Multi-layer high-barrier paper-based composite packaging material and preparation method thereof

Abstract

The invention relates to the technical field of packaging materials, in particular to a multi-layer high-barrier paper-based composite packaging material and a preparation method thereof.The multi-layer high-barrier paper-based composite packaging material sequentially comprises an outer protective layer, a printing paper base layer, a bonding layer, a high-barrier functional layer, a bonding layer and an inner heat sealing layer from outside to inside; the preparation method of the nano barrier filler contained in the components of the high-barrier functional layer comprises the following steps: step 1, purifying montmorillonite; step 2, modifying dioctadecyl dimethyl ammonium chloride; step 3, grafting with a silane coupling agent; and 4, compounding the graphene oxide. According to the composite packaging film disclosed by the invention, a synergistic barrier network and a filler-flexibilizer interaction network are constructed through a chemical means of organification-coupling-covalent bonding, so that the barrier property, toughness and strength of the material are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, and in particular to a multi-layer high-barrier paper-based composite packaging material and its preparation method. Background Technology

[0002] With the increasing demand for packaging preservation, anti-corrosion, and anti-oxidation in the food, pharmaceutical, and precision electronics industries, high-barrier packaging films have become a key material. These films must effectively block the penetration of small molecules such as oxygen and water vapor to extend the shelf life of the contents and ensure product performance stability. Currently, the mainstream packaging film matrix materials are mainly polypropylene (PP) and polyethylene (PE). These polyolefin materials have advantages such as good processability, low cost, and stable mechanical properties. However, their loose molecular chain structure results in extremely poor barrier properties against oxygen and water vapor (oxygen permeability is typically >500 cm³ / (m²・24h・0.1 MPa), and water vapor permeability >10 g / (m²・24h)), making it difficult to meet the requirements of high-barrier applications. Patent CN117400610A discloses an ultra-high barrier multilayer co-extruded film for food packaging, comprising an upper surface layer, a core layer, and a lower surface layer arranged sequentially from top to bottom. The upper surface layer is composed of ethylene-vinyl alcohol copolymer, nylon 6, modified graphene, and additives; the core layer is composed of ethylene-vinyl alcohol copolymer, modified polypropylene, modified graphene, and additives; and the lower surface layer is composed of polyvinylidene fluoride, modified polypropylene, modified composite microspheres, and additives. This invention improves the compatibility of graphene and composite microspheres by modifying them, and improves the hydrophilicity and permeability of polypropylene by modifying it with maleic anhydride. However, the increased hydrophilicity of the modified polypropylene leads to increased hydrophilicity of the lower surface layer and the core layer. As the film is used for a longer period, the ethylene-vinyl alcohol copolymer in the core layer and the upper surface layer will be exposed to high humidity conditions, resulting in a decrease in the barrier properties of the film.

[0003] To improve barrier performance, the industry often adopts two improvement approaches: one is to introduce high-barrier resins (such as ethylene-vinyl alcohol copolymer, EVOH), whose highly polar hydroxyl groups and ether bonds in the molecular chain can form a dense hydrogen bond network, and the oxygen permeability can be as low as 5 cm³ / (m²・24h・0.1MPa). However, EVOH has extremely poor compatibility with non-polar polyolefins, and direct blending easily leads to interfacial delamination, resulting in a sharp drop in the mechanical properties of the membrane (such as impact resistance), and the cost of using EVOH alone is high. The second approach is to add nano-barrier fillers (such as montmorillonite), which utilizes its sheet-like structure to construct a "maze-like" barrier path and extend the penetration distance of small molecules. However, unmodified montmorillonite has a hydrophilic layered structure and weak interfacial bonding with the hydrophobic polyolefin matrix, which easily aggregates and forms defects. Not only does the barrier effect not meet expectations, but it also leads to increased membrane brittleness and easy cracking.

[0004] In summary, existing technologies cannot simultaneously achieve a synergistic balance of "high barrier properties, excellent toughness, and good compatibility," and there is an urgent need to develop a composite packaging film technology that can take into account the performance of these three aspects. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a multilayer high-barrier paper-based composite packaging material and its preparation method. The multilayer high-barrier paper-based composite packaging material of this invention achieves nanoscale dispersion of nanofillers in the matrix by combining "organization-coupling-covalent bonding" chemical methods to create a high-barrier functional layer. Through multi-step reactions, the composite material becomes an organic whole, achieving synergistic and balanced performance. By constructing a synergistic barrier network and a "filler-toughening agent" interaction network, the material's barrier properties, toughness, and strength are significantly improved.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows: A multi-layer high-barrier paper-based composite packaging material, comprising, from the outside to the inside, an outer protective layer, a printed paper base layer, an adhesive layer, a high-barrier functional layer, an adhesive layer, and an inner heat-sealing layer; the high-barrier functional layer comprises the following components by weight: The base resin is polypropylene or polyethylene, which contains 70-85 parts; nano-barrier filler, which contains 10-15 parts; ethylene-vinyl alcohol copolymer, which contains 8-15 parts; compatibilizer, which contains 4-8 parts; composite toughening agent, which contains 5-10 parts; antioxidant, which contains 0.3-0.8 parts; and lubricant, which contains 0.5-1.5 parts. The preparation method of the nano-barrier filler includes the following steps: Step 1: Add montmorillonite to deionized water and disperse it at 70-80℃ with high-speed stirring at 800-1000 rpm for 3-4 hours. Then let it stand for 18-24 hours to form a suspension with three layers: upper, middle and lower. Extract the middle layer suspension and centrifuge it at 10000-12000 rpm. Collect the precipitate and dry it to obtain product 1. Step 2: Disperse product 1 in deionized water to obtain a suspension. Add bis(octadecyldimethylammonium chloride) to ethanol, and add the ethanol solution of bis(octadecyldimethylammonium chloride) to the suspension of product 1 under stirring. React at 80-85℃ for 5-6 hours, and then purify to obtain product 2. Step 3: Mix product 2 with toluene and ultrasonically disperse at 400-500W for 40-50 min. Then add silane coupling agent KH-550, heat to 112-118℃, and reflux under nitrogen protection for 12-14 h to obtain product 3. Step 4: Disperse product 3 in N,N-dimethylformamide solvent to obtain a suspension of product 3. Sonicate the suspension for 25-35 min. Disperse graphene oxide in N,N-dimethylformamide and ultrasonically exfoliate at 350-450 W for 1-2 h to obtain a uniform graphene oxide dispersion. Add the graphene oxide dispersion to the suspension of product 3 with stirring. React at 60-70℃ with stirring for 10-12 h. After the reaction is completed, purify the product to obtain the final product.

[0007] Preferably, in step 1, the weight ratio of montmorillonite to deionized water is 100:600-800; in step 2, the weight ratio of product 1 to deionized water is 100:500-600; and the weight ratio of product 1, dioctadecyldimethylammonium chloride, and ethanol is 100:25-30:80-100.

[0008] Preferably, in step 3, the weight ratio of product 2 to toluene and silane coupling agent KH-550 is 100:350-450:10-15.

[0009] Preferably, in step 4, the weight ratio of product 3 to N,N-dimethylformamide and graphene oxide is 100:350-450:3-8, and the weight ratio of graphene oxide to N,N-dimethylformamide in the graphene oxide dispersion is 3-8:200.

[0010] Preferably, the preparation method of the composite toughening agent includes the following steps: Step a: Take polyolefin elastomer particles and heat xylene to 100-105℃ to dissolve the olefin elastomer particles, then add maleic anhydride and dicumyl peroxide, and react at 108-115℃ for 6-7 hours to obtain a maleic anhydride-grafted polyolefin mixture; disperse fumed silica in a mixed solvent of ethanol and water, ultrasonically disperse, add silane coupling agent KH-550, adjust the pH to 4-5, and stir at 70-75℃ for 5-6 hours to obtain an activated nano silica dispersion; mix the maleic anhydride-grafted polyolefin mixture with the activated nano silica dispersion, stir at 80-85℃ for 3-4 hours, and purify to obtain a core-shell structured composite powder; Step b: The composite powder obtained in step a is melt-extruded with benzoyl peroxide and glycidyl methacrylate at the following temperatures: Zone 1 160-170℃, Zone 2 175-185℃, Zone 3 180-190℃, die head 185-195℃, and screw speed 260-300 rpm.

[0011] Preferably, in step a, the weight ratio of the polyolefin elastomer particles to the mixed solvent of xylene, maleic anhydride, dicumyl peroxide, silica, ethanol and water is 100:400-500:4-5:1.5-2.0:40-50:300-400, and the volume ratio of ethanol to water in the mixed solvent of ethanol and water is 9:1.

[0012] Preferably, in step b, the weight ratio of the composite powder, benzoyl peroxide, and glycidyl methacrylate is 100:2.5-3.5:8-10.

[0013] Preferably, the base resin is linear low-density polyethylene, the compatibilizer is maleic anhydride-grafted polypropylene, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1-2, and the lubricant is ethylene bis-stearamide.

[0014] The preparation method of the above-mentioned multi-layer high-barrier paper-based composite packaging material is as follows: the outer protective layer, the printed paper base layer, the adhesive layer, the high-barrier functional layer, and the inner heat-sealing layer are composited to obtain the final product.

[0015] The present invention has the following beneficial effects: The multilayer high-barrier paper-based composite packaging material of this invention, through the preparation of the high-barrier functional layer, incorporates nano-barrier fillers, composite toughening agents, ethylene-vinyl alcohol copolymers, compatibilizers, and other components into the matrix polypropylene or polyethylene. Through a chemical approach of "organization-coupling-covalent bonding," nano-fillers are dispersed at the nanoscale within the matrix. Through multi-step reactions, covalent or strong ionic bonds are introduced at multiple interfaces, including filler-matrix, filler-filler, and matrix-EVOH, making the composite material an organic whole and achieving synergistic and balanced performance. By constructing a synergistic barrier network and a "filler-toughening agent" interaction network, the material's barrier properties, toughness, and strength are significantly improved. In the preparation of the nano-barrier filler, step 1 removes inert impurities, obtaining high-purity montmorillonite. This not only avoids interference from impurities in subsequent reactions but, more importantly, provides a pure and efficient "reaction matrix" for subsequent chemical modification, ensuring that the modifier acts only on the target montmorillonite sheets. Step 2: The quaternary ammonium salt groups of bis(octadecyldimethylammonium chloride) (a cationic surfactant) bind to the negative charge on the surface of montmorillonite sheets through electrostatic attraction. The long-chain alkyl groups (C18) are oriented between the montmorillonite layers, changing the hydrophilicity of montmorillonite to a hydrophobicity, significantly improving its compatibility with the polyolefin matrix. Furthermore, the steric hindrance of the long-chain alkyl groups widens the interlayer spacing of the montmorillonite, reserving space for subsequent coupling agent integration and graphene oxide composite formation, avoiding the disruption of pathways caused by sheet aggregation. Step 3: The silane coupling agent KH-550 (aminopropyltriethoxysilane) undergoes hydrolysis to generate silanol (-Si-OH), which condenses with the silanol groups on the montmorillonite surface to form a strong Si-O-Si covalent bond. Simultaneously, an active amine group (-NH2) is introduced at the other end of KH-550. This not only adds a "molecular bridge" between the filler and polymer, greatly enhancing interfacial adhesion, but more importantly, it provides a chemical anchoring point (-NH2) for the fourth step reaction. Step 4 involves an amidation reaction between the carboxyl groups (-COOH) on the surface of graphene oxide (GO) and the amino groups (-NH2) on the surface of the previously modified montmorillonite, chemically bonding the GO nanosheets to the montmorillonite through strong covalent bonds. This not only achieves uniform dispersion of GO itself but also constructs a multi-level network structure of "interlaced stacking" at the nanoscale, forming a more tortuous and dense synergistic barrier network than a single filler. This significantly extends the diffusion path of gases and small molecules, resulting in extremely high oxygen and water vapor barrier properties of the film. The nano-barrier filler achieves hierarchical optimization through four steps of modification: purification, organication, coupling, and composite, constructing a dense, multi-level interlaced barrier network that significantly enhances the small molecule barrier capability.

[0016] The polyolefin segments of the compatibilizer molecules are compatible with the matrix resin, while their anhydride groups (-CO-O-CO-) can react with the hydroxyl groups (-OH) of EVOH, thus acting as "ambassadors" to strongly bind the two together, preventing macroscopic phase separation and ensuring a uniform material structure. The synergistic effect of the composite toughening agent and filler allows for chemical bridging between them, enabling the toughening agent to not only be dispersed in the matrix but also connected to the entire reinforcing network through chemical bonds. In this way, when subjected to external impact, energy can be effectively dissipated through this powerful network, achieving both toughening and reinforcement while also providing excellent barrier properties.

[0017] Furthermore, the synergistic effect of the nano-barrier filler and the composite toughening agent coordinates "barrier-toughness-compatibility" to achieve an overall performance improvement. Structural complementarity: The sheet-like structure of the nano-barrier filler constructs a "transversely dense barrier layer" in the matrix, while the core-shell structure of the composite toughening agent is distributed in the gaps between the barrier layers as "longitudinal elastic support points." On the one hand, the elastic particles of the core-shell structure can absorb the internal stress generated by the aggregation of nano-fillers, avoiding increased brittleness of the membrane due to the addition of nano-fillers; on the other hand, the sheet-like barrier layer can fill the tiny gaps between the core-shell structures, preventing the toughening agent from introducing permeation channels, thus achieving a "defect-free superposition" of barrier performance and toughness. Interfacial Synergy: The KH-550 amino group (-NH2) on the surface of the nano-barrier filler can undergo a ring-opening reaction with the GMA epoxy group (-COC-) of the composite toughening agent shell, and simultaneously undergo an amidation reaction with the POE-grafted anhydride group (-CO-O-CO-), allowing the nano-filler and toughening agent to be chemically bonded together to form a continuous interfacial phase of "barrier sheet-core-shell particles-matrix". This interfacial phase can eliminate interfacial defects among the three components, not only improving the overall mechanical properties of the membrane, but also further extending the small molecule permeation path, thus further enhancing the barrier performance compared to adding nano-filler alone. The "multi-level staggered barrier network" of the nano-barrier filler and the "core-shell-epoxy grafted structure" of the composite toughening agent work synergistically. The toughening agent solves the brittleness problem of the nano-filler through elastic deformation and interfacial reinforcement, while the nano-filler compensates for the permeation defects of the toughening agent through a dense barrier network. Ultimately, the membrane possesses high barrier properties, excellent toughness, and mechanical properties, fully meeting the high-barrier packaging requirements of food, pharmaceuticals, and other products.

[0018] The preparation method of the present invention has controllable process, high production efficiency, and is suitable for industrial production. Detailed Implementation

[0019] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0020] All raw materials used below are commercially available.

[0021] Linear low-density polyethylene, grade DFDA-7042, Suzhou Deyi Polyplastics Co., Ltd.; Ethylene-vinyl alcohol copolymer, Dongguan Xinshengli Plastic New Material Technology Co., Ltd.; Maleic anhydride grafted polypropylene, Shanghai Xianshun Plastics Co., Ltd.; Antioxidant 1010, hindered phenol, volatile matter ≤0.5%, Jiangsu Xinluda Polymer Materials Co., Ltd.; Antioxidant 168, volatile matter ≤0.5%, Jiangsu Xinluda Polymer Materials Co., Ltd.; Ethylene bis-stearamide, 110-30-5, Wuhan Shuer Biotechnology Co., Ltd.; Montmorillonite is sodium-based montmorillonite, specification 325 mesh, Lingshou County Shunlei Mineral Products Processing Plant; Polyolefin elastomer, brand: Dow Chemical, USA; Organic nano-montmorillonite, DK10, dry powder particle size (D98) / um: ≤20, Zhejiang Fenghong New Material Co., Ltd. Example 1 A multi-layer high-barrier paper-based composite packaging material, comprising, from the outside to the inside, an outer protective layer, a printed paper base layer, an adhesive layer, a high-barrier functional layer, an adhesive layer, and an inner heat-sealing layer; the high-barrier functional layer comprises the following components by weight: The composition includes 80 parts of base resin (polyethylene), 12 parts of nano-barrier filler, 12 parts of ethylene-vinyl alcohol copolymer, 6 parts of compatibilizer, 8 parts of composite toughening agent, 0.5 parts of antioxidant, and 1 part of lubricant. The base resin is linear low-density polyethylene, the compatibilizer is maleic anhydride-grafted polypropylene, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.5, and the lubricant is ethylene bis-stearamide. The preparation method of the nano-barrier filler includes the following steps: Step 1: Add montmorillonite to deionized water and disperse it at 75°C with high-speed stirring at 900 rpm for 3.5 h. Then let it stand for 21 h to form a suspension with three layers: upper, middle and lower. Extract the middle layer suspension and centrifuge it at 11000 rpm. Collect the precipitate and vacuum dry it at 85°C to constant weight to obtain product 1. In Step 1, the weight ratio of montmorillonite to deionized water is 100:700. Step 2: Disperse product 1 in deionized water to obtain a suspension of product 1. Place dioctadecyl dimethyl ammonium chloride in a round-bottom flask with a reflux condenser, add ethanol and heat to 65°C, stir to dissolve. Add the ethanol solution of dioctadecyl dimethyl ammonium chloride dropwise to the suspension of product 1 at 4 mL / min with stirring at 1100 rpm. React at 82°C for 5.5 h, then filter, wash three times with hot water at 65°C, and then wash twice with anhydrous ethanol until no white precipitate is formed when tested with 0.1 mol / L silver nitrate solution. Dry under vacuum at 85°C to constant weight to obtain product 2. In step 2, the weight ratio of product 1 to deionized water is 100:500, and the weight ratio of product 1, dioctadecyl dimethyl ammonium chloride, and ethanol is 100:27:90. Step 3: Product 2 is mixed with toluene and ultrasonically dispersed at 450W for 45 min. Then, silane coupling agent KH-550 is added, the temperature is raised to 115℃, and the mixture is refluxed under nitrogen protection for 13 h. After cooling, the mixture is filtered, washed twice with toluene, and dried at 82℃ for 7 h to obtain product 3. In step 3, the weight ratio of product 2 to toluene and silane coupling agent KH-550 is 100:400:12. Step 4: Take product 3, disperse it in N,N-dimethylformamide solvent, and sonicate it for 30 min. Disperse graphene oxide in N,N-dimethylformamide and sonicate it for 1.5 h at 400 W to obtain a uniform graphene oxide dispersion. Add the graphene oxide dispersion dropwise to a montmorillonite N,N-dimethylformamide suspension at 2 mL / min with stirring. React at 65 °C with stirring for 11 h. After the reaction is complete, filter the solution and wash it three times with N,N-dimethylformamide and anhydrous ethanol, respectively. Finally, vacuum dry it at 80 °C for 24 h and pulverize it through an 800-mesh sieve to obtain the final product. In Step 4, the weight ratio of product 3 to N,N-dimethylformamide and graphene oxide is 100:400:5. In the graphene oxide dispersion, the weight ratio of graphene oxide to N,N-dimethylformamide is 5:200.

[0022] The preparation method of the composite toughening agent includes the following steps: Step a: Take 100 parts of polyolefin elastomer particles and add them together with 450 parts of xylene into a reaction vessel. Purge with nitrogen for 20 minutes, then heat to 102℃ to completely dissolve the polyolefin elastomer particles. Next, add 4.5 parts of maleic anhydride and 1.8 parts of dicumyl peroxide, and react at 110℃ for 6.5 hours to obtain a maleic anhydride-grafted polyolefin mixture. Disperse 45 parts of fumed silica in a mixed solvent of 350 parts of ethanol and water (volume ratio 9:1) and ultrasonically disperse for 40 minutes. Add 6 parts of silane coupling agent KH-550, adjust the pH to 4-5 with acetic acid, and stir at 72℃ for 5.5 h to obtain an activated nano silica dispersion; mix maleic anhydride grafted polyolefin mixture with activated nano silica dispersion, stir at 80-85℃ for 3.5 h to allow the anhydride groups and amine groups to react fully, then pour the mixture into excess acetone to precipitate, filter, wash 3 times with acetone, and vacuum dry at 70℃ for 12 h to obtain a core-shell structured composite powder; Step b: 100 parts of the composite powder obtained in step a are melt-extruded with 3 parts of benzoyl peroxide and 9 parts of glycidyl methacrylate in a twin-screw extruder. The temperature is set as follows: Zone 1 165℃, Zone 2 180℃, Zone 3 185℃, Die head 190℃, and screw speed 280 rpm. This allows the glycidyl methacrylate monomer to be grafted onto the molecular chain of the polyolefin elastomer particle shell through a free radical reaction, thus obtaining the final product.

[0023] The method for preparing the high-barrier functional layer is as follows: (1) Raw material pretreatment: The ethylene-vinyl alcohol copolymer was dried in a vacuum oven at 85°C for 11 hours, the nano barrier filler was dried in a vacuum oven at 90°C for 5 hours, and the composite toughening agent was dried in a vacuum oven at 60°C for 4 hours. (2) Premixing: The base resin polyethylene, compatibilizer, antioxidant, lubricant, nano barrier filler dried in step (1), ethylene-vinyl alcohol copolymer, and composite toughening agent are added to a high-speed mixer according to the above weight proportions and mixed at a speed of 1100 rpm for 13 min to obtain a uniform premix. (3) Melt blending extrusion and casting film formation: The premix obtained in step (2) is fed into the feed hopper of a twin-screw extruder. After melting, plasticizing, mixing and devolatilizing, the premix is ​​extruded into molten sheet through a T-die. The processing temperature of the twin-screw extruder is set in the following zones from the feed port to the die head: Zone 1 175℃, Zone 2 185℃, Zone 3 195℃, Zone 4 205℃, Zone 5 210℃, and the die head 215℃. The screw speed is 300 rpm. (4) Cooling, shaping, and winding: The molten sheet extruded from the T-die is immediately attached to a mirror cooling roller with a surface temperature controlled at 20-25℃ for rapid cooling and shaping, and then wound into a film to obtain a high-barrier functional layer with a thickness of 30-50μm.

[0024] The preparation method of the above-mentioned multi-layer high-barrier paper-based composite packaging material is as follows: The first step involves directly coating molten low-density polyethylene onto the corona-treated outer surface of a paper base under pressure (single-sided coating). After being squeezed and cooled by a cooling steel roller and a rubber pressure roller, a continuous and dense outer protective layer with a thickness of 20μm is formed. The extrusion temperature is 180℃, the air gap distance is 130mm, and the cooling roller temperature is 18℃. The second step involves applying polyurethane adhesive to the inner side of the paper base (the side without outer protection) using a ceramic anilox roller at a coating amount of 3 g / m². The paper base coated with adhesive is then pressed and bonded to one side of the high-barrier functional layer using a composite roller at a pressure of 0.5 MPa. Polyurethane adhesive is then applied to the other side of the high-barrier functional layer at a coating amount of 2 g / m², and then pressed and bonded to the heat-sealing film using a composite roller at a pressure of 0.3 MPa. The mixture is then placed in a curing chamber and kept at 45°C for 32 hours to allow the adhesive to fully cross-link and react, thus obtaining the final product.

[0025] Example 2 A multi-layer high-barrier paper-based composite packaging material, comprising, from the outside to the inside, an outer protective layer, a printed paper base layer, an adhesive layer, a high-barrier functional layer, an adhesive layer, and an inner heat-sealing layer; the high-barrier functional layer comprises the following components by weight: The composition includes 70 parts of base resin (polyethylene), 15 parts of nano-barrier filler, 15 parts of ethylene-vinyl alcohol copolymer, 8 parts of compatibilizer, 5 parts of composite toughening agent, 0.3 parts of antioxidant, and 0.5 parts of lubricant. The base resin is linear low-density polyethylene, the compatibilizer is maleic anhydride-grafted polypropylene, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:2, and the lubricant is ethylene bis-stearamide. The preparation method of the nano-barrier filler includes the following steps: Step 1: Add montmorillonite to deionized water and disperse it at 70°C with high-speed stirring at 1000 rpm for 3 hours. Then let it stand for 18 hours to form a suspension with three layers: upper, middle and lower. Extract the middle layer suspension and centrifuge it at 10000 rpm. Collect the precipitate and vacuum dry it at 85°C to constant weight to obtain product 1. In Step 1, the weight ratio of montmorillonite to deionized water is 100:600. Step 2: Disperse product 1 in deionized water to obtain a suspension of product 1. Place bis(octadecyldimethyl)ammonium chloride in a round-bottom flask with a reflux condenser, add ethanol and heat to 70°C, stir to dissolve. Add the ethanol solution of bis(octadecyldimethyl)ammonium chloride dropwise to the suspension of product 1 at 3 mL / min with stirring at 1000 rpm. React at 80°C for 6 h, then filter, wash three times with hot water at 60°C, and then wash twice with anhydrous ethanol until no white precipitate is formed when tested with 0.1 mol / L silver nitrate solution. Dry under vacuum at 85°C to constant weight to obtain product 2. In step 2, the weight ratio of product 1 to deionized water is 100:550, and the weight ratio of product 1, bis(octadecyldimethyl)ammonium chloride, and ethanol is 100:25:100. Step 3: Product 2 is mixed with toluene and ultrasonically dispersed at 500W for 40 min. Then, silane coupling agent KH-550 is added, the temperature is raised to 112℃, and the mixture is refluxed under nitrogen protection for 12 h. After cooling, the mixture is filtered, washed twice with toluene, and dried at 85℃ for 6 h to obtain product 3. In step 3, the weight ratio of product 2 to toluene and silane coupling agent KH-550 is 100:350:15. In step 4, the weight ratio of product 3 to N,N-dimethylformamide and graphene oxide is 100:450:3. In the graphene oxide dispersion, the weight ratio of graphene oxide to N,N-dimethylformamide is 3:200. The rest is the same as in Example 1.

[0026] In the preparation method of the composite toughening agent, in step a, the weight ratio of the polyolefin elastomer particles to the mixed solvent of xylene, maleic anhydride, dicumyl peroxide, silica, ethanol and water is 100:500:4:1.5:40:400, and the volume ratio of ethanol to water in the mixed solvent is 9:1; in step b, the weight ratio of the composite powder, benzoyl peroxide and glycidyl methacrylate is 100:2.5:10, and the rest is the same as in Example 1.

[0027] The preparation methods of the above-mentioned high-barrier functional layer and multi-layer high-barrier paper-based composite packaging material are the same as those in Example 1.

[0028] Example 3 A multi-layer high-barrier paper-based composite packaging material, comprising, from the outside to the inside, an outer protective layer, a printed paper base layer, an adhesive layer, a high-barrier functional layer, an adhesive layer, and an inner heat-sealing layer; the high-barrier functional layer comprises the following components by weight: The composition includes 85 parts of base resin polyethylene, 10 parts of nano-barrier filler, 8 parts of ethylene-vinyl alcohol copolymer, 4 parts of compatibilizer, 10 parts of composite toughening agent, 0.8 parts of antioxidant, and 1.5 parts of lubricant. The base resin is linear low-density polyethylene, the compatibilizer is maleic anhydride-grafted polypropylene, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1, and the lubricant is ethylene bis-stearamide. The preparation method of the nano-barrier filler includes the following steps: Step 1: Add montmorillonite to deionized water and disperse it at 800 rpm for 4 hours at 80°C. Then let it stand for 24 hours to form a suspension with three layers: upper, middle and lower. Extract the middle layer suspension and centrifuge it at 12000 rpm. Collect the precipitate and vacuum dry it at 85°C to constant weight to obtain product 1. In Step 1, the weight ratio of montmorillonite to deionized water is 100:800. Step 2: Disperse product 1 in deionized water to obtain a suspension of product 1. Place dioctadecyl dimethyl ammonium chloride in a round-bottom flask with a reflux condenser, add ethanol and heat to 60°C, stirring to dissolve. Add the ethanol solution of dioctadecyl dimethyl ammonium chloride dropwise to the suspension of product 1 at 5 mL / min with stirring at 1200 rpm. React at 85°C for 5 h, then filter, wash three times with hot water at 70°C, and then wash twice with anhydrous ethanol until no white precipitate is formed when tested with 0.1 mol / L silver nitrate solution. Dry under vacuum at 85°C to constant weight to obtain product 2. In step 2, the weight ratio of product 1 to deionized water is 100:600, and the weight ratio of product 1, dioctadecyl dimethyl ammonium chloride, and ethanol is 100:30:80. Step 3: Product 2 is mixed with toluene and ultrasonically dispersed at 400W for 50 min. Then, silane coupling agent KH-550 is added, the temperature is raised to 118℃, and the mixture is refluxed under nitrogen protection for 14 h. After cooling, the mixture is filtered, washed twice with toluene, and dried at 80℃ for 8 h to obtain product 3. In step 3, the weight ratio of product 2 to toluene and silane coupling agent KH-550 is 100:450:10. In step 4, the weight ratio of product 3 to N,N-dimethylformamide and graphene oxide is 100:350:8. In the graphene oxide dispersion, the weight ratio of graphene oxide to N,N-dimethylformamide is 8:200. The rest is the same as in Example 1.

[0029] In the preparation method of the composite toughening agent, in step a, the weight ratio of the polyolefin elastomer particles to the mixed solvent of xylene, maleic anhydride, dicumyl peroxide, silica, ethanol and water is 100:400:5:2.0:50:300, and the volume ratio of ethanol to water in the mixed solvent is 9:1; in step b, the weight ratio of the composite powder, benzoyl peroxide and glycidyl methacrylate is 100:3.5:8, and the rest is the same as in Example 1.

[0030] The preparation methods of the above-mentioned high-barrier functional layer and multi-layer high-barrier paper-based composite packaging material are the same as those in Example 1.

[0031] Comparative Example 1 A high-barrier functional layer, wherein the nano-barrier filler is replaced with commercially available organic nano-montmorillonite, and the rest is the same as in Example 1.

[0032] Comparative Example 2 A high-barrier functional layer, wherein the composite toughening agent is replaced with a common commercially available polyolefin elastomer, and the rest is the same as in Example 1.

[0033] Comparative Example 3 A high-barrier functional layer, wherein the nano-barrier filler is replaced with commercially available organic nano-montmorillonite, the composite toughening agent is replaced with commercially available polyolefin elastomer, and the rest is the same as in Example 1.

[0034] Comparative Example 4 A multi-layer high-barrier paper-based composite packaging material, wherein the high-barrier functional layer of Comparative Example 1 is used, and the rest is the same as in Example 1.

[0035] Comparative Example 5 A multi-layer high-barrier paper-based composite packaging material, wherein the high-barrier functional layer of Comparative Example 2 is used, and the rest is the same as in Example 1.

[0036] Comparative Example 6 A multi-layer high-barrier paper-based composite packaging material, wherein the high-barrier functional layer of Comparative Example 3 is used, and the rest is the same as in Example 1.

[0037] Performance testing: The oxygen permeability of the high-barrier functional layers prepared in Examples 1-3 and Comparative Examples 1-3 was tested according to GB / T1038.1-2022 to characterize the oxygen barrier performance of the high-barrier functional layers. The water vapor transmission rate of the high-barrier functional layers prepared in Examples 1-3 and Comparative Examples 1-3 was tested according to GB / T1037-2021 to characterize the water vapor barrier performance of the high-barrier functional layers. The elongation at break and tensile strength of the high-barrier functional layers prepared according to the test examples and comparative examples were used to characterize the toughness of the high-barrier functional layers. The results are shown in Table 1.

[0038] The oxygen barrier properties and water vapor barrier properties of the composite packaging materials obtained in Examples 1-3 and Comparative Examples 4-6 were tested in accordance with GB / T1038.1-2022 and GB / T1037-2021, and the results are shown in Table 2.

[0039] Table 1. Performance Test Results Table 2 As shown in Tables 1 and 2, the barrier properties of the high-barrier functional layers and composite packaging materials in Examples 1-3 are significantly better than those in the comparative examples. This demonstrates that the nano-barrier filler of the present invention forms a more complex and tortuous permeation path in the high-barrier functional layer film through the "montmorillonite-graphene oxide" hybrid nanofiller, greatly delaying the passage of gases and water vapor. Simultaneously, in synergy with the composite toughening agent, it maintains good tensile properties and exhibits high tensile strength.

[0040] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0041] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A multi-layer high-barrier paper-based composite packaging material, characterized in that, From the outside in, it comprises, in sequence, an outer protective layer, a printed paper base layer, an adhesive layer, a high-barrier functional layer, an adhesive layer, and an inner heat-sealing layer; the high-barrier functional layer comprises the following components by weight: The base resin is polypropylene or polyethylene, which contains 70-85 parts; nano-barrier filler, which contains 10-15 parts; ethylene-vinyl alcohol copolymer, which contains 8-15 parts; compatibilizer, which contains 4-8 parts; composite toughening agent, which contains 5-10 parts; antioxidant, which contains 0.3-0.8 parts; and lubricant, which contains 0.5-1.5 parts. The preparation method of the nano-barrier filler includes the following steps: Step 1: Add montmorillonite to deionized water and disperse it at 70-80℃ with high-speed stirring at 800-1000 rpm for 3-4 hours. Then let it stand for 18-24 hours to form a suspension with three layers: upper, middle and lower. Extract the middle layer suspension and centrifuge it at 10000-12000 rpm. Collect the precipitate and dry it to obtain product 1. Step 2: Disperse product 1 in deionized water to obtain a suspension. Add bis(octadecyldimethylammonium chloride) to ethanol, and add the ethanol solution of bis(octadecyldimethylammonium chloride) to the suspension of product 1 under stirring. React at 80-85℃ for 5-6 hours, and then purify to obtain product 2. Step 3: Mix product 2 with toluene and ultrasonically disperse at 400-500W for 40-50 min. Then add silane coupling agent KH-550, heat to 112-118℃, and reflux under nitrogen protection for 12-14 h to obtain product 3. Step 4: Disperse product 3 in N,N-dimethylformamide solvent to obtain a suspension of product 3. Sonicate the suspension for 25-35 min. Disperse graphene oxide in N,N-dimethylformamide and ultrasonically exfoliate at 350-450 W for 1-2 h to obtain a uniform graphene oxide dispersion. Add the graphene oxide dispersion to the suspension of product 3 with stirring. React at 60-70℃ with stirring for 10-12 h. After the reaction is completed, purify the product to obtain the final product.

2. The multi-layer high-barrier paper-based composite packaging material according to claim 1, characterized in that, In step 1, the weight ratio of montmorillonite to deionized water is 100:600-800. In step 2, the weight ratio of product 1 to deionized water is 100:500-600. The weight ratio of product 1, dioctadecyldimethylammonium chloride, and ethanol is 100:25-30:80-100.

3. The multi-layer high-barrier paper-based composite packaging material according to claim 1, characterized in that, In step 3, the weight ratio of product 2 to toluene and silane coupling agent KH-550 is 100:350-450:10-15.

4. The multi-layer high-barrier paper-based composite packaging material according to claim 1, characterized in that, In step 4, the weight ratio of product 3 to N,N-dimethylformamide and graphene oxide is 100:350-450:3-8, and the weight ratio of graphene oxide to N,N-dimethylformamide in the graphene oxide dispersion is 3-8:

200.

5. The multi-layer high-barrier paper-based composite packaging material according to claim 1, characterized in that, The preparation method of the composite toughening agent includes the following steps: Step a: Take polyolefin elastomer particles and heat xylene to 100-105℃ to dissolve the olefin elastomer particles, then add maleic anhydride and dicumyl peroxide, and react at 108-115℃ for 6-7 hours to obtain a maleic anhydride-grafted polyolefin mixture; disperse fumed silica in a mixed solvent of ethanol and water, ultrasonically disperse, add silane coupling agent KH-550, adjust the pH to 4-5, and stir at 70-75℃ for 5-6 hours to obtain an activated nano silica dispersion; mix the maleic anhydride-grafted polyolefin mixture with the activated nano silica dispersion, stir at 80-85℃ for 3-4 hours, and purify to obtain a core-shell structured composite powder; Step b: The composite powder obtained in step a is melt-extruded with benzoyl peroxide and glycidyl methacrylate at the following temperatures: Zone 1 160-170℃, Zone 2 175-185℃, Zone 3 180-190℃, die head 185-195℃, and screw speed 260-300 rpm.

6. The multi-layer high-barrier paper-based composite packaging material according to claim 5, characterized in that, In step a, the weight ratio of the polyolefin elastomer particles to the mixed solvent of xylene, maleic anhydride, dicumyl peroxide, silica, ethanol and water is 100:400-500:4-5:1.5-2.0:40-50:300-400, and the volume ratio of ethanol to water in the mixed solvent of ethanol and water is 9:

1.

7. The multi-layer high-barrier paper-based composite packaging material according to claim 5, characterized in that, In step b, the weight ratio of the composite powder, benzoyl peroxide, and glycidyl methacrylate is 100:2.5-3.5:8-10.

8. The multi-layer high-barrier paper-based composite packaging material according to claim 1, characterized in that, The base resin is linear low-density polyethylene, the compatibilizer is maleic anhydride-grafted polypropylene, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1-2, and the lubricant is ethylene bis-stearamide.

9. The method for preparing the multilayer high-barrier paper-based composite packaging material as described in any one of claims 1-8, characterized in that, Specifically, the outer protective layer, the printed paper base layer, the adhesive layer, the high-barrier functional layer, and the inner heat-sealing layer are combined to obtain the final product.

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