Antibacterial high-barrier full-biodegradable multifunctional coating paper and preparation method thereof

Abstract

This invention discloses an antibacterial, high-barrier, fully biodegradable multifunctional coated paper and its preparation method. The coated paper comprises a paper base layer and, from the inside out, a heat-sealing layer, a high-barrier layer, and a functional surface layer. The heat-sealing layer contains polylactic acid (PLA), PBAT, epoxy plasticizer, and coupling agent, significantly improving interfacial adhesion and heat resistance. The high-barrier layer contains modified PLA, bio-based barrier resin, and nanofiber whiskers, utilizing the maze effect to achieve high barrier properties. The functional surface layer contains PLA, PBAT, and natural antibacterial agents, endowing the material with antibacterial and preservation functions. This application, through a three-layer co-extruded fully biodegradable structure design, solves the problems of poor barrier properties, easy delamination, and lack of antibacterial function in existing degradable coated papers, achieving a synergistic effect of high barrier properties, high adhesion, and full degradation, making it suitable for the food packaging field.

Description

Technical Field

[0001] This application relates to the field of packaging materials technology, specifically to an antibacterial, high-barrier, fully biodegradable multifunctional coated paper and its preparation method. Background Technology

[0002] With increasing global concern about plastic pollution, the development of biodegradable packaging materials has become a hot topic in the industry. Laminated paper, due to its excellent waterproof and oil-resistant properties, is widely used in food containers and other packaging applications. Traditional laminated paper typically uses non-degradable plastics such as polyethylene (PE) as the lamination layer, providing excellent barrier and mechanical properties for the packaging.

[0003] To address the problem of plastic pollution, coated papers made from biodegradable materials such as polylactic acid (PLA) have appeared on the market. However, the biodegradable materials in existing fully biodegradable coated papers have significantly lower barrier properties against water vapor and oxygen than traditional PE coated papers, failing to meet the packaging requirements for cooked foods, oily foods, and long-shelf-life foods. Furthermore, existing coated papers largely rely on petroleum-based materials, which cannot degrade in the natural environment.

[0004] Meanwhile, existing biodegradable coating materials have poor adhesion to paper substrates, making them prone to peeling and delamination during processing and use. Furthermore, their heat resistance and processing adaptability are poor. Single-material biodegradable coated paper also cannot provide antibacterial and preservation functions, limiting the further application of coated paper packaging materials in the food industry. Summary of the Invention

[0005] To address the issues of insufficient barrier properties and poor adhesion to the paper substrate, which easily lead to delamination in existing fully biodegradable coated paper, this application provides an antibacterial, high-barrier, fully biodegradable multifunctional coated paper and its preparation method.

[0006] The first aspect of this application provides an antibacterial, high-barrier, fully biodegradable multifunctional coated paper, comprising a paper base layer and a coated layer laminated on the paper base layer. The coated layer comprises, from the inside out, a heat-sealing layer, a high-barrier layer, and a functional surface layer, each layer being a fully biodegradable material. The heat-sealing layer comprises polylactic acid, polybutylene adipate / terephthalate, an epoxy plasticizer, and a coupling agent. The high-barrier layer comprises modified polylactic acid, a bio-based barrier resin, and nanofiber reinforcing materials. The functional surface layer comprises polylactic acid, polybutylene adipate / terephthalate, and a natural antibacterial agent.

[0007] This invention achieves synergistic effects of barrier, adhesion, and antibacterial properties through a three-layer co-extrusion fully biodegradable structure consisting of a heat-sealing layer, a high-barrier layer, and a functional surface layer. In the heat-sealing layer, polylactic acid (PLA) and poly(butylene adipate / terephthalate) provide excellent heat-sealing performance and flexibility, while the epoxy plasticizer and coupling agent work synergistically to significantly improve the interfacial adhesion between the biodegradable material and the paper substrate, overcoming the problems of easy peeling and delamination in traditional biodegradable coatings, while also improving the heat resistance and processing adaptability of the coated paper. In the high-barrier layer, modified PLA and bio-based barrier resin provide basic barrier against oxygen and water vapor, while nanofiber reinforcement forms a dense physical maze effect within the film layer, significantly extending the penetration path of gases and oils, enabling the fully biodegradable material system to reach or approach the barrier level of traditional PE coated paper. The addition of natural antibacterial agents to the functional surface layer provides long-lasting antibacterial and freshness-preserving effects. Combined with the matrix support of polylactic acid and poly(butylene adipate / terephthalate), it offers excellent surface protection and scratch resistance. The entire coating layer is made of fully biodegradable material, which can completely degrade in the natural environment after use, without causing white pollution.

[0008] Further, by weight, the heat-sealing layer comprises: 40-60 parts of polylactic acid, 30-50 parts of polybutylene adipate / terephthalate, 1-3 parts of epoxy plasticizer, and 0.5-1.5 parts of coupling agent.

[0009] Furthermore, the heat-sealing layer also includes 0.1-0.5 parts of an opening agent; the epoxy plasticizer is epoxidized soybean oil; and the coupling agent is a silane coupling agent. The opening agent effectively prevents film adhesion, epoxidized soybean oil has excellent plasticizing effect and good biocompatibility, and the silane coupling agent forms a strong chemical bond between the resin and the paper-based fibers. Specifically, the weight parts of the opening agent can be selected from any value among 0.15, 0.2, 0.26, and 0.35.

[0010] Further, by weight, the high barrier layer comprises: 25-40 parts of modified polylactic acid, 20-35 parts of bio-based barrier resin, and 1-5 parts of nanofiber reinforcing material; the high barrier layer also comprises 0.1-0.3 parts of antioxidant; the nanofiber reinforcing material is nanofiber whiskers.

[0011] Further, by weight, the functional surface layer comprises: 35-55 parts polylactic acid, 50-65 parts polybutylene adipate / terephthalate, and 0.5-2 parts a natural antibacterial agent; the natural antibacterial agent is chitosan. Chitosan has broad-spectrum antibacterial properties and is a natural biodegradable material with good compatibility with the polylactic acid / polybutylene adipate / terephthalate matrix.

[0012] Furthermore, the paper base layer is food-grade 100% wood pulp kraft paper, and the basis weight of the paper base layer is 30-120g / L. The moisture content is 4%-7%, and there is no fluorescent agent on the surface.

[0013] The second aspect of this application provides a method for preparing the aforementioned antibacterial, high-barrier, fully biodegradable multifunctional coated paper, comprising the following steps: raw material pretreatment: drying the raw materials for the heat-sealing layer, high-barrier layer, and functional surface layer separately; multilayer co-extrusion melting: adding the three layers of materials separately into an extruder for melting, and then co-extruding and laminating them; coating and laminating: preheating the paper base surface after surface treatment, and then casting the co-extruded coating melt onto the paper base surface for lamination; cooling and setting: after cooling, allowing it to stand for aging treatment to obtain the antibacterial, high-barrier, fully biodegradable multifunctional coated paper. This preparation process is mild, and the vacuum drying and multilayer co-extrusion casting method ensure the stability of each functional component during processing, avoiding the failure of heat-sensitive components. The process can be directly integrated with existing coating production lines and is suitable for mass industrial production.

[0014] Preferably, in the raw material pretreatment, the drying temperature is 80-90℃, the vacuum drying time is 4-6h, and the moisture content after drying is controlled below 0.05%; in the multi-layer co-extrusion melt, the heat-sealing layer temperature is controlled at 160-180℃, the high-barrier layer temperature is controlled at 170-190℃, the functional surface layer temperature is controlled at 165-185℃, and the co-extrusion composite temperature is controlled at 175-190℃.

[0015] Preferably, in the lamination process, the paper base is corona treated with a dyne value of 38-44 mN / m, the preheating temperature is 30-60℃, the lamination pressure is 0.3-0.8 MPa, and the lamination speed is 80-200 m / min.

[0016] Preferably, in the cooling and shaping process, the temperature of the cooling roller is 15-25°C, and the static aging treatment time is 12-24 hours.

[0017] The present invention has the following beneficial effects: This invention significantly improves the adhesion between the biodegradable coating layer and the paper base layer by introducing epoxy plasticizer and coupling agent into the heat-sealing layer, solving the problems of easy peeling and delamination of traditional biodegradable coatings, while also improving the heat resistance and processing adaptability of the coated paper.

[0018] The high-barrier layer is made of modified polylactic acid, bio-based barrier resin and nanofiber reinforced material. The labyrinth effect of nanofibers greatly extends the permeation path of gas and oil, so that the barrier performance of biodegradable material reaches or approaches the level of traditional PE coated paper, thus meeting the needs of high-barrier packaging.

[0019] The functional surface layer incorporates natural antibacterial agents such as chitosan, giving the coated paper excellent antibacterial and preservation effects. It has an antibacterial rate of over 90% against common pathogens, extending the shelf life of food and ensuring high safety.

[0020] The entire coating layer and paper base are made of environmentally friendly materials. After 56 days of use, the compost biodegradation rate exceeds 90%, and it can be completely degraded without white pollution, which meets the requirements of sustainable development. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the antibacterial, high-barrier, fully biodegradable multifunctional coated paper provided in the embodiments of this application.

[0022] Explanation of reference numerals in the attached diagram: 1-Paper base layer; 2-Heat-sealing layer; 3-High barrier layer; 4-Functional surface layer. Detailed Implementation

[0023] To facilitate understanding of this application, a more complete description will be provided below. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0024] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0025] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0026] The "epoxy plasticizer" described in this application refers to a plasticizer containing epoxy groups in its molecular structure. In this field, it not only reduces the melt viscosity of resin systems and improves processing fluidity, but also, due to its polar epoxy groups, can form hydrogen bonds or even chemical bonds with the hydroxyl groups on the surface of paper fibers, thereby significantly improving the interfacial adhesion between the coating layer and the paper base layer, while also enhancing the system's heat resistance. Specific sub-concepts include, but are not limited to, epoxidized soybean oil and epoxidized linseed oil.

[0027] The "coupling agent" mentioned in this application refers to an interface modifier capable of improving the interfacial compatibility between inorganic fillers or polar substrates and organic polymers. In this invention, the hydrophilic group at one end of the coupling agent binds to the paper-based fibers, while the lipophilic group at the other end entangles with the degradable resin segments, forming a molecular bridge, effectively solving the problem of poor adhesion between biodegradable resin and paper substrate. Specific sub-concepts include, but are not limited to, silane coupling agents, titanate coupling agents, etc.

[0028] The "modified polylactic acid" mentioned in this application refers to polylactic acid modified by chemical or physical methods to overcome the defects of pure polylactic acid, such as slow crystallization rate and high brittleness at room temperature. Modification methods include, but are not limited to, graft modification, chain extension modification, or copolymerization with flexible segments. The modified polylactic acid exhibits increased crystallinity and enhanced toughness, thereby maintaining biodegradability while providing the high-barrier layer with better film-forming properties and mechanical support.

[0029] The "bio-based barrier resin" described in this application refers to a polymeric resin derived from biomass that has a dense molecular structure and extremely low permeability to oxygen and water vapor. These resins typically contain a large number of polar groups or highly oriented crystalline regions, making it difficult for gas molecules to pass through. Specific sub-concepts include, but are not limited to, polyhydroxyalkanoates (PHA), polyglycolic acid (PGA), or specific bio-based polyamides.

[0030] The "nanofiber reinforced material" described in this application refers to a fibrous material with radial dimensions in the nanometer range and length in the micrometer range, possessing extremely high aspect ratio and mechanical strength. In the high-barrier layer of this invention, this material is uniformly dispersed in the resin matrix, forming a dense physical network structure. Specific sub-concepts include, but are not limited to, nanocellulose whiskers, nanochitosan whiskers, etc.

[0031] The "maze effect" described in this application refers to the phenomenon where, when nanofiber reinforced materials are uniformly dispersed in a polymer matrix with a high aspect ratio, gas molecules such as oxygen and water vapor cannot pass through the membrane in a straight line. Instead, they must bypass these impermeable nanofibers, thereby significantly extending the permeation path and reducing the effective diffusion coefficient. Macroscopically, this manifests as a significant improvement in barrier performance.

[0032] The term "natural antibacterial agent" as used in this application refers to substances derived from nature, highly safe for human use, biodegradable in the natural environment, and possessing broad-spectrum antibacterial and bactericidal functions. Specific subcategories include, but are not limited to, chitosan and lysozyme.

[0033] The "opening agent" described in this application, also known as an anti-blocking agent, is a commonly used additive in plastic film processing. It can slightly increase the surface roughness of the film to prevent interlayer adhesion during winding or high-temperature storage. Specific sub-concepts include inorganic opening agents such as silica microparticles, or organic opening agents such as erucamide.

[0034] The "corona treatment" described in this application is a physical modification process that uses high-frequency, high-voltage corona discharge to ionize air and generate plasma, which bombards the surface of a substrate, thereby introducing oxygen-containing polar groups and increasing the surface micro-roughness. The surface tension (measured in dynes) of the treated substrate is significantly increased, which is beneficial for the wetting and chemical bonding of the molten resin on the substrate surface and is a key step in ensuring the composite strength of the coating layer.

[0035] The first aspect of this invention provides an antibacterial, high-barrier, fully biodegradable multifunctional coated paper, such as... Figure 1 As shown, the coated paper comprises, from bottom to top, a paper base layer 1 and a coating layer laminated on the paper base layer 1. The coating layer comprises, from the inside to the outside, a heat-sealing layer 2, a high-barrier layer 3, and a functional surface layer 4. Each layer of the coating layer is a fully biodegradable material. The heat-sealing layer 2 comprises polylactic acid, polybutylene adipate / terephthalate, epoxy plasticizer, and coupling agent. The high-barrier layer 3 comprises modified polylactic acid, bio-based barrier resin, and nanofiber reinforcing material. The functional surface layer 4 comprises polylactic acid, polybutylene adipate / terephthalate, and natural antibacterial agent.

[0036] The paper base layer 1 provides support strength and printability; the heat-sealing layer 2 is in direct contact with the paper base layer 1 and provides good heat-sealing performance and flexibility, as well as ensuring the packaging seal strength and interlayer adhesion; the high barrier layer 3 is located in the middle and is used to achieve efficient barrier against oxygen, water vapor and grease; the functional surface layer 4 is located on the outermost side and is used to provide surface protection, antibacterial and scratch resistance.

[0037] The paper base layer 1 has no fluorescent agent on its surface, which meets the GB 4806.8 standard for food contact paper. It not only provides support strength but also gives the coated paper good printability.

[0038] This invention achieves synergistic effects of barrier, adhesion, and antibacterial properties through a three-layer co-extrusion fully biodegradable structure consisting of a heat-sealing layer, a high-barrier layer, and a functional surface layer. In the heat-sealing layer, polylactic acid (PLA) and poly(butylene adipate / terephthalate) provide excellent heat-sealing performance and flexibility, while the epoxy plasticizer and coupling agent work synergistically to significantly improve the interfacial adhesion between the biodegradable material and the paper substrate, overcoming the problems of easy peeling and delamination in traditional biodegradable coatings, while also improving the heat resistance and processing adaptability of the coated paper. In the high-barrier layer, modified PLA and bio-based barrier resin provide basic barrier against oxygen and water vapor, while nanofiber reinforcement forms a dense physical maze effect within the film layer, significantly extending the penetration path of gases and oils, enabling the fully biodegradable material system to reach or approach the barrier level of traditional PE coated paper. The addition of natural antibacterial agents to the functional surface layer provides long-lasting antibacterial and freshness-preserving effects. Combined with the matrix support of polylactic acid and poly(butylene adipate / terephthalate), it offers excellent surface protection and scratch resistance. The entire coating layer is made of fully biodegradable material, which can completely degrade in the natural environment after use, without causing white pollution.

[0039] In a preferred embodiment, polylactic acid and poly(butylene adipate / terephthalate) are common fully biodegradable resins in the art; epoxy plasticizers and coupling agents are widely available; modified polylactic acid can be grafted to improve toughness; bio-based barrier resins can be selected from biomass materials with excellent barrier properties; and natural antibacterial agents are naturally and safely sourced.

[0040] In a preferred embodiment, the heat-sealing layer comprises, by weight: 40-60 parts polylactic acid, 30-50 parts polybutylene adipate / terephthalate, 1-3 parts epoxy plasticizer, and 0.5-1.5 parts coupling agent.

[0041] At this ratio, the blend system of polylactic acid and poly(butylene adipate) / terephthalate exhibits suitable melt flowability and flexibility, and the epoxy plasticizer and coupling agent can effectively penetrate the interface, improving adhesion and heat resistance. Specifically, the weight parts of polylactic acid can be selected from any value among 41, 45, 49, 53, and 56; the weight parts of poly(butylene adipate) / terephthalate can be selected from any value among 48, 44, 40, 36, and 34.

[0042] In a preferred embodiment, the heat-sealing layer further includes 0.1-0.5 parts of an opening agent; the epoxy plasticizer is epoxidized soybean oil; and the coupling agent is a silane coupling agent.

[0043] The opening agent effectively prevents film adhesion, epoxidized soybean oil has excellent plasticizing effect and good biocompatibility, and the silane coupling agent forms a strong chemical bond between the resin and the paper-based fiber. Specifically, the weight parts of the opening agent can be selected from any value among 0.15, 0.2, 0.26, and 0.35.

[0044] In a preferred embodiment, the high barrier layer comprises, by weight: 25-40 parts modified polylactic acid, 20-35 parts bio-based barrier resin, and 1-5 parts nanofiber reinforcing material; the high barrier layer further comprises 0.1-0.3 parts antioxidant; the nanofiber reinforcing material is nanofiber whiskers.

[0045] The high aspect ratio of nanofiber whiskers creates a highly efficient barrier, while antioxidants prevent thermal oxidative degradation during processing. Specifically, the modified polylactic acid can be selected from any value among 26, 29, 32, and 35 by weight; the bio-based barrier resin can be selected from any value among 21, 25, 28, and 31 by weight; and the nanofiber whiskers can be selected from any value among 1.2, 2, 3, and 4 by weight.

[0046] In a preferred embodiment, the functional surface layer comprises, by weight: 35-55 parts polylactic acid, 50-65 parts polybutylene adipate / terephthalate, and 0.5-2 parts natural antibacterial agent; wherein the natural antibacterial agent is chitosan.

[0047] Chitosan possesses broad-spectrum antibacterial properties and is a natural biodegradable material with good compatibility with polylactic acid / polyadipate / butyl terephthalate matrices. Specifically, the weight percentages of polylactic acid can be selected from any value among 36, 40, 44, and 48; the weight percentages of polyadipate / butyl terephthalate can be selected from any value among 50, 55, 59, and 63; and the weight percentages of chitosan can be selected from any value among 0.6, 1.0, 1.3, and 1.5.

[0048] In a preferred embodiment, the paper base layer is food-grade 100% wood pulp kraft paper, and the basis weight of the paper base layer is 30-120g / L. The moisture content is 4%-7%, and the surface is free of fluorescent agents. This basis weight and moisture content of kraft paper provide sufficient support strength and ensure the adhesion of the laminated coating, meeting food contact safety standards.

[0049] A second aspect of this invention provides a method for preparing the above-mentioned antibacterial, high-barrier, fully biodegradable multifunctional coated paper, comprising the following steps: Raw material pretreatment: Dry the raw materials for the heat-sealing layer, high-barrier layer, and functional surface layer separately; Multilayer co-extrusion melt: Three layers of material are added separately to an extruder and melted, then co-extruded and laminated; Coating lamination: After surface treatment and preheating of the paper base, the co-extruded melt of the coating is cast onto the surface of the paper base for lamination; cooling and shaping: after cooling, static aging treatment is performed to obtain antibacterial, high-barrier, fully biodegradable multifunctional coated paper.

[0050] The preparation method is mild, and the vacuum drying and multi-layer co-extrusion casting method ensure the stability of each functional component during processing, avoid the failure of heat-sensitive components, and the process can be directly connected to existing coating production lines, making it suitable for mass industrial production.

[0051] In a preferred embodiment, during the raw material pretreatment, the drying temperature is 80-90℃, the vacuum drying time is 4-6 hours, and the moisture content after drying is controlled below 0.05%. During the multi-layer co-extrusion melt extrusion, the heat-sealing layer temperature is controlled at 160-180℃, the high-barrier layer temperature at 170-190℃, the functional surface layer temperature at 165-185℃, and the co-extrusion composite temperature at 175-190℃. Strict control of the moisture content prevents air bubbles from forming during molding, and the temperature difference control between layers ensures the interface fusion quality during casting and lamination. Specifically, the drying temperature can be selected from 85℃; the vacuum drying time can be selected from 5 hours.

[0052] In a preferred embodiment, during the lamination process, the paper substrate undergoes corona treatment with a dyne value of 38-44 mN / m, a preheating temperature of 30-60°C, a lamination pressure of 0.3-0.8 MPa, and a lamination speed of 80-200 m / min. Corona treatment increases the surface tension of the paper substrate, preheating eliminates surface moisture and improves adhesion, and the specific pressure and speed ensure sufficient wetting and bonding of the melt to the paper substrate. Specifically, the preheating temperature can be selected from 40°C or 50°C; the lamination pressure can be selected from 0.5 MPa.

[0053] In a preferred embodiment, during the cooling and setting process, the cooling roller temperature is 15-25°C, and the settling and aging treatment time is 12-24 hours. Rapid cooling and setting solidifies the labyrinth barrier structure, while the aging treatment eliminates internal stress and prevents delamination. Specifically, the cooling roller temperature can be selected from 20°C; the settling and aging treatment time can be selected from 18 hours.

[0054] In some preferred embodiments, the epoxy plasticizer may be selected from either epoxidized soybean oil or epoxidized linseed oil; the coupling agent may be selected from either silane coupling agent or titanate coupling agent.

[0055] In some preferred embodiments, the nanofiber reinforcing material may be selected from either nanocellulose whiskers or nanochitosan whiskers; the natural antibacterial agent may be selected from either chitosan or lysozyme.

[0056] In some preferred embodiments, the basis weight of the paper base layer can be selected from 30 g / 50g / 80g / 100g / 120g / Any one of the following; the moisture content can be selected from 4%, 5%, 6%, and 7%.

[0057] To better illustrate the advantages of the present invention, the present invention will be further described below through detailed specific embodiments and comparative embodiments: Example 1

[0058] This embodiment 1 provides an antibacterial, high-barrier, fully biodegradable multifunctional coated paper and its preparation method.

[0059] The raw materials for preparing antibacterial, high-barrier, fully biodegradable multifunctional coated paper include: food-grade all-wood pulp kraft paper (basis weight 80g / L). It has a moisture content of 5%, no fluorescent agent on the surface, and meets the GB 4806.8 standard for food contact paper.

[0060] The raw materials for preparing the heat-sealing layer include, by weight: 41 parts polylactic acid (PLA), 48 parts polybutylene adipate / terephthalate (PBAT), 1.2 parts epoxidized soybean oil, 0.55 parts silane coupling agent, and 0.15 parts opening agent.

[0061] The raw materials for preparing the high barrier layer include, by weight: 26 parts modified polylactic acid, 21 parts bio-based barrier resin, 1.2 parts nanofiber whiskers, and 0.12 parts antioxidant.

[0062] The raw materials for preparing the functional surface layer include, by weight, 36 parts of polylactic acid (PLA), 63.4 parts of polybutylene adipate / terephthalate (PBAT), and 0.6 parts of chitosan.

[0063] The preparation method of antibacterial, high-barrier, fully biodegradable multifunctional coated paper includes the following steps: Raw material pretreatment: The heat-sealing layer, high barrier layer and functional surface layer raw materials are vacuum dried at 85℃ for 5 hours, and the moisture content is controlled below 0.05%.

[0064] Multi-layer co-extrusion melting: The three layers of material are added to three extruders respectively. The temperature of the heat-sealing layer is controlled at 170℃, the temperature of the high-barrier layer is controlled at 180℃, and the temperature of the functional surface layer is controlled at 175℃. After the three layers are co-extruded and compounded, the compounding temperature is controlled at 185℃.

[0065] Coating and lamination: The paper base is treated with corona to a dyne value of 40mN / m and preheated at 50℃ before entering the lamination process. The co-extruded melt of the coating is cast onto the surface of the paper base. The lamination pressure is 0.5MPa and the lamination speed is 120m / min.

[0066] Cooling and shaping: After rapid cooling and shaping at 20℃ using cooling rollers, and then aging treatment for 18 hours, the result is as follows: Figure 1 The antibacterial, high-barrier, fully biodegradable multifunctional coated paper shown is shown.

[0067] The oxygen permeability of the coated paper prepared in this embodiment was tested to be 38 cm⁻¹. 3 / (m 3 •24h•0.1MPa), water vapor transmission rate is 25 g / ( It exhibits good barrier properties (24h); the heat-sealing strength reaches 12.5 N / 15mm, meeting the packaging sealing strength requirements; the antibacterial rate against Escherichia coli is 91.2%, and the antibacterial rate against Staphylococcus aureus is 90.5%, showing significant antibacterial and preservation effects; the biodegradation rate reaches 92% after 56 days, achieving complete natural degradation.

[0068] Example 2

[0069] This embodiment 2 provides an antibacterial, high-barrier, fully biodegradable multifunctional coated paper and its preparation method.

[0070] The raw materials for preparing the heat-sealing layer include, by weight: 45 parts polylactic acid (PLA), 44 parts polybutylene adipate / terephthalate (PBAT), 1.7 parts epoxidized soybean oil, 0.75 parts silane coupling agent, and 0.2 parts opening agent.

[0071] The raw materials for preparing the high barrier layer include, by weight: 29 parts modified polylactic acid, 25 parts bio-based barrier resin, 2 parts nanofiber whiskers, and 0.15 parts antioxidant.

[0072] The raw materials for preparing the functional surface layer include, by weight: 40 parts of polylactic acid (PLA), 59 parts of polybutylene adipate / terephthalate (PBAT), and 1.0 part of chitosan.

[0073] The preparation method includes the following steps: Raw material pretreatment: The heat-sealing layer, high barrier layer and functional surface layer raw materials are vacuum dried at 85℃ for 5 hours, and the moisture content is controlled below 0.05%.

[0074] Multi-layer co-extrusion melt: The three layers of material are added to three extruders respectively. The temperature of the heat-sealing layer is controlled at 172℃, the temperature of the high-barrier layer is controlled at 182℃, and the temperature of the functional surface layer is controlled at 178℃. After the three layers are co-extruded and compounded, the compounding temperature is controlled at 186℃.

[0075] Coating and lamination: The paper base is treated with corona to a dyne value of 41mN / m and preheated at 50℃ before entering the lamination process. The co-extruded melt of the coating is cast onto the surface of the paper base. The lamination pressure is 0.5MPa and the lamination speed is 130m / min.

[0076] Cooling and shaping: After rapid cooling and shaping at 20°C by cooling rollers, and aging treatment for 18 hours, antibacterial, high-barrier, fully biodegradable multifunctional coated paper is obtained.

[0077] The paper base and other parameters are the same as in Example 1.

[0078] Testing showed that the oxygen permeability of the coated paper prepared in this embodiment decreased to 29 cm⁻¹. 3 / (m 3 ·24h·0.1MPa), water vapor transmission rate decreased to 18 g / ( •24h), the barrier performance is significantly improved compared with Example 1; the heat sealing strength is increased to 14.2 N / 15mm; the antibacterial rate against Escherichia coli and Staphylococcus aureus is increased to 94.5% and 93.8% respectively, with excellent antibacterial effect; the biodegradation rate reaches 94% after 56 days, with outstanding environmental performance.

[0079] Example 3

[0080] This embodiment 3 provides an antibacterial, high-barrier, fully biodegradable multifunctional coated paper and its preparation method.

[0081] The raw materials for preparing the heat-sealing layer include, by weight: 49 parts polylactic acid (PLA), 40 parts polybutylene adipate / terephthalate (PBAT), 2.1 parts epoxidized soybean oil, 0.9 parts silane coupling agent, and 0.26 parts opening agent.

[0082] The raw materials for preparing the high barrier layer include, by weight: 32 parts modified polylactic acid, 28 parts bio-based barrier resin, 3 parts nanofiber whiskers, and 0.18 parts antioxidant.

[0083] The raw materials for preparing the functional surface layer include, by weight, 44 parts of polylactic acid (PLA), 54.7 parts of polybutylene adipate / terephthalate (PBAT), and 1.3 parts of chitosan.

[0084] The preparation method includes the following steps: Raw material pretreatment: The heat-sealing layer, high barrier layer and functional surface layer raw materials are vacuum dried at 85℃ for 5 hours, and the moisture content is controlled below 0.05%.

[0085] Multi-layer co-extrusion melt: The three layers of material are added to three extruders respectively. The temperature of the heat-sealing layer is controlled at 175℃, the temperature of the high-barrier layer is controlled at 185℃, and the temperature of the functional surface layer is controlled at 180℃. After the three layers are co-extruded and compounded, the compounding temperature is controlled at 188℃.

[0086] Coating and lamination: The paper base is treated with corona to a dyne value of 42mN / m and preheated at 50℃ before entering the lamination process. The co-extruded melt of the coating is cast onto the surface of the paper base. The lamination pressure is 0.6MPa and the lamination speed is 140m / min.

[0087] Cooling and shaping: After rapid cooling and shaping at 20°C by cooling rollers, and aging treatment for 18 hours, antibacterial, high-barrier, fully biodegradable multifunctional coated paper is obtained.

[0088] The paper base and other parameters are the same as in Example 1.

[0089] Testing showed that the oxygen permeability of the coated paper prepared in this embodiment was further reduced to 21 cm⁻¹. 3 / (m 3 ·24h·0.1MPa), water vapor transmission rate decreased to 12 g / ( • 24h), barrier performance is close to that of traditional PE coated paper; heat seal strength reaches 15.8 N / 15mm, sealing is firm; antibacterial rate against Escherichia coli and Staphylococcus aureus reaches 96.8% and 96.2% respectively, with significant preservation effect; biodegradation rate reaches 95% after 56 days.

[0090] Example 4

[0091] Example 4 provides an antibacterial, high-barrier, fully biodegradable multifunctional coated paper and its preparation method.

[0092] The raw materials for preparing the heat-sealing layer include, by weight: 53 parts polylactic acid (PLA), 36 parts polybutylene adipate / terephthalate (PBAT), 2.5 parts epoxidized soybean oil, 1.15 parts silane coupling agent, and 0.35 parts opening agent.

[0093] The raw materials for preparing the high barrier layer include, by weight: 35 parts modified polylactic acid, 31 parts bio-based barrier resin, 4 parts nanofiber whiskers, and 0.22 parts antioxidant.

[0094] The raw materials for preparing the functional surface layer include, by weight, 48 parts of polylactic acid (PLA), 50.5 parts of polybutylene adipate / terephthalate (PBAT), and 1.5 parts of chitosan.

[0095] The preparation method includes the following steps: Raw material pretreatment: The heat-sealing layer, high barrier layer and functional surface layer raw materials are vacuum dried at 85℃ for 5 hours, and the moisture content is controlled below 0.05%.

[0096] Multi-layer co-extrusion melting: The three layers of material are added to three extruders respectively. The temperature of the heat-sealing layer is controlled at 178℃, the temperature of the high-barrier layer is controlled at 188℃, and the temperature of the functional surface layer is controlled at 182℃. After the three layers are co-extruded and compounded, the compounding temperature is controlled at 189℃.

[0097] Coating and lamination: The paper base is treated with corona to a dyne value of 43mN / m and preheated at 50℃ before entering the lamination process. The co-extruded melt of the coating is cast onto the surface of the paper base. The lamination pressure is 0.6MPa and the lamination speed is 150m / min.

[0098] Cooling and shaping: After rapid cooling and shaping at 20°C by cooling rollers, and aging treatment for 18 hours, antibacterial, high-barrier, fully biodegradable multifunctional coated paper is obtained.

[0099] The paper base and other parameters are the same as in Example 1.

[0100] Testing showed that the oxygen permeability of the coated paper prepared in this embodiment was as low as 16 cm⁻¹. 3 / (m 3 • 24h • 0.1MPa), water vapor transmission rate as low as 8 g / ( It boasts excellent overall barrier properties (24h), meeting the requirements for high-barrier food packaging; its heat-sealing strength reaches 16.5 N / 15mm, exhibiting strong adhesion to paper bases and exhibiting no delamination during use; its antibacterial rates against Escherichia coli and Staphylococcus aureus are as high as 97.5% and 97.1% respectively, effectively extending the shelf life of food; and its biodegradability reaches 96% after 56 days, achieving a perfect combination of high performance and environmental protection.

[0101] Comparative Example 1

[0102] Comparative Example 1 provides a coated paper and its preparation method.

[0103] The difference from Example 1 is that the coating layer of Comparative Example 1 is a single-layer structure, does not contain a high-barrier layer and a functional surface layer, and does not contain epoxidized soybean oil and silane coupling agent in the heat-sealing layer.

[0104] The raw materials for preparing coated paper include: food-grade all-wood pulp kraft paper (basis weight 80g / L). It has a moisture content of 5%, no fluorescent agent on the surface, and meets the GB 4806.8 standard for food contact paper.

[0105] The raw materials for preparing the single-layer coating layer include, by weight, 41 parts of polylactic acid (PLA), 58.85 parts of polybutylene adipate / terephthalate (PBAT), and 0.15 parts of opening agent.

[0106] The preparation method of coated paper includes the following steps: Raw material pretreatment: The coating material is vacuum dried at 85℃ for 5 hours, and the moisture content is controlled below 0.05%.

[0107] Single-layer extrusion melting: The material is added to the extruder and the temperature is controlled at 175℃.

[0108] Coating and lamination: The paper base is treated with corona to a dyne value of 40mN / m and preheated at 50℃ before entering the lamination process. The molten coating is cast onto the surface of the paper base. The lamination pressure is 0.5MPa and the lamination speed is 120m / min.

[0109] Cooling and shaping: The paper is rapidly cooled and shaped at 20°C using a cooling roller, and then allowed to stand for aging treatment for 18 hours to obtain coated paper.

[0110] Comparative Example 2

[0111] Comparative Example 2 provides a coated paper and its preparation method.

[0112] The difference from Example 1 is that no nanofiber whiskers are added to the high barrier layer of this comparative example, while the proportions of other components are kept the same as in Example 1.

[0113] The raw materials for preparing coated paper include: food-grade all-wood pulp kraft paper (basis weight 80g / L). It has a moisture content of 5%, no fluorescent agent on the surface, and meets the GB 4806.8 standard for food contact paper.

[0114] The raw materials for preparing the heat-sealing layer include, by weight: 41 parts polylactic acid (PLA), 48 parts polybutylene adipate / terephthalate (PBAT), 1.2 parts epoxidized soybean oil, 0.55 parts silane coupling agent, and 0.15 parts opening agent.

[0115] The raw materials for preparing the high barrier layer include, by weight: 27.2 parts modified polylactic acid, 21 parts bio-based barrier resin, and 0.12 parts antioxidant.

[0116] The raw materials for preparing the functional surface layer include, by weight, 36 parts of polylactic acid (PLA), 63.4 parts of polybutylene adipate / terephthalate (PBAT), and 0.6 parts of chitosan.

[0117] The preparation method of coated paper includes the following steps: Raw material pretreatment: The heat-sealing layer, high barrier layer and functional surface layer raw materials are vacuum dried at 85℃ for 5 hours, and the moisture content is controlled below 0.05%.

[0118] Multi-layer co-extrusion melting: The three layers of material are added to three extruders respectively. The temperature of the heat-sealing layer is controlled at 170℃, the temperature of the high-barrier layer is controlled at 180℃, and the temperature of the functional surface layer is controlled at 175℃. After the three layers are co-extruded and compounded, the compounding temperature is controlled at 185℃.

[0119] Coating and lamination: The paper base is treated with corona to a dyne value of 40mN / m and preheated at 50℃ before entering the lamination process. The co-extruded melt of the coating is cast onto the surface of the paper base. The lamination pressure is 0.5MPa and the lamination speed is 120m / min.

[0120] Cooling and shaping: The paper is rapidly cooled and shaped at 20°C using a cooling roller, and then allowed to stand for aging treatment for 18 hours to obtain coated paper.

[0121] Comparative Example 3

[0122] Comparative Example 3 provides a coated paper and its preparation method.

[0123] Difference from Example 1: No chitosan natural antibacterial agent was added to the functional surface layer of this comparative example.

[0124] The raw materials for preparing coated paper include: food-grade all-wood pulp kraft paper (basis weight 80g / L). It has a moisture content of 5%, no fluorescent agent on the surface, and meets the GB 4806.8 standard for food contact paper.

[0125] The raw materials for preparing the heat-sealing layer include, by weight: 41 parts polylactic acid (PLA), 48 parts polybutylene adipate / terephthalate (PBAT), 1.2 parts epoxidized soybean oil, 0.55 parts silane coupling agent, and 0.15 parts opening agent.

[0126] The raw materials for preparing the high barrier layer include, by weight: 26 parts modified polylactic acid, 21 parts bio-based barrier resin, 1.2 parts nanofiber whiskers, and 0.12 parts antioxidant.

[0127] The raw materials for preparing the functional surface layer include, by weight, 47.93 parts of polylactic acid (PLA) and 52.07 parts of polybutylene adipate / terephthalate (PBAT).

[0128] The preparation method of coated paper includes the following steps: Raw material pretreatment: The heat-sealing layer, high barrier layer and functional surface layer raw materials are vacuum dried at 85℃ for 5 hours, and the moisture content is controlled below 0.05%.

[0129] Multi-layer co-extrusion melting: The three layers of material are added to three extruders respectively. The temperature of the heat-sealing layer is controlled at 170℃, the temperature of the high-barrier layer is controlled at 180℃, and the temperature of the functional surface layer is controlled at 175℃. After the three layers are co-extruded and compounded, the compounding temperature is controlled at 185℃.

[0130] Coating and lamination: The paper base is treated with corona to a dyne value of 40mN / m and preheated at 50℃ before entering the lamination process. The co-extruded melt of the coating is cast onto the surface of the paper base. The lamination pressure is 0.5MPa and the lamination speed is 120m / min.

[0131] Cooling and shaping: The paper is rapidly cooled and shaped at 20°C using a cooling roller, and then allowed to stand for aging treatment for 18 hours to obtain coated paper.

[0132] To better demonstrate the beneficial effects of the technical solution of the present invention, the coated paper prepared in the above embodiments and comparative examples was subjected to the following performance tests, wherein the specific test equipment and test methods are as follows: Test subjects: High-barrier fully biodegradable coated paper prepared in Examples 1-4, coated paper prepared in Comparative Examples 1-3, and traditional PE coated paper (control group). Packaging test subjects were oily pastries and cooked braised foods.

[0133] Test equipment: oxygen transmission rate tester, water vapor transmission rate tester, heat seal strength tester, electronic tensile testing machine, constant temperature and humidity chamber, antibacterial performance tester.

[0134] Test methods and standards: 1. Oxygen permeability test: The test was conducted according to GB / T 19789-2021 "Test Method for Oxygen Permeability of Plastic Films and Sheets for Packaging Materials - Coulometric Test". The test temperature was controlled at 23±0.5℃, the relative humidity was 0% (dry nitrogen carrier gas), and the sample area was 50.24 cm². 2 The partial pressure of oxygen was 0.1 MPa. Three samples were tested for each sample, and the arithmetic mean was taken.

[0135] 2. Water vapor transmission rate test: The test was conducted according to GB / T 26253-2010, "Determination of Water Vapor Transmission Rate of Plastic Films and Sheets - Infrared Detector Method". The test temperature was controlled at 38±0.6℃, and the relative humidity at 90±2%. This method has high sensitivity and is suitable for testing high-barrier materials and multilayer composite materials. Three samples were tested for each sample, and the arithmetic mean was taken. (If laboratory conditions limit the use of the cup method, GB / T 1037-2021 can be used, but the infrared detection method is more accurate for high-barrier coated paper.) 3. Heat seal strength test: Sample preparation and testing were conducted according to QB / T 2358-1998, "Test Method for Heat Seal Strength of Plastic Film Packaging Bags". The coated paper was cut into strips of 150mm × 15mm. Two strips were aligned and overlapped, and heat-sealed using a heat-sealing tester at 150℃, 0.3MPa, and 0.5s (Note: This temperature condition is suitable for PLA / PBAT biodegradable materials; high-temperature degradation should be avoided). After cooling, a peel test was performed using an electronic tensile testing machine at a tensile speed of 300mm / min, determining the maximum load at which the heat-sealed area broke. Five samples were tested for each type of packaging, and the arithmetic mean was taken.

[0136] 4. Antibacterial performance test: The tests were conducted according to GB / T 31402-2015 "Test Method for Antimicrobial Properties of Plastic Surfaces". *Escherichia coli* (ATCC 25922) and *Staphylococcus aureus* (ATCC 6538) were selected as test strains. Bacterial solutions were inoculated onto the sample surface, covered with a sterile film, and incubated for 24 hours at 37°C and a relative humidity above 90%. The number of recovered colonies was calculated using the plate count method, and the antimicrobial rate was calculated using the formula: R(%) = (A - B) / A × 100%, where A is the number of recovered colonies in the control group (blank PE film or comparative sample without antimicrobial agent), and B is the number of recovered colonies in the example sample. Three parallel tests were performed for each sample.

[0137] 5. Biodegradability test: The test was conducted according to GB / T 19277.1-2011, "Determination of the final aerobic biodegradability of materials under controlled composting conditions—Method by determination of released carbon dioxide—Part 1: General Method". The samples were placed in a controlled composting environment at 58±2℃, and the biodegradability of the material was calculated by measuring the amount of carbon dioxide released. The test period was 56 days. Cellulose was used as a positive control, and its biodegradability should be greater than 70%.

[0138] 6. Simulation test of actual packaging application: Simulation experiments were conducted based on actual application scenarios. Food models with high oil content (such as pastries with an oil content of about 20%) and cooked braised foods were selected as packaging objects. The food samples were respectively placed into packaging bags or lunch boxes made of coated paper prepared in Examples 1-4 and Comparative Examples 1-3, and sealed and stored for 7 days at a temperature of 23±2℃ and a relative humidity of 50±5%.

[0139] Leakage observation: On the 7th day, observe the bottom of the packaging container and the heat-sealed edge for any oil stains or moisture seepage, and record it as "leakage present" or "no leakage". Sensory evaluation: Open the packaging and observe whether there are mold spots on the surface of the food, whether the color has changed significantly to brown, and whether there is a putrid or sour smell. If there is no obvious mold, the color is normal and there is no odor, it is judged as "no spoilage"; if there are slight mold spots or odor, it is judged as "slight spoilage"; if there is obvious spoilage, it is judged as "obvious spoilage".

[0140] The test results are shown in Table 1 below:

[0141]

[0142] Table 1 As shown in Table 1, the fully biodegradable coated paper prepared in Examples 1-4 of this invention exhibits a biodegradation rate exceeding 90% under 56-day composting conditions, compared to traditional PE coated paper, indicating complete natural degradation. In contrast, PE coated paper shows almost no degradation, demonstrating the outstanding environmental advantages of the material of this invention. The biodegradation rates of Comparative Examples 1-3 also all exceed 90%, indicating that all components are fully biodegradable materials, possessing an environmentally friendly foundation.

[0143] Specifically, comparing the data of Example 1 and Comparative Example 2, it can be seen that when no nanofiber whiskers were added to the high-barrier layer, the oxygen permeability of Comparative Example 2 increased from 38% to 68%, and the water vapor permeability increased from 25% to 52%. This demonstrates that the "physical maze effect" formed by the nanofiber whiskers within the membrane effectively extends the gas permeation path and significantly improves the material's barrier properties.

[0144] Comparative Example 1, employing a single-layer structure without the addition of an adhesion promoter, exhibits an oxygen permeability of 135% and a water vapor permeability of 89%, both significantly higher than those of Example 1. This demonstrates that the three-layer co-extrusion structure employed in this invention effectively achieves functional zoning, avoiding the problem of insufficient barrier performance of a single material.

[0145] Comparing Example 1 and Comparative Example 3, Comparative Example 3, which did not contain chitosan, had slightly higher oxygen permeability (40) and water vapor permeability (27) than Example 1. This indicates that chitosan plays a certain role in filling and densifying the functional surface layer, which helps to improve the overall barrier performance.

[0146] The heat-sealing strength of Comparative Example 1 was only 4.5 N / 15 mm, far lower than that of Example 1 (12.5 N / 15 mm). This indicates that the synergistic effect of epoxidized soybean oil and silane coupling agent in the heat-sealing layer improved the interfacial bonding between the biodegradable resin and the paper-based fiber, solving the problem of easy delamination and peeling. The heat-sealing strength of Comparative Example 2 (12.8 N / 15 mm) was slightly higher than that of Example 1. This is because the removal of the hard nanofiber whiskers slightly improved the flexibility of the high-barrier resin matrix, but this also led to a significant decrease in barrier performance.

[0147] Comparative Example 3 (without chitosan) showed no antibacterial effect against Escherichia coli and Staphylococcus aureus, while Examples 1-4 and Comparative Example 2 (with chitosan) all achieved antibacterial rates of over 90%. This indicates that chitosan in the functional surface layer is a key component that imparts antibacterial and preservative properties to the coated paper.

[0148] In summary, the technical solution provided by this invention has the following beneficial technical effects: (1) Excellent interfacial bonding and processing adaptability. This invention innovatively introduces epoxy plasticizer and silane coupling agent into the heat-sealing layer. The two work synergistically to construct a strong chemical bond and physical entanglement structure between the biodegradable resin and the paper-based fiber. Example data shows that this structure significantly improves the adhesion between the coating layer and the paper base, with a heat-sealing strength of up to 16.5 N / 15mm. This effectively solves the industry problem of easy delamination and peeling of traditional biodegradable coated paper, while also endowing the material with excellent heat resistance and processing adaptability, ensuring the sealing integrity of the packaging.

[0149] (2) Breakthrough high barrier properties. This invention utilizes the high aspect ratio of nanofiber whiskers to construct a dense "physical maze effect" within the film layer by compounding modified polylactic acid, bio-based barrier resin, and nanofiber whiskers in a high barrier layer. Test results show that as the content of nanofiber whiskers increases, the oxygen permeability decreases to a minimum of 16 cm⁻¹. 3 / (m 3 At 24h and 0.1MPa, the water vapor transmission rate dropped to a minimum of 8 g / ( With a barrier performance approaching that of traditional petroleum-based PE coated paper (24h), it breaks through the technical bottleneck of insufficient barrier performance of fully biodegradable materials and can meet the packaging requirements of cooked food, oily food and long shelf-life food.

[0150] (3) It has a highly efficient antibacterial and preservation function. The natural chitosan antibacterial agent added to the functional surface layer endows the coated paper with broad-spectrum and long-lasting antibacterial properties. Experiments have shown that the antibacterial rate of the coated paper of this invention against Escherichia coli and Staphylococcus aureus both exceed 90%, and can reach up to 97.5%. It can effectively inhibit the growth of microorganisms in the packaging, significantly extend the shelf life of food, and improve the safety and functionality of the packaging.

[0151] (4) Environmentally friendly and pollution-free throughout the entire life cycle. All layers of the coating layer of this invention are made of fully biodegradable materials, and the paper base layer is made of food-grade wood pulp kraft paper. Composting experiments show that the biodegradation rate exceeds 90% after 56 days, reaching a maximum of 96%. After use, it can be completely degraded into carbon dioxide and water in the natural environment, solving the problem of white pollution from the source and meeting the environmental protection policies and sustainable development requirements under the global ban on plastics.

[0152] 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 multifunctional antibacterial, high-barrier, fully biodegradable coated paper, characterized in that, It includes a paper base layer and a coating layer laminated on the paper base layer. The coating layer includes, from the inside out, a heat-sealing layer, a high-barrier layer and a functional surface layer. Each layer is made of fully biodegradable material. The heat-sealing layer comprises polylactic acid, polybutylene adipate / terephthalate, epoxy plasticizer, and coupling agent; The high-barrier layer comprises modified polylactic acid, bio-based barrier resin, and nanofiber reinforcing material; The functional surface layer comprises polylactic acid, polybutylene adipate / terephthalate, and natural antibacterial agents.

2. The antibacterial, high-barrier, fully biodegradable multifunctional coated paper according to claim 1, characterized in that, By weight, the heat-sealing layer comprises: 40-60 parts of polylactic acid, 30-50 parts of polybutylene adipate / terephthalate, 1-3 parts of epoxy plasticizer, and 0.5-1.5 parts of coupling agent.

3. The antibacterial, high-barrier, fully biodegradable multifunctional coated paper according to claim 2, characterized in that, The heat-sealing layer further includes 0.1-0.5 parts of an opening agent; the epoxy plasticizer is epoxidized soybean oil; and the coupling agent is a silane coupling agent.

4. The antibacterial, high-barrier, fully biodegradable multifunctional coated paper according to claim 1, characterized in that, By weight, the high barrier layer comprises: 25-40 parts of modified polylactic acid, 20-35 parts of bio-based barrier resin, and 1-5 parts of nanofiber reinforcing material; the high barrier layer further comprises 0.1-0.3 parts of antioxidant; the nanofiber reinforcing material is nanofiber whiskers.

5. The antibacterial, high-barrier, fully biodegradable multifunctional coated paper according to claim 1, characterized in that, By weight, the functional surface layer comprises: 35-55 parts of polylactic acid, 50-65 parts of polybutylene adipate / terephthalate, and 0.5-2 parts of a natural antibacterial agent; the natural antibacterial agent is chitosan.

6. The antibacterial, high-barrier, fully biodegradable multifunctional coated paper according to claim 1, characterized in that, The paper base layer is food-grade 100% wood pulp kraft paper, and the basis weight of the paper base layer is 30-120g / L. The moisture content is 4%-7%, and there is no fluorescent agent on the surface.

7. A method for preparing the antibacterial, high-barrier, fully biodegradable multifunctional coated paper according to any one of claims 1-6, characterized in that, Includes the following steps: Raw material pretreatment: Dry the raw materials for the heat-sealing layer, high-barrier layer, and functional surface layer separately; Multilayer co-extrusion melt: Three layers of material are added to an extruder and melted, and then co-extruded together. Coating and lamination: After preheating the paper base surface, the co-extruded melt is cast onto the paper base surface for lamination; Cooling and shaping: After cooling, the paper is left to stand for aging treatment to obtain antibacterial, high-barrier, fully biodegradable multifunctional coated paper.

8. The preparation method according to claim 7, characterized in that, In the raw material pretreatment, the drying temperature is 80-90℃, the vacuum drying time is 4-6h, and the moisture content after drying is controlled below 0.05%; in the multi-layer co-extrusion melt, the heat-sealing layer temperature is controlled at 160-180℃, the high-barrier layer temperature is controlled at 170-190℃, the functional surface layer temperature is controlled at 165-185℃, and the co-extrusion composite temperature is controlled at 175-190℃.

9. The preparation method according to claim 7, characterized in that, In the aforementioned lamination process, the paper base undergoes corona treatment, with a dyne value of 38-44 mN / m, a preheating temperature of 30-60℃, a lamination pressure of 0.3-0.8 MPa, and a lamination speed of 80-200 m / min.

10. The preparation method according to claim 7, characterized in that, In the cooling and shaping process, the temperature of the cooling roller is 15-25℃, and the static aging treatment time is 12-24h.

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