A heat-resistant retort packaging material and its application

Abstract

The present invention discloses a heat-resistant retort packaging material and its application, belonging to the field of polymer composite materials. It adopts a five-layer structure: the outer layer is polypropylene, maleic anhydride grafted polypropylene and calcium ion modified glucomannan to enhance the wet-heat stability; the barrier layer consists of tannic acid grafted nano-zinc oxide / polytrifluorochloroethylene composite film and silicon oxide layer, with a dual barrier effect; the heat-resistant layer is reinforced by polypropylene and glass fiber to enhance the mechanical properties; the heat-sealing layer is supercritical carbon dioxide embedded silver ion microcapsule polyethylene, with both antibacterial and heat-sealing strength. Prepared by processes such as biaxial stretching and UV curing, after retorting at 121 °C for 40 minutes, the oxygen transmission rate ≤ 3 cm³ / (m²·day·atm), the water vapor transmission rate ≤ 2 g / (m²·day), the tensile strength ≥ 45 MPa, the antibacterial rate ≥ 99.5%, and the recovery rate of polypropylene substrate ≥ 95%. It is applicable to acidic or high-fat food and pharmaceutical sterile packaging, with a shelf life ≥ 24 months, and has high barrier, antibacterial and environmental protection properties.

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 especially 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, there is an urgent need to achieve performance breakthroughs in the barrier properties, mechanical strength, medium resistance corrosion and antibacterial properties of high-temperature resistant retort packaging materials. 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 micro-cracks 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, cannot be heated by microwave, and the recycling process is complex, posing challenges to environmental protection and unable to meet the current trend requirements 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 hazard to food safety 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), resulting in 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, leading to a decrease in the dimensional stability of the film material, and further 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 a pinhole effect in the heat-sealing layer or barrier layer, and there is also a potential food safety hazard of excessive migration (such as zinc ion migration > 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 adopting methods such as surface grafting of tannic acid to improve interfacial compatibility, 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. The overall tensile strength can reach over 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 in 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 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 over 30%, affecting the effective loading and long-term release effect of the antibacterial agent. The use of supercritical carbon dioxide fluid technology can effectively reduce the processing temperature, achieve 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 a market trend perspective, high-value-added food packaging, such as acidic sauces and high-fat dairy products, places higher requirements on 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 and comprehensive mechanical properties of all-polypropylene materials without sacrificing environmental protection has become an important direction for future research. 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] In view of the technical bottlenecks of existing high-temperature retort packaging materials in terms of barrier property, antibacterial property, 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 retort packaging material of the present invention are as follows:

[0008] The described high-temperature retort packaging material has the following five-layer structure from outside to inside:

[0009] Outer layer: A composition of polypropylene, maleic anhydride-grafted polypropylene, and modified glucomannan with a degree of deacetylation ≥ 90%;

[0010] Barrier layer: A composite film containing polychlorotrifluoroethylene and nano-zinc oxide with surface-grafted tannic acid. The nano-zinc oxide is surface-grafted with tannic acid to form a photocatalytic synergistic antibacterial system;

[0011] Adhesive layer: Composed of epoxy-modified silicone resin and polyurethane adhesive, where the mass ratio of the epoxy group to the siloxane chain segment is 1:3 - 5;

[0012] High-temperature resistant layer: Containing polypropylene and glass fiber reinforcements treated with silane coupling agents, where the diameter of the glass fiber is 5 - 10 μm and the aspect ratio ≥ 50;

[0013] 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;

[0014] The thickness ratio of each layer is: outer layer 15-25 μm, barrier layer 10-20 μm, adhesive layer 2-5 μm, high-temperature resistant layer 50-80 μm, heat-sealing layer 30-50 μm;

[0015] For the described high-temperature retort packaging material, in the outer layer:

[0016] The mass ratio of the polypropylene, maleic anhydride grafted polypropylene, and modified glucomannan is (75-85):(10-15):(5-10);

[0017] For the described high-temperature retort packaging material, in the outer layer:

[0018] The preparation method of the maleic anhydride grafted polypropylene includes: 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 pelletizing to obtain maleic anhydride grafted polypropylene;

[0019] 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 ≥90%;

[0020] For the described high-temperature retort packaging material, in the barrier layer:

[0021] The particle size of the described nano-zinc oxide is 20-50 nm, the grafting rate of tannic acid is 15-25%, and a silicon oxide layer with a deposition thickness of 50-100 nm is deposited on the surface of the barrier layer, and the oxygen-silicon atom ratio of the silicon oxide layer is 1.5-1.8;

[0022] The preparation method of the described high-temperature retort packaging material includes the following steps:

[0023] (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 ≥40 dyne / cm;

[0024] (2) Preparation of the barrier layer: Coating a dispersion of nano-zinc oxide grafted with tannic acid on the surface of a polychlorotrifluoroethylene film, and performing irradiation with a wavelength of 365 nm and an irradiation intensity of 800-1200 mJ / cm² in an inert gas environment with an oxygen content ≤200 ppm2 UV curing, followed by depositing 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;

[0025] (3) Preparation of the high-temperature resistant layer: Co-extrusion casting of polypropylene and surface-treated glass fiber, controlling the temperature of the casting roll at 25 - 35 °C, and the drawing ratio at 5 - 7 times;

[0026] (4) Preparation of the heat-sealing layer: Embedding 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;

[0027] (5) Interlayer lamination: Using a two-component polyurethane adhesive for dry lamination at a coating amount of 3.5 - 4.5 g / m 2 and curing at 50 - 60 °C for 24 - 48 h.

[0028] Application of the described high-temperature resistant retort packaging material in 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-sealing strength retention rate ≥ 90%, suitable for aseptic packaging of acidic pH 3 - 5 or high-fat content ≥ 20% contents, and the shelf life ≥ 24 months.

[0029] 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. The synergistic effect of modified glucomannan and maleic anhydride grafted polypropylene in the outer layer 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 polychlorotrifluoroethylene composite, combined with a silicon oxide deposition layer, forming a double-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 it is 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. The composite system of epoxy-modified silicone resin and polyurethane in the adhesive layer makes the interlayer peel strength ≥ 6 N / 15mm, and there is no interface delamination after cooking, overcoming the problem of adhesive force attenuation caused by wet and heat aging of traditional adhesives. The high-temperature resistant layer modifies random copolymerized polypropylene with hydrogenated styrene-butadiene block copolymer and introduces glass fibers with a high aspect ratio (aspect ratio ≥ 50), enabling the material to have a notched impact strength ≥ 88 kJ / m² at -40 °C, which is 76% higher than that of 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 to embed silver ion microcapsules (Ag@CD), with a silver ion slow-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 makes the heat-sealing strength ≥ 25 N / 15mm, and the retention rate after cooking ≥ 90%, solving the contradiction between the low strength of the traditional CPP heat-sealing layer (< 20 N / 15mm) and the difficulty in compatible antibacterial function. In addition, the all-polypropylene substrate structure enables the material to have a recyclability rate ≥ 95%, meeting the EU EN 13432 standard, and significantly reducing the environmental load compared with the traditional polyester / aluminum foil / PP composite film (recycling rate < 5%). 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 suitable for 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

[0030] In the examples and comparative examples, the ratios are all mass percentages unless otherwise specified. Example 1

[0031] Preparation process

[0032] Preparation of the outer layer

[0033] Components: 75 parts by mass of polypropylene, 10 parts by mass of maleic anhydride graft copolymerized polypropylene, and 5 parts by mass of modified glucomannan.

[0034] Preparation of maleic anhydride graft copolymerized polypropylene:

[0035] Mix polypropylene particles, maleic anhydride, and initiator in a mass ratio of 95:4:1.

[0036] Melt blend at 170 °C using a twin-screw extruder and extrude into pellets.

[0037] Preparation of modified glucomannan:

[0038] Heat konjac glucomannan in a calcium hydroxide solution at pH 7 to 75 °C for treatment.

[0039] Obtain a crystalline structure with a degree of deacetylation of 90% after spray drying.

[0040] Molding:

[0041] After melt blending the three components, form a film through a biaxial stretching process (longitudinal to transverse stretching ratio of 3.5:1).

[0042] Corona treatment, strength 40 dyne / cm.

[0043] Thickness: 15 μm.

[0044] Preparation of the barrier layer

[0045] Components: polychlorotrifluoroethylene and nano-zinc oxide with tannic acid grafted on the surface.

[0046] Nano-zinc oxide: particle size 20 nm, tannic acid grafting rate 15%.

[0047] Process:

[0048] Coat the nano-zinc oxide dispersion on the surface of the polychlorotrifluoroethylene film.

[0049] Under an inert gas environment with an oxygen content of 200 ppm, cure with ultraviolet light at a wavelength of 365 nm and an irradiation intensity of 800 mJ / cm².

[0050] 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).

[0051] Thickness: 10 μm.

[0052] Preparation of the adhesive layer

[0053] Components: Epoxy-modified silicone resin and polyurethane adhesive, mass ratio of epoxy group to siloxane segment is 1:3.

[0054] Thickness: 2 μm.

[0055] Preparation of the high-temperature resistant layer

[0056] Components: 90 parts by mass of polypropylene, 10 parts by mass of glass fiber treated with silane coupling agent.

[0057] Glass fiber: diameter 5 μm, aspect ratio 50.

[0058] Process: Co-extrusion casting, casting roll temperature 25 °C, draw ratio 5 times.

[0059] Thickness: 50 μm.

[0060] Preparation of the heat-sealing layer

[0061] Components: 95 parts by mass of polyethylene, 5 parts by mass of silver ion microcapsules.

[0062] Silver ion microcapsules: Using porous cyclodextrin as the wall material, silver loading 5%.

[0063] Process: Embedded in the polyethylene matrix by supercritical carbon dioxide fluid technology, extrusion temperature 180 °C, die head pressure 8 MPa.

[0064] Thickness: 30 μm.

[0065] Interlayer lamination

[0066] Use two-component polyurethane adhesive, coating amount 3.5 g / m².

[0067] Cure at 50 °C for 24 h.

[0068] Performance testing

[0069] Condition: Sterilization treatment at 121 °C for 40 minutes.

[0070] Result:

[0071] Water vapor transmission rate: 1.8 g / (m²·day).

[0072] Oxygen transmission rate: 2.5 cm³ / (m²·day·atm).

[0073] Antibacterial rate (Escherichia coli and Staphylococcus aureus): 99.6%.

[0074] Heat-sealing strength retention rate: 92%.

[0075] Tensile strength: 46 MPa.

[0076] Shelf life (for acidic pH 3 contents): 25 months. Example 2

[0077] Preparation process

[0078] Preparation of the outer layer

[0079] Components: 80 parts by mass of polypropylene, 12.5 parts by mass of maleic anhydride grafted polypropylene, 7.5 parts by mass of modified glucomannan.

[0080] Preparation of maleic anhydride grafted polypropylene:

[0081] Same as Example 1, temperature 185°C.

[0082] Preparation of modified glucomannan:

[0083] pH 8.5, heated to 85°C, degree of deacetylation 95%.

[0084] Molding: Same as Example 1.

[0085] Thickness: 20 μm.

[0086] Preparation of the barrier layer

[0087] Nano zinc oxide: particle size 35 nm, tannic acid grafting rate 20%.

[0088] Process:

[0089] Irradiation intensity 1000 mJ / cm².

[0090] Thickness of the silicon oxide layer 75 nm, oxygen to silicon atomic ratio 1.65, radio frequency power 400 W.

[0091] Thickness: 15 μm.

[0092] Preparation of the adhesive layer

[0093] Mass ratio of epoxy group to siloxane segment: 1:4.

[0094] Thickness: 3.5 μm.

[0095] Preparation of the high-temperature resistant layer

[0096] Glass fiber: diameter 7.5 μm, aspect ratio 75.

[0097] Process: Casting roll temperature 30°C, draw ratio 6 times.

[0098] Thickness: 65 μm.

[0099] Preparation of heat-sealing layer

[0100] Silver ion microcapsule: Silver loading is 6.5%.

[0101] Process: Extrusion temperature is 190 °C, die head pressure is 10 MPa.

[0102] Thickness: 40 μm.

[0103] Interlayer compounding

[0104] Coating amount is 4 g / m², curing at 55 °C for 36 h.

[0105] Performance testing

[0106] Results:

[0107] Water vapor transmission rate: 1.5 g / (m²·day).

[0108] Oxygen transmission rate: 2.0 cm³ / (m²·day·atm).

[0109] Antibacterial rate: 99.8%.

[0110] Retention rate of heat-sealing strength: 95%.

[0111] Tensile strength: 48 MPa.

[0112] Shelf life (20% high-fat content): 26 months. Example 3

[0113] Preparation process

[0114] Preparation of outer layer

[0115] Components: 85 parts by mass of polypropylene, 15 parts by mass of maleic anhydride grafted polypropylene, 10 parts by mass of modified glucomannan.

[0116] Preparation of maleic anhydride grafted polypropylene:

[0117] Same as Example 1, temperature is 200 °C.

[0118] Preparation of modified glucomannan:

[0119] pH is 10, heated to 95 °C, degree of deacetylation is 98%.

[0120] Molding: Same as Example 1.

[0121] Thickness: 25 μm.

[0122] Preparation of barrier layer

[0123] Nanometer zinc oxide: Particle size is 50 nm, tannic acid grafting rate is 25%.

[0124] Process:

[0125] Irradiation intensity: 1200 mJ / cm².

[0126] Thickness of silicon oxide layer: 100 nm, oxygen to silicon atomic ratio: 1.8, RF power: 500 W.

[0127] Thickness: 20 μm.

[0128] Preparation of adhesive layer

[0129] Mass ratio of epoxy group to siloxane segment: 1:5.

[0130] Thickness: 5 μm.

[0131] Preparation of high-temperature resistant layer

[0132] Glass fiber: diameter 10 μm, aspect ratio 100.

[0133] Process: temperature of casting roller 35°C, draw ratio 7 times.

[0134] Thickness: 80 μm.

[0135] Preparation of heat-sealing layer

[0136] Silver ion microcapsule: silver loading 8%.

[0137] Process: extrusion temperature 200°C, die head pressure 12 MPa.

[0138] Thickness: 50 μm.

[0139] Interlayer lamination

[0140] Coating amount: 4.5 g / m², curing at 60°C for 48 h.

[0141] Performance testing

[0142] Results:

[0143] Water vapor transmission rate: 1.2 g / (m²·day).

[0144] Oxygen transmission rate: 1.8 cm³ / (m²·day·atm).

[0145] Antibacterial rate: 99.9%.

[0146] Heat-sealing strength retention rate: 96%.

[0147] Tensile strength: 50 MPa.

[0148] Shelf life (for acidic pH 3 content): 27 months. Comparative Example 1

[0149] Preparation process

[0150] Outer layer: 85 parts by mass of polypropylene, 15 parts by mass of maleic anhydride grafted polypropylene, 0 parts by mass of modified glucomannan; thickness 15 μm.

[0151] Other layers: The same as in Example 1.

[0152] Performance test

[0153] Result:

[0154] Water vapor transmission rate: 3.5 g / (m²·day).

[0155] Oxygen transmission rate: 4.0 cm³ / (m²·day·atm).

[0156] Antibacterial rate: 90%.

[0157] Heat seal strength retention rate: 85%.

[0158] Tensile strength: 40 MPa.

[0159] Analysis: Lack of modified glucomannan leads to a decrease in hydrothermal stability and a weakening of barrier and antibacterial properties. Comparative Example 2

[0160] Preparation process

[0161] Barrier layer: Only polychlorotrifluoroethylene, without nano-zinc oxide grafted with tannic acid on the surface; thickness 10 μm.

[0162] Other layers: The same as in Example 1.

[0163] Performance test

[0164] Result:

[0165] Water vapor transmission rate: 2.5 g / (m²·day).

[0166] Oxygen transmission rate: 5.0 cm³ / (m²·day·atm).

[0167] Antibacterial rate: 85%.

[0168] Heat seal strength retention rate: 90%.

[0169] Analysis: Without nano-zinc oxide, the barrier and antibacterial properties decrease significantly. Comparative Example 3

[0170] Preparation process

[0171] Heat seal layer: Only polyethylene, without silver ion microcapsules; thickness 30 μm.

[0172] Other layers: The same as in Example 1.

[0173] Performance test

[0174] Results:

[0175] Water vapor transmission rate: 2.0 g / (m²·day).

[0176] Oxygen transmission rate: 2.8 cm³ / (m²·day·atm).

[0177] Antibacterial rate: 50%.

[0178] Heat-sealing strength retention rate: 88%.

[0179] Analysis: Without the antibacterial agent, the antibacterial performance is significantly reduced. Comparative Example 4

[0180] Preparation process

[0181] Thickness of each layer: The outer layer is 10 μm, the barrier layer is 25 μm, the adhesive layer is 1 μm, the high-temperature resistant layer is 90 μm, and the heat-sealing layer is 20 μm.

[0182] Other parameters: The same as in Example 1.

[0183] Performance test

[0184] Results:

[0185] Water vapor transmission rate: 2.8 g / (m²·day).

[0186] Oxygen transmission rate: 4.0 cm³ / (m²·day·atm).

[0187] Antibacterial rate: 95%.

[0188] Heat-sealing strength retention rate: 80%.

[0189] Easy to delaminate.

[0190] Analysis: Improper thickness leads to a decrease in barrier and adhesive properties, and poor overall stability.

[0191] Conclusion

[0192] Examples 1 - 3 show that the material exhibits excellent barrier properties, antibacterial properties, and mechanical strength at both the 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 beyond the range, highlighting the advantages of the technical solution.

[0193] Finally, it should be noted that the above embodiments are only used to illustrate the implementation process and features of the present invention, rather than limiting the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced, and 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 heat-resistant retort packaging material, characterized in that, From the outside to the inside, there are the following five-layer structures: Outer layer: A composition of polypropylene, maleic anhydride grafted polypropylene, and modified glucomannan with a degree of deacetylation ≥ 90%. The mass ratio of polypropylene, maleic anhydride grafted polypropylene, and modified glucomannan is (75 - 85):(10 - 15):(5 - 10). The preparation method of the maleic anhydride grafted polypropylene includes: mixing polypropylene particles, maleic anhydride, and an initiator in a mass percentage of 95:4:1, and melt-blending them at a temperature of 170 - 200 °C using a twin-screw extruder; 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 degree of deacetylation ≥ 90%. Barrier layer: A composite film containing poly(chlorotrifluoroethylene) and nano-zinc oxide with tannic acid grafted on the surface. The nano-zinc oxide has tannic acid grafted on its surface to form a photocatalytic synergistic antibacterial system. 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 thickness of 50 - 100 nm is deposited on the surface of the barrier layer. The oxygen-to-silicon atomic ratio of the silicon oxide layer is 1.5 - 1.

8. Adhesive layer: Composed of epoxy-modified silicone resin and polyurethane adhesive, where the mass ratio of the epoxy group to the siloxane chain segment is 1:3 - 5. High-temperature resistant layer: Contains polypropylene and glass fiber reinforcements treated with a silane coupling agent, where the glass fiber diameter is 5 - 10 μm and the 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 percentage. The thickness ratio of each layer is: outer layer 15 - 25 μm, barrier layer 10 - 20 μm, adhesive layer 2 - 5 μm, high-temperature resistant layer 50 - 80 μm, heat-sealing layer 30 - 50 μm.

2. The heat-resistant retort packaging material according to claim 1, characterized in that, The preparation method of the 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. The longitudinal and transverse stretching ratios are 3.5:1, and corona treatment is carried out with a corona strength ≥ 40 dyne / cm. (2)Barrier layer preparation: Coat the surface of polytrifluorochloroethylene with a nano-zinc oxide dispersion liquid grafted with tannic acid on the surface, 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 ≤ 200 ppm. Subsequently, 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 of polypropylene and surface-treated glass fibers, controlling the temperature of the casting roll at 25 - 35 °C, and the stretching ratio is 5 - 7 times. (4) Preparation of the heat-sealing layer: Embed silver ion microcapsules into the 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: Use a two-component polyurethane adhesive for dry lamination at a coating amount of 3.5 - 4.5 g / m 2 and cure at 50 - 60 °C for 24 - 48 h.

3. Use of a high-temperature cooking-resistant packaging material as described in any one of claims 1-2 in high-temperature sterilization packaging of food and pharmaceutical products, characterized in that: After being subjected to retort treatment 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-sealing strength retention rate ≥ 90%, and it is suitable for aseptic packaging of contents with an acidic pH of 3 - 5 or a high-fat content ≥ 20%, and the shelf life ≥ 24 months.