High-temperature-cooking-resistant packaging material and application thereof

Abstract

The invention discloses a packaging material resistant to high-temperature cooking and application thereof, and belongs to the field of polymer composites.The packaging material is of a five-layer structure, an outer layer is made of polypropylene, maleic anhydride grafted polypropylene and calcium ion modified gulcomannan, and the damp-heat stability is improved; the barrier layer is composed of a tannic acid grafted nano zinc oxide / polytrifluorochloroethylene composite film and a silicon oxide layer, and has a double barrier effect; the high-temperature-resistant layer is reinforced by polypropylene and glass fibers, so that the mechanical property is improved; the heat sealing layer is made of supercritical carbon dioxide silver ion-embedded microcapsule polyethylene and has antibacterial and heat sealing strength. After the polypropylene material is cooked at 121 DEG C for 40 minutes, the oxygen permeation rate is smaller than or equal to 3 cm / (m.day. Atm), the water vapor permeation rate is smaller than or equal to 2 g / (m.day), the tensile strength is larger than or equal to 45 MPa, the antibacterial rate is larger than or equal to 99.5%, and the recovery rate of a polypropylene base material is larger than or equal to 95%. The packaging film is suitable for aseptic packaging of acidic or high-fat food and medicines, has the shelf life of more than or equal to 24 months, and has high barrier property, antibacterial property and environmental protection property.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer composite materials, and particularly relates to a high-temperature resistant retort packaging material with a multi-layer composite structure, which is particularly suitable for the aseptic packaging of food and pharmaceutical products under high-temperature sterilization conditions, and has high barrier properties, antibacterial properties, mechanical strength and long-term stability, and can meet the long-term storage requirements of acidic or high-fat contents. Background Art

[0002] With the rapid growth of the demand for aseptic packaging in the food and pharmaceutical industries, high-temperature resistant retort packaging materials urgently need to achieve performance breakthroughs in terms of barrier properties, mechanical strength, corrosion resistance to media and antibacterial properties. Existing high-temperature retort packaging materials generally adopt multi-layer composite structures such as polyester, nylon, polypropylene and aluminum foil. Although they have the ability to withstand high-temperature sterilization above 121 °C, there are still many technical bottlenecks and application limitations in their comprehensive performance. Although the traditional aluminum foil composite structure shows excellent oxygen barrier properties, with an oxygen transmission rate as low as 1 cm³ / (m²·day·atm), its rigid structure results in insufficient flexibility, and microcracks are easily generated during cooking, transportation and storage, which seriously affects the integrity of the barrier layer, leading to a rapid increase in the oxygen transmission rate and water vapor transmission rate. In addition, aluminum foil is opaque, not microwave-heatable, and the recycling process is complex, posing challenges to environmental protection and unable to meet the current trends of circular economy and green packaging.

[0003] Although materials such as polyester and nylon provide certain mechanical strength and heat resistance, the interfacial bonding between them and polyolefins or aluminum foils usually relies on solvent-based adhesives, which not only increases the process cost but also poses a potential food safety hazard due to solvent residues. As a commonly used substrate, polypropylene has good thermal stability, but due to its relatively hard texture, its heat-sealing performance and flexibility are insufficient, and the heat-sealing strength is generally lower than 25 N / 15mm. Under high-temperature cooking conditions, affected by temperature and medium, its molecular chains are prone to breakage, resulting in a heat-sealing strength attenuation of more than 30%, which affects the packaging integrity and shelf life. In terms of the barrier layer, high-barrier materials such as ethylene-vinyl alcohol copolymer (EVOH) perform excellently in a dry environment, but are prone to hydrolysis in a high-humidity or acidic environment (pH < 5), leading to a significant decrease in barrier performance, and the oxygen transmission rate can increase to more than 10 cm³ / (m²·day·atm). In addition, the high-humidity and high-temperature environment will accelerate the water absorption and swelling of the nylon layer, resulting in a decrease in the dimensional stability of the film material, and thus affecting the integrity of the heat-sealing interface. Regarding the risk of microbial contamination, although traditional inorganic antibacterial agents such as nano-zinc oxide and silver ions have antibacterial effects, their interfacial compatibility with the polyolefin matrix is poor, and they are prone to agglomeration during processing to form microdefects, resulting in pinhole effects in the heat-sealing layer or barrier layer, and there are also potential food safety hazards of excessive migration amounts (such as zinc ion migration amount > 0.1 mg / kg). More seriously, the agglomeration of some inorganic nanoparticles intensifies after high-temperature cooking, and the antibacterial performance decays rapidly, unable to meet the long-term antibacterial requirements. In terms of the high-temperature resistant layer, although the commonly used cast polypropylene film has a high crystallinity (isotacticity ≥ 94%) and good high-temperature cooking performance, its tensile strength is only 30 - 35 MPa, and the low-temperature notched impact strength ≤ 50 kJ / m², which cannot meet the impact resistance requirements of high-fat or frozen foods during logistics and storage. Although glass fiber-reinforced polypropylene can improve the mechanical properties, its interfacial bonding with the matrix is weak, and it is prone to delamination and demarcation during high-temperature cooking, resulting in a decrease in the overall stability of the material.

[0004] In recent years, nano-composite barrier layers have become a research hotspot. By compounding nano-zinc oxide with a polymer matrix and improving the interfacial compatibility by methods such as surface grafting of tannic acid, the nano-particles can form coordination bonds or hydrogen bond networks with the matrix, significantly enhancing the dispersion uniformity and hydrothermal stability. For example, for the composite film of tannic acid-grafted nano-zinc oxide and polychlorotrifluoroethylene, its oxygen permeability can be stably maintained below 3 cm³ / (m²·day·atm). Even after being steamed at 121°C for 40 minutes, its barrier performance can still remain stable. However, the dispersion of nano-particles, surface modification, and energy consumption in the preparation process are still bottlenecks restricting their large-scale application. Especially during the ultraviolet curing or high-temperature melting process, the energy consumption is relatively high, and the production cost is higher than that of traditional composite films. The development of bio-based modified materials provides new ideas for green packaging. After being cross-linked and modified with calcium ions, the hygroscopicity of deacetylated glucomannan is significantly reduced, its thermal decomposition temperature ≥ 300°C, and it can achieve good interfacial bonding with maleic anhydride-grafted polypropylene through ester bonds and hydrogen bonds, with an overall tensile strength of more than 40 MPa. Such composite systems not only improve the hydrothermal stability and mechanical properties but also have high degradability and environmental protection characteristics. However, deacetylated glucomannan still faces problems such as raw material cost control and the stability of modification efficiency during large-scale production. In terms of long-term antibacterial properties, the technology of cyclodextrin microcapsules loaded with silver ions has gradually matured. Its slow-release characteristics enable the release rate of silver ions to be controlled at 0.05 μg / (cm²·day), ensuring an antibacterial rate ≥ 99.5% and the migration amount meeting the food safety standards. However, in the traditional melt blending preparation process, the microcapsules are prone to breakage due to high shear force and high-temperature conditions, with a breakage rate of more than 30%, affecting the effective loading and long-term release effect of the antibacterial agent. Using supercritical carbon dioxide fluid technology can effectively reduce the processing temperature, achieve the uniform embedding of silver ion microcapsules, and improve the stability of the antibacterial agent and the environmental protection of the processing process. However, this technology has high requirements for equipment and a large cost investment.

[0005] From the perspective of market trends, high-value-added food packaging, such as acidic sauces and high-fat dairy products, poses higher requirements for packaging materials, which need to have acid corrosion resistance, anti-grease penetration, low-temperature impact resistance, and dimensional stability. Currently, in existing multi-layer composite materials, the barrier layer is prone to degradation in an acidic environment, and the penetration rate of fat-soluble components is high, resulting in a shelf life of usually 6 - 12 months, making it difficult to meet the demand for a shelf life of more than 24 months. The development trends of green manufacturing and circular economy have promoted the research and development of aluminum-free and single-material (such as all-polypropylene) structural materials. The all-polypropylene structure has good recyclability, with a recovery rate of over 95%, but there is still a gap in its barrier performance compared with traditional aluminum foil composite films. How to improve the barrier properties and comprehensive mechanical properties of all-polypropylene materials without sacrificing environmental protection has become an important research direction in the future. In addition, the popularization of ultra-high temperature short-time sterilization (145°C / 3 min) technology has put forward higher requirements for the dimensional stability (thermal shrinkage rate ≤ 1.5%) and sealing integrity of packaging materials. Under the condition of 145°C, the heat-sealing strength of existing polychlorotrifluoroethylene films decays by ≥ 50%, and the interfacial compatibility problem between the barrier layer and the antibacterial layer leads to unstable overall performance, making it unable to fully meet the requirements of the ultra-high temperature short-time sterilization process. At the same time, the risk of additive migration under ultra-high temperature short-time sterilization conditions increases, and a barrier and antibacterial system with higher stability needs to be developed. Summary of the Invention

[0006] Aiming at the technical bottlenecks of existing high-temperature cooking resistant packaging materials in terms of barrier properties, antibacterial properties, mechanical strength, and environmental adaptability, the present invention proposes a packaging material with a five-layer composite structure, which realizes a comprehensive improvement in performance under high-temperature sterilization conditions through innovative material combinations, interface optimization, and process design.

[0007] The preparation method and application technical solution of a high-temperature cooking resistant packaging material of the present invention are as follows: The described high-temperature cooking resistant packaging material has the following five-layer structure from outside to inside: Outer layer: A composition of polypropylene, maleic anhydride grafted polypropylene, and modified glucomannan with a degree of deacetylation ≥ 90%; Barrier layer: A composite film containing polychlorotrifluoroethylene and nano-zinc oxide grafted with tannic acid on the surface. The nano-zinc oxide is grafted with tannic acid on the surface to form a photocatalytic synergistic antibacterial system; Adhesive layer: Composed of epoxy-modified silicone resin and polyurethane adhesive, where the mass ratio of epoxy groups to siloxane segments is 1:3 - 5; High-temperature resistant layer: Containing polypropylene and a glass fiber reinforcement treated with a silane coupling agent, where the glass fiber has a diameter of 5 - 10 μm and an aspect ratio ≥ 50; Heat-sealing layer: A composite material composed of polyethylene and silver ion microcapsules, where the silver ion microcapsules use porous cyclodextrin as the wall material and the silver loading is 5 - 8 mass percentages; The thickness ratios of each layer are as follows: the outer layer is 15 - 25 μm, the barrier layer is 10 - 20 μm, the adhesive layer is 2 - 5 μm, the high-temperature resistant layer is 50 - 80 μm, and the heat-sealing layer is 30 - 50 μm; For the described high-temperature resistant retort packaging material, in the outer layer: The mass ratio of the polypropylene, maleic anhydride grafted polypropylene, and modified glucomannan is (75 - 85):(10 - 15):(5 - 10); For the described high-temperature resistant retort packaging material, in the outer layer: The preparation method of the maleic anhydride grafted polypropylene includes: mixing polypropylene particles with maleic anhydride and an initiator in a mass percentage of 95:4:1, and performing melt blending with a twin-screw extruder at a temperature of 170 - 200 °C; extruding and pelletizing to obtain maleic anhydride grafted polypropylene; The preparation method of the modified glucomannan includes: heating konjac glucomannan in a calcium hydroxide solution with a pH of 7 - 10 to 75 - 95 °C for treatment, and spray drying to obtain a crystalline structure with a deacetylation degree of ≥90%; For the described high-temperature resistant retort packaging material, in the barrier layer: The particle size of the nano zinc oxide is 20 - 50 nm, the grafting rate of tannic acid is 15 - 25%, and a silicon oxide layer with a surface deposition thickness of 50 - 100 nm is deposited on the barrier layer surface, and the oxygen to silicon atom ratio of the silicon oxide layer is 1.5 - 1.8; The preparation method of the described high-temperature resistant retort packaging material includes the following steps: (1) Preparation of the outer layer: After melt blending polypropylene, maleic anhydride grafted polypropylene, and modified glucomannan, form a film through a biaxial stretching process, with a longitudinal to transverse stretching ratio of 3.5:1, and perform corona treatment with a corona strength of ≥40 dyne / cm; (2) Preparation of the barrier layer: Coat the surface of a polyvinylidene fluoride film with a nano zinc oxide dispersion grafted with tannic acid, and perform ultraviolet curing with a wavelength of 365 nm and an irradiation intensity of 800 - 1200 mJ / cm 2 in an inert gas environment with an oxygen content of ≤200 ppm, and then deposit a silicon oxide layer by plasma enhanced chemical vapor deposition with a silane to oxygen flow ratio of 1:3 and a radio frequency power of 300 - 500 W; (3) Preparation of the high-temperature resistant layer: Co-extrusion casting is performed on polypropylene and surface-treated glass fibers, and the temperature of the casting roll is controlled at 25 - 35 °C, with a stretching ratio of 5 - 7 times; (4) Preparation of the heat-sealing layer: Embed silver ion microcapsules into a polyethylene matrix using supercritical carbon dioxide fluid, with an extrusion temperature of 180 - 200 °C and a die head pressure of 8 - 12 MPa; (5) Interlayer lamination: Using a two-component polyurethane adhesive, dry lamination is carried out at a coating amount of 3.5 - 4.5 g / m 2 , and it is cured at 50 - 60 °C for 24 - 48 h.

[0008] The application of the described high-temperature retort packaging material in the high-temperature sterilization packaging of food and pharmaceutical products. After being treated by retorting at 121 °C for 40 minutes, the water vapor transmission rate ≤ 2 g / (m²·day), the oxygen transmission rate ≤ 3 cm³ / (m²·day·atm), the antibacterial rate against Escherichia coli and Staphylococcus aureus ≥ 99.5%, the heat seal strength retention rate ≥ 90%, it is suitable for aseptic packaging of acidic pH 3 - 5 or high-fat content ≥ 20% of the contents, and the shelf life ≥ 24 months.

[0009] Through the design of a multi-layer composite structure and process innovation, the present invention significantly improves the comprehensive performance of packaging materials under high-temperature cooking conditions. In the outer layer, the synergistic effect of modified glucomannan and maleic anhydride grafted polypropylene inhibits moisture absorption and swelling through calcium ion cross-linking, enabling the material to maintain stable mechanical properties (tensile strength ≥ 38 MPa) in a high-temperature and high-humidity environment. At the same time, the corona treatment strength ≥ 40 dyne / cm solves the problem of poor printing suitability of the traditional polypropylene outer layer. The barrier layer is composed of nano-zinc oxide grafted with tannic acid on the surface and poly(chlorotrifluoroethylene) composite, combined with a silicon oxide deposition layer, forming a dual-barrier network of hydrogen bonds and coordination bonds. After cooking at 121 °C for 40 minutes, the oxygen transmission rate ≤ 3 cm³ / (m²·day·atm) and the water vapor transmission rate ≤ 2 g / (m²·day). Although slightly higher than that of the traditional aluminum foil composite film (oxygen transmission rate ≤ 1 cm³ / (m²·day·atm)), it avoids the barrier failure caused by aluminum foil cracking and has a stability improvement of more than 80% in an acidic environment with pH 3 - 5. In the adhesive layer, the composite system of epoxy-modified silicone resin and polyurethane enables the interlayer peel strength ≥ 6 N / 15mm, and there is no interface delamination after cooking, overcoming the problem of adhesive force attenuation caused by hydrothermal aging of traditional adhesives. The high-temperature resistant layer modifies random copolymer polypropylene with hydrogenated styrene-butadiene block copolymer and introduces glass fibers with a high aspect ratio (aspect ratio ≥ 50), making the notched impact strength of the material ≥ 88 kJ / m² at -40 °C, a 76% increase compared to ordinary RCPP (≤ 50 kJ / m²). At the same time, the tensile strength ≥ 45 MPa meets the anti-deformation requirements for packaging high-fat contents. The heat-sealing layer uses supercritical carbon dioxide-embedded silver ion microcapsules (Ag@CD), with a silver ion release rate ≤ 0.05 μg / (cm²·day), an antibacterial rate ≥ 99.5%, and a microcapsule breakage rate ≤ 3%. It avoids the sudden release of silver ions caused by traditional melt blending (migration amount ≤ 0.01 mg / kg, far lower than the national standard limit of 0.1 mg / kg). At the same time, the blend system of metallocene polyethylene and high-density polyethylene enables the heat-sealing strength ≥ 25 N / 15mm, and the retention rate after cooking ≥ 90%, solving the contradiction between the low heat-sealing strength of the traditional CPP heat-sealing layer (< 20 N / 15mm) and the difficulty of compatible antibacterial function. In addition, the all-polypropylene substrate structure enables the material recyclability ≥ 95%, meeting the EU EN 13432 standard. Compared with the traditional polyester / aluminum foil / PP composite film (recycling rate < 5%), it significantly reduces the environmental load. Verified by actual application, the shelf life of this material for acidic sauces (pH 3.5) and high-fat prefabricated dishes (fat content 25%) is extended to more than 24 months, and the attenuation rate of water and oxygen barrier performance ≤ 10%. It is applicable to strict processes such as ultra-high temperature short-time sterilization (145 °C / 3min), filling the technical gaps in long-term antibacterial, corrosion resistance to media, and green recycling of existing materials. Detailed implementation manners

[0010] In the examples and comparative examples, the ratios are all mass percentages unless otherwise specified. Example 1

[0011] Preparation process Preparation of the outer layer Components: 75 parts by mass of polypropylene, 10 parts by mass of maleic anhydride grafted polypropylene, and 5 parts by mass of modified glucomannan.

[0012] Preparation of maleic anhydride grafted polypropylene: Mix polypropylene particles, maleic anhydride, and initiator in a mass ratio of 95:4:1.

[0013] Melt blend at 170 °C using a twin-screw extruder and extrude into pellets.

[0014] Preparation of modified glucomannan: Heat konjac glucomannan in a calcium hydroxide solution at pH 7 to 75 °C for treatment.

[0015] After spray drying, a crystalline structure with a degree of deacetylation of 90% is obtained.

[0016] Forming: After melt blending the three components, a film is formed by a biaxial stretching process (longitudinal to transverse stretching ratio of 3.5:1).

[0017] Corona treatment, strength 40 dyne / cm.

[0018] Thickness: 15 μm.

[0019] Preparation of the barrier layer Components: poly(chlorotrifluoroethylene) and nano-zinc oxide with tannic acid grafted on the surface.

[0020] Nano-zinc oxide: particle size 20 nm, tannic acid grafting rate 15%.

[0021] Process: Coat the surface of the poly(chlorotrifluoroethylene) film with the nano-zinc oxide dispersion.

[0022] Under an inert gas environment with an oxygen content of 200 ppm, ultraviolet light curing is carried out at a wavelength of 365 nm and an irradiation intensity of 800 mJ / cm².

[0023] Deposit a silicon oxide layer with a thickness of 50 nm and an oxygen to silicon atomic ratio of 1.5 by plasma enhanced chemical vapor deposition (silane to oxygen flow ratio of 1:3, radio frequency power of 300 W).

[0024] Thickness: 10 μm.

[0025] Preparation of the adhesive layer Components: Epoxy-modified silicone resin and polyurethane adhesive, with a mass ratio of epoxy groups to siloxane segments of 1:3.

[0026] Thickness: 2 μm.

[0027] Preparation of high-temperature resistant layer Components: 90 parts by mass of polypropylene and 10 parts by mass of glass fiber treated with silane coupling agent.

[0028] Glass fiber: diameter 5 μm, aspect ratio 50.

[0029] Process: Co-extrusion casting, casting roll temperature 25°C, draw ratio 5 times.

[0030] Thickness: 50 μm.

[0031] Preparation of heat-sealing layer Components: 95 parts by mass of polyethylene and 5 parts by mass of silver ion microcapsules.

[0032] Silver ion microcapsules: Using porous cyclodextrin as the wall material, silver loading 5%.

[0033] Process: Embedding into the polyethylene matrix using supercritical carbon dioxide fluid technology, extrusion temperature 180°C, die head pressure 8 MPa.

[0034] Thickness: 30 μm.

[0035] Interlayer lamination Using a two-component polyurethane adhesive, coating amount 3.5 g / m².

[0036] Curing at 50°C for 24 h.

[0037] Performance testing Conditions: Sterilization treatment at 121°C for 40 minutes.

[0038] Results: Water vapor transmission rate: 1.8 g / (m²·day).

[0039] Oxygen transmission rate: 2.5 cm³ / (m²·day·atm).

[0040] Antibacterial rate (Escherichia coli and Staphylococcus aureus): 99.6%.

[0041] Retention rate of heat-sealing strength: 92%.

[0042] Tensile strength: 46 MPa.

[0043] Shelf life (for acidic pH 3 contents): 25 months. Example 2

[0044] Preparation process Preparation of the outer layer Components: 80 parts by mass of polypropylene, 12.5 parts by mass of maleic anhydride grafted polypropylene, and 7.5 parts by mass of modified glucomannan.

[0045] Preparation of maleic anhydride grafted polypropylene: Same as Example 1, at a temperature of 185°C.

[0046] Preparation of modified glucomannan: pH 8.5, heated to 85°C, and the degree of deacetylation is 95%.

[0047] Molding: Same as Example 1.

[0048] Thickness: 20 μm.

[0049] Preparation of the barrier layer Nano zinc oxide: particle size 35 nm, tannic acid grafting rate 20%.

[0050] Process: Irradiation intensity 1000 mJ / cm².

[0051] Thickness of the silicon oxide layer is 75 nm, oxygen to silicon atomic ratio is 1.65, and radio frequency power is 400 W.

[0052] Thickness: 15 μm.

[0053] Preparation of the adhesive layer Mass ratio of epoxy group to siloxane segment: 1:4.

[0054] Thickness: 3.5 μm.

[0055] Preparation of the high-temperature resistant layer Glass fiber: diameter 7.5 μm, aspect ratio 75.

[0056] Process: Temperature of the casting roll is 30°C, draw ratio is 6 times.

[0057] Thickness: 65 μm.

[0058] Preparation of the heat-sealing layer Silver ion microcapsule: silver loading 6.5%.

[0059] Process: Extrusion temperature 190°C, die head pressure 10 MPa.

[0060] Thickness: 40 μm.

[0061] Interlayer lamination Coating amount 4 g / m², curing at 55°C for 36 h.

[0062] Performance testing Results: Water vapor transmission rate: 1.5 g / (m²·day).

[0063] Oxygen transmission rate: 2.0 cm³ / (m²·day·atm).

[0064] Antibacterial rate: 99.8%.

[0065] Heat-sealing strength retention rate: 95%.

[0066] Tensile strength: 48 MPa.

[0067] Shelf life (20% high-fat content): 26 months. Example 3

[0068] Preparation process Preparation of the outer layer Components: 85 parts by mass of polypropylene, 15 parts by mass of maleic anhydride-grafted polypropylene, and 10 parts by mass of modified glucomannan.

[0069] Preparation of maleic anhydride-grafted polypropylene: Same as Example 1, at a temperature of 200°C.

[0070] Preparation of modified glucomannan: pH 10, heated to 95°C, and the degree of deacetylation is 98%.

[0071] Molding: Same as Example 1.

[0072] Thickness: 25μm.

[0073] Preparation of the barrier layer Nanometer zinc oxide: particle size 50 nm, tannic acid grafting rate 25%.

[0074] Process: Irradiation intensity 1200 mJ / cm².

[0075] Thickness of the silicon oxide layer 100nm, oxygen to silicon atomic ratio 1.8, radio frequency power 500W.

[0076] Thickness: 20μm.

[0077] Preparation of the adhesive layer Mass ratio of epoxy group to siloxane chain segment: 1:5.

[0078] Thickness: 5μm.

[0079] Preparation of the high-temperature resistant layer Glass fiber: diameter 10μm, aspect ratio 100.

[0080] Process: Temperature of the casting roll 35°C, draw ratio 7 times.

[0081] Thickness: 80 μm.

[0082] Preparation of heat-sealing layer Silver ion microcapsule: Silver loading 8%.

[0083] Process: Extrusion temperature 200 °C, die head pressure 12 MPa.

[0084] Thickness: 50 μm.

[0085] Interlayer lamination Coating amount 4.5 g / m², curing at 60 °C for 48 h.

[0086] Performance test Results: Water vapor transmission rate: 1.2 g / (m²·day).

[0087] Oxygen transmission rate: 1.8 cm³ / (m²·day·atm).

[0088] Antibacterial rate: 99.9%.

[0089] Heat-sealing strength retention rate: 96%.

[0090] Tensile strength: 50 MPa.

[0091] Shelf life (for acidic pH 3 contents): 27 months. Comparative example 1

[0092] Preparation process Outer layer: 85 parts by mass of polypropylene, 15 parts by mass of maleic anhydride graft copolymerized polypropylene, 0 parts by mass of modified glucomannan; thickness 15 μm.

[0093] Other layers: The same as in Example 1.

[0094] Performance test Results: Water vapor transmission rate: 3.5 g / (m²·day).

[0095] Oxygen transmission rate: 4.0 cm³ / (m²·day·atm).

[0096] Antibacterial rate: 90%.

[0097] Heat-sealing strength retention rate: 85%.

[0098] Tensile strength: 40 MPa.

[0099] Analysis: Lack of modified glucomannan leads to a decrease in hydrothermal stability, and a weakening of barrier and antibacterial properties. Comparative example 2

[0100] Preparation process Barrier layer: only polychlorotrifluoroethylene, without surface-grafted tannic acid nano-zinc oxide; thickness 10 μm.

[0101] Other layers: the same as in Example 1.

[0102] Performance test Results: Water vapor transmission rate: 2.5 g / (m²·day).

[0103] Oxygen transmission rate: 5.0 cm³ / (m²·day·atm).

[0104] Antibacterial rate: 85%.

[0105] Heat seal strength retention rate: 90%.

[0106] Analysis: Without nano-zinc oxide, the barrier and antibacterial properties decrease significantly. Comparative Example 3

[0107] Preparation process Heat seal layer: only polyethylene, without silver ion microcapsules; thickness 30 μm.

[0108] Other layers: the same as in Example 1.

[0109] Performance test Results: Water vapor transmission rate: 2.0 g / (m²·day).

[0110] Oxygen transmission rate: 2.8 cm³ / (m²·day·atm).

[0111] Antibacterial rate: 50%.

[0112] Heat seal strength retention rate: 88%.

[0113] Analysis: Without antibacterial agent, the antibacterial property decreases significantly. Comparative Example 4

[0114] Preparation process Thickness of each layer: outer layer 10 μm, barrier layer 25 μm, adhesive layer 1 μm, high-temperature resistant layer 90 μm, heat seal layer 20 μm.

[0115] Other parameters: the same as in Example 1.

[0116] Performance test Results: Water vapor transmission rate: 2.8 g / (m²·day).

[0117] Oxygen transmission rate: 4.0 cm³ / (m²·day·atm).

[0118] Antibacterial rate: 95%.

[0119] Heat-sealing strength retention rate: 80%.

[0120] Prone to delamination.

[0121] Analysis: Improper thickness leads to a decline in barrier and adhesion properties, resulting in poor overall stability.

[0122] Conclusion Examples 1-3 show that the material exhibits excellent barrier properties, antibacterial properties, and mechanical strength at both parameter endpoints and intermediate values, meeting the technical requirements of the claims. Comparative Examples 1-4 verify the necessity of each layer of material and process by removing key components or adjusting parameters outside the range, highlighting the advantages of the technical solution.

[0123] Finally, it should be noted that the above examples are only used to illustrate the implementation process and characteristics of the present invention, rather than limiting the technical solution of the present invention. Although the present invention has been described in detail with reference to the above examples, those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced. Any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A high temperature resistant retort packaging material, characterized in that: From outside to inside, there are five layers of structure: Outer layer: a composition of polypropylene, maleic anhydride graft copolymerized polypropylene and modified glucomannan with a deacetylation degree of ≥90%; Barrier layer: a composite film comprising polytrifluorochloroethylene and nano zinc oxide with tannic acid grafted on the surface, wherein the surface of the nano zinc oxide is grafted with tannic acid to form a photocatalytic synergistic antibacterial system; Adhesive layer: composed of epoxy-modified silicone resin and polyurethane adhesive, in which the mass ratio of epoxy group to siloxane chain segment is 1:3-5; High temperature resistant layer: contains polypropylene and glass fiber reinforcement treated with silane coupling agent, wherein the glass fiber has a diameter of 5-10 μm and an aspect ratio of ≥50; Heat sealing layer: a composite material composed of polyethylene and silver ion microcapsules, wherein the silver ion microcapsules use porous cyclodextrin as the wall material and the silver loading amount is 5-8% by mass; The thickness ratio of each layer is: outer layer 15-25μm, barrier layer 10-20μm, adhesive layer 2-5μm, high temperature resistant layer 50-80μm, heat sealing layer 30-50μm.

2. The high temperature resistant retort packaging material according to claim 1, characterized in that: In the outer layer: The mass ratio of the polypropylene, maleic anhydride grafted copolymerized polypropylene and modified glucomannan is (75-85): (10-15): (5-10).

3. The high temperature resistant retort packaging material according to claim 1, characterized in that: In the outer layer: The preparation method of maleic anhydride graft copolymer polypropylene comprises: mixing polypropylene particles, maleic anhydride and initiator in a mass percentage of 95:4:1, and melt blending at a temperature of 170-200°C using a twin-screw extruder; extruding and granulating to obtain maleic anhydride graft copolymer polypropylene; The preparation method of the modified glucomannan comprises: heating konjac glucomannan to 75-95° C. in a calcium hydroxide solution with a pH of 7-10, and spray drying to obtain a crystalline structure with a deacetylation degree of ≥90%.

4. The high temperature resistant retort packaging material according to claim 1, characterized in that: In the barrier layer: The particle size of the nano zinc oxide is 20-50 nm, the tannic acid grafting rate is 15-25%, and a silicon oxide layer with a thickness of 50-100 nm is deposited on the surface of the barrier layer, and the oxygen-silicon atomic ratio of the silicon oxide layer is 1.5-1.

8.

5. The high temperature resistant retort packaging material according to claim 1, characterized in that: The method for preparing the high temperature resistant retort packaging material comprises the following steps: (1) Preparation of outer layer: After polypropylene, maleic anhydride grafted copolymer polypropylene and modified glucomannan are melt-blended, a film is formed by a biaxial stretching process, the longitudinal to transverse stretching ratio is 3.5:1, and a corona treatment is performed, and the corona strength is ≥40 dyne / cm; (2) Preparation of barrier layer: The nano zinc oxide dispersion with tannic acid grafted on the surface was coated on the surface of polytrifluorochloroethylene, and the irradiation was carried out at a wavelength of 365nm and an irradiation intensity of 800-1200 mJ / cm in an inert gas environment with an oxygen content of ≤200 ppm. 2 UV curing, followed by deposition of silicon oxide layer by plasma enhanced chemical vapor deposition with a silane to oxygen flow ratio of 1:3 and a radio frequency power of 300-500W; (3) Preparation of high temperature resistant layer: co-extrude polypropylene and surface treated glass fiber for casting, the casting roll temperature is controlled at 25-35°C, and the stretching ratio is 5-7 times; (4) Preparation of heat seal layer: silver ion microcapsules are embedded in polyethylene matrix using supercritical carbon dioxide fluid, with an extrusion temperature of 180-200°C and a die pressure of 8-12 MPa; (5) Interlayer composite: Use two-component polyurethane adhesive with a viscosity of 3.5-4.5g / m 2 Dry compounding is carried out with a coating amount and ripened at 50-60℃ for 24-48h.

6. Use of a high temperature cooking resistant packaging material according to any one of claims 1 to 5 in high temperature sterilization packaging of food and pharmaceutical products, characterized in that: After cooking at 121℃ for 40 minutes, the water vapor transmission rate is ≤2 g / (m²·day), the oxygen transmission rate is ≤3 cm³ / (m²·day·atm), the antibacterial rate against Escherichia coli and Staphylococcus aureus is ≥99.5%, the heat seal strength retention rate is ≥90%, and it is suitable for aseptic packaging of contents with acidic pH 3-5 or high fat content ≥20%, with a shelf life of ≥24 months.