An aluminum-foil-free recyclable ultra-high barrier paper-based composite packaging material and a solvent-free composite preparation method thereof

Abstract

This invention discloses a foil-free, recyclable, ultra-high barrier paper-based composite packaging material and its solvent-free composite preparation method, belonging to the field of non-carbonated liquid food packaging technology. The packaging material includes a first polyolefin film layer, a printing ink layer, a paper substrate layer, a second polyolefin film layer, and a high-barrier composite film layer. The high-barrier composite film layer consists of a PET substrate film and a nanocomposite coating coated on its inner side. The nanocomposite coating uses nanocellulose as the film-forming matrix and is compounded with montmorillonite, chitosan, nano-silica, and other components. The preparation method employs a solvent-free composite process, including color printing, creasing and perforation, high-barrier film preparation, composite, and curing steps. This invention completely eliminates aluminum foil, achieves a paper fiber recycling rate of ≥90%, maintains stable barrier performance, has low production costs, and emits no VOCs, making it suitable for long-shelf-life packaging of liquid foods such as milk and juice.

Description

Technical Field

[0001] This invention belongs to the field of non-carbonated liquid food packaging technology, specifically relating to a paper-based composite packaging material that is aluminum foil-free, possesses ultra-high oxygen and water vapor barrier properties, and is fully recyclable, as well as its preparation method using a solvent-free lamination process. This packaging material is suitable for long-shelf-life packaging of liquid foods such as milk, juice, tea, and plant-based protein beverages, and can replace traditional non-recyclable paper-based composite packaging containing aluminum foil. Background Technology

[0002] Currently, in the long shelf-life (6-12 months) packaging market for non-carbonated liquid foods, Tetra Pak and Combibloc aluminum foil-based composite packaging dominate the market. The core barrier layer is 6-9μm aluminum foil, which provides excellent oxygen and water vapor barrier properties, thereby ensuring the product's shelf life.

[0003] However, with the tightening of global environmental policies and the implementation of the "dual-carbon" strategy, the recyclability of packaging materials has become a core requirement of the industry. Solvent-free lamination processes, due to their advantages of no VOC emissions and energy efficiency, have been gradually applied in the packaging lamination field. However, in the current technology, there are no successful reports of combining solvent-free lamination processes with specific high-barrier nano-coatings to prepare aluminum foil-free, recyclable, high-barrier paper-based composite packaging materials.

[0004] Existing technologies have the following drawbacks: 1. Poor recyclability: In traditional aluminum foil packaging, aluminum foil is tightly bonded to plastic and paper fibers through a composite process. Existing hydrodynamic pulping processes cannot effectively separate aluminum foil, and broken aluminum flakes contaminate the pulp and clog equipment, making it impossible to recycle the entire package and resulting in resource waste. 2. Insufficient performance of aluminum foil-free alternatives: Existing aluminum foil-free solutions in the industry all have significant defects and cannot simultaneously meet the requirements of high barrier properties, high humidity stability, environmental protection, and low cost. EVOH coatings are highly humidity-sensitive, and their barrier performance deteriorates significantly in high humidity environments. Liquid food packaging environments are high in humidity, making it impossible to effectively inhibit food oxidation. PVDC coatings contain chlorine, which can easily generate harmful substances during recycling, making environmentally friendly recycling impossible and posing a risk of secondary pollution. The production cost of silicon oxide / aluminum film is extremely high, more than 30% higher than traditional aluminum foil packaging, and the coating is brittle and prone to pinholes, making it unsuitable for large-scale industrial application. Single nanocellulose coatings have extremely poor water vapor barrier properties and cannot meet the core requirements of liquid food for water vapor barrier. 3. High production costs and low efficiency: Traditional aluminum foil packaging often uses dry lamination processes, which result in VOC emissions, high energy consumption, and low efficiency. Existing aluminum foil-free alternatives (such as silicon oxide / aluminum plating) are expensive or require additional complex coating processes, further increasing production costs and making large-scale promotion difficult.

[0005] This invention aims to overcome the aforementioned shortcomings and achieve a breakthrough in "aluminum foil-free, high-barrier, recyclable, and low-cost" solutions. This invention eliminates aluminum foil and designs a layered structure that can be recycled as a whole, achieving a paper fiber recycling rate of ≥90% and allowing for the separation and recycling of plastic components. Furthermore, a novel high-barrier nanocomposite coating is developed to address the problem of unstable barrier performance under high humidity in existing solutions, achieving an OTR ≤ 1.5 cm. 3 / (m 2 ·d) WVTR ≤ 1.5 g / (m 2 •d) This process meets the requirement of a shelf life of 6 to 12 months. The present invention employs a solvent-free lamination process, which reduces energy consumption by more than 70% and adhesive usage by more than 50% compared to dry lamination, resulting in an overall production cost reduction of 15 to 25%, enabling industrial-scale production. Summary of the Invention

[0006] This invention provides a foil-free, recyclable, ultra-high barrier paper-based composite packaging material. It eliminates aluminum foil and uses a "nanocomposite coating + PET substrate film" to form a high barrier composite film layer, which is combined with PE film and paper substrate. The layers are tightly bonded through a solvent-free lamination process.

[0007] The packaging material comprises, from the outside in, the following layers: a first polyolefin film layer, a printing ink layer, a paper substrate layer, a high-barrier composite film layer, and a second polyolefin film layer. The high-barrier composite film layer consists of a PET substrate film and a nanocomposite coating applied to its inner side (facing the food). This coating uses nanocellulose as the film-forming matrix, combined with montmorillonite, chitosan, and nano-silica to form a dense structure, achieving ultra-high barrier properties. The layers are bonded together using a solvent-free lamination process, resulting in zero VOC emissions.

[0008] This invention also provides a solvent-free composite preparation method for the packaging material, the process of which includes: color printing, embossing and perforation → preparation of high-barrier film → lamination of high-barrier film and PE film → three-in-one lamination → curing → slitting → packaging.

[0009] The specific preparation method of solvent-free aluminum foil-free recyclable ultra-high barrier paper-based composite packaging material is as follows: Step 1: Color printing and creasing / perforation. Select paper substrate that meets the specifications, and first perform corona treatment on its surface to ensure a surface tension ≥ 42 dynes, improving ink adhesion. Use recyclable water-based ink and print product information on the paper substrate surface using flexographic or gravure printing methods. Creasing and perforation are performed simultaneously during the printing process. The creasing depth is controlled to 30%–70% of the paper thickness to facilitate subsequent packaging (such as folding boxes). The perforation density is 1–3 holes / cm². 2 The aperture is 0.5-1mm, used for packaging venting; the linear speed of the entire process is controlled at 50-250 m / min to ensure the consistency and stability of printing, creasing, and punching.

[0010] Step 2: Prepare a high-barrier composite membrane. ① Coating: Select a PET substrate film that meets the specifications, and perform corona treatment on its inner side (towards the food) to ensure that the surface tension is ≥45 dynes and improve the coating adhesion; use a gravure coating machine to coat the prepared high barrier coating liquid onto the inner side of the PET substrate film, and control the dry film thickness to 5-15μm, preferably 8-12μm.

[0011] ②Drying: The coated PET / coated film is sent to a segmented drying equipment. It is first pre-dried at 80-90℃ for 1-2 minutes to remove some of the moisture in the coating, and then finally dried at 100-120℃ for 2-3 minutes until the moisture content of the coating is ≤0.5%. In some embodiments, after drying, the coating undergoes a slow in-situ mineralization reaction at room temperature to generate n-HA.

[0012] ③ Solvent-free lamination: Using a solvent-free laminator, the dried high-barrier film (PET / coating) is laminated with the second polyolefin film layer, ensuring that the coating side faces the PE film; a 100% solids content two-component solvent-free polyurethane adhesive is selected, and the adhesive application rate is controlled at 1.5–4 g / m². 2 The lamination line speed is 150~300 m / min, and the lamination pressure is 0.4~0.6 MPa, so that the PET / coated film and the PE film are tightly bonded to obtain a "high barrier film (PET / coated) / PE film" double-layer composite film for later use.

[0013] Step 3: Three-in-one solvent-free composite A solventless laminating machine is used to laminate the first polyolefin film layer, the paper substrate treated in step 1, and the high-barrier composite film obtained in step 2 (with the uncoated side of the PET film facing the paper substrate) in a single operation. The lamination sequence from the outside to the inside is: first PE film layer → printing ink layer → paper substrate layer → high-barrier composite film layer (PET / coated) → second PE film layer. The lamination line speed is controlled at 150–250 m / min, the lamination pressure at 0.5–0.7 MPa, and the adhesive application rate at 1.5–3 g / m. 2 This ensures that each layer is tightly bonded, without any defects such as delamination or bubbles.

[0014] Step 4: Mature The composite packaging material is placed in a curing chamber and left to stand for 24 to 72 hours at 40 to 60°C and ≤50% humidity to allow the solvent-free adhesive to fully crosslink and cure, ensuring an interlayer peel strength ≥1.5 N / 15 mm. In some embodiments, the curing process can further stabilize n-HA and strengthen the coating structure.

[0015] Step 5: Slitting, Inspection, and Packaging According to actual packaging needs, the cured packaging materials are cut into corresponding specifications; the cut products undergo full performance testing, including OTR, WVTR, paper fiber recovery rate, interlayer peel strength, solvent residue and other indicators; after passing the tests, they are packaged and shipped out.

[0016] The solvent-free lamination process described above has the following advantages: First, it is environmentally friendly, with no VOC emissions and no solvent residue, avoiding environmental pollution and human health hazards caused by solvents, and complying with food contact safety standards and global environmental policies. Second, it is energy-efficient and highly effective, eliminating the need for solvent drying tunnels. Factory verification shows that energy consumption is reduced by approximately 70% compared to traditional dry lamination; production efficiency is significantly improved, with linear speeds reaching 300 m / min, far exceeding traditional dry lamination processes (≤150 m / min), making it suitable for large-scale industrial production. Third, it offers significant cost advantages, with solvent-free adhesive application amounts only 30-50% of those in dry lamination, and no additional solvent recovery process required. Calculations show that the overall production cost is 15-25% lower than traditional aluminum foil packaging and more than 30% lower than existing aluminum foil-free alternatives (such as silicon oxide / aluminum plating), facilitating large-scale promotion. Fourth, it has high bonding strength. The adhesive layer formed after the solvent-free adhesive is cured is dense and firm, with an interlayer peel strength of ≥1.5 N / 15mm. This avoids delamination of packaging materials during processing, transportation, and use, and ensures the overall stability of the packaging performance.

[0017] The beneficial effects of this invention include: 1. Excellent recyclability: Utilizing a fully recyclable material system with good compatibility among layers, the paper fiber recycling rate can reach ≥90% through a hydrodynamic pulping process. The separated PE and PET films can be recycled as low-grade plastics, achieving closed-loop recycling of packaging materials and solving the pain points of traditional aluminum foil packaging being non-recyclable and polluting the environment. 2. Ultra-high and stable barrier performance: The high-barrier composite film layer effectively extends the permeation path of gases and water vapor, while strengthening water resistance through cross-linking reactions, meeting the 6-12 month shelf-life requirements of liquid foods. The in-situ generated n-HA further enhances the coating's density and toughness, ensuring performance degradation of ≤8% under high humidity conditions, while preventing coating brittleness. 3. Significant cost and environmental advantages: Production costs are reduced by 15-25% compared to traditional aluminum foil packaging and by more than 30% compared to aluminum foil-free solutions with silicon oxide / aluminum plating. It is chlorine-free, VOCs-free, and solvent-free, making it green and environmentally friendly, complying with food contact safety standards and global environmental policies, and enhancing product market competitiveness. 4. Excellent processing performance and application range: It is compatible with existing paper-based packaging production lines, with simple and efficient processes and high production efficiency; the packaging material has good mechanical strength, stiffness and forming performance, and can be used for packaging various non-carbonated liquid foods such as milk, juice, tea, and plant protein beverages, with a wide range of applications; it improves coating toughness, reduces the risk of coating cracking during processing, and improves product qualification rate. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the layered structure of the packaging material of the present invention.

[0019] Figure 2 This is a process flow diagram of the solvent-free composite preparation method of the present invention.

[0020] Explanation of reference numerals in the attached figures: 1—First polyolefin film layer; 2—Printing ink layer; 3—Paper substrate layer; 4—PET substrate film / nanocomposite coating; 5—Second polyolefin film layer. Detailed Implementation

[0021] In this invention, a foil-free, recyclable, ultra-high barrier paper-based composite packaging material is proposed. Instead of aluminum foil, it uses a "nanocomposite coating + PET substrate film" to form a high barrier composite film layer, and combines it with a PE film and a paper substrate. The layers are tightly bonded through a solvent-free lamination process.

[0022] The packaging material, from the outside in, includes: a first polyolefin film layer / a printing ink layer / a paper substrate layer / a high-barrier composite film layer / a second polyolefin film layer, such as... Figure 1 As shown, the high-barrier composite film consists of a PET substrate film and a nanocomposite coating applied to its inner side (facing the food). This coating uses nanocellulose as the film-forming matrix, combined with montmorillonite, chitosan, and nano-silica to form a dense structure, achieving ultra-high barrier properties. The layers are bonded together using a solvent-free lamination process, resulting in zero VOC emissions.

[0023] This invention also provides a solvent-free composite preparation method for the packaging material, the process of which includes: color printing, embossing and perforation → high-barrier film preparation → high-barrier film and PE film lamination → three-in-one lamination → curing → slitting → packaging, as follows. Figure 2 As shown.

[0024] In the above-mentioned scheme, the present invention further adds trace amounts of sodium dihydrogen phosphate and calcium chloride to the nanocomposite coating system. After coating, the system reacts slowly at room temperature to generate n-HA (nano-hydroxyapatite) in situ. The particle size is controlled at 20-50 nm, which further fills the pores of the coating, strengthens its density, improves the mechanical properties of the coating, avoids the coating from cracking, and does not affect the recyclability of the material.

[0025] The specific formulation (by weight) of the high-barrier nanocomposite coating of the present invention and the function of each component are as follows: 100 parts by weight of nanocellulose, selected from cellulose nanofibers (CNF) or nanocrystals (CNC), with a diameter of 5-20 nm and an aspect ratio >100, can form a continuous and dense film structure as a film-forming matrix, and has good compatibility with paper / PET, ensuring the recyclability of the material.

[0026] The montmorillonite, 30-50 parts by weight, is sodium-based montmorillonite with an interlayer spacing of 1-2 nm and an aggregate particle size of ≤5 μm. Its lamellar structure can form a labyrinth effect, prolonging the gas permeation path and significantly improving the barrier performance of the coating.

[0027] Chitosan, with a weight of 5-15 parts, a degree of deacetylation ≥85%, and a viscosity of 100-300 mPa·s in a certain solvent, can improve the film-forming properties and flexibility of the coating, prevent the coating from cracking, and at the same time, work synergistically with nanocellulose and montmorillonite to construct a dense structure.

[0028] 10-20 parts by weight of nano-silica, with a particle size of 10-30 nm and a specific surface area ≥200 m² / g, can fill the tiny pores inside the coating, increase the coating density, and reduce the permeation channels of gas and water vapor.

[0029] The crosslinking agent, 1-5 parts by weight, can be glutaraldehyde or water-based epoxy resin, which can cause crosslinking reaction of each component of the coating to form a three-dimensional network structure, improve the water resistance and mechanical strength of the coating, and reduce the performance degradation under high humidity environment.

[0030] The wetting agent, consisting of 0.5 to 2 parts by weight, is a polyether-modified siloxane with a surface tension ≤30 mN / m. It can improve the wettability of the coating liquid on the PET film surface, ensure uniform coating, and avoid defects such as pinholes and missed coating.

[0031] 400–700 parts by weight of deionized water with a conductivity ≤10 μS / cm is used as the dispersion medium to ensure uniform dispersion of all components, forming a stable coating liquid without harmful impurities, and meeting food contact safety requirements.

[0032] Sodium dihydrogen phosphate (0.5–1.5 parts by weight) and calcium chloride (0.8–2.0 parts by weight), both of analytical grade and with a particle size ≤10 μm, react slowly at room temperature after coating to generate n-HA (particle size 20–50 nm) in situ, filling the micropores of the coating, strengthening its density, and improving its toughness to prevent brittleness.

[0033] Preparation method of high-barrier coating liquid: Deionized water is added to a high-speed disperser, followed by nano-cellulose, montmorillonite, and nano-silica in sequence. The speed is adjusted to 2000-5000 rpm, and the mixture is dispersed for 30-60 minutes to ensure uniform dispersion of each component. Then, pre-prepared chitosan, crosslinking agent, and wetting agent are added, and dispersion continues for 10-20 minutes. Finally, the mixture is allowed to stand for 15-30 minutes to degas, resulting in a uniform, bubble-free coating liquid for later use. Alternatively, in some embodiments, after adding chitosan, crosslinking agent, and wetting agent in the above preparation process, some water is slightly evaporated, and sodium dihydrogen phosphate solution and calcium chloride solution are added in sequence, followed by dispersion for 2-10 minutes.

[0034] Coating process parameters: Gravure coating is used, and the dry film thickness of the coating is controlled to be 5-15 μm, with the optimal value being 8-12 μm; a segmented drying process is adopted, first pre-drying at 80-90℃ for 1-2 minutes to remove some moisture from the coating, and then final drying at 100-120℃ for 2-3 minutes to ensure that the moisture content of the coating is ≤0.5%. After drying, a dense structure can be formed. Alternatively, in some embodiments, an in-situ mineralization reaction can slowly occur at room temperature after coating, and n-HA is generated in situ after drying.

[0035] The first polyolefin film layer (outer layer) is made of LDPE or LLDPE with a density of 0.91–0.93 g / cm³. 3 With a thickness of 10–30 μm, it adopts a solvent-free lamination method. Its main function is to protect the printed layer, provide good abrasion resistance and surface smoothness, facilitate subsequent packaging and molding, and ensure overall recyclability.

[0036] The printing ink layer uses recyclable water-based ink with a thickness of <5μm. It is printed using flexographic or gravure printing methods and is used to provide relevant information such as product name, specifications, and production date. The water-based ink has no solvent residue, is recyclable, and does not affect the overall recyclability of the packaging.

[0037] The paper substrate layer is made of bamboo pulp paper or recycled paper with a basis weight of 80-350 g / m². The thickness corresponds to the basis weight and no additional composite treatment is required. Its main function is to provide mechanical strength and stiffness to the packaging material and support the overall structure. Bamboo pulp paper / recycled paper is environmentally friendly and recyclable, which is in line with the "dual carbon" strategy. It also has good compatibility with nanocellulose coating and improves recycling efficiency.

[0038] The second polyolefin membrane layer has the same material and specifications as the first polyolefin membrane layer, with a thickness of 10-30μm. It adopts a solvent-free composite method to achieve tight bonding between the paper substrate layer and the high-barrier composite membrane layer, while also playing an auxiliary barrier role to reduce gas and water vapor permeation. The material is the same as the outer layer, which facilitates subsequent recycling and separation.

[0039] The high-barrier composite film consists of a PET substrate film and a nano-composite coating. The PET substrate film is 10–30 μm thick, the nano-composite coating is 5–15 μm thick, and the overall thickness is 15–45 μm. It is applied using a coating and solvent-free lamination method to serve as a barrier layer in packaging materials, ensuring stable barrier performance. The coating is applied to the inside of the PET substrate film (facing the food), forming the high-barrier composite film.

[0040] The specific preparation method is as follows: Step 1: Color printing and creasing / perforation. Select paper substrates that meet the specifications, and first perform corona treatment on their surfaces to ensure a surface tension ≥ 42 dynes, thereby improving ink adhesion. Use recyclable water-based inks to print product information on the paper substrate surface through flexographic or gravure printing. During the printing process, creasing and perforation are performed simultaneously. The creasing depth is controlled to be 30%–70% of the paper thickness to facilitate subsequent packaging (such as folding boxes). The perforation density is 1–3 holes / cm. 2 The aperture is 0.5-1mm, used for packaging venting; the linear speed of the entire process is controlled at 50-250 m / min to ensure the consistency and stability of printing, creasing, and punching.

[0041] Step 2: Prepare a high-barrier composite membrane. ① Coating: Select a PET substrate film that meets the specifications, and perform corona treatment on its inner side (towards the food) to ensure that the surface tension is ≥45 dynes and improve the coating adhesion; use a gravure coating machine to coat the prepared high barrier coating liquid onto the inner side of the PET substrate film, and control the dry film thickness to 5-15μm, preferably 8-12μm.

[0042] ②Drying: The coated PET / coated film is sent to a segmented drying equipment. It is first pre-dried at 80-90℃ for 1-2 minutes to remove some of the moisture in the coating, and then finally dried at 100-120℃ for 2-3 minutes until the moisture content of the coating is ≤0.5%. In some embodiments, after drying, the coating undergoes a slow in-situ mineralization reaction at room temperature to generate n-HA.

[0043] ③ Solvent-free lamination: Using a solvent-free laminator, the dried high-barrier film (PET / coating) is laminated with the second polyolefin film layer, ensuring that the coating side faces the PE film; a 100% solids content two-component solvent-free polyurethane adhesive is selected, and the adhesive application rate is controlled at 1.5–4 g / m². 2 The lamination line speed is 150~300 m / min, and the lamination pressure is 0.4~0.6 MPa, so that the PET / coated film and the PE film are tightly bonded to obtain a "high barrier film (PET / coated) / PE film" double-layer composite film for later use.

[0044] Step 3: Three-in-one solvent-free composite A solventless laminating machine is used to laminate the first polyolefin film layer, the paper substrate treated in step 1, and the high-barrier composite film obtained in step 2 (with the uncoated side of the PET film facing the paper substrate) in a single operation. The lamination sequence from the outside to the inside is: first PE film layer → printing ink layer → paper substrate layer → high-barrier composite film layer (PET / coated) → second PE film layer. The lamination line speed is controlled at 150–250 m / min, the lamination pressure at 0.5–0.7 MPa, and the adhesive application rate at 1.5–3 g / m. 2This ensures that each layer is tightly bonded, without any defects such as delamination or bubbles.

[0045] Step 4: Mature The composite packaging material is placed in a curing chamber and left to stand for 24 to 72 hours at 40 to 60°C and ≤50% humidity to allow the solvent-free adhesive to fully crosslink and cure, ensuring an interlayer peel strength ≥1.5 N / 15 mm. In some embodiments, the curing process can further stabilize n-HA and strengthen the coating structure.

[0046] Step 5: Slitting, Inspection, and Packaging According to actual packaging needs, the cured packaging materials are cut into corresponding specifications; the cut products undergo full performance testing, including OTR, WVTR, paper fiber recovery rate, interlayer peel strength, solvent residue and other indicators; after passing the tests, they are packaged and shipped out.

[0047] The solvent-free lamination process described above has the following advantages: First, it is environmentally friendly, with no VOC emissions and no solvent residue, avoiding environmental pollution and human health hazards caused by solvents, and complying with food contact safety standards and global environmental policies. Second, it is energy-efficient and highly effective, eliminating the need for solvent drying tunnels. Factory verification shows that energy consumption is reduced by approximately 70% compared to traditional dry lamination; production efficiency is significantly improved, with linear speeds reaching 300 m / min, far exceeding traditional dry lamination processes (≤150 m / min), making it suitable for large-scale industrial production. Third, it offers significant cost advantages, with solvent-free adhesive application amounts only 30-50% of those in dry lamination, and no additional solvent recovery process required. Calculations show that the overall production cost is 15-25% lower than traditional aluminum foil packaging and more than 30% lower than existing aluminum foil-free alternatives (such as silicon oxide / aluminum plating), facilitating large-scale promotion. Fourth, it has high bonding strength. The adhesive layer formed after the solvent-free adhesive is cured is dense and firm, with an interlayer peel strength of ≥1.5 N / 15mm. This avoids delamination of packaging materials during processing, transportation, and use, and ensures the overall stability of the packaging performance.

[0048] The technical solution of the present invention will be further described in detail in the following sections through specific embodiments and comparative examples. First, the test standards are shown.

[0049] (I) Testing Standards 1. OTR (Oxygen Transmission Rate): Tested according to ASTM D3985 standard, under the following conditions: 23℃±1℃, 50% RH±2%, and a test area of ​​50cm². 2 The test lasted 24 hours, and each sample was tested in 3 parallel groups. The average value was taken. 2. WVTR (Water Vapor Transmission Rate): Tested according to ASTM F1249 standard, under the following conditions: 38℃±1℃, 90%RH±2%, and a test area of ​​50cm². 2 The test lasted 24 hours, and each sample was tested in 3 parallel groups. The average value was taken. 3. Paper fiber recovery rate: The hydraulic recycled pulp simulation test was conducted under the following conditions: 60℃±2℃, pH7.0±0.2, stirring speed 300r / min, stirring time 30min. Paper fibers were separated by filtration using a standard sieve (pore size 0.1mm). The paper fiber recovery rate was calculated. Three parallel tests were conducted for each sample, and the average value was taken. 4. Interlayer peel strength: Tested according to GB / T 8808 standard (180° peel), test speed 300mm / min, sample width 15mm, 5 test points for each sample, and average value after removing outliers; 5. Solvent residue: Tested according to GB / T 10004 standard using headspace-gas chromatography, detection limit ≤0.1 mg / m³. 2 If no detectable, it is deemed to meet the requirements; 6. High Humidity Barrier Stability: The OTR under conditions of 38℃±1℃ and 90% RH±2% was tested, and the difference between the OTR under conditions of 23℃±1℃ and 50% RH±2% was calculated to obtain the performance degradation rate. Degradation rate = (High Humidity OTR - Normal Temperature OTR) / Normal Temperature OTR × 100%; 7. Coating toughness: The coating is tested by bending (GB / T 15232 standard). The coating is repeatedly bent at 180° with a bending radius of 5 times the coating thickness. After 10 bends, the coating is observed to see if cracking or peeling occurs. 8. n-HA formation effect: The distribution of n-HA inside the coating was observed by scanning electron microscopy (SEM) at a magnification of 50,000 to determine the mineralization uniformity. The particle size was measured using Image-Pro Plus software, and 50 n-HA particles were randomly selected to calculate the average particle size. 9. Processing stability test: Simulate industrial production speed (200m / min), continuously produce 1000m of packaging material, and statistically analyze the defect rates such as coating omissions, delamination, and bubbles. A defect rate ≤0.5% is considered to meet the requirements of industrial production. 10. Shelf life test: The packaging materials are made into standard packaging boxes, filled with the corresponding liquid food (milk, juice, etc.), and placed according to the actual storage conditions (room temperature, low temperature, high temperature). The sensory and physicochemical indicators (acidity, peroxide value, etc.) of the food are tested regularly to determine the shelf life.

[0050] (II) Examples Example 1 (250ml room temperature milk packaging) Raw material selection: 280 g / m 2 Bamboo pulp paper (basis weight deviation ±5g / m) 2 Thickness 350μm±10μm, tensile strength ≥35N / 15mm; 12μm PET film (corona value 48 dynes±2 dynes, light transmittance ≥90%, tensile strength ≥180MPa); 15μm LDPE film (density 0.92 g / cm³). 3 ±0.01g / cm 3 Melting point 110℃±5℃, heat seal strength ≥15N / 15mm; recyclable water-based ink (solid content ≥45%, adhesion ≥4B, no heavy metal residue); two-component solvent-free polyurethane adhesive (NCO / OH=1.3±0.1, solid content 100%, viscosity 2000mPa·s±500mPa·s, food contact grade).

[0051] Coating formulation (parts by weight): 100 parts of nanocellulose (CNF, diameter 10-15nm, aspect ratio 120±20, purity ≥98%), 40 parts of sodium montmorillonite (interlayer spacing 1.5nm±0.2nm, particle size ≤5μm, organically modified with quaternary ammonium salt, degree of modification ≥80%), 10 parts of chitosan (degree of deacetylation ≥85%, viscosity adjusted to 200±50 mPa·s under weak acid environment, molecular weight 50000-100000Da), 15 parts of nano silica (particle size 10-30nm, specific surface area ≥200 m² / g, purity ≥99.5%), 3 parts of glutaraldehyde (concentration 50%, food grade), 1 part of wetting agent (polyether-modified siloxane, surface tension 28 mN / m±2 mN / m, HLB value 12-14), and 1 part of deionized water (conductivity 8...). 550 samples (μS / cm±2μS / cm, pH7.0±0.2).

[0052] Preparation process: The preparation was carried out according to the solvent-free composite preparation method. Key parameters: coating dry thickness 10μm±1μm; adhesive application rate of high barrier film and PE film composite 2.5 g / m 2 ±0.2g / m 2 Linear speed 200 m / min ± 10 m / min, composite pressure 0.5 MPa ± 0.05 MPa; three-in-one composite coating amount 2.0 g / m 2 ±0.2g / m 2 Linear velocity 180 m / min ± 10 m / min, composite pressure 0.6 MPa ± 0.05 MPa; curing conditions 50℃ ± 2℃ / 48h ± 2h, curing chamber humidity ≤ 50% ± 5%.

[0053] Performance test results: OTR (23℃, 50% RH): 1.2 cm 3 / (m2 ·d)±0.1cm 3 / (m 2 ·d); OTR (38℃, 90% RH): 1.3 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); WVTR (38℃, 90% RH): 1.1 g / (m 2 ·d)±0.1g / (m 2 •d); Paper fiber recovery rate: 92.5%±0.5%; interlaminar peel strength: 1.9 N / 15mm±0.1 N / 15mm; solvent residue: not detected (detection limit ≤0.1 mg / m³). 2 High humidity performance degradation rate: 8.3%±0.5%; Coating bending test: 180° repeated bending 10 times, no cracking or peeling; Processing stability: 1000m continuous production, defect rate 0.3%, meeting the requirements of industrial mass production; Shelf life test: 6 months of storage at room temperature (25℃±2℃), milk showed no oxidation or spoilage, and acidity and peroxide value met the GB 25190-2010 standard; Production cost: 22% lower than traditional aluminum foil packaging, and 32% lower than the aluminum foil-free silicon oxide coating solution.

[0054] Results: The product exhibits stable performance, good processability, and can be mass-produced industrially. Its barrier properties are comparable to traditional aluminum foil packaging, while also possessing excellent recyclability and cost advantages.

[0055] Example 2 (500ml low-temperature juice packaging) The difference compared to Example 1 is as follows: 1. Coating formulation adjustment: 30 parts montmorillonite, 15 parts chitosan, and 10 parts nano-silica; 2. Process parameter adjustment: Coating dry thickness 8μm±1μm; Curing conditions 60℃±2℃ / 72h±2h; 3. Raw material adjustment: 350 g / m² paper substrate was selected. 2 Recycled paper (basis weight deviation ±5g / m) 2 Thickness 450μm±10μm, impact strength ≥5J); PET film thickness 15μm±1μm, PE film thickness 20μm±1μm; 4. New test: Juice browning test, which detects the color difference (ΔE) of juice during storage. ΔE ≤ 2.0 is considered as no obvious browning.

[0056] Performance test results: OTR (23℃, 50% RH): 1.4cm 3 / (m 2 ·d)±0.1cm3 / (m 2 ·d); OTR (38℃, 90% RH): 1.5cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); WVTR (38℃, 90% RH): 1.4g / (m 2 ·d)±0.1g / (m 2 •d); Paper fiber recovery rate: 91.2%±0.5%; interlayer peel strength: 1.7N / 15mm±0.1N / 15mm; solvent residue: not detected; high humidity performance degradation rate: 9.8%±0.5%; coating bending test: 180° repeated bending 10 times, no obvious cracking; processing stability: continuous production of 1000m, defect rate 0.4%; juice browning test: 8 months of low temperature (4℃±1℃) storage, ΔE=1.5, no obvious browning, no odor; shelf life: 8 months, meeting the requirements of low temperature juice packaging.

[0057] Results: After adjusting the formula and process parameters, the product performance still meets the design requirements. The solution has good stability, excellent impact resistance and browning resistance, and can be used for 500ml low-temperature juice packaging.

[0058] Example 3 (250ml long-lasting room temperature milk packaging) The difference compared to Example 1 is as follows: 1. New components in the coating formulation: 1.0 part by weight of sodium dihydrogen phosphate (analytical grade, purity ≥99.5%, particle size ≤10μm) and 1.5 parts by weight of calcium chloride (analytical grade, purity ≥99.5%, particle size ≤10μm); prepared in advance as an aqueous solution.

[0059] 2. Process adjustment: After coating and drying, place at room temperature (25℃±2℃) for 24h±2h to ensure sufficient in-situ formation of n-HA; the curing conditions are 50℃±2℃ / 48h±2h. The curing process promotes further stabilization of n-HA and strengthens the coating structure. 3. New tests: Coating hardness test (pencil hardness method, GB / T 6739 standard), n-HA particle size distribution test.

[0060] Performance test results: OTR (23℃, 50% RH): 1.0 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); OTR (38℃, 90% RH): 1.1 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); WVTR (38℃, 90% RH): 0.9 g / (m 2 ·d)±0.1g / (m 2 •d); Paper fiber recovery rate: 92.1%±0.5%; interlayer peel strength: 2.1 N / 15mm±0.1 N / 15mm; solvent residue: not detected; high humidity performance degradation rate: 7.5%±0.5%; coating bending test: 180° repeated bending 10 times, no cracking or peeling; coating hardness: 2H; SEM observation: n-HA is uniformly distributed inside the coating, without agglomeration, particle size 30-40nm, average particle size 35nm; processing stability: continuous production 1000m, defect rate 0.2%; shelf life test: 12 months of storage at room temperature (25℃±2℃), milk did not deteriorate, taste was normal, and physicochemical indicators met national standards; compared with Example 1: high humidity performance degradation rate decreased by 10.8%, interlayer peel strength increased by 10.5%, coating hardness increased by 1 level, and shelf life was extended by 6 months.

[0061] Results: The n-HA generated in this embodiment effectively improves the density, toughness and hardness of the coating. Its barrier properties and mechanical properties are superior to those of the embodiment 1, and it does not affect recyclability. It can meet the requirements of 12-month long-lasting room temperature milk packaging.

[0062] Example 4 (500ml lightweight plant protein beverage packaging) The difference compared to Example 3 is as follows: 1. Coating formulation adjustment: Sodium dihydrogen phosphate 0.8 parts by weight, calcium chloride 1.2 parts by weight, montmorillonite 35 parts, chitosan 8 parts; 2. Process parameter adjustment: Coating dry thickness 12μm±1μm; Curing conditions 40℃±2℃ / 72h±2h; 3. Lightweight adjustment of raw materials: 80 g / m² paper substrate is selected. 2 Bamboo pulp paper (basis weight deviation ±3g / m³) 2 (Thickness 100μm±5μm); PET film thickness 10μm±1μm, PE film thickness 10μm±1μm; 4. New test: Plant protein beverage stratification test. Observe whether the beverage stratifies during storage. If no stratification occurs, it is considered to meet the requirements.

[0063] Performance test results: OTR (23℃, 50% RH): 1.3 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); OTR (38℃, 90% RH): 1.4 cm 3 / (m2 ·d)±0.1cm 3 / (m 2 ·d); WVTR (38℃, 90% RH): 1.2 g / (m 2 ·d)±0.1g / (m 2 •d); Paper fiber recovery rate: 90.5%±0.5%; interlayer peel strength: 1.8 N / 15mm±0.1 N / 15mm; solvent residue: not detected; high humidity performance degradation rate: 7.9%±0.5%; coating bending test: no cracking; SEM observation: n-HA uniformly distributed, particle size 20-50nm, average particle size 32nm; processing stability: continuous production for 1000m, defect rate 0.4%; plant protein beverage stratification test: 10 months of room temperature storage, no stratification, no off-odor; lightweight advantages: packaging weight reduced by 35% compared to Example 3, production cost reduced by 10% compared to Example 3, and reduced by 25% compared to traditional aluminum foil packaging.

[0064] Results: After parameter adjustments, the performance of this solution remains excellent. It achieves lightweight design while effectively controlling costs and can be used for 500ml plant protein beverage packaging needs, balancing performance, environmental protection, and cost.

[0065] Example 5 (100ml portable tea beverage packaging) The difference compared to Example 1 is as follows: 1. Paper substrate adjustment: Select 120 g / m² paper. 2 Recycled paper (basis weight deviation ±3g / m) 2 Thickness 150μm±5μm, surface roughness Ra≤0.5μm); 2. Coating formulation adjustment: 35 parts montmorillonite, 12 parts chitosan, and 12 parts nano-silica; 3. Process parameter adjustment: coating dry thickness 9μm±1μm; composite linear speed 220 m / min±10m / min; curing conditions 55℃±2℃ / 36h±2h; 4. New test: Surface abrasion resistance test (GB / T 7706 standard), using an abrasion tester, load 500g, 100 abrasion cycles, observe whether the printed layer peels off and whether the surface is damaged. If there is no peeling or damage, it is considered to meet the requirements.

[0066] Performance test results: OTR (23℃, 50% RH): 1.3 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); OTR (38℃, 90% RH): 1.4 cm 3 / (m 2·d)±0.1cm 3 / (m 2 ·d); WVTR (38℃, 90% RH): 1.2 g / (m 2 ·d)±0.1g / (m 2 •d); Paper fiber recovery rate: 91.8%±0.5%; interlayer peel strength: 1.8 N / 15mm±0.1 N / 15mm; solvent residue: not detected; high humidity performance degradation rate: 9.2%±0.5%; coating bending test: no cracking; surface abrasion resistance test: after 100 cycles of friction, the printed layer did not peel off and the surface was not damaged; processing stability: after 1000m of continuous production, the defect rate was 0.3%; shelf life test: after 7 months of storage at room temperature, the tea beverage did not oxidize and the flavor remained unchanged; portability advantage: the packaging is lightweight, easy to carry, has good printing effect, and excellent abrasion resistance.

[0067] Results: Despite the low-grammage paper substrate design, the product still maintains excellent barrier properties and recyclability, outstanding abrasion resistance and portability, and can be used for 100ml portable small-sized liquid food packaging.

[0068] Example 6 (300ml high-temperature storage room-temperature milk packaging) The difference compared to Example 3 is as follows: 1. Coating formulation adjustment: The crosslinking agent is selected as 4 parts of waterborne epoxy resin (waterborne epoxy resin solid content ≥50%, viscosity 1500-2500mPa·s), 1.2 parts by weight of sodium dihydrogen phosphate, and 1.8 parts by weight of calcium chloride. 2. Process parameter adjustment: Coating dry thickness 11μm±1μm; Curing conditions 60℃±2℃ / 48h±2h; 3. New test: High temperature storage stability test. The packaging material is placed in an environment of 35℃±2℃ and 60%±5% humidity for 12 months. The integrity of the coating and the barrier performance are tested regularly. If there is no coating peeling and the barrier performance decreases by ≤10%, it is considered to meet the requirements.

[0069] Performance test results: OTR (23℃, 50% RH): 0.9 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); OTR (38℃, 90% RH): 1.0 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); WVTR (38℃, 90% RH): 0.8 g / (m 2 ·d)±0.1g / (m 2•d); Paper fiber recovery rate: 91.9%±0.5%; interlayer peel strength: 2.2 N / 15mm±0.1 N / 15mm; solvent residue: not detected; high humidity performance degradation rate: 7.1%±0.5%; coating bending test: no cracking; SEM observation: n-HA is uniformly distributed, the coating has excellent density and no pores; high temperature storage stability test: after 12 months of storage at 35℃, the coating did not peel off, and the OTR degradation rate was 8.9%, which meets the requirements; shelf life test: after 12 months of storage at 35℃, the milk did not deteriorate, and the physicochemical indicators met the national standards.

[0070] Results: This solution can significantly improve the high temperature resistance and density of the coating, making it suitable for high-temperature storage environments up to 35°C. It solves the problem of packaging barrier performance degradation under high temperature conditions, further expands the application range of products, and meets the packaging needs of high-temperature regions.

[0071] Example 7 (1L large-capacity juice packaging) The difference compared to Example 1 is as follows: 1. Polyolefin membrane layer adjustment: The first and second polyolefin membrane layers are made of 18μm LLDPE membrane (density 0.93 g / cm³). 3 ±0.01g / cm 3 (Tensile strength ≥200MPa, elongation at break ≥500%) 2. Paper substrate adjustment: Select 300 g / m² paper. 2 Bamboo pulp paper (basis weight deviation ±5g / m) 2 Thickness 380μm±10μm, tensile strength ≥40N / 15mm, impact strength ≥6J). 3. Process parameter adjustment: coating dry thickness 10μm±1μm; composite pressure 0.6MPa±0.05MPa; curing conditions 50℃±2℃ / 72h±2h; 4. New test: Drop test (GB / T 4857.5 standard), free drop from a height of 1.5m (face drop, edge drop, corner drop 3 times each), observe whether the packaging is damaged or delaminated; Load test, after the packaging is filled with juice, stack 5 layers and leave for 72 hours, observe whether the packaging is deformed or damaged.

[0072] Performance test results: OTR (23℃, 50% RH): 1.2 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); OTR (38℃, 90% RH): 1.3 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2·d); WVTR (38℃, 90% RH): 1.1 g / (m 2 ·d)±0.1g / (m 2 •d); Paper fiber recovery rate: 92.3%±0.5%; interlayer peel strength: 2.0 N / 15mm±0.1 N / 15mm; solvent residue: not detected; high humidity performance degradation rate: 8.3%±0.5%; coating bending test: no cracking or peeling; drop test: 1.5m drop without damage or delamination; load test: stacked 5 layers for 72h, no deformation or damage; processing stability: continuous production of 1000m, defect rate 0.3%; shelf life test: 8 months of room temperature storage, no browning or off-odor in the juice.

[0073] Results: After replacing LDPE film with LLDPE film, the packaging toughness, drop resistance and load-bearing capacity were significantly improved, which can meet the needs of 1L large-capacity packaging, while maintaining excellent barrier performance and recyclability, and solving the problems of easy breakage and delamination of large-capacity packaging.

[0074] (III) Comparative Example Comparative Example 1 (Traditional Tetra Pak with aluminum foil, lamination process) Structure: PE / paper / PE / aluminum foil / PE / PE, aluminum foil thickness 8μm±0.5μm; Preparation process: traditional lamination process (VOCs emission, high energy consumption); Raw materials: paper substrate and PE film consistent with Example 1.

[0075] Performance test results: OTR (23℃, 50% RH) = 0.7 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); WVTR (38℃, 90% RH)=0.8 g / (m 2 ·d)±0.1g / (m 2 •d); Paper fiber recovery rate ≤45%±2% (During the hydraulic regeneration pulping process, aluminum foil cannot be separated, contaminating the pulp and clogging the equipment); Interlayer peel strength: 2.0 N / 15mm±0.1 N / 15mm; Production cost is 25%±2% higher than Example 1; VOCs emission: Significant emission (emission concentration ≥50mg / m³) 3 Processing stability: 1.2% defect rate for continuous production of 1000m (aluminum foil is prone to breakage, leading to downtime and waste); Shelf life: 12 months.

[0076] Results: Traditional aluminum foil packaging has slightly better barrier properties, but its recyclability is extremely poor (paper fiber recycling rate is less than 50% of that in Example 1), production costs are high, VOCs emissions are present, processing stability is poor, and it does not meet environmental protection requirements and the "dual carbon" strategy. Its overall performance is inferior to all embodiments of the present invention.

[0077] Comparative Example 2 (EVOH coated cardboard box, existing aluminum foil-free solution) Structure: PE / paper / EVOH / PE; Preparation process: dry composite process (with VOC emissions); EVOH coating thickness 10μm±1μm; Raw materials: paper substrate and PE film consistent with Example 1.

[0078] Performance test results: OTR (23℃, 50% RH) = 1.8 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); OTR (38℃, 90% RH) = 10.5 cm 3 / (m 2 ·d)±0.5cm 3 / (m 2 ·d); WVTR (38℃, 90% RH) = 2.8 g / (m 2 ·d)±0.2g / (m 2 •d); Paper fiber recovery rate: 85%±1%; Interlayer peel strength: 1.4 N / 15mm±0.1 N / 15mm; VOCs emission: Yes (emission concentration ≥30mg / m³) 3 High humidity performance degradation rate: 83.3%±2% (EVOH is highly sensitive to humidity; under high humidity conditions, the molecular chains loosen, and the barrier performance deteriorates sharply); Shelf life: ≤3 months (cannot meet the long shelf life requirement of 6-12 months for liquid foods); Coating bending test: no cracking; Processing stability: 0.8% defect rate after 1000m of continuous production.

[0079] Results: The existing EVOH foil-free solution exhibits a sharp deterioration in barrier performance under high humidity conditions (the attenuation rate is more than 10 times that of Example 1), which cannot meet the requirements for long shelf life of liquid food. In addition, it emits VOCs and its recyclability is lower than that of all embodiments of the present invention, resulting in a significant gap in overall performance.

[0080] Comparative Example 3 (pure nanocellulose coated packaging, no compound components) Compared with the present invention, the difference is that the high-barrier composite film layer is only a PET film + pure nanocellulose coating (without montmorillonite, chitosan, nano silica, and crosslinking agent), and the coating thickness is 10μm±1μm; the preparation process is the same as in Example 1.

[0081] Performance test results: OTR (23℃, 50% RH) = 3.2 cm 3 / (m 2 ·d)±0.2cm 3 / (m 2 ·d); OTR (38℃, 90% RH) = 8.6 cm 3 / (m 2 ·d)±0.3cm 3 / (m 2 ·d); WVTR (38℃, 90% RH) = 11.5 g / (m 2 ·d)±0.5g / (m 2 •d); Paper fiber recovery rate: 93%±0.5%; interlayer peel strength: 1.2 N / 15mm±0.1 N / 15mm; coating bending test: obvious cracking occurs (pure nanocellulose coating is brittle and lacks toughness); high humidity performance degradation rate: 75%±2% (no compound components, many pores in the coating, easy to absorb water in high humidity environment, barrier performance drops sharply); shelf life: ≤2 months; processing stability: continuous production of 1000m, defect rate 1.5% (coating is prone to cracking and incomplete coating).

[0082] Results: The pure nanocellulose coating has extremely poor water vapor barrier properties (WVTR is more than 10 times that of Example 1), its performance degrades severely under high humidity conditions, and the coating is brittle and has poor processing stability, which cannot meet the core requirements of liquid food packaging.

[0083] Comparative Example 4 (Combined Coating of Nanocellulose + Montmorillonite + Chitosan) Compared with the present invention, the difference is that: the high-barrier composite film layer is a PET film + nanocellulose + montmorillonite + chitosan combined coating (without nano silica and crosslinking agent), with a coating thickness of 10μm; the coating formula (parts by weight) is: 100 parts nanocellulose, 40 parts montmorillonite, 10 parts chitosan, 1 part wetting agent, and 550 parts deionized water; other preparation processes are the same as in Example 1.

[0084] Performance test results: OTR (23℃, 50% RH) = 2.2 cm 3 / (m 2 ·d); OTR (38℃, 90% RH) = 5.9cm 3 / (m 2 ·d); WVTR (38℃, 90% RH) = 7.6 g / (m 2 •d); Paper fiber recovery rate: 92.3%; interlayer peel strength: 1.3 N / 15mm; coating bending test: no obvious cracking; high humidity performance degradation rate: 68.2%; shelf life: ≤4 months.

[0085] Results: Due to the lack of pore filling by nano-silica and the three-dimensional network reinforcement effect of crosslinking agent, there are many micropores inside the coating. The barrier performance is significantly reduced under high humidity conditions (the reduction rate is more than 8 times that of Example 1), and the shelf life is short.

[0086] Comparative Example 5 (Combined coating of montmorillonite, chitosan, and nano-silica) Compared with the present invention, the difference is that: the high-barrier composite film layer is a PET film + montmorillonite + chitosan + nano silica combined coating (without nanocellulose and crosslinking agent), with a coating thickness of 10μm; the coating formula (parts by weight): 40 parts montmorillonite, 10 parts chitosan, 15 parts nano silica, 1 part wetting agent, and 550 parts deionized water; the rest of the preparation process is the same as in Example 1.

[0087] Performance test results: OTR (23℃, 50% RH) = 2.8 cm 3 / (m 2 ·d); OTR (38℃, 90% RH) = 7.5cm 3 / (m 2 ·d); WVTR (38℃, 90% RH) = 9.2 g / (m 2 •d); Paper fiber recycling rate: 78%; interlayer peel strength: 1.1 N / 15mm; coating bending test: slight cracking; high humidity performance degradation rate: 62.7%; shelf life: ≤3 months.

[0088] Results: Without nanocellulose as a film-forming matrix, the components could not form a continuous and dense structure, resulting in poor barrier properties and high humidity stability, as well as decreased compatibility with paper substrates (paper fiber recovery rate was 14.5% lower than in Example 1).

[0089] Comparative Example 6 (Pure Polyester Coated Packaging) Compared with the present invention, the difference is that the high-barrier composite film layer is a PET film + pure polyester coating (replacing the nanocellulose coating), and the coating thickness is 10μm; the rest of the preparation process is the same as in Example 1.

[0090] Performance test results: OTR (23℃, 50% RH) = 1.3 cm 3 / (m 2 ·d); OTR (38℃, 90% RH) = 1.5cm 3 / (m 2 ·d); WVTR (38℃, 90% RH) = 1.3 g / (m 2•d); Paper fiber recycling rate: 65%; interlayer peel strength: 1.8 N / 15mm; coating bending test: no cracking; VOC emissions: slight emissions; shelf life: 6 months.

[0091] Results: The pure polyester coating has good barrier properties, but poor compatibility with paper substrates, resulting in a significant decrease in paper fiber recycling rate (only 70% of that in Example 1), making it impossible to achieve overall recyclability, and there are slight VOC emissions.

[0092] Comparative Example 7 (Traditional mineral coating packaging) Compared with the present invention, the difference is that: 2 parts by weight of pre-made n-HA (particle size 20-50nm) are directly added to the coating to replace sodium dihydrogen phosphate and calcium chloride; other preparation processes are the same as in Example 1.

[0093] Performance test results: OTR (23℃, 50% RH) = 1.5 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); OTR (38℃, 90% RH) = 1.7 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); WVTR (38℃, 90% RH) = 1.5 g / (m 2 ·d)±0.1g / (m 2 •d); Paper fiber recovery rate: 91%±0.5%; interlayer peel strength: 1.4 N / 15mm±0.1N / 15mm; coating bending test: severe cracking and peeling (poor compatibility between pre-made n-HA and coating matrix, unable to form a stable three-dimensional network structure, resulting in poor coating toughness); high humidity performance degradation rate: 13.3%±0.5%; shelf life: 6 months; SEM observation: uneven distribution of n-HA, with obvious agglomeration, unable to effectively fill coating pores; processing stability: continuous production of 1000m, defect rate 1.0% (coating is easy to peel off).

[0094] Results: The method of directly adding mineral filler had poor compatibility between n-HA and the coating matrix, resulting in severe coating brittleness and poor barrier and mechanical properties (OTR and WVTR were higher than those of Example 3, and the attenuation rate was 1.8 times that of Example 3).

[0095] Comparative Example 8 (Silicone oxide coated, aluminum foil-free packaging) Structure: PE / paper / PE / PET (silicon oxide coating) / PE; Preparation process: vacuum coating + dry lamination (VOCs emission, difficult to process); Silicon oxide coating thickness 50nm±5nm; Raw materials: paper substrate, PE film, PET film, the same as in Example 1.

[0096] Performance test results: OTR (23℃, 50% RH) = 0.9 cm 3 / (m 2 ·d)±0.1cm 3 / (m 2 ·d); WVTR (38℃, 90% RH) = 0.9 g / (m 2 ·d)±0.1g / (m 2 •d); Paper fiber recovery rate: 88%±1%; interlayer peel strength: 1.7 N / 15mm±0.1 N / 15mm; production cost is 35%±2% higher than Example 1 (vacuum plating process is complex and energy consumption is high); VOCs emission: there is emission (emission concentration ≥20mg / m³). 3 The coating is prone to pinholes, resulting in a high breakage rate (≥8%) during processing. Processing stability: 8.5% defect rate after 1000m of continuous production (the coating is brittle and easily damaged). Shelf life: 12 months.

[0097] Results: The silicon oxide plating solution without aluminum foil has excellent barrier performance, but the production cost is high (35% higher than Example 1), there are VOC emissions, and the coating is brittle and has a high processing breakage rate.

[0098] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A foil-free, recyclable, ultra-high barrier paper-based composite packaging material, characterized in that, From the outside in, it includes a first polyolefin film layer, a printing ink layer, a paper substrate layer, a high-barrier composite film layer, and a second polyolefin film layer. The high-barrier composite film layer consists of a PET substrate film and a nanocomposite coating applied to its inner side (facing the food side); The nanocomposite coating comprises nanocellulose, montmorillonite, chitosan, nanosilica, crosslinking agent, wetting agent, and deionized water.

2. The aluminum foil-free, recyclable, ultra-high barrier paper-based composite packaging material according to claim 1, characterized in that, The nanocomposite coating has the following formula by weight: 100 parts nanocellulose, 30-50 parts montmorillonite, 5-15 parts chitosan, 10-20 parts nano silica, 1-5 parts crosslinking agent, 0.5-2 parts wetting agent, and 400-700 parts deionized water.

3. The aluminum foil-free, recyclable, ultra-high barrier paper-based composite packaging material according to claim 1 or 2, characterized in that, The nanocellulose is selected from cellulose nanofibers (CNF) or nanocrystals (CNC), with a diameter of 5-20 nm and an aspect ratio >100; the montmorillonite is sodium-based montmorillonite; the degree of deacetylation of the chitosan is ≥85%; the nano silica has a particle size of 10-30 nm and a specific surface area ≥200 m² / g; the crosslinking agent is selected from glutaraldehyde or waterborne epoxy resin; the wetting agent is polyether-modified siloxane with a surface tension ≤30 mN / m; and the deionized water has a conductivity ≤10 μS / cm.

4. The aluminum foil-free, recyclable, ultra-high barrier paper-based composite packaging material according to any one of claims 1-3, characterized in that, Both the first and second polyolefin film layers are made of LDPE or LLDPE, with a density of 0.91–0.93 g / cm³. 3 The thickness is 10-30μm; the printing ink layer is made of recyclable water-based ink with a thickness of <5μm; the paper substrate layer is made of bamboo pulp paper or recycled paper with a basis weight of 80-350 g / m²; the PET substrate film has a thickness of 10-30μm, and the nanocomposite coating has a thickness of 5-15μm.

5. The aluminum foil-free, recyclable, ultra-high barrier paper-based composite packaging material according to any one of claims 1-4, characterized in that, The nanocomposite coating also contains 0.5-1.5 parts by weight of sodium dihydrogen phosphate and 0.8-2.0 parts by weight of calcium chloride. After coating, it reacts slowly at room temperature to generate n-HA (nano-hydroxyapatite) with a particle size of 20-50 nm.

6. A solvent-free composite preparation method for an aluminum foil-free, recyclable, ultra-high barrier paper-based composite packaging material, characterized in that, Includes the following steps: (1) Color printing and creasing and perforation: Select paper substrate, perform corona treatment on its surface, use recyclable water-based ink for printing, and simultaneously perform creasing and perforation treatment; (2) Preparation of high barrier film: Select PET substrate film, perform corona treatment on its inner side, apply high barrier coating liquid to the inner side of PET substrate film, and dry it by segmented drying process to obtain high barrier film; Solvent-free composite of high barrier film and polyolefin film: The obtained high barrier film and the second polyolefin film layer are bonded by solvent-free composite process, wherein the coating side faces the polyolefin film to obtain a double-layer composite film; (3) Three-in-one solventless composite: The first polyolefin film layer, the paper substrate treated in step (1), and the high barrier composite film obtained in step (2) are composited in one step. The composite sequence from the outside to the inside is the first polyolefin film layer → printing ink layer → paper substrate layer → high barrier composite film layer → second polyolefin film layer. (4) Curing: Place the composite packaging material in a curing chamber and let it stand to allow the solvent-free adhesive to fully cross-link and cure; (5) Cutting, testing and packaging: Cut and test the matured packaging materials, and package them for shipment after they pass the test.

7. The solvent-free composite preparation method of the aluminum foil-free recyclable ultra-high barrier paper-based composite packaging material according to claim 6, characterized in that, In step (1), the surface tension of the paper substrate after corona treatment is ≥42 dynes, the indentation depth is 30% to 70% of the paper thickness, and the perforation density is 1 to 3 per cm. 2 The aperture is 0.5-1mm, and the linear velocity is controlled at 50-250 m / min throughout the process.

8. The solvent-free composite preparation method of the aluminum foil-free recyclable ultra-high barrier paper-based composite packaging material according to claim 6 or 7, characterized in that, In step (2), the coating liquid is prepared by adding deionized water to a high-speed disperser, then adding nano-cellulose, montmorillonite, and nano-silica in sequence, adjusting the speed to 2000-5000 rpm, and dispersing for 30-60 minutes to ensure uniform dispersion of each component; then adding pre-prepared chitosan, as well as crosslinking agent and wetting agent, and continuing to disperse for 10-20 minutes; finally, letting it stand for 15-30 minutes to degas, resulting in a uniform, bubble-free coating liquid; after corona treatment, the inner surface tension of the PET substrate film is ≥45 dynes, and the coating is applied using a gravure coating method, with a dry film thickness of 5-15 μm; the segmented drying process is as follows: first, pre-drying at 80-90℃ for 1-2 minutes, and then finally drying at 100-120℃ for 2-3 minutes, until the coating moisture content is ≤0.5%.

9. The solvent-free composite preparation method of the aluminum foil-free recyclable ultra-high barrier paper-based composite packaging material according to any one of claims 6-8, characterized in that, In steps (2) and (3), the solvent-free lamination uses a 100% solids content two-component solvent-free polyurethane adhesive. In step (2), the amount of adhesive applied is 1.5–4 g / m². 2 The lamination speed is 150~300 m / min, and the lamination pressure is 0.4~0.6 MPa; the lamination coating amount in step (3) is 1.5~3 g / m. 2 The composite linear speed is 150-250 m / min, and the composite pressure is 0.5-0.7 MPa.

10. A solvent-free composite preparation method for aluminum foil-free recyclable ultra-high barrier paper-based composite packaging material according to any one of claims 6-9, characterized in that, The curing conditions are 40~60℃, humidity ≤50%, and standing time 24~72 hours. After curing, the interlayer peel strength is ≥1.5 N / 15mm. Sodium dihydrogen phosphate and calcium chloride are also added to the nanocomposite coating. After coating and drying, it is placed at room temperature.

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