Paper-based packaging film and self-repairing barrier material thereof

Abstract

The invention provides a paper-based packaging film and a self-repairing barrier material thereof. The self-repairing barrier material comprises a matrix layer and a barrier functional layer, the base body layer is an oriented polyethylene film, the barrier functional layer is arranged on the surface of one side of the base body layer, and the barrier functional layer comprises a barrier base body, and self-repairing microcapsules and an inorganic nano filler which are dispersed in the barrier base body. The self-repairing barrier material provided by the embodiment of the invention is applied to a sterile paper-based packaging structure so as to solve the problem that the barrier property of an aluminum foil substitute material is reduced under microdefects. Specifically, according to the self-repairing barrier material in the embodiment of the invention, a packaging material which can still keep excellent barrier performance after being slightly damaged is constructed. The material has the barrier effect equivalent to that of a traditional aluminum foil structure on oxygen, water vapor and light in the normal state, and when micro cracks appear, the material can automatically heal the defects, and the content is continuously protected from being influenced by the environment.

Description

Technical Field

[0001] This application relates to the technical field of packaging materials, specifically to a paper-based packaging film and its self-healing barrier material. Background Technology

[0002] Traditional aseptic paper-based packaging materials for liquid foods typically consist of a six-layer structure composed of paper, aluminum foil, and polyolefin plastics. The aluminum foil layer provides excellent barrier properties, effectively blocking oxygen, water vapor, and light, thus ensuring a long shelf life for the contents. However, due to the tightly bonded layers, the presence of aluminum foil makes this type of packaging difficult to recycle. Statistics show that my country consumes approximately 50 billion aseptic packages annually, totaling about 500,000 tons, but the recycling rate is less than 10%. The aluminum foil is firmly bonded to the paper and plastic, and conventional recycling requires costly separation equipment. Unrecycled packaging materials are usually incinerated or landfilled, creating an environmental burden. To improve environmental friendliness, the aluminum foil layer has been considered for removal; however, removing the aluminum foil drastically reduces the barrier effect, making it difficult to protect the contents. Therefore, developing a novel high-barrier material to replace the aluminum foil layer is extremely important.

[0003] To balance environmental protection and performance, "single-material" packaging has become a trend, which means using only one type of recyclable material to construct the packaging structure whenever possible. In aseptic paper-based packaging, achieving a single plastic material (e.g., using all polyolefins such as PE) is expected to improve recycling rates, reduce carbon footprint, and allow the packaging to be microwaved after the aluminum foil is removed. Currently available aluminum foil alternatives for high-barrier materials include biaxially oriented polyester film (BOPET), biaxially oriented nylon film (BOPA), polyvinylidene chloride coated film (PVDC coated PET / OPP), ethylene-alcohol copolymer (EVOH) co-extruded film, and vacuum-metallized film. However, these materials are essentially still a "third material" besides paper and polyolefins, and cannot fundamentally solve the recycling problems caused by multi-material composites. At the same time, these alternative materials have shortcomings in terms of barrier consistency and self-healing ability: for example, the barrier performance of hydrophilic high-barrier polymers such as EVOH or PVOH decreases significantly under high humidity conditions; and vacuum-metallized layers or coated films are prone to microcracks or pinholes when bent or abraded, resulting in a sudden and irreversible decrease in barrier performance. In reality, once micropores appear in the packaging barrier layer, oxygen and moisture can easily penetrate, rendering the originally sealed sterile barrier ineffective. During the manufacturing, transportation, and use of packaging materials, minute damage that is difficult to detect with the naked eye often occurs, such as creases, scratches, or pinholes. These defects significantly increase the permeability of oxygen and moisture, threatening the quality of the contents and shelf life. Current technology has not yet endowed packaging materials with the ability to self-repair such damage. Once the barrier layer is damaged, its barrier performance often permanently declines, making it difficult to meet the long-term protection requirements of sterile packaging. Summary of the Invention

[0004] The first aspect of this application provides a self-healing barrier material, which includes a matrix layer and a barrier functional layer; the matrix layer is an oriented polyethylene film, and the barrier functional layer is disposed on one side surface of the matrix layer, the barrier functional layer including a barrier matrix and self-healing microcapsules and inorganic nanofillers dispersed in the barrier matrix.

[0005] In some alternative embodiments, the matrix layer is a multilayer co-extruded structure.

[0006] In some alternative embodiments, the barrier matrix is ​​a moisture-resistant cross-linked modified polyvinyl alcohol.

[0007] In some optional embodiments, the shell material of the self-healing microcapsule is urea-formaldehyde resin or polyurea, and the core material includes resin and curing agent respectively encapsulated in different microcapsules; or the core material is selected from unsaturated polyester resin, light-curing resin, water-curing resin and oxygen-curing resin.

[0008] In some alternative embodiments, the particle size of the self-healing microcapsules ranges from 1 to 50 micrometers.

[0009] In some optional embodiments, the self-healing microcapsules are added at a weight ratio of 5 to 15 wt% of the total solid components of the barrier functional layer.

[0010] In some optional embodiments, the inorganic nanofiller is layered nanoclay.

[0011] In some optional embodiments, the inorganic nanofiller is added in a weight ratio of 1 to 5 wt% of the total solid composition of the barrier functional layer.

[0012] Secondly, this application provides a paper-based packaging film, which includes a waterproof heat-sealing layer, a paper base layer, an adhesive layer, a self-healing barrier material layer, and a heat-sealing layer stacked sequentially, wherein the self-healing barrier material layer is prepared using the self-healing barrier material described in the above embodiments.

[0013] In some optional embodiments, the waterproof heat-sealing layer is selected from any one of polyethylene, polypropylene resin, ethylene / vinyl acetate copolymer, and ethylene / acrylate copolymer; the thickness of the waterproof heat-sealing layer is 10–20 g / m. 2 .

[0014] In some optional embodiments, the heat-sealing layer comprises three layers of PE film, the material of which is selected from ethylene acrylate resin or modified PE adhesive, and the thickness of each layer is 3 to 10 g / m. 2 .

[0015] The self-healing barrier material provided in this application is applied to aseptic paper-based packaging structures to address the problem of decreased barrier performance of aluminum foil substitutes under micro-defects. Specifically, the self-healing barrier material in this application constructs a packaging material that maintains excellent barrier performance even after suffering minor damage (such as pinholes or creases). Under normal conditions, this material has a barrier effect on oxygen, water vapor, and light comparable to that of traditional aluminum foil structures. When micro-cracks appear, the material can automatically self-heal these defects, continuing to protect the contents from environmental influences. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the laminated structure of an embodiment of the self-healing barrier material of this application; Figure 2 This is a schematic diagram of the laminated structure of an embodiment of the paper-based packaging film of this application. Detailed Implementation

[0018] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the application. Similarly, the following embodiments are only some, not all, embodiments of the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present application.

[0019] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movement of components in a specific posture (as shown in the figures). If the specific posture changes, the directional indication will also change accordingly. The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or components inherent to these processes, methods, products, or devices.

[0020] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0021] First, this application provides a self-healing barrier material; please refer to [link to relevant documentation]. Figure 1 , Figure 1 This is a schematic diagram of the stacked structure of an embodiment of the self-healing barrier material of this application. The self-healing barrier material 10 includes a matrix layer 100 and a barrier functional layer 200.

[0022] Specifically, the substrate layer 100 is an oriented polyethylene film, and the barrier functional layer 200 is disposed on one side surface of the substrate layer 100. The substrate layer 100 provides support and basic barrier properties; the barrier functional layer 200 is a self-healing high-barrier coating applied to the substrate layer 100, giving the whole structure high barrier properties and self-healing ability.

[0023] Substrate layer 100 (MDOPE film): A machine-oriented PE film is selected as the carrier substrate for the barrier layer. MDOPE refers to a film material obtained by stretching and oriented a PE film in the machine direction (MD). Through the MDO process (longitudinal stretching process), the PE molecular chains are highly aligned in the orientation direction, effectively improving crystallinity, thereby significantly improving the barrier properties, mechanical strength, and heat resistance of the PE film. A typical MDO process includes four steps: preheating, stretching, annealing, and cooling. First, the PE film is heated to about 5-7°C below its melting point, then rapidly stretched in a semi-molten state at a certain draw ratio to thin the film in the machine direction; then, it is heat-set for a short time at a temperature close to the melting point to eliminate internal stress, and finally cooled and set. By controlling the draw ratio and temperature, PE films with different degrees of orientation and crystallinity can be obtained.

[0024] Preferably, the thickness of the MDOPE film in this invention is in the range of about 20 to 50 μm, the orientation stretch ratio is 5 to 10 times, and the overall crystallinity of the film material reaches about 50% to 80%.

[0025] The base film can adopt a multi-layer co-extrusion structure to optimize the orientation effect, such as 3-layer, 5-layer or 7-layer co-extruded PE, so that the crystallinity of each layer is distributed in a gradient: the outer layer can use HDPE or MDPE with higher crystallinity to increase the stiffness and flatness of the film, the middle layer can use LDPE and other materials to improve the orientation uniformity, and the innermost layer can use low crystallinity PE to take into account the heat sealing performance.

[0026] For example, using a five-layer co-extrusion blown film followed by MDO orientation, the design can be as follows: the outermost layer is a blend of HDPE / LDPE (high crystallinity), the second layer is MDPE, the middle layer is LDPE, and the fourth and fifth layers are LLDPE (low crystallinity, also suitable for heat sealing). The crystallinity difference between each layer is controlled within the range of 5% to 20% to ensure uniform thickness and mechanical stability during the orientation process. The MDOPE film produced by the above process has a regular molecular chain arrangement, and its oxygen permeability and water vapor permeability are reduced by orders of magnitude compared to unoriented PE film. For example, the oxygen permeability of unoriented ordinary PE sheets may exceed several hundred cc / m²•day, and the water vapor permeability may exceed tens of g / m²•day, while the OTR of the oriented MDOPE film can be reduced to single digits or even lower under 23°C and 0%RH conditions, which can initially meet the barrier requirements of aseptic packaging at a certain thickness. The MDOPE matrix film also provides good dimensional stability and strength, making it able to withstand the mechanical stress of subsequent coating, lamination, and packaging processes without being easily damaged. It should be noted that MDOPE film itself complies with food contact material regulations (such as FDA, EU, GB 4806.7, etc.), and is safe and reliable to use.

[0027] The barrier functional layer 200 includes a barrier matrix 210 and self-healing microcapsules 220 and inorganic nanofillers 230 dispersed within the barrier matrix 210.

[0028] On one side of the aforementioned substrate layer 100, a modified polyvinyl alcohol (PVOH)-based high-barrier coating is coated, in which self-healing microcapsules and inorganic nanofillers are dispersed. Polyvinyl alcohol (PVOH), due to its highly ordered molecular structure, exhibits excellent oxygen barrier properties and is widely used in food packaging barrier coatings. However, PVOH itself is readily soluble in water, and its barrier performance decreases sharply with increased humidity. Therefore, this invention uses moisture-resistant crosslinked PVOH as the barrier matrix. By adding crosslinking agents (such as boric acid, glutaraldehyde, epoxy resin, etc.) to the PVOH solution for chemical crosslinking, or by using copolymer modification (such as partial acetate esterification) to improve hydrophobicity, the resulting coating does not easily swell upon contact with water and can maintain good barrier performance in high-humidity environments. The PVA coating crosslinked with a boric acid-hydrochloric acid system can achieve an oxygen permeability as low as 0.89 cc / m²•day and a water vapor permeability of approximately 5.17 g / m²•day at 50% RH, while maintaining high mechanical strength even in humid environments. Cross-linked PVOH coatings retain biodegradability and recyclability; for example, 99.7% of acid-modified PVA coatings can be redispersed and removed during paper recycling. Therefore, cross-linked PVOH provides high barrier properties without compromising the recyclability of packaging.

[0029] A certain proportion of self-healing microcapsules are mixed and dispersed within a PVOH matrix. These microcapsules encapsulate a self-curing polymeric repair agent. When microcracks or pinholes appear in the barrier layer, the stress at the crack tip causes adjacent microcapsules to rupture. The released repair agent immediately flows and fills the crack, undergoing in-situ polymerization and curing under external environmental stimuli (such as oxygen, moisture, temperature, or ultraviolet light). The resulting new polymer effectively seals and bonds the crack, preventing further defect propagation and restoring the integrity of the barrier layer.

[0030] When the membrane is damaged, the microcapsules, acting as a "sensor-response" unit, release a repair agent that reacts and polymerizes with a pre-dispersed initiator or catalyst in the matrix, rapidly filling and bonding the cracks to achieve self-healing. The formulation of the repair agent within the microcapsules can vary depending on the needs. For example, a dry vegetable oil or unsaturated resin that undergoes free radical polymerization upon contact with oxygen can be used as the core material, allowing it to automatically oxidize, harden, and seal the pores when air penetrates the damaged area; alternatively, a prepolymer that cross-links upon contact with moisture (such as a prepolymer containing isocyanate groups) can be used, inducing curing when ambient humidity increases; or a light-curing resin can be used, exposing the packaging material to UV light of an appropriate wavelength after damage to trigger self-healing. A preferred embodiment of this invention uses a repair system that can be triggered at room temperature, such as microcapsules that can be cured by oxygen or trace amounts of water in the air. This allows for automatic healing when the packaging experiences minor damage and comes into contact with air, requiring no additional intervention. For example, urea-formaldehyde resin or polyurea can be used as the shell material, encapsulating two-component epoxy resin (resin and curing agent exist in different microcapsules) or unsaturated polyester resin as the core material. When the microcapsule ruptures due to cracks, a curing reaction occurs when the two components mix or the resin is exposed to oxygen / water in the air. The filling and sealing of the crack can be completed within minutes to hours at room temperature. The particle size of the microcapsule can be 1–50 micrometers, preferably 10–20 micrometers, specifically 10 micrometers, 12 micrometers, 15 micrometers, 18 micrometers, 20 micrometers, etc., to ensure uniform dispersion and not significantly weaken the coating density (the typical pinhole diameter of aluminum foil is about 10–50 micrometers, so the microcapsule size is equivalent to or smaller than the defect size, which helps to achieve efficient repair). The amount of microcapsule added can be determined according to the repair requirements. The weight ratio of self-healing microcapsules added is 5–15 wt% of the total solid composition of the barrier functional layer. It is necessary to balance the following: too high a microcapsule content may affect the initial barrier properties and mechanical strength of the coating, while too low a content will result in insufficient self-healing probability. In this invention, an addition amount of approximately 5 to 10 wt% is selected, which can impart self-healing function to the coating while maintaining its integrity.

[0031] In addition, an appropriate amount of inorganic nanofillers (such as sheet clay, nano-silica, graphene oxide, etc.) are introduced into the barrier coating. These nanofillers improve the barrier performance of the coating by forming tortuous permeation paths within the polymer matrix, effectively extending the path of gas molecules through the coating ("maze effect"). Furthermore, certain nanomaterials (such as layered montmorillonite and nano-graphene oxide) can enhance the mechanical properties and thermal stability of the coating, reducing the tendency for microcracks to form under stress. This invention preferably uses layered nano-clay (montmorillonite undergoing organic processing to achieve interlayer exfoliation), added at a weight ratio of 1–5 wt% of the total solid composition of the barrier functional layer. After uniform dispersion, the filler has a high sheet diameter / thickness ratio, forming a highly barrier inorganic network within the coating. Studies have shown that adding nano-clay to substrates such as PE can reduce oxygen permeability by several times. The addition of nanofillers, combined with the aforementioned cross-linked PVOH matrix and microcapsules, further reduces permeability and improves the sealing effect after self-healing while maintaining flexibility in the barrier coating.

[0032] In summary, the self-healing high-barrier layer, through an innovative combination of "MDOPE matrix layer + cross-linked PVOH barrier / self-healing coating," achieves barrier performance similar to aluminum foil on a single polyolefin substrate, while also possessing the function of self-repairing micro-damage. The performance targets of the high-barrier layer designed in this invention under standard conditions are: Oxygen Transmission Rate (OTR) ≤ 0.3 cc / m²•day at 23℃ and 50%RH, and Water Vapor Transmission Rate (WVTR) ≤ 1 g / m²•day at 38℃ and 90%RH, approaching the barrier level of traditional aluminum foil layers. Even in high humidity environments, due to the cross-linking modification of PVOH, the barrier layer can maintain a low transmittance and will not completely lose its function. Simultaneously, when pinholes or microcracks appear, the repair material released by the microcapsules can quickly fill the pores, restoring the OTR and WVTR to near their initial state. This barrier layer can simultaneously block oxygen, moisture, and a certain degree of light (if higher light blocking is required, an ultra-thin inorganic barrier layer, such as aluminum plating or Al2O3 plating, can be added on top of the PVOH coating).

[0033] The preparation process of the self-healing barrier material in this application embodiment is as follows.

[0034] MDO Orientation Process: First, a thick multilayer PE-based film preform (e.g., a co-extruded preform with a thickness of 0.2–0.3 mm) is prepared using blown film or casting processes. Then, the film is machine-stretched on an MDO orientation machine. Orientation parameters are set according to the target film properties; for example, the preheating temperature is approximately 110–115°C (slightly lower than the PE main melt peak temperature by 5–7°C), the stretch ratio (fast roll / slow roll speed ratio) is controlled at 5–8 times, and the stretching speed and temperature profiles are optimized to avoid film necking or breakage. After orientation, the film is annealed and heat-set at approximately 100°C for 1–3 seconds, then cooled and rolled to obtain the MDO PE base film. The resulting oriented film has a thickness of approximately 30–50 μm, is transparent and smooth, and exhibits significantly improved crystallinity and barrier properties. Film thickness and performance can be controlled by adjusting the orientation ratio; for example, a higher stretch ratio can further reduce the oxygen permeability of the film, but excessive orientation may lead to increased film brittleness, requiring a trade-off between performance and process stability.

[0035] Coating of the barrier functional layer 200: Pre-prepared self-healing microcapsules and nanofillers are added to a cross-linked PVOH aqueous solution (solid content 10-20%) and thoroughly stirred to obtain a uniform coating solution. The component ratios in the coating solution are as follows: PVOH resin (partial alcoholysis degree 88%, degree of polymerization 1700) 100 parts, cross-linking agent (borax or glutaraldehyde, etc.) 5 parts, microcapsule repair agent 10 parts (based on in-capsule solids) 2 parts, nano-montmorillonite 2 parts, with the remainder being water and additives. The above coating is applied to one side of the MDOPE substrate film (substrate layer 100) using gravure coating or roller coating processes. The coating amount is controlled to achieve a dry film thickness of approximately 1-3 μm (corresponding to a wet coating weight of approximately 5-8 g / m²). 2 Dry weight approximately 2–3 g / m³ 2 After coating, the film passes through a hot air drying tunnel at 60–100°C to rapidly remove moisture and initiate the initial cross-linking reaction, resulting in a thin, high-barrier coating firmly adhered to the PE film surface. To enhance the adhesion between the coating and the PE film, the PE base film can be subjected to corona or plasma surface treatment before coating to improve its surface tension and roughness. The dried coating should be smooth, free of bubbles, and without any unruptured microcapsules exposed on the surface to ensure optimal initial barrier performance.

[0036] In addition, this application also provides a paper-based packaging film, please refer to [link to relevant documentation]. Figure 2 , Figure 2 This is a schematic diagram of the stacked structure of a paper-based packaging film according to an embodiment of the present application. The paper-based packaging film in this embodiment includes a waterproof heat-sealing layer 20a, a paper base layer 30a, an adhesive layer 40a, a self-healing barrier material layer 10a, and a heat-sealing layer 50a stacked in sequence.

[0037] The waterproof heat-sealing layer 20a, also known as the outer layer, is a thin-film-grade polyolefin resin used to provide moisture and dirt protection, and to meet the heat-sealing requirements for packaging corners and closures. Suitable materials include various polyethylene (PE) or polypropylene (PP) resins, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene polyethylene (mPE), and high-density polyethylene (HDPE), as well as ethylene / vinyl acetate copolymer (EVA) and ethylene / acrylate copolymer. This layer is typically laminated onto the paper layer by extrusion coating, with a thickness of approximately 10–20 g / m². The outer layer serves both as waterproof protection and as the medium for subsequent heat-sealing processes.

[0038] Optionally, the paper base layer 30a is a thicker paperboard or paper, primarily providing the packaging material with the necessary mechanical strength and stiffness. It can be made of natural pulp paper, coated paper, or multi-layer composite paperboard, with a basis weight typically in the range of 150–300 g / m². The paper layer can be divided into coated layers, surface layers, core layers, and bottom layers (e.g., using multi-layer laminated paperboard to improve tensile strength). The outer surface of the paper layer is usually printed with the required graphics and text. This printing layer uses food-grade inks, which do not affect barrier properties and are not specifically limited here. As the main substrate, the paper layer provides the necessary support strength and processing stiffness for the packaging.

[0039] The adhesive layer 40a, also known as the composite layer, is bonded to the paper base layer 30a and the self-healing barrier material layer 10a via a polyolefin hot melt adhesive layer to ensure strong interlayer adhesion. This composite adhesive layer (adhesive layer 40a) can be a thin layer of PE or PP produced by melt extrusion, with a typical thickness of 15–40 g / m². The resin used can be the same as or similar to the outer layer (e.g., LDPE, LLDPE, etc.), and the melt index (190℃ / 2.16kg) should preferably be 5–10 g / 10min to facilitate extrusion processing. This adhesive layer firmly connects the base paper to the subsequent barrier functional layers into a unified whole.

[0040] The self-healing barrier material layer 10a is prepared using the self-healing barrier material described in the previous embodiment. For details, please refer to the relevant description in the previous embodiment, which will not be repeated here.

[0041] Optionally, the heat-sealing layer 50a, also known as the inner layer, is the innermost plastic layer of the packaging material that directly contacts the contents and is used for heat sealing. Its material must meet food contact safety and heat-sealing strength requirements. Since this invention pursues a single plastic material, the inner layer is also made of polyolefin resin (preferably PE). One embodiment uses three layers of PE film as the inner layer: Inner layer 1 is used for bonding with the barrier layer, and can be made of ethylene acrylate resin or other modified PE adhesive layers. This adhesive layer can be considered part of the inner layer, and its function is similar to an adhesive, with a thickness of approximately 3–10 g / m² for each layer; Inner layers 2 and 3 serve as the main heat-sealing layers. The inner PE layers can be metallocene PE or ethylene copolymer to obtain a lower heat-sealing temperature and good sealing performance, with a thickness of approximately 5–10 g / m² for each layer. The inner layer is melt-coated onto the inner side of the barrier layer through an extrusion coating process to form a complete composite structure. In the structure of this application embodiment, all polymer layers except the cardboard are made of polyolefin material (mainly PE), thus achieving a single plastic material and greatly simplifying recycling.

[0042] The aforementioned functions are achieved through lamination and coating. The coated self-healing barrier material is bonded to the cardboard (paper base 30a) via extrusion lamination. Specifically, a traditional paper-plastic extrusion lamination process can be used: first, a layer of approximately 12–15 g / m² is extruded and coated onto one side of the cardboard. 2 The paper / barrier film is bonded together with molten PE resin as the composite adhesive layer, and then laminated with an MDOPE film coated with a barrier layer on one side while still hot. After being compacted by cooling rollers, the paper / barrier film is bonded. Care must be taken to control the extrusion temperature and pressure to avoid excessive temperature or shear damage to the PVOH barrier coating. Typically, the extrusion temperature of PE resin is approximately 270–300°C. The molten film will bond with the paper and film at temperatures above 200°C, but the PVOH coating will not completely degrade upon brief contact with this temperature. After the paper / film is laminated, a thin inner adhesive layer of PE (approximately 3–5 g / m²) is extruded and coated onto the other side of the exposed barrier film. Immediately afterwards, a second inner PE layer of approximately 15–20 g / m² is extruded as a heat-sealing layer, and then laminated onto the barrier film. Finally, an outer layer of approximately 10–15 g / m² is extruded and coated onto the other side of the paper as a protective layer for the paper substrate, forming the final multilayer co-extruded structure. The entire lamination process is compatible with existing aseptic packaging material production lines.

[0043] Post-processing and rewinding: After lamination, the paper-based packaging rolls are cooled and shaped, and the edges are trimmed. If necessary, winding tension control can be used to prevent premature rupture of the high-barrier coating due to self-adhesion or microcapsule pressure during storage. Finally, it can be used according to the conventional aseptic brick packaging forming-filling process without special adjustments to downstream equipment.

[0044] Through the above structural design and process approach, the self-healing high-barrier aseptic packaging material (paper-based packaging film) provided by this invention not only ensures the basic performance requirements of packaging but also achieves an innovative balance between environmental protection and functionality. The following specific embodiments further illustrate the formulation and effects of this invention.

[0045] To verify the technical effects of the present invention, the following representative embodiments are provided. All tests were conducted in accordance with national standards. The oxygen transmission rate (OTR) test was performed according to GB / T 19789-2005 "Test of Oxygen Transmission Rate of Plastic Films and Sheets for Packaging Materials - Coulometric Test Method", and the water vapor transmission rate (WVTR) test was performed according to GB / T 26253-2010 "Determination of Water Vapor Transmission Rate of Plastic Films and Sheets - Infrared Detector Method". Self-healing efficiency is defined as: the degree of recovery of the barrier performance of a material after treatment with artificial micro-defects under standard conditions (the recovery ratio compared to the performance loss initially caused by the defect).

[0046] The specific parameters for each embodiment are as follows.

[0047] Materials and Structure: Coated white paperboard (230 g / m²) was selected as the paper substrate. First, a five-layer PE film preform was prepared using a co-extrusion blown film method. The layers, from the outside to the inside, were: HDPE / LLDPE (mass ratio 7:3), MDPE, LDPE, LLDPE, and LLDPE. This preform was preheated to ~110°C on an MDO (Medium-Density Extrusion) machine, stretched longitudinally five times, and annealed for 2 seconds to obtain an MDOPE matrix film with a thickness of approximately 30 μm. Its crystallinity, as determined by DSC, was approximately 55%. Then, a cross-linked PVOH self-healing barrier coating was applied to one side of the MDOPE film using a gravure coating method. The coating solution consisted of a 10% aqueous solution of partially hydrolyzed PVOH (degree of polymerization ≈1700), with the addition of 5 wt% microcapsules (urea-formaldehyde resin shells containing a two-component epoxy / amine curing agent, with an average particle size of 15 μm) and 2 wt% organically modified montmorillonite nanoparticles. The cross-linking agents were 0.5 wt% borax (relative to PVOH) and 0.3 wt% glyoxal. After hot air drying at 60℃, a transparent coating with a thickness of approximately 2 μm was formed. The resulting high-barrier film (structure: MDOPE + coating) was then laminated with cardboard: a 20 g / m² LDPE composite layer was extruded and coated onto the inside of the cardboard, adhering tightly to the coated side of the high-barrier film, and then cold-pressed for bonding. Subsequently, a 3 g / m² modified PE adhesive layer is first extruded onto the other side of the exposed high-barrier film (i.e., the MDOPE film side), followed by the extrusion of 20 g / m² metallocene PE as an inner heat-sealing layer. Finally, 15 g / m² LDPE is coated onto the outside of the cardboard as an outer waterproof / heat-sealing layer, and then cold-pressed to obtain the final composite structure roll material.

[0048] Performance testing: The oxygen permeability (OTR) of the undamaged sample at 23°C and 50%RH was 0.08 cc / (m²•day), and the water vapor permeability (WVTR) at 38°C and 90%RH was 0.6 g / (m²•day). Compared with a composite material of the same structure but without a barrier coating (the latter, due to the absence of aluminum foil or coating, actually measured an OTR > 200 cc / (m²•day) and a WVTR > 50 g / (m²•day)), the barrier performance of the material of this invention is improved by several orders of magnitude, meeting the barrier requirements for aseptic packaging. Next, a self-healing performance test was conducted: a small hole of approximately 50 μm in diameter was punctured in the sample using a fine needle (simulating a puncture defect). It was found that when the defect was first generated, the material's OTR rose to approximately 4.5 cc / (m²•day), and the WVTR rose to 8.0 g / (m²•day). After the sample was placed in a 23℃, 50%RH environment for 24 hours, the OTR decreased to 0.15 cc / (m²•day) and the WVTR decreased to 0.7 g / (m²•day). Compared with the initial values, the oxygen and water vapor permeability recovered to approximately 95% and 94% of their respective performance, with a self-healing efficiency of over 90%. With further extended placement time, the permeability changes tended to stabilize, with no new increases observed, indicating that the microcapsule repair agent had fully filled and sealed the pinholes. Microscopic observation of the healed defect sites revealed the formation of a transparent resin filler, barely visible to the naked eye, at the pinholes, effectively blocking the original pores. Comparative experiments showed that the barrier performance of the cross-linked PVOH coating sample without microcapsules was almost completely restored after the same pinhole damage (OTR remained around 4.6 cc / (m²•day)), demonstrating the effectiveness of the microcapsule self-healing mechanism.

[0049] Additional tests: The material obtained in Example 1 was subjected to heat-sealing and molding tests on a standard aseptic packaging filling machine. The results showed that the material sealed well at the heat-sealing temperature, with no barrier layer melting or delamination. The Tetra Pak brick packaging samples produced remained intact and leak-free after simulated logistics drop and vibration tests, and the milk inside showed normal sensory characteristics after a 3-month accelerated aging test. These results demonstrate that the material of this invention can meet the requirements of existing aseptic packaging production lines and applications.

[0050] Compared with existing technologies, the application of the self-healing high-barrier material of this invention in aseptic paper-based packaging has the following significant advantages: 1. Strong barrier performance with minimal micro-defects: Thanks to the synergistic effect of the self-healing microcapsules and cross-linked PVOH coating, the material of this invention exhibits minimal degradation in barrier performance after the appearance of defects such as microcracks and pinholes, and can automatically recover most of its barrier function within a short time. Experiments have shown that, compared with traditional high-barrier membranes without self-healing function, the oxygen permeability of the self-healing membrane increases only slightly after pinhole damage, and it can automatically heal at room temperature, with a barrier attenuation rate far lower than that of traditional materials.

[0051] 2. Improved Packaging Durability and Shelf Life Stability: Paper-based packaging with a self-healing high-barrier layer exhibits greater resistance to accidental impacts and bending during manufacturing, transportation, and sales. Even if minor damage occurs during distribution, the packaging barrier properties can self-repair, preventing premature exposure of the contents to oxygen or moisture and subsequent spoilage. This enhances product shelf stability and reduces food spoilage losses due to packaging failure.

[0052] 3. Eliminating Aluminum Foil for Environmental Protection and Recyclability: The packaging material of this invention eliminates the need for an aluminum foil layer. Instead, it features an extremely thin, high-barrier functional coating (primarily composed of biodegradable PVOH and a small amount of microcapsules). The plastic portion of the packaging is entirely made of a single polyolefin material, with a high proportion that is easily separated from cardboard during recycling, achieving separate recycling and reuse of paper and plastic. Compared to traditional aluminum foil composite materials, the material of this invention has higher recycling value, lower processing costs, and is more environmentally friendly.

[0053] 4. Reducing Carbon Footprint and Adhering to Sustainable Development: The production and recycling of aluminum foil involve high energy consumption and high emissions. This invention replaces aluminum foil with a renewable, high-barrier coating, significantly reducing carbon emissions throughout the packaging's lifecycle. On one hand, eliminating aluminum foil reduces the carbon footprint of raw materials; on the other hand, the increased recycling rate reduces the amount of packaging waste incinerated and landfilled. Overall, the new aseptic packaging structure aligns with the green and low-carbon development trend and responds to the policy goals of packaging reduction and recyclability by 2025.

[0054] 5. Maintaining Packaging Functionality: Despite structural innovations, the packaging material of this invention maintains essentially the same performance characteristics as traditional aseptic packaging. The cardboard thickness and the basis weight of each plastic layer remain unchanged, and the packaging's sealing, heat-sealing strength, stiffness, and printability all meet industry requirements. The sterilization and filling process conditions for the contents can be withstood by the new material without delamination or performance degradation. This means that food production companies can directly replace existing materials with the material of this invention without modifying equipment. Furthermore, the packaging also features microwaveability, meeting consumer convenience needs. In summary, this invention achieves environmental friendliness without sacrificing the basic functionality of packaging.

[0055] The paper-based packaging film in this embodiment, by introducing a self-healing high-barrier material layer, enables aseptic packaging to still meet long shelf-life requirements after removing the aluminum foil, and offers multiple additional advantages: First, all plastic layers are made of a single material such as polyolefin, making them easier to recycle and reducing environmental impact; second, the packaging can withstand microwave heating without sparks or damage, expanding its application scenarios; third, even if subjected to impact and folding during manufacturing and use, the material can self-repair, ensuring stable product quality. In short, this invention aims to maintain the aseptic packaging's "unchanged barrier performance and functionality" while removing the aluminum foil layer, achieving an environmentally friendly and recyclable packaging structure with a reduced carbon footprint, in line with national sustainable development policies.

[0056] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. Any equivalent device or equivalent process transformation made based on the content of this application specification and drawings, or direct or indirect application in other related technical fields, are similarly included in the patent protection scope of this application.

Claims

1. A self-healing barrier material, characterized in that, The self-healing barrier material includes a matrix layer and a barrier functional layer; the matrix layer is an oriented polyethylene film, and the barrier functional layer is disposed on one side surface of the matrix layer. The barrier functional layer includes a barrier matrix and self-healing microcapsules and inorganic nanofillers dispersed in the barrier matrix.

2. The self-healing barrier material according to claim 1, characterized in that, The matrix layer has a multi-layer co-extruded structure.

3. The self-healing barrier material according to claim 1, characterized in that, The barrier matrix is ​​a moisture-resistant cross-linked modified polyvinyl alcohol.

4. The self-healing barrier material according to claim 3, characterized in that, The shell material of the self-healing microcapsule is urea-formaldehyde resin or polyurea, and the core material includes resin and curing agent respectively encapsulated in different microcapsules; or the core material is selected from unsaturated polyester resin, light-curing resin, water-curing resin and oxygen-curing resin.

5. The self-healing barrier material according to claim 4, characterized in that, The particle size range of the self-healing microcapsules is 1–50 micrometers.

6. The self-healing barrier material according to claim 4, characterized in that, The self-healing microcapsules are added at a weight ratio of 5 to 15 wt% of the total solid components of the barrier functional layer.

7. The self-healing barrier material according to claim 3, characterized in that, The inorganic nanofiller is layered nanoclay.

8. The self-healing barrier material according to claim 7, characterized in that, The inorganic nanofiller is added in a weight ratio of 1 to 5 wt% of the total solid composition of the barrier functional layer.

9. A paper-based packaging film, characterized in that, The paper-based packaging film comprises a waterproof heat-sealing layer, a paper base layer, an adhesive layer, a self-healing barrier material layer, and a heat-sealing layer stacked sequentially, wherein the self-healing barrier material layer is prepared using the self-healing barrier material as described in any one of claims 1-8.

10. The paper-based packaging film according to claim 9, characterized in that, The waterproof heat-sealing layer is selected from any one of polyethylene, polypropylene resin, ethylene / vinyl acetate copolymer, and ethylene / acrylate copolymer; the thickness of the waterproof heat-sealing layer is 10-20 g / m². 2 .

11. The paper-based packaging film according to claim 9, characterized in that, The heat-sealing layer comprises three layers of PE film, the material of which is selected from ethylene acrylic resin or modified PE adhesive, and the thickness of each layer is 3-10 g / m. 2 .

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