High-temperature-resistant food plastic packaging bag and preparation method thereof

Abstract

The invention relates to the technical field of high-performance polypropylene, and discloses a high-temperature-resistant food plastic packaging bag and a preparation method thereof. The packaging bag sequentially comprises a nylon outer layer, an aluminum foil barrier layer, an inner nylon layer and an environment-friendly enhanced casting polypropylene heat sealing layer from outside to inside. The environment-friendly enhanced casting polypropylene heat sealing layer is prepared from the following components in percentage by mass: 80 to 90 percent of homo-polypropylene, 3 to 8 percent of modified nano silicon dioxide, 5 to 13 percent of maleic anhydride grafted polypropylene, 0.1 to 0.5 percent of antioxidant and 1 to 5 percent of functional aid. The preparation method comprises the following steps: preparation of the environment-friendly enhanced casting polypropylene film, printing, three-time dry compounding, processing after curing and the like. Through interlayer structure optimization, heat sealing layer formula improvement and application of the environment-friendly adhesive, synergistic improvement of high temperature resistance, environmental protection, high safety and excellent mechanical properties is achieved, the raw materials meet the food contact safety standard, the preparation technology is mature and controllable, and the heat-sealing film is suitable for industrial large-scale production and has good economic and social benefits.

Description

Technical Field

[0001] This invention relates to the field of high-performance polypropylene technology, specifically to a high-temperature resistant food plastic packaging bag and its preparation method. Background Technology

[0002] High-temperature resistant food plastic packaging bags are food packaging containers that can be used for high-temperature sterilization, with retort pouches being a representative product. With the development of the food industry and the increasing demands of consumers for food safety and environmental protection, existing food retort pouches have gradually revealed many shortcomings: On the one hand, the heat-sealing layer of traditional retort pouches mostly uses ordinary cast polypropylene (RCPP), which has limited high-temperature resistance. During high-temperature cooking at 121℃ and above, problems such as decreased heat-sealing strength and deformation easily occur, affecting the packaging's sealing performance. On the other hand, the composite adhesives of traditional retort pouches are mostly petroleum-based polyurethane adhesives, which are not only non-renewable, but some products also pose a risk of excessive residual solvents, threatening food safety. Furthermore, the inorganic reinforcing fillers added to the existing heat-sealing layer have poor compatibility with the polypropylene matrix, leading to unstable film mechanical properties and a tendency to crack.

[0003] High-performance polypropylene (PP) has become a research focus due to its excellent heat resistance, chemical stability, and recyclability potential. However, ordinary polypropylene suffers from poor barrier properties and weak bonding with polar materials (such as nylon and aluminum foil), making it difficult to directly replace the layers in traditional structures to meet the stringent requirements of retort pouches. Existing technologies mostly focus on simple material replacement or physical blending, failing to achieve systematic innovation at the level of interfacial bonding mechanisms and intrinsic property enhancement, resulting in shortcomings in products regarding retort stability, barrier properties, or environmental friendliness. Summary of the Invention

[0004] The purpose of this invention is to provide a high-temperature resistant food plastic packaging bag and its preparation method to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides a high-temperature resistant food plastic packaging bag, which comprises, from the outside to the inside: a nylon outer layer, an aluminum foil barrier layer, an inner nylon layer, and an environmentally friendly reinforced cast polypropylene heat-sealing layer.

[0006] The environmentally friendly reinforced cast polypropylene heat-sealing layer comprises, by weight percentage: 80-90% homopolymer polypropylene, 3-8% modified nano silica, 5-13% maleic anhydride grafted polypropylene, 0.1-0.5% antioxidant, and 1-5% functional additives.

[0007] The product employs a four-layer composite structure: "Nylon outer layer 1 - Aluminum foil barrier layer 2 - Inner nylon layer 3 - Environmentally friendly reinforced cast polypropylene heat-sealing layer 4," with each layer functioning synergistically and complementaryly. The nylon outer layer 1 provides excellent mechanical strength and printability, ensuring the integrity of the packaging appearance and printing stability; the aluminum foil barrier layer 2 effectively blocks oxygen, moisture, and light, extending the shelf life of food; the inner nylon layer 3 further enhances the composite film's puncture resistance and flexibility, preventing packaging damage due to collisions during transportation; the environmentally friendly reinforced cast polypropylene heat-sealing layer 4 is the core functional layer, with food-grade homopolymer polypropylene as the matrix material in its formulation, ensuring the basic heat-sealing performance and food safety of the heat-sealing layer; and the 30-8 modified with KH-570... 0nm spherical nano-silica achieves good compatibility with the polypropylene matrix through the bridging effect of silane coupling agent. At the same time, the "microfiber reinforcement" effect of nanoparticles significantly improves the high temperature resistance and mechanical strength of the heat-sealing layer. Maleic anhydride-grafted polypropylene serves as a compatibilizer, and its polar groups can combine with the non-polar segments of polypropylene and the hydroxyl groups on the surface of nano-silica, respectively, to further improve the dispersibility of fillers and avoid performance defects caused by filler agglomeration. Antioxidants can inhibit the oxidative degradation of polypropylene during processing and use, extending the service life of retort pouches.

[0008] Preferably, the nylon outer layer and the aluminum foil barrier layer, the aluminum foil barrier layer and the inner nylon layer, and the inner nylon layer and the environmentally friendly reinforced cast polypropylene heat-sealing layer are all composited using a bio-based polyurethane adhesive. The bio-based polyurethane adhesive is a two-component system with epoxidized soybean oil derivatives as the polyol component and aliphatic isocyanates as the curing agent. Using bio-based polyurethane adhesive for interlayer composite, with epoxidized soybean oil derivatives as the polyol component, is renewable and environmentally friendly. The aliphatic isocyanate curing agent ensures the adhesive's resistance to yellowing and high temperature resistance, avoiding the environmental hazards and safety risks of traditional petroleum-based adhesives. Through the above structural and formulation design, the basic guarantee for the retort pouch's high temperature resistance, environmental friendliness, high safety, and excellent mechanical properties is achieved.

[0009] Preferably, the bio-based polyurethane adhesive is a two-component system with epoxidized soybean oil derivatives as polyol components and aliphatic isocyanates as curing agents.

[0010] Preferably, the functionalized additive consists of hollow mesoporous silica and nano-silver particles and α-titanium phosphate filled within the hollow mesoporous silica. This scheme achieves efficient, stable, and safe controllable antibacterial function under high-temperature cooking conditions by constructing a "core-shell hollow confined" composite structure: the hollow mesoporous silica shell provides a robust physical barrier and a large loading space, while its internal mesoporous channels confine and fix the nano-silver particles, effectively preventing their migration and aggregation at high temperatures; the α-titanium phosphate filled within the channels, as a heat-resistant and stable inorganic material, further encapsulates and anchors the nano-silver, and works synergistically with the silica shell to jointly resist hydrothermal erosion during cooking, protecting the activity of the nano-silver; simultaneously, this composite structure, through precise control of the interaction between the channel size and the filler, enables the slow and continuous release of silver ions, thereby achieving a long-lasting antibacterial effect while ensuring that the amount of silver ion migration is far below food safety standards, solving the technical problem of easy inactivation and migration of traditional silver-loaded materials in high-temperature and high-humidity environments.

[0011] Preferably, the grafting rate of the maleic anhydride-grafted polypropylene is 0.8-1.2%.

[0012] Preferably, the modified nano-silica is spherical particles with a particle size of 30-80 nm, which have been surface modified with silane coupling agent KH-570.

[0013] Preferably, the thickness of the nylon outer layer is 12-18 μm, the thickness of the aluminum foil barrier layer is 7-9 μm, the thickness of the inner nylon layer is 12-15 μm, and the thickness of the environmentally friendly reinforced cast polypropylene heat-sealing layer is 50-70 μm. The outer nylon layer 1 has a thickness controlled between 12-18 μm, ensuring sufficient mechanical strength and printing clarity while avoiding material waste and reduced flexibility due to excessive thickness. The aluminum foil barrier layer 2 has a thickness of 7-9 μm, ensuring excellent barrier performance while maintaining flexibility during composite processing, avoiding breakage issues caused by excessively thick aluminum foil. The inner nylon layer 3 has a thickness of 12-15 μm, effectively enhancing the puncture and tear resistance of the composite film, synergistically improving the overall mechanical properties of the retort pouch with the outer nylon layer 1. The environmentally friendly reinforced cast polypropylene heat-sealing layer 4 has a thickness of 50-70 μm. This thickness range ensures sufficient heat-sealing strength and morphological stability during high-temperature retort processing, avoiding weak heat sealing due to excessive thickness or increased material costs due to excessive thickness. Through optimized matching of the thicknesses of each layer, a balanced improvement in the overall performance of the retort pouch is achieved.

[0014] Preferably, the aluminum foil barrier layer is a soft aluminum foil with a tensile strength of not less than 120 MPa. Using a soft aluminum foil ensures good flexibility during the lamination process, avoiding wrinkles and breakage caused by excessively hard aluminum foil. Limiting the tensile strength to not less than 120 MPa ensures sufficient mechanical strength to withstand the stretching during lamination, slitting, bag making, and transportation, preventing damage that could lead to loss of barrier performance. The combination of soft aluminum foil and high tensile strength ensures both process adaptability and the structural integrity and barrier effect of the barrier layer.

[0015] On the other hand, the present invention also provides a method for preparing the above-mentioned high-temperature resistant food plastic packaging bag, comprising the following steps: S1: Homopolymer polypropylene, nano silica, maleic anhydride grafted polypropylene and antioxidant are mixed according to the formula, melt-blended and granulated, and then cast and cooled to form an environmentally friendly reinforced cast polypropylene heat-sealing layer. S2: Print the inner surface of the outer nylon layer, then combine it with the aluminum foil barrier layer, the inner nylon layer and the environmentally friendly reinforced cast polypropylene heat-sealing layer in sequence and cure it to obtain a semi-finished product. S3: Cut and bag the semi-finished product.

[0016] Preferably, in step S2, the composite is performed using a bio-based polyurethane adhesive.

[0017] Specifically, in step S1, mixing is carried out in a high-speed mixer for 5-10 minutes; melt blending and granulation are carried out in a twin-screw extruder at an extrusion temperature of 180-210℃, a screw speed of 250-320 rpm, and a vacuum degree of -0.04 to -0.06 MPa; casting is carried out in a casting machine at a casting temperature of 210-225℃, a cooling roller temperature of 18-28℃, and a draw ratio of 8-12. In step S2, lamination is performed using a bio-based polyurethane adhesive with a working concentration of 32-36%, cured for 30 minutes after preparation, and a curing agent index of 1.05-1.10. The lamination process can be performed in stages. The first stage involves dry lamination of the reverse-printed nylon outer layer 1 and the aluminum foil barrier layer 2 using a bio-based polyurethane adhesive. The lamination is then cured at 50-60℃ for 48-72 hours to obtain the Ny / Al layer, with an adhesive application rate of 3.0-3.8 g / m³. 2 (Dry base), laminating machine speed 70-90 m / min; Second lamination step: Using bio-based polyurethane adhesive, dry laminate the Ny / Al layer with the inner nylon layer 3, then cure at 50-60℃ for 48-72 h to obtain the Ny / Al / Ny layer, with an adhesive application rate of 3.0-3.5 g / m 2(Dry base), laminating machine speed 60-80m / min; Third lamination step: Using bio-based polyurethane adhesive, the Ny / Al / Ny layer is dry-laminated with the environmentally friendly reinforced cast polypropylene layer 4 obtained in step S1, and then cured at 50-60℃ for 72-96h to obtain the final semi-finished product, with an adhesive application rate of 2.8-3.5g / m 2 (Dry basis), compounding machine speed 50-70m / min. The third curing step takes longer than the first two steps because: Thicker adhesive layer: To achieve a strong bond between the environmentally friendly reinforced cast polypropylene layer 4 and the inner nylon layer 3, a higher amount of adhesive may be required.

[0018] Interfacial chemical reactions exist: The PP-g-MAH in the environmentally friendly reinforced cast polypropylene layer 4 needs time to migrate to the interface and react with the amide groups of nylon, which requires a longer curing period to ensure that the reaction proceeds fully.

[0019] Step S1 involves preparing an environmentally friendly reinforced CPP film through high-speed mixing, twin-screw melt blending and granulation, and casting. A reasonable mixing time ensures uniform dispersion of the raw materials, and the temperature range of the twin-screw extruder ensures complete melting of the polypropylene without degradation. The casting temperature matches the molding requirements of polypropylene, guaranteeing film quality. Step S2 uses high-temperature resistant retortable printing ink conforming to GB4806.13-2023 "National Food Safety Standard for Composite Materials and Products for Food Contact" for reverse printing. This avoids direct contact between the ink and food, while ensuring the printed pattern does not peel off or migrate during high-temperature cooking, guaranteeing food safety and packaging appearance. The step-by-step dry lamination process in Step S2 adjusts the amount of adhesive and the laminating machine speed for different interlayer combinations, ensuring strong adhesion between layers. The adhesive amount range matches the bonding requirements of the bio-based adhesive, and the machine speed adjustment balances production efficiency and lamination quality. The curing conditions in Step S6 ensure the bio-based adhesive is fully cured, improving interlayer bonding strength. Subsequent slitting and bag-making processes ensure the dimensional accuracy of the retortable bags. The entire preparation process is reasonable, and the parameters of each step are coordinated to provide process assurance for achieving the excellent performance of the retort pouch.

[0020] The beneficial effects of this invention are as follows: 1. Excellent high temperature resistance: The environmentally friendly reinforced CPP heat-sealing layer can withstand high-temperature cooking at 121℃ for 30 minutes, with a heat-sealing strength retention rate of ≥90%, solving the problems of high-temperature deformation and sealing failure of traditional retort pouches; 2. Excellent environmental performance: the heat-sealing layer uses food-contact grade environmentally friendly materials, reducing dependence on petroleum-based resources and minimizing environmental impact; 3. Stable mechanical properties, effectively resisting external impacts during transportation and use; drop tests show no leakage or damage, effectively resisting external impacts during transportation and use. 4. High safety: all raw materials meet food contact safety standards, and residual solvents in adhesives are ≤5mg / m³. 2 There is no risk of heavy metal contamination. 5. The preparation process is mature, can be produced using existing conventional equipment, has strong parameter controllability, is suitable for large-scale industrial production, and has significant economic and social benefits.

[0021] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 A schematic diagram of the structure of a high-temperature resistant food plastic packaging bag according to an embodiment of the present invention is shown.

[0023] Explanation of reference numerals in the attached figures: 1. Nylon outer layer, 2. Aluminum foil barrier layer, 3. Inner nylon layer, 4. Environmentally friendly reinforced cast polypropylene heat-sealing layer. Detailed Implementation

[0024] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0025] It should be noted that all reagents and raw materials used in this invention are commercially available, and the reagents are of analytical grade.

[0026] Maleic anhydride-grafted polypropylene was purchased from Jia Yi Rong Polymer (Shanghai) Co., Ltd., model number CMG5701.

[0027] The homopolymer polypropylene was purchased from Borouge Plastics (Shanghai) Co., Ltd., model HD915CF.

[0028] The nano-silica was purchased from Hubei Huifu Nanomaterials Co., Ltd., model number FA-32.

[0029] The printing ink was purchased from Fujian Green Spring New Material Co., Ltd., model number GS-01.

[0030] The aliphatic isocyanate was purchased from Wanhua Chemical Group Co., Ltd., and its product name is WANNATE. ® HDI.

[0031] The epoxidized soybean oil derivative was purchased from Nantong Haierma Technology Co., Ltd., model number HM-10100R, product name is bio-based polyol.

[0032] Hollow mesoporous silica was purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., model number XFF29.

[0033] The specific modification method for the modified nano-silica used in the specific embodiments is as follows: 10g of nano-silica was weighed and dispersed in 200mL of anhydrous ethanol. The mixture was sonicated for 30min to obtain a nano-silica suspension. 3g of KH-570 silane coupling agent was mixed with 50mL of anhydrous ethanol and 5mL of deionized water and pre-hydrolyzed for 15min. The hydrolyzed KH-570 solution was added dropwise to the nano-silica suspension and mechanically stirred and refluxed at 80℃ for 4h. After the reaction was completed, the product was separated by centrifugation, washed three times with ethanol, and dried in a vacuum drying oven at 80℃ for 12h to obtain modified nano-silica.

[0034] The preparation method of the functionalized additives used in the specific embodiments is as follows: Step 1: Loading nano-silver inside hollow mesoporous silica 10g of hollow mesoporous silica was dispersed in 200mL of water to obtain a silica dispersion; Add 3.4g of silver nitrate to the silica dispersion, stir to dissolve, then add 3.5g of ascorbic acid as a reducing agent, and stir to react for 7h at 60℃ in the dark. After the reaction was completed, the mixture was centrifuged, washed with water, and dried at 80°C to obtain the silver-loaded intermediate.

[0035] Step 2: Constructing a heat-resistant protective layer of α-titanium ammonium phosphate Disperse 5g of silver-loaded intermediate in 100mL of deionized water, add 3.3g of titanium oxysulfate, stir until completely dissolved, add 2.3g of phosphoric acid (85wt%) while stirring, and adjust the pH to 2.0 with ammonia (v / v, 28%) to obtain a mixture; The mixture was transferred to a reaction vessel and hydrothermally reacted at 180°C for 24 hours. After the reaction, it was centrifuged, washed with water, and dried at 100°C to obtain an intermediate coated with α-titanium hydrogen phosphate. The intermediate coated with α-titanium hydrogen phosphate was dispersed in 1 mol / L ammonia water (solid-liquid ratio 1 g: 50 mL), and ion exchange was performed at 60 °C for 6 h. Finally, the product was centrifuged, washed with water, and dried at 100 °C to obtain the functionalized additive.

[0036] The preparation method of bio-based polyurethane adhesive is as follows: Aliphatic isocyanate WANNATE is mixed in a molar ratio of -NCO:-OH = 1.08:1. ® HDI and bio-based polyol HM-10100R were mixed with 0.1% of the total mass of aliphatic isocyanate and bio-based polyol catalyst dibutyltin dilaurate, and then vacuum degassed after thorough stirring.

[0037] Example 1 1. Preparation of environmentally friendly reinforced cast polypropylene heat-sealing layer 4: Ingredients (mass percentage): Add 80% homopolymer polypropylene, 5% modified nano silica, 11.5% PP-g-MAH, 0.5% antioxidant 1010, and 3% functional additives to a high-speed mixer and mix for 8 minutes to obtain a mixture; Granulation: The mixture is added to a twin-screw extruder for granulation to obtain granules. The temperature of the twin-screw extruder is set to 185℃ / 195℃ / 205℃ / 205℃ / 200℃ (die head), the speed is 280 rpm, and the vacuum degree is -0.05MPa. Casting: The granules are introduced into the casting machine for casting and cooling to form an environmentally friendly reinforced cast polypropylene heat-sealing layer 4. The temperature of the casting extruder is 220℃, the temperature of the cooling roller is 25℃, the traction speed is 100m / min, the traction ratio is 10, and the thickness is 60μm.

[0038] 2. Printing: Ink is used to print on the inner surface of the 15μm thick nylon outer layer 1.

[0039] 3. First Lamination: Using bio-based polyurethane adhesive (prepared and left to stand for 30 minutes before use, the same applies below), the printed nylon outer layer 1 and aluminum foil barrier layer 2 are dry-laminated, and then cured at 55℃ for 65 hours to obtain the Ny / Al layer, with an adhesive application rate of 3.5 g / m². 2 The machine speed is 80 m / min.

[0040] 4. Second lamination: Using a bio-based polyurethane adhesive, the Ny / Al layer and the inner nylon layer 3 are dry-laminated, and then cured at 55℃ for 65 hours to obtain the Ny / Al / Ny layer. The adhesive application rate is 3.2 g / m². 2 The machine speed is 70 m / min.

[0041] 5. Third lamination: Using bio-based polyurethane adhesive, the Ny / Al / Ny layer is dry-laminated with the environmentally friendly reinforced cast polypropylene heat-sealing layer 4, and then cured at 55℃ and 50% relative humidity for 84 hours to obtain a semi-finished product with an adhesive application rate of 3.2 g / m². 2 The machine speed is 60 m / min.

[0042] 6. Cut the semi-finished product into paper bags to obtain packaging bags.

[0043] Example 2 The difference compared to Example 1 is as follows: In step 1, the raw material ratio of the environmentally friendly reinforced cast polypropylene heat-sealing layer 4 is as follows: homopolymer polypropylene 90%, modified nano silica 3%, PP-g-MAH 5.7%, antioxidant 1010 0.3%, and functional additives 1%.

[0044] In step 3, the amount of adhesive applied is 3.0 g / m². 2 The machine speed is 70 m / min; in step 4, the amount of adhesive applied is 3.0 g / m. 2 The machine speed is 60 m / min; in step 4, the amount of adhesive applied is 2.8 g / m. 2 Machine speed 50m / min, 58℃ for 90h curing.

[0045] Example 3 The difference compared to Example 1 is as follows: In step 1, the raw material ratio of the environmentally friendly reinforced cast polypropylene heat-sealing layer 4 is as follows: homopolymer polypropylene 81.9%, modified nano silica 8%, PP-g-MAH 5%, antioxidant 1010 0.1%, and functional additives 5%.

[0046] In step 3, the amount of adhesive applied is 3.8 g / m². 2 The machine speed is 90 m / min; in step 4, the amount of adhesive applied is 3.5 g / m. 2 The machine speed is 80 m / min; in step 4, the amount of adhesive applied is 3.5 g / m. 2 Machine speed 70m / min, 52℃ for 96h curing.

[0047] Example 4 The difference compared to Example 1 is as follows: In step 1, the raw material ratio of the environmentally friendly reinforced cast polypropylene heat-sealing layer 4 is as follows: homopolymer polypropylene 80%, modified nano silica 3.6%, PP-g-MAH 15%, antioxidant 1010 0.2%, and functional additives 1.2%.

[0048] In step 3, the amount of adhesive applied is 3.6 g / m. 2 The machine speed is 85 m / min; in step 4, the amount of adhesive applied is 3.3 g / m. 2 The machine speed is 75 m / min; in step 4, the amount of adhesive applied is 3.3 g / m. 2 Machine speed 65m / min, 56℃ for 90h curing.

[0049] Comparative Example 1 Compared with Example 1, only the KH-570 modified nano-silica in the environmentally friendly reinforced cast polypropylene heat-sealing layer 4 was replaced with unmodified nano-silica. The other raw material composition, interlayer structure and preparation process parameters were the same as in Example 1.

[0050] Comparative Example 2 Compared with Example 1, the environmentally friendly reinforced cast polypropylene heat-sealing layer removes maleic anhydride-grafted polypropylene and correspondingly increases the content of homopolymer polypropylene to 94.5%. The remaining raw material composition, interlayer structure and preparation process parameters are the same as those in Example 1.

[0051] Comparative Example 3 Compared with Example 1, the epoxidized soybean oil derivative in the bio-based polyurethane adhesive was replaced with polyester polyol (purchased from Wanhua Chemical Group Co., Ltd., model WANTHANOL®WHP-2024), while the remaining raw material composition, interlayer structure and preparation process parameters were the same as in Example 1.

[0052] Comparative Example 4 Compared with Example 1, the environmentally friendly reinforced cast polypropylene heat-sealing layer does not use functional additives, and the content of homopolymer polypropylene is increased to 83%. The remaining raw material composition, interlayer structure and preparation process parameters are the same as those in Example 1.

[0053] Comparative Example 5 Compared with Example 1, the functionalized additive does not contain the α-ammonia-titanium phosphate heat-resistant protective layer, while the composition of other raw materials, interlayer structure and preparation process parameters are the same as those in Example 1.

[0054] The packaging bags prepared in Examples 1-4 and Comparative Examples 1-5 were subjected to relevant performance tests. The test standards and methods are as follows: 1. Breaking force: According to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for thin plastics and sheets", a universal testing machine is used to cut the sample into a standard dumbbell shape and stretch it at a specified speed until it breaks. The maximum force (breaking force) is recorded.

[0055] 2. Heat seal strength: According to GB / T 2358-1998 "Test method for heat seal strength of plastic film packaging bags", the sample is heat-sealed and cut into strips. The heat seal is peeled off at a constant speed on the testing machine, and the maximum peel force is recorded.

[0056] 3. Peel strength after cooking: Refer to GB / T 8808-1988 "Peel test method for flexible composite plastic materials", cook the sample (121℃, 30min) and cut it into 15mm wide pieces to test the peel force between Ny and the heat seal layer.

[0057] 4. Pendulum impact resistance: According to GB / T 8809-2015 "Plastic film pendulum impact test method", a pendulum impact tester is used to let the pendulum fall freely to impact the film sample on the fixed fixture, and the energy consumed to penetrate the sample is measured.

[0058] 5. Cooking test: Refer to GB / T 10004-2008 "Dry lamination and extrusion lamination of plastic composite films and bags for packaging". Fill the packaging bag with an equal weight of simulated material (such as brine), seal it and place it in an autoclave. Treat it at 121℃ for 30 minutes. After cooling, check whether the bag is broken, delaminated or deformed.

[0059] 6. Antibacterial properties: According to GB / T 31402-2023 "Determination of antibacterial activity of plastics and other non-porous materials", the sample was contacted with a culture medium inoculated with Escherichia coli, and the bacteria were counted after incubation to calculate the inhibition rate.

[0060] 7. Silver ion migration: Referring to GB 31604.1-2023 "National Food Safety Standard General Rules for Migration Test of Food Contact Materials and Articles", the sample was contacted with 4% acetic acid at a certain temperature and time, and the silver content in the simulant was determined by instruments such as inductively coupled plasma mass spectrometry (ICP-MS).

[0061] 8. Solvent Residue: In accordance with GB / T 10004-2008 "Dry Lamination and Extrusion Lamination of Plastic Composite Films and Bags for Packaging", headspace gas chromatograph was used. The sample was placed in a sealed bottle and heated. The headspace gas was extracted to analyze the total amount of solvent residues such as benzene and esters.

[0062] 9. Primary aromatic amine migration: According to GB 31604.52-2021 "National Food Safety Standard for Determination of Aromatic Primary Amine Migration in Food Contact Materials and Articles", the sample was contacted with 4% acetic acid, and qualitative and quantitative analysis was performed using liquid chromatography-tandem mass spectrometry (LC-MS / MS).

[0063] The performance test results are shown in Table 1.

[0064] Table 1 Performance Test Results

[0065] The test results above show that the high-temperature resistant food plastic packaging bags prepared in Examples 1-4 of this invention have excellent overall performance. However, the comparative examples differ from the technical solution of this invention, with one or more performance aspects failing to meet the standards. The specific analysis is as follows: 1. Comparative Example 1 uses unmodified nano-silica. Due to the poor compatibility between unmodified nano-silica and the polypropylene matrix, it is easy to agglomerate in the matrix and cannot form an effective reinforcing effect. As a result, the tensile strength and pendulum impact resistance are significantly lower than those of Example 1. Slight delamination occurs in the cooking test. This proves that nano-silica modified with KH-570 is crucial for improving the heat-sealing layer performance and interlayer bonding.

[0066] 2. In Comparative Example 2, maleic anhydride-grafted polypropylene was removed. Without the bridging effect of the compatibilizer, the compatibility between nano-silica and the polypropylene matrix was further reduced, and the performance degradation was more obvious. The peel strength after cooking dropped sharply (3.2N), and the heat sealing strength and impact energy were also significantly reduced. The cooking test showed obvious delamination, which verified the key role of maleic anhydride-grafted polypropylene in improving filler dispersibility and enhancing interlayer compatibility.

[0067] 3. Comparative Example 3 used polyester polyol. Although some mechanical properties were similar to those of Example 1, the residual solvent in the adhesive was as high as 8.0 mg / m³. 2 (far exceeding ≤5mg / m 2 The standard (and its environmental protection and safety are significantly inferior to that of the present invention), which demonstrates the advantages of bio-based polyurethane adhesives in terms of environmental protection and safety.

[0068] 4. No functional additives were added in Comparative Example 4, and the mechanical and interfacial properties remained good. This confirms that the antibacterial properties shown in Example 1 are entirely derived from the functional additives, and the introduction of these additives did not have a negative impact on the original system.

[0069] 5. In Comparative Example 5, the absence of a heat-resistant protective layer resulted in a severe decrease in antibacterial performance (only 65%), and a surge in silver ion migration, approaching the safety limit. This directly demonstrates the dual key role of the α-ammonia phosphate titanium heat-resistant protective layer: (1) protecting the nano-silver from agglomeration and oxidation during cooking, maintaining high antibacterial activity; (2) acting as a slow-release barrier, strictly controlling the silver ion migration rate, and ensuring food safety. Without this protective layer, the functional additives are essentially ineffective after cooking and pose safety hazards.

[0070] In summary, through the synergistic combination of various technical features, this invention enables the packaging bag to meet all standard requirements and achieves a significant improvement in overall performance. All conditions and parameters in the solution are necessary to achieve excellent performance.

[0071] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Furthermore, it should be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0072] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A high-temperature resistant food plastic packaging bag, comprising, from the outside to the inside: Nylon outer layer, aluminum foil barrier layer, inner nylon layer and environmentally friendly reinforced cast polypropylene heat-sealing layer; The environmentally friendly reinforced cast polypropylene heat-sealing layer is characterized by comprising, by mass percentage: 80-90% homopolymer polypropylene, 3-8% modified nano silica, 5-13% maleic anhydride grafted polypropylene, 0.1-0.5% antioxidant, and 1-5% functional additives.

2. The high-temperature resistant food plastic packaging bag according to claim 1, characterized in that, The outer nylon layer and the aluminum foil barrier layer, the aluminum foil barrier layer and the inner nylon layer, and the inner nylon layer and the environmentally friendly reinforced cast polypropylene heat-sealing layer are all bonded together using bio-based polyurethane adhesives.

3. The high-temperature resistant food plastic packaging bag according to claim 2, characterized in that, The bio-based polyurethane adhesive is a two-component system with epoxidized soybean oil derivatives as polyol components and aliphatic isocyanates as curing agents.

4. The high-temperature resistant food plastic packaging bag according to claim 1, characterized in that, The functionalized additive consists of hollow mesoporous silica and nano-silver particles and α-aminophosphate titanium filled in the hollow mesoporous silica.

5. The high-temperature resistant food plastic packaging bag according to claim 1, characterized in that, The grafting rate of the maleic anhydride-grafted polypropylene is 0.8-1.2%.

6. The high-temperature resistant food plastic packaging bag according to claim 1, characterized in that, The modified nano-silica is spherical particles with a particle size of 30-80 nm, which have been surface modified with silane coupling agent KH-570.

7. The method for preparing high-temperature resistant food plastic packaging bags according to claim 1, characterized in that, The thickness of the outer nylon layer is 12-18 μm, the thickness of the aluminum foil barrier layer is 7-9 μm, the thickness of the inner nylon layer is 12-15 μm, and the thickness of the environmentally friendly reinforced cast polypropylene heat-sealing layer is 50-70 μm.

8. The method for preparing high-temperature resistant food plastic packaging bags according to claim 1, characterized in that, The aluminum foil barrier layer is a soft aluminum foil.

9. A method for preparing a high-temperature resistant food plastic packaging bag according to any one of claims 1-8, characterized in that, Includes the following steps: S1: Homopolymer polypropylene, nano silica, maleic anhydride grafted polypropylene and antioxidant are mixed according to the formula, melt-blended and granulated, and then cast and cooled to form an environmentally friendly reinforced cast polypropylene heat-sealing layer. S2: Print the inner surface of the outer nylon layer, then combine it with the aluminum foil barrier layer, the inner nylon layer and the environmentally friendly reinforced cast polypropylene heat-sealing layer in sequence and cure it to obtain a semi-finished product. S3: Cut and bag the semi-finished product.

10. The method for preparing a high-temperature resistant food plastic packaging bag according to claim 9, characterized in that, In step S2, the composite is performed using a bio-based polyurethane adhesive.

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