A tear-resistant, high-toughness functional polyester film and its preparation process

Abstract

This invention relates to the field of film product technology, specifically to a tear-resistant, high-toughness functional polyester film and its preparation process. This invention overcomes the problem of poor toughness in polyester films. The invention involves preparing copolyester particles, which are then melt-extruded with triphenyl phosphate and tris(2,4-di-tert-butylphenyl) phosphite followed by rapid cooling to obtain a substrate layer. A core-shell toughening agent is prepared, mixed with a polyurethane prepolymer and a photoinitiator, and coated onto the surface of the substrate layer to obtain a toughening layer. Surface-grafted carbon nanotubes are prepared and combined with sulfuric acid-swelled aramid nanofibers to form a composite system, which is then electrospinned to form a tear-resistant layer. An isocyanate prepolymer, a silane coupling agent, and nano-silica sol are mixed and sprayed onto the surface of the tear-resistant layer, followed by in-situ polymerization and post-curing to obtain an interfacial bonding layer. The resulting polyester film exhibits excellent toughness.

Description

Technical Field

[0001] This invention relates to the field of film product technology, specifically to a tear-resistant, high-toughness functional polyester film and its preparation process. Background Technology

[0002] Due to its excellent comprehensive properties, such as mechanical properties, optical properties, and chemical stability, polyester layered films are widely used in many fields such as packaging, electronics, and optics. For example, in liquid crystal displays (LCDs) and organic light-emitting diode displays (OLEDs), polyester films serve as the support material and protective film for polarizers, playing an indispensable role in maintaining the stability and clarity of the display effect. In the manufacture of optical lenses, polyester films are used for lens packaging and protection to prevent the lenses from being scratched.

[0003] However, with the rapid development of optical technology, more stringent requirements have been placed on the performance of polyester films. During the production, assembly, and daily use of optical equipment, polyester films often face various mechanical stresses. For example, in the bonding process of polarizers, polyester films need to be precisely and tightly bonded to other optical components. If the film lacks sufficient toughness during this process, it is prone to cracking or developing micro-cracks due to stretching and bending. This not only affects the performance of the polarizer but may also lead to defects in the entire display module, reducing product yield. In some wearable optical devices, because the devices need to be frequently bent and twisted with human movement, the poor tear resistance and low toughness of traditional polyester films make it difficult for them to withstand these complex mechanical deformations, greatly limiting the innovative development of optical devices in the direction of miniaturization and flexibility.

[0004] Therefore, developing a high-toughness functional polyester film is of great practical significance for promoting technological progress in the field of optics and improving product quality and reliability. To this end, a tear-resistant high-toughness functional polyester film and its preparation process are proposed. Summary of the Invention

[0005] The present invention aims to provide a tear-resistant, high-toughness functional polyester film and its preparation process. The process involves preparing copolyester particles, which are then melt-extruded with triphenyl phosphate and tris(2,4-di-tert-butylphenyl) phosphite followed by rapid cooling to obtain a substrate layer. A core-shell toughening agent is prepared, mixed with a polyurethane prepolymer and a photoinitiator, and coated onto the surface of the substrate layer to obtain a toughening layer. Surface-grafted carbon nanotubes are prepared and combined with sulfuric acid-swelled aramid nanofibers to form a composite system, which is then electrospinned to form a tear-resistant layer. An isocyanate prepolymer, a silane coupling agent, and nano-silica sol are mixed and sprayed onto the surface of the tear-resistant layer, followed by in-situ polymerization and post-curing to obtain an interfacial bonding layer. The resulting polyester film exhibits excellent toughness.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] It should be noted that all parts in this invention are parts by weight.

[0008] This invention provides a process for preparing a tear-resistant, high-toughness functional polyester film. The preparation method is as follows: copolyester particles, triphenyl phosphate, and tris(2,4-di-tert-butylphenyl) phosphite are melt-extruded and then rapidly cooled by a cooling roller to obtain a substrate layer; a mixture of polyurethane prepolymer, core-shell toughening agent, and photoinitiator is coated onto the surface of the substrate layer using a microgravure coating machine to obtain a toughening layer; electrospinning is performed on the surface of the toughening layer to obtain a tear-resistant layer; a prepolymer mixture is uniformly sprayed onto the surface of the tear-resistant layer using a high-pressure spray gun to obtain an interface bonding layer; then, after preheating on a 95°C preheating roller for 3 minutes, longitudinal and transverse stretching are performed; finally, high-temperature setting and cooling are performed before winding to obtain the polyester film.

[0009] The copolyester particles were prepared from 1,4-cyclohexanediethanol, 2,6-naphthalenedicarboxylic acid and terephthalic acid;

[0010] The prepolymer mixture was prepared from isocyanate prepolymer, silane coupling agent KH550 and nano-silica sol.

[0011] Preferably, the substrate layer preparation process is as follows: copolyester particles are dried in a vacuum oven at 120°C for 4 hours to obtain dried copolyester. Then, the dried copolyester, 0.3 parts of triphenyl phosphate, and 0.1 parts of tris(2,4-di-tert-butylphenyl) phosphite are added to a twin-screw extruder for melt extrusion to obtain a melt. The die section temperature of the twin-screw extruder is 290-320°C. The melt is then subjected to rapid cooling treatment through a cooling roller at 30°C to obtain a substrate layer with a thickness of 80 μm.

[0012] Preferably, the copolyester particle preparation process is as follows: 12 parts of 1,4-cyclohexanediethanol, 15 parts of 2,6-naphthalenedicarboxylic acid and 73 parts of terephthalic acid are added to a reaction vessel, and nitrogen gas is introduced into the reaction vessel. The temperature is raised to 180-200℃ and reacted for 2.5 hours to obtain a pre-esterified product; the temperature is further raised to 250-280℃, while the pressure in the reaction vessel is reduced to 1-10 Pa, and the reaction is carried out for 4 hours to obtain a polycondensation product; the polycondensation product is cooled into strips by a casting machine, and then cut into particles by a pelletizer to obtain copolyester particles.

[0013] Preferably, the toughening layer preparation process is as follows: 70-85 parts of polyurethane prepolymer and 10-25 parts of core-shell toughening agent are stirred and mixed at 90°C for 30 minutes. After adding 3 parts of photoinitiator, the mixture is ultrasonically dispersed to obtain a mixture. The mixture is then coated onto the surface of the substrate layer using a microgravure coating machine to a coating thickness of 20 μm. Subsequently, a photoinitiator is applied at a wavelength of 365 nm and an intensity of 80 mW / cm². 2The toughened layer is obtained by UV curing under the following conditions for 2 minutes, followed by curing in a 60℃ oven for 1 hour.

[0014] Preferably, the core-shell toughening agent is prepared as follows: Under nitrogen protection, 45 parts of methyl methacrylate, 1.5 parts of divinylbenzene and 120 parts of deionized water are mixed and pre-emulsified at 60-80℃ for 30 min. Then, 0.7 parts of potassium persulfate initiator are added, and the mixture is heated to 75℃ and reacted for 4 h to obtain a polymethyl methacrylate core emulsion. The polymethyl methacrylate core emulsion is diluted to a solid content of 10%, and 12 parts of glycidyl methacrylate and 7 parts of styrene are added and reacted for 30 min. Then, potassium persulfate initiator is added dropwise, and the mixture is reacted at 70-95℃ for 6 h. After centrifugation, washing and drying, the core-shell toughening agent is obtained.

[0015] Preferably, the tear-resistant layer preparation process is as follows: 10-15 parts of aramid nanofibers are swollen in 98wt% concentrated sulfuric acid for 30 min, and washed with deionized water until neutral to obtain sulfuric acid-swollen aramid nanofibers; 5-10 parts of modified carbon nanotubes, sulfuric acid-swollen aramid nanofibers and 0.6 parts of sodium dodecylbenzenesulfonate are added to 80 parts of N-methylpyrrolidone, and ball-milled and dispersed for 4 h to obtain a spinning solution; electrospinning is performed on the toughening layer surface under the conditions of voltage 17-25kV, receiving distance 15cm and solution flow rate 0.8mL / h to obtain the tear-resistant layer.

[0016] The preferred preparation process for modified carbon nanotubes is as follows: 15 parts of multi-walled carbon nanotubes are added to a 30wt% phosphoric acid solution and ultrasonically treated in a 60℃ constant temperature water bath for 2 hours. Then, the nanotubes are washed and dried with deionized water to obtain phosphorylated carbon nanotubes. 60 parts of dimethyl terephthalate and 38 parts of 1,4-butanediol are added to a three-necked flask, and the mixture is heated to 180℃ under nitrogen protection. 0.5 parts of tetrabutyl titanate catalyst are added and reacted for 2 hours. The temperature is then raised to 230-255℃, the vacuum is reduced to 50 Pa, and the reaction continues for 3 hours. Finally, 1.2 parts of a terminator are added. Ethylene glycol monomethyl ether was reacted at 230 °C for 40 min to obtain hydroxyl-terminated polyester oligomers. 30 parts of the hydroxyl-terminated polyester oligomers were dissolved in 200 parts of xylene, and 10 parts of phosphorylated carbon nanotubes were added. The mixture was ultrasonically dispersed at 120 °C for 1 h, and 0.5 parts of dicyclohexylcarbodiimide were added. The mixture was heated to 160 °C and stirred under nitrogen protection for 6 h to obtain a reaction solution. The reaction solution was hot-filtered through a 0.45 μm filter membrane, washed three times successively with xylene and acetone to remove unreacted oligomers, and then vacuum-dried at 60 °C for 12 h to obtain modified carbon nanotubes.

[0017] Preferably, the interface bonding layer preparation process is as follows: isocyanate prepolymer, silane coupling agent KH550, and nano-silica sol are mixed uniformly at a mass ratio of 7.5:1.5:1-4 to obtain a prepolymer mixture; the prepolymer mixture is uniformly sprayed onto the surface of the tear-resistant layer using a high-pressure spray gun, with a spraying amount of 7-11 g / m². 2 Then, in-situ polymerization is carried out at 50°C for 20 minutes, and finally post-curing is performed in an oven at 75°C for 20-50 minutes to form an interface bonding layer with a thickness of 100nm.

[0018] Preferably, the longitudinal stretching has a stretch ratio of 3.8, a temperature of 105°C, and a speed of 300% / min; the transverse stretching has a stretch ratio of 4.3, a temperature of 115°C, and a speed of 280% / min; the high-temperature setting temperature is 180°C, and the time is 8 min; the cooling and winding process first reduces the temperature to 100°C at a rate of 5°C / min, and then performs room temperature water cooling, with a winding tension of 2.5 N / cm. 2 .

[0019] Another aspect of the present invention provides a tear-resistant and high-toughness functional polyester film, the polyester film being composed of a substrate layer, a toughening layer, a tear-resistant layer, and an interface bonding layer; the polyester film is prepared by any of the above-mentioned preparation processes.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. The substrate layer of this invention is composed of a copolyester backbone of rigid 2,6-naphthalenedicarboxylic acid and flexible 1,4-cyclohexanediethanol, forming an alternating distribution of ordered crystalline and amorphous regions, which endows the film with intrinsic tear resistance; the molecular chain stacking of the naphthalene ring structure enhances rigidity and resists crack propagation caused by external forces; the helical conformation of the cyclohexane unit provides molecular chain extensibility, dissipates energy through local slip, prevents brittle fracture, and improves the toughness of the film; phosphate ester stabilizers optimize melt flowability, suppress processing defects, and the quenching process refines the crystal size and reduces structural weak points.

[0022] 2. The toughening layer of this invention, formed by photocuring, utilizes a dynamically cross-linked polyurethane network with adaptive resilience. The introduction of a core-shell toughening agent further enhances energy absorption efficiency. When the film is subjected to external force, the reversible extension and breakage of the polyurethane molecular chains can consume a large amount of energy. The core-shell structure, through shell fracture and core plastic deformation, synergistically consumes energy, delaying the material failure process. The dynamically cross-linked structure releases internal stress through bond reconstruction during repeated bending, avoiding the accumulation of permanent microscopic damage and endowing the film with excellent toughness.

[0023] 3. The tear-resistant layer of this invention employs a composite system of aramid nanofibers and surface-grafted carbon nanotubes, constructing a highly oriented nanofiber network through electrospinning. The high specific surface area of ​​the nanoscale aramid fibers enhances interfacial bonding, forming a continuous force transmission path; the hydroxyl-grafted polyester oligomers of the modified carbon nanotubes ensure uniform dispersion and penetration into the fiber gaps, inhibiting the propagation of micro-damage through crack bridging and pull-out effects; simultaneously, the nanoscale reinforcement significantly reduces the material's density, endowing the film with both lightweight and high strength without significantly increasing its thickness. This nano-synergistic reinforcement mechanism significantly improves the toughness of the polyester film.

[0024] 4. The interfacial bonding layer of this invention significantly improves interlayer bonding efficiency through a multi-level chemical crosslinking and nano-reinforcement strategy. The isocyanate prepolymer forms a dense covalent network with the hydroxyl groups on the surface of the tear-resistant layer, anchoring the reinforcing phase and the matrix and preventing failure caused by interfacial delamination. The silane coupling agent further bridges the inorganic nano-silica sol and the organic phase, constructing a molecular-level interpenetrating structure through in-situ condensation reaction to disperse local stress. The nano-silica sol fills the interfacial micropores and forms physical interlocks, slowing down the propagation rate of cracks crossing the interface. The dynamic crosslinking system endows the interface with adaptive deformation capability, consuming energy through bonding reconstruction under external force, avoiding stress concentration that leads to delamination, and improving the toughness of the polyester film. Attached Figure Description

[0025] Figure 1 The figures show the toughness test results of Examples 3, 5-7, and Comparative Examples 4-7 of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Please see Figure 1 This invention provides a tear-resistant, high-toughness functional polyester film and its preparation process, the technical solution of which is as follows:

[0028] The material information involved in this invention is as follows:

[0029] 1,4-Cyclohexanediethanol CAS: 105-08-8; 2,6-Naphthalenedicarboxylic acid CAS: 1141-38-4; Triphenyl phosphate CAS: 115-86-6; Tris(2,4-di-tert-butylphenyl) phosphite CAS: 31570-04-4; Methyl methacrylate CAS: 80-62-6; Divinylbenzene CAS: 1321-74-0; Potassium persulfate CAS: 7727-21-1; Glycidyl methacrylate CAS: 106-91-2; Styrene CAS: 100-42-5; Polyurethane prepolymer (molecular weight 3000 g / mol) CAS: 103837-45-2; Photoinitiator Irgacure 184 CAS: 947-19-3; Multi-walled carbon nanotubes CAS: 1333-86-4; Dimethyl terephthalate CAS: 120-61-6; 1,4-Butanediol CAS: 110-63-4; Tetrabutyl titanate CAS: 5593-70-4; Ethylene glycol monomethyl ether CAS: 109-86-4; Xylene CAS: 1330-20-7; Dicyclohexylcarbodiimide CAS: 538-75-0; Sodium dodecylbenzenesulfonate CAS: 25155-30-0; N-methylpyrrolidone CAS: 872-50-4; Silane coupling agent KH550 CAS: 919-30-2; Isocyanate prepolymer Desmodur N3300 was purchased from Guangzhou Haoyi New Material Technology Co., Ltd.; nano-silica sol was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.; aramid nanofibers were prepared according to the method in patent CN115652465B.

[0030] Example 1

[0031] 12 parts of 1,4-cyclohexanediethanol, 15 parts of 2,6-naphthalenedicarboxylic acid, and 73 parts of terephthalic acid were added to a reactor, and nitrogen gas was introduced into the reactor. The temperature was raised to 180°C and reacted for 2.5 hours to obtain a pre-esterified product. 0.2 parts of tetrabutyl titanate were added, and the temperature was further raised to 250°C while the pressure inside the reactor was reduced to 1 Pa. The reaction was continued for 4 hours to obtain a polycondensation product. The polycondensation product was cooled into strips using a casting machine, and then cut into granules using a pelletizer to obtain copolyester granules (3 mm). The copolyester granules were placed in a 120°C container... The dried copolyester was dried in a vacuum oven for 4 hours. Then, the dried copolyester, 0.3 parts of triphenyl phosphate, and 0.1 parts of tris(2,4-di-tert-butylphenyl) phosphite were added to a twin-screw extruder for melt extrusion to obtain a melt. The temperature of the feeding section of the twin-screw extruder was 250°C, the temperature of the melting section was 285°C, and the temperature of the die section was 290°C. A coat hanger type flat die was used, with a die lip width of 1.2 mm and a gap of 0.8 mm. The melt was then subjected to quenching treatment through a cooling roller at a temperature of 30°C to obtain a substrate layer with a thickness of 80 μm.

[0032] Under nitrogen protection, 45 parts of methyl methacrylate, 1.5 parts of divinylbenzene, and 120 parts of deionized water were mixed and pre-emulsified at 60°C for 30 min. Then, 0.7 parts of potassium persulfate initiator were added, and the mixture was heated to 75°C and reacted for 4 h to obtain a polymethyl methacrylate core emulsion. The polymethyl methacrylate core emulsion was diluted to a solid content of 10%, and 12 parts of glycidyl methacrylate and 7 parts of styrene were added and reacted for 30 min. Then, 0.5 parts of potassium persulfate initiator were added dropwise, and the mixture was reacted at 70°C for 6 h. After centrifugation, washing, and drying, a core-shell toughening agent (shell epoxy content ≥10 mmol / g) was obtained. 70 parts of polyurethane prepolymer and 10 parts of the core-shell toughening agent were stirred and mixed at 90°C for 30 min (500 rpm), and 3 parts of photoinitiator Irgacure were added. After 184 minutes, the mixture was ultrasonically dispersed (40 kHz, 15 min) to obtain a mixture. This mixture was then coated onto the substrate surface using a microgravure coater to a thickness of 20 μm. Following this, an optical emission test was performed at a wavelength of 365 nm and an intensity of 80 mW / cm². 2 Under the conditions of UV curing, the irradiation time is 2 minutes, and then it is cured in an oven at 60℃ for 1 hour to obtain the toughened layer;

[0033] 15 parts of multi-walled carbon nanotubes were added to a 30 wt% phosphoric acid solution (250 parts), and ultrasonically treated in a 60℃ constant temperature water bath for 2 hours (300W). The mixture was then washed and dried with deionized water to obtain phosphorylated carbon nanotubes. 60 parts of dimethyl terephthalate and 38 parts of 1,4-butanediol were added to a three-necked flask, and the mixture was heated to 180℃ under nitrogen protection. 0.5 parts of tetrabutyl titanate catalyst were added and reacted for 2 hours. The temperature was then raised to 230℃, the vacuum was reduced to 50 Pa, and the reaction continued for 3 hours. 1.2 parts of ethylene glycol monomethyl ether (hydroxyl group to carboxyl group molar ratio 1.2:1) were added as a terminator, and the mixture was reacted at 230℃ for 40 minutes to obtain a hydroxyl-terminated polyester oligomer. 30 parts of the hydroxyl-terminated polyester oligomer were dissolved in 200 parts of xylene, and 10 parts of phosphorylated carbon nanotubes were added. The mixture was ultrasonically dispersed at 120℃ (250W) for 1 hour. 0.5 parts of dicyclohexylcarbodiimide were heated to 160℃ and stirred (500 rpm) for 6 h under nitrogen protection (ester bond formation) to obtain a reaction solution. The reaction solution was hot-filtered through a 0.45 μm filter membrane (80℃), washed three times with xylene and acetone to remove unreacted oligomers, and vacuum dried at 60℃ for 12 h to obtain modified carbon nanotubes. 10 parts of aramid nanofibers were swollen in 98 wt% concentrated sulfuric acid for 30 min and washed with deionized water until neutral to obtain sulfuric acid-swollen aramid nanofibers. 5 parts of modified carbon nanotubes, sulfuric acid-swollen aramid nanofibers, and 0.6 parts of sodium dodecylbenzenesulfonate were added to 80 parts of N-methylpyrrolidone and ball-milled for 4 h to obtain a spinning solution. Electrospinning was performed on the toughened layer surface under the conditions of 17 kV voltage, 15 cm receiving distance, and 0.8 mL / h solution flow rate to obtain a tear-resistant layer.

[0034] The isocyanate prepolymer Desmodur N3300, silane coupling agent KH550, and nano-silica sol were mixed uniformly at a mass ratio of 7.5:1.5:1 to obtain a prepolymer mixture. The prepolymer mixture was then uniformly sprayed onto the tear-resistant layer surface using a high-pressure spray gun (nozzle diameter 0.3 mm, pressure 0.3 MPa) at a coating weight of 7 g / m². 2 Next, in-situ polymerization was carried out at 50℃ for 20 min, followed by post-curing in a 75℃ oven for 20 min to form an interface bonding layer with a thickness of 100 nm. Then, after preheating on a 95℃ preheating roller for 3 min, longitudinal and transverse stretching were performed. Finally, high-temperature setting and cooling winding were conducted to obtain a polyester film with a thickness of 50 μm. The longitudinal stretching had a stretch ratio of 3.8, a temperature of 105℃, and a speed of 300% / min; the transverse stretching had a stretch ratio of 4.3, a temperature of 115℃, and a speed of 280% / min; the high-temperature setting temperature was 180℃ for 8 min; the cooling winding was first reduced to 100℃ at a rate of 5℃ / min, followed by room temperature water cooling, with a winding tension of 2.5 N / cm. 2 .

[0035] Examples 2-4

[0036] The preparation method and parameters of Example 1 are as follows, with specific differences shown in Table 1; in Table 1, temperature 1 is the reaction temperature at which the pre-esterified product is obtained when preparing copolyester particles; temperature 2 and pressure are the reaction temperature and pressure at which the polycondensation product is obtained when preparing copolyester particles.

[0037] Comparative Example 1

[0038] The preparation method and parameters of Example 1 are the same, except that triphenyl phosphate was not added when preparing the substrate layer.

[0039] Comparative Example 2

[0040] The preparation method and parameters of Example 1 were used, except that tris(2,4-di-tert-butylphenyl) phosphite was not added when preparing the substrate layer.

[0041] Comparative Example 3

[0042] The preparation method and parameters of Example 1 are the same, except that the copolyester particles were not dried when preparing the substrate layer.

[0043] Experiment Example 1: Toughness Test

[0044] The elongation at break was tested according to the standard GB / T 1040.3-2006; the results are shown in Table 1.

[0045] Table 1. Toughness tests of Examples 1-4 and Comparative Examples 1-3

[0046] Example Temperature 1 / ℃ Temperature 2 / ℃ Pressure / Pa Die head section temperature / ℃ Elongation at break / % Example 1 180 250 1 290 235 Example 2 185 255 4 300 237 Example 3 190 265 6 310 240 Example 4 200 280 10 320 236 Comparative Example 1 180 250 1 290 227 Comparative Example 2 180 250 1 290 224 Comparative Example 3 180 250 1 290 220

[0047] As shown in Table 1, in Examples 1-4, the copolyester backbone composed of rigid 2,6-naphthalenedicarboxylic acid and flexible 1,4-cyclohexanediethanol forms an alternating distribution of ordered crystalline and amorphous regions, endowing the film with intrinsic tear resistance. The naphthalene ring structure's molecular chain stacking enhances rigidity, resisting crack propagation caused by external forces; the helical conformation of the cyclohexane units provides molecular chain extensibility, dissipating energy through localized slip and preventing brittle fracture; phosphate ester stabilizers optimize melt flowability, suppress processing defects, and the rapid cooling process refines crystal size, reducing structural weak points. In Example 3, the polyester film with the best toughness and an elongation at break of 240% was obtained when the temperature was 190°C, the temperature was 265°C, the pressure was 6 Pa, and the die head temperature was 310°C. In Comparative Example 1, the absence of triphenyl phosphate during substrate preparation resulted in reduced inter-chain spacing and lower free volume of chain segments. Restricted chain movement led to stress concentration and rapid crack propagation. Tris(2,4-di-tert-butylphenyl) phosphite provides antioxidant protection by capturing free radicals and decomposing hydrogen peroxide. In Comparative Example 2, tris(2,4-di-tert-butylphenyl) phosphite was not added during the preparation of the substrate layer. In the high-temperature section of the twin-screw extruder, the copolyester backbone underwent a β-fracture reaction. After the copolyester backbone fractured, the entanglement between molecular chains decreased. When the material was subjected to external forces, the molecular chains easily slid relative to each other, failing to effectively transfer and disperse stress, thus leading to a decrease in film toughness. In Comparative Example 3, the copolyester particles were not dried during the preparation of the substrate layer. At the extrusion temperature, the copolyester backbone underwent acid-catalyzed hydrolysis. Water and degradation products (carboxylic acids, alcohols) volatilized during the rapid cooling stage, and the resulting micropores became stress concentration sources, further reducing film toughness.

[0048] Examples 5-7

[0049] The preparation method and parameters of Example 3 are as follows, with specific differences shown in Table 2; in Table 2, temperature 1 is the pre-emulsification temperature when preparing the core-shell toughening agent; temperature 2 is the reaction temperature after adding 0.5 parts of potassium persulfate initiator when preparing the core-shell toughening agent.

[0050] Comparative Example 4

[0051] The preparation method and parameters of Example 3 are the same, except that when preparing the core-shell toughening agent, the polymethyl methacrylate core emulsion was not coated with a shell.

[0052] Comparative Example 5

[0053] The preparation method and parameters of Example 3 are the same, except that the core-shell toughening agent prepared in this invention is replaced with KaneAceMX-125 from Kaneka Corporation of Japan.

[0054] Comparative Example 6

[0055] The preparation method and parameters of Example 3 are the same, except that no core-shell toughening agent is added when preparing the toughening layer.

[0056] Comparative Example 7

[0057] The preparation method and parameters of Example 3 are the same, except that the toughened layer was not cured in an oven after UV curing.

[0058] Experiment Example 2 Toughness Test

[0059] The elongation at break and tensile strength were tested according to GB / T 1040.3-2006; the results are shown in Table 2 and... Figure 1 As shown.

[0060] Table 2 Toughness tests of Examples 3, 5-7 and Comparative Examples 4-7

[0061]

[0062]

[0063] From Table 2 and Figure 1 As can be seen, in Examples 3 and 5-7, the dynamic cross-linked polyurethane network formed by photocuring in the toughening layer possesses adaptive resilience, and the introduction of the core-shell toughening agent further enhances the energy absorption efficiency. When the film is subjected to external force, the reversible extension and breakage of the polyurethane molecular chains can consume a large amount of energy, while the core-shell structure consumes energy through the synergistic effect of shell fracture and core plastic deformation, thus delaying the material failure process. The dynamic cross-linked structure releases internal stress through bond reconstruction during repeated bending, avoiding the accumulation of permanent micro-damage and endowing the film with excellent toughness. In Example 5, when the first temperature is 70°C, the second temperature is 80°C, the amount of polyurethane prepolymer is 75 parts, and the amount of shell toughening agent is 15 parts, the film obtained has the best toughness and a tensile strength of 235 N / mm. 2The elongation at break was 244%. In Comparative Example 4, after obtaining the polymethyl methacrylate (PMMA) core emulsion, no shell coating was applied during the preparation of the core-shell toughening agent. The uncoated rigid PMMA core had no chemical bond with the polyurethane matrix (epoxy group content = 0), leading to large-scale phase separation at the two-phase interface and impairing stress transfer efficiency. In Comparative Example 5, the core-shell toughening agent prepared in this invention was replaced with KaneAce MX-125 from Kaneka Corporation of Japan. MX-125's reactivity with isocyanate was less than that of the core-shell toughening agent prepared in this invention, resulting in a weak interface between the toughening agent and the matrix. Furthermore, large-diameter particles caused stress concentration in the matrix, accelerating crack initiation. In Comparative Example 6, no core-shell toughening agent was added during the preparation of the toughening layer. The polyurethane network lacked a second phase, leading to multiple crazes, and molecular chain slip dominated the fracture process. In Comparative Example 7, the toughening layer was not cured in an oven after UV curing, which resulted in insufficient relaxation of the entangled network, leading to a brittle response under impact load. Furthermore, the unreacted Irgacure 184 photoinitiator decomposed to generate free radicals, causing micro-degradation of the material and a decrease in film toughness.

[0064] Examples 8-10

[0065] The preparation method and parameters of Example 5 are as follows, with specific differences shown in Table 3. The temperature in Table 3 is the temperature after adding 0.5 parts of the catalyst tetrabutyl titanate and reacting for 2 hours when preparing hydroxyl-terminated polyester oligomers.

[0066] Comparative Example 8

[0067] The preparation method and parameters of Example 5 are the same, except that the multi-walled carbon nanotubes were not phosphorylated when preparing the tear-resistant layer.

[0068] Comparative Example 9

[0069] The preparation method and parameters of Example 5 are the same, except that hydroxyl-terminated polyester oligomers were not used to graft phosphorylated carbon nanotubes onto the surface when preparing the tear-resistant layer.

[0070] Comparative Example 10

[0071] The preparation method and parameters of Example 5 are the same, except that the aramid nanofibers were not subjected to sulfuric acid swelling treatment when preparing the tear-resistant layer.

[0072] Comparative Example 11

[0073] The preparation method and parameters of Example 5 were used, except that the reaction solution was not thermally filtered through a 0.45 μm filter membrane when preparing the modified carbon nanotubes.

[0074] Example 12

[0075] The preparation method and parameters of Example 5 are the same, except that modified carbon nanotubes were not added when preparing the tear-resistant layer.

[0076] Example 13

[0077] The preparation method and parameters of Example 5 are the same, except that sulfuric acid was not added to swell aramid nanofibers when preparing the tear-resistant layer.

[0078] Experiment Example 3 Toughness Test

[0079] The fracture strength was tested according to the standard GB / T 16578-2009; the results are shown in Table 3.

[0080] Table 3 Toughness tests of Examples 5, 8-10 and Comparative Examples 8-13

[0081]

[0082] As shown in Table 3, in Examples 5 and 8-10, the tear-resistant layer adopted a composite system of aramid nanofibers and surface-grafted carbon nanotubes, and a highly oriented nanofiber network was constructed through electrospinning. The high specific surface area of ​​the nanoscale aramid fibers enhances the interfacial bonding force, forming a continuous force transmission path; the hydroxyl-grafted polyester oligomers of the modified carbon nanotubes ensure uniform dispersion and penetration into the fiber gaps, inhibiting the propagation of micro-damage through crack bridging and pull-out effects; simultaneously, the nanoscale reinforcement significantly reduces the density of the material, endowing the film with both lightweight and high strength without significantly increasing the thickness. This nano-synergistic reinforcement mechanism significantly improves the toughness of the polyester film. In Example 8, when the temperature was 240℃, the amount of aramid nanofibers was 12 parts, the amount of modified carbon nanotubes was 8 parts, and the electrospinning voltage was 20kV, the film obtained had the best toughness and a tensile strength of 229MPa. In Comparative Example 8, the multi-walled carbon nanotubes were not phosphorylated during the preparation of the tear-resistant layer. Under external force, the carbon nanotubes could not effectively disperse and transfer stress, failing to fully exert their reinforcing effect, thus leading to a decrease in the film's toughness. In Comparative Example 9, hydroxyl-terminated polyester oligomers were not used for surface grafting of phosphorylated carbon nanotubes during the preparation of the tear-resistant layer. The carbon nanotubes easily aggregated in the spinning solution, forming stress concentration points. When the film was torn by external force, these aggregated carbon nanotubes could not evenly bear the stress, easily leading to rapid crack propagation and decreased film toughness. Sulfuric acid swelling treatment can increase the molecular chain spacing of aramid nanofibers, exposing more active groups, which is beneficial for their better integration with other components. In Comparative Example 10, the aramid nanofibers were not swelled with sulfuric acid during the preparation of the tear-resistant layer, resulting in a reduced interfacial contact area between the fiber and the modified carbon nanotubes. The fibers were prone to relative sliding, failing to effectively prevent crack propagation, thus reducing the film's toughness. In Comparative Example 11, the reaction solution was not thermally filtered through a 0.45 μm filter membrane during the preparation of modified carbon nanotubes. Impurities and defects caused stress concentration and accelerated crack initiation. In Comparative Example 12, modified carbon nanotubes were not added during the preparation of the tear-resistant layer. The aramid fiber composite material lacking carbon nanotubes could not form a hierarchical reinforcement structure (in the original design, fibers bore macroscopic loads, and carbon nanotubes suppressed microcracks), resulting in decreased toughness. In Comparative Example 13, sulfuric acid-swelled aramid nanofibers were not added during the preparation of the tear-resistant layer, making it impossible to construct a three-dimensional mechanical framework. Furthermore, the random distribution of unoriented carbon nanotubes led to the loss of anisotropy in the film, resulting in decreased toughness.

[0083] Examples 11-13

[0084] The preparation method and parameters of Example 8 are as follows, with specific differences shown in Table 4; the mass ratio of the three components in Table 4 is the mass ratio of isocyanate prepolymer Desmodur N3300, silane coupling agent KH550 and nano silica sol.

[0085] Comparative Example 14

[0086] The preparation method and parameters of Example 8 are the same, except that in-situ polymerization was not performed when preparing the interface bonding layer.

[0087] Comparative Example 15

[0088] The preparation method and parameters of Example 8 were used in accordance with the same method and parameters, except that no nano-silica sol was added when preparing the interface bonding layer, and the amount of isocyanate prepolymer Desmodur N3300 was 15 parts and the amount of silane coupling agent KH550 was 3 parts.

[0089] Comparative Example 16

[0090] The preparation method and parameters of Example 8 are the same, except that the wet film thickness is 100 μm when preparing the interface bonding layer.

[0091] Comparative Example 17

[0092] The preparation method and parameters of Example 8 are the same, except that no post-curing was performed after in-situ polymerization when preparing the interface bonding layer.

[0093] Experiment Example 4 Toughness Test

[0094] The fracture strength was tested according to the standard GB / T 16578-2009; the results are shown in Table 4.

[0095] Table 4 Toughness tests of Examples 8, 11-13 and Comparative Examples 14-17

[0096] Example The quality ratio of the three <![CDATA[Spray amount / g / m 2 > Post-curing time / min Fracture strength / MPa Example 8 7.5：1.5：1 7 20 229 Example 11 7.5：1.5：2 9 30 234 Example 12 7.5：1.5：3 11 40 232 Example 13 7.5：1.5：4 9 50 230 Comparative Example 14 7.5：1.5：1 7 20 209 Comparative Example 15 / 7 20 217 Comparative Example 16 7.5：1.5：1 7 20 201 Comparative Example 17 7.5：1.5：1 7 / 211

[0097] As shown in Table 4, in Examples 8 and 11-13, the interfacial bonding layer significantly improved the interlayer bonding efficiency through a multi-level chemical crosslinking and nano-reinforcement strategy. The isocyanate prepolymer forms a dense covalent network with the hydroxyl groups on the surface of the tear-resistant layer, anchoring the reinforcing phase and the matrix, preventing failure caused by interfacial delamination. The silane coupling agent further bridges the inorganic nano-silica sol and the organic phase, constructing a molecular-level interpenetrating structure through in-situ condensation reaction, dispersing local stress. The nano-silica sol fills the interfacial micropores and forms physical interlocks, slowing down the crack propagation rate when it crosses the interface. The dynamic crosslinking system endows the interface with adaptive deformation capability, consuming energy through bond reconstruction under external force, avoiding stress concentration and delamination, and improving the toughness of the polyester film. In Example 11, when the mass ratio of the three components was 7.5:1.5:2, the spraying amount was 9 g / m². 2The film with the best toughness and a tensile strength of 234 MPa was obtained when the post-curing time was 30 min. In Comparative Example 14, in-situ polymerization was not performed when preparing the interfacial bonding layer, and the prepolymer mixture could not fully react to form a stable polymer network, resulting in insufficient cohesion of the interfacial bonding layer and insufficient adhesion strength between it and the tear-resistant layer. Under external force, cracks easily propagate at the interface, thereby reducing the toughness of the film. Nano-silica sol has a high specific surface area and activity, and can fill the gaps in the polymer network, playing a role in reinforcement and toughening. In Comparative Example 15, no nano-silica sol was added when preparing the interfacial bonding layer, and the strength and toughness of the interfacial bonding layer decreased, and its tear resistance was weakened; moreover, due to the lack of filling and reinforcement effects of nano-silica sol, the interfacial bonding layer is more prone to deformation and cracking under external tensile force, thus affecting the toughness of the film. In Comparative Example 16, the wet film thickness during the preparation of the interfacial bonding layer was 100 μm. A thicker wet film leads to uneven stress distribution within the interfacial bonding layer, and may also result in incomplete curing or internal defects. These defects become stress concentration points, making the film prone to cracking from these weak points when subjected to tearing forces, thus reducing the film's toughness. Post-curing allows these groups to react fully, increasing the polymer's crosslinking density and molecular weight, thereby enhancing the mechanical properties of the interfacial bonding layer. In Comparative Example 17, no post-curing was performed after in-situ polymerization during the preparation of the interfacial bonding layer, resulting in insufficient strength and stability, making it prone to damage and tearing under external forces.

[0098] 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.

Claims

1. A process for preparing a tear-resistant, high-toughness functional polyester film, characterized in that: The preparation method is as follows: Copolyester particles, triphenyl phosphate, and tris(2,4-di-tert-butylphenyl) phosphite are melt-extruded and then rapidly cooled by a cooling roller to obtain a substrate layer; a mixture of polyurethane prepolymer, core-shell toughening agent, and photoinitiator is coated onto the surface of the substrate layer using a microgravure coating machine, followed by UV curing and curing in a 60°C oven for 1 hour to obtain a toughening layer; electrospinning is performed on the surface of the toughening layer to obtain a tear-resistant layer; isocyanate prepolymer, silane coupling agent KH550, and nano-silica sol are mixed uniformly at a mass ratio of 7.5:1.5:1-4 to obtain a prepolymer mixture; the prepolymer mixture is uniformly sprayed onto the surface of the tear-resistant layer using a high-pressure spray gun at a spraying amount of 7-11 g / m². 2 Then, in-situ polymerization is carried out at 50°C for 20 minutes, and finally post-curing is performed in an oven at 75°C for 20-50 minutes to form an interface bonding layer with a thickness of 100nm; then, after preheating on a preheating roller, longitudinal stretching and transverse stretching are performed, and finally, high-temperature setting and cooling are performed to obtain the polyester film. The copolyester particles were prepared from 1,4-cyclohexanediethanol, 2,6-naphthalenedicarboxylic acid and terephthalic acid; The tear-resistant layer is prepared as follows: 10-15 parts of aramid nanofibers are swollen in concentrated sulfuric acid for 30 minutes, and washed with deionized water until neutral to obtain sulfuric acid-swollen aramid nanofibers; 5-10 parts of modified carbon nanotubes, the sulfuric acid-swollen aramid nanofibers, and 0.6 parts of sodium dodecylbenzenesulfonate are added to 80 parts of N-methylpyrrolidone, and dispersed by ball milling to obtain a spinning solution; electrospinning is performed on the surface of the toughened layer under a voltage of 17-25 kV to obtain the tear-resistant layer; The modified carbon nanotubes are prepared as follows: Multi-walled carbon nanotubes are added to a phosphoric acid solution and ultrasonically treated in a constant temperature water bath at 60°C. Then, they are washed and dried with deionized water to obtain phosphorylated carbon nanotubes. Dimethyl terephthalate and 1,4-butanediol are added to a three-necked flask, and the temperature is raised to 180°C under nitrogen protection. Tetrabutyl titanate is added as a catalyst and reacted for 2 hours. The temperature is then raised to 230-255°C, the vacuum is reduced to 50 Pa, and the reaction continues for 3 hours. Ethylene glycol monomethyl ether is added as a terminator, and the reaction is carried out at 230°C to obtain a hydroxyl-terminated polyester oligomer. The hydroxyl-terminated polyester oligomer is dissolved in xylene, and the phosphorylated carbon nanotubes are added. The mixture is ultrasonically dispersed at 120°C, and dicyclohexylcarbodiimide is added. The temperature is raised to 160°C, and the mixture is stirred under nitrogen protection to obtain a reaction solution. The reaction solution is then hot-filtered to obtain the modified carbon nanotubes.

2. The preparation process of a tear-resistant, high-toughness functional polyester film according to claim 1, characterized in that: The substrate layer is prepared as follows: the copolyester particles are dried in a vacuum oven at 120°C for 4 hours to obtain a dried copolyester. Then, the dried copolyester, the triphenyl phosphate, and the tris(2,4-di-tert-butylphenyl) phosphite are added to a twin-screw extruder for melt extrusion to obtain a melt. The die section temperature of the twin-screw extruder is 290-320°C. The melt is then subjected to rapid cooling treatment to obtain the substrate layer.

3. The preparation process of a tear-resistant, high-toughness functional polyester film according to claim 2, characterized in that: The copolyester particles are prepared as follows: 1,4-cyclohexanediethanol, 2,6-naphthalenedicarboxylic acid and terephthalic acid are added to a reaction vessel, nitrogen gas is introduced into the reaction vessel, and the temperature is raised to 180-200℃ for 2.5 h to obtain a pre-esterified product; Continue heating to 250-280℃, while reducing the pressure inside the reactor to 1-10Pa, and react for 4 hours to obtain the polycondensation product; cool the polycondensation product into strips and cut it into granules to obtain the copolyester granules.

4. The preparation process of a tear-resistant, high-toughness functional polyester film according to claim 1, characterized in that: The toughening layer is prepared as follows: 70-85 parts of the polyurethane prepolymer and 10-25 parts of the core-shell toughening agent are stirred and mixed at 90°C for 30 minutes. After adding the photoinitiator, the mixture is ultrasonically dispersed to obtain a mixture. The mixture is coated onto the surface of the substrate layer using the microgravure coating machine. Then, the ultraviolet curing is performed, and the mixture is cured in a 60°C oven for 1 hour to obtain the toughening layer.

5. The preparation process of a tear-resistant, high-toughness functional polyester film according to claim 4, characterized in that: The core-shell toughening agent is prepared as follows: Under nitrogen protection, methyl methacrylate, divinylbenzene and deionized water are mixed and pre-emulsified at 60-80℃. Potassium persulfate initiator is added, and the mixture is heated to 75℃ and reacted for 4 hours to obtain a polymethyl methacrylate core emulsion. The polymethyl methacrylate core emulsion is diluted to a solid content of 10%, glycidyl methacrylate and styrene are added and reacted for 30 minutes. The potassium persulfate initiator is added dropwise, and the mixture is reacted at 70-95℃ for 6 hours. After centrifugation, washing and drying, the core-shell toughening agent is obtained.

6. The preparation process of a tear-resistant, high-toughness functional polyester film according to claim 1, characterized in that: The longitudinal stretching has a stretch ratio of 3.8, a temperature of 105℃, and a speed of 300% / min; the transverse stretching has a stretch ratio of 4.3, a temperature of 115℃, and a speed of 280% / min; the high-temperature setting temperature is 180℃, and the time is 8 minutes; the cooling and winding process first reduces the temperature to 100℃ at a rate of 5℃ / min, then performs room temperature water cooling, with a winding tension of 2.5 N / cm. 2 .

7. A tear-resistant, high-toughness functional polyester film, characterized in that: The polyester film comprises a substrate layer, a toughening layer, a tear-resistant layer, and an interface bonding layer; the polyester film is prepared by the preparation process described in any one of claims 1-6.

Images