A polyester film and a method for producing the same

Abstract

This invention belongs to the field of thin films and relates to a polyester film and its preparation method. The polyester film consists of an upper surface layer, an intermediate layer, and a lower surface layer. The upper surface layer is composed of the following substances in weight percentage: functional masterbatch M 5-30%, pure polyester chips 70-95%. The intermediate layer is composed of the following substances in weight percentage: modified polyester 3-50%, pure polyester chips 50-97%. The lower surface layer is composed of the following substances in weight percentage: functional masterbatch N 5-15%, pure polyester chips 85-95%. This polyester film has advantages such as fewer surface bumps, good thickness uniformity, and temperature resistance, which greatly improves product quality and increases the yield of deep-processed products. The product can be widely used in flexible displays, especially in the field of foldable screen displays.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of thin films, and relates to a polyester film and a preparation method thereof. BACKGROUND

[0002] Polyethylene terephthalate, as a synthetic polymer material well known by people, can be used for spinning (commonly known as polyester), engineering plastics, thin films, etc. The polyester film is prepared by melt co-extrusion and two-way stretching of polyethylene terephthalate material, and is widely used in packaging, industry, electricity, electronics, display, protection, explosion-proof, etc. due to its good mechanical properties, thermal properties, electrical insulation and optical properties.

[0003] With the development of society and the progress of technology, people's demand for high-quality life is also getting higher and higher, and the requirements for details of electronic products are more stringent. The composition of electronic products includes many, and these parts that constitute electronic products are indispensable in the production process. Some process release layer on the film and use it as release film; some process adhesive layer on the film and use it as protective film; some plating layer on the film and use it as functional layer, such as anti-glare, conductive, etc. However, no matter how the above-mentioned processing is performed, there are very high requirements for the surface properties of the film. For example, the film surface has concave-convex points when it is just produced, or has concave-convex points after being placed for a period of time, which will affect the quality of the finished product when downstream processing; if the film thickness is not uniform, it is easy to produce scratches or tension lines when downstream processing, which will lead to normal production; if the film is unstable inside after being heated in the subsequent processing process, foreign matter will be produced on the surface of the film, affecting the cleanliness of the film surface of the deep processing product.

[0004] In view of the many high-performance requirements in different fields, the existing technical solutions to solve the problems in the field of polyester film are as follows: 1. Soft winding is used for winding, the vertical pressure is reduced during winding, thereby reducing the stress between the film layers and reducing the generation of concave-convex points. 2. The stretching ratio is increased to increase the molecular chain orientation and improve the thickness uniformity of the film. 3. The film surface is processed with a primer layer or a functional coating layer to block the generation of foreign matter on the film surface during the heating process.

[0005] Although the technical personnel have carried out a large amount of research on polyester film, the existing technical solutions to solve the problems of polyester film still have many deficiencies: 1. When soft winding is used for winding, the film surface is easy to be scratched or scratched during transportation, which affects the product quality due to the fact that the film is effectively reduced. 2. The large stretching ratio can improve the thickness uniformity of the film to a certain extent, but the increase of the stretching ratio will make the film brittle, and it is also easy to cause film breakage during production. 3. The primer layer or functional coating layer processing increases the cost and process complexity, and also has problems such as coating firmness and weather resistance, which affects the service life of the film. SUMMARY

[0006] The application provides a polyester film and a preparation method thereof.

[0007] To achieve the above technical purposes, the application adopts the technical scheme of a polyester film composed of an upper surface layer, a middle layer and a lower surface layer.

[0008] The upper surface layer is composed of the following substances in percentage by weight:

[0009] Functional masterbatch M 5-30%

[0010] Pure polyester chip 70-95%;

[0011] The middle layer is composed of the following substances in percentage by weight:

[0012] Modified polyester 3-50%

[0013] Pure polyester chip 50-97%;

[0014] The lower surface layer is composed of the following substances in percentage by weight:

[0015] Functional masterbatch N 5-15%

[0016] Pure polyester chip 85-95%;

[0017] The functional masterbatch M and the functional masterbatch N are both composed of the following substances in percentage by weight:

[0018] Inorganic particles 0.3-15%

[0019] Modified polyester 85-99.7%

[0020] The modified polyester is obtained by esterification and polycondensation of a dibasic acid and a dibasic alcohol at a molar ratio of 1:(1.2-1.43), under the action of 100 ppm-300 ppm of a catalyst and 25 ppm-80 ppm of a stabilizer.

[0021] As the improved technical scheme of the application, the dibasic alcohol includes the following substances in mole fraction:

[0022] 1,1'-bis(4-hydroxy-3-methylphenyl)cyclohexane 3-25%

[0023] Trans-1-methyl-1,2-cyclopentanediol 2-15%

[0024] Neopentyl glycol 1-10%

[0025] Ethylene glycol 50-94%.

[0026] As the improved technical solution of the application, the inorganic particle size is 0.3-5 μm, and the porosity is 0.6-2.2 ml / g; the modified polyester intrinsic viscosity η is 0.56-0.66 dl / g, and the relationship between the carboxyl end group content P and the intrinsic viscosity η is 10.5≤P / η≤17.5.

[0027] As the improved technical solution of the application, the diacid is selected from one or any molar ratio of multiple combinations of terephthalic acid, isophthalic acid, phthalic acid, adipic acid, and dodecanedioic acid.

[0028] As the improved technical solution of the application, the catalyst is selected from one or any weight ratio of multiple combinations of antimony, aluminum, germanium, titanium, zinc, and magnesium.

[0029] As the improved technical solution of the application, the stabilizer is selected from one or any weight ratio of multiple combinations of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, tetrabutyl titanate, tetraethyl titanate, and tri-n-butyl phosphate.

[0030] As the improved technical solution of the application, the pure polyester chip is a polyethylene terephthalate chip, and the intrinsic viscosity is 0.56-0.66 dl / g.

[0031] As the improved technical solution of the application, the inorganic particle is selected from one or any weight ratio of multiple combinations of aluminum oxide, titanium dioxide, silicon dioxide, calcium carbonate, barium sulfate, kaolin, and zirconium oxide.

[0032] As the improved technical solution of the application, the pure polyester chip is a polyethylene terephthalate chip, and the intrinsic viscosity is 0.56-0.66 dl / g.

[0033] As the improved technical solution of the application, the inorganic particle is selected from one or any weight ratio of multiple combinations of aluminum oxide, titanium dioxide, silicon dioxide, calcium carbonate, barium sulfate, kaolin, and zirconium oxide.

[0034] As the improved technical solution of the application, the thickness of the polyester film is 8-100 μm.

[0035] As the improved technical solution of the application, the thickness ratio of the upper surface layer to the middle layer of the polyester film is (1:21)-(3:20), and the thickness ratio of the lower surface layer to the middle layer is (1:21)-(3:20).

[0036] Another object of the present application is to provide a method for preparing the aforementioned polyester film, comprising the following steps:

[0037] Obtaining the ingredients for the upper layer in a proportioning amount: mixing and processing the functional masterbatch M with the pure polyester chip, namely the A layer extrusion layer;

[0038] Obtaining the ingredients for the middle layer in a proportioning amount: mixing and processing the modified polyester with the pure polyester chip, namely the B layer extrusion layer;

[0039] Obtaining the ingredients for the middle layer in a proportioning amount: mixing and processing the functional masterbatch N with the pure polyester chip, namely the C layer extrusion layer;

[0040] The A layer, the B layer and the C layer are respectively sent into the corresponding melt extrusion system for extrusion, and then enter the three-layer die for co-extrusion at 255℃ to 275℃;

[0041] The polyester film is prepared through the processes of casting, longitudinal stretching, transverse stretching, setting, cooling, traction and winding.

[0042] As the improved technical solution of the present application, the longitudinal stretching ratio of the longitudinal stretching process is 2.9 to 3.9, the transverse stretching ratio of the transverse stretching process is 3.6 to 5.2, and the heat setting temperature in the setting process is 220℃ to 240℃.

[0043] The beneficial effects obtained by the present application are embodied in:

[0044] 1. The polyester raw material is modified, the high molecular chain segment structure is micro-designed, the new monomer is introduced, and the polyester high molecule is endowed with new performance, which is simple in process and low in cost.

[0045] 2. The main performance indicators of the inorganic particles are designed, and the modified polyester is organically combined, so that the polyester film has the excellent performance of less concave-convex points on the surface, good thickness uniformity and temperature resistance.

[0046] 3. The relationship between the intrinsic viscosity and the terminal carboxyl group of the modified polyester is reasonably controlled, so that the excellent performance of the modified polyester is ensured, and the thickness uniformity and temperature resistance of the polyester film are improved.

[0047] 4. The polyester high molecular chain segment is designed and modified, so that the problem of uneven mixing caused by physical blending modification of the polyester is effectively avoided. DETAILED DESCRIPTION

[0048] 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.

[0049] 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 this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0050] Glossary:

[0051] Functional masterbatch M, functional masterbatch N are named to distinguish different types of functional masterbatch, and the carboxyl end content P is named to distinguish the number of carboxyl end. The letter itself has no meaning.

[0052] A kind of polyester film, which is composed of upper surface layer (A layer), middle layer (B layer) and lower surface layer (C layer). A layer and C layer are usually used as functional layer to give special properties, while A layer and C layer can give the same properties or different properties. B layer is generally used as a middle support layer and can also be functional.

[0053] The thickness of the polyester film is 8 μm to 100 μm.

[0054] The thickness ratio of A layer to B layer is 1:21 to 3:20, and the thickness ratio of C layer to B layer is 1:21 to 3:20. A layer and C layer are surface layers, which are generally thinner than the middle layer. If it is too thick, it is not conducive to the realization of function, such as slipperiness, and it will also increase the cost of film manufacturing. Therefore, a suitable thickness ratio or range is usually designed.

[0055] (1) Upper surface layer.

[0056] The upper surface layer is composed of the following substances in weight percentage: functional masterbatch M 5-30% and pure polyester chip 70-95%. The functional masterbatch M is composed of the following substances in weight percentage: inorganic particles 0.3-15% and modified polyester 85-99.7%.

[0057] When the A layer functional masterbatch M addition is less than 5%, the effect of modified polyester is easily reduced. At the same time, due to the too small addition of effective components in the functional masterbatch, it is difficult to play its role of slipperiness and avoiding scratches during winding. When the A layer functional masterbatch M addition is greater than 30%

[0058] , too many particles are added, which affects the appearance of film surface. Therefore, the weight ratio of functional masterbatch M is 5-30%.

[0059] (2) Middle layer.

[0060] The middle layer is composed of the following substances in weight percentage: modified polyester 3-50% and pure polyester chip 50-97%.

[0061] When the amount of modified polyester added to layer B is less than 3%, the amount of modified polyester is too small to exert its effect; when the amount of modified polyester added to layer B is greater than 50%, the amount of modified polyester is too large, resulting in excessive performance, increased cost, and waste. Therefore, the optimal amount of modified polyester added is 3-50%.

[0062] (3) Lower surface layer.

[0063] The lower surface layer is composed of the following substances in weight percentages: functional masterbatch N 5-15% and pure polyester chips 85-95%. The functional masterbatch N is composed of the following substances in weight percentages: inorganic particles 0.3-15% and modified polyester 85-99.7%. This composition design allows the inorganic particles to be more evenly dispersed in the modified polyester, ensuring the stability of the various properties of the produced polyester film. The combination of inorganic particles and modified polyester allows the functional masterbatch to possess the characteristics of the particles themselves while also having the characteristics of the modified polyester.

[0064] When the nitrogen (N) content in the C-layer functional masterbatch is less than 5%, it easily reduces the effectiveness of the modified polyester. Simultaneously, due to the insufficient addition of effective components in the functional masterbatch, it is difficult to achieve its functions of smoothing and preventing scratches during winding. When the nitrogen (N) content in the C-layer functional masterbatch is greater than 15%,...

[0065] When adding too many particles, it affects the appearance of the membrane surface, such as smoothness. Therefore, the optimal addition amount of functional masterbatch N is 5-15%. The formulation composition and thickness of layer A and layer C can be designed separately according to the actual application performance requirements of the product, making it highly operable.

[0066] (4) Modified polyester.

[0067] The modified polyester is obtained by pulping a dicarboxylic acid and a diol at a molar ratio of 1:(1.2 to 1.43), with a catalyst of 100 ppm to 300 ppm and a stabilizer of 25 ppm to 80 ppm for 15 minutes, followed by nitrogen protection, and then esterification at 230°C to 265°C and 260 kPa for 3 to 5 hours.

[0068] The esterification endpoint is determined based on the amount of water discharged. After complete esterification, a vacuum is applied, and the polycondensation reaction is carried out for 2.5 to 4.5 hours at 265°C to 280°C and 25 Pa to 65 Pa. After spinning, cooling, pelletizing, and drying, the modified polyester described in this invention is obtained, with an intrinsic viscosity of 0.56 dl / g to 0.66 dl / g. The relationship between the terminal carboxyl group content P and the intrinsic viscosity η is 10.5 ≤ P / η ≤ 17.5.

[0069] The diol comprises the following substances in the following mole fractions:

[0070] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 3-25%

[0071] trans-1-methyl-1,2-cyclopentanediol 2-15%

[0072] Neopentyl glycol 1-10%

[0073] Ethylene glycol 50-94%.

[0074] In 1,1'-bis(4-hydroxy-3-methylphenyl)cyclohexane, the dihydroxyl groups provide bonding sites, binding the monomer to the polymer chain segments and improving the overall compatibility of the polyester. The presence of dimethylphenyl enhances the rigidity of the alcohol chain segments to some extent, which helps resist film deformation during post-processing. The six-membered carbon ring chair conformation provides elastic support for the polyester polymer chain segments. Even during film production, unevenness on the roller surface or foreign matter in the environment can cause bumps on the film surface, which facilitates microscopic self-repair of film deformation. The distribution of cyclic carbon chain side groups effectively suppresses the formation of cyclic polymers during downstream processing and heating, ensuring the cleanliness of the polyester film surface.

[0075] Trans-1-methyl-1,2-cyclopentanediol, existing in a semi-chair-dominant conformation, enhances molecular chain stability. The trans conformation and the methyl functional group exhibit less steric hindrance compared to rigid functional groups, facilitating polymer chain mobility and significantly improving the placement of unevenness on the film surface. It also facilitates polymer chain orientation during rapid stretching, improving anisotropic stretching uniformity. The distribution of five-membered carbon ring side groups effectively suppresses the formation of cyclic polymers during polyester film heating, ensuring the cleanliness of the polyester film surface.

[0076] Neopentyl glycol, primarily distributed in a linear chain, ensures rapid molecular chain orientation during stretching, effectively improving the longitudinal and transverse stretching uniformity of the film. The dimethyl group's fixing effect on the molecular chains ensures stability after rapid molecular chain orientation, avoiding problems such as uneven film surface and uneven longitudinal and transverse thickness caused by shrinkage after stretching. Through the appropriate design of several alcohol monomers in suitable proportions, the synergistic effect can be optimized.

[0077] The dicarboxylic acid is selected from one or any combination of terephthalic acid, isophthalic acid, phthalic acid, adipic acid, and dodecanedicarboxylic acid, with terephthalic acid and adipic acid being preferred, and terephthalic acid being even more preferred.

[0078] The catalyst is selected from one or any combination of antimony-based, aluminum-based, germanium-based, titanium-based, zinc-based, and magnesium-based catalysts, with antimony-based and titanium-based catalysts being preferred, and antimony glycolide being even more preferred. The dosage is 100ppm to 300ppm.

[0079] The stabilizer is selected from one or any combination of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, tetrabutyl titanate, and tri-n-butyl phosphate; trimethyl phosphate and triphenyl phosphate are preferred, and triphenyl phosphate is further preferred. The dosage is 25 ppm to 80 ppm. The use of stabilizers during polyester synthesis ensures the color stability of the polyester material and prevents yellowing.

[0080] Preferably, for the polyester film with a thickness of 8μm to 100μm of the present invention, the production speed is relatively fast, requiring the polymer chain segments to respond quickly to the tensile force to ensure uniform orientation. High viscosity results in high resistance to molecular chain movement and a slow response speed. The intrinsic viscosity range of the present invention can effectively reduce thickness unevenness; the intrinsic viscosity η of the modified polyester is 0.56 dl / g to 0.66 dl / g. The intrinsic viscosity of the modified polyester is limited. When the intrinsic viscosity is less than 0.56 dl / g, it easily leads to a deterioration in the mechanical properties of the film; when the intrinsic viscosity is greater than 0.66 dl / g, it is not conducive to improving the tensile uniformity of the polyester film, resulting in poor thickness uniformity.

[0081] The relationship between the modified polyester terminal carboxyl group content P and the intrinsic viscosity η is 10.5 ≤ P / η ≤ 17.5. Controlling the terminal carboxyl group content can effectively solve the problem of temperature resistance in subsequent film processing. When P / η is less than 10.5, it is not conducive to the forward reaction of polyester synthesis; when P / η is greater than 17.5, there are too many terminal carboxyl groups, and during the downstream heating process of the polyester film, the ends are prone to form rings, affecting the appearance of the polyester film; the carboxyl groups are highly polar and easily absorb water molecules from the air and adhere to the film surface, affecting the surface properties.

[0082] (5) Pure polyester chips.

[0083] The pure polyester chips are polyethylene terephthalate chips with an intrinsic viscosity of 0.56 dl / g to 0.66 dl / g. This viscosity range corresponds to the viscosity of the modified polyester, avoiding problems such as laminar flow, retention, and poor compatibility caused by viscosity differences.

[0084] (6) Inorganic particles.

[0085] In the preceding text, the inorganic particles are selected from one or more of aluminum oxide, titanium dioxide, silicon dioxide, calcium carbonate, barium sulfate, kaolin, and zirconium oxide in any weight ratio. A combination of silicon dioxide and calcium carbonate is preferred, and calcium carbonate is even more preferred.

[0086] The inorganic particles have a particle size of 0.3μm to 5μm. When the particle size of the inorganic particles is less than 0.3μm, it is difficult to exert the particle smoothing and anti-adhesion effects, resulting in scratches and adhesion problems during the production of polyester film. When the particle size is greater than 5μm, the contact between the particles and the polyester interface increases, causing film breakage problems, and also affecting the gloss of the film surface.

[0087] The porosity of the inorganic particles ranges from 0.6 ml / g to 2.2 ml / g. When the porosity is less than 0.6 ml / g, the particles themselves have few pores and poor compatibility with polyester. During film stretching, they tend to migrate towards the film surface and then detach, easily creating bumps or depressions on the film surface, or, over time, affecting film performance. When the porosity is greater than 2.2 ml / g, the increased porosity and specific surface area of ​​the inorganic particles make them prone to aggregation, leading to the formation of crystal points. When the crystal point size is large, it easily creates bumps or depressions on the film surface, and also reduces the surface hardness of the particles, resulting in a loss of the slippery effect.

[0088] (7) Functional masterbatch M or functional masterbatch N.

[0089] Its preparation method is as follows:

[0090] The modified polyester with an intrinsic viscosity of 0.56 dl / g to 0.66 dl / g and a relationship between the terminal carboxyl group content P and the intrinsic viscosity η of 10.5 ≤ P / η ≤ 17.5 was selected as the base material. Then, 0.3 to 15% of inorganic particles with a particle size of 0.3 μm to 5 μm and a porosity of 0.6 ml / g to 2.2 ml / g and 85 to 99.7% of the modified polyester were mixed evenly and fed into a twin-screw extruder. Vacuum was applied, and the mixture was filamentized, cooled, pelletized, and dried to obtain the functional masterbatch M / functional masterbatch N described in this invention. The intrinsic viscosity of functional masterbatch M / functional masterbatch N was 0.50 dl / g to 0.60 dl / g.

[0091] The functional masterbatch M / functional masterbatch N of this invention is prepared by twin-screw granulation instead of synthesis. The main reason is that the long-term high-temperature process of esterification and polycondensation during synthesis will damage the pores of inorganic particles and affect the performance of the masterbatch.

[0092] (8) A method for preparing a polyester film.

[0093] The method for preparing polyester film includes the following steps:

[0094] The components used to obtain the specified proportions for the upper surface layer are: functional masterbatch M and pure polyester chips are mixed and processed, i.e., the A layer extrusion layer;

[0095] The intermediate layer used to obtain the specified proportions consists of a mixture of modified polyester and pure polyester chips, i.e., the B-layer extrusion layer.

[0096] The components used to obtain the proportioned intermediate layer are: functional masterbatch N and pure polyester chips are mixed and processed, i.e., the C layer extrusion layer;

[0097] Layers A, B, and C are respectively fed into the corresponding melt extrusion system for extrusion, and then enter the three-layer die for co-extrusion at a temperature of 255℃~275℃. The extruded layers are then cast onto the casting roll to form a three-layer co-extruded sheet.

[0098] The casting is subjected to longitudinal stretching, with a longitudinal stretching ratio of 2.9 to 3.9.

[0099] The longitudinal stretching sheet is then stretched laterally, with a lateral stretching ratio of 3.6 to 5.2.

[0100] The stretched film is heat-set at a temperature of 220℃~240℃.

[0101] Then proceed with cooling, traction, and winding.

[0102] It should be noted that, without affecting the technical effect of the present invention, corona pretreatment or a base coating pretreatment with a thickness of 0.01μm to 0.20μm can be performed on one or both sides of the polyester film of the present invention.

[0103] The present invention will be further described below with reference to the embodiments, but the implementation and protection scope of the present invention are not limited to these embodiments.

[0104] Example 1

[0105] Preparation of modified polyester:

[0106] The mixture was prepared with a dicarboxylic acid to diol molar ratio of 1:1.2, a catalyst dosage of 100 ppm, and a stabilizer dosage of 25 ppm. After thorough mixing, the mixture was added to a polyester synthesis reactor and pulped for 15 minutes under nitrogen protection. Esterification was carried out for 3 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied, and polycondensation was carried out for 2.5 hours at 265℃~280℃ and 25Pa. After fiber formation, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.56 dl / g was obtained. The relationship between the terminal carboxyl group content P and the intrinsic viscosity η was P / η=10.

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

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

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

[0110] Neopentyl glycol 1%

[0111] Ethylene glycol 94%.

[0112] The composition of the dicarboxylic acid is (in mole fraction):

[0113] 91% terephthalic acid

[0114] 9% isophthalic acid

[0115] The catalyst composition is as follows (by weight fraction):

[0116] 90% Antimony Glycol

[0117] 10% aluminum glycol

[0118] The stabilizer composition is as follows (by weight fraction):

[0119] Triphenyl phosphate 80%

[0120] Trimethyl phosphate 20%

[0121] Preparation of functional masterbatch M / functional masterbatch N:

[0122] The modified polyester with an intrinsic viscosity of 0.56 dl / g and a relationship between the end carboxyl group content P and intrinsic viscosity η of P / η = 10.5 was selected as the base material. Then, 0.3% by weight of calcium carbonate particles with a particle size of 0.3 μm and a porosity of 0.6 ml / g and 99.7% by weight of modified polyester were mixed evenly and fed into a twin-screw extruder. Vacuum was applied, and the mixture was filamentized, cooled, pelletized, and dried to obtain the functional masterbatch M / functional masterbatch N described in this invention. The intrinsic viscosity of functional masterbatch M / functional masterbatch N was 0.50 dl / g.

[0123] The following materials were pre-mixed and treated before being fed into the corresponding melt extrusion system. They were co-extruded at 255°C using a three-layer die, casting onto a casting roll to form an A / B / C structure extruded sheet. The extruded sheet was then longitudinally stretched at a stretching temperature of 55°C to 88°C with a stretching ratio of 3.9: 30% by weight of functional masterbatch M with an intrinsic viscosity of 0.50 dl / g and 70% by weight of pure polyester chips with an intrinsic viscosity of 0.56 dl / g (layer A); 50% by weight of modified polyester with an intrinsic viscosity of 0.56 dl / g and a carboxyl group content P with an intrinsic viscosity η of P / η = 10.5; and 50% by weight of pure polyester chips with an intrinsic viscosity of 0.56 dl / g (layer B); and 15% by weight of functional masterbatch N with an intrinsic viscosity of 0.50 dl / g and 85% by weight of pure polyester chips with an intrinsic viscosity of 0.56 dl / g (layer C). The longitudinally stretched sheet is stretched laterally at a temperature of 90℃ to 123℃ with a stretch ratio of 5.2. The stretched film is then shaped at a temperature of 240℃. The film is then cooled, drawn, and wound to obtain a polyester film with a thickness of 8μm, wherein the thickness ratio of layer A to layer B is 1:21, and the thickness ratio of layer C to layer B is 2:25.

[0124] Example 2

[0125] Preparation of modified polyester:

[0126] 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. After thorough mixing, the mixture was 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 hours at 265℃~280℃ and 30Pa. After fiber formation, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.58 dl / g was obtained. The relationship between the end carboxyl group content P and the intrinsic viscosity η was P / η=11.

[0127] The composition of the diol is as follows (in mole fraction):

[0128] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 5%

[0129] trans-1-methyl-1,2-cyclopentanediol 8%

[0130] Neopentyl glycol 6%

[0131] Ethylene glycol 81%.

[0132] Preparation of functional masterbatch M / functional masterbatch N:

[0133] The modified polyester with an intrinsic viscosity of 0.58 dl / g and a relationship between the end carboxyl group content P and intrinsic viscosity η of P / η = 11 was selected as the base material. Then, 0.5% by weight of calcium carbonate particles with a particle size of 0.5 μm and a porosity of 0.7 ml / g and 99.5% by weight of modified polyester were mixed evenly and fed into a twin-screw extruder. Vacuum was turned on, and the mixture was filamentized, cooled, pelletized, and dried to obtain the functional masterbatch M / functional masterbatch N described in this invention. The intrinsic viscosity of functional masterbatch M / functional masterbatch N was 0.51 dl / g.

[0134] The following materials were pre-mixed and processed before being fed into the corresponding melt extrusion system: 20% by weight of functional masterbatch M with an intrinsic viscosity of 0.51 dl / g and 80% by weight of pure polyester chips with an intrinsic viscosity of 0.59 dl / g (layer A); 40% by weight of modified polyester with an intrinsic viscosity of 0.58 dl / g and a relationship between terminal carboxyl group content P and intrinsic viscosity η of P / η = 11 and 60% by weight of pure polyester chips with an intrinsic viscosity of 0.59 dl / g (layer B); and 13% by weight of functional masterbatch N with an intrinsic viscosity of 0.51 dl / g and 87% by weight of pure polyester chips with an intrinsic viscosity of 0.59 dl / g (layer C). At 260℃, the film is co-extruded through a three-layer die and cast onto a casting roll to form an A / B / C structure extruded film. The film is then longitudinally stretched at a temperature of 55℃ to 88℃ with a longitudinal stretch ratio of 3.8. The longitudinally stretched film is then transversely stretched at a temperature of 90℃ to 123℃ with a transverse stretch ratio of 5.0. The stretched film is then shaped at a temperature of 240℃. Finally, the film is cooled, drawn, and wound to obtain a 19μm thick polyester film, in which the thickness ratio of layer A to layer B is 1:10, and the thickness ratio of layer C to layer B is 1:21.

[0135] Example 3

[0136] Preparation of modified polyester:

[0137] The mixture of terephthalic acid and diol in a molar ratio of 1:1.3, with 180 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 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 0.62 dl / g. The relationship between the terminal carboxyl group content P and the intrinsic viscosity η was P / η = 12.

[0138] The composition of the diol is as follows (in mole fraction):

[0139] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 10%

[0140] trans-1-methyl-1,2-cyclopentanediol 6%

[0141] Neopentyl glycol 5%

[0142] Ethylene glycol 79%.

[0143] Preparation of functional masterbatch M / functional masterbatch N:

[0144] The modified polyester with an intrinsic viscosity of 0.62 dl / g and a relationship between the terminal carboxyl group content P and intrinsic viscosity η of P / η = 12, prepared above, was selected as the base material. Then, 1.5% by weight of calcium carbonate particles with a particle size of 1.0 μm and a porosity of 1.0 ml / g and 98.5% by weight of the modified polyester were mixed evenly and fed into a twin-screw extruder. Vacuum was applied, and the mixture was filamentized, cooled, pelletized, and dried to obtain the functional masterbatch M / functional masterbatch N described in this invention. The intrinsic viscosity of functional masterbatch M / functional masterbatch N is 0.56 dl / g.

[0145] The following materials were pre-mixed and treated before being fed into the corresponding melt extrusion system. At 265°C, they were co-extruded through a three-layer die, forming an A / B / C structure extruded sheet. The mixture consisted of: 15% by weight of functional masterbatch M with an intrinsic viscosity of 0.56 dl / g and 85% by weight of pure polyester chips with an intrinsic viscosity of 0.60 dl / g (layer A); 35% by weight of modified polyester with an intrinsic viscosity of 0.62 dl / g and a carboxyl group content P with an intrinsic viscosity η that corresponds to P / η = 12; 65% by weight of pure polyester chips with an intrinsic viscosity of 0.60 dl / g (layer B); and 10% by weight of functional masterbatch N with an intrinsic viscosity of 0.56 dl / g and 90% by weight of pure polyester chips with an intrinsic viscosity of 0.60 dl / g (layer C). The cast sheet is longitudinally stretched at a temperature of 55℃ to 88℃ with a longitudinal stretching ratio of 3.8. The longitudinally stretched sheet is then transversely stretched at a temperature of 90℃ to 123℃ with a transverse stretching ratio of 4.9. The stretched film is then shaped at a temperature of 235℃. Finally, the film is cooled, drawn, and wound to obtain a polyester film with a thickness of 23μm, wherein the thickness ratio of layer A to layer B is 3:50, and the thickness ratio of layer C to layer B is 1:10.

[0146] Example 4

[0147] Preparation of modified polyester:

[0148] The mixture of terephthalic acid and diol in a molar ratio of 1:1.35, ethylene glycol antimony at 180 ppm, and triphenyl phosphate at 50 ppm was 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 mixture underwent polycondensation for 3.5 hours at 265℃–280℃ and 50 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. The relationship between the end carboxyl group content P and the intrinsic viscosity η was P / η = 13.5.

[0149] The composition of the diol is as follows (in mole fraction):

[0150] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 18%

[0151] 5% trans-1-methyl-1,2-cyclopentanediol

[0152] Neopentyl glycol 3%

[0153] Ethylene glycol 74%.

[0154] Preparation of functional masterbatch M / functional masterbatch N:

[0155] The modified polyester with an intrinsic viscosity of 0.63 dl / g and a relationship between the end carboxyl group content P and intrinsic viscosity η of P / η = 13.5 was selected as the base material. Then, 5% by weight of silica and calcium carbonate combined particles with a particle size of 2.0 μm and a porosity of 1.3 ml / g were mixed evenly with 95% by weight of modified polyester. The mixture was fed into a twin-screw extruder, vacuum was applied, and the mixture was filamentized, cooled, pelletized, and dried to obtain the functional masterbatch M / functional masterbatch N described in this invention. The intrinsic viscosity of functional masterbatch M / functional masterbatch N was 0.55 dl / g.

[0156] A mixture of 15% by weight of functional masterbatch M with an intrinsic viscosity of 0.56 dl / g and 85% by weight of pure polyester chips with an intrinsic viscosity of 0.61 dl / g (layer A); 35% by weight of modified polyester with an intrinsic viscosity of 0.63 dl / g and a carboxyl group content P with an intrinsic viscosity η that has a P / η = 13.5 relationship and 65% by weight of pure polyester chips with an intrinsic viscosity of 0.61 dl / g (layer B); and 6% by weight of functional masterbatch N with an intrinsic viscosity of 0.55 dl / g and 94% by weight of pure polyester chips with an intrinsic viscosity of 0.61 dl / g (layer C), after pre-mixing and other treatments, is fed into a corresponding melt extrusion system. At 265°C, it undergoes co-extrusion through a three-layer die and is cast onto a casting roll to form an A / B / C structure extruded sheet. The casting sheet is then longitudinally stretched at a stretching temperature of 55°C–88°C with a stretching ratio of 3.6. The longitudinally stretched sheet is stretched laterally at a temperature of 90℃ to 123℃ and a stretch ratio of 4.6. The stretched film is then shaped at a temperature of 235℃. The film is then cooled, drawn, and wound to obtain a 50μm thick polyester film, wherein the thickness ratio of layer A to layer B is 3:25 and the thickness ratio of layer C to layer B is 1:13.

[0157] Example 5

[0158] Preparation of modified polyester:

[0159] 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 50 ppm of triphenyl phosphate. After thorough mixing, the mixture was added to a polyester synthesis reactor and pulped for 15 minutes under nitrogen protection. Esterification was carried out for 3 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied, and polycondensation was carried out for 4 hours at 265℃~280℃ and 35Pa. After fiber formation, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.65 dl / g was obtained. The relationship between the end carboxyl group content P and the intrinsic viscosity η was P / η=15.

[0160] The composition of the diol is as follows:

[0161] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 20%

[0162] 9% trans-1-methyl-1,2-cyclopentanediol

[0163] Neopentyl glycol 3%

[0164] Ethylene glycol 68%.

[0165] Preparation of functional masterbatch M / functional masterbatch N:

[0166] The modified polyester with an intrinsic viscosity of 0.65 dl / g and a relationship between the end carboxyl group content P and intrinsic viscosity η of P / η = 15 was selected as the base material. Then, 7.5% by weight of calcium carbonate particles with a particle size of 3.5 μm and a porosity of 1.7 ml / g and 92.5% by weight of modified polyester were mixed evenly and fed into a twin-screw extruder. Vacuum was applied, and the mixture was filamentized, cooled, pelletized, and dried to obtain the functional masterbatch M / functional masterbatch N described in this invention. The intrinsic viscosity of functional masterbatch M / functional masterbatch N was 0.58 dl / g.

[0167] The following materials were pre-mixed and treated before being fed into the corresponding melt extrusion system. They were co-extruded through a three-layer die at 265°C and cast onto a casting roll to form an A / B / C structure extruded sheet. The mixture consisted of 12% by weight of functional masterbatch M with an intrinsic viscosity of 0.58 dl / g and 88% by weight of pure polyester chips with an intrinsic viscosity of 0.62 dl / g (layer A); 30% by weight of modified polyester with an intrinsic viscosity of 0.65 dl / g and a terminal carboxyl group content P with an intrinsic viscosity η that had a P / η = 15 relationship with the intrinsic viscosity η; 70% by weight of pure polyester chips with an intrinsic viscosity of 0.62 dl / g (layer B); and 12% by weight of functional masterbatch N with an intrinsic viscosity of 0.58 dl / g and 88% by weight of pure polyester chips with an intrinsic viscosity of 0.62 dl / g (layer C). The cast sheet is longitudinally stretched at a temperature of 55℃ to 88℃ with a longitudinal stretching ratio of 3.5. The longitudinally stretched sheet is then transversely stretched at a temperature of 90℃ to 123℃ with a transverse stretching ratio of 4.7. The stretched film is then shaped at a temperature of 235℃. Finally, the film is cooled, drawn, and wound to obtain a polyester film with a thickness of 50μm, wherein the thickness ratio of layer A to layer B is 3:25, and the thickness ratio of layer C to layer B is 1:13.

[0168] Example 6

[0169] Preparation of modified polyester:

[0170] The mixture was prepared with terephthalic acid and diol in a molar ratio of 1:1.43, ethylene glycol antimony added at 250 ppm, and triphenyl phosphate added at 70 ppm. After thorough mixing, the mixture was added to a polyester synthesis reactor and pulped for 15 minutes under nitrogen protection. Esterification was carried out for 4 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied, and polycondensation was carried out for 4.5 hours at 265℃~280℃ and 65Pa. After fiber formation, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.66 dl / g was obtained. The relationship between the end carboxyl group content P and the intrinsic viscosity η was P / η=15.5.

[0171] The composition of the diol is as follows (in mole fraction):

[0172] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 16%

[0173] 5% trans-1-methyl-1,2-cyclopentanediol

[0174] Neopentyl glycol 7%

[0175] Ethylene glycol 72%.

[0176] Preparation of functional masterbatch M / functional masterbatch N:

[0177] The modified polyester with an intrinsic viscosity of 0.66 dl / g and a relationship between the end carboxyl group content P and intrinsic viscosity η of P / η = 15.5 was selected as the base material. Then, 10% by weight of calcium carbonate particles with a particle size of 5.0 μm and a porosity of 2.2 ml / g and 90% by weight of modified polyester were mixed evenly and fed into a twin-screw extruder. Vacuum was applied, and the mixture was filamentized, cooled, pelletized, and dried to obtain the functional masterbatch M / functional masterbatch N described in this invention. The intrinsic viscosity of functional masterbatch M / functional masterbatch N is 0.60 dl / g.

[0178] The following materials were pre-mixed and processed before being fed into the corresponding melt extrusion system: 5% by weight of functional masterbatch M with an intrinsic viscosity of 0.60 dl / g and 95% by weight of pure polyester chips with an intrinsic viscosity of 0.66 dl / g (layer A); 25% by weight of modified polyester with an intrinsic viscosity of 0.66 dl / g and a relationship between terminal carboxyl group content P and intrinsic viscosity η of P / η = 15.5 and 75% by weight of pure polyester chips with an intrinsic viscosity of 0.66 dl / g (layer B); and 8% by weight of functional masterbatch N with an intrinsic viscosity of 0.60 dl / g and 92% by weight of pure polyester chips with an intrinsic viscosity of 0.66 dl / g (layer C). At 270℃, the film is co-extruded through a three-layer die and cast onto a casting roll to form an A / B / C structure extruded film. The film is then longitudinally stretched at a temperature of 55℃ to 88℃ with a longitudinal stretch ratio of 3.3. The longitudinally stretched film is then transversely stretched at a temperature of 90℃ to 123℃ with a transverse stretch ratio of 4.3. The stretched film is then shaped at a temperature of 230℃. Finally, the film is cooled, drawn, and wound to obtain a 75μm thick polyester film, in which the thickness ratio of layer A to layer B is 3:23 and the thickness ratio of layer C to layer B is 1:21.

[0179] Example 7

[0180] Preparation of modified polyester:

[0181] The mixture of terephthalic acid and diol in a molar ratio of 1:1.3, with 300 ppm of antimony glycol and 80 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 5 hours at 230℃–265℃ and 260 kPa. After esterification, a vacuum was applied, and the mixture underwent polycondensation 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 0.65 dl / g. The relationship between the end carboxyl group content P and the intrinsic viscosity η was P / η = 15.5.

[0182] The composition of the diol is as follows (in mole fraction):

[0183] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 20%

[0184] 10% of trans-1-methyl-1,2-cyclopentanediol

[0185] Neopentyl glycol 6%

[0186] Ethylene glycol 64%.

[0187] Preparation of functional masterbatch M / functional masterbatch N:

[0188] The modified polyester with an intrinsic viscosity of 0.65 dl / g and a relationship between the end carboxyl group content P and intrinsic viscosity η of P / η = 15.5 was selected as the base material. Then, 10% by weight of calcium carbonate particles with a particle size of 1.5 μm and a porosity of 1.1 ml / g and 90% by weight of modified polyester were mixed evenly and fed into a twin-screw extruder. Vacuum was applied, and the mixture was filamentized, cooled, pelletized, and dried to obtain the functional masterbatch M / functional masterbatch N described in this invention. The intrinsic viscosity of functional masterbatch M / functional masterbatch N was 0.56 dl / g.

[0189] The following materials were pre-mixed and treated before being fed into the corresponding melt extrusion system. At 275°C, they were co-extruded through a three-layer die, flowing onto a casting roll to form an A / B / C structure extruded sheet. The extruded sheet was then longitudinally stretched at a temperature of 55°C–88°C with a longitudinal stretching temperature of 2.9: 9% by weight of functional masterbatch M with an intrinsic viscosity of 0.56 dl / g and 91% by weight of pure polyester chips with an intrinsic viscosity of 0.63 dl / g (layer A); 18% by weight of modified polyester with an intrinsic viscosity of 0.65 dl / g and a carboxyl group content P with an intrinsic viscosity η that has a P / η = 15.5 relationship; 82% by weight of pure polyester chips with an intrinsic viscosity of 0.63 dl / g (layer B); and 9% by weight of functional masterbatch N with an intrinsic viscosity of 0.56 dl / g and 91% by weight of pure polyester chips with an intrinsic viscosity of 0.63 dl / g (layer C). The longitudinally stretched film is then stretched laterally at a temperature of 90℃ to 123℃ with a stretch ratio of 4.6. The stretched film is then set at a temperature of 225℃. Finally, the film is cooled, drawn, and wound to obtain a 75μm thick polyester film, wherein the thickness ratio of layer A to layer B is 3:26, and the thickness ratio of layer C to layer B is also 3:26.

[0190] Example 8

[0191] Preparation of modified polyester:

[0192] 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 40 ppm of triphenyl phosphate. After thorough mixing, the mixture was added to a polyester synthesis reactor and pulped for 15 minutes under nitrogen protection. Esterification was carried out for 3 hours at 230℃~265℃ and 260KPa. After esterification, vacuum was applied and polycondensation was carried out for 4 hours at 265℃~280℃ and 30Pa. After fiber formation, cooling, pelletizing, and drying, a modified polyester with an intrinsic viscosity of 0.64 dl / g was obtained. The relationship between the end carboxyl group content P and the intrinsic viscosity η was P / η=16.5.

[0193] The composition of the diol is as follows (in mole fraction):

[0194] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 25%

[0195] trans-1-methyl-1,2-cyclopentanediol 15%

[0196] Neopentyl glycol 10%

[0197] 50% ethylene glycol.

[0198] Preparation of functional masterbatch M / functional masterbatch N:

[0199] The modified polyester with an intrinsic viscosity of 0.64 dl / g and a relationship between the end carboxyl group content P and intrinsic viscosity η of P / η = 16.5 was selected as the base material. Then, 15% by weight of calcium carbonate particles with a particle size of 2.5 μm and a porosity of 1.6 ml / g and 85% by weight of modified polyester were mixed evenly and fed into a twin-screw extruder. Vacuum was applied, and the mixture was filamentized, cooled, pelletized, and dried to obtain the functional masterbatch M / functional masterbatch N described in this invention. The intrinsic viscosity of functional masterbatch M / functional masterbatch N is 0.51 dl / g.

[0200] The following materials were pre-mixed and processed before being fed into the corresponding melt extrusion system: 5% by weight of functional masterbatch M with an intrinsic viscosity of 0.51 dl / g and 95% by weight of pure polyester chips with an intrinsic viscosity of 0.60 dl / g (layer A); 10% by weight of modified polyester with an intrinsic viscosity of 0.64 dl / g and a relationship between terminal carboxyl group content P and intrinsic viscosity η of P / η = 16.5 and 90% by weight of pure polyester chips with an intrinsic viscosity of 0.60 dl / g (layer B); and 7% by weight of functional masterbatch N with an intrinsic viscosity of 0.51 dl / g and 93% by weight of pure polyester chips with an intrinsic viscosity of 0.60 dl / g (layer C). At 270℃, the film is co-extruded through a three-layer die and cast onto a casting roll to form an A / B / C structure extruded film. The film is then longitudinally stretched at a temperature of 55℃ to 88℃ with a longitudinal stretch ratio of 3.1. The longitudinally stretched film is then transversely stretched at a temperature of 90℃ to 123℃ with a transverse stretch ratio of 3.9. The stretched film is then shaped at a temperature of 220℃. Finally, the film is cooled, drawn, and wound to obtain a 100μm thick polyester film, in which the thickness ratio of layer A to layer B is 1:10, and the thickness ratio of layer C to layer B is 3:25.

[0201] Example 9

[0202] Preparation of modified polyester:

[0203] The mixture of terephthalic acid and diol in a molar ratio of 1:1.25, ethylene glycol antimony added at 180 ppm, and triphenyl phosphate added at 30 ppm was added and thoroughly mixed. The mixture was then added to a polyester synthesis reactor and pulped for 15 minutes under nitrogen protection. Esterification was carried out for 3 hours at 230℃~265℃ and 260 kPa. After esterification, vacuum was applied, and polycondensation was performed for 3.5 hours at 265℃~280℃ and 25 Pa. The resulting product was then filamentized, cooled, pelletized, and dried to obtain a modified polyester with an intrinsic viscosity of 0.62 dl / g. The relationship between the end carboxyl group content P and the intrinsic viscosity η was P / η = 17.5.

[0204] The composition of the diol is as follows (in mole fraction):

[0205] 1,1'-Bis(4-hydroxy-3-methylphenyl)cyclohexane 15%

[0206] trans-1-methyl-1,2-cyclopentanediol 8%

[0207] Neopentyl glycol 6%

[0208] Ethylene glycol 71%.

[0209] Preparation of functional masterbatch M / functional masterbatch N:

[0210] The modified polyester with an intrinsic viscosity of 0.62 dl / g and a relationship between the end carboxyl group content P and intrinsic viscosity η of P / η = 17.5 was selected as the base material. Then, 5% by weight of calcium carbonate particles with a particle size of 3.0 μm and a porosity of 1.9 ml / g and 95% by weight of modified polyester were mixed evenly and fed into a twin-screw extruder. Vacuum was applied, and the mixture was filamentized, cooled, pelletized, and dried to obtain the functional masterbatch M / functional masterbatch N described in this invention. The intrinsic viscosity of functional masterbatch M / functional masterbatch N is 0.56 dl / g.

[0211] A mixture of 15% by weight of functional masterbatch M with an intrinsic viscosity of 0.56 dl / g and 85% by weight of pure polyester chips with an intrinsic viscosity of 0.63 dl / g (layer A); 3% by weight of modified polyester with an intrinsic viscosity of 0.62 dl / g and a relationship between end-carboxyl content P and intrinsic viscosity η of P / η = 17.5; 97% by weight of pure polyester chips with an intrinsic viscosity of 0.63 dl / g (layer B); 5% by weight of functional masterbatch N with an intrinsic viscosity of 0.56 dl / g; and 95% by weight of pure polyester chips with an intrinsic viscosity of 0.63 dl / g (layer C) are pre-mixed and fed into the corresponding melt extrusion system. At 270°C, the mixture is co-extruded through a three-layer die and cast onto a casting roll to form an A / B / C structure extruded sheet. The cast sheet is longitudinally stretched at a temperature of 55℃ to 88℃ with a longitudinal stretching ratio of 3.3. The longitudinally stretched sheet is then transversely stretched at a temperature of 90℃ to 123℃ with a transverse stretching ratio of 3.6. The stretched film is then shaped at a temperature of 230℃. Finally, the film is cooled, drawn, and wound to obtain a 100μm thick polyester film, wherein the thickness ratio of layer A to layer B is 3:20, and the thickness ratio of layer C to layer B is 3:20.

[0212] Comparative Example 1

[0213] A mixture of 15% by weight of a functional masterbatch with an intrinsic viscosity of 0.56 dl / g, containing 1.5% by weight of 1.0 μm calcium carbonate particles, and 85% by weight of pure polyester chips with an intrinsic viscosity of 0.60 dl / g (layer A); 35% by weight of polyester with an intrinsic viscosity of 0.76 dl / g and a carboxyl group content of 5%, and 65% by weight of pure polyester chips with an intrinsic viscosity of 0.60 dl / g (layer B); and 10% by weight of a functional masterbatch with an intrinsic viscosity of 0.56 dl / g, containing 1.5% by weight of 1.0 μm calcium carbonate particles, and 90% by weight of pure polyester chips with an intrinsic viscosity of 0.60 dl / g (layer C), is pre-mixed and fed into the corresponding melt extrusion system. At 265°C, it is co-extruded through a three-layer die and cast onto a casting roll to form an A / B / C structure extruded sheet. The cast sheet is longitudinally stretched at a temperature of 55℃ to 88℃ with a longitudinal stretching ratio of 3.8. The longitudinally stretched sheet is then transversely stretched at a temperature of 90℃ to 123℃ with a transverse stretching ratio of 4.9. The stretched film is then shaped at a temperature of 235℃. Finally, the film is cooled, drawn, and wound to obtain a polyester film with a thickness of 23μm, wherein the thickness ratio of layer A to layer B is 3:50, and the thickness ratio of layer C to layer B is 1:10.

[0214] Comparative Example 2

[0215] A mixture of 12% functional masterbatch with an intrinsic viscosity of 0.58 dl / g, containing 7.5% by weight of 3.5 μm calcium carbonate particles, and 88% by weight of pure polyester chips with an intrinsic viscosity of 0.62 dl / g (layer A); 30% by weight of polyester with an intrinsic viscosity of 0.65 dl / g and 70% by weight of pure polyester chips with an intrinsic viscosity of 0.62 dl / g (layer B); and 12% by weight of functional masterbatch with an intrinsic viscosity of 0.58 dl / g, containing 7.5% by weight of 3.5 μm calcium carbonate particles, and 88% by weight of pure polyester chips with an intrinsic viscosity of 0.62 dl / g (layer C), is pre-mixed and fed into the corresponding melt extrusion system. At 265°C, it is co-extruded through a three-layer die and cast onto a casting roll to form an A / B / C structure extruded sheet. The cast sheet is longitudinally stretched at a temperature of 55℃ to 88℃ with a longitudinal stretching ratio of 3.5. The longitudinally stretched sheet is then transversely stretched at a temperature of 90℃ to 123℃ with a transverse stretching ratio of 4.7. The stretched film is then shaped at a temperature of 235℃. Finally, the film is cooled, drawn, and wound to obtain a polyester film with a thickness of 50μm, wherein the thickness ratio of layer A to layer B is 3:25, and the thickness ratio of layer C to layer B is 1:13.

[0216] Comparative Example 3

[0217] A mixture of 15% by weight of functional masterbatch with an intrinsic viscosity of 0.56 dl / g (containing 5% concentration of 3.0 μm calcium carbonate particles) and 85% by weight of pure polyester chips with an intrinsic viscosity of 0.63 dl / g (layer A); 3% by weight of polyester with an intrinsic viscosity of 0.62 dl / g and 97% by weight of pure polyester chips with an intrinsic viscosity of 0.63 dl / g (layer B); and 5% by weight of functional masterbatch with an intrinsic viscosity of 0.56 dl / g (containing 5% concentration of 3.0 μm calcium carbonate particles) and 95% by weight of pure polyester chips with an intrinsic viscosity of 0.63 dl / g (layer C), after pre-mixing and other treatments, is fed into the corresponding melt extrusion system. At 270℃, the film is co-extruded through a three-layer die and cast onto a casting roll to form an A / B / C structure extruded film. The film is then longitudinally stretched at a temperature of 55℃ to 88℃ with a longitudinal stretch ratio of 3.3. The longitudinally stretched film is then transversely stretched at a temperature of 90℃ to 123℃ with a transverse stretch ratio of 3.6. The stretched film is then shaped at a temperature of 230℃. Finally, the film is cooled, drawn, and wound to obtain a 100μm thick polyester film, wherein the thickness ratio of layer A to layer B is 3:20, and the thickness ratio of layer C to layer B is 3:20.

[0218] Specific implementation effects

[0219]

[0220] Thickness test method: GB / T 33399-2016.

[0221] Counting of bumps and dents: After packaging the small shafts in a standardized manner, place them in a temperature and humidity controlled warehouse (23℃, 50% RH) for 21 days (this timeframe is based on the typical cycle from film production to customer use). After placement, remove the packaging from the small shafts, peel off 2m of the outer ring, and take a 1m×1m shaft sample. Count the number of bumps and dents on the film surface. The method is for inspectors to observe under double-row fluorescent lights, using reflected light, with the fluorescent light and the film surface at a 45° angle, and the inspector's line of sight also at a 45° angle to the film surface.

[0222] Uneven thickness: Take any position on the film, along a 2m length in both the MD (longitudinal) and TD (transverse) directions, and measure the thickness at 5mm intervals according to the method in GB / T 33399-2016. Measure the thickness T. n At position (n = 1 - 400)(μm)400, the maximum thickness value is denoted as T. max The minimum thickness value is denoted as T. min The average thickness value is denoted as T. a Therefore, uneven thickness = [(T max -Tmin ) / T a ×100%.

[0223] Temperature resistance: Take three A4-sized films at any position on the film as the test samples, keeping the test surface of the samples clean and free from contamination; during sampling and testing, do not touch the test surface of the samples with your hands or other easily contaminated instruments; fold the three films into small boxes of fixed size (12.5±0.1)cm×(20±0.1)cm, and heat-treat them at 180℃ / 30min; then, cool to room temperature, add 10mL of N,N-dimethylformamide to the three sets of film boxes, and soak the bottom surface of the film boxes for 5min; then transfer the above soaked solution into a reagent bottle for high performance liquid chromatography, and use high performance liquid chromatography to test the solid content in the solution, and take the average value of the three sets of data.

[0224] By comparing Example 3 with Comparative Example 1, Example 5 with Comparative Example 2, and Example 9 with Comparative Example 3, it can be seen that under the same conditions of polyester film thickness and film-making process, the polyester film of the present invention has significantly better placement of bumps, thickness unevenness, and temperature resistance than ordinary polyester film.

[0225] 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.

[0226] 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 polyester film, characterized in that, It consists of an upper surface layer, a middle layer, and a lower surface layer; The upper surface layer consists of the following substances in weight percentages. composition: Functional masterbatch M 5-30% 70-95% pure polyester chips; The intermediate layer is composed of the following substances in weight percentage: Modified polyester 3-50% Pure polyester chips: 50-97%; The lower surface layer is composed of the following substances in weight percentage: Functional masterbatch N 5-15% 85-95% pure polyester chips; Both functional masterbatch M and functional masterbatch N are composed of the following substances in weight percentage: Inorganic particles 0.3–15% Modified polyester 85-99.7%; The modified polyester is obtained by esterification polycondensation of a diacid and a diol at a molar ratio of 1:(1.2-1.43), under the action of a catalyst of 100ppm-300ppm and a stabilizer of 25ppm-80ppm; the diol comprises the following substances in molar 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 polyester film according to claim 1, characterized in that, The inorganic particles have a particle size of 0.3μm to 5μm and a porosity of 0.6ml / g to 2.2ml / g; the modified polyester has an intrinsic viscosity η of 0.56dl / g to 0.66dl / g, and the relationship between the terminal carboxyl group content P and the intrinsic viscosity η is 10.5≤P / η≤17.

5.

3. A 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.

4. A polyester film according to claim 1, characterized in that, 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 catalysts.

5. A polyester film according to claim 1, characterized in that, The stabilizer is selected from one or a combination of any weight ratio of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, tetrabutyl titanate, tetraethyl titanate, and tri-n-butyl phosphate.

6. A polyester film according to claim 1, characterized in that, The pure polyester chips are polyethylene terephthalate chips with an intrinsic viscosity of 0.56 dl / g to 0.66 dl / g.

7. A polyester film according to claim 1, characterized in that, The inorganic particles are selected from one or more of aluminum oxide, titanium dioxide, silicon dioxide, calcium carbonate, barium sulfate, kaolin, and zirconium oxide in any weight ratio.

8. A polyester film according to claim 1, characterized in that, The thickness of the polyester film is 8μm to 100μm.

9. A polyester film according to claim 1, characterized in that, The polyester film has a thickness ratio of (1:21) to (3:20) between the upper surface layer and the middle layer, and a thickness ratio of (1:21) to (3:20) between the lower surface layer and the middle layer.

10. A method for preparing a polyester film as described in any one of claims 1-9, characterized in that, Includes the following steps: The components used to obtain the specified proportions for the upper surface layer are: functional masterbatch M and pure polyester chips are mixed and processed, i.e., the A layer extrusion layer; The intermediate layer used to obtain the specified proportions consists of a mixture of modified polyester and pure polyester chips, i.e., the B-layer extrusion layer. The components used to obtain the required proportions for the lower surface layer are: functional masterbatch N mixed with pure polyester chips, i.e., the C layer extrusion layer; Layers A, B, and C are respectively fed into the corresponding melt extrusion system for extrusion, and then co-extruded in a three-layer die at 255℃~275℃; Polyester film is produced through casting, longitudinal stretching, transverse stretching, shaping, cooling, traction, and winding.

11. The preparation method according to claim 10, characterized in that, The longitudinal stretching ratio of the longitudinal stretching process is 2.9 to 3.9, and the transverse stretching ratio of the transverse stretching process is 3.6 to 5.2; the heat setting temperature of the heat setting process is 220℃ to 240℃.

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