A polyethylene film with high oxygen barrier properties and its preparation method

Abstract

This invention discloses a polyethylene film with high oxygen barrier properties and its preparation method, belonging to the field of polymer film technology. This invention achieves excellent oxygen barrier performance by optimizing the multilayer synergistic structure of the MDOPE substrate film, branched polyethyleneimine undercoat, polyelectrolyte coating, and metal plating. Specifically, the MDOPE substrate possesses high stiffness and temperature resistance, exhibiting excellent post-processing adaptability; the undercoat forms a chemical anchor between the non-polar MDOPE and the polar polyelectrolyte; free carboxyl or amine groups in the polyelectrolyte coordinate with aluminum atoms during the vapor deposition process, significantly improving coating adhesion. Furthermore, the polyelectrolyte coating forms a dense ionic cross-linked network insensitive to water molecules, possessing both high oxygen and water vapor barrier properties. Overall, it meets the requirements for the recyclability of a single PE material, can be recycled within the existing PE recycling stream, aligns with environmental packaging policies, and has high application and economic value.

Description

Technical Field

[0001] This invention relates to the field of polymer film technology, and more specifically, to a polyethylene film with high oxygen barrier properties and its preparation method. Background Technology

[0002] With Europe and the United States imposing policy requirements on the recyclability of flexible packaging, single-material recyclable flexible packaging is gradually being used in the market to replace traditional multi-layer composite packaging. Polyethylene (PE) has good toughness and heat-sealing properties, making it an important material in the flexible packaging industry. Using all-PE packaging provides performance close to that of traditional composite packaging while being easy to recycle and reuse. However, polyethylene is a non-polar material, and its barrier properties against oxygen molecules, which are also non-polar, are poor. Therefore, the application of ordinary all-PE packaging has significant limitations in food packaging with long shelf-life requirements, necessitating the development of polyethylene films with high oxygen barrier properties.

[0003] Currently, the main technical routes for improving the oxygen barrier properties of polyethylene films include multilayer co-extrusion with added barrier layers, coating with barrier coatings, and vacuum metal / oxide plating. For example, Chinese patent CN117246015A discloses an oxygen-barrier polyethylene film and its preparation method. This film comprises a five-layer structure: a base layer, inner layer I, intermediate layer, inner layer II, and outer layer. The base layer and outer layer are modified polyethylene, and the intermediate layer is polyvinyl alcohol. The film, possessing oxygen and water barrier properties, is obtained through a five-layer co-extrusion process. However, this technical solution employs a multilayer co-extrusion process, which requires significant equipment investment and is complex. Furthermore, PVA, as the intermediate barrier layer, is significantly affected by humidity; water molecules disrupt the hydrogen bond network between PVA molecules, reducing its oxygen barrier effect, resulting in a substantial decrease in barrier performance under high humidity environments. Another example is Chinese patent CN119371704A, which discloses a high-barrier coating for food packaging and its preparation method. This high-barrier coating comprises an MDOPE film, a modified PVA coating, and an alumina barrier layer arranged sequentially. This method involves coating the MDOPE surface with a modified PVA coating and then layering it with an alumina coating, which improves the barrier properties to some extent. However, the PVA coating still suffers from barrier degradation under high humidity, and the adhesion between the PVA and the MDOPE substrate needs to be improved, requiring additional surface treatment processes.

[0004] There are commercially available solutions that directly coat MDOPE surfaces with PVA coatings, but PVA is greatly affected by humidity. Water vapor can disrupt the hydrogen bond network between molecules, reducing its oxygen barrier effect. Even with processes like aluminizing or alumina plating, the material's barrier properties are still affected under high humidity. Research shows that polyelectrolyte coatings, through the formation of dense ionic bonds between cations and anions, can effectively reduce oxygen permeability. For example, Chinese patent CN102481597A describes the use of polyelectrolyte complexes to provide an oxygen barrier layer for polymer films. This involves coating at least three alternating layers, with adjacent layers being anionic and cationic polyelectrolyte layers, forming a polyelectrolyte complex at the interface of the alternating layers. Another example is Chinese patent CN1857918A, which discloses a method for preparing a high-barrier self-assembled multilayer composite film by alternately immersing a substrate in anionic and cationic polyelectrolyte solutions, adsorbing layer by layer to form a multilayer self-assembled film. However, these methods require multiple alternating coatings or multiple immersion adsorptions, making them cumbersome and time-consuming in actual production, hindering mass production. Summary of the Invention

[0005] Based on this, to solve one of the aforementioned technical problems, this invention introduces a polyethylene film with high oxygen barrier properties. This is achieved by sequentially depositing a primer, a polyelectrolyte coating, and a metal plating layer onto an MDOPE substrate film. The polyelectrolyte coating is formed by pre-mixing cationic and anionic polymers and then coating them in a single step. During the drying process, ammonia volatilizes, causing the two polymers to form a dense ionic cross-linked network, avoiding the cumbersome process of multiple alternating coatings. Simultaneously, the metal plating layer further enhances the barrier performance and strengthens the adhesion between the coating and the substrate. This invention features a simple process and maintains good oxygen barrier properties even in high humidity environments, making it suitable as a barrier substrate film for recyclable all-PE packaging. This invention provides a polyethylene film with high oxygen barrier properties and its preparation method, the specific technical solution of which is as follows: A polyethylene film with high oxygen barrier properties, wherein the polyethylene film comprises, from bottom to top: an MDOPE substrate film, a base coating, a polyelectrolyte coating, and a metal plating layer; The oxygen permeability of the polyethylene film is less than 0.2 cm. 3 / m 2 ·day·atm.

[0006] Furthermore, the MDOPE substrate film is a 20-30 μm film obtained by stretching it 4-6 times in the mechanical direction, and the MDOPE substrate film is corona treated, with a film density greater than 0.940 g / cm³. 3 .

[0007] Furthermore, the base coating is formed by a base coating liquid, the raw materials for which the base coating liquid is prepared include branched polyethyleneimine, the molecular weight of which is 1000~80000.

[0008] Furthermore, the polyelectrolyte coating is formed by coating and drying a polyelectrolyte mixture solution of a cationic polymer solution and anionic polymer solution.

[0009] Further, the anionic polymer solution has a mass percentage concentration of 2.5-20 wt%, and the pH value of the anionic polymer solution is adjusted to 7-12 using ammonia; the cationic polymer solution has a mass percentage concentration of 2.5-20 wt%, and the pH value of the cationic polymer solution is adjusted to 7-12 using ammonia.

[0010] Furthermore, the molar ratio of cations to anions in the polyelectrolyte mixed solution is (1~4):(1~2).

[0011] Further, the anionic polymer is at least one of polyacrylic acid, polyvinyl sulfonic acid, and polyacrylamide, with a molecular weight of 1,000 to 1,000,000; the cationic polymer is at least one of polyvinylpyridine, vinylimidazolium polymer, and polyethyleneimine, with a molecular weight of 1,000 to 1,000,000.

[0012] Furthermore, the coating amount of the mixture is 0.1~5.0 g / m³. 2 .

[0013] Furthermore, the metal coating is a vacuum-deposited aluminum layer and / or aluminum oxide layer, with a coating thickness of 200~800 angstroms.

[0014] In addition, the present invention also provides a method for preparing a polyethylene film with high oxygen barrier properties, the preparation method comprising the following steps: S1. Prepare an MDOPE substrate film and subject the surface of the MDOPE substrate film to corona treatment; S2. Apply a primer to the corona-electrode surface of the MDOPE substrate film, and after drying, form a primer layer; S3. Prepare an aqueous solution of cationic polymer and adjust the pH value to 7-12 using ammonia; prepare an aqueous solution of anionic polymer and adjust the pH value to 7-12 using ammonia; then mix them evenly according to the molar ratio of cationic to anionic groups of (1-4):(1-2) to obtain a polyelectrolyte mixed solution. S4. The polyelectrolyte mixture is applied to the surface of the base layer and dried to form a polyelectrolyte coating. S5. A metal coating is deposited on the surface of the polyelectrolyte coating by vacuum evaporation to form a metal coating, thereby obtaining a polyethylene film with high oxygen barrier properties.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention achieves a significant high oxygen barrier effect by optimizing the structure of the polyethylene film and the composition of each layer, resulting in a synergistic effect. The MDOPE substrate used possesses high stiffness, high tensile strength, and excellent temperature resistance. This substrate is not easily deformed by heat during subsequent printing, lamination, or bag making processes, especially when passing through an oven, providing excellent processing adaptability for flexible packaging plants. The base coating uses branched polyethyleneimine with a suitable molecular weight, forming a strong chemical anchor between the non-polar MDOPE corona-electrolyte coating and the polar polyelectrolyte coating, solving the problem of poor adhesion between polar and non-polar materials. The free carboxyl groups (-COOH) or amine groups in the polyelectrolyte coating that have not participated in ionic cross-linking coordinate or chemically bond with aluminum atoms during vacuum evaporation, significantly improving the adhesion of the metal coating to the substrate surface. This multi-layer synergistic effect achieves high adhesion and interfacial stability.

[0016] 2. The polyelectrolyte coating of this invention forms a dense ionic cross-linked network through pre-mixing and one-time coating of cationic and anionic polymers. This ionic cross-linked network is insensitive to water molecules, has a high barrier effect against oxygen, and also exhibits excellent water vapor barrier properties. Furthermore, the polyelectrolyte coating can be formed in a single coating process, significantly shortening the production flow, reducing equipment costs and energy consumption, and offering a wide operating window. This avoids the stringent control over the number of layers, immersion time, and rinsing steps required in multi-layer alternating coating processes, significantly improving the feasibility and efficiency of mass production.

[0017] 3. This invention is based on MDOPE (uniaxially oriented polyethylene) substrate, combined with a base coating, a water-based polyelectrolyte coating and a metal plating layer. The overall structure is still mainly polyethylene, which meets recycling requirements and can be recycled in the existing PE recycling stream. While ensuring high barrier properties, it meets the policy requirements of environmentally friendly packaging and has high application value and economic value overall. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] An embodiment of the present invention provides a polyethylene film with high oxygen barrier properties, wherein the polyethylene film comprises, from bottom to top: an MDOPE substrate film, a base coating, a polyelectrolyte coating, and a metal plating layer; The oxygen permeability of the polyethylene film is less than 0.2 cm. 3 / m 2 ·day·atm.

[0021] In one embodiment, the MDOPE substrate film is a 20-30 μm film obtained by stretching it 4-6 times in the mechanical direction, and the MDOPE substrate film is corona treated, with a film density greater than 0.940 g / cm³. 3 .

[0022] In one embodiment, the base coating is formed from a primer liquid, the raw material for which the primer liquid is prepared includes branched polyethyleneimine, the molecular weight of which is 1000~80000.

[0023] In one embodiment, the coating amount of the primer is 0.05~0.2 g / m³. 2 .

[0024] In one embodiment, the polyelectrolyte coating is formed by coating and drying a polyelectrolyte mixture solution of a cationic polymer solution and anionic polymer solution.

[0025] In one embodiment, the anionic polymer solution has a mass percentage concentration of 2.5-20 wt%, and the pH of the anionic polymer solution is adjusted to 7-12 using ammonia; the cationic polymer solution has a mass percentage concentration of 2.5-20 wt%, and the pH of the cationic polymer solution is adjusted to 7-12 using ammonia.

[0026] In one embodiment, the molar ratio of cations to anions in the polyelectrolyte mixture is (1~4):(1~2).

[0027] In one embodiment, the anionic polymer is at least one of polyacrylic acid, polyvinyl sulfonic acid, and polyacrylamide, with a molecular weight of 1,000 to 1,000,000; the cationic polymer is at least one of polyvinylpyridine, vinylimidazolium polymer, and polyethyleneimine, with a molecular weight of 1,000 to 1,000,000.

[0028] In one embodiment, the coating amount of the mixture is 0.1~5.0 g / m³. 2 .

[0029] In one embodiment, the metal coating is a vacuum-deposited aluminum layer and / or aluminum oxide layer with a coating thickness of 200-800 angstroms.

[0030] In addition, the present invention also provides a method for preparing a polyethylene film with high oxygen barrier properties, the preparation method comprising the following steps: S1. Prepare an MDOPE substrate film and subject the surface of the MDOPE substrate film to corona treatment; S2. Apply a primer to the corona-electrode surface of the MDOPE substrate film, and after drying, form a primer layer; S3. Prepare an aqueous solution of cationic polymer and adjust the pH value to 7-12 using ammonia; prepare an aqueous solution of anionic polymer and adjust the pH value to 7-12 using ammonia; then mix them evenly according to the molar ratio of cationic to anionic groups of (1-4):(1-2) to obtain a polyelectrolyte mixed solution. S4. The polyelectrolyte mixture is applied to the surface of the base layer and dried to form a polyelectrolyte coating. S5. A metal coating is deposited on the surface of the polyelectrolyte coating by vacuum evaporation to form a metal coating, thereby obtaining a polyethylene film with high oxygen barrier properties.

[0031] In one embodiment, step S1, the method for preparing the MDOPE substrate film includes: blowing a mixed resin into a base film, and then stretching it at 115~125°C in 4~6 times the mechanical direction to obtain an MDOPE substrate film with a thickness of 20~30μm.

[0032] In one embodiment, the mixed resin comprises the following raw materials in parts by weight: 40-60 parts of high-density polyethylene, 35-55 parts of medium-density metallocene polyethylene, and 5-10 parts of low-density polyethylene.

[0033] In one embodiment, the density of the mixed resin is >0.94 g / cm³. 3If the density is too low, the MDO film will not have sufficient temperature resistance and will have low tensile strength, causing it to stretch and deform during subsequent processes such as oven drying or bag making. In addition, this invention optimizes the composition and ratio of the mixed resins to obtain an MDOPE film with high stiffness and high tensile strength.

[0034] In one embodiment, in step S2, the primer is an aqueous solution of branched polyethyleneimine with a molecular weight of 1000~80000 and a coating amount of 0.05~0.2 g / m³. 2 This invention forms a base coating using a branched polyethyleneimine aqueous solution, which improves the adhesion of the polar coating to the MDOPE film surface. However, it limits the coating amount; too high a coating amount results in an overly thick base coating, which not only increases costs and affects application, but also makes the base coating prone to moisture absorption and other changes.

[0035] In one embodiment, in step S3, the mass percentage concentration of the cationic polymer aqueous solution is 2.5~20wt%, and the mass percentage concentration of the anionic polymer aqueous solution is 2.5~20wt%. This invention achieves high barrier properties by mixing the cationic and anionic solutions, allowing the cationic and anionic polymers to form intermolecular ionic bonds. The dense cross-linked network effectively prevents the passage of small molecules such as oxygen and water molecules. Using ammonia as a pH adjuster can adjust the ionization degree of the polyelectrolytes, stabilize the two polyelectrolyte solutions, and prevent reactions that could lead to gelation or precipitation when the two polyelectrolyte solutions are mixed. After coating onto the substrate, high-temperature drying causes the ammonia to evaporate, allowing the cationic and anionic polymers to form a stable ionic bond network. In addition, the concentrations of the cationic polymer aqueous solution and the anionic polymer aqueous solution are limited. If the solution concentration is below 5%, the subsequent reaction efficiency is low. If the concentration is above 35%, the solution viscosity is too high, especially after mixing with the cationic aqueous solution, which is not conducive to the subsequent coating process. The cationic polymer aqueous solution needs to be adjusted to weak alkalinity. If the solution is acidic, gelation will occur, making it impossible to carry out subsequent process steps. If the solution is too alkaline, the cationic polymer cannot form protonated cations, resulting in low reaction efficiency with the anionic aqueous solution.

[0036] The ease with which a gas permeates through a membrane is typically expressed using the permeability coefficient. The permeability coefficient P = solubility coefficient S * diffusion coefficient D. The solubility coefficient is determined by the interaction between the gas and the polymer, while the diffusion coefficient is related to the polymer's chemical structure and physical morphology, including chain segment mobility, steric hindrance, crystallization, and cross-linking. Non-polar polymers such as polyethylene and polypropylene have good compatibility with oxygen, allowing oxygen to easily permeate through their amorphous regions. Therefore, polyethylene and polypropylene have poor oxygen barrier properties. PVA and EVOH molecules are highly polar, while oxygen molecules have high symmetry and low polarization, resulting in poor compatibility with polar polymers. Furthermore, PVA and EVOH molecules have a certain degree of crystallinity, forming a dense hydrogen bond network in the amorphous regions, creating a high barrier to oxygen. However, under high humidity conditions, water molecules can form hydrogen bonds with PVA and EVOH molecules, disrupting the original hydrogen bond network and crystallization, thus reducing oxygen barrier properties. This invention utilizes cationic and anionic polymers to form a dense polar ionic cross-linked network on the surface of the substrate film, achieving high oxygen barrier properties. At the same time, the influence of water molecules on ionic bonds is lower than that of intramolecular and intermolecular hydrogen bonds, so the film maintains high oxygen barrier properties in high humidity environments.

[0037] In one embodiment, the cationic polymer is at least one of polyvinylpyridine, vinylimidazolium polymer, and polyethyleneimine, with a molecular weight of 1,000 to 1,000,000.

[0038] In one embodiment, the anionic polymer is selected from at least one of polyacrylic acid, polyvinyl sulfonic acid, and polyacrylamide, and has a molecular weight of 1,000 to 1,000,000.

[0039] In one embodiment, in step S4, the coating method is gravure coating, blade coating, metering bar coating, or spray coating, and the drying temperature is 70-90°C. During the drying process of this invention, ammonia gas volatilizes, and the anionic polymer and cationic polymer form a dense ionic gel network. The polyelectrolyte coating and the primer PEI also have a strong bonding effect, improving the adhesion between the coating and the substrate.

[0040] In one embodiment, in step S5, the metal coating is an aluminum layer and / or an aluminum oxide layer, with a vapor deposition thickness of 200-800 angstroms. This step further enhances the barrier properties of the film, while the free acrylic groups in the coating that have not formed ionic bonds can strengthen the adhesion of the vapor-deposited aluminum atoms to the substrate surface.

[0041] The above-mentioned solution forms a multi-level synergistic barrier system by sequentially constructing a PEI primer, a polyelectrolyte ionic bond network formed by one-time coating, and a vacuum-deposited metal layer on an MDOPE substrate. This system enables the film to maintain extremely low and stable oxygen permeability within a wide humidity range of 0% to 80%, effectively overcoming the defect of the traditional PVA coating's barrier properties dropping sharply in high humidity environments. At the same time, this method only requires one coating, which is significantly simpler than the multi-layer alternating coating process and suitable for industrial mass production. Furthermore, the free groups in the polyelectrolyte can enhance the adhesion of the coating and protect the integrity of the coating, ultimately giving the film excellent water vapor barrier properties and post-processing adaptability. Under the environmental goal of achieving recyclable packaging made of a single PE material, this method has better application value.

[0042] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments.

[0043] Example 1: A method for preparing a polyethylene film with high oxygen barrier properties includes the following steps: S1. By weight, 60 parts of high-density polyethylene AT6900, 35 parts of medium-density metallocene polyethylene 5940ST, and 5 parts of low-density polyethylene 2420D are mixed and blown into a base film with a thickness of 125 μm. The film is then stretched in 5.0 times the mechanical direction at 118°C to obtain a 25 μm MDOPE film. The surface of the MDOPE base film is then subjected to corona treatment. S2. 0.1 g / m 2 The coating amount is such that a base coating liquid (branched polyethyleneimine solution with a molecular weight of 20,000) is applied to the corona-electrode surface of the MDOPE substrate film, and after drying in an oven, a base coating layer is formed. S3. Prepare a 10 wt% aqueous solution of polyethyleneimine cationic groups and adjust the pH to 10 using ammonia; prepare a 10 wt% aqueous solution of polyacrylic acid anionic groups and adjust the pH to 10 using ammonia; then mix them evenly at a molar ratio of 3:1 for cationic to anionic groups to obtain a polyelectrolyte mixed solution. S4. 1.2 g / m 2 The amount of coating is determined by applying the polyelectrolyte mixture solution onto the surface of the base layer and drying it at 85°C to form a polyelectrolyte coating. S5. Using vacuum evaporation, an aluminum coating is deposited on the surface of the polyelectrolyte coating to form an aluminum coating with a thickness of 500 angstroms, thereby obtaining a polyethylene film with high oxygen barrier properties.

[0044] Example 2: A method for preparing a polyethylene film with high oxygen barrier properties includes the following steps: S1. By weight, 60 parts of high-density polyethylene AT6900, 35 parts of medium-density metallocene polyethylene 5940ST, and 5 parts of low-density polyethylene 2420D are mixed and blown into a base film with a thickness of 125 μm. The film is then stretched in 5.0 times the mechanical direction at 118°C to obtain a 25 μm MDOPE film. The surface of the MDOPE base film is then subjected to corona treatment. S2. 0.1 g / m 2 The coating amount is such that a base coating liquid (branched polyethyleneimine solution with a molecular weight of 50,000) is applied to the corona-electrode surface of the MDOPE substrate film, and after drying in an oven, a base coating layer is formed. S3. Prepare a 10 wt% aqueous solution of polyethyleneimine cationic groups and adjust the pH to 10 using ammonia; prepare a 10 wt% aqueous solution of polyacrylic acid anionic groups and adjust the pH to 10 using ammonia; then mix them evenly at a molar ratio of 1:2 for cationic to anionic groups to obtain a polyelectrolyte mixed solution. S4. 1.2 g / m 2 The amount of coating is determined by applying the polyelectrolyte mixture solution onto the surface of the base layer and drying it at 85°C to form a polyelectrolyte coating. S5. Using vacuum evaporation, an aluminum coating is deposited on the surface of the polyelectrolyte coating to form an aluminum coating with a thickness of 500 angstroms, thereby obtaining a polyethylene film with high oxygen barrier properties.

[0045] Example 3: A method for preparing a polyethylene film with high oxygen barrier properties includes the following steps: S1. By weight, 60 parts of high-density polyethylene AT6900, 35 parts of medium-density metallocene polyethylene 5940ST, and 5 parts of low-density polyethylene 2420D are mixed and blown into a base film with a thickness of 125 μm. The film is then stretched in 5.0 times the mechanical direction at 118°C to obtain a 25 μm MDOPE film. The surface of the MDOPE base film is then subjected to corona treatment. S2. 0.1 g / m 2 The coating amount is such that a base coating liquid (branched polyethyleneimine solution with a molecular weight of 20,000) is applied to the corona-electrode surface of the MDOPE substrate film, and after drying in an oven, a base coating layer is formed. S3. Prepare a 10 wt% cationic polyvinylpyridine aqueous solution and adjust the pH to 10 using ammonia; prepare a 10 wt% anionic polyacrylamide aqueous solution and adjust the pH to 10 using ammonia; then mix them evenly at a molar ratio of 3:2 for cationic to anionic groups to obtain a polyelectrolyte mixed solution. S4. 1.2 g / m 2The amount of coating is determined by applying the polyelectrolyte mixture solution onto the surface of the base layer and drying it at 85°C to form a polyelectrolyte coating. S5. Using vacuum evaporation, an aluminum coating is deposited on the surface of the polyelectrolyte coating to form an aluminum coating with a thickness of 500 angstroms, thereby obtaining a polyethylene film with high oxygen barrier properties.

[0046] Comparative Example 1: A method for preparing a polyethylene film includes the following steps: S1. By weight, 60 parts of high-density polyethylene AT6900, 35 parts of medium-density metallocene polyethylene 5940ST, and 5 parts of low-density polyethylene 2420D are mixed and blown into a base film with a thickness of 125 μm. The film is then stretched in 5.0 times the mechanical direction at 118°C to obtain a 25 μm MDOPE film. The surface of the MDOPE base film is then subjected to corona treatment. S2. 1.2 g / m 2 The coating amount is such that a PVA aqueous solution is coated on the corona-electrode surface of the MDOPE substrate film, and after drying in an oven, a base coating is formed. S3. Using vacuum evaporation, an aluminum coating is deposited on the surface of the base coating to form an aluminum coating with a thickness of 500 angstroms, thereby obtaining a polyethylene film.

[0047] Comparative Example 2: A method for preparing a polyethylene film includes the following steps: S1. By weight, 60 parts of high-density polyethylene AT6900, 35 parts of medium-density metallocene polyethylene 5940ST, and 5 parts of low-density polyethylene 2420D are mixed and blown into a base film with a thickness of 125 μm. The film is then stretched in 5.0 times the mechanical direction at 118°C to obtain a 25 μm MDOPE film. The surface of the MDOPE base film is then subjected to corona treatment. S2. 0.1 g / m 2 The coating amount is such that a base coating liquid (branched polyethyleneimine solution with a molecular weight of 50,000) is applied to the corona-electrode surface of the MDOPE substrate film, and after drying in an oven, a base coating layer is formed. S3. Prepare a 10 wt% aqueous solution of polyethyleneimine cationic groups and adjust the pH to 10 using ammonia; prepare a 10 wt% aqueous solution of polyacrylic acid anionic groups and adjust the pH to 10 using ammonia; then mix them evenly at a molar ratio of 3:1 for cationic to anionic groups to obtain a polyelectrolyte mixed solution. S4. 1.2 g / m 2 The amount of coating is determined by applying the polyelectrolyte mixture solution onto the surface of the base layer, and then drying it at 85°C to form a polyelectrolyte coating, thereby obtaining a polyethylene film.

[0048] Comparative Example 3: A method for preparing a polyethylene film includes the following steps: S1. By weight, 60 parts of high-density polyethylene AT6900, 35 parts of medium-density metallocene polyethylene 5940ST, and 5 parts of low-density polyethylene 2420D are mixed and blown into a base film with a thickness of 125 μm. The film is then stretched in 5.0 times the mechanical direction at 118°C to obtain a 25 μm MDOPE film. The surface of the MDOPE base film is then subjected to corona treatment. S2. 0.1 g / m 2 The coating amount is such that a base coating liquid (branched polyethyleneimine solution with a molecular weight of 20,000) is applied to the corona-electrode surface of the MDOPE substrate film, and after drying in an oven, a base coating layer is formed. S3. Prepare a 10 wt% cationic polyethyleneimine aqueous solution and adjust the pH to 10 using ammonia; prepare a 10 wt% anionic polyacrylic acid aqueous solution and adjust the pH to 10 using ammonia; then mix them at a cationic to anionic molar ratio of 1:3. After stirring, severe agglomeration was observed in the solution, producing a large amount of insoluble precipitate. The system was in a gel-like state and could not form a uniform and stable coating solution, thus making subsequent coating and aluminum plating processes impossible. This comparative example is used to verify that when the molar ratio of cationic to anionic groups exceeds the range defined in this invention, the polyelectrolyte mixture solution undergoes gelation failure due to excessive ionic crosslinking.

[0049] Comparative Example 4: A method for preparing a polyethylene film includes the following steps: S1. By weight, 60 parts of high-density polyethylene AT6900, 35 parts of medium-density metallocene polyethylene 5940ST, and 5 parts of low-density polyethylene 2420D are mixed and blown into a base film with a thickness of 125 μm. The film is then stretched in 5.0 times the mechanical direction at 118°C to obtain a 25 μm MDOPE film. The surface of the MDOPE base film is then subjected to corona treatment. S2. 0.1 g / m 2 The coating amount is such that a base coating liquid (branched polyethyleneimine solution with a molecular weight of 20,000) is applied to the corona-electrode surface of the MDOPE substrate film, and after drying in an oven, a base coating layer is formed. S3. Using vacuum evaporation, an aluminum coating is deposited on the surface of the base coating to form an aluminum coating with a thickness of 500 angstroms, thereby obtaining a polyethylene film with high oxygen barrier properties.

[0050] After aluminum plating, the polyethylene film samples in Examples 1-3 were tested with an optical density meter, and the OD was greater than 2.0.

[0051] The polyethylene films prepared in Examples 1-3 and the polyethylene film samples in Comparative Examples 1-4 were subjected to performance tests. The oxygen transmission rate of the films was tested using a Mocon oxygen permeability tester, and the test method was in accordance with ASTM D3985. The water vapor transmission rate of the films was tested using a Mocon water vapor transmission rate tester, and the test method was in accordance with ASTM F1249. The results are shown in Tables 1 and 2 below.

[0052] Table 1: Oxygen Transmission Rate Test (Unit: cm) 3 / m 2 (day atm)

[0053] Table 2: Water vapor transmission rate test (unit: g / m²) 2 (day atm)

[0054] Analysis of the data in Tables 1 and 2 shows that, through the sequential construction of a branched polyethyleneimine undercoat, a polyelectrolyte ionic cross-linking network formed by pre-mixing cationic and anionic polymers and then coating it onto an MDOPE substrate film, and the vacuum evaporation of a metal layer, and by strictly controlling the molar ratio of cationic to anionic groups within the range of (1~4):(1~2) and the pH of the polyelectrolyte solution between 7 and 12, the resulting polyethylene film exhibits a stable oxygen permeability of 0.07~0.1 cm⁻¹ across a wide humidity range of 0% to 80%. 3 / m 2 The day-atm value is far below the threshold of 0.2, and the water vapor transmission rate is as low as 0.2~0.3 g / m³. 2·day·atm. Compared with Example 1, the OTR of the PVA coating in Comparative Example 1 increased sharply to 3.5 under high humidity, indicating that the polyelectrolyte coating of the present invention has better barrier performance in high humidity environment than the traditional PVA barrier coating; the OTR of Comparative Example 2 without coating is as high as 1.9~2.2, indicating that the barrier performance of the polyethylene film decreases without vacuum metallization; in Comparative Example 3, when the molar ratio exceeds 1:3, the solution gels and cannot be coated. After stirring, it was found that the solution agglomerates severely, producing a large number of insoluble precipitates. The system is in a gel state and cannot form a uniform and stable coating liquid. Therefore, subsequent coating and metallization processes cannot be carried out, indicating that the limited addition ratio of the components in the present invention can achieve better coating effect; the OTR of Comparative Example 4 without polyelectrolyte coating is 183~200. The lack of polyelectrolyte ionic bond network leads to performance that is significantly worse than that of Example 1. The free groups in the polyelectrolyte coating have a significant impact on the adhesion and barrier performance of the metallized layer. This invention demonstrates that by leveraging the synergistic effect of the polyelectrolyte ionic bond network and the metal coating, it simplifies the process (one-time coating) while overcoming the shortcomings of traditional PVA coatings where the hydrogen bond network is destroyed in high humidity environments, leading to a sharp drop in barrier properties. It also solves the problem of insufficient barrier properties when there is no coating or only aluminum plating, achieving ultra-high and stable oxygen barrier performance and excellent water vapor barrier performance under the target of recyclability of all-PE single material.

[0055] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0056] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A polyethylene film with high oxygen barrier properties, characterized in that, The polyethylene film comprises, from bottom to top: an MDOPE substrate film, a base coating, a polyelectrolyte coating, and a metal plating layer; The oxygen permeability of the polyethylene film is less than 0.2 cm. 3 / m 2 ·day·atm.

2. The polyethylene film according to claim 1, characterized in that, The MDOPE substrate film is a 20-30 μm film obtained by stretching it 4-6 times in the mechanical direction. The MDOPE substrate film is corona treated and has a film density greater than 0.940 g / cm³. 3 .

3. The polyethylene film with high oxygen barrier properties according to claim 1, characterized in that, The base coating is formed by a base coating liquid, the raw materials for which the base coating liquid is prepared include branched polyethyleneimine, the molecular weight of which is 1000~80000.

4. The polyethylene film with high oxygen barrier properties according to claim 1, characterized in that, The polyelectrolyte coating is formed by coating and drying a polyelectrolyte mixture solution of cationic polymer solution and anionic polymer solution.

5. The polyethylene film with high oxygen barrier properties according to claim 4, characterized in that, The anionic polymer solution has a mass percentage concentration of 2.5-20 wt%, and the pH value of the anionic polymer solution is adjusted to 7-12 using ammonia; the cationic polymer solution has a mass percentage concentration of 2.5-20 wt%, and the pH value of the cationic polymer solution is adjusted to 7-12 using ammonia.

6. The polyethylene film with high oxygen barrier properties according to claim 4, characterized in that, The molar ratio of cations to anions in the polyelectrolyte mixture is (1~4):(1~2).

7. The polyethylene film with high oxygen barrier properties according to claim 4, characterized in that, The anionic polymer is at least one of polyacrylic acid, polyvinyl sulfonic acid, and polyacrylamide, with a molecular weight of 1,000 to 1,000,000; the cationic polymer is at least one of polyvinylpyridine, vinylimidazolium polymer, and polyethyleneimine, with a molecular weight of 1,000 to 1,000,000.

8. The polyethylene film with high oxygen barrier properties according to claim 1, characterized in that, The coating amount of the mixture is 0.1~5.0 g / m³. 2 .

9. The polyethylene film with high oxygen barrier properties according to claim 1, characterized in that, The metal coating is a vacuum-deposited aluminum layer and / or aluminum oxide layer, with a coating thickness of 200~800 angstroms.

10. A method for preparing a polyethylene film with high oxygen barrier properties, characterized in that, The preparation method is used to prepare a polyethylene film with high oxygen barrier properties as described in any one of claims 1 to 9, and the preparation method includes the following steps: S1. Prepare an MDOPE substrate film and subject the surface of the MDOPE substrate film to corona treatment; S2. Apply a primer to the corona-electrode surface of the MDOPE substrate film, and after drying, form a primer layer; S3. Prepare an aqueous solution of cationic polymer and adjust the pH value to 7-12 using ammonia; prepare an aqueous solution of anionic polymer and adjust the pH value to 7-12 using ammonia; then mix them evenly according to the molar ratio of cationic to anionic groups of (1-4):(1-2) to obtain a polyelectrolyte mixed solution. S4. The polyelectrolyte mixture is applied to the surface of the base layer and dried to form a polyelectrolyte coating. S5. A metal coating is deposited on the surface of the polyelectrolyte coating by vacuum evaporation to form a metal coating, thereby obtaining a polyethylene film with high oxygen barrier properties.

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