High-barrier composite film and preparation method thereof

Abstract

The invention discloses a high-barrier composite film and a preparation method thereof. The high-barrier composite film at least sequentially comprises a substrate layer, a barrier layer and a heat sealing layer, the substrate layer is a polyester layer, the substrate layer and the blocking layer are compounded through an adhesive layer, and the blocking layer and the heat sealing layer are compounded through an adhesive layer. According to the high-barrier composite film, the hydrotalcite modified by a specific method is introduced into an ethylene-vinyl alcohol copolymer matrix, the toughening agent and the compatilizer are supplemented for melt blending, the prepared barrier layer film is high in compactness and good in compatibility, the barrier layer, the substrate layer and the heat sealing layer are prepared into a multi-layer film through a dry-method compounding process, and the high-barrier composite film is high in barrier property and high in barrier property. The final product not only shows excellent gas barrier property and meets the application requirements of high-performance packaging materials, but also has good mechanical properties, processability and interlayer composite strength, and the overall structure is stable and reliable.

Description

Technical Field

[0001] This invention belongs to the field of composite thin film materials technology, specifically relating to a high-barrier composite thin film and its preparation method. Background Technology

[0002] High-barrier composite films are multilayer plastic films that exhibit high barrier properties against gases (such as oxygen, nitrogen, and carbon dioxide) and / or liquids (such as water vapor, oil, and alcohol). In numerous fields, including food, pharmaceuticals, medical devices, and precision electronic components, the barrier properties of packaging materials are key performance indicators for ensuring the quality of contents, extending shelf life, and preventing oxidative deterioration or moisture-induced failure. Particularly in the food packaging sector, excellent oxygen and water vapor barrier properties effectively inhibit microbial growth and preserve food flavor and nutrition. Therefore, the development and application of high-performance barrier films have significant commercial value and practical implications.

[0003] Currently, one of the most widely used high-barrier resin materials in industry is ethylene-vinyl alcohol copolymer (EVOH). EVOH molecules contain a large number of hydroxyl groups (-OH), which can form strong intramolecular and intermolecular hydrogen bonds, resulting in a tight packing of polymer segments and exhibiting extremely low permeability to nonpolar gases such as oxygen. However, pure EVOH resin still has some inherent shortcomings in practical applications. First, EVOH materials are rigid and brittle, easily cracking due to bending or impact during processing and use, leading to localized loss of barrier properties. Second, the hydrophilic hydroxyl groups on the EVOH molecular chain make it highly sensitive to water molecules. In high-humidity environments, water molecules can penetrate into the EVOH matrix, disrupting its hydrogen bond network, weakening the dense structure of the stacked segments, and drastically reducing gas barrier performance.

[0004] To overcome the aforementioned shortcomings, existing technologies typically employ physical blending modification to improve the overall performance of EVOH-based composites. A common approach is to add toughening agents (such as elastomers) to EVOH to improve its flexibility and impact resistance, while simultaneously adding compatibilizers to ensure the homogeneity and stability of the blend system. Another, more fundamental approach is to fill the EVOH matrix with inorganic nanofillers, using these fillers to extend the permeation path of gas molecules, thereby further enhancing the material's barrier properties. Commonly used inorganic fillers include montmorillonite, kaolin, and nano-silica. By melt-blending these fillers with EVOH, the material's barrier properties can be enhanced to a certain extent.

[0005] However, existing blending modification methods still have significant technical shortcomings. The core issue lies in the inherent interfacial incompatibility between inorganic fillers and the organic polymer matrix. Inorganic fillers are typically hydrophilic, while the polymer matrix is ​​an organic phase, resulting in very weak interfacial bonding. During melt blending, inorganic filler particles are prone to agglomeration, making it difficult to achieve uniform nanoscale dispersion within the matrix. This leads to stress concentration points, affecting the material's mechanical properties, and the voids around the agglomerates can even become shortcuts for gas permeation. Although existing technologies attempt to treat the filler surface using coupling agents, these methods often have limited modification effects and fail to construct an interfacial layer on the filler surface that both promotes dispersion and forms a strong interaction with the EVOH matrix. Therefore, fundamentally solving the interfacial problem between inorganic fillers and the EVOH matrix to fully realize their potential for enhanced barrier properties remains a pressing technical challenge in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a high-barrier composite film and its preparation method.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A high-barrier composite film, comprising at least in sequence: a substrate layer, a barrier layer, and a heat-sealing layer; the substrate layer is a polyester layer, and the substrate layer and the barrier layer, and the barrier layer and the heat-sealing layer are bonded together by an adhesive layer.

[0008] Preferably, the polyester layer is a biaxially oriented polyethylene terephthalate film or a polybutylene terephthalate film.

[0009] Preferably, the heat-sealing layer is a cast polypropylene film or a linear low-density polyethylene film; the adhesive is a polyurethane adhesive.

[0010] Preferably, the barrier layer comprises, by weight, the following raw materials: 90-100 parts of ethylene-vinyl alcohol copolymer, 5-10 parts of POE, 3-5 parts of modified hydrotalcite, 2-3 parts of maleic anhydride-grafted polyethylene, and 0.2-0.3 parts of antioxidant.

[0011] Preferably, the preparation method of the modified hydrotalcite includes the following steps: S1. Disperse hydrotalcite in an alkaline dopamine solution, stir until homogeneous, add tetraethyl orthosilicate, and carry out a constant temperature reaction. After the reaction is complete, filter, wash, and dry to obtain composite hydrotalcite. S2. Add the composite hydrotalcite from step S1 to acetone, then add trimellitic anhydride and heat to react. After the reaction is complete, filter, wash and dry to obtain modified hydrotalcite.

[0012] Preferably, in step S1, the mass concentration of the alkaline dopamine solution is 3-5 g / L, the pH is 8-9, the mass ratio of the hydrotalcite, alkaline dopamine solution, and tetraethyl orthosilicate is 100:400-600:10-15, the temperature of the isothermal reaction is 50-70℃, and the time is 12-20 h.

[0013] In this invention, hydrotalcite is used as the substrate. It is a layered bimetallic hydroxide with a sheet thickness on the nanoscale. This high aspect ratio sheet structure is the ideal geometric configuration for realizing the maze effect, which makes the permeation path of gas extremely tortuous and long during the permeation process. This is the physical basis for improving the barrier performance. In addition, hydrotalcite itself is rich in surface hydroxyl groups, which provides abundant reaction sites for subsequent surface chemical modification. By adding dopamine and tetraethyl orthosilicate for co-deposition, the polymeric network of PDA and the inorganic network of SiO2 interweave and intertwine during growth, forming a highly dense and seamless PDA / SiO2 hybrid interface layer. Compared with a single PDA coating, this PDA / SiO2 hybrid interface layer has stronger barrier capabilities. The phenolic hydroxyl groups of PDA can undergo dehydration condensation with the silanol groups (Si-OH) generated by the hydrolysis of TEOS to form strong Si-OC covalent bonds. On the one hand, it is tightly bound to the hydrotalcite through covalent bonds and strong physical adsorption forces; on the other hand, the large number of primary amine groups on the PDA units exposed on its surface is beneficial for subsequent processes.

[0014] Preferably, in step S2, the mass ratio of the composite hydrotalcite to trimellitic anhydride is 100:8-13, and the heating reaction temperature is 40-50℃ for 2-4 hours.

[0015] In this invention, composite hydrotalcite is reacted with trimellitic anhydride. The amino groups on the surface of the composite hydrotalcite react with the anhydride rings in the trimellitic anhydride to form amide bonds. Since the trimellitic anhydride molecule itself contains an independent carboxyl group, and its anhydride ring transforms into another carboxyl group after ring opening, two highly polar carboxyl groups are introduced onto the surface of the hydrotalcite. These carboxyl groups form a strong and dense hydrogen bond network with a large number of hydroxyl groups (-OH) on the EVOH molecular chain. This strong interaction force firmly anchors the EVOH molecular chain to the surface of the hydrotalcite, greatly restricting the movement of polymer chain segments and filling the free volume of the interface region. Furthermore, the benzene ring contained in trimellitic anhydride is a rigid planar structure that can extend from the surface of the hydrotalcite and insert into the spaces between the EVOH polymer chains, further hindering and binding the movement of the EVOH chain segments, reducing the permeability of the polymer, and thus significantly improving the barrier properties of the material.

[0016] Preferably, the barrier layer is prepared by the following method: Weigh the raw materials according to the formula, add ethylene-vinyl alcohol copolymer, POE, modified hydrotalcite, maleic anhydride grafted polyethylene and antioxidant into a high-speed mixer, mix for 10-15 minutes, then add to a twin-screw extruder, melt extrude and granulate at 160-220℃, and dry to obtain barrier layer masterbatch; make barrier layer film by casting or blow molding process from barrier layer masterbatch.

[0017] This invention also protects a method for preparing a high-barrier composite film as described above, comprising the following steps: An adhesive is coated on one side of the substrate layer, and then dry-laminated with the barrier layer and cured to obtain a double-layer film. Then, an adhesive is coated on one side of the barrier layer of the double-layer film, and then dry-laminated with the heat-sealing layer. After lamination, it is cured to obtain a high-barrier composite film.

[0018] Preferably, the coating amount of the adhesive is 3-5 g / m². 2 The dry compounding process is carried out at a temperature of 40-60℃ and a pressure of 0.3-0.5MPa, and the curing process is carried out at a temperature of 40-50℃ and a time of 24-72h.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The high barrier composite film provided by the present invention is prepared by introducing hydrotalcite modified by a specific method into the ethylene-vinyl alcohol copolymer matrix and then melt-blending it with toughening agent and compatibilizer. The resulting barrier layer film has high density and good compatibility. The barrier layer is then combined with the base layer and heat-sealing layer to form a multilayer film through a dry composite process. The final product not only exhibits excellent gas barrier performance and meets the application requirements of high-performance packaging materials, but also has good mechanical properties, processing performance and interlayer composite strength, and the overall structure is stable and reliable.

[0020] (2) The high-barrier composite film provided by the present invention, wherein the modified hydrotalcite added to the barrier layer firstly utilizes the characteristic that the self-polymerization of dopamine and the sol-gel reaction of tetraethyl orthosilicate can proceed simultaneously under similar pH conditions, and a homogeneous and dense organic-inorganic hybrid coating PDA / SiO2 is co-deposited on the surface of hydrotalcite in one step. This composite coating not only improves the dispersibility of hydrotalcite in the organic matrix, but more importantly, the amine groups on its surface provide more sites for subsequent reactions; subsequently, trimellitic anhydride, which has both anhydride rings and independent carboxyl groups, is selected as the graft monohydric acid. The filler utilizes its anhydride ring to undergo an efficient and selective ring-opening reaction with the amine groups on the surface of the composite coating, introducing a side chain containing a rigid benzene ring and two strongly polar carboxyl groups onto the surface of the hydrotalcite. When these side chains are blended with the ethylene-vinyl alcohol copolymer matrix, the rigid benzene ring can restrict the movement of polymer chain segments, while the high-density carboxyl groups can form a strong multi-point hydrogen bond network with the hydroxyl groups of the ethylene-vinyl alcohol copolymer. This greatly enhances the interfacial bonding force between the filler and the matrix, effectively reduces the free volume of the composite material, and thus significantly improves the barrier properties of the composite film.

[0021] (3) The high barrier composite film provided by the present invention has POE elastomer introduced into the barrier layer formulation, which effectively improves the toughness of the ethylene-vinyl alcohol copolymer matrix and reduces the brittleness of the material. The addition of maleic anhydride grafted polyethylene acts as an efficient compatibilizer, which solves the compatibility problem between the strongly polar ethylene-vinyl alcohol copolymer and the weakly polar POE, ensuring the homogeneous stability of the blend system and avoiding the performance degradation caused by phase separation. The synergistic effect of each component ensures that the barrier layer masterbatch has good processing stability in the subsequent casting or blow molding process, and endows the final film with excellent comprehensive physical and mechanical properties. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.

[0024] In the following embodiments, the resin grade of the biaxially oriented polyethylene terephthalate film is SKPET BB7755 (Korea), and the film thickness is 12-15 μm; the grade of the cast polypropylene film is Shanghai Petrochemical FC801, and the thickness is 20-25 μm; the polyurethane adhesive is a two-component solvent-based polyurethane adhesive; the grade of the ethylene-vinyl alcohol copolymer is Kuraray EVOH E171B; the grade of POE is ExxonMobil POE 6102; the grade of maleic anhydride polyethylene is Mitsui Chemicals ADMER NF408E; the mesh size of the hydrotalcite is 2500 mesh; and the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 2:1.

[0025] Example 1 A high-barrier composite film, comprising, in sequence, a substrate layer, a barrier layer, and a heat-sealing layer; the substrate layer is a polyester layer, and the substrate layer and the barrier layer, and the barrier layer and the heat-sealing layer are bonded together by an adhesive layer.

[0026] The polyester layer is a biaxially oriented polyethylene terephthalate film or a polybutylene terephthalate film; the heat-sealing layer is a cast polypropylene film or a linear low-density polyethylene film; and the adhesive is a polyurethane adhesive. By weight, the barrier layer comprises the following raw materials: 95 parts ethylene-vinyl alcohol copolymer, 7 parts POE, 4 parts modified hydrotalcite, 2.5 parts maleic anhydride-grafted polyethylene, and 0.25 parts antioxidant. The method for preparing the modified hydrotalcite includes the following steps: S1. Disperse 100g of hydrotalcite in 500mL of alkaline dopamine solution with a concentration of 4g / L and a pH of 8.5. After stirring evenly, add 13g of tetraethyl orthosilicate and react at 60℃ for 16h. After the reaction is completed, filter, wash and dry to obtain composite hydrotalcite. S2. Add 100g of composite hydrotalcite from step S1 to 800mL of acetone, then add 11g of trimellitic anhydride, and react at 45℃ for 3h. After the reaction is complete, filter, wash and dry to obtain modified hydrotalcite.

[0027] The barrier layer is prepared as follows: Weigh the raw materials according to the formula, add ethylene-vinyl alcohol copolymer, POE, modified hydrotalcite, maleic anhydride grafted polyethylene and antioxidant to a high-speed mixer and mix for 15 minutes. Then add it to a twin-screw extruder and set the temperature of each zone of the extruder to 160℃-170℃-185℃-210℃-215℃-210℃-205℃. Perform melt extrusion granulation and drying to obtain barrier layer masterbatch. The barrier layer masterbatch is then used to make barrier layer films with a thickness of 35-40μm through casting or blow molding processes.

[0028] A method for preparing a high-barrier composite film includes the following steps: Apply adhesive to one side of the substrate layer at a rate of 4 g / m². 2 The mixture was then dry-laminated with a barrier layer at 50°C and 0.4 MPa pressure, followed by curing at 45°C for 48 hours to obtain a bilayer film. An adhesive was then coated onto the barrier layer side of the bilayer film at a coating weight of 4 g / m². 2 Then, it is dry-laminated with the heat-sealing layer at 50°C and 0.4MPa pressure. After lamination, it is cured at 45°C for 48 hours to obtain a high-barrier composite film with an average thickness of 78μm.

[0029] Example 2 A high-barrier composite film, comprising, in sequence, a substrate layer, a barrier layer, and a heat-sealing layer; the substrate layer is a polyester layer, and the substrate layer and the barrier layer, and the barrier layer and the heat-sealing layer are bonded together by an adhesive layer.

[0030] The polyester layer is a biaxially oriented polyethylene terephthalate film or a polybutylene terephthalate film; the heat-sealing layer is a cast polypropylene film or a linear low-density polyethylene film; and the adhesive is a polyurethane adhesive. By weight, the barrier layer comprises the following raw materials: 90 parts ethylene-vinyl alcohol copolymer, 10 parts POE, 5 parts modified hydrotalcite, 3 parts maleic anhydride-grafted polyethylene, and 0.2 parts antioxidant. The method for preparing the modified hydrotalcite includes the following steps: S1. Disperse 100g of hydrotalcite in 400mL of alkaline dopamine solution with a concentration of 3g / L and pH of 9. After stirring evenly, add 10g of tetraethyl orthosilicate and react at 50℃ for 20h. After the reaction is completed, filter, wash and dry to obtain composite hydrotalcite. S2. Add 100g of composite hydrotalcite from step S1 to 800mL of acetone, then add 8g of trimellitic anhydride, and react at 40℃ for 4h. After the reaction is complete, filter, wash and dry to obtain modified hydrotalcite.

[0031] The barrier layer is prepared as follows: Weigh the raw materials according to the formula, add ethylene-vinyl alcohol copolymer, POE, modified hydrotalcite, maleic anhydride grafted polyethylene and antioxidant to a high-speed mixer and mix for 10 minutes. Then add it to a twin-screw extruder and set the temperature of each zone of the extruder to 160℃-170℃-185℃-210℃-215℃-210℃-205℃. Perform melt extrusion granulation and drying to obtain barrier layer masterbatch. The barrier layer masterbatch is then used to make barrier layer films with a thickness of 35-40μm through casting or blow molding processes.

[0032] A method for preparing a high-barrier composite film includes the following steps: Apply adhesive to one side of the substrate layer at a rate of 3 g / m². 2 The mixture was then dry-laminated with a barrier layer at 40°C and 0.5 MPa pressure, followed by curing at 50°C for 24 hours to obtain a bilayer film. An adhesive was then coated onto the barrier layer side of the bilayer film at a coating weight of 3 g / m². 2 Then, it is dry-laminated with the heat-sealing layer at 40℃ and 0.5MPa pressure. After lamination, it is cured at 50℃ for 24h to obtain a high-barrier composite film with an average thickness of 80μm.

[0033] Example 3 A high-barrier composite film, comprising, in sequence, a substrate layer, a barrier layer, and a heat-sealing layer; the substrate layer is a polyester layer, and the substrate layer and the barrier layer, and the barrier layer and the heat-sealing layer are bonded together by an adhesive layer.

[0034] The polyester layer is a biaxially oriented polyethylene terephthalate film or a polybutylene terephthalate film; the heat-sealing layer is a cast polypropylene film or a linear low-density polyethylene film; and the adhesive is a polyurethane adhesive. By weight, the barrier layer comprises the following raw materials: 100 parts ethylene-vinyl alcohol copolymer, 5 parts POE, 3 parts modified hydrotalcite, 2 parts maleic anhydride-grafted polyethylene, and 0.3 parts antioxidant. The method for preparing the modified hydrotalcite includes the following steps: S1. Disperse 100g of hydrotalcite in 600mL of alkaline dopamine solution with a concentration of 5g / L and a pH of 8. After stirring evenly, add 15g of tetraethyl orthosilicate and react at 70℃ for 12h. After the reaction is completed, filter, wash and dry to obtain composite hydrotalcite. S2. Add 100g of composite hydrotalcite from step S1 to 800mL of acetone, then add 13g of trimellitic anhydride, and react at 50℃ for 2h. After the reaction is complete, filter, wash and dry to obtain modified hydrotalcite.

[0035] The barrier layer is prepared as follows: Weigh the raw materials according to the formula, add ethylene-vinyl alcohol copolymer, POE, modified hydrotalcite, maleic anhydride grafted polyethylene and antioxidant to a high-speed mixer and mix for 15 minutes. Then add it to a twin-screw extruder and set the temperature of each zone of the extruder to 160℃-170℃-185℃-210℃-215℃-210℃-205℃. Perform melt extrusion granulation and drying to obtain barrier layer masterbatch. The barrier layer masterbatch is then used to make barrier layer films with a thickness of 35-40μm through casting or blow molding processes.

[0036] A method for preparing a high-barrier composite film includes the following steps: Apply adhesive to one side of the substrate layer at a rate of 5 g / m². 2 The film was then dry-laminated with a barrier layer at 60°C and 0.3 MPa pressure, followed by curing at 40°C for 72 hours to obtain a bilayer film. An adhesive was then coated onto the barrier layer side of the bilayer film at a coating weight of 5 g / m². 2 Then, it is dry-laminated with the heat-sealing layer at 60℃ and 0.3MPa pressure. After lamination, it is cured at 40℃ for 72h to obtain a high-barrier composite film with an average thickness of 77μm.

[0037] Comparative Example 1 A high-barrier composite film, comprising, in sequence, a substrate layer, a barrier layer, and a heat-sealing layer; the substrate layer is a polyester layer, and the substrate layer and the barrier layer, and the barrier layer and the heat-sealing layer are bonded together by an adhesive layer.

[0038] The polyester layer is a biaxially oriented polyethylene terephthalate film or a polybutylene terephthalate film; the heat-sealing layer is a cast polypropylene film or a linear low-density polyethylene film; and the adhesive is a polyurethane adhesive. By weight, the barrier layer comprises the following raw materials: 95 parts ethylene-vinyl alcohol copolymer, 7 parts POE, 4 parts hydrotalcite, 2.5 parts maleic anhydride-grafted polyethylene, and 0.25 parts antioxidant. The barrier layer is prepared as follows: Weigh the raw materials according to the formula, add ethylene-vinyl alcohol copolymer, POE, hydrotalcite, maleic anhydride grafted polyethylene and antioxidant to a high-speed mixer and mix for 15 minutes. Then add it to a twin-screw extruder and set the temperature of each zone of the extruder to 160℃-170℃-185℃-210℃-215℃-210℃-205℃. Perform melt extrusion granulation and drying to obtain barrier layer masterbatch. The barrier layer masterbatch is then used to make barrier layer films with a thickness of 35-40μm through casting or blow molding processes.

[0039] A method for preparing a high-barrier composite film includes the following steps: Apply adhesive to one side of the substrate layer at a rate of 4 g / m². 2 The mixture was then dry-laminated with a barrier layer at 50°C and 0.4 MPa pressure, followed by curing at 45°C for 48 hours to obtain a bilayer film. An adhesive was then coated onto the barrier layer side of the bilayer film at a coating weight of 4 g / m². 2 Then, it is dry-laminated with the heat-sealing layer at 50°C and 0.4MPa pressure. After lamination, it is cured at 45°C for 48 hours to obtain a high-barrier composite film with an average thickness of 78μm.

[0040] Compared with Example 1, this comparative example did not modify the hydrotalcite.

[0041] Comparative Example 2 A high-barrier composite film, comprising, in sequence, a substrate layer, a barrier layer, and a heat-sealing layer; the substrate layer is a polyester layer, and the substrate layer and the barrier layer, and the barrier layer and the heat-sealing layer are bonded together by an adhesive layer.

[0042] The polyester layer is a biaxially oriented polyethylene terephthalate film or a polybutylene terephthalate film; the heat-sealing layer is a cast polypropylene film or a linear low-density polyethylene film; and the adhesive is a polyurethane adhesive. By weight, the barrier layer comprises the following raw materials: 95 parts ethylene-vinyl alcohol copolymer, 7 parts POE, 4 parts modified hydrotalcite, 2.5 parts maleic anhydride-grafted polyethylene, and 0.25 parts antioxidant. The method for preparing the modified hydrotalcite includes the following steps: 100g of hydrotalcite was dispersed in 500mL of an alkaline dopamine solution with a concentration of 4g / L and a pH of 8.5. After stirring evenly, 13g of tetraethyl orthosilicate was added, and the mixture was reacted at a constant temperature of 60℃ for 16h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified hydrotalcite.

[0043] The barrier layer is prepared as follows: Weigh the raw materials according to the formula, add ethylene-vinyl alcohol copolymer, POE, modified hydrotalcite, maleic anhydride grafted polyethylene and antioxidant to a high-speed mixer and mix for 15 minutes. Then add it to a twin-screw extruder and set the temperature of each zone of the extruder to 160℃-170℃-185℃-210℃-215℃-210℃-205℃. Perform melt extrusion granulation and drying to obtain barrier layer masterbatch. The barrier layer masterbatch is then used to make barrier layer films with a thickness of 35-40μm through casting or blow molding processes.

[0044] A method for preparing a high-barrier composite film includes the following steps: Apply adhesive to one side of the substrate layer at a rate of 4 g / m². 2The mixture was then dry-laminated with a barrier layer at 50°C and 0.4 MPa pressure, followed by curing at 45°C for 48 hours to obtain a bilayer film. An adhesive was then coated onto the barrier layer side of the bilayer film at a coating weight of 4 g / m². 2 Then, it is dry-laminated with the heat-sealing layer at 50°C and 0.4MPa pressure. After lamination, it is cured at 45°C for 48 hours to obtain a high-barrier composite film with an average thickness of 78μm.

[0045] Compared to Example 1, no trimellitic anhydride was introduced into the modified hydrotalcite of this comparative example.

[0046] Comparative Example 3 A high-barrier composite film, comprising, in sequence, a substrate layer, a barrier layer, and a heat-sealing layer; the substrate layer is a polyester layer, and the substrate layer and the barrier layer, and the barrier layer and the heat-sealing layer are bonded together by an adhesive layer.

[0047] The polyester layer is a biaxially oriented polyethylene terephthalate film or a polybutylene terephthalate film; the heat-sealing layer is a cast polypropylene film or a linear low-density polyethylene film; and the adhesive is a polyurethane adhesive. By weight, the barrier layer comprises the following raw materials: 95 parts ethylene-vinyl alcohol copolymer, 7 parts POE, 4 parts modified hydrotalcite, 2.5 parts maleic anhydride-grafted polyethylene, and 0.25 parts antioxidant. The method for preparing the modified hydrotalcite includes the following steps: S1. Disperse 100g of hydrotalcite in 500mL of alkaline dopamine solution with a concentration of 4g / L and a pH of 8.5. After stirring evenly, add 13g of tetraethyl orthosilicate and react at 60℃ for 16h. After the reaction is completed, filter, wash and dry to obtain composite hydrotalcite. S2. Add 100g of composite hydrotalcite from step S1 to 800mL of acetone, then add 11g of benzoyl chloride and 10g of triethylamine, and react at 45℃ for 3h. After the reaction is complete, filter, wash and dry to obtain modified hydrotalcite.

[0048] The barrier layer is prepared as follows: Weigh the raw materials according to the formula, add ethylene-vinyl alcohol copolymer, POE, modified hydrotalcite, maleic anhydride grafted polyethylene and antioxidant to a high-speed mixer and mix for 15 minutes. Then add it to a twin-screw extruder and set the temperature of each zone of the extruder to 160℃-170℃-185℃-210℃-215℃-210℃-205℃. Perform melt extrusion granulation and drying to obtain barrier layer masterbatch. The barrier layer masterbatch is then used to make barrier layer films with a thickness of 35-40μm through casting or blow molding processes.

[0049] A method for preparing a high-barrier composite film includes the following steps: Apply adhesive to one side of the substrate layer at a rate of 4 g / m². 2 The mixture was then dry-laminated with a barrier layer at 50°C and 0.4 MPa pressure, followed by curing at 45°C for 48 hours to obtain a bilayer film. An adhesive was then coated onto the barrier layer side of the bilayer film at a coating weight of 4 g / m². 2 Then, it is dry-laminated with the heat-sealing layer at 50°C and 0.4MPa pressure. After lamination, it is cured at 45°C for 48 hours to obtain a high-barrier composite film with an average thickness of 78μm.

[0050] Compared with Example 1, the modified hydrotalcite in this comparative example was prepared by replacing trimellitic anhydride with benzoyl chloride.

[0051] The high-barrier composite films prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. Tensile strength (longitudinal) and elongation at break (longitudinal) were tested according to standard GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets"; oxygen permeability was tested according to standard GB / T 19789-2021 "Test of oxygen permeability of plastic films and sheets for packaging materials - Coulometric method" at 23°C and 50%RH; water vapor permeability was tested according to standard GB / T 26253-2010 "Determination of water vapor permeability of plastic films and sheets - Infrared detector method" at 38°C and 90%RH; interlayer peel strength was tested according to standard GB / T 8808-1988 "Peel test method for flexible composite plastic materials". The test results are shown in Table 1 below.

[0052] Table 1 As can be seen from Table 1 above, the high-barrier composite film provided by this invention exhibits extremely low oxygen / water vapor permeability and excellent mechanical properties, while its interlayer peel strength is >5.0. N / 15mm indicates that the film improves the core performance without sacrificing the basic application performance of the composite film, possessing extremely high industrial practical value. In contrast, Comparative Example 1, due to the modification of the hydrotalcite, suffers from severely deteriorated mechanical properties caused by stress concentration due to filler agglomeration, and also exhibits the worst barrier performance. In Comparative Example 2, the modified hydrotalcite did not incorporate trimellitic anhydride. Although the PDA / SiO2 coating on the surface improved the physical dispersion, making its performance superior to Comparative Example 1, the weak van der Waals forces at the interface failed to effectively suppress the movement of ethylene-vinyl alcohol copolymer segments and resist the erosion of the interface by water molecules, resulting in a decrease in barrier performance. In Comparative Example 3, trimellitic anhydride was replaced with benzoyl chloride. However, the 2-chloroacetanilide molecule does not contain a carboxyl group and lacks sites that can form strong hydrogen bonds with the hydroxyl groups of the ethylene-vinyl alcohol copolymer. The affinity of the grafted amide groups and benzene ring structures for the ethylene-vinyl alcohol copolymer matrix is ​​limited, and the barrier performance is still significantly inferior to that of the embodiments of the present invention.

[0053] The above description is a further detailed explanation of the present invention in conjunction with specific implementation examples. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the protection scope of the present invention.

[0054] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-barrier composite film, characterized in that, The high-barrier composite film comprises at least the following in sequence: a base layer, a barrier layer, and a heat-sealing layer; the base layer is a polyester layer, and the base layer and the barrier layer, as well as the barrier layer and the heat-sealing layer, are bonded together by an adhesive layer.

2. The high-barrier composite film according to claim 1, characterized in that, The polyester layer is a biaxially oriented polyethylene terephthalate film or a polybutylene terephthalate film.

3. The high-barrier composite film according to claim 1, characterized in that, The heat-sealing layer is a cast polypropylene film or a linear low-density polyethylene film; the adhesive is a polyurethane adhesive.

4. The high-barrier composite film according to claim 1, characterized in that, By weight, the barrier layer comprises the following raw materials: 90-100 parts of ethylene-vinyl alcohol copolymer, 5-10 parts of POE, 3-5 parts of modified hydrotalcite, 2-3 parts of maleic anhydride-grafted polyethylene, and 0.2-0.3 parts of antioxidant.

5. The high-barrier composite film according to claim 1, characterized in that, The preparation method of the modified hydrotalcite includes the following steps: S1. Disperse hydrotalcite in an alkaline dopamine solution, stir until homogeneous, add tetraethyl orthosilicate, and carry out a constant temperature reaction. After the reaction is complete, filter, wash, and dry to obtain composite hydrotalcite. S2. Add the composite hydrotalcite from step S1 to acetone, then add trimellitic anhydride and heat to react. After the reaction is complete, filter, wash and dry to obtain modified hydrotalcite.

6. The high-barrier composite film according to claim 1, characterized in that, In step S1, the alkaline dopamine solution has a mass concentration of 3-5 g / L and a pH of 8-9. The mass ratio of the hydrotalcite, alkaline dopamine solution, and tetraethyl orthosilicate is 100:400-600:10-15. The isothermal reaction is carried out at a temperature of 50-70°C for 12-20 hours.

7. The high-barrier composite film according to claim 1, characterized in that, In step S2, the mass ratio of the composite hydrotalcite to trimellitic anhydride is 100:8-13, and the heating reaction temperature is 40-50℃ for 2-4 hours.

8. The high-barrier composite film according to claim 1, characterized in that, The barrier layer is prepared as follows: Weigh the raw materials according to the formula, add ethylene-vinyl alcohol copolymer, POE, modified hydrotalcite, maleic anhydride grafted polyethylene and antioxidant into a high-speed mixer, mix for 10-15 minutes, then add to a twin-screw extruder, melt extrude and granulate at 160-220℃, and dry to obtain barrier layer masterbatch; make barrier layer film by casting or blow molding process from barrier layer masterbatch.

9. A method for preparing a high-barrier composite film as described in any one of claims 1-8, characterized in that, Includes the following steps: An adhesive is coated on one side of the substrate layer, and then dry-laminated with the barrier layer and cured to obtain a double-layer film. Then, an adhesive is coated on one side of the barrier layer of the double-layer film, and then dry-laminated with the heat-sealing layer. After lamination, it is cured to obtain a high-barrier composite film.

10. The preparation method according to claim 9, characterized in that, The adhesive is applied at a rate of 3-5 g / m². 2 The dry compounding process is carried out at a temperature of 40-60℃ and a pressure of 0.3-0.5MPa, and the curing process is carried out at a temperature of 40-50℃ and a time of 24-72h.

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