Tear-resistant polyester tooth socket film containing nano antibacterial layer and preparation method of tear-resistant polyester tooth socket film

Abstract

The invention discloses a tear-resistant polyester tooth socket film containing a nano antibacterial layer and a preparation method of the tear-resistant polyester tooth socket film. The tooth socket film adopts a three-layer composite structure consisting of an outer layer, a middle layer and an inner layer, the outer layer is composed of PETG, TPU, nano cellulose crystals and a compatilizer, so that the membrane material is endowed with excellent toughness and tear resistance; the middle layer is a high-rigidity supporting layer composed of PCTG and a toughening agent; the inner layer is an antibacterial layer formed by carrying surface modified nano zinc oxide and nano silicon dioxide on light-cured waterborne polyurethane; the preparation method comprises the following steps: S1, respectively preparing each layer of master batch and antibacterial liquid; S2, carrying out three-layer co-extrusion casting to form a base film; and S3, firmly compounding the nano antibacterial layer on the surface of the base film through a micro gravure coating and ultraviolet curing technology. The technical problems that a traditional tooth socket film is not lasting in antibacterial performance, and mechanical strength and light transmittance are difficult to consider at the same time are solved, and the final product has high transparency, excellent tear strength and long-acting antibacterial safety.

Description

Technical Field

[0001] This invention relates to the field of polyester dental brace film preparation technology, specifically to a tear-resistant polyester dental brace film containing a nano-antibacterial layer and its preparation method. Background Technology

[0002] Polyester braces film, a common orthodontic aid, is mainly used to cover the surface of braces, protecting the mucous membrane, preventing scratches, and improving wearing comfort. With increasing demands for oral health and hygiene, braces film not only needs good optical transparency and fit, but is also expected to possess durable antibacterial properties and sufficient mechanical strength to withstand the complex stress conditions experienced during daily wear.

[0003] Most polyester dental braces films on the market are made from ordinary PET or TPU materials through casting or calendering processes. To improve their antibacterial properties, a common technique is to blend in organic antibacterial agents, such as triclosan or quaternary ammonium compounds, into the polyester matrix. In terms of enhancing mechanical properties, toughness is mainly improved by adjusting the molecular weight of the material or by performing biaxial stretching. However, these conventional physical blending and processing methods have inherent limitations in achieving functional integration.

[0004] The key problems that existing technologies cannot solve are as follows: First, physically blended organic antibacterial agents tend to release rapidly in the early stages of use, resulting in a short antibacterial effective period and potential biosafety risks, making it difficult to achieve long-term, stable and safe antibacterial effects. Second, although conventional reinforcement methods can improve toughness to some extent, the material is still prone to irreversible tearing when dealing with complex stresses in the oral cavity. It is often difficult to balance tear resistance and light transmittance, which limits the durability and reliability of the product. Summary of the Invention

[0005] The problem with existing technologies is that existing polyester dental braces films cannot achieve long-lasting, safe antibacterial properties while also maintaining excellent tear resistance and high optical transparency. To address these technical problems, this invention provides a tear-resistant polyester dental brace film containing a nano-antibacterial layer and its preparation method.

[0006] The technical solution of the present invention is: a tear-resistant polyester dental brace film containing a nano-antibacterial layer, the dental brace film being a three-layer composite structure consisting of an outer layer, a middle layer, and an inner layer; by weight, the outer layer is composed of 70-85 parts PETG copolyester, 15-30 parts thermoplastic polyurethane (TPU), 3-8 parts nano-cellulose crystals, and 1-5 parts compatibilizer; the middle layer is composed of 85-100 parts PCTG copolyester and 5-10 parts toughening agent; the inner layer is composed of 80-90 parts light-cured medical-grade waterborne polyurethane (WPU), 5-15 parts nano-zinc oxide modified with a silane coupling agent, 5-10 parts nano-silica, 0.5-2 parts photoinitiator 1173, and 1-3 parts leveling agent.

[0007] Note: The inner layer completely eliminates organic antibacterial agents that pose biosafety risks, constructing a novel inorganic-organic composite antibacterial system composed of surface-modified nano-zinc oxide, nano-silica, and photocurable WPU. This material system design, based on synergistic toughening and isolating slow-release, creates a long-lasting and safe antibacterial layer, resulting in a simultaneous improvement in various performance indicators.

[0008] Furthermore, the toughening agent is MBS resin; the nanocellulose crystals have a particle size of 50-200 nanometers and an aspect ratio of 20-100; and the compatibilizer is maleic anhydride-grafted PETG.

[0009] Explanation: MBS resin was selected to toughen PCTG, effectively improving its brittleness while maintaining high transparency. The particle size and aspect ratio of nanocellulose were precisely controlled, ensuring that it could both act as highly efficient nano-reinforcing points to significantly improve the toughness of the outer layer and perfectly maintain transparency due to its size being much smaller than the wavelength of light. Maleic anhydride-grafted PETG was specified as a compatibilizer, which greatly improved the interfacial compatibility between nanocellulose and the polymer matrix through chemical reaction, preventing agglomeration and allowing the reinforcing effect to be fully realized. The synergy of these three elements is the core of achieving high transparency and high toughness in the outer layer.

[0010] Furthermore, the thickness ratio of the outer layer, the middle layer, and the inner layer is 1-1.5:2-3:0.05-0.1.

[0011] Note: This specific thickness ratio is key to achieving optimal performance. It ensures that the middle layer acts as the main load-bearing framework, providing core rigidity; the outer layer, with its moderate thickness, provides optimal tear resistance without compromising overall flexibility; and the inner layer, as an extremely thin functional layer, achieves maximum antibacterial effect with minimal usage without affecting comfort. This design allows the three layers to complement each other's performance advantages, resulting in an overall balance of rigidity and toughness, and a concentrated range of functions.

[0012] A method for preparing a tear-resistant polyester dental brace film containing a nano-antibacterial layer includes the following steps: S1. Preparation of masterbatch layers: S1.1 Preparation of outer layer masterbatch: According to the formula, PETG copolyester, thermoplastic polyurethane (TPU), nanocellulose crystals and compatibilizer are placed in a high-speed mixer and dried and mixed at 60-80℃ for 2-4 hours. Then, the mixture is melt-blended, extruded and granulated through a first twin-screw extruder to obtain the outer layer masterbatch. S1.2 Preparation of intermediate layer masterbatch: According to the formula, PCTG copolyester and toughening agent are dried and mixed at 50-70℃ for 1-3 hours, and then melt-blended, extruded and granulated by a second twin-screw extruder to obtain intermediate layer masterbatch; S1.3, Preparation of the inner layer antibacterial solution: Nano zinc oxide was dispersed in anhydrous ethanol, wherein the mass-volume ratio of nano zinc oxide to anhydrous ethanol was 1:5-10. Then, 3-8% of silane coupling agent KH-550 was added, and the mixture was magnetically stirred and refluxed at 60-70℃ for 2-4 hours. Subsequently, the mixture was centrifuged, washed, and dried to obtain surface-modified nano zinc oxide. According to the formula, the surface-modified nano zinc oxide and nano silica are added together to the photocurable medical-grade waterborne polyurethane, and then photoinitiator 1173 and leveling agent are added. The mixture is ultrasonically dispersed for 30-60 minutes at 500-800W power using an ultrasonic cell disruptor to obtain a uniform and stable inner antibacterial liquid. S2, Three-layer co-extrusion casting: The outer layer masterbatch obtained in S1.1 and the intermediate layer masterbatch obtained in S1.2 are respectively fed into the corresponding extruders of the three-layer co-extrusion casting film machine. By independently controlling the screw speed of each extruder, the output amount of each layer of melt entering the co-extrusion die is precisely controlled, thereby achieving the target thickness ratio of the outer layer, intermediate layer and inner layer. The temperature of each section of the outer layer extruder is set to 200-240℃, and the temperature of each section of the intermediate layer extruder is set to 190-230℃. After the three-layer composite melt is bonded on the casting roller at 120-150℃ through the T-die, it is cast, cooled and shaped to obtain the base film. The die lip gap of the T-die is set to 0.5-1.0 mm. S3. Coating and curing of the nano-antibacterial layer: The antibacterial liquid prepared in S1.3 is uniformly coated onto the inner surface of the base film described in S2 using a microgravure coating method to obtain a wet film material, which is then cured with ultraviolet light to obtain a tear-resistant polyester dental brace film containing a nano-antibacterial layer.

[0013] Description: This process involves first preparing functionalized outer layer masterbatch, middle layer masterbatch, and inner layer antibacterial liquid separately. Then, a base film with an externally tough and internally rigid mechanical gradient structure is constructed using a three-layer co-extrusion casting technique. Finally, ultraviolet light curing technology is used to firmly bond the nano-antibacterial layer to the inner surface of the base film, forming an integrated three-layer composite functional film. This process effectively overcomes the technical bottlenecks of traditional physical blending methods, such as easy migration of functional components, short shelf life, and difficulty in simultaneously achieving mechanical and optical properties. The process parameters for each step have been systematically optimized and synergistically matched. In particular, the differentiated processing windows set for the characteristics of different functional layer material systems ensure uniform dispersion and interfacial bonding of nano-cellulose crystals in the polymer matrix, achieving efficient molding of the PCTG support layer and guaranteeing stable loading and long-lasting sustained release of the nano-antibacterial components in the photocuring network. The final product exhibits excellent tear resistance, long-lasting broad-spectrum antibacterial activity, excellent optical transparency, and good biocompatibility. Its overall performance far exceeds that of conventional single-layer or existing blended modified dental film products.

[0014] Furthermore, in S1.1, the first twin-screw extruder is divided into five temperature control zones from the feed port to the die head, with the temperatures set as follows: Zone 1, the solid conveying zone, is 190-200℃; Zone 2, the initial melting section, is 200-210℃; Zone 3, the melt mixing section, is 210-220℃; Zone 4, the homogenization and dispersion section, is 220-225℃; and Zone 5, the metering and pressure building section, is 225-230℃. The screw speed of the first twin-screw extruder is 200-400 rpm.

[0015] Note: The gentle gradient of 190-230℃ in the outer layer ensures stable melting of the PETG / TPU matrix, while providing an optimal dispersion window for nanocellulose, avoiding thermal degradation, and ensuring the toughness of the outer layer.

[0016] Furthermore, in S1.2, the second twin-screw extruder is divided into five temperature control zones from the feed port to the die head, with the temperatures set as follows: Zone 1, the solid conveying and preheating zone, is 220-230℃; Zone 2, the initial melting section, is 230-240℃; Zone 3, the melt mixing section, is 240-250℃; Zone 4, the homogenization and dispersion section, is 250-255℃; and Zone 5, the metering and pressure building section, is 255-260℃. The screw speed of the second twin-screw extruder is 200-400 rpm.

[0017] Note: The higher temperature profile of the intermediate layer (220-260℃) matches the processing characteristics of PCTG, ensuring thorough blending with MBS and imparting high rigidity to the intermediate layer. These two sets of customized temperature parameters are fundamental to optimizing the performance of each masterbatch layer.

[0018] Furthermore, the wet film thickness of the wet film material described in S3 is controlled to be 10-30 micrometers.

[0019] Note: Precisely controlling the wet film thickness to 10-30 micrometers is key to achieving a high-performance nano-antibacterial layer. This thickness allows for the formation of a continuous, dense functional coating: too thin a coating may result in incomplete coating and uneven antibacterial effect; too thick a coating may lead to poor curing, increased internal stress, and reduced transparency. This optimized thickness ensures long-lasting antibacterial effects while perfectly balancing coating adhesion, flexibility, and overall optical performance.

[0020] Further, the ultraviolet curing method described in S3 is as follows: the wet film material is passed through an ultraviolet curing device at a speed of 3-10 m / min, under a nitrogen protection environment, using a wavelength of 365nm and an intensity of 800-1200mJ / cm. 2 The material is cured by ultraviolet light to form a stable nano-antibacterial layer, resulting in a tear-resistant polyester dental film containing the nano-antibacterial layer.

[0021] Note: The UV curing process, combined with a nitrogen-protected environment, sets optimal curing conditions for the coating. Specific light intensity and linear velocity ensure efficient photoinitiator reaction, while nitrogen protection crucially eliminates the oxygen inhibition effect, enabling deep curing of the coating and achieving high hardness, high wear resistance, and anti-extraction properties, thus ensuring the long-lasting stability and safety of the antibacterial layer.

[0022] Furthermore, the length-to-diameter ratio of the screws of the first twin-screw extruder and the second twin-screw extruder in S1 is 40-48:1, respectively.

[0023] Note: This aspect ratio provides sufficient melting and mixing space and residence time for the material, ensuring that the nanocellulose is dispersed at the nanoscale in the outer matrix and avoiding agglomeration; at the same time, it ensures that PCTG is fully plasticized in the middle layer and uniformly compatible with MBS. This is a prerequisite for obtaining a masterbatch with uniform performance and excellent quality.

[0024] The beneficial effects of this invention are: This invention achieves significant beneficial effects through a three-layer composite structure design. In the outer layer, 70-85 parts PETG and 15-30 parts TPU constitute a matrix with a balanced rigidity and toughness. The introduction of 3-8 parts nanofiber cellulose crystals is crucial; after bonding with the matrix interface, they produce a significant synergistic toughening effect with TPU. This is not a simple superposition, but rather acts as nano-reinforcing points, greatly dissipating impact energy by inducing crazing and deflection cracks, resulting in a leap in tear resistance. Simultaneously, due to its nano-size effect, it has minimal impact on transparency. The middle layer, consisting of 85-100 parts high-rigidity PCTG, serves as a supporting framework, forming a biomimetic structure with an outer toughness and inner rigidity. When facing complex stresses, the outer layer effectively disperses stress through deformation, while the inner layer provides robust resistance, jointly ensuring the overall tear resistance and dimensional stability of the membrane material. Its effect is far superior to that of a single homogeneous material. In the inner layer design, 5-15 parts of surface-modified nano-zinc oxide and 5-10 parts of nano-silica form a unique physical blend isolation structure in the UV-cured WPU. The nano-silica not only acts as a dispersing carrier but also effectively slows down the ion release rate of the nano-zinc oxide, thus achieving a long-lasting antibacterial effect. Furthermore, UV curing technology firmly anchors it, avoiding the rapid migration and dissolution problems of traditional blended antibacterial agents. The components of each layer interact and complement each other under their specific proportions, ultimately enabling the dental liner film to simultaneously possess excellent tear resistance, high transparency, long-lasting antibacterial properties, and safety in use, comprehensively solving the technical problems that existing technologies struggle to address simultaneously. Detailed Implementation

[0025] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0026] Example 1: A tear-resistant polyester dental brace film with a nano-antibacterial layer, comprising a three-layer composite structure of an outer layer, a middle layer, and an inner layer; by weight, the outer layer consists of 77 parts PETG copolyester, 23 parts thermoplastic polyurethane (TPU), 5 parts nanocellulose crystals, and 3 parts compatibilizer; the middle layer consists of 90 parts PCTG copolyester and 8 parts toughening agent; the inner layer consists of 85 parts light-cured medical-grade waterborne polyurethane (WPU), 10 parts nano zinc oxide modified with a silane coupling agent, 8 parts nano silica, 1 part photoinitiator 1173, and 2 parts leveling agent; the toughening agent is MBS resin; the nanocellulose crystals have a particle size of 100-150 nm and an aspect ratio of 60; the compatibilizer is maleic anhydride-grafted PETG; the thickness ratio of the outer, middle, and inner layers is 1.25:2.5:0.06.

[0027] Example 2: This example is basically the same as Example 1, except that the dental aligner membrane is a three-layer composite structure consisting of an outer layer, a middle layer, and an inner layer. By weight, the outer layer consists of 70 parts PETG copolyester, 15 parts thermoplastic polyurethane (TPU), 3 parts nanocellulose crystals, and 1 part compatibilizer. The middle layer consists of 85 parts PCTG copolyester and 5 parts toughening agent. The inner layer consists of 80 parts light-cured medical-grade waterborne polyurethane (WPU), 5 parts nano zinc oxide modified with a silane coupling agent, 5 parts nano silica, 0.5 parts photoinitiator 1173, and 1 part leveling agent. The toughening agent is MBS resin. The nanocellulose crystals have a particle size of 50-60 nanometers and an aspect ratio of 20. The compatibilizer is maleic anhydride-grafted PETG. The thickness ratio of the outer, middle, and inner layers is 1:2:0.05.

[0028] Example 3: This example is basically the same as Example 1, except that the dental aligner membrane is a three-layer composite structure consisting of an outer layer, a middle layer, and an inner layer. By weight, the outer layer consists of 85 parts PETG copolyester, 30 parts thermoplastic polyurethane (TPU), 8 parts nanocellulose crystals, and 5 parts compatibilizer. The middle layer consists of 100 parts PCTG copolyester and 10 parts toughening agent. The inner layer consists of 90 parts light-cured medical-grade waterborne polyurethane (WPU), 15 parts nano zinc oxide modified with a silane coupling agent, 10 parts nano silica, 2 parts photoinitiator 1173, and 3 parts leveling agent. The toughening agent is MBS resin. The nanocellulose crystals have a particle size of 150-200 nanometers and an aspect ratio of 100. The compatibilizer is maleic anhydride-grafted PETG. The thickness ratio of the outer, middle, and inner layers is 1.5:3:0.1.

[0029] Example 4: This example is a method for preparing the tear-resistant polyester dental aligner film containing a nano-antibacterial layer as described in Example 1, except that it includes the following steps: S1. Preparation of masterbatch layers: S1.1 Preparation of outer layer masterbatch: According to the formula, PETG copolyester, thermoplastic polyurethane (TPU), nano-cellulose crystals, and compatibilizer are placed in a high-speed mixer and dried and mixed at 70°C for 3 hours. Then, the mixture is melt-blended, extruded, and granulated using a first twin-screw extruder to obtain the outer layer masterbatch. The first twin-screw extruder is divided into five temperature control zones from the feed port to the die head, with the following temperature settings: Zone 1 (solid conveying zone) is 195°C, Zone 2 (melting initiation zone) is 205°C, Zone 3 (melting and mixing zone) is 215°C, Zone 4 (homogenization and dispersion zone) is 223°C, and Zone 5 (metering and pressure building zone) is 228°C. The screw speed of the first twin-screw extruder is 300 rpm. S1.2 Preparation of intermediate layer masterbatch: PCTG copolyester and toughening agent were dried and mixed at 60°C for 2 hours according to the formula. Then, the mixture was melt-blended, extruded, and granulated using a second twin-screw extruder to obtain the intermediate layer masterbatch. The second twin-screw extruder was divided into five temperature control zones from the feed port to the die head, with the following temperature settings: Zone 1 (solid conveying and preheating zone) was 225°C, Zone 2 (melting initiation zone) was 235°C, Zone 3 (melting and mixing zone) was 245°C, Zone 4 (homogenization and dispersion zone) was 252°C, and Zone 5 (metering and pressure building zone) was 258°C. The screw speed of the second twin-screw extruder was 300 rpm. The length-to-diameter ratio of the screws of the first and second twin-screw extruders was 44:1. S1.3, Preparation of the inner layer antibacterial solution: Nano zinc oxide was dispersed in anhydrous ethanol, wherein the mass-volume ratio of nano zinc oxide to anhydrous ethanol was 1:8. Then, 5% of the weight of nano zinc oxide silane coupling agent KH-550 was added. The mixture was magnetically stirred and refluxed at 65°C for 3 hours. Subsequently, it was centrifuged, washed, and dried to obtain surface-modified nano zinc oxide. According to the formula, the surface-modified nano zinc oxide and nano silica are added together to the photocurable medical-grade waterborne polyurethane, and then photoinitiator 1173 and leveling agent are added. The mixture is then ultrasonically dispersed for 45 minutes at 650W power using an ultrasonic cell disruptor to obtain a uniform and stable inner antibacterial liquid. S2, Three-layer co-extrusion casting: The outer layer masterbatch obtained in S1.1 and the intermediate layer masterbatch obtained in S1.2 are respectively fed into the corresponding extruders of the three-layer co-extrusion casting film machine. By independently controlling the screw speed of each extruder, the output amount of each layer of melt entering the co-extrusion die is precisely controlled, thereby achieving the target thickness ratio of the outer layer, intermediate layer and inner layer. The temperature of each section of the outer layer extruder is set to 220℃, and the temperature of each section of the intermediate layer extruder is set to 210℃. After the three-layer composite melt is bonded on the casting roller at 135℃ through a T-die, it is cast, cooled and shaped to obtain the base film. The die lip gap of the T-die is set to 0.8 mm. S3. Coating and curing of the nano-antibacterial layer: The antibacterial liquid prepared in S1.3 is uniformly coated onto the inner surface of the base film described in S2 using a microgravure coating method to obtain a wet film material. This wet film material is then cured under ultraviolet light to obtain a tear-resistant polyester dental brace film containing a nano-antibacterial layer. The wet film thickness is controlled to be 20 micrometers. The ultraviolet curing method is as follows: the wet film material is passed through an ultraviolet curing device at a speed of 7 m / min under nitrogen protection, using a wavelength of 365 nm and an intensity of 1000 mJ / cm. 2 The material is cured by ultraviolet light to form a stable nano-antibacterial layer, resulting in a tear-resistant polyester dental film containing the nano-antibacterial layer.

[0030] Example 5: This example is basically the same as Example 4, except that in S1.1, the first twin-screw extruder is divided into five temperature control zones from the feed port to the die head. The temperature is set as follows: Zone 1, the solid conveying zone, is 190°C; Zone 2, the initial melting section, is 200°C; Zone 3, the melt mixing section, is 210°C; Zone 4, the homogenization and dispersion section, is 220°C; and Zone 5, the metering and pressure building section, is 225°C. The screw speed of the first twin-screw extruder is 200 rpm.

[0031] Example 6: This example is basically the same as Example 4, except that in S1.1, the first twin-screw extruder is divided into five temperature control zones from the feed port to the die head. The temperatures are set as follows: Zone 1, the solid conveying zone, is 200°C; Zone 2, the initial melting section, is 210°C; Zone 3, the melt mixing section, is 220°C; Zone 4, the homogenization and dispersion section, is 225°C; and Zone 5, the metering and pressure building section, is 230°C. The screw speed of the first twin-screw extruder is 400 rpm.

[0032] Example 7: This example is basically the same as Example 4, except that in S1.2, the second twin-screw extruder is divided into five temperature control zones from the feed port to the die head. The temperature is set as follows: Zone 1, the solid conveying and preheating zone, is 220°C; Zone 2, the initial melting section, is 230°C; Zone 3, the melt mixing section, is 240°C; Zone 4, the homogenization and dispersion section, is 250°C; and Zone 5, the metering and pressure building section, is 255°C. The screw speed of the second twin-screw extruder is 200 rpm.

[0033] Example 8: This example is basically the same as Example 4, except that in S1.2, the second twin-screw extruder is divided into five temperature control zones from the feed port to the die head. The temperature is set as follows: Zone 1, the solid conveying and preheating zone, is 230°C; Zone 2, the initial melting section, is 240°C; Zone 3, the melt mixing section, is 250°C; Zone 4, the homogenization and dispersion section, is 255°C; and Zone 5, the metering and pressure building section, is 260°C. The screw speed of the second twin-screw extruder is 400 rpm.

[0034] Example 9: This example is basically the same as Example 4, except that the wet film thickness of the wet film material in S3 is controlled to be 10 micrometers; the ultraviolet curing method is as follows: the wet film material is passed through an ultraviolet curing device at a speed of 3 m / min, under nitrogen protection, using a wavelength of 365 nm and an intensity of 800 mJ / cm. 2 The material is cured by ultraviolet light to form a stable nano-antibacterial layer, resulting in a tear-resistant polyester dental film containing the nano-antibacterial layer.

[0035] Example 10: This example is basically the same as Example 4, except that the wet film thickness of the wet film material in S3 is controlled to be 30 micrometers; the ultraviolet curing method is as follows: the wet film material is passed through an ultraviolet curing device at a speed of 10 m / min, under nitrogen protection, using a wavelength of 365 nm and an intensity of 1200 mJ / cm. 2 The material is cured by ultraviolet light to form a stable nano-antibacterial layer, resulting in a tear-resistant polyester dental film containing the nano-antibacterial layer.

[0036] Example 11: This example is basically the same as Example 4, except that the length-to-diameter ratio of the screws of the first twin-screw extruder and the second twin-screw extruder in S1 is 40:1.

[0037] Example 12: This example is basically the same as Example 4, except that the length-to-diameter ratio of the screws of the first twin-screw extruder and the second twin-screw extruder in S1 is 48:1.

[0038] Example 13: This example is basically the same as Example 4, except that it includes the following steps: S1. Preparation of masterbatch layers: S1.1 Preparation of outer layer masterbatch: According to the formula, PETG copolyester, thermoplastic polyurethane (TPU), nanocellulose crystals and compatibilizer are placed in a high-speed mixer, dried and mixed at 60°C for 2 hours, and then melt-blended, extruded and granulated through a first twin-screw extruder to obtain the outer layer masterbatch. The first twin-screw extruder is divided into five temperature control zones from the feed port to the die head, with the following temperature settings: Zone 1 (solid conveying zone) is 190℃, Zone 2 (melting initiation zone) is 200℃, Zone 3 (melting and mixing zone) is 210℃, Zone 4 (homogenization and dispersion zone) is 220℃, and Zone 5 (metering and pressure building zone) is 225℃; the screw speed of the first twin-screw extruder is 200 rpm. S1.2 Preparation of intermediate layer masterbatch: PCTG copolyester and toughening agent were dried and mixed at 50°C for 1 hour according to the formula, and then melt-blended, extruded and granulated by a second twin-screw extruder to obtain intermediate layer masterbatch; The second twin-screw extruder is divided into five temperature control zones from the feed port to the die head. The temperature settings are as follows: Zone 1, the solid conveying and preheating zone, is 220°C; Zone 2, the initial melting section, is 230°C; Zone 3, the melt mixing section, is 240°C; Zone 4, the homogenization and dispersion section, is 250°C; and Zone 5, the metering and pressure building section, is 255°C. The screw speed of the second twin-screw extruder is 200 rpm. S1.3, Preparation of the inner layer antibacterial solution: Nano zinc oxide was dispersed in anhydrous ethanol, wherein the mass-volume ratio of nano zinc oxide to anhydrous ethanol was 1:5. Then, 3% of the weight of nano zinc oxide silane coupling agent KH-550 was added. The mixture was magnetically stirred and refluxed at 60°C for 2 hours. Subsequently, it was centrifuged, washed, and dried to obtain surface-modified nano zinc oxide. According to the formula, the surface-modified nano zinc oxide and nano silica are added together to the photocurable medical-grade waterborne polyurethane, and then photoinitiator 1173 and leveling agent are added. The mixture is then ultrasonically dispersed for 30 minutes at 500W power using an ultrasonic cell disruptor to obtain a uniform and stable inner layer antibacterial liquid. The length-to-diameter ratio of the screws in the first twin-screw extruder and the second twin-screw extruder is 40:1, respectively; S2, Three-layer co-extrusion casting: The outer layer masterbatch obtained in S1.1 and the intermediate layer masterbatch obtained in S1.2 are respectively fed into the corresponding extruders of the three-layer co-extrusion casting film machine. By independently controlling the screw speed of each extruder, the output amount of each layer of melt entering the co-extrusion die is precisely controlled, thereby achieving the target thickness ratio of the outer layer, intermediate layer and inner layer. The temperature of each section of the outer layer extruder is set to 200℃, and the temperature of each section of the intermediate layer extruder is set to 190℃. After the three-layer composite melt is bonded on the casting roller at 120℃ through the T-die, it is cast, cooled and shaped to obtain the base film. The die lip gap of the T-die is set to 0.5 mm. S3. Coating and curing of the nano-antibacterial layer: The antibacterial liquid prepared in S1.3 is uniformly coated onto the inner surface of the base film described in S2 using a microgravure coating method to obtain a wet film material. Then, it is cured with ultraviolet light to obtain a tear-resistant polyester dental brace film containing a nano-antibacterial layer. The wet film thickness of the wet film material is controlled to be 10 micrometers. The ultraviolet curing method is as follows: the wet film material is passed through an ultraviolet curing device at a speed of 3 m / min, under nitrogen protection, using a wavelength of 365 nm and an intensity of 800 mJ / cm. 2 The material is cured by ultraviolet light to form a stable nano-antibacterial layer, resulting in a tear-resistant polyester dental film containing the nano-antibacterial layer.

[0039] Example 14: This example is basically the same as Example 4, except that it includes the following steps: S1. Preparation of masterbatch layers: S1.1 Preparation of outer layer masterbatch: According to the formula, PETG copolyester, thermoplastic polyurethane (TPU), nanocellulose crystals and compatibilizer are placed in a high-speed mixer, dried and mixed at 80°C for 4 hours, and then melt-blended, extruded and granulated through a first twin-screw extruder to obtain the outer layer masterbatch. The first twin-screw extruder is divided into five temperature control zones from the feed port to the die head, with the following temperature settings: Zone 1 (solid conveying zone) is 200℃, Zone 2 (melting initiation zone) is 210℃, Zone 3 (melting and mixing zone) is 220℃, Zone 4 (homogenization and dispersion zone) is 225℃, and Zone 5 (metering and pressure building zone) is 230℃; the screw speed of the first twin-screw extruder is 400 rpm. S1.2 Preparation of intermediate layer masterbatch: According to the formula, PCTG copolyester and toughening agent are dried and mixed at 70°C for 3 hours, and then melt-blended, extruded and granulated by a second twin-screw extruder to obtain intermediate layer masterbatch; The second twin-screw extruder is divided into five temperature control zones from the feed port to the die head. The temperature settings are as follows: Zone 1, the solid conveying and preheating zone, is 230°C; Zone 2, the initial melting section, is 240°C; Zone 3, the melt mixing section, is 250°C; Zone 4, the homogenization and dispersion section, is 255°C; and Zone 5, the metering and pressure building section, is 260°C. The screw speed of the second twin-screw extruder is 400 rpm. S1.3, Preparation of the inner layer antibacterial solution: Nano zinc oxide was dispersed in anhydrous ethanol, wherein the mass-volume ratio of nano zinc oxide to anhydrous ethanol was 1:10. Then, 8% of the weight of nano zinc oxide silane coupling agent KH-550 was added. The mixture was magnetically stirred and refluxed at 70°C for 4 hours. Subsequently, it was centrifuged, washed, and dried to obtain surface-modified nano zinc oxide. According to the formula, the surface-modified nano zinc oxide and nano silica are added together to the photocurable medical-grade waterborne polyurethane, and then photoinitiator 1173 and leveling agent are added. The mixture is then ultrasonically dispersed for 60 minutes at 800W power using an ultrasonic cell disruptor to obtain a uniform and stable inner layer antibacterial liquid. The length-to-diameter ratio of the screws in the first twin-screw extruder and the second twin-screw extruder is 48:1, respectively. S2, Three-layer co-extrusion casting: The outer layer masterbatch obtained in S1.1 and the intermediate layer masterbatch obtained in S1.2 are respectively fed into the corresponding extruders of the three-layer co-extrusion casting film machine. By independently controlling the screw speed of each extruder, the output amount of each layer of melt entering the co-extrusion die is precisely controlled, thereby achieving the target thickness ratio of the outer layer, intermediate layer and inner layer. The temperature of each section of the outer layer extruder is set to 240℃, and the temperature of each section of the intermediate layer extruder is set to 230℃. After the three-layer composite melt is bonded on the casting roller at 150℃ through a T-die, it is cast, cooled and shaped to obtain the base film. The die lip gap of the T-die is set to 1.0 mm. S3. Coating and curing of the nano-antibacterial layer: The antibacterial liquid prepared in S1.3 is uniformly coated onto the inner surface of the base film described in S2 using a microgravure coating method to obtain a wet film material. Then, it is cured with ultraviolet light to obtain a tear-resistant polyester dental brace film containing a nano-antibacterial layer. The wet film thickness of the wet film material is controlled to be 30 micrometers. The ultraviolet curing method is as follows: the wet film material is passed through an ultraviolet curing device at a speed of 10 m / min, under a nitrogen protection environment, using a wavelength of 365 nm and an intensity of 1200 mJ / cm. 2 The material is cured by ultraviolet light to form a stable nano-antibacterial layer, resulting in a tear-resistant polyester dental film containing the nano-antibacterial layer.

[0040] Comparative Example 1: This comparative example has the same product composition as Example 1, but its structure is a single-layer film instead of a three-layer composite structure. According to the material ratio of Example 1, all raw materials for the outer layer, middle layer, and inner layer are mixed at one time, melt-blended and cast in a twin-screw extruder, and then coated with an antibacterial layer and cured according to the same process as in Example 4, to verify the necessity of the three-layer composite structure.

[0041] Comparative Example 2: This comparative example has the same three-layer structure and thickness ratio as Example 1, but the preparation of its inner antibacterial liquid is different: instead of adding surface-modified nano zinc oxide and nano silica, the same weight of 18 parts of traditional organic antibacterial agent triclosan is directly added to the aqueous polyurethane to verify the advantages of the nanocomposite inorganic antibacterial system compared with traditional organic antibacterial agents.

[0042] Comparative Example 3: This comparative example uses the same raw materials and structure as Example 4, but in the preparation process, the twin-screw extruders in steps S1.1 and S1.2 use a uniform conventional polyester processing temperature, with all temperature control zones at 200°C. In step S1, the length-to-diameter ratio of the screws of the first and second twin-screw extruders is 30:1, respectively, to verify the effect of refined extrusion process parameters on the performance of specific materials.

[0043] Comparative Example 4: This comparative example uses the same raw materials and structure as Example 4, but in the preparation process, the ultraviolet curing in step S3 is not carried out under nitrogen protection, but is cured in air with the same parameters.

[0044] To investigate the tear-resistant polyester dental brace film performance of the above examples and control examples, the main materials were determined according to the experimental formulation, and samples were obtained for testing. Light transmittance and haze were measured using a haze meter equipped with an integrating sphere, according to ASTM D1003. Tear strength was tested according to the Elemandorf tear test (ASTM D1922) to measure the toughness of the film material. Antibacterial performance was quantitatively tested against Escherichia coli ATCC 25922 according to national standard GB / T 31402, with a particular focus on the antibacterial rate after 7 days to verify its durability. Coating adhesion was evaluated using the cross-cut adhesion test (ASTM D3359), with grade 0 being the best and grade 5 the worst; the results are shown in Table 1. Specific investigations are as follows: Table 1 Performance test results of tear-resistant polyester dental brace film samples from Examples 1-14 and Control Examples 1-4

[0045] 1. Investigate the influence of the composition and ratio of each layer of materials on the overall performance of the dental liner: A comparison of Examples 1-3 shows that Example 1 maintains the best balance in tear resistance, light transmittance, and antibacterial rate, exhibiting superior overall performance. Changing the raw material ratio parameters significantly affects the performance of the prepared polyester dental brace film sample. Example 2 has the lowest tear resistance due to its low nanocellulose content. A comparison of Examples 4, 9, and 10 shows that Example 4 uses the same preparation method as Example 1, and the test results are the same as Example 1. Example 10 has the best antibacterial performance because it has the largest wet film thickness, allowing for a more sufficient loading of nano-antibacterial agents and resulting in a better long-lasting antibacterial effect. Changing the type and ratio parameters of the raw materials in each layer has a synergistic effect on the mechanical, optical, and antibacterial properties of the film material. Compared with Control Examples 1 and 2, it can be seen that the overall performance of the samples using a single-layer structure or traditional organic antibacterial agents is significantly reduced. The antibacterial rate of Control Example 2 decreases sharply due to the migration of antibacterial agents, and its coating adhesion is also significantly worse than that of Example 1. It can be seen that the three-layer composite structure and nano-inorganic antibacterial system of the present invention are the key to achieving high performance. The polyester dental film prepared by the material ratio scheme of Example 1 has the best overall performance.

[0046] 2. Investigate the influence of extrusion process parameters on the properties of the base film: A comparison of Examples 1, 5, 6, 7, 8 and 13, 14 shows that Examples 1 and 14 have the best overall performance. Example 13 uses lower process parameters, resulting in a significant decrease in both tear strength and light transmittance. In contrast, Example 14 uses process parameters that achieve better mechanical properties and light transmittance. Example 6 uses higher screw speed and temperature, resulting in better tear strength than Example 5. However, the excessively high temperature caused a slight decrease in light transmittance in Example 8. Changing the screw speed and temperature parameters will have a significant impact on the dispersion uniformity and mechanical properties of the base film. Compared with Example 3, which was processed at a conventional temperature, its tear resistance and light transmittance were significantly lower than those of the Example, proving that the precise temperature control of the present invention plays a decisive role in the dispersion and interfacial bonding of nanocellulose.

[0047] 3. Investigate the impact of antibacterial layer coating and curing processes on the performance of functional layers: A comparison of Examples 1, 9, and 10 shows that the sample prepared according to the method of Example 1 achieves the best balance between antibacterial properties, adhesion, and light transmittance. Example 9 has slightly lower antibacterial durability than Example 10 due to its thinner wet film thickness, but its coating adhesion is better. This indicates that the coating thickness and curing process have a regulatory effect on the performance of the functional layer. In Comparative Example 4, which did not use nitrogen protection for curing, the coating adhesion decreased significantly, confirming that the inert atmosphere has a key influence on the degree of photocuring. The antibacterial layer prepared using the parameters within the scope of this invention performed better in terms of durability and bonding strength.

[0048] 4. Investigate the synergistic effects of screw configuration and process combination on material properties: A comparison of Examples 1, 11, and 12 shows that Example 1, with a screw having a length-to-diameter ratio of 44:1, exhibits the best overall performance. Example 12, with a higher length-to-diameter ratio, shows a slight increase in tear resistance but a slight decrease in light transmittance, indicating that the screw configuration needs to be matched with the material system. A comprehensive comparison of Example 1 with Comparative Examples 1, 3, and 4 shows that any deviation from the parameters of this invention, such as single-layer structure, conventional extrusion, or lack of nitrogen protection, will lead to significant performance degradation. This confirms that there is a close synergistic effect between the material combination, process parameters, and structural design provided by this invention. The overall performance of the polyester dental film prepared using the full-process parameters of this invention is significantly better than that of the prior art.

Claims

1. A tear-resistant polyester dental brace film containing a nano-antibacterial layer, characterized in that, The dental aligner membrane is a three-layer composite structure consisting of an outer layer, a middle layer, and an inner layer. By weight, the outer layer is composed of 70-85 parts PETG copolyester, 15-30 parts thermoplastic polyurethane (TPU), 3-8 parts nano-cellulose crystals, and 1-5 parts compatibilizer. The middle layer is composed of 85-100 parts PCTG copolyester and 5-10 parts toughening agent. The inner layer is composed of 80-90 parts light-cured medical-grade waterborne polyurethane (WPU), 5-15 parts nano-zinc oxide modified with silane coupling agent, 5-10 parts nano-silica, 0.5-2 parts photoinitiator 1173, and 1-3 parts leveling agent.

2. The tear-resistant polyester dental brace film containing a nano-antibacterial layer according to claim 1, characterized in that, The toughening agent is MBS resin; the nanocellulose crystals have a particle size of 50-200 nanometers and an aspect ratio of 20-100; the compatibilizer is maleic anhydride-grafted PETG.

3. The tear-resistant polyester dental brace film containing a nano-antibacterial layer according to claim 1, characterized in that, The thickness ratio of the outer layer, middle layer and inner layer is 1-1.5:2-3:0.05-0.

1.

4. The method for preparing a tear-resistant polyester dental brace film containing a nano-antibacterial layer according to claim 1, characterized in that, Includes the following steps: S1. Preparation of masterbatch layers: S1.1 Preparation of outer layer masterbatch: According to the formula, PETG copolyester, thermoplastic polyurethane (TPU), nanocellulose crystals and compatibilizer are placed in a high-speed mixer and dried and mixed at 60-80℃ for 2-4 hours. Then, the mixture is melt-blended, extruded and granulated through a first twin-screw extruder to obtain the outer layer masterbatch. S1.2 Preparation of intermediate layer masterbatch: According to the formula, PCTG copolyester and toughening agent are dried and mixed at 50-70℃ for 1-3 hours, and then melt-blended, extruded and granulated by a second twin-screw extruder to obtain intermediate layer masterbatch; S1.3, Preparation of the inner layer antibacterial solution: Nano zinc oxide was dispersed in anhydrous ethanol, wherein the mass-volume ratio of nano zinc oxide to anhydrous ethanol was 1:5-10. Then, 3-8% of silane coupling agent KH-550 was added, and the mixture was magnetically stirred and refluxed at 60-70℃ for 2-4 hours. Subsequently, the mixture was centrifuged, washed, and dried to obtain surface-modified nano zinc oxide. According to the formula, the surface-modified nano zinc oxide and nano silica are added together to the photocurable medical-grade waterborne polyurethane, and then photoinitiator 1173 and leveling agent are added. The mixture is then ultrasonically dispersed for 30-60 minutes at 500-800W power using an ultrasonic cell disruptor to obtain the inner antibacterial liquid. S2, Three-layer co-extrusion casting: The outer layer masterbatch obtained in S1.1 and the intermediate layer masterbatch obtained in S1.2 are respectively fed into the corresponding extruders of the three-layer co-extrusion casting film machine. The temperature of each section of the outer layer extruder is set to 200-240℃, and the temperature of each section of the intermediate layer extruder is set to 190-230℃. The three-layer composite melt is bonded on the casting roller at 120-150℃ through a T-die, and then cast, cooled and shaped to obtain the base film. S3. Coating and curing of the nano-antibacterial layer: The inner antibacterial liquid prepared in S1.3 is uniformly coated onto the inner surface of the base film described in S2 to obtain a wet film material, which is then cured with ultraviolet light to obtain a tear-resistant polyester dental brace film containing a nano antibacterial layer.

5. The method for preparing a tear-resistant polyester dental brace film containing a nano-antibacterial layer according to claim 4, characterized in that, In S1.1, the first twin-screw extruder is divided into five temperature control zones from the feed port to the die head, with the temperature settings as follows: Zone 1 is 190-200℃, Zone 2 is 200-210℃, Zone 3 is 210-220℃, Zone 4 is 220-225℃, and Zone 5 is 225-230℃; the screw speed of the first twin-screw extruder is 200-400 rpm.

6. The method for preparing a tear-resistant polyester dental brace film containing a nano-antibacterial layer according to claim 4, characterized in that, In S1.2, the second twin-screw extruder is divided into five temperature control zones from the feed port to the die head, with the temperature settings as follows: Zone 1 is 220-230℃, Zone 2 is 230-240℃, Zone 3 is 240-250℃, Zone 4 is 250-255℃, and Zone 5 is 255-260℃; the screw speed of the second twin-screw extruder is 200-400 rpm.

7. The method for preparing a tear-resistant polyester dental brace film containing a nano-antibacterial layer according to claim 4, characterized in that, The wet film thickness of the wet film material described in S3 is controlled to be 10-30 micrometers.

8. The method for preparing a tear-resistant polyester dental brace film containing a nano-antibacterial layer according to claim 4, characterized in that, The UV curing method described in S3 is as follows: the wet film material is passed through a UV curing device at a speed of 3-10 m / min, under a nitrogen protection environment, using a wavelength of 365nm and an intensity of 800-1200mJ / cm. 2 The film is cured by irradiation with ultraviolet light to obtain a tear-resistant polyester dental crown film containing a nano-antibacterial layer.

9. The method for preparing a tear-resistant polyester dental brace film containing a nano-antibacterial layer according to claim 4, characterized in that, The length-to-diameter ratio of the screws in the first and second twin-screw extruders S1 is 40-48:1, respectively.

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