic viscosity of 0.65 dl / g and a silica-based slip polyester masterbatch containing silica particles with an average particle size of 2.0 μm, a concentration of 0.3%, and an intrinsic viscosity of 0.60 dl / g, wherein the silica particles with an average particle size of 2.0 μm constitute 800 ppm of the total polyester film. The material is added to the corresponding extrusion system, melted at 275℃, extruded through a die, and cast onto a casting roller to form a three-layer A / B / C extruded casting. The casting is then longitudinally stretched at a temperature of 70℃~85℃ with a longitudinal stretching ratio of 2.8. The longitudinally stretched film is then transversely stretched at a temperature of 105℃~128℃ with a transverse stretching ratio of 3.5. The stretched film is then shaped and cooled at a shaped temperature of 225℃. Finally, the film is cooled, drawn, and wound to obtain a 125μm thick optical polyester film. The relationship between the thickness Ma of layer A and the thickness Mb of layer B is Mb / Ma=3, and the relationship between the thickness Mc of layer C and the thickness Mb of layer B is Mb / Mc=11.

[0191] Specific implementation effects

[0192]

[0193]

[0194] Thickness test method: GB / T 33399-2016.

[0195] Bending resistance test method:

[0196] ① Dynamic bending at room temperature: Cut 3 strips each along the MD (longitudinal) and TD (transverse) directions according to the 25mm×150mm specification. Use an automated bending test device (model: SG-5020) to conduct a dynamic bending test at room temperature: temperature 25℃, bending speed 30rpm, radius of curvature R=1.8mm, bending angle ∠α=180°, and 250,000 bending cycles. After reaching the required number of bending cycles, use a strong flashlight (model: RJW7102A / LT) to observe the appearance of each strip (6 strips in total) from any angle. If there is no damage or whitening, mark it with "◎"; if n (quantity) ≥ 1 strip is damaged or whitening, mark it with "×".

[0197] ② Low-temperature dynamic bending: Cut 3 strips each along the MD (longitudinal) and TD (transverse) directions, according to a 25mm × 150mm specification. Use a self-contained bending test device (model: SG-5020) to conduct a room-temperature dynamic bending test: temperature -20℃, bending speed 30rpm, radius of curvature R=1.8mm, bending angle ∠α=180°, and 15,000 bending cycles. After reaching the required number of bending cycles, observe the appearance of each strip (6 strips in total) from any angle using a high-intensity flashlight (model: RJW7102A / LT). If there is no damage or whitening, mark with "◎"; if n (quantity) ≥ 1 strip is damaged or whitened, mark with "×".

[0198] By comparing Example 4 with Comparative Example 1, Example 6 with Comparative Example 2, and Example 9 with Comparative Example 3, it can be seen that under the same conditions of polyester film thickness, film-making process, and surface silica addition concentration, the bending resistance of the flexible display optical polyester film of the present invention is significantly better than that of ordinary polyester film.

[0199] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0200] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A flexible display optical polyester film, characterized in that, The optical polyester film is made by biaxial stretching and has a single-layer A, double-layer A / B, triple-layer A / B / A or triple-layer A / B / C structure. The A layer, C layer, and / or B layer contain modified polyester; the modified polyester is obtained by esterification polycondensation of diacid and diol at a molar ratio of 1:(1.2-1.43); The diol comprises the following substances in the following mole fractions: 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 3–25% trans-1-methyl-1,2-cyclopentanediol 2–15% Neopentyl glycol 1-10% Ethylene glycol 50-94%.

2. The flexible display optical polyester film according to claim 1, characterized in that, The dicarboxylic acid is selected from one or a combination of any molar ratio of terephthalic acid, isophthalic acid, phthalic acid, adipic acid, and dodecanedicarboxylic acid.

3. The flexible display optical polyester film according to claim 1, characterized in that, The esterification polycondensation process also includes the action of a catalyst of 100ppm-300ppm; the catalyst is selected from one or a combination of various catalysts in any weight ratio from the antimony-based, aluminum-based, germanium-based, titanium-based, zinc-based, and magnesium-based systems.

4. The flexible display optical polyester film according to claim 1, characterized in that, The esterification polycondensation process also includes the role of a stabilizer of 25ppm-80ppm; the stabilizer is selected from one or a combination of multiple substances in any weight ratio of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, tetrabutyl titanate, tetraethyl titanate, and tri-n-butyl phosphate.

5. The flexible display optical polyester film according to claim 1, characterized in that, The thickness of the optical polyester film is 6μm to 125μm.

6. The flexible display optical polyester film according to claim 1, characterized in that, The optical polyester film has a single layer A with a thickness of 6μm to 125μm.

7. The flexible display optical polyester film according to claim 1, characterized in that, The optical polyester film has a double-layer A / B structure, and the relationship between the thickness Ma of layer A and the thickness Mb of layer B is 3≤Mb / Ma≤14.

8. The flexible display optical polyester film according to claim 1, characterized in that, The optical polyester film has a three-layer A / B / A structure, and the relationship between the thickness Ma of layer A and the thickness Mb of layer B is 6≤Mb / Ma≤19.

9. The flexible display optical polyester film according to claim 1, characterized in that, The optical polyester film structure is a three-layer A / B / C structure. The relationship between the thickness Ma of layer A and the thickness Mb of layer B is 3≤Mb / Ma≤29. The relationship between the thickness Mc of layer C and the thickness Mb of layer B is 3≤Mb / Ma≤29. The thickness Ma of layer A and the thickness Mc of layer C may be the same or different.

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