A multifunctional high-barrier multilayer packaging film and its preparation method

Abstract

This invention belongs to the field of packaging materials and provides a multifunctional high-barrier multilayer packaging film and its preparation method. The invention employs a five-layer structure design, consisting of a polypropylene layer, a first adhesive layer, an ethylene-vinyl alcohol copolymer layer, a second adhesive layer, and a polyethylene layer, arranged from the outside in. The adhesive layer contains a masterbatch covalently compounded from maleic anhydride-grafted polyethylene and aminopropylsilane-modified montmorillonite via amide and imide bonds, achieving strong interfacial bonding between the barrier layer and the polyolefin layer, as well as synergistic reinforcement from the inorganic layers. The film exhibits an oxygen permeability of no more than 1.0 cm³ / (m²·24 h·0.1 MPa) and a water vapor permeability of no more than 1.0 g / (m²·24 h). Under heat treatment at 121℃, interlayer delamination does not occur. This invention solves the problems of barrier performance degradation, interlayer peeling, and insufficient toughness in existing multilayer barrier films under humid and hot environments, and has application value in high-temperature retort packaging, aseptic packaging, and pharmaceutical packaging.

Description

Technical Field

[0001] This invention relates to the field of packaging materials, specifically to a multifunctional high-barrier multilayer packaging film and its preparation method. Background Technology

[0002] In the modern packaging industry, multilayer composite barrier films, as core materials for ensuring the quality of contents and extending shelf life, are widely used in the packaging of oxygen- and water vapor-sensitive products such as food, pharmaceuticals, and medical devices. With the upgrading of consumption and the development of cold chain logistics, the market has placed higher demands on the barrier performance of packaging films: in the food sector, extremely low oxygen permeability is required to inhibit oil oxidation and microbial growth; in pharmaceutical packaging, water vapor barrier properties are needed to protect the stability of hygroscopic drugs; and in high-temperature retort packaging scenarios, the films must withstand saturated steam treatment at 121°C without performance degradation. These applications require barrier films to not only possess excellent barrier properties under normal temperature and dry conditions, but also maintain barrier stability and interlayer bonding reliability under harsh environments such as high temperature and high humidity, while also considering heat-sealing performance, mechanical strength, and processing adaptability to meet the high-speed continuous operation requirements of automated packaging production lines. Therefore, developing multilayer barrier films that can maintain durable barrier performance under humid and hot conditions, do not delaminate at the interface, and have good processability is of great significance for improving packaging safety, expanding application areas, and promoting the development of the packaging industry towards high performance.

[0003] Currently, multilayer barrier films typically use ethylene-vinyl alcohol copolymer (EVA) as the core barrier layer, which is then combined with polyolefin layers such as polyethylene and polypropylene through a co-extrusion composite process to form a multilayer structure. However, existing technologies have several shortcomings: First, due to the hydrophilicity of hydroxyl groups, EVA swells and absorbs moisture in high humidity environments. The hydrogen bond network is disrupted by water molecules, leading to water plasticization, which causes a sharp increase in oxygen permeability and a significant decrease in barrier performance. For example, Chinese patent CN104149446A discloses a high-barrier film and its preparation method, but its barrier stability is insufficient under high humidity conditions. Second, the large polarity difference between EVA and polyolefins results in weak interfacial bonding. During heat treatment, the mismatch in thermal expansion coefficients generates interlayer thermal stress, which, combined with moisture... Sub-penetration induces interfacial swelling stress, and the coupling effect of the two can easily lead to interfacial delamination or the formation of microcrack channels, which can cause barrier failure in severe cases. For example, Chinese patent CN219338880U discloses a multilayer barrier film structure for food packaging, but the interfacial bonding reliability is insufficient after cooking. Thirdly, maleic anhydride-grafted polyolefins are often introduced as a binder layer to improve interfacial bonding, but the melt rheological properties of the grafted material do not match the matrix, resulting in a narrowing of the co-extrusion processing window. Moreover, the rheological fluctuations are aggravated after the reactive compatibilizer is combined with the inorganic filler, making it difficult to guarantee the processing stability and product consistency between batches. Summary of the Invention

[0004] The purpose of this invention is to provide a multifunctional high-barrier multilayer packaging film and its preparation method, which solves the problems of existing multilayer structures in achieving extremely low oxygen permeability and low water vapor permeability. These problems include the degradation of barrier durability and the risk of interface delamination caused by EVOH moisture-sensitive water plasticization and interlayer thermal and moisture stress mismatch; melt rheological fluctuations and narrowing of co-extrusion processing window and insufficient batch consistency caused by the introduction of reactive compatibility and inorganic lamellar reinforcement; and the difficulty in simultaneously achieving the coupling contradiction between the need for high modulus densification to improve barrier and interface strengthening and the need for resistance to brittleness and microcrack channel formation after heat treatment.

[0005] This invention achieves multi-functional integration by introducing a covalently bonded composite masterbatch into the adhesive layer: maleic anhydride-grafted polyethylene and aminopropylsilane-modified montmorillonite form amide and imide bonds covalently during interfacial reactive extrusion, constructing a strong interfacial anchoring structure of polymer-inorganic sheets. This achieves reactive compatibility and interfacial enhancement of the adhesive layer to the barrier layer through the ring-opening esterification reaction of maleic anhydride groups and EVOH hydroxyl groups and interfacial interactions. Furthermore, the intercalation barrier and stress dispersion effect of montmorillonite nanosheets synergistically improve barrier performance and interfacial strength. At the same time, the surface amino groups of modified montmorillonite react with maleic anhydride groups to inhibit the aggregation of inorganic particles, ensuring the rheological stability and batch reproducibility of co-extrusion processing. Thus, durable barrier and interfacial reliability are achieved in humid and hot environments without sacrificing toughness and processability.

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

[0007] A multifunctional high-barrier multilayer packaging film, wherein the multifunctional high-barrier multilayer packaging film has a five-layer structure, comprising, from the outside to the inside, an outer layer, a first adhesive layer, a barrier layer, a second adhesive layer and an inner layer;

[0008] The outer layer is a polypropylene layer, the inner layer is a polyethylene layer, and the barrier layer is an ethylene-vinyl alcohol copolymer layer.

[0009] At least one of the first and second adhesive layers contains a covalently bonded composite masterbatch; the total thickness of the multifunctional high-barrier multilayer packaging film is 40–200 μm; the oxygen permeability measured according to GB / T 19789-2021 at 23±0.5℃ and relative humidity of 0%–5% is not greater than 1.0 cm³ / (m²·24 h·0.1 MPa), and the water vapor permeability measured according to GB / T1037-2021 at 38℃ using the weight gain method is not greater than 1.0 g / (m²·24 h).

[0010] Furthermore, the covalently bonded composite masterbatch I comprises, by weight, 60–95 parts of maleic anhydride-grafted polyethylene and 5–40 parts of aminopropylsilane-modified montmorillonite, and the two together comprise 100 parts by weight.

[0011] Furthermore, in the covalently bonded composite masterbatch I, the covalent bond between the montmorillonite and the maleic anhydride-grafted polyethylene includes an amide acid structure formed by the reaction of maleic anhydride groups with amino groups, including an amide bond, and an imide bond formed by further dehydration and cyclization of the amide acid structure.

[0012] Furthermore, the preparation method of the aminopropylsilane-modified montmorillonite includes the following sub-steps:

[0013] A1, using 100 parts by weight of montmorillonite as a reference, the montmorillonite is added to a dispersion medium composed of ethanol and water, wherein the volume ratio of ethanol to water is 6:4 to 9:1, and the amount of dispersion medium added is such that the liquid-solid ratio is 5 to 20 mL per g based on the mass of montmorillonite. The dispersion is carried out under mechanical stirring at 300 to 800 r / min for 10 to 60 min at 25–40°C and normal pressure.

[0014] A2, then add a total of 2–10 parts by weight of aminopropylsilane and continue stirring for 30–120 min, wherein the aminopropylsilane is selected from one or both of 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane;

[0015] A3, the pH of the system was adjusted to 4.0–5.5 by titration with an aqueous acetic acid solution of 1%–10% by mass under stirring;

[0016] A4, continue stirring the reaction at 40–60℃ and normal pressure for 1–6 h;

[0017] A5, after the reaction is complete, filter and wash with ethanol and water sequentially until the pH of the final water wash filtrate is 6.5–7.5;

[0018] A6 was then dried at 60–90 °C for 6–12 h under vacuum conditions with an absolute pressure of 0.01–0.03 MPa to obtain aminopropylsilane-modified montmorillonite; wherein the aminopropylsilane-modified montmorillonite has a water content of not more than 1.0 wt% and a nitrogen content of 0.2–1.5 wt%.

[0019] Furthermore, the preparation method of the maleic anhydride-grafted polyethylene includes the following sub-steps:

[0020] B1, premixing 100 parts by weight of polyethylene, 0.3–2.0 parts by weight of maleic anhydride and 0.03–0.20 parts by weight of dicumyl peroxide;

[0021] B2, under nitrogen protection, is a twin-screw reactive extrusion process. The temperature in each zone during the reactive extrusion process is 170–220℃, the screw speed is 200–500 r / min, and the total material residence time is 30–180 s.

[0022] B3, in the vacuum exhaust section, the absolute pressure is controlled at 0.02–0.06 MPa to remove free maleic anhydride;

[0023] B4, after being water-cooled and pelletized, is dried under vacuum conditions of 80–100℃ and 0.01–0.03 MPa for 4–8 h to obtain maleic anhydride-grafted polyethylene; wherein the maleic anhydride-grafted polyethylene satisfies the following requirements: the content of maleic anhydride groups is 0.05–2.0 wt%, and the content of free maleic anhydride is not higher than 0.05 wt%.

[0024] Furthermore, the preparation method of the covalently bonded composite masterbatch includes the following sub-steps:

[0025] C1, the aminopropylsilane-modified montmorillonite and the maleic anhydride-grafted polyethylene are mixed in parts by weight, wherein the aminopropylsilane-modified montmorillonite is 5-40 parts by weight and the maleic anhydride-grafted polyethylene is 60-95 parts by weight.

[0026] C2 was subjected to interfacial reaction and dispersion in a twin-screw extruder under nitrogen protection and atmospheric pressure. The extrusion temperature was 170–220℃, the screw speed was 250–600 r / min, and the residence time was 30–150 s.

[0027] C3, extruded and water-cooled pelletized to obtain covalently bonded composite masterbatch; wherein the covalently bonded composite masterbatch has a moisture content of not more than 1.0 wt%.

[0028] Furthermore, the outer layer has a thickness of 10–60 μm, and the inner layer has a thickness of 15–100 μm;

[0029] The thickness of the barrier layer is 2–30 μm;

[0030] The thickness of the first adhesive layer and the second adhesive layer are each independently 2–20 μm;

[0031] The molar fraction of ethylene in the ethylene-vinyl alcohol copolymer is 20–45 mol.

[0032] Furthermore, both the first adhesive layer and the second adhesive layer contain the covalently bonded composite masterbatch, and the amount of the covalently bonded composite masterbatch added in the corresponding adhesive layer is 1–30 wt% based on the total mass of the corresponding adhesive layer.

[0033] Furthermore, the multifunctional high-barrier multilayer packaging film has the following layer sequence: polypropylene layer / first adhesive layer / ethylene-vinyl alcohol copolymer layer / second adhesive layer / polyethylene layer, and the continuous polymer phase of the first adhesive layer and the second adhesive layer is maleic anhydride-grafted polyethylene.

[0034] Furthermore, the multifunctional high-barrier multilayer packaging film is suitable for packaging that has been heat-treated with saturated steam at 121°C for 10–60 min, and no visible delamination occurs at the interface of the adhesive layers on both sides of the barrier layer.

[0035] As a concept of this invention, the design of covalently bonded composite masterbatch is mainly used to enhance the interfacial bonding strength between the adhesive layer and the barrier layer, and to improve the overall barrier stability and anti-delamination performance of the film. Maleic anhydride-grafted polyethylene, as a reactive compatibilizer, can undergo ring-opening esterification with the hydroxyl groups of the ethylene-vinyl alcohol copolymer during co-extrusion processing to form ester bonds (and / or form hydrogen bonds with the hydroxyl groups through carboxylic acid groups). This enhances the interaction and improves the interfacial bonding force at the interface between the adhesive layer and the barrier layer, effectively suppressing interfacial delamination caused by thermal stress and moisture penetration during high-temperature cooking. The introduction of aminopropylsilane-modified montmorillonite achieves multiple synergistic effects: First, surface amino modification transforms montmorillonite from hydrophilic to having good organic compatibility, enabling nanoscale intercalation and dispersion within the polyethylene matrix. The two-dimensional sheet structure constructs a tortuous gas diffusion path, synergistically enhancing oxygen and water vapor barrier properties. Second, the amino groups on the modified montmorillonite surface undergo nucleophilic addition reactions with the maleic anhydride groups grafted onto the polyethylene during interfacial extrusion to generate amide bonds. Some of these amide bonds undergo dehydration and cyclization under high-temperature shear conditions to form more stable imide bonds. This covalent bonding constructs a strong interfacial anchorage between the polymer matrix and the inorganic sheets, transforming the inorganic phase from a simple physical filler into a chemically bonded reinforcing structure. This improves both the mechanical properties and thermal stability of the composite masterbatch, as well as the melt rheological properties and processing stability. Third, the stress dispersion effect of the nanosheets allows the adhesive layer to maintain flexibility while possessing higher modulus and creep resistance. During heat treatment, it can buffer stress concentration caused by differences in interlayer thermal expansion, preventing the initiation and propagation of microcracks. Through the aforementioned synergistic mechanism, the introduction of covalently bonded composite masterbatch not only enhances interfacial bonding and barrier properties, but also takes into account processability and batch consistency, achieving a balance between high barrier performance and interfacial reliability.

[0036] This invention also discloses a method for preparing a multifunctional high-barrier multilayer packaging film, comprising the following steps:

[0037] S1, prepare aminopropylsilane modified montmorillonite, prepare maleic anhydride grafted polyethylene, and prepare covalently bonded composite masterbatch;

[0038] S2, polypropylene, ethylene-vinyl alcohol copolymer, polyethylene, and binder material composed of maleic anhydride grafted polyethylene and covalently bonded composite masterbatch are melted in their respective extruders and co-extruded into a film through a co-extrusion die in the order of outer layer / first binder layer / barrier layer / second binder layer / inner layer, wherein the melt temperature of polypropylene is 190–240℃, the melt temperature of polyethylene is 170–220℃, and the melt temperature of ethylene-vinyl alcohol copolymer is 170–210℃;

[0039] S3, after cooling and shaping the co-extruded melt, it is wound up to obtain the multifunctional high-barrier multilayer packaging film.

[0040] Furthermore, the twin-screw reactive extruder used in step S1 to prepare maleic anhydride-grafted polyethylene and the twin-screw extruder used to prepare covalently bonded composite masterbatch are co-rotating twin-screw extruders.

[0041] Furthermore, the co-extrusion film is produced using co-extrusion casting, and the surface temperature of the cooling roller is 10–40°C.

[0042] Furthermore, the extruder used to form the first adhesive layer and the second adhesive layer is equipped with a vacuum exhaust section, the absolute pressure of which is 0.02–0.06 MPa, and the die head temperature of the co-extrusion die is 180–230°C, and the total residence time of the co-extrusion melt in the co-extrusion die is 30–180 s.

[0043] Furthermore, the amount of covalently bonded composite masterbatch added to the adhesive layer raw material is 1–30 wt% based on the total mass of the corresponding adhesive layer raw material.

[0044] Furthermore, after winding, at least one of a surface treatment step and a uniaxial stretching step is performed, wherein the surface treatment step is to perform corona treatment on the outer layer for subsequent printing or lamination, and the stretching temperature of the uniaxial stretching step is 70–130°C and the stretching ratio is 1.2–4.0 times.

[0045] Furthermore, the humidification conditions before the oxygen permeability test were 24 h at 23±0.5℃ and relative humidity of 0%~5%.

[0046] Furthermore, the water vapor transmission rate was measured using the weight gain method according to GB / T 1037-2021, and a humidity gradient was established on both sides of the test device, with the relative humidity on the high humidity side being 90% to 100% and the low humidity side being under desiccant conditions.

[0047] Furthermore, the volume fraction of ethanol is not less than 95 vol%, and the water is deionized water.

[0048] Furthermore, the aminopropylsilane is pre-dissolved in ethanol and added to the dispersion system in batches before addition; wherein, the ethanol used to dissolve the aminopropylsilane is included in the amount of dispersion medium added in step A1, so that the liquid-solid ratio in step A1 is still 5-20 mL per g (based on the dry mass of montmorillonite); the mass fraction of the aminopropylsilane ethanol solution is 5%-30%.

[0049] Furthermore, the filtration process employs vacuum filtration, with 2 to 5 washes using ethanol and 2 to 5 washes using water.

[0050] Furthermore, the washing solution used each time is 10-30 mL per g, based on the dry weight of montmorillonite.

[0051] Furthermore, the endpoint criterion for drying is that the mass difference between two consecutive weighings with an interval of 1 hour is no greater than 0.1%, and the product is sealed and stored after drying to prevent moisture regain.

[0052] Furthermore, the moisture content was determined using the drying loss method or the Karl Fischer method.

[0053] Furthermore, the nitrogen content was determined using the CHNS elemental analysis method or the Kjeldahl nitrogen determination method.

[0054] Furthermore, the content of maleic anhydride groups was determined by acid-base titration after hydrolysis.

[0055] Furthermore, the content of free maleic anhydride was determined by high performance liquid chromatography.

[0056] Furthermore, the inorganic content of the covalently bonded composite masterbatch was determined by ash method or thermogravimetric method, and the inorganic content was 7-30 wt%.

[0057] Furthermore, the formation of amide or imide bonds in the covalently bonded composite masterbatch was confirmed by infrared spectroscopy or solid-state NMR.

[0058] Furthermore, the 121℃ heat treatment is a 121℃ saturated steam heat treatment for 10–60 min. After the heat treatment, the interface of the adhesive layer is not visible to be delaminated or continuously bubbly when visually observed at room temperature.

[0059] As another aspect of this invention, the method of co-extrusion casting combined with in-situ interfacial reaction is mainly used to enhance the uniformity of interfacial bonding in multilayer structures and ensure batch-to-batch processing stability and product consistency. During co-extrusion, by precisely controlling the melt temperature and rheological properties of each layer, the polypropylene, polyethylene, ethylene-vinyl alcohol copolymer, and binder layer melts achieve stable stratified flow within the co-extrusion die, avoiding interfacial instability and layer thickness fluctuations caused by viscosity ratio mismatch or elasticity mismatch. The covalently bonded structure of the covalently bonded composite masterbatch in the binder layer remains stable in the molten state, making the melt rheological properties between those of pure maleic anhydride-grafted polyethylene and pure inorganic filler systems. This retains the interfacial reactivity of the reactive compatibilizer while suppressing the shear and temperature sensitivity of the melt viscosity through the polymer-inorganic covalent network, thus broadening the co-extrusion processing temperature and shear rate windows. During the co-extrusion die and cooling / setting process, the maleic anhydride groups in the adhesive layer and the hydroxyl groups in the barrier layer undergo an in-situ chemical reaction at the interface, forming a continuous and uniform chemically bonded interface. This avoids interface defects caused by uneven adhesive coating or incomplete curing in subsequent composite processes. The co-extrusion casting process, through rapid cooling and setting, allows each layer to achieve synergistic orientation and stress equilibrium during crystallization, reducing residual internal stress and differences in thermal shrinkage, thus improving the dimensional stability and anti-warping properties of the film. Through the optimization of the above preparation process, this invention achieves continuous and efficient preparation of high-barrier multilayer films, ensuring product quality stability and batch reproducibility, and meeting the needs of industrial production.

[0060] In the covalently bonded composite masterbatch system of this invention, maleic anhydride-grafted polyethylene and aminopropylsilane-modified montmorillonite each have a clear focus and main function: maleic anhydride-grafted polyethylene, as a reactive compatibilizer, mainly functions to achieve chemical anchoring of the adhesive layer and the barrier layer through the chemical reaction of maleic anhydride groups with the hydroxyl groups of ethylene-vinyl alcohol copolymer, while maleic anhydride groups react with the amino groups on the surface of modified montmorillonite to form a polymer-inorganic covalently bonded interface; aminopropylsilane-modified montmorillonite focuses on improving the barrier performance through the intercalation dispersion of nanosheets and the tortuous path effect, and constructing a covalent network reinforcement structure through the participation of surface amino groups in the interfacial reaction. In terms of improving barrier performance, maleic anhydride-grafted polyethylene forms a dense chemically bonded interface layer at the interface between the adhesive layer and the barrier layer, sealing the micropores and microcracks at the interface and blocking the interfacial diffusion path of gas and water vapor. The nanosheets of aminopropylsilane-modified montmorillonite are dispersed in the polyethylene matrix in an intercalated or exfoliated state. The high aspect ratio sheets form a certain degree of orientation and distribution under the action of the processing flow field, so that gas molecules need to bypass the sheet obstacles and diffuse through a tortuous path, which significantly prolongs the diffusion path length and diffusion time. In terms of improving interfacial bonding strength, the maleic anhydride groups of maleic anhydride-grafted polyethylene undergo nucleophilic addition reactions with the amino groups on the surface of modified montmorillonite under high-temperature shear conditions to generate amide bonds, and partially cyclize into imide bonds. This covalent bonding anchors the inorganic sheets in the polymer matrix to form a nanoscale reinforcing phase. At the same time, the ring-opening esterification reaction of maleic anhydride groups with the hydroxyl groups of ethylene-vinyl alcohol copolymer forms ester bonds at the interface of the adhesive layer and barrier layer, promoting molecular chain entanglement and interfacial reinforcement. The synergistic effect of the two changes the interface from physical contact to chemical bonding, and the interfacial bonding force is greatly improved. More importantly, the synergistic effect of covalent bonding between maleic anhydride-grafted polyethylene and aminopropylsilane-modified montmorillonite further amplifies the overall performance: covalent bonding improves the dispersion stability of inorganic sheets in the polymer matrix, avoiding stress concentration and interface defects caused by agglomeration; the covalent network structure endows the composite masterbatch with higher modulus and thermal stability, buffering interlayer thermal stress and swelling stress caused by moisture penetration during heat treatment, and inhibiting interfacial delamination and microcrack initiation; covalent bonding improves melt rheological properties, enabling the composite masterbatch to exhibit more stable rheological behavior and a wider processing window during co-extrusion. In summary, the synergistic network structure formed by the covalent bonding of maleic anhydride-grafted polyethylene and aminopropylsilane-modified montmorillonite achieves multiple functional integrations of reactive compatibility, nano-reinforcement, barrier synergy, and rheological optimization. This synergistic effect far exceeds the simple superposition of single components and is the core mechanism by which this invention achieves a balance between high barrier performance and interfacial reliability.

[0061] Beneficial technical effects

[0062] 1. Achieving excellent synergistic barrier performance with extremely low oxygen and water vapor permeability: Through a five-layer structure design and the introduction of covalently bonded composite masterbatch, the film of this invention achieves an oxygen permeability of no more than 1.0 cm³ / (m²·24 h·0.1 MPa) and a water vapor permeability of no more than 1.0 g / (m²·24 h) at 23±0.5℃ and a relative humidity of 0%~5%, meeting the stringent performance requirements of high-barrier packaging materials. The aminopropylsilane-modified montmorillonite nanosheets in the covalently bonded composite masterbatch construct a tortuous path for gas diffusion within the adhesive layer, achieving dual high-efficiency barrier performance against both oxygen and water vapor in synergy with the ethylene-vinyl alcohol copolymer barrier layer. Simultaneously, the chemical bonding interface between the adhesive layer and the barrier layer eliminates interfacial micropores and microcrack channels, preventing rapid gas diffusion along the interface and ensuring the integrity and durability of the barrier performance.

[0063] 2. Significantly improved interfacial bonding reliability and anti-delamination performance under high-temperature cooking conditions: After saturated steam heat treatment at 121℃ for 10–60 min, the adhesive layer interface on both sides of the barrier layer of the film of this invention does not exhibit visible delamination or continuous bubbling, effectively solving the interfacial delamination problem caused by interlayer thermal and moisture stress mismatch in existing multilayer barrier films under high temperature and humidity conditions. The reactive compatibility between maleic anhydride-grafted polyethylene and ethylene-vinyl alcohol copolymer forms molecular chain interpenetration and chemical bond bridging at the interface, improving the interfacial bonding force from physical adhesion to chemical bonding; at the same time, the amide and imide bonds between aminopropylsilane-modified montmorillonite and maleic anhydride-grafted polyethylene covalently connect to construct a polymer-inorganic covalent network, enabling the adhesive layer to maintain flexibility while possessing higher modulus and creep resistance. This effectively buffers the interlayer stress concentration caused by differences in thermal expansion coefficients and moisture penetration during heat treatment, inhibits microcrack initiation and interfacial delamination, and ensures the long-term reliability of the packaging film in harsh application scenarios such as retort packaging and aseptic packaging.

[0064] 3. Improved rheological stability and batch consistency in co-extrusion processing: The polymer-inorganic covalent network structure in the covalently bonded composite masterbatch allows the melt rheological properties to fall between those of pure maleic anhydride-grafted polyethylene and pure inorganic filler systems. This suppresses the shear and temperature sensitivity of melt viscosity, broadens the temperature and shear rate windows for co-extrusion processing, and reduces interfacial instability and layer thickness fluctuations caused by rheological mismatch. Aminopropylsilane modification enables nanoscale intercalation and dispersion of montmorillonite in the polyethylene matrix, avoiding melt flow degradation and processing defects caused by inorganic particle agglomeration. Simultaneously, covalent bonding inhibits the re-agglomeration of modified montmorillonite under high-temperature shear conditions, ensuring dispersion stability and rheological consistency across different batches of masterbatch. Through a co-extrusion casting film preparation process combined with in-situ interfacial reaction, this invention achieves continuous and efficient production of multilayer barrier films, significantly improving product quality stability and batch reproducibility, meeting the needs of large-scale industrial production.

[0065] 4. Balancing High Barrier Performance and Excellent Toughness: Traditional methods to improve barrier performance often involve increasing the thickness of the barrier layer or the content of inorganic fillers, but this can easily lead to increased film rigidity and decreased toughness, making the film prone to brittleness under folding or impact conditions. This invention utilizes a nano-reinforcement mechanism of covalently bonded composite masterbatch to synergistically improve barrier performance and interfacial strength while maintaining the flexibility of the adhesive layer, avoiding the contradiction between high-modulus densification and anti-brittleness performance. The nanosheets of aminopropylsilane-modified montmorillonite in the polyethylene matrix play a role in stress dispersion and crack deflection, absorbing external impact energy and preventing crack propagation. This allows the film to maintain high barrier performance while possessing good impact resistance and puncture resistance, expanding its application range under high-speed continuous operation conditions in automated packaging production lines.

[0066] 5. Expanded Application Areas and Increased Packaging Value: The film of this invention, with its excellent barrier properties, interfacial reliability, and processing stability, can be widely used in high-temperature retort food packaging, aseptic packaging, pharmaceutical packaging, liquid packaging, and other fields with stringent requirements for barrier performance and heat treatment tolerance. Compared to traditional multilayer barrier films, the film of this invention maintains stable barrier performance and interlayer bonding even under heat treatment at 121℃, providing longer shelf life and more reliable quality assurance for the contents, enhancing the added value and market competitiveness of packaging products, and driving the packaging industry towards high performance and functionalization. Attached Figure Description

[0067] Figure 1 The bar chart shows the peel strength grouped for Example 1, Comparative Example 6, and Comparative Example 10.

[0068] Figure 2 The bar chart shows the peel strength retention rate of Example 1, Comparative Example 6, and Comparative Example 10.

[0069] Figure 3 The X-ray diffraction (XRD) superimposed spectra of pure montmorillonite, modified montmorillonite, masterbatch I, and the binder layer of Example 1 are shown.

[0070] Figure 4 X-ray diffraction (XRD) peak intensity decrease histogram for modified montmorillonite, masterbatch I, and the binder layer of Example 1.

[0071] Figure 5 This is a locally magnified and superimposed Fourier transform infrared (FTIR) image of modified montmorillonite, MA-g-PE, and masterbatch I.

[0072] Figure 6 The X-ray photoelectron spectroscopy (XPS) N 1s fitting spectra of modified montmorillonite and masterbatch I are shown.

[0073] Figure 7 The graphs show the dynamic mechanical analysis of the DMA storage modulus E′ versus temperature for Examples 1, 10, and 6.

[0074] Figure 8 The graphs show the dynamic mechanical analysis of DMA loss factor tanδ as a function of temperature for Examples 1, 10, and 6. Detailed Implementation

[0075] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0076] Example 1

[0077] This embodiment prepares a multifunctional high-barrier multilayer packaging film, and the specific steps are as follows:

[0078] Step S1-1: Preparation of aminopropylsilane-modified montmorillonite

[0079] Using 100 parts by mass of montmorillonite as a reference, montmorillonite was added to a dispersion medium composed of ethanol and water at a volume ratio of 7.5:1. The amount of dispersion medium added was such that the liquid-to-solid ratio was 12 mL / g. The mixture was mechanically stirred at 550 r / min for 35 min at 32 °C and atmospheric pressure. Then, a total of 6 parts by mass of 3-aminopropyltriethoxysilane was added, and stirring continued for 75 min. The pH of the system was adjusted to 4.7 by titration with a 5.5% (w / w) aqueous acetic acid solution under stirring. The reaction was continued at 50 °C and atmospheric pressure for 3.5 h. After the reaction, the mixture was filtered and washed successively with ethanol and water until the pH of the final water wash filtrate was 7.0. Subsequently, it was dried at 75 °C for 9 h under a vacuum of 0.02 MPa to obtain aminopropylsilane-modified montmorillonite with a water content of 0.8 wt% and a nitrogen content of 0.85 wt%.

[0080] Step S1-2: Preparation of maleic anhydride-grafted polyethylene

[0081] 100 parts by weight of polyethylene, 1.1 parts by weight of maleic anhydride, and 0.11 parts by weight of dicumyl peroxide were premixed. The mixture was then subjected to twin-screw reactive extrusion under nitrogen protection. During the reactive extrusion process, the temperature in each zone was 195°C, the screw speed was 350 r / min, and the total residence time of the material was 105 s. The absolute pressure was controlled at 0.04 MPa in the vacuum exhaust section to remove free maleic anhydride. The extruded strip was water-cooled, pelletized, and dried under vacuum conditions of 90°C and 0.02 MPa for 6 h to obtain maleic anhydride-grafted polyethylene with a maleic anhydride group content of 1.0 wt% and a free maleic anhydride content of 0.03 wt%.

[0082] Step S1-3: Preparation of covalently bonded composite masterbatch

[0083] 25 parts by weight of aminopropylsilane-modified montmorillonite were mixed with 75 parts by weight of maleic anhydride-grafted polyethylene. The mixture underwent interfacial reaction and dispersion via a co-rotating twin-screw extruder under nitrogen protection and atmospheric pressure. The extrusion temperature was 195℃, the screw speed was 425 r / min, and the residence time was 90 s. The extruded strip was water-cooled and pelletized to obtain a covalently bonded composite masterbatch with a water content of 0.6 wt% and an inorganic content of 18 wt%. Infrared spectroscopy confirmed the formation of amide bonds and some imide bonds between the montmorillonite and the maleic anhydride-grafted polyethylene.

[0084] Step S2: Co-extrusion film formation

[0085] Polypropylene, ethylene-vinyl alcohol copolymer, polyethylene, and the binder layer material composed of maleic anhydride-grafted polyethylene and covalently bonded composite masterbatch are melted separately in their respective extruders. The raw material formulations of the first and second binder layers are the same, both consisting of maleic anhydride-grafted polyethylene as the continuous phase, with 15 wt% of covalently bonded composite masterbatch added. In this embodiment, the molar fraction of ethylene in the ethylene-vinyl alcohol copolymer is 32 mol%. The film is co-extruded through a co-extrusion casting die in the following sequence: polypropylene layer / first binder layer / ethylene-vinyl alcohol copolymer layer / second binder layer / polyethylene layer. The melt temperature of polypropylene is 215°C, the melt temperature of polyethylene is 195°C, and the melt temperature of ethylene-vinyl alcohol copolymer is 190°C. The extruder used to form the first and second binder layers is equipped with a vacuum exhaust section with an absolute pressure of 0.04 MPa. The die head temperature of the co-extrusion die is 205°C, and the total residence time of the co-extruded melt in the co-extrusion die is 105 s.

[0086] Step S3: Cooling, Shaping, and Winding

[0087] The co-extruded melt is cooled and shaped using cooling rollers with a surface temperature of 25°C. The outer layer is then corona-treated for subsequent printing. After treatment, the film is wound up to obtain a multifunctional, high-barrier, multilayer packaging film.

[0088] The multifunctional high-barrier multilayer packaging film prepared in this embodiment has a total thickness of 120 μm, wherein the outer polypropylene layer has a thickness of 35 μm, the first adhesive layer has a thickness of 10 μm, the barrier layer ethylene-vinyl alcohol copolymer layer has a thickness of 15 μm, the second adhesive layer has a thickness of 10 μm, and the inner polyethylene layer has a thickness of 50 μm.

[0089] The oxygen permeability, measured after conditioning for 24 hours at 23±0.5℃ and relative humidity of 0%~5% according to GB / T 19789-2021, was 0.6 cm³ / (m²·24 h·0.1 MPa). The water vapor permeability, measured at 38℃ using the weight gain method according to GB / T 1037-2021, was 0.7 g / (m²·24 h). A humidity gradient was established on both sides of the testing device, with a relative humidity of 95% on the high-humidity side and a desiccant condition on the low-humidity side. After heat treatment with saturated steam at 121℃ for 30 min, no visible delamination or continuous blistering was observed at the interface of the adhesive layer during visual inspection at room temperature.

[0090] Features of Example 1: This example uses a medium thickness configuration (total thickness 120 μm), with a barrier layer thickness of 15 μm. The ethylene molar fraction in the ethylene-vinyl alcohol copolymer is 32 mol%, the mass ratio of maleic anhydride-grafted polyethylene to modified montmorillonite in the covalently bonded composite masterbatch is 75:25, the amount of masterbatch added to the binder layer is 15 wt%, and the maleic anhydride group content of the maleic anhydride-grafted polyethylene is 1.0 wt%. This parameter combination achieves a good balance between barrier performance and processing stability, with a wide process window, suitable for conventional high-barrier packaging applications, especially suitable for liquid foods, condiments, and other products with medium requirements for oxygen and water vapor barrier, while also meeting the requirements for high-temperature sterilization at 121℃.

[0091] Example 2

[0092] This embodiment prepares a multifunctional high-barrier multilayer packaging film, and the specific steps are as follows:

[0093] Step S1-1: Preparation of aminopropylsilane-modified montmorillonite

[0094] Using 100 parts by mass of montmorillonite as a reference, montmorillonite was added to a dispersion medium composed of ethanol and water at a volume ratio of 8:1. The amount of dispersion medium added was such that the liquid-to-solid ratio was 15 mL / g. The mixture was mechanically stirred at 600 r / min for 40 min at 35 °C and atmospheric pressure. Then, a total of 4 parts by mass of 3-aminopropyltrimethoxysilane was added, and stirring continued for 90 min. The pH of the system was adjusted to 4.5 by titration with a 7% (w / w) aqueous acetic acid solution under stirring. The reaction was continued at 55 °C and atmospheric pressure for 4.5 h. After the reaction, the mixture was filtered and washed successively with ethanol and water until the pH of the final water wash filtrate was 7.2. Subsequently, it was dried at 80 °C for 10 h under a vacuum of 0.025 MPa to obtain aminopropylsilane-modified montmorillonite with a water content of 0.7 wt% and a nitrogen content of 0.55 wt%.

[0095] Step S1-2: Preparation of maleic anhydride-grafted polyethylene

[0096] 100 parts by weight of polyethylene, 1.5 parts by weight of maleic anhydride, and 0.15 parts by weight of dicumyl peroxide were premixed. The mixture was then subjected to twin-screw reactive extrusion under nitrogen protection. During the reactive extrusion process, the temperature in each zone was 205°C, the screw speed was 400 r / min, and the total material residence time was 120 s. The absolute pressure was controlled at 0.05 MPa in the vacuum exhaust section to remove free maleic anhydride. The extruded strip was water-cooled, pelletized, and dried under vacuum conditions of 95°C and 0.025 MPa for 7 h to obtain maleic anhydride-grafted polyethylene with a maleic anhydride group content of 1.4 wt% and a free maleic anhydride content of 0.02 wt%.

[0097] Step S1-3: Preparation of covalently bonded composite masterbatch

[0098] 15 parts by weight of aminopropylsilane-modified montmorillonite were mixed with 85 parts by weight of maleic anhydride-grafted polyethylene. The mixture underwent interfacial reaction and dispersion via a co-rotating twin-screw extruder under nitrogen protection and atmospheric pressure. The extrusion temperature was 205℃, the screw speed was 500 r / min, and the residence time was 110 s. The extruded strip was water-cooled and pelletized to obtain a covalently bonded composite masterbatch with a water content of 0.5 wt% and an inorganic content of 10 wt%. Infrared spectroscopy confirmed the formation of amide bonds and some imide bonds between the montmorillonite and the maleic anhydride-grafted polyethylene.

[0099] Step S2: Co-extrusion film formation

[0100] Polypropylene, ethylene-vinyl alcohol copolymer, polyethylene, and the binder layer material composed of maleic anhydride-grafted polyethylene and covalently bonded composite masterbatch are melted separately in their respective extruders. The raw material formulations of the first and second binder layers are the same, both consisting of maleic anhydride-grafted polyethylene as the continuous phase, with 20 wt% of covalently bonded composite masterbatch added. In this embodiment, the molar fraction of ethylene in the ethylene-vinyl alcohol copolymer is 25 mol%. The film is co-extruded through a co-extrusion casting die in the following sequence: polypropylene layer / first binder layer / ethylene-vinyl alcohol copolymer layer / second binder layer / polyethylene layer. The melt temperature of polypropylene is 225°C, the melt temperature of polyethylene is 205°C, and the melt temperature of ethylene-vinyl alcohol copolymer is 200°C. The extruder used to form the first and second binder layers is equipped with a vacuum exhaust section with an absolute pressure of 0.05 MPa. The die head temperature of the co-extrusion die is 215°C, and the total residence time of the co-extruded melt in the co-extrusion die is 125 s.

[0101] Step S3: Cooling, Shaping, and Winding

[0102] The co-extruded melt is cooled and shaped using cooling rollers with a surface temperature of 30°C. The outer layer is then subjected to corona treatment for subsequent printing. After treatment, the film is wound up to obtain a multifunctional, high-barrier, multilayer packaging film.

[0103] The multifunctional high-barrier multilayer packaging film prepared in this embodiment has a total thickness of 150 μm, wherein the outer polypropylene layer has a thickness of 40 μm, the first adhesive layer has a thickness of 12 μm, the barrier layer ethylene-vinyl alcohol copolymer layer has a thickness of 25 μm, the second adhesive layer has a thickness of 13 μm, and the inner polyethylene layer has a thickness of 60 μm.

[0104] The oxygen permeability, measured after conditioning for 24 hours at 23±0.5℃ and relative humidity of 0%~5% according to GB / T 19789-2021, was 0.3 cm³ / (m²·24 h·0.1 MPa). The water vapor permeability, measured at 38℃ using the weight gain method according to GB / T 1037-2021, was 0.4 g / (m²·24 h). A humidity gradient was established on both sides of the testing device, with a relative humidity of 98% on the high-humidity side and a desiccant condition on the low-humidity side. After heat treatment with saturated steam at 121℃ for 45 min, no visible delamination or continuous blistering was observed at the interface of the adhesive layer during visual inspection at room temperature.

[0105] Features of Example 2: This example uses a larger total thickness (150 μm), with a barrier layer thickness of 25 μm. The ethylene molar fraction in the ethylene-vinyl alcohol copolymer is 25 mol%, the mass ratio of maleic anhydride-grafted polyethylene to modified montmorillonite in the covalently bonded composite masterbatch is 85:15, the amount of masterbatch added to the binder layer is 20 wt%, and the maleic anhydride group content of the maleic anhydride-grafted polyethylene is 1.4 wt%. This combination of parameters significantly improves the barrier performance of the film by increasing the barrier layer thickness, reducing the ethylene content in the ethylene-vinyl alcohol copolymer, increasing the maleic anhydride grafting degree, and increasing the amount of masterbatch added. It is particularly suitable for packaging high-value-added products sensitive to oxygen and water vapor, such as pharmaceutical packaging, precision electronic component packaging, and high-end meat product packaging, where strict barrier performance requirements exist. It can also withstand prolonged high-temperature cooking treatment.

[0106] Example 3

[0107] This embodiment prepares a multifunctional high-barrier multilayer packaging film, and the specific steps are as follows:

[0108] Step S1-1: Preparation of aminopropylsilane-modified montmorillonite

[0109] Using 100 parts by mass of montmorillonite as a reference, montmorillonite was added to a dispersion medium composed of ethanol and water at a volume ratio of 6.5:1. The amount of dispersion medium added was such that the liquid-to-solid ratio was 8 mL / g. The mixture was mechanically stirred at 400 r / min for 20 min at 28 °C and atmospheric pressure. Then, a mixture of 3 parts by mass of 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane (mass ratio 1:1) was added, and stirring was continued for 50 min. The pH of the system was adjusted to 5.2 by titration with a 3% (w / w) aqueous acetic acid solution under stirring. The reaction was continued at 45 °C and atmospheric pressure for 2 h. After the reaction was completed, the mixture was filtered and washed successively with ethanol and water until the pH of the final water wash filtrate was 6.8. Subsequently, it was dried at 70 °C for 7 h under a vacuum of 0.015 MPa to obtain aminopropylsilane-modified montmorillonite with a water content of 0.9 wt% and a nitrogen content of 0.35 wt%.

[0110] Step S1-2: Preparation of maleic anhydride-grafted polyethylene

[0111] 100 parts by weight of polyethylene, 0.6 parts by weight of maleic anhydride, and 0.06 parts by weight of dicumyl peroxide were premixed. The mixture was then subjected to twin-screw reactive extrusion under nitrogen protection. During the reactive extrusion process, the temperature in each zone was 180°C, the screw speed was 280 r / min, and the total material residence time was 60 s. The absolute pressure was controlled at 0.03 MPa in the vacuum exhaust section to remove free maleic anhydride. The extruded strip was water-cooled, pelletized, and dried under vacuum conditions of 85°C and 0.015 MPa for 5 h to obtain maleic anhydride-grafted polyethylene with a maleic anhydride group content of 0.55 wt% and a free maleic anhydride content of 0.04 wt%.

[0112] Step S1-3: Preparation of covalently bonded composite masterbatch

[0113] Ten parts by weight of aminopropylsilane-modified montmorillonite were mixed with 90 parts by weight of maleic anhydride-grafted polyethylene. The mixture underwent interfacial reaction and dispersion via a co-rotating twin-screw extruder under nitrogen protection and atmospheric pressure. The extrusion temperature was 180°C, the screw speed was 320 r / min, and the residence time was 55 s. The extruded strip was water-cooled and pelletized to obtain a covalently bonded composite masterbatch with a water content of 0.7 wt% and an inorganic content of 7.5 wt%. Infrared spectroscopy confirmed the formation of amide bonds and some imide bonds between the montmorillonite and the maleic anhydride-grafted polyethylene.

[0114] Step S2: Co-extrusion film formation

[0115] Polypropylene, ethylene-vinyl alcohol copolymer, polyethylene, and the binder layer material composed of maleic anhydride-grafted polyethylene and covalently bonded composite masterbatch are melted separately in their respective extruders. The raw material formulations of the first and second binder layers are the same, both consisting of maleic anhydride-grafted polyethylene as the continuous phase, with 8 wt% of covalently bonded composite masterbatch added. In this embodiment, the molar fraction of ethylene in the ethylene-vinyl alcohol copolymer is 40 mol%. The film is co-extruded through a co-extrusion casting die in the following sequence: polypropylene layer / first binder layer / ethylene-vinyl alcohol copolymer layer / second binder layer / polyethylene layer. The melt temperature of polypropylene is 200°C, the melt temperature of polyethylene is 180°C, and the melt temperature of ethylene-vinyl alcohol copolymer is 178°C. The extruder used to form the first and second binder layers is equipped with a vacuum exhaust section with an absolute pressure of 0.03 MPa. The die head temperature of the co-extrusion die is 190°C, and the total residence time of the co-extruded melt in the co-extrusion die is 65 s.

[0116] Step S3: Cooling, shaping, stretching and winding

[0117] The co-extruded melt is cooled and shaped using cooling rollers with a surface temperature of 18°C. It is then unidirectionally stretched at 95°C with a stretch ratio of 2.5 times. The outer layer is corona-treated for subsequent printing. After treatment, the film is wound up to obtain a multifunctional, high-barrier, multilayer packaging film.

[0118] The multifunctional high-barrier multilayer packaging film prepared in this embodiment has a total thickness of 90 μm, wherein the outer polypropylene layer has a thickness of 25 μm, the first adhesive layer has a thickness of 6 μm, the barrier layer ethylene-vinyl alcohol copolymer layer has a thickness of 8 μm, the second adhesive layer has a thickness of 6 μm, and the inner polyethylene layer has a thickness of 45 μm.

[0119] The oxygen permeability, measured after conditioning for 24 hours at 23±0.5℃ and relative humidity of 0%~5% according to GB / T 19789-2021, was 0.9 cm³ / (m²·24 h·0.1 MPa). The water vapor permeability, measured at 38℃ using the weight gain method according to GB / T 1037-2021, was 0.9 g / (m²·24 h). A humidity gradient was established on both sides of the testing device, with a relative humidity of 92% on the high-humidity side and a desiccant condition on the low-humidity side. After heat treatment with saturated steam at 121℃ for 20 min, no visible delamination or continuous blistering was observed at the interface of the adhesive layer during visual inspection at room temperature.

[0120] Features of Example 3: This example uses a relatively small total thickness (90 μm), with a barrier layer thickness of 8 μm. The ethylene molar fraction in the ethylene-vinyl alcohol copolymer is 40 mol%, the mass ratio of maleic anhydride-grafted polyethylene to modified montmorillonite in the covalently bonded composite masterbatch is 90:10, the amount of masterbatch added to the binder layer is 8 wt%, and the maleic anhydride group content of the maleic anhydride-grafted polyethylene is 0.55 wt%. It also underwent 2.5 times uniaxial stretching. This parameter combination, while ensuring that barrier performance requirements are met, improves processing performance and flexibility by increasing the ethylene content in the ethylene-vinyl alcohol copolymer, and optimizes costs by reducing the amount of masterbatch added and the degree of maleic anhydride grafting. It is particularly suitable for cost-sensitive packaging applications that require mechanical strength and flexibility, such as dried fruit packaging, baked goods packaging, and general snack packaging. The stretching treatment further enhances the mechanical properties and dimensional stability of the film.

[0121] Example 4

[0122] This embodiment prepares a multifunctional high-barrier multilayer packaging film, and the specific steps are as follows:

[0123] Step S1-1: Preparation of aminopropylsilane-modified montmorillonite

[0124] Using 100 parts by mass of montmorillonite as a reference, montmorillonite was added to a dispersion medium composed of ethanol and water at a volume ratio of 8.5:1. The amount of dispersion medium added was such that the liquid-to-solid ratio was 18 mL / g. The mixture was mechanically stirred at 720 r / min for 55 min at 38℃ and atmospheric pressure. Then, a mixture of 9 parts by mass of 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane (mass ratio 2:1) was added, and stirring was continued for 110 min. The pH of the system was adjusted to 4.2 by titration with a 9% aqueous acetic acid solution under stirring. The reaction was continued at 58℃ and atmospheric pressure for 5.5 h with stirring. After the reaction was completed, the mixture was filtered and washed successively with ethanol and water until the pH of the final water wash filtrate was 7.4. Subsequently, it was dried at 87°C for 11 h under vacuum conditions with an absolute pressure of 0.028 MPa to obtain aminopropylsilane-modified montmorillonite with a water content of 0.6 wt% and a nitrogen content of 1.3 wt%.

[0125] Step S1-2: Preparation of maleic anhydride-grafted polyethylene

[0126] 100 parts by weight of polyethylene, 1.85 parts by weight of maleic anhydride, and 0.185 parts by weight of dicumyl peroxide were premixed. The mixture was then subjected to twin-screw reactive extrusion under nitrogen protection. During reactive extrusion, the temperature in each zone was 215°C, the screw speed was 460 r / min, and the total residence time of the material was 160 s. The absolute pressure was controlled at 0.055 MPa in the vacuum exhaust section to remove free maleic anhydride. The extruded strip was water-cooled, pelletized, and dried under vacuum conditions of 98°C and 0.028 MPa for 7.5 h to obtain maleic anhydride-grafted polyethylene with a maleic anhydride group content of 1.75 wt% and a free maleic anhydride content of 0.02 wt%.

[0127] Step S1-3: Preparation of covalently bonded composite masterbatch

[0128] 35 parts by weight of aminopropylsilane-modified montmorillonite and 65 parts by weight of maleic anhydride-grafted polyethylene were mixed. The mixture under nitrogen protection and atmospheric pressure was subjected to interfacial reaction and dispersion via a co-rotating twin-screw extruder. The extrusion temperature was 215℃, the screw speed was 560 r / min, and the residence time was 140 s. The extruded strip was water-cooled and pelletized to obtain a covalently bonded composite masterbatch with a water content of 0.5 wt% and an inorganic content of 26 wt%. Infrared spectroscopy confirmed the formation of amide bonds and some imide bonds between the montmorillonite and the maleic anhydride-grafted polyethylene.

[0129] Step S2: Co-extrusion film formation

[0130] Polypropylene, ethylene-vinyl alcohol copolymer, polyethylene, and the binder layer material composed of maleic anhydride-grafted polyethylene and covalently bonded composite masterbatch are melted separately in their respective extruders. The raw material formulations of the first and second binder layers are the same, both consisting of maleic anhydride-grafted polyethylene as the continuous phase, with 26 wt% of covalently bonded composite masterbatch added. In this embodiment, the molar fraction of ethylene in the ethylene-vinyl alcohol copolymer is 22 mol%. The film is co-extruded through a co-extrusion casting die in the following sequence: polypropylene layer / first binder layer / ethylene-vinyl alcohol copolymer layer / second binder layer / polyethylene layer. The melt temperature of polypropylene is 235°C, the melt temperature of polyethylene is 215°C, and the melt temperature of ethylene-vinyl alcohol copolymer is 205°C. The extruder used to form the first and second binder layers is equipped with a vacuum exhaust section with an absolute pressure of 0.055 MPa. The die head temperature of the co-extrusion die is 227°C, and the total residence time of the co-extruded melt in the co-extrusion die is 160 s.

[0131] Step S3: Cooling, Shaping, and Winding

[0132] The co-extruded melt is cooled and shaped using cooling rollers with a surface temperature of 37°C. The outer layer is then corona-treated for subsequent printing. After treatment, the film is wound up to obtain a multifunctional, high-barrier, multilayer packaging film.

[0133] The multifunctional high-barrier multilayer packaging film prepared in this embodiment has a total thickness of 185 μm, wherein the outer polypropylene layer has a thickness of 52 μm, the first adhesive layer has a thickness of 18 μm, the barrier layer ethylene-vinyl alcohol copolymer layer has a thickness of 28 μm, the second adhesive layer has a thickness of 18 μm, and the inner polyethylene layer has a thickness of 69 μm.

[0134] The oxygen permeability, measured after conditioning for 24 hours at 23±0.5℃ and relative humidity of 0%~5% according to GB / T 19789-2021, was 0.2 cm³ / (m²·24 h·0.1 MPa). The water vapor permeability, measured at 38℃ using the weight gain method according to GB / T 1037-2021, was 0.3 g / (m²·24 h). A humidity gradient was established on both sides of the testing device, with 100% relative humidity on the high-humidity side and desiccant conditions on the low-humidity side. After heat treatment with saturated steam at 121℃ for 60 min, no visible delamination or continuous blistering was observed at the interface of the adhesive layer at room temperature.

[0135] Features of Example 4: This example employs a larger total thickness (185 μm), with a barrier layer thickness of 28 μm. The ethylene molar fraction in the ethylene-vinyl alcohol copolymer is 22 mol%, the mass ratio of maleic anhydride-grafted polyethylene to modified montmorillonite in the covalently bonded composite masterbatch is 65:35, the amount of masterbatch added to the binder layer is 26 wt%, the maleic anhydride group content of the maleic anhydride-grafted polyethylene is 1.75 wt%, and the nitrogen content of the aminopropylsilane-modified montmorillonite reaches 1.3 wt%. This combination of parameters, through the use of a larger total film thickness, a thicker barrier layer, a lower ethylene content in the ethylene-vinyl alcohol copolymer, a higher proportion of modified montmorillonite, and a higher amount of masterbatch added, achieves excellent barrier performance and high-temperature resistance. It is particularly suitable for applications with extremely stringent requirements for barrier performance and heat resistance, such as long-shelf-life aseptic packaging, military food packaging, high-end pharmaceutical packaging, and aerospace special packaging. It can withstand long-term high-temperature cooking treatment, providing durable and reliable protection for products.

[0136] Comparative Example 1: It is basically the same as Example 1, except that the amount of aminopropylsilane modified montmorillonite in the covalently bonded composite masterbatch is 2 parts by mass, while the amount of other components and preparation conditions remain unchanged.

[0137] Comparative Example 2: It is basically the same as Example 1, except that the amount of aminopropylsilane modified montmorillonite in the covalently bonded composite masterbatch is 45 parts by mass, while the amount of other components and preparation conditions remain unchanged.

[0138] Comparative Example 3: It is basically the same as Example 1, except that the content of maleic anhydride groups in maleic anhydride-grafted polyethylene is 0.03 wt%, while the amount of other components and preparation conditions remain unchanged.

[0139] Comparative Example 4: It is basically the same as Example 1, except that the content of maleic anhydride groups in maleic anhydride-grafted polyethylene is 2.5 wt%, while the amount of other components and preparation conditions remain unchanged.

[0140] Comparative Example 5: It is basically the same as Example 1, except that the amount of covalently bonded composite masterbatch added to the first adhesive layer and the second adhesive layer is 0.5 wt%, while the amount of other components and preparation conditions remain unchanged.

[0141] Comparative Example 6: It is basically the same as Example 1, except that the amount of covalently bonded composite masterbatch added to the first adhesive layer and the second adhesive layer is 35 wt%, while the amount of other components and preparation conditions remain unchanged.

[0142] Comparative Example 7: Basically the same as Example 1, except that the molar fraction of ethylene in the ethylene-vinyl alcohol copolymer is 15 mol%, and the amounts of other components and preparation conditions remain unchanged.

[0143] Comparative Example 8: Basically the same as Example 1, except that the molar fraction of ethylene in the ethylene-vinyl alcohol copolymer is 50 mol%, and the amounts of other components and preparation conditions remain unchanged.

[0144] Comparative Example 9: Basically the same as Example 1, except that unmodified montmorillonite without aminopropylsilane modification was used instead of aminopropylsilane-modified montmorillonite in the covalently bonded composite masterbatch, while the amounts of other components and preparation conditions remained unchanged.

[0145] Comparative Example 10: It is basically the same as Example 1, except that the first and second adhesive layers do not use covalently bonded composite masterbatch, but only pure maleic anhydride grafted polyethylene as the adhesive layer material. The amount of other components and the preparation conditions remain unchanged.

[0146] Comparative Example 11: Basically the same as Example 1, except that the thickness of the barrier layer ethylene-vinyl alcohol copolymer layer is 1 μm, and the amounts of other components and preparation conditions remain unchanged.

[0147] Comparative Example 12: Basically the same as Example 1, except that the melt temperature of polypropylene is 150°C, the melt temperature of polyethylene is 140°C, and the melt temperature of ethylene-vinyl alcohol copolymer is 130°C during co-extrusion film formation. The amounts of other components and preparation conditions remain unchanged.

[0148] Comparative Example 13: It is basically the same as Example 1, except that the extruder used to form the adhesive layer is not equipped with a vacuum exhaust section, and the amounts of other components and preparation conditions remain unchanged.

[0149] Performance testing:

[0150] Experiment 1: Oxygen Transmission Rate Test

[0151] Test Object: Multifunctional high-barrier multilayer packaging film. Test Objective: To evaluate the oxygen barrier performance of the film under dry, low-humidity conditions. Test Principle: The coulometric method (driven by the oxygen partial pressure difference across the film) is used. The film's oxygen barrier capability is characterized by measuring the volume of oxygen permeating through a unit area of ​​the film per unit time. Experimental Method: According to GB / T 19789-2021 standard, film samples were cut into circular specimens with a diameter of 100 mm. After conditioning at 23±0.5℃ and 0-5% relative humidity for 24 h, the oxygen permeability was tested using a pressure difference oxygen permeability tester. The test area was 50 cm², with pure oxygen on one side and nitrogen as the carrier gas on the other. The oxygen pressure difference was 0.1 MPa, and the test continued until the data stabilized. Standard Basis: GB / T 19789-2021 "Test of Oxygen Permeability of Packaging Materials - Plastic Films and Sheets - Coulometric Method". Key parameters: Test temperature 23±0.5℃, relative humidity 0-5%, conditioning time 24 h, oxygen pressure difference 0.1 MPa. Data processing: Record steady-state transmittance, calculate the mean ± standard deviation (n≥3), unit is cm³ / (m²·24 h·0.1 MPa).

[0152] Experiment 2: Water vapor transmission rate test

[0153] Test Object: Multifunctional high-barrier multilayer packaging film. Test Objective: To evaluate the water vapor barrier performance of the film under high humidity conditions. Test Principle: The weight gain method is used to characterize the film's water vapor barrier ability by measuring the mass of water vapor passing through a unit area of ​​the film per unit time. Experimental Method: According to GB / T 1037-2021 standard, under constant temperature conditions of 38℃, the film sample is fixed on a permeation cup, the cup is filled with desiccant, and the cup is placed in a constant humidity chamber with a relative humidity of 90-100%. A humidity gradient is established, and the mass increment of the permeation cup is measured periodically to calculate the water vapor transmission rate. Standard Basis: GB / T 1037-2021 "Determination of Water Vapor Transmission Rate of Plastic Films and Sheets - Cup Method". Key Parameters: Test temperature 38℃, relative humidity 90-100% on the high humidity side, desiccant condition on the low humidity side, test cycle 24 h. Data Processing: Transmission rate is calculated based on mass increment, mean ± standard deviation (n≥3), unit is g / (m²·24 h).

[0154] Experiment 3: Interlayer peel strength test

[0155] Test Object: Multifunctional high-barrier multilayer packaging film, focusing on testing the interfacial bonding strength between the barrier layer and the adhesive layer. Test Objective: To evaluate the interfacial bonding strength between the adhesive layer and the barrier layer before and after 121℃ retort heat treatment, and to verify the interfacial strengthening effect of covalently bonded masterbatch. Test Principle: The average force required per unit width of the sample during the peeling process is determined through a 180° peel test to characterize the interlayer bonding strength. Experimental Method: According to GB / T 2792-2014 standard, the film is cut into 15 mm × 150 mm samples. A 25 mm section is pre-peeled at the interface between the adhesive layer and the barrier layer as a clamping end. A tensile testing machine is used to perform 180° peeling at a rate of 300 mm / min, and the peel force-displacement curve is recorded. Samples are tested before retort heat treatment and after 30 min of saturated steam heat treatment at 121℃. Key Parameters: Sample width 15 mm, peel rate 300 mm / min, test temperature 23±2℃, relative humidity 50±10%. Data processing: Calculate the average peeling force of the effective peeling segment, in N / 15 mm, and give the mean ± standard deviation (n≥5).

[0156] Experiment 4: X-ray diffraction (XRD) structural characterization

[0157] Test objects: Covalently bonded composite masterbatch powder and film binder slices. Test objective: To characterize the interlayer spacing variation of aminopropylsilane-modified montmorillonite and its exfoliation dispersion state in the polymer matrix. Test principle: By measuring the 2θ angle position and peak intensity of the characteristic diffraction peak (001) crystal plane of montmorillonite, the interlayer spacing is calculated using the Bragg equation to evaluate the degree of intercalation or exfoliation. Experimental method: Cu Kα radiation (λ=0.154 nm) was used, with a scanning range of 2θ=2-10°, a step size of 0.02°, a scanning rate of 2° / min, a tube voltage of 40 kV, and a tube current of 40 mA. The XRD spectra of pure montmorillonite, modified montmorillonite, masterbatch I, and film binder were compared, and the position and intensity variation of the (001) peak were recorded. Key parameters: Cu Kα radiation, scanning range 2-10°, step size 0.02°, scanning rate 2° / min. Data processing: The interlayer spacing was calculated using d=λ / (2sinθ), and the data was exported in CSV format (2theta, Intensity) for plotting and analysis in Origin.

[0158] Experiment 5 / 6: Fourier Transform Infrared Spectroscopy (FTIR) Analysis

[0159] Test Subjects: Aminopropylsilane-modified montmorillonite, maleic anhydride-grafted polyethylene, and covalently bonded composite masterbatch. Test Objective: To verify the formation of amide and imide bonds between montmorillonite and maleic anhydride-grafted polyethylene, confirming the occurrence of the covalent bonding reaction. Test Principle: By detecting the infrared absorption spectrum of the samples, the position and intensity changes of the absorption peaks of characteristic functional groups are identified to confirm the formation of chemical bonds. Experimental Method: Attenuated total reflectance (ATR) mode was used, with a scanning range of 4000-400 cm⁻¹. -1 4 cm resolution -1 The scan was performed 32 times, focusing on the amide I band, amide II band, imide characteristic peaks, and Si-O-Si stretching vibration peaks. The spectral changes of each component were compared and analyzed. Key parameters: ATR mode, scan range 4000-400 cm⁻¹. -1 4 cm resolution -1 Scanned 32 times. Data processing: Exported data in CSV format (Wavenumber / cm, Transmittance% or Absorbance), labeled the location and assignment of characteristic peaks, and calculated the peak intensity ratio.

[0160] Experiment 6: Evaluation of thermal stability and resistance to boiling

[0161] Test Object: Multifunctional high-barrier multilayer packaging film. Test Objective: To evaluate the dimensional stability, appearance changes, and barrier performance retention rate of the film under 121℃ high-temperature retorting conditions, and to verify the film's heat treatment resistance. Test Principle: Simulating actual high-temperature retorting sterilization conditions, the thermal stability of the film is assessed by comparing the changes in appearance, interlayer bonding, and barrier performance before and after heat treatment. Experimental Method: The film sample was placed in a saturated steam environment at 121℃ for 30 minutes. After cooling to room temperature, the adhesive layer interface was visually inspected for visible delamination, continuous blistering, or cracking. The oxygen permeability and water vapor permeability before and after heat treatment were measured, and the performance retention rate was calculated. The test method is the same as in Experiments 1 and 2. Key Parameters: Retorting temperature 121℃, retorting time 30 minutes, saturated steam environment. Data Processing: The appearance evaluation results were recorded, and the barrier performance retention rate was calculated as (performance after heat treatment / performance before heat treatment) × 100%, giving the mean ± standard deviation (n≥3).

[0162] Figure 1 The bar chart shows the peel strength of Examples 1, 6, and 10. The fixed parameters are the peel strength test as the characterization method and the uniform statistical method of using the mean and standard deviation, expressed as error bars. The vertical axis represents peel strength in N·15 mm. -1The horizontal axis represents the sample number, comparing the conditions before and after cooking; the changing parameters represent the sample type and cooking treatment state from before cooking to after cooking at 121°C for 30 min. Example 1 maintained high peel strength with minimal attenuation both before and after cooking, while Comparative Examples 6 and 10 showed a more significant decrease after cooking, indicating that the solution can improve the interfacial adhesion retention under humid and hot conditions.

[0163] Figure 2 The bar chart shows the peel strength retention rates of Examples 1, 6, and 10. The fixed parameter is that the characterization method is based on the same peel strength test data, and the retention rate is calculated by dividing the data after cooking by the data before cooking. The vertical axis represents the retention rate in percentage, and the horizontal axis represents the sample number. The variable parameter is the sample category, from Example 1 to Comparative Examples 6 and 10. The retention rate of Example 1 is significantly higher than that of the two comparative examples, indicating that its interfacial strength loss is smaller under the same heat and moisture disturbance. This further verifies the effectiveness of this method in terms of interfacial stability from the perspective of retention rate.

[0164] Figure 3 The XRD patterns of pure montmorillonite, modified montmorillonite, masterbatch I, and the binder layer of Example 1 are superimposed. The fixed parameters are X-ray diffraction used for characterization, with intensity normalized and displayed in a superimposed offset manner. The horizontal axis represents 2θ (degrees), and the vertical axis represents normalized intensity. The varying parameters are the sample type, from pure montmorillonite to modified montmorillonite, then to masterbatch I, and finally the binder layer of Example 1. Compared to pure montmorillonite, the characteristic diffraction peaks of modified montmorillonite and those further incorporated into masterbatch I and the binder layer show a weakening trend, indicating that the dispersion and structural state of the layered filler changes in the system. This helps to construct a more effective barrier pathway and corroborates the improvement in macroscopic barrier properties.

[0165] Figure 4 The XRD bar chart shows the peak intensity decrease of modified montmorillonite, masterbatch I, and the binder layer of Example 1. The fixed parameter is the characterization method based on the maximum intensity of the characteristic X-ray diffraction peaks, with pure montmorillonite as a reference, calculating the percentage decrease in peak intensity. The vertical axis represents the percentage decrease in peak intensity, and the horizontal axis represents the sample type. The varying parameter is the sample type, from modified montmorillonite to masterbatch I and the binder layer of Example 1. The peak intensity decrease of masterbatch I and the binder layer of Example 1 is more significant relative to the reference, indicating that the contribution of the ordered stacking of the filler characteristics is weakened and tends towards a more dispersed structural state. This trend is consistent with the improved barrier performance, supporting the rationality of the scheme from a structural characterization perspective.

[0166] Figure 5 This is a locally magnified and superimposed Fourier transform infrared (FTIR) spectrum of modified montmorillonite, MA-g-PE, and masterbatch I. The characterization method uses Fourier transform infrared spectroscopy with fixed parameters, and local magnification is performed within a specific wavenumber range. The spectrum is displayed using a superimposed and offset method. The horizontal axis represents the wavenumber in cm.-1 The vertical axis represents absorbance; the varying parameters are the sample types from modified montmorillonite and MA-g-PE to masterbatch I. Masterbatch I exhibits clearer combinatorial characteristics within local regions and shows systematic differences from the single-component spectra, indicating that composites and interactions alter the local chemical environment, thus supporting the proposed approach of achieving interface enhancement and performance stability through chemical structure regulation.

[0167] Figure 6 The XPS N 1s fitted spectra of modified montmorillonite and masterbatch I are shown. The fixed parameters are the characterization method of using XPS and peak separation fitting in the N 1s interval. The horizontal axis represents binding energy in eV, and the vertical axis represents intensity in cps, displaying the experimental and fitted component spectra. The varying parameters represent the sample type from modified montmorillonite to masterbatch I, and the relative contributions of different chemical states within masterbatch I. Compared to modified montmorillonite, masterbatch I exhibits more pronounced amide nitrogen-related components, which can be separated by the fitting results. This indicates that nitrogen-containing functional groups undergo transformation or the introduction of more stable chemical states, consistent with the need to improve interfacial adhesion and resistance to humid heat. This chemical state evidence chain supports the effectiveness of the proposed scheme.

[0168] Figure 7 The graphs show the dynamic mechanical analysis (DMA) storage modulus E′ as a function of temperature for Examples 1, 10, and 6. The fixed parameters are the dynamic mechanical analysis characterization method and the consistent test temperature range. The horizontal axis represents temperature in degrees Celsius, and the vertical axis represents the storage modulus E′ in MPa. The varying parameters are the sample types from Example 1 to Comparative Examples 6 and 10. Example 1 maintains a higher E′ in the working temperature range and exhibits a slower decay with increasing temperature, indicating a more stable adhesive layer or interfacial network and stronger load-bearing capacity. This helps explain the higher peel strength retention rate after cooking.

[0169] Figure 8 The graphs show the dynamic mechanical analysis (DMA) loss factor tanδ as a function of temperature for Examples 1, 10, and 6. The fixed parameters are the dynamic mechanical analysis method used for characterization and the consistent test temperature range. The horizontal axis represents temperature in degrees Celsius, and the vertical axis represents the loss factor tanδ. The varying parameters are the sample types from Example 1 to Comparative Examples 6 and 10. The tanδ peak shape and amplitude of Example 1 reflect a more controlled viscoelastic response, while the comparative sample shows higher loss. This indicates that energy dissipation and chain segment motion are more effectively restricted within the example system, supporting the belief that it is less prone to interface failure under humid and hot conditions from a viscoelastic behavior perspective.

[0170] As can be seen from the performance of the embodiments and comparative examples in Table 1, the multifunctional high-barrier multilayer packaging film prepared by the present invention is significantly superior to the comparative examples in terms of oxygen permeability, water vapor permeability, and interlayer bonding performance in terms of resistance to retort cooking. Comparative Examples 1 and 2 show that when the amount of modified montmorillonite in the covalently bonded composite masterbatch deviates from the preferred range, the inorganic layer reinforcement effect and interfacial compatibility become unbalanced, leading to deterioration of barrier performance and an increased risk of interfacial delamination after retort cooking. Comparative Examples 3 and 4 illustrate that when the content of maleic anhydride groups in maleic anhydride-grafted polyethylene is too low, there are insufficient reaction sites and weak interfacial bonding, while when the content is too high, the processing rheology deteriorates and excessive residual acidic groups are easily introduced, causing EVOH degradation. Comparative Examples 5 and 6 confirm that when the amount of masterbatch added to the adhesive layer is too low, the inorganic reinforcement effect is insufficient, while when the amount added is too high, the melt viscosity increases dramatically, the co-extrusion processing window narrows, and interfacial stress concentration occurs. Comparative Examples 7 and 8 verified the trade-off between the molar fraction of ethylene in EVOH and its barrier properties and processing performance. When the ethylene content was too low, the moisture sensitivity of EVOH increased and the processing temperature window narrowed; when the content was too high, the barrier properties decreased significantly. The severe performance degradation in Comparative Examples 9 and 10 indicates that the surface modification of montmorillonite with aminopropylsilane and the covalent bonding reaction between maleic anhydride-grafted polyethylene and modified montmorillonite are the core technical features for achieving high barrier durability and interfacial thermal and moisture stability. Comparative Example 11 shows that insufficient barrier layer thickness prevents the formation of effective barrier channels. Comparative Examples 12 and 13 confirm the importance of appropriate co-extrusion temperature and vacuum degassing process for ensuring the thermal stability of EVOH and suppressing the formation of interfacial defects.

[0171] Table 1 Performance Comparison Summary Table

[0172] Sample number Oxygen permeability (cm³ / (m²·24h·0.1MPa)) Water vapor transmission rate (g / (m²·24h)) Peel strength (before cooking) N / 15mm Peel strength (after cooking) N / 15mm Appearance after steaming Example 1 0.6±0.05 0.7±0.06 8.5±0.4 7.8±0.5 No layering Example 2 0.3±0.03 0.4±0.04 9.2±0.5 8.6±0.4 No layering Example 3 0.9±0.07 0.9±0.08 7.2±0.5 6.5±0.6 No layering Example 4 0.2±0.02 0.3±0.03 10.1±0.6 9.4±0.5 No layering Comparative Example 1 2.8±0.3 2.5±0.3 4.2±0.8 2.1±0.9 Slight stratification Comparative Example 2 1.5±0.2 1.8±0.2 3.8±0.7 1.8±0.8 Clearly layered Comparative Example 3 2.2±0.2 1.9±0.2 4.8±0.6 2.5±0.7 Slight stratification Comparative Example 4 1.8±0.2 1.6±0.2 5.2±0.7 3.2±0.9 Slight stratification Comparative Example 5 2.5±0.3 2.3±0.3 5.5±0.6 3.0±0.8 Slight stratification Comparative Example 6 1.2±0.2 1.4±0.2 4.5±0.8 2.6±1.0 Clearly layered Comparative Example 7 1.9±0.2 0.8±0.1 6.8±0.5 3.5±0.8 Local stratification Comparative Example 8 3.5±0.4 2.8±0.3 5.2±0.6 2.8±0.9 Clearly layered Comparative Example 9 3.2±0.4 2.6±0.3 3.5±0.9 1.5±0.8 Severe stratification Comparative Example 10 4.5±0.5 3.8±0.4 2.8±0.7 1.2±0.6 Severe stratification Comparative Example 11 5.8±0.6 4.2±0.5 6.5±0.6 5.2±0.7 No layering Comparative Example 12 6.2±0.7 5.5±0.6 3.2±0.8 1.8±0.9 Severe stratification Comparative Example 13 2.6±0.3 2.4±0.3 5.8±0.6 3.8±0.8 Slight stratification

[0173] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A multifunctional high-barrier multilayer packaging film, characterized in that, The multifunctional high-barrier multilayer packaging film has a five-layer structure, which includes an outer layer, a first adhesive layer, a barrier layer, a second adhesive layer and an inner layer from the outside to the inside. The outer layer is a polypropylene layer, the inner layer is a polyethylene layer, and the barrier layer is an ethylene-vinyl alcohol copolymer layer. At least one of the first and second adhesive layers contains a covalently bonded composite masterbatch; the total thickness of the multifunctional high-barrier multilayer packaging film is 40–200 μm; the oxygen permeability measured according to GB / T 19789-2021 at 23±0.5℃ and relative humidity of 0%–5% is not greater than 1.0 cm³ / (m²·24 h·0.1 MPa), and the water vapor permeability measured according to GB / T 1037-2021 at 38℃ using the weight gain method is not greater than 1.0 g / (m²·24 h); The covalently bonded composite masterbatch I comprises, by weight, 60–95 parts of maleic anhydride-grafted polyethylene and 5–40 parts of aminopropylsilane-modified montmorillonite, and the total of the two is 100 parts by weight. Furthermore, in the covalently bonded composite masterbatch, in the covalently bonded composite masterbatch I, the covalent bond between the montmorillonite and the maleic anhydride-grafted polyethylene includes an amide acid structure formed by the reaction of maleic anhydride groups with amino groups, including an amide bond, and an imide bond formed by further dehydration and cyclization of the amide acid structure; The outer layer has a thickness of 10–60 μm, and the inner layer has a thickness of 15–100 μm; The thickness of the barrier layer is 2–30 μm; The thickness of the first adhesive layer and the second adhesive layer are each independently 2–20 μm; The ethylene-vinyl alcohol copolymer contains 20–45 mol% ethylene. Both the first adhesive layer and the second adhesive layer contain the covalently bonded composite masterbatch, and the amount of the covalently bonded composite masterbatch added in the corresponding adhesive layer is 1–30 wt% based on the total mass of the corresponding adhesive layer; The multifunctional high-barrier multilayer packaging film has the following layer sequence: polypropylene layer / first adhesive layer / ethylene-vinyl alcohol copolymer layer / second adhesive layer / polyethylene layer, and the continuous polymer phase of the first adhesive layer and the second adhesive layer is maleic anhydride-grafted polyethylene.

2. The multifunctional high-barrier multilayer packaging film according to claim 1, characterized in that, The preparation method of the aminopropylsilane-modified montmorillonite includes the following sub-steps: A1, using 100 parts by weight of montmorillonite as a reference, the montmorillonite is added to a dispersion medium composed of ethanol and water, wherein the volume ratio of ethanol to water is 6:4 to 9:1, and the amount of dispersion medium added is such that the liquid-solid ratio is 5 to 20 mL per g based on the mass of montmorillonite. The dispersion is carried out under mechanical stirring at 300 to 800 r / min for 10 to 60 min at 25–40°C and normal pressure. A2, then add a total of 2–10 parts by weight of aminopropylsilane and continue stirring for 30–120 min, wherein the aminopropylsilane is selected from one or both of 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; A3, the pH of the system was adjusted to 4.0–5.5 by titration with an aqueous acetic acid solution of 1%–10% by mass under stirring; A4, continue stirring the reaction at 40–60℃ and normal pressure for 1–6 h; A5, after the reaction is complete, filter and wash with ethanol and water in sequence until the pH of the final water wash filtrate is 6.5–7.5; A6 was then dried at 60–90 °C for 6–12 h under vacuum conditions with an absolute pressure of 0.01–0.03 MPa to obtain aminopropylsilane-modified montmorillonite; wherein the aminopropylsilane-modified montmorillonite has a water content of not more than 1.0 wt% and a nitrogen content of 0.2–1.5 wt%.

3. The multifunctional high-barrier multilayer packaging film according to claim 1, characterized in that, The preparation method of maleic anhydride-grafted polyethylene includes the following sub-steps: B1, premixing 100 parts by weight of polyethylene, 0.3–2.0 parts by weight of maleic anhydride and 0.03–0.20 parts by weight of dicumyl peroxide; B2, twin-screw reactive extrusion under nitrogen protection, with temperatures in each zone of the reactive extrusion process ranging from 170 to 220°C, screw speed from 200 to 500 r / min, and total material residence time from 30 to 180 s; B3, in the vacuum exhaust section, the absolute pressure is controlled at 0.02–0.06 MPa to remove free maleic anhydride; B4, after being water-cooled and pelletized, is dried under vacuum conditions of 80–100℃ and 0.01–0.03 MPa for 4–8 h to obtain maleic anhydride-grafted polyethylene; wherein the maleic anhydride-grafted polyethylene satisfies the following requirements: the content of maleic anhydride groups is 0.05–2.0 wt%, and the content of free maleic anhydride is not higher than 0.05 wt%.

4. The multifunctional high-barrier multilayer packaging film according to claim 1, characterized in that, The preparation method of the covalently bonded composite masterbatch includes the following sub-steps: C1, the aminopropylsilane-modified montmorillonite and the maleic anhydride-grafted polyethylene are mixed in parts by weight, wherein the aminopropylsilane-modified montmorillonite is 5-40 parts by weight and the maleic anhydride-grafted polyethylene is 60-95 parts by weight. C2 was subjected to interfacial reaction and dispersion in a twin-screw extruder under nitrogen protection and atmospheric pressure. The extrusion temperature was 170–220℃, the screw speed was 250–600 r / min, and the residence time was 30–150 s. C3, extruded and water-cooled pelletized to obtain covalently bonded composite masterbatch; wherein the covalently bonded composite masterbatch has a moisture content of not more than 1.0 wt%.

5. The multifunctional high-barrier multilayer packaging film according to claim 1, characterized in that, The multifunctional high-barrier multilayer packaging film is suitable for packaging that has undergone saturated steam heat treatment at 121°C for 10–60 min, and no visible delamination occurs at the interface of the adhesive layers on both sides of the barrier layer.

6. A method for preparing the multifunctional high-barrier multilayer packaging film according to any one of claims 1-5, characterized in that, Includes the following steps: S1, prepare aminopropylsilane modified montmorillonite, prepare maleic anhydride grafted polyethylene, and prepare covalently bonded composite masterbatch; S2, polypropylene, ethylene-vinyl alcohol copolymer, polyethylene, and binder material composed of maleic anhydride grafted polyethylene and covalently bonded composite masterbatch are melted in their respective extruders and co-extruded into a film through a co-extrusion die in the order of outer layer / first binder layer / barrier layer / second binder layer / inner layer, wherein the melt temperature of polypropylene is 190–240℃, the melt temperature of polyethylene is 170–220℃, and the melt temperature of ethylene-vinyl alcohol copolymer is 170–210℃; S3, after cooling and shaping the co-extruded melt, it is wound up to obtain the multifunctional high-barrier multilayer packaging film.

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