High-barrier coating liquid, packaging film and preparation method and application thereof

Abstract

This invention relates to a high-barrier coating liquid, a packaging film, and their preparation method and applications, belonging to the field of biodegradable packaging materials technology. It solves the problems of existing packaging materials being generally non-degradable, highly dependent on petroleum-based resources, and the difficulty of simultaneously achieving high transparency, high barrier performance, and high environmental stability in existing single-material packaging systems. The high-barrier coating liquid provided by this invention comprises 1-10 parts of natural polysaccharide, 0.1-5 parts of a polyvalent metal ion compound, 0.5-5 parts of a bio-based plasticizer, and 80-98 parts of water. The bio-based plasticizer is added to the natural polysaccharide solution to obtain a polysaccharide solution. The polysaccharide solution is mixed with an aqueous solution of the polyvalent metal ion compound, and stirred to carry out a coordination crosslinking reaction to obtain the high-barrier coating liquid. The high-barrier coating liquid is coated onto the surface of a substrate layer, dried, and cured to obtain the packaging film. The packaging film provided by this invention can be applied to the aseptic packaging of pharmaceuticals, food, or medical devices.

Description

Technical Field

[0001] This invention relates to the field of biodegradable packaging materials technology, specifically to a high-barrier coating liquid, a packaging film, and their preparation methods and applications. Background Technology

[0002] In the field of high-performance packaging materials, especially in applications such as food, pharmaceuticals, and medical devices where storage environments are highly sensitive, the permeation of oxygen and water vapor is a key factor leading to the oxidation and deterioration of contents, the deactivation of active ingredients, and the growth of microorganisms. Therefore, developing high-barrier material systems that combine excellent oxygen and moisture barrier properties has become one of the core research directions in materials engineering and packaging technology. Existing technologies typically employ polar polymers, such as polyvinyl alcohol (PVA), for coating modification, constructing a dense molecular network structure to reduce the gas permeation rate. For example, Chinese invention patent CN117777793A discloses a composite coating liquid based on a PVA / acrylic acid system, which, through the synergistic effect of chemical crosslinking and physical blending, results in a coating that exhibits excellent oxygen and water barrier properties in a dry state. However, the inherent drawback of this type of material is that its molecular structure contains a large number of hydrophilic hydroxyl groups, making it highly susceptible to moisture absorption and expansion under high humidity or high-temperature steam conditions, leading to a significant decrease in its barrier performance. To address this technical deficiency, Chinese invention patent application number 200610155089.4 discloses a method for preparing an ultra-high oxygen barrier retort-resistant composite film for packaging, which yields an ultra-high oxygen barrier retort-resistant film and improves the defect of decreased oxygen barrier performance of packaging materials in high humidity environments. However, this material relies on non-biodegradable materials such as ethylene-vinyl alcohol copolymer (EVOH) and polyvinylidene chloride (PVDC), as well as petroleum-based materials such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), making it difficult to meet the dual requirements of green environmental protection and high safety in the current high-end packaging field.

[0003] Meanwhile, as end-user applications increasingly demand adaptability to high-temperature sterilization (such as 121℃ moist heat sterilization), the structural stability and barrier performance retention of materials under high-temperature and high-humidity coupled environments are gradually becoming important indicators for evaluating their overall performance. Furthermore, high-performance packaging materials still require transparency for visual inspection, and these properties directly determine the safety and quality stability of the contents. However, in existing single-material systems, multiple properties such as barrier performance, environmental stability, and transparency impose differentiated and even mutually restrictive requirements on the internal structure of packaging materials, often resulting in inherent contradictions that are difficult to reconcile. For example, achieving high oxygen barrier properties usually relies on dense molecular chain stacking, high crystallinity, or the addition of barrier fillers, but this inevitably leads to light scattering, resulting in increased material haze and decreased transparency. At the same time, high oxygen barrier materials often rely on hydrogen bonds or dipole interactions between polar groups to form a dense network. These polar groups are also hydrophilic and easily adsorb water molecules in high temperature and high humidity environments, destroying the molecular network structure, causing molecular chain plasticization and increased free volume, which in turn leads to a sharp deterioration in barrier performance. In addition, hydrophobic modification or chemical cross-linking methods adopted to improve resistance to damp heat sterilization are prone to problems such as micro-phase separation and uneven cross-linking, ultimately degrading the optical transparency of the material. Therefore, in order to solve the above-mentioned defects, existing technologies usually adopt multi-layer material composite (such as Chinese invention patent CN1974206A), high-temperature curing (such as Chinese invention patent CN101608023A), and pre-coated primer (such as Chinese invention patent CN117777793A). This not only increases the difficulty of packaging material preparation, but also relies on petroleum-based materials, ignoring the needs of the food, pharmaceutical and medical device fields for green and environmentally friendly properties and safety of packaging materials.

[0004] Natural polysaccharides (such as chitosan, sodium alginate, and starch) have the advantages of being widely available, biodegradable, and having good film-forming properties. However, they have poor moisture barrier properties, low mechanical strength, and conventional chemical cross-linking can damage their biocompatibility. Therefore, how to achieve a synergistic improvement in barrier properties, moisture and heat resistance, and optical transparency while maintaining the green and biodegradable characteristics of natural polysaccharides has become a key technical problem that urgently needs to be solved in the field of high-performance green packaging materials. Summary of the Invention

[0005] To address the problems of existing packaging materials being generally non-degradable, highly dependent on petroleum-based resources, and the inability of existing single-material packaging systems to simultaneously achieve high transparency, high barrier properties, and high environmental stability, this invention proposes a high-barrier coating liquid, a packaging film, its preparation method, and its applications. The technical solution of this invention is as follows: A high-barrier coating liquid, by mass parts, comprises the following components: 1-10 parts of natural polysaccharide, 0.1-5 parts of polyvalent metal ion compound, 0.5-5 parts of bio-based plasticizer, and 80-100 parts of solvent; The natural polysaccharide is one or a combination of at least two of chitosan, carboxymethyl cellulose, and sodium alginate. The polyvalent metal ion compound is one or a combination of at least two of the following: a soluble salt of zinc, a soluble salt of calcium, or a soluble salt of iron. Furthermore, the zinc soluble salt is one or a combination of at least two of zinc lactate, zinc chloride, and zinc sulfate; the calcium soluble salt is one or a combination of at least two of calcium chloride, calcium lactate, and calcium gluconate; and the iron soluble salt is one or a combination of at least two of ferrous sulfate, ferric chloride, and ferrous lactate.

[0006] The bio-based plasticizer is one or a combination of at least two of glycerol, sorbitol, and citrate.

[0007] Furthermore, the molecular weight of the natural polysaccharide is 100,000 to 500,000; Furthermore, the molar ratio of the metal ions in the polyvalent metal ion compound to the coordinating groups in the natural polysaccharide is 1:2 to 1:10. Within this range, the polyvalent metal ion compound and the natural polysaccharide can form a continuous and dense coordination network. Below this range, a barrier layer cannot be formed, and above this range, phase separation occurs.

[0008] Furthermore, the coating liquid also contains 0.1 to 1 part of reinforcing agent by weight.

[0009] Further, the reinforcing agent is one or a combination of at least two of the following: nanocellulose, montmorillonite, nanosilica, starch nanocrystals, and gelatin. The nanocellulose is one or a combination of at least two of the following: cellulose nanocrystals and cellulose nanofibers, and the molecular formula of the nanocellulose is (C6H2O). 10 O5) n The nanocellulose is preferably selected from one or at least a combination of two of the following: sulfonated cellulose nanofiber dispersion (CNC-C04) and carboxymethylated cellulose nanofiber dry powder (C-CNC99) produced by Guilin Qihong Technology Co., Ltd.; carboxylated modified nanocellulose (TL-001), carboxylated nanocellulose crystals (TL-007), TEMPO oxidized nanocellulose (TL-015), and nanocellulose dry powder (TLP002) produced by Nanjing Tianlu Nanotechnology Co., Ltd.; anionic modified nanocellulose (NAT-4002) produced by Matexcel Corporation of the United States; or Chaobianli® nanocellulose produced by Jinan Shengquan Group Co., Ltd.

[0010] The solvent is deionized water or an aqueous solution of acetic acid.

[0011] A method for preparing the above-mentioned high-barrier coating liquid includes the following preparation steps: A bio-based plasticizer was added to a natural polysaccharide solution to obtain a polysaccharide solution; the polysaccharide solution was then mixed with an aqueous solution of a polyvalent metal ion compound and stirred to carry out a coordination crosslinking reaction to obtain a high-barrier coating solution.

[0012] Furthermore, the stirring temperature is 20~60℃, preferably 30~50℃; the stirring time is 10~60min, preferably 20~40min; and the solvent of the natural polysaccharide solution is deionized water or acetic acid aqueous solution.

[0013] A method for preparing a packaging film includes the following steps: applying the above-mentioned high-barrier coating liquid to the surface of a substrate layer, drying and curing to obtain a packaging film.

[0014] Furthermore, the substrate is any one of nylon 6 film, polyethylene terephthalate film, polypropylene film, and polylactic acid film; the thickness of the substrate layer is 15~30 μm; The drying and curing temperature is 50~90℃, preferably 70~90℃; the coating method is anilox roller coating, doctor blade coating, or spray coating; and the coating amount of the high-barrier coating liquid is 0.5~1 g / m³. 2 .

[0015] A packaging film prepared by the above-described preparation method.

[0016] One application of the above-mentioned packaging film is in the field of aseptic packaging for pharmaceuticals, food, or medical devices. In practical applications, such as in pharmaceutical packaging, the raw materials of the high-barrier coating liquid are preferably zinc lactate combined with chitosan, or calcium lactate combined with sodium alginate. This ensures that the anions are all of bio-based origin, maximally inhibits phase separation, provides mild reaction conditions, and guarantees a light transmittance greater than 90%, effectively improving the transparency and safety of the packaging film. In applications such as food packaging and aseptic packaging for medical devices, the preferred polyvalent metal ion compound is zinc chloride or calcium chloride. These metal ion compounds react quickly, form a dense network, and exhibit excellent barrier properties, significantly improving barrier efficiency and reducing costs, while also possessing excellent resistance to moist heat sterilization.

[0017] Compared with existing technologies, this invention solves the problems of existing packaging materials being generally non-degradable, highly dependent on petroleum-based resources, and the difficulty of existing single packaging material systems simultaneously achieving high transparency, high barrier properties, and high environmental stability. Specifically, the beneficial effects are as follows: 1. This invention utilizes a green and controllable metal coordination crosslinking strategy. By introducing multivalent metal ions to reversibly coordinate with functional groups on natural polysaccharide molecular chains, a three-dimensional crosslinked network structure (such as Zn) with dynamically tunable characteristics is constructed. 2+ Ca preferentially forms stable coordination bonds with amino ligands. 2+ It forms a multi-point complex structure with carboxylate groups. This network structure effectively fills the gaps between molecular chains, constructing a dense "gas barrier." While maintaining the flexibility of the packaging film, the oxygen permeability can be as low as 0.8 cm⁻¹. 3 / (m 2 (24h·0.1 MPa); Simultaneously, this cross-linked network structure reduces the exposure of hydrophilic groups, enhancing the moisture barrier properties of the packaging film, with a water vapor permeability as low as 18.5 g / (m²). 2 (24h) This invention solves the industry problem of performance degradation of natural polysaccharide materials under high humidity conditions. Furthermore, the packaging film provided by this invention effectively inhibits microscopic phase separation and interface scattering, resulting in a light transmittance greater than 90%. In extreme application environments, after 30 minutes of moist heat sterilization at 121℃, the barrier performance of the packaging material still maintains 92%, and the light transmittance maintains 98.7%. This indicates that the coordination network constructed in this invention still possesses excellent structural stability and performance retention under high temperature-high humidity coupling conditions. Simultaneously, the coordination bonds are dynamic and reversible weak interactions, which, while imparting high stability to the system, avoid the brittleness problems caused by traditional covalent cross-linking. This achieves a multifunctional synergistic unity of high transparency, high barrier performance, and high environmental stability, breaking through the long-standing performance coupling bottleneck of natural polysaccharide materials and providing an engineering-feasible material path for pharmaceutical and food packaging under high-temperature sterilization conditions.

[0018] 2. This invention utilizes all-natural polysaccharides, bio-based plasticizers, and biodegradable polymers (such as PLA and thermoplastic starch) to construct a fully bio-based material system. While ensuring synergistic optimization of barrier properties and mechanical properties, it achieves complete renewability of raw material sources and biodegradability of end-use materials, reducing dependence on petroleum-based resources and minimizing environmental burden from the source. Simultaneously, the multiple components form a stable composite structure through intermolecular forces, balancing film-forming properties and structural stability. Furthermore, this packaging film material contains no toxic or harmful residues, exhibits excellent biocompatibility and safety, better meets the stringent safety requirements of food packaging and medical aseptic packaging, and is conducive to satisfying increasingly stringent environmental regulations and sustainable development orientations.

[0019] 3. This invention employs a preparation process combining single-layer coating and all-aqueous phase processing. It achieves integrated construction of structure and function through one-step film formation, eliminating the need for complex steps such as multi-layer lamination, pre-coating with a primer, or high-temperature curing, significantly simplifying the process. Simultaneously, it avoids the use of organic solvents, reducing VOC emission risks and demonstrating excellent environmental friendliness. Regarding process conditions, this invention achieves film formation and structural fixation through low-temperature drying, effectively reducing energy consumption, minimizing the risk of thermal degradation, and significantly improving material performance stability. Furthermore, the process provided by this invention is less prone to interlayer delamination, bubbles, or interface defects, resulting in high product consistency and suitability for continuous, large-scale production. Thus, it achieves the construction of high-performance packaging materials while simultaneously considering industrial feasibility and economic efficiency. Attached Figure Description

[0020] Figure 1 The reaction principle diagram for preparing the high-barrier coating liquid in Example 1 is shown. Detailed Implementation

[0021] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as limiting the present invention.

[0022] Example 1. S1: By mass, dissolve 5 parts chitosan (molecular weight 200,000) in 90 parts of 1% acetic acid aqueous solution, add 2 parts glycerol and 0.3 parts nanocellulose (CNC-C04 purchased from Guilin Qihong Technology Co., Ltd.) to obtain a polysaccharide solution; dissolve 1.5 parts zinc lactate in 10 parts deionized water to obtain a zinc lactate aqueous solution; stir the polysaccharide solution and zinc lactate aqueous solution at 40℃ for 30 min to allow Zn to react. 2+ It undergoes a coordination complexation reaction with the amino coordinating groups in the chitosan repeating unit, wherein Zn 2+ A high-barrier coating solution was obtained by using a molar ratio of 1:5 between the amino coordinating groups in the chitosan and the coating solution.

[0023] S2: The high-barrier coating solution is applied to a 25 μm thick polylactic acid film at a coating weight of 0.8 g / m. 2 The film is dried and cured at 80°C to obtain the packaging film.

[0024] In this embodiment, such as Figure 1 The diagram shows the reaction principle of the high-barrier coating solution in Example 1. It can be seen from the diagram that the chitosan molecular chain is rich in primary amino (–NH2) and hydroxyl (–OH) groups containing lone pairs of electrons. The nitrogen atom in the amino group has a strong electron-donating ability and can act as a Lewis base to provide lone pairs of electrons to metal ions; while Zn... 2+As a typical Lewis acid, Zn has empty orbitals that can accept electron pairs, thus forming stable coordinate bonds between them. Through this electron pair donation and acceptance mechanism, Zn... 2+ It can undergo polydentate or bridging coordination with multiple amino coordination sites on adjacent or different molecular chains, thereby constructing cross-linking nodes between molecular chains and forming a continuous three-dimensional network structure. This coordination cross-linking can improve the bonding strength between packaging film molecular chains, restrict chain segment movement, and reduce free volume, thus effectively inhibiting the diffusion of gas and water molecules. At the same time, coordination bonds have stronger resistance to hydrolysis and thermal disturbance than hydrogen bonds, and can maintain structural stability under high temperature and high humidity conditions, which helps to achieve a synergistic improvement in mechanical properties, barrier properties, and environmental stability.

[0025] Example 2. S1: By mass, dissolve 3 parts sodium alginate in 90 parts deionized water, add 1.5 parts sorbitol to obtain a polysaccharide solution; dissolve 0.8 parts calcium chloride in 5 parts deionized water to obtain a calcium chloride aqueous solution; stir the polysaccharide solution and the calcium chloride aqueous solution at 40℃ for 30 min, so that Ca... 2+ It undergoes a coordination complexation reaction with the carboxylate group in the repeating unit of sodium alginate, wherein Ca 2+ The molar ratio of the sodium alginate to the carboxylate group is 1:2, a ratio that precisely satisfies the stoichiometric relationship of the sodium alginate "egg-box model" cross-linked structure. At this ratio, Ca... 2+ It can fully coordinate with the carboxylate group on the G unit to form a multi-point coordination network and construct a complete three-dimensional ionic cross-linking network. At the same time, it avoids micro-phase separation caused by excessive metal ions, thereby achieving synergistic optimization of mechanical properties, barrier properties and optical transparency, and obtaining a high-barrier coating liquid.

[0026] S2: The high-barrier coating liquid is applied to a 30 μm thick thermoplastic starch film at a coating weight of 0.8 g / m. 2 The film is dried and cured at 80°C to obtain the packaging film.

[0027] In this embodiment, Ca 2+ With the carboxylate group (–COO) in the sodium alginate molecular chain - The ionic crosslinking structure undergoes a coordination complexation reaction, forming multi-point coordination with the carboxyl oxygen atoms on adjacent guluronic acid (G unit) segments to construct a typical "egg-box model" structure. This creates bridging and crosslinking nodes between different molecular chains, resulting in a continuous three-dimensional network structure. This coordination crosslinking structure enhances the bonding strength between molecular chains, reduces the free volume of the system, and extends the diffusion path of gas and water molecules, thereby maintaining the stability of this ionic crosslinking structure in an aqueous environment and suppressing structural relaxation caused by water absorption and swelling.

[0028] Example 3. S1: By mass, add 3 parts sodium alginate to 90 parts deionized water while stirring to prevent clumping. Stir at 55℃ for 60 min until the sodium alginate is completely dissolved, forming a transparent, viscous solution. Add 1.5 parts sorbitol and 0.2 parts nano-silica, and continue stirring for 30 min to ensure uniform dispersion of the bio-based plasticizer and reinforcing agent. Cool to room temperature and filter through a 200-mesh filter to remove undissolved matter and impurities, obtaining a sodium alginate composite solution. Dissolve 0.6 parts ferric chloride (FeCl3·6H2O) in 5 parts deionized water and stir at room temperature for 10 min until completely dissolved, obtaining a ferric chloride aqueous solution. Under 38℃ water bath conditions, place the sodium alginate composite solution in a stirrer and stir at 400 rpm. Slowly add the ferric chloride aqueous solution dropwise to the sodium alginate solution through a constant pressure dropping funnel, controlling the dropping rate at 2.5 rpm. The solution was added at a rate of mL / min. During the addition, the solution gradually changed from colorless and transparent to light yellowish-brown, and the viscosity gradually increased. After the addition was complete, stirring was continued at 40℃ for 40 min to allow the Fe... 3+ It undergoes a full coordination complexation reaction with the carboxyl group on the sodium alginate molecular chain, wherein Fe 3+ The molar ratio of the carboxylate group to the carboxylate group is 1:6.8. After the reaction is completed, the mixture is allowed to stand for 15 min to remove bubbles, resulting in a uniform and stable high-barrier coating solution.

[0029] S2: The high-barrier coating liquid is applied to a 30 μm thick thermoplastic starch film at a coating weight of 0.8 g / m. 2 The film is dried and cured at 80℃ to obtain a light yellowish-brown packaging film.

[0030] In this embodiment, Fe is introduced. 3+ Not only with the carboxylate group (–COO) on the sodium alginate molecular chain - It undergoes coordination complexation to form a stable cross-linked structure, and simultaneously serves as an environmentally responsive color-changing functional center embedded in the system. Its color-changing nature originates from Fe. 3+ In different coordination environments (such as H2O, –OH, –NH2, –COO) - Differences in dd transitions caused by changes in ligand field strength, and Fe 3+ / Fe 2+ The reversible redox transition between these states. Under conditions of -20 to 50°C and 20% to 70% relative humidity, the packaging film is light yellowish-brown; under high-temperature sterilization conditions (moist heat sterilization at 121°C under saturated steam for 30 min), Fe... 3+ From the original Fe 3+ –H2O / –COO - Coordination towards Fe 3+–OH / –NH2 coordination reconstruction, the color changes from light yellowish-brown to dark yellowish-brown, indicating that the sterilization process is complete; in a high-humidity environment (relative humidity ≥90%, room temperature or high temperature), Fe 3+ Hydrolysis occurs to form Fe(OH)3 colloid, and the color changes from light yellowish-brown to orange-yellow. This color change indicates that the packaging film has been exposed to a high-humidity environment. When the color of the packaging film changes from yellowish-brown to light green or colorless, it proves that Fe... 3+ Reduced to Fe 2+ This indicates that the packaging film material has come into contact with a reducing agent, resulting in leakage of the packaging film or oxidation of the contents; under acidic conditions (pH ≤ 4.0), –COO - Protonation to –COOH leads to a decrease in coordination ability, Fe 3+ As the coordination environment weakens, the color changes from yellowish-brown to pale yellow, indicating that the contents inside the packaging film have deteriorated. Thus, the packaging film provided in this embodiment achieves a visual response to changes in temperature, humidity, reducing properties, and pH.

[0031] Example 4. The difference between this embodiment and Embodiment 1 is that the coating amount of the high-barrier coating liquid on the thermoplastic starch film is 0.4 g / m². 2 The remaining preparation steps and conditions are the same as in Example 1, and a packaging film is prepared.

[0032] Example 5. The difference between this embodiment and Embodiment 1 is that the coating amount of the high-barrier coating liquid on the thermoplastic starch film is 1.5 g / m². 2 The film was pre-dried at 60°C for 5 min and then dried at 85°C for 10 min. The remaining preparation steps and conditions were the same as in Example 1, and the packaging film was prepared.

[0033] Comparative Example 1. The difference between this comparative example and Example 1 is that only chitosan acetate aqueous solution is coated on the polylactic acid film, while the rest of the preparation steps and conditions are the same as in Example 1, resulting in a packaging film.

[0034] Comparative Example 2. The difference between this comparative example and Example 2 is that only sodium alginate acetic acid aqueous solution is coated on the thermoplastic starch film, while the rest of the preparation steps and conditions are the same as in Example 2, resulting in a packaging film.

[0035] Comparative Example 3. S1: By mass fraction, slowly add 10 parts of PVA (degree of alcoholysis 98-99%, degree of polymerization 1700-1800) to 90 parts of deionized water, stirring while heating to 95°C. Maintain this temperature at 95°C and stir for 90 minutes until the PVA is completely dissolved, obtaining a 10% PVA aqueous solution. After cooling to room temperature, filter through a 200-mesh filter to remove insoluble matter, allow to stand to remove bubbles, and obtain the PVA coating solution.

[0036] S2: Apply the PVA coating solution to a 25 μm thick polylactic acid film with a coating amount of 0.8 g / m. 2 The film is dried and cured at 80°C to obtain the packaging film.

[0037] (a) Mechanical property testing: The packaging films prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to mechanical property tests according to GB / T 1040.3-2006 standard. The test temperature was 23℃, the relative humidity was 50%, and the tensile speed was 50 mm / min. Each sample was tested in parallel five times, and the average value was taken. The test results are shown in Table 1 below. As can be seen from the table, the tensile strengths of Examples 1-3 were 42.5 MPa, 38.2 MPa, and 43.5 MPa, respectively, and the elongation at break were 18.5%, 22.3%, and 15.5%, respectively. Compared with Comparative Examples 1 and 2, which did not introduce metal ions, the tensile strength increased by as much as 184%, and the elongation at break increased by as much as 165%. This shows that after introducing metal ions into the polysaccharide molecular chain, the present invention constructs stable physical-chemical synergistic cross-linking nodes between molecules through coordination, thereby forming a dense and continuous three-dimensional network structure. This structure effectively restricts the slippage and untangling of molecular chains under external forces, improving the material's load-bearing capacity. Simultaneously, the coordination bonds, as reversible dynamic interaction points, can undergo a certain degree of breakage and recombination during stress, thus imparting a certain degree of toughness to the system while maintaining high strength, achieving synergistic optimization between strength and ductility. Furthermore, the tensile strengths of Examples 4 and 5 are 32.5 MPa and 48.2 MPa, respectively, and the elongation at break are 14.2% and 16.8%, respectively. Compared to Example 1, Example 4 suffers from reduced coating liquid dosage, resulting in insufficient coating continuity and interfacial bonding, leading to a decrease in overall mechanical properties. While Example 5 enhances material rigidity by increasing coating amount, it simultaneously suppresses ductility and reduces flexibility. This demonstrates that Example 1 of the present invention achieves an effective balance between material strength and ductility, resulting in packaging materials with superior comprehensive mechanical properties.

[0038] Based on this, to further evaluate the structural stability of the packaging film under extreme application environments, packaging films prepared in Examples 1-2 and Comparative Examples 1-2 were sterilized in an autoclave for 30 min under saturated steam (121℃±1℃, gauge pressure 0.105~0.125 MPa, relative humidity 100%). After high-pressure steam moist heat sterilization, the samples were removed after the autoclave cooled naturally to below 40℃ and placed in a constant temperature and humidity chamber (23℃±2℃, relative humidity 50%±5%) for equilibration for 24 h. Subsequently, mechanical property tests were conducted using the same methods as described above, and the results are also listed in Table 1. As can be seen from the table, the packaging film prepared in Example 1 retained a tensile strength of up to 92.5% after moist heat sterilization, while the tensile strength of the packaging film prepared in Comparative Example 1 was only 43.5% of that before moist heat sterilization. This demonstrates that packaging films without a coordination crosslinking structure are prone to structural degradation in high-temperature (121°C) and high-humidity (100% RH) environments, including molecular chain relaxation, hydrogen bond network disruption, and water absorption swelling, leading to a significant decrease in mechanical properties. In contrast, this invention utilizes a coordination crosslinking network constructed between metal ions and polysaccharide molecules. This multi-point coordination significantly enhances the bonding strength between molecular chains and suppresses the weakening effect of water molecules on the internal forces of the system. This network structure exhibits higher structural stability and resistance to environmental disturbances under humid and hot conditions, effectively preventing irreversible damage to the material structure. This synergistic improvement in high strength, high toughness, and high stability effectively addresses the technical deficiency of insufficient stability in polysaccharide-based materials under high-temperature and high-humidity conditions.

[0039] Table 1

[0040] (II) Barrier performance test: The oxygen permeability of the packaging films prepared in Examples 1-5 and Comparative Examples 1-3 was tested using a differential pressure gas permeameter according to GB / T 1038-2000 standard. The test conditions were 23℃, and the tests were conducted at 0% relative humidity (dry state) and 90% relative humidity (wet state), respectively. Simultaneously, each group of samples was placed in an autoclave and sterilized at 121℃ for 30 min. The oxygen permeability in the dry state was then tested again to evaluate its barrier stability under high temperature and high humidity conditions. The water vapor permeability of the packaging films was tested using the gravimetric method according to GB / T1037-2021 standard, under the conditions of 38℃ and 90% relative humidity. The test results are shown in Table 2 below. As can be seen from the table, the oxygen permeability of the packaging film prepared in Example 1 under dry conditions was 0.8 cm⁻¹. 3 / (m 2 (24h·0.1 MPa), reaching the ultra-high barrier level (≤1.0 cm). 3 / (m 2(24h, 0.1 MPa); Under 90% high humidity conditions, the oxygen permeability only increased to 1.1 cm. 3 / (m 2 The increase in pressure (0.1 MPa over 24 hours) was relatively small, indicating that the material can maintain a low gas permeation flux even in high humidity environments, demonstrating good resistance to moisture sensitivity. After 30 minutes of moist heat sterilization at 121°C, the oxygen barrier performance retention rate of the packaging film provided in Example 1 was 88.9%, and the water vapor barrier performance retention rate was 92.0%, indicating that the material can still maintain a high level of barrier capability under high temperature and high humidity coupled environments. In contrast, the packaging film prepared in Comparative Example 1 only retained 33.6% of its oxygen barrier performance after moist heat sterilization at 121°C, showing serious performance degradation; the commercially available PVA coated packaging film provided in Comparative Example 3 also showed a significant decrease in barrier performance after sterilization, with a retention rate of only 31.5%, indicating that the traditional structure mainly based on hydrogen bonding is easily damaged under high humidity and heat conditions, making it difficult to meet the requirements of high-end packaging applications. The coordination crosslinking network constructed in this invention achieves a synergistic improvement in barrier performance and environmental stability, and has significant advantages in engineering applications.

[0041] Table 2

[0042] (III) Optical performance testing: The packaging films prepared in Examples 1-5 and Comparative Examples 1-2 were tested for optical performance using a transmittance / haze meter according to GB / T 2410-2008 standard. The test wavelength was set to 550 nm and the test temperature to 23℃. Each sample was tested in parallel five times, and the average value was taken. The test results are shown in Table 3 below. As can be seen from the table, the transmittance of the packaging film prepared in Example 1 reached 92.3%, and the haze was 3.8%; the transmittance of Example 4 reached 93.5%, and the haze was 2.8%. Compared with Comparative Examples 1 and 2 without the addition of metal ions, the transmittance remained basically unchanged, and the haze did not increase significantly or even showed a decreasing trend. This indicates that the introduction of metal ions in this invention did not adversely affect the optical uniformity of the material. This shows that the coordination crosslinking strategy of introducing metal ions and polysaccharide molecules in this invention enhances mechanical properties and barrier properties while better maintaining the optical transparency of the film, effectively avoiding the problem that mechanical properties and transparency cannot be simultaneously coordinated in traditional filler-reinforced or phase-separation modified packaging film materials.

[0043] Furthermore, after being sterilized at 121°C for 30 min, the packaging film prepared in Example 1 still maintained a light transmittance of 98.7%, which was much higher than the 94.8% of Comparative Example 1. This further confirms the excellent resistance to damp heat of the coordination crosslinking network. In particular, it can maintain a light transmittance level close to the initial state even under harsh conditions such as sterilization at 121°C. This ensures that the packaging material has both functionality and appearance performance in practical applications, demonstrating the comprehensive technical advantages of multi-performance synergistic optimization.

[0044] Table 3

[0045] In summary, this invention utilizes all-natural polysaccharides, bio-based plasticizers, and biodegradable polymers to construct a fully bio-based material system, achieving complete renewability of raw material sources and biodegradability of end-use materials. By introducing multivalent metal ions and reversibly coordinating with functional groups on the natural polysaccharide molecular chains, a three-dimensional cross-linked network structure with dynamically tunable characteristics is constructed. This significantly improves the oxygen and moisture barrier properties of the packaging film, achieving an oxygen permeability as low as 0.8 cm⁻¹. 3 / (m 2 (24h·0.1 MPa), water vapor transmission rate as low as 18.5 g / (m²) 2 This invention (24h) solves the industry problem of performance degradation of natural polysaccharide materials under high humidity environments. Furthermore, after 30 minutes of moist heat sterilization at 121℃, the barrier properties of the packaging material still retain 92%, and the light transmittance retains 98.7%. This invention achieves a multi-functional synergistic unity of high transparency, high barrier properties, and high environmental stability. In addition, this invention employs a preparation process combining single-layer coating and all-aqueous phase processing, significantly simplifying the process flow; film formation and structural fixation can be completed through low-temperature drying, effectively reducing energy consumption, minimizing the risk of thermal degradation, and significantly improving material performance stability. This provides an engineering-feasible material path for pharmaceutical and food packaging under high-temperature sterilization conditions.

[0046] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-barrier coating liquid, characterized in that, By mass, it includes the following components: 1-10 parts of natural polysaccharide, 0.1-5 parts of polyvalent metal ion compound, 0.5-5 parts of bio-based plasticizer, and 80-100 parts of solvent; The natural polysaccharide is one or a combination of at least two of chitosan, carboxymethyl cellulose, and sodium alginate. The polyvalent metal ion compound is one or a combination of at least two of the following: a soluble salt of zinc, a soluble salt of calcium, or a soluble salt of iron. The bio-based plasticizer is one or a combination of at least two of glycerol, sorbitol, and citrate.

2. The high-barrier coating liquid according to claim 1, characterized in that, The molecular weight of the natural polysaccharide is 100,000 to 500,000; the molar ratio of the metal ion in the polyvalent metal ion compound to the coordinating group in the natural polysaccharide is 1:2 to 1:

10.

3. The high-barrier coating liquid according to claim 1, characterized in that, The coating liquid further contains 0.1 to 1 part of reinforcing agent by weight; the solvent is deionized water or an aqueous acetic acid solution.

4. The high-barrier coating liquid according to claim 3, characterized in that, The reinforcing agent is one or a combination of at least two of the following: nanocellulose, montmorillonite, nanosilica, starch nanocrystals, and gelatin.

5. A method for preparing a high-barrier coating liquid as described in any one of claims 1-4, characterized in that, The preparation steps include the following: A bio-based plasticizer was added to a natural polysaccharide solution to obtain a polysaccharide solution; the polysaccharide solution was then mixed with an aqueous solution of a polyvalent metal ion compound and stirred to carry out a coordination crosslinking reaction to obtain a high-barrier coating solution.

6. The method for preparing the high-barrier coating liquid according to claim 5, characterized in that, The stirring temperature is 20~60℃; the stirring time is 10~60 min; the solvent of the natural polysaccharide solution is deionized water or acetic acid aqueous solution.

7. A method for preparing a packaging film, characterized in that, The process includes the following steps: applying the high-barrier coating liquid of any one of claims 1-4 or the high-barrier coating liquid prepared by the preparation method of any one of claims 5-6 onto the surface of a substrate layer, drying and curing to obtain a packaging film.

8. The method for preparing the packaging film according to claim 7, characterized in that, The substrate is any one of nylon 6 film, polyethylene terephthalate film, polypropylene film, and polylactic acid film; the thickness of the substrate layer is 15~30 μm; the drying and curing temperature is 50~90℃; the coating method is anilox roller coating, doctor blade coating, or spray coating; the coating amount of the high-barrier coating liquid is 0.5~1 g / m³. 2 .

9. A packaging film, characterized in that, It is prepared by the preparation method according to any one of claims 7-8.

10. An application of the packaging film as described in claim 9, characterized in that, It is used in the field of aseptic packaging for pharmaceuticals, food, or medical devices.

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