A high-humidity resistant and high-barrier coated film and its preparation method

Abstract

This invention discloses a high-humidity resistant, high-barrier coating film and its preparation method, belonging to the field of polymer composite materials technology. The coating film includes a base film and a coating layer, wherein the coating layer is composed of a coating liquid containing ethylene-vinyl alcohol copolymer, acetoacetyl-modified polyvinyl alcohol, aminosilane-modified boron nitride nanosheets, hydroxyl-modified potassium titanate whiskers, an aqueous multifunctional aziridine crosslinking agent, and an epoxy-silane coupling agent. By constructing a multiphase synergistic system of polymer matrix-nanomaterial-crosslinking network, a three-dimensional barrier network is built using the synergistic effect of two-dimensional nanosheets and one-dimensional whiskers. Simultaneously, the number of hydrophilic groups is reduced through a specific crosslinking reaction, significantly improving the barrier stability of the material in high-humidity environments. It exhibits excellent oxygen and water vapor barrier properties, good mechanical strength, thermal stability, and aging resistance, and can be widely used in high-end packaging fields for food, pharmaceuticals, and precision instruments.

Description

Technical Field

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

[0002] In the field of packaging materials, especially for food, pharmaceutical, and precision instrument packaging, the requirements for gas barrier properties are extremely stringent. Ethylene-vinyl alcohol copolymer (EVOH) and polyvinyl alcohol (PVA) exhibit excellent gas barrier properties due to their rich hydroxyl groups in their molecular chains, which can form a dense hydrogen bond network, making them traditional high-barrier materials. However, the inherent high humidity sensitivity of these materials is their fatal flaw: in high humidity environments, water molecules can penetrate between the polymer molecular chains, disrupt the hydrogen bond network, and combine with hydroxyl groups, leading to a sharp decline in their barrier properties.

[0003] Existing technologies improve performance through multilayer composites or material blending. Patent application CN108395564A discloses a high-barrier PE coated film for liquid food packaging, which involves coating a modified EVOH latex on the outer side of a modified PE film and a modified MXD6 latex on the inner side. This structure aims to utilize the inherent barrier properties of EVOH and the auxiliary barrier effect of MXD6. However, the preparation process of the modified EVOH latex is complex, involving free radical copolymerization and alcoholysis reactions, and it does not fundamentally solve the problem of barrier performance degradation caused by the hydrophilicity of hydroxyl groups in high-humidity environments. Patent application CN106700979A discloses a high-barrier composite film for food packaging, employing a multilayer structure of polypropylene film, water-resistant film, polytetrafluoroethylene film, and silicone polyethylene film. The water-resistant film contains multiple components such as polyvinyl alcohol and nano-neodymium oxide. This method focuses on physical layering and the compounding of multiple additives, resulting in a cumbersome process, and the compatibility and long-term stability between layers may face challenges.

[0004] In summary, existing high-barrier packaging material technologies, whether multilayer composites or material blends, all suffer from significant degradation in barrier performance under high humidity conditions and long-term stability issues. Therefore, developing a novel coated film with a relatively simple process that can maintain excellent and stable barrier performance under high humidity conditions has significant technical and application value. Summary of the Invention

[0005] One of the objectives of this invention is to provide a high-humidity, high-barrier coating film, which solves the problem of decreased barrier performance of the coating film in a high-humidity environment.

[0006] The second objective of this invention is to provide a method for preparing a high-humidity resistant and high-barrier coating film, which is used to prepare the above-mentioned high-humidity resistant and high-barrier coating film.

[0007] The objective of this invention can be achieved through the following technical solution: a high-humidity resistant and high-barrier coating film, comprising a base film and a coating layer coated on at least one surface of the base film, the coating layer being formed by a coating liquid comprising the following components: a polymer matrix comprising ethylene-vinyl alcohol copolymer (EVOH) and acetyl-modified polyvinyl alcohol (modified PVA); a nanomaterial system comprising aminosilane-modified boron nitride nanosheets and hydroxyl-modified potassium titanate whiskers; a crosslinking and curing system comprising an aqueous multifunctional aziridine crosslinking agent and an organotin catalyst; an interface compatibilizer comprising an epoxy silane coupling agent; and a dispersion medium.

[0008] The polymer matrix employs a composite system of EVOH and acetoacetyl-modified PVA, forming a complementary balance between rigidity and reactivity. EVOH provides a continuous phase and a gas-tight framework, while the introduced acetoacetyl groups significantly enhance the density of crosslinking reactive sites in the system.

[0009] The nanomaterial system constructs a barrier topology with significant tortuosity through a multidimensional combination of two-dimensional boron nitride nanosheets and one-dimensional potassium titanate whiskers. Specifically, the aminosilane-modified boron nitride nanosheets extend the gas permeation path through in-plane barrier effects, while the hydroxyl-modified potassium titanate whiskers prevent the recombination of nanosheet layers through axial bonding. Together, they form a stable three-dimensional nanobarrier network.

[0010] The crosslinking curing system employs a combination of an aqueous multifunctional aziridine crosslinking agent and an organotin catalyst. This agent reacts efficiently with active functional groups (especially acetyl groups) in the polymer matrix to form a stable covalent crosslinking network. This network significantly reduces the mobility of polymer segments in high-humidity environments through conformational fixation and free volume regulation.

[0011] The interface compatibilizer is an epoxy-based silane coupling agent, whose reactive groups at both ends of the molecule form chemical bonds with the surface of the nanomaterial and the polymer matrix, respectively, achieving molecular-level bridging of the organic-inorganic interface and ensuring effective stress transfer and interface stability. This synergistic effect of multiple components and mechanisms ultimately stabilizes the barrier properties of the material under high humidity conditions.

[0012] Furthermore, in the nanomaterial system, the mass ratio of the aminosilane-modified boron nitride nanosheets to the hydroxyl-modified potassium titanate whiskers is (1.8-2.5):1.

[0013] When the mass ratio is below 1.8, the nanowires are relatively excessive, which may affect the flexibility and transparency of the coating due to excessive cross-linking; when it is above 2.5, the nanosheet content is too high, which is prone to agglomeration, and the bridging effect of the nanowires is insufficient, making it difficult to form a complete three-dimensional network.

[0014] Furthermore, the ethylene content of the ethylene-vinyl alcohol copolymer is 28-45 mol.

[0015] When the ethylene content is too low, the material has excellent barrier properties, but a narrow processing window, low melt strength, and is extremely sensitive to humidity; when the ethylene content is too high, the crystallinity of the material decreases too much, the barrier properties deteriorate significantly, and it cannot meet the high barrier requirements.

[0016] Furthermore, the mass ratio of the ethylene-vinyl alcohol copolymer to the acetoacetyl-modified polyvinyl alcohol is (1.5-2.2):1.

[0017] An excessively high PVA ratio can lead to excessive hydrophilicity in the system, which is detrimental to moisture resistance and may cause brittleness due to excessive crosslinking density; an excessively high EVOH ratio results in insufficient crosslinking sites, making it impossible to form a sufficiently dense crosslinking network to lock the polymer chain segments, thus limiting the improvement in high-humidity stability.

[0018] Furthermore, the dispersion medium is a mixed solvent of water and ethanol or isopropanol, wherein the mass ratio of water to alcohol is (70-85):(30-15).

[0019] When the alcohol content is too low, the effect of improving wetting and drying rates is not obvious; when the alcohol content is too high, it will have an adverse effect on the solubility of the polymer, leading to decreased solution stability or gel formation.

[0020] Furthermore, the coating liquid, by weight, comprises: 13-18 parts of ethylene-vinyl alcohol copolymer, 7-10 parts of acetoacetyl-modified polyvinyl alcohol, 1.8-3.0 parts of aminosilane-modified boron nitride nanosheets, 0.9-1.4 parts of hydroxyl-modified potassium titanate whiskers, 2.8-4.0 parts of aqueous multifunctional aziridine crosslinking agent, 0.06-0.12 parts of organotin catalyst, 0.4-0.75 parts of epoxy silane coupling agent, and 80-100 parts of dispersion medium.

[0021] The dosage of each component is a direct result of its functional requirements and interactions. For example, the total number of nanomaterials (2.7–4.4 parts) was determined after extensive dispersion experiments and performance tests, ensuring that it significantly improves performance without causing dispersion difficulties or severe degradation of optical properties due to excessive dosage. The number of crosslinking agents (2.8–4.0 parts) is matched with the total number of polymers (20–28 parts) to ensure sufficient crosslinking density; its specific range is determined by measuring the gel content and swelling degree of samples with different degrees of crosslinking.

[0022] Furthermore, the dried thickness of the coating layer is 0.8-5 μm.

[0023] When the thickness is less than 0.8 μm, it is difficult to form a continuous and defect-free film, and the barrier performance is unstable and has poor reproducibility. When it exceeds 5 μm, the additional performance of the coating is limited, but the internal stress increases significantly, making it easy to generate microcracks when bending. At the same time, the haze increases and the cost-effectiveness ratio decreases.

[0024] Furthermore, the base film is polyethylene terephthalate film (PET), biaxially oriented polypropylene film (BOPP), or polyamide film (PA).

[0025] PET possesses excellent mechanical strength, transparency, and dimensional stability; BOPP offers high cost-effectiveness and good moisture barrier properties; PA exhibits excellent toughness, particularly good puncture resistance. The selection of these three materials allows this invention to flexibly adapt to the needs of different application scenarios.

[0026] A method for preparing a high-humidity resistant and high-barrier coated film includes the following steps:

[0027] S1: Preparation of coating solution;

[0028] S2: The coating liquid is applied to the surface of the base film, and after drying and curing, a coating layer is formed to obtain the high humidity resistant and high barrier coating film.

[0029] Furthermore, the preparation of the coating liquid in step S1 specifically includes:

[0030] S11: Boron nitride nanosheets were modified with aminosilane and potassium titanate whiskers were modified with hydroxysilane, respectively.

[0031] S12: The modified nanomaterials are dispersed in a partial dispersion medium under ultrasonic conditions to form a nano-dispersion.

[0032] S13: Dissolve ethylene-vinyl alcohol copolymer in a partial dispersion medium to form EVOH solution; dissolve acetyl-modified polyvinyl alcohol in hot water to form PVA solution;

[0033] S14: Mix the EVOH solution, PVA solution and nano-dispersion, add an interfacial compatibilizer, and emulsify at high speed to obtain a mixture;

[0034] S15: After cooling the mixture, add it to the cross-linking curing system, and obtain the coating liquid after vacuum degassing.

[0035] Furthermore, in S11, the silane coupling agent used for the aminosilane modification is KH-550, and the reaction is carried out under nitrogen protection at 70-75°C for 5-6 hours; the silane coupling agent used for the hydroxysilane modification is KH-560, and the reaction is carried out at pH=4-5 at 75-80°C for 4-5 hours.

[0036] The amino group of KH-550 reacts with the edge defect sites of BNNS, requiring sufficient temperature (70-75℃) and time (5-6h) and an inert atmosphere to prevent silane self-condensation. The epoxy group of KH-560 is more likely to undergo ring-opening reaction with the hydroxyl groups on the surface of potassium titanate whiskers under acidic conditions (pH 4-5) and heating (75-80℃).

[0037] Furthermore, in S12, the ultrasonic dispersion power is 800-900W, the time is 30-40 minutes, and the temperature is kept below 40℃.

[0038] Power (800–900 W) and time (30–40 min) are sufficient to overcome the van der Waals forces between nanoparticles, achieving primary dispersion. Temperature control (<40 °C) prevents localized overheating that could lead to solvent vaporization or modifier decomposition.

[0039] Furthermore, in S13, the temperature for dissolving the ethylene-vinyl alcohol copolymer is 80-90°C; the temperature for dissolving the acetoacetyl-modified polyvinyl alcohol is 85-92°C.

[0040] The dissolution of EVOH and PVA requires overcoming lattice energy. A specific temperature range (80-90℃, 85-92℃) is the equilibrium point for their full dissolution without causing drastic degradation.

[0041] Furthermore, in S14, the high-speed emulsification speed is 10000-12000 rpm, the time is 15-25 minutes, and the emulsification temperature is controlled at 50±2℃.

[0042] High rotation speed and sufficient time ensure uniform mixing of the nano-dispersion and polymer solution at the microscale. Temperature control (50±2℃) prevents solvent evaporation and premature crosslinking.

[0043] Furthermore, in step S15, the vacuum degree of the vacuum degassing is not lower than -0.095 MPa, and the degassing time is 30 to 45 minutes; the viscosity of the coating liquid is controlled at 300-400 mPa·s.

[0044] High vacuum and sufficient time ensure the removal of air bubbles entrapped during mixing and emulsification, preventing pinhole defects in the coating. The viscosity range is an ideal window for microgravure coating processes, guaranteeing transfer rates and coating uniformity.

[0045] Furthermore, in S2, the coating method is microgravure coating, and the wet film thickness is 15-20μm.

[0046] Microgravure coating is suitable for high-precision thin-film coating in this viscosity range. The wet film thickness (15-20 μm) is matched with the solids content to obtain the target dry film thickness.

[0047] Furthermore, the drying and curing process employs a staged curing process, including: preheating at 65-70°C for 30-40 seconds, then primary curing at 85-90°C for 60-90 seconds, and finally curing at 105-115°C for 2-3 minutes.

[0048] The graded curing strategy is as follows: the preheating zone (65-70℃) allows the solvent to evaporate slowly, avoiding surface skin formation; the main curing zone (85-90℃) promotes most of the cross-linking reaction; and the post-curing zone (105-115℃) ensures that the cross-linking reaction is complete, forming a stable network structure, thereby obtaining the best performance.

[0049] The beneficial effects of this invention are:

[0050] (1) This invention constructs a synergistic system integrating "polymer-nano-crosslinking" three networks. It innovatively uses acetoacetyl-modified polyvinyl alcohol and ethylene-vinyl alcohol copolymer to form a reactive polymer matrix. At the same time, it introduces aminosilane-modified boron nitride nanosheets and hydroxyl-modified potassium titanate whiskers to construct a multidimensional barrier network. It also uses aziridine crosslinking agent and epoxy silane coupling agent to achieve molecular-level interface bridging and crosslinking curing. Finally, a dense and stable coating layer is formed on the surface of the base film. Thus, it solves the two key technical problems of gas barrier path optimization and hydrophilic group passivation at the molecular scale, so that the coating film can maintain excellent and stable barrier performance in high humidity environment.

[0051] (2) The ethylene-vinyl alcohol copolymer and acetoacetyl-modified polyvinyl alcohol used in this invention achieve an ideal balance between material rigidity and reactivity. The ethylene-vinyl alcohol copolymer, as the continuous phase, provides a basic airtight framework and mechanical support; while the introduced acetoacetyl-modified polyvinyl alcohol significantly increases the density of active crosslinking sites on the polymer molecular chain, laying the molecular foundation for the subsequent formation of a dense three-dimensional crosslinking network. The two work together to form a polymer matrix that has both excellent initial barrier properties and high reactivity.

[0052] (3) The present invention employs a multidimensional combination of two-dimensional boron nitride nanosheets and one-dimensional potassium titanate whiskers to form a nanocomposite structure with a significant topological barrier effect. The boron nitride nanosheets, through their large specific surface area and layered structure, provide a tortuous permeation path for gas molecules; the potassium titanate whiskers, interspersed between the layers, act as nanobridges, preventing the nanosheets from re-stacking and enhancing the mechanical stability of the nanonetwork. The complementarity of their size and morphology synergistically constructs a stable and efficient three-dimensional nanobarrier network, greatly delaying the penetration dynamics of gas and water vapor.

[0053] (4) The multifunctional aziridine crosslinking agent used in this invention reacts efficiently with the active functional groups (especially acetyl acetyl groups) in the polymer matrix to form a stable covalent crosslinking network. This network significantly reduces the mobility of polymer chain segments in high humidity environments through conformational locking, reducing free volume, and effectively reducing the overall concentration and accessibility of hydrophilic hydroxyl groups in the material. The epoxy silane coupling agent acts as a molecular bridge, with its reactive groups at both ends forming strong chemical bonds with the surface of the nanomaterial and the polymer matrix, respectively, achieving a strong and tough bond between the organic and inorganic phases at the interface, ensuring stress transfer and interfacial stability during long-term use. Detailed Implementation

[0054] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0055] Example 1

[0056] This embodiment provides a high-humidity-resistant and high-barrier coated film, which is prepared through the following steps:

[0057] S1. Pretreatment of nanomaterials: Take 2.2g of boron nitride nanosheets and reflux them at 70℃ for 5 hours in an anhydrous ethanol solution (concentration 1.5wt%) of KH-550 silane coupling agent under nitrogen protection. After centrifugation and washing, dry them under vacuum at 75℃ for 12 hours to obtain amino-modified boron nitride nanosheets. Take 1.0g of potassium titanate whiskers and react them at 75℃ for 4 hours in an aqueous solution (concentration 1.5wt%, pH=4.5) of KH-560 silane coupling agent. After centrifugation and washing, dry them under vacuum at 85℃ for 12 hours to obtain hydroxyl-modified potassium titanate whiskers.

[0058] S2. Preparation of polymer solution: Dissolve 15g of EVOH (ethylene content 32mol%) in a mixed solvent of 70g of deionized water and 20g of ethanol at 85℃ and stir mechanically for 1.5 hours to obtain EVOH solution; Dissolve 8g of acetyl-modified PVA (degree of hydrolysis 95%) in hot water at 90℃ to prepare a 25wt% PVA aqueous solution;

[0059] S3. Preparation of nano-dispersion: 2.2g of pretreated boron nitride nanosheets and 1.0g of potassium titanate whiskers were added to 100mL of water-ethanol mixed solvent (water:ethanol=4:1) and ultrasonically dispersed at 850W power for 35 minutes (pulse mode, ice water bath temperature control <40℃).

[0060] S4. Mixed emulsification: Mix EVOH solution, PVA solution and nano dispersion, add 0.5g epoxy silane coupling agent, emulsify at high speed of 11000rpm for 20 minutes, and control the temperature at 50±2℃.

[0061] S5. Crosslinking and Degassing: Cool the mixture to below 35°C, add 3.2g of aqueous multifunctional aziridine crosslinking agent and 0.08g of dibutyltin dilaurate (catalyst), and stir at low speed for 15 minutes. Then degas under a vacuum of -0.098MPa for 40 minutes to obtain the coating liquid (viscosity approximately 350mPa·s).

[0062] S6. Coating and Curing: Using micro-gravure coating, the coating liquid is applied to a 12μm thick corona-treated PET base film, with a wet film thickness of 18μm. After preheating at 65℃ for 30 seconds, main curing at 85℃ for 60 seconds, and post-curing at 105℃ for 120 seconds, a high-humidity resistant and high-barrier coated film is obtained.

[0063] Example 2

[0064] The difference between this embodiment and Example 1 is as follows: the amount of EVOH (ethylene content 38mol%) is 17g, the amount of modified PVA is 8.5g; the amount of boron nitride nanosheets is 2.5g, the amount of potassium titanate whiskers is 1.2g; the amount of crosslinking agent is 3.5g, the amount of catalyst is 0.09g; the dispersion medium is 68g water and 22g ethanol; the dissolution temperature of EVOH is 88℃; the remaining raw materials and preparation process are the same as in Example 1.

[0065] Example 3

[0066] The difference between this embodiment and Example 1 is as follows: the amount of EVOH (ethylene content 28mol%) is 14g, the amount of modified PVA is 7.5g; the amount of boron nitride nanosheets is 1.8g, the amount of potassium titanate whiskers is 0.9g; the amount of crosslinking agent is 2.8g, the amount of catalyst is 0.07g; the dispersion medium is 72g water and 18g ethanol; the dissolution temperature of EVOH is 82℃; the remaining raw materials and preparation process are the same as in Example 1.

[0067] Example 4

[0068] The difference between this embodiment and Example 1 is that: the amount of EVOH (ethylene content 42mol%) is 16g, the amount of modified PVA is 9g; the amount of boron nitride nanosheets is 2.8g, the amount of potassium titanate whiskers is 1.3g; the amount of crosslinking agent is 3.8g, the amount of catalyst is 0.10g; the dispersion medium is 66g water and 24g ethanol; the remaining raw materials and preparation process are the same as in Example 1.

[0069] Example 5

[0070] The difference between this embodiment and Example 1 is that: the amount of EVOH (ethylene content 35mol%) is 15.5g, the amount of modified PVA is 8.2g; the amount of boron nitride nanosheets is 2.3g, the amount of potassium titanate whiskers is 1.1g; the amount of crosslinking agent is 3.3g, the amount of catalyst is 0.085g; the dispersion medium is 69g water and 21g ethanol; the remaining raw materials and preparation process are the same as in Example 1.

[0071] Example 6

[0072] The difference between this embodiment and Example 1 is that: the amount of EVOH (ethylene content 45mol%) is 18g, the amount of modified PVA is 10g; the amount of boron nitride nanosheets is 3.0g, the amount of potassium titanate whiskers is 1.4g; the amount of crosslinking agent is 4.0g, the amount of catalyst is 0.12g; the dispersion medium is 64g water and 26g ethanol; the remaining raw materials and preparation process are the same as in Example 1.

[0073] Comparative Example 1

[0074] This comparative example differs from Example 1 in that it does not contain nanomaterials. The specific implementation steps are as follows:

[0075] 1. Prepare EVOH solution and PVA solution according to the method in Example 1;

[0076] 2. After mixing the two, add 0.5g of epoxy silane coupling agent and emulsify at high speed;

[0077] 3. After cooling, add 3.2g of crosslinking agent and 0.08g of catalyst, degas and then coat and cure; (all nanomaterial addition and pretreatment steps are omitted) The remaining raw materials and preparation process are the same as in Example 1.

[0078] Comparative Example 2

[0079] The difference between this comparative example and Example 1 is that it does not contain a crosslinking agent. The specific implementation steps are as follows:

[0080] 1. The pretreatment of nanomaterials, polymer dissolution, and preparation of nano-dispersion were completed according to the method in Example 1;

[0081] 2. Mix the EVOH solution, PVA solution and nano-dispersion, add 0.5g of epoxy silane coupling agent, and emulsify at high speed;

[0082] 3. Directly perform vacuum degassing followed by coating and curing; (omitting the steps of adding crosslinking agent and catalyst) The remaining raw materials and preparation process are the same as in Example 1.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 1 is that it contains only boron nitride nanosheets. The specific implementation steps are as follows:

[0085] 1. Only 3.2g of boron nitride nanosheets were modified with aminosilane;

[0086] 2. Prepare the polymer solution according to the method in Example 1;

[0087] 3. Prepare a nano-dispersion by dispersing modified boron nitride nanosheets (using 3.2g of boron nitride nanosheets to replace all nanomaterials). The remaining raw materials and preparation process are the same as in Example 1.

[0088] Comparative Example 4

[0089] The difference between this comparative example and Example 1 is that it contains only potassium titanate whiskers. The specific implementation steps are as follows:

[0090] 1. Hydroxysilane modification was performed only on 3.2g of potassium titanate whiskers;

[0091] 2. Prepare the polymer solution according to the method in Example 1;

[0092] 3. Prepare a nano-dispersion by dispersing modified potassium titanate whiskers (using 3.2g of potassium titanate whiskers to replace all nanomaterials). The remaining raw materials and preparation process are the same as in Example 1.

[0093] Comparative Example 5

[0094] The difference between this comparative example and Example 1 is that it uses ordinary PVA, and the specific implementation steps are as follows:

[0095] 1. Perform nanomaterial pretreatment and dispersion according to the method in Example 1;

[0096] 2. Dissolve 8g of ordinary PVA (95% degree of hydrolysis) in hot water at 90°C instead of acetyl-modified PVA; (using ordinary PVA instead of modified PVA) the remaining raw materials and preparation process are the same as in Example 1.

[0097] Comparative Example 6

[0098] The difference between this comparative example and Example 1 is that the unmodified nanomaterials were used, and the specific implementation steps are as follows:

[0099] 1. Directly use 2.2g of unmodified boron nitride nanosheets and 1.0g of unmodified potassium titanate whiskers;

[0100] 2. Prepare nano-dispersions according to the method of Example 1 (without surface modification treatment); (the surface modification step of nanomaterials is omitted) The remaining raw materials and preparation process are the same as in Example 1.

[0101] Performance testing

[0102] Performance tests were conducted on Examples 1-6 and Comparative Examples 1-6, as detailed below:

[0103] 1. Oxygen permeability tests were conducted on the high-humidity resistant and high-barrier coated films obtained in the various embodiments and comparative examples of this application according to ASTM D3985-17 Standard Test Method for Oxygen Permeability of Plastic Films and Sheets (Test conditions: 23°C, 90%RH).

[0104] 2. Tensile strength tests were performed on the high-humidity resistant and high-barrier coated films obtained in the various embodiments and comparative examples of this application, according to ASTM D882-18 Standard Test Method for Tensile Properties of Plastic Films and Sheets.

[0105] 3. According to ASTM D648-18 Standard Test Method for Deflection Temperature of Plastics under Bending Load, the heat distortion temperature (load 1.82 MPa) of the high-humidity resistant and high-barrier coating films obtained in the various embodiments and comparative examples of this application was tested.

[0106] 4. According to the equilibrium swelling method, the crosslinking density of the high-humidity resistant and high-barrier coating layers obtained in the various embodiments and comparative examples of this application was tested.

[0107] 5. In accordance with ISO 4611:2010 Plastics – Determination of the effects of damp heat, water mist and salt spray, the high-barrier coating films obtained in the various embodiments and comparative examples of this application were subjected to damp heat aging tests (conditions: 85°C / 85%RH, 1000 hours), and the changes in their oxygen permeability were measured.

[0108] The results are shown in Table 1:

[0109]

[0110] As shown in Table 1, the oxygen permeability (90% RH) data for all examples are significantly better than those for the comparative examples, proving that the core objective of this invention—improving barrier performance under high humidity conditions—has been successfully achieved. Specifically, Example 3 exhibits the best barrier performance, which is related to its higher crosslinking density and optimized material ratio. In contrast, the oxygen permeability of Comparative Example 1 (without nanomaterials) is about 10 times higher than that of the examples, fully demonstrating the key role of nanomaterials in constructing the barrier network. The data for Comparative Example 2 (without crosslinking agent) shows that even with the presence of nanomaterials, the lack of a crosslinking network cannot effectively inhibit the plasticizing effect of water molecules on polymer chains. Furthermore, Comparative Examples 3 and 4, using single nanomaterials respectively, have oxygen permeability better than Comparative Examples 1 and 2, but still far inferior to all examples. This confirms the importance of the synergistic effect of two-dimensional boron nitride nanosheets and one-dimensional potassium titanate whiskers in constructing an efficient three-dimensional barrier network.

[0111] Tensile strength data showed that the examples generally outperformed the comparative examples. Example 3 performed best, which is related to its moderate ethylene content in EVOH and optimized nanomaterial ratio. Comparative Example 1 had the lowest tensile strength, indicating the enhancing effect of nanomaterials on mechanical properties. Heat distortion temperature showed a significant positive correlation with crosslinking density. The heat distortion temperatures of Examples 1-6 were in the range of 146-156°C, and the higher the crosslinking density, the higher the heat distortion temperature. Example 3 had the highest crosslinking density and heat distortion temperature, indicating that its three-dimensional network structure was the most complete. Comparative Example 1 had the lowest crosslinking density and the lowest heat distortion temperature, further confirming the enhancing effect of the crosslinking network on thermal stability.

[0112] Comparative Example 5 (using ordinary PVA) showed poor performance across the board, particularly in crosslinking density and damp heat aging stability, demonstrating the crucial role of acetyl-acetyl modification in improving crosslinking efficiency and network stability. Comparative Example 6 (unmodified nanomaterials) exhibited performance between the single nanomaterial comparative examples and the actual examples, indicating that even without surface modification, nanomaterials can still provide some performance enhancement, but insufficient interfacial bonding limits the full realization of its effects.

[0113] The change rate of oxygen permeability after humid heat aging is a key indicator for evaluating the humid heat resistance performance. All examples showed a change rate between +14% and +24%, demonstrating excellent stability. However, Comparative Example 1 showed a change rate as high as +320%, indicating that the system lacking nanomaterials and cross-linked networks severely deteriorated under humid heat conditions. Furthermore, while the change rates of Comparative Examples 3 and 4 were significantly better than Comparative Example 1, they were still significantly worse than the examples, indicating that a single nanomaterial system cannot provide sufficient long-term stability, further confirming the value of multidimensional nano-synergistic systems.

[0114] From Example 1 to Example 6, different performance characteristics were obtained by systematically adjusting the proportions of each component. Example 3 achieved optimal barrier properties and hydrothermal stability while maintaining good mechanical properties, representing a superior formulation combination. Although the performance of Example 6 decreased slightly, it was still significantly better than all comparative examples, demonstrating the rationality and feasibility of the formulation range of the present invention.

[0115] In summary, this invention successfully prepared a coating film exhibiting excellent barrier properties, good mechanical properties, outstanding thermal stability, and superior resistance to humid heat aging under high humidity conditions by organically combining an EVOH / modified PVA polymer matrix, a dual nanomaterial synergistic system, an aziridine crosslinking network, and a silane interfacial compatibilizer. The test results of each comparative example, from the opposite perspective, validated the necessity of each component and process step, particularly the synergistic effect of the dual nanomaterials and the crucial role of the chemical crosslinking network, fully demonstrating the innovation and technical advantages of this invention.

[0116] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A high-humidity resistant, high-barrier coated film, characterized by, The coating film comprises a base film and a coating layer coated on at least one surface of the base film, and the coating layer is formed by a coating liquid comprising: a polymer matrix comprising ethylene-vinyl alcohol copolymer and acetyl-acetyl-modified polyvinyl alcohol; a nanomaterial system comprising amino-silane-modified boron nitride nanosheet and hydroxyl-modified potassium titanate whisker; a cross-linking curing system comprising water-based multifunctional aziridine cross-linking agent and organic tin catalyst; an interfacial compatibilizer: epoxy-silane coupling agent; and a dispersion medium; the mass ratio of the ethylene-vinyl alcohol copolymer to the acetyl-acetyl-modified polyvinyl alcohol is (1.5-2.2):

1. The ethylene content of the ethylene-vinyl alcohol copolymer is 28-45 mol%; the mass ratio of the amino-silane-modified boron nitride nanosheet to the hydroxyl-modified potassium titanate whisker is (1.8-2.5):1; and the dispersion medium is a mixed solvent of water and ethanol or isopropanol, wherein the mass ratio of water to alcohol is (70-85):(30-15).

2. The high-humidity resistant, high-barrier coated film according to claim 1, characterized by, The coating liquid comprises, by weight: ethylene-vinyl alcohol copolymer 13-18 parts, acetyl-acetyl-modified polyvinyl alcohol 7-10 parts, amino-silane-modified boron nitride nanosheet 1.8-3.0 parts, hydroxyl-modified potassium titanate whisker 0.9-1.4 parts, water-based multifunctional aziridine cross-linking agent 2.8-4.0 parts, organic tin catalyst 0.06-0.12 parts, epoxy-silane coupling agent 0.4-0.75 parts, and dispersion medium 80-100 parts.

3. The high-humidity resistant, high-barrier coated film according to claim 1, characterized by, The dry thickness of the coating layer is 0.8-5 μm; and the base film is polyethylene terephthalate film, biaxially oriented polypropylene film or polyamide film.

4. The high-humidity resistant, high-barrier coated film according to claim 1, characterized by, The method for preparing the high-humidity-resistant and high-barrier coating film of any one of claims 1-4 comprises the following steps:

5. A method for producing a high-humidity resistant, high-barrier coated film, characterized by, S1: preparing a coating liquid; S2: coating the coating liquid on the surface of a base film, and forming a coating layer after drying and curing to obtain the high-humidity-resistant and high-barrier coating film. The preparation of the coating liquid in S1 specifically comprises:

6. The method for preparing a high-humidity resistant and high-barrier coated film according to claim 5, characterized by, S11: separately modifying the boron nitride nanosheet with amino-silane and modifying the potassium titanate whisker with hydroxyl-silane; S12: dispersing the modified nanomaterials in part of the dispersion medium under ultrasonic conditions to form a nanodispersion; S13: dissolving ethylene-vinyl alcohol copolymer in part of the dispersion medium to form an EVOH solution, and dissolving acetyl-acetyl-modified polyvinyl alcohol in hot water to form a PVA solution; S14: mixing the EVOH solution, the PVA solution and the nanodispersion, adding an interfacial compatibilizer, and obtaining a mixed liquid after high-speed emulsification; S15: cooling the mixed liquid, adding a cross-linking curing system, and obtaining the coating liquid after vacuum defoaming. In S11, the amino-silane modification uses silane coupling agent KH-550, and the reaction is carried out at 70-75°C for 5-6 hours under nitrogen protection; and the hydroxyl-silane modification uses silane coupling agent KH-560, and the reaction is carried out at pH=4-5 and 75-80°C for 4-5 hours.

7. The method of claim 6, wherein the coating film has a high moisture resistance and a high barrier property. ​ 8. The method of claim 6, wherein the coating film has a high moisture resistance and a high barrier property. In the S12, the power of ultrasonic dispersion is 800-900 W, the time is 30-40 minutes, and the temperature is kept below 40℃; in the S13, the temperature for dissolving ethylene-vinyl alcohol copolymer is 80-90℃, and the temperature for dissolving acetyl-acetyl-modified polyvinyl alcohol is 85-92℃.

9. The method of claim 6, wherein the coating film has a high moisture resistance and a high barrier property. In the S14, the rotating speed of high-speed emulsification is 10000-12000 rpm, the time is 15-25 minutes, and the emulsification temperature is controlled at 50±2℃; in the S15, the vacuum degree of vacuum defoaming is not less than -0.095 MPa, and the defoaming time is 30-45 minutes; the viscosity of the coating liquid is controlled at 300-400 mPa·s.

10. The method of claim 5, wherein the coating film has a high moisture resistance and a high barrier property. In the S2, the coating method is micro-gravure coating, and the wet film thickness is 15-20 μm; the drying and curing process adopts staged curing, including preheating at 65-70℃ for 30-40 seconds, main curing at 85-90℃ for 60-90 seconds, and finally curing at 105-115℃ for 2-3 minutes.

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