Retort-resistant packaging film and method of making same

Abstract

The application provides a kind of cooking-resistant packaging film material and its preparation method, belong to packaging film material field.The packaging film material is composed of the following chemical raw materials: random copolymerization polypropylene: 30-50 parts, cyclic olefin copolymer: 5-10 parts, hyperbranched polyester with terminal epoxy group: 3-5 parts, epoxy modified nano silicon dioxide: 1-2 parts, maleic anhydride grafted polyolefin: 8-12 parts, ethylene-methyl acrylate-glycidyl methacrylate terpolymer: 3-6 parts, polyamide elastomer: 3-5 parts, organic modified montmorillonite: 1-2 parts, silicone composite master batch: 1-3 parts, antioxidant: 0.2-0.5 parts, lubricant: 0.2-0.5 parts.Each component realizes the synergistic improvement of the cooking-resistant performance, barrier property and mechanical property of the packaging film material through the synergistic effect of chemical crosslinking network construction, interface compatibilization and physical barrier.

Description

Technical Field

[0001] This application relates to the field of packaging film technology, and in particular to a retortible packaging film and its preparation method. Background Technology

[0002] Cast polypropylene (CPP) film is widely used as the inner layer substrate of retort-resistant composite films due to its high transparency, good stiffness, low heat-sealing temperature, excellent moisture resistance and good heat resistance.

[0003] However, existing polypropylene-based retort membrane materials still have significant shortcomings in terms of overall performance. Homopolymer polypropylene films are prone to embrittlement after high-temperature retort treatment, leading to cracking at the seal; while random copolymer polypropylene improves flexibility and transparency, its heat resistance and barrier properties are relatively insufficient, making it only suitable for ordinary or semi-high-temperature retort membranes. Therefore, how to synergistically improve retort resistance, barrier properties, and mechanical properties has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] This application provides a retortible packaging film and its preparation method to solve the following technical problem: how to synergistically improve the retort resistance, barrier properties and mechanical properties of the packaging film.

[0005] In a first aspect, embodiments of this application provide a retortible packaging film material, which, by weight, is composed of the following chemical raw materials: random copolymer polypropylene: 30-50 parts, cyclic olefin copolymer: 5-10 parts, hyperbranched polyester with epoxy groups at the end: 3-5 parts, epoxy-modified nano-silica: 1-2 parts, maleic anhydride-grafted polyolefin: 8-12 parts, ethylene-methyl acrylate-glycidyl methacrylate terpolymer: 3-6 parts, polyamide elastomer: 3-5 parts, organically modified montmorillonite: 1-2 parts, organosilicon composite masterbatch: 1-3 parts, antioxidant: 0.2-0.5 parts, lubricant: 0.2-0.5 parts.

[0006] Optionally, the preparation method of the hyperbranched polyester with epoxy groups at the end includes the following steps: S101. Under inert gas protection, the hydroxyl-terminated hyperbranched polyester is stirred and kept at a constant temperature of 60°C. The catalyst boron trifluoride diethyl ether is added. Epichlorohydrin is added in a constant pressure dropping funnel. Under nitrogen protection, epichlorohydrin is added dropwise at a rate of 5 drops / second. After the addition is complete, the reaction is kept at a constant temperature for 3 hours to carry out the ring-opening reaction. S102. After the reaction is complete, cool down to 30°C and add saturated sodium hydroxide solution to a constant pressure dropping funnel at a rate of 5 drops / second. After the addition is complete, keep the temperature constant for 4 hours to carry out the closed-loop reaction and obtain the reaction solution. S103. The reaction solution is post-treated to obtain the hyperbranched polyester with epoxy groups at the end.

[0007] Optionally, the mass of the boron trifluoride ether is 0.5% to 1.5% of the mass of the hydroxyl-terminated hyperbranched polyester; The molar ratio of the hydroxyl-terminated hyperbranched polyester to the epichlorohydrin is 1:1.2; The molar ratio of epichlorohydrin to sodium hydroxide is 1:1.2.

[0008] Optionally, the epoxy-modified nano-silica is KH-560 modified nano-silica.

[0009] Optionally, the mass ratio of the nano-silica to the KH-560 is 1:(0.5 to 0.8).

[0010] Optionally, the preparation method of the organically modified montmorillonite includes the following steps: S201. Disperse sodium montmorillonite in deionized water to obtain a suspension; S202. Add hexadecyltriphenyl quaternary phosphonium salt to the suspension, adjust the pH to 6-8, and stir the reaction at 75-85°C for 2-4 hours to obtain the second reaction solution; S203. The second reaction solution is filtered and washed with deionized water until no halogen ions are detected. Then it is vacuum dried at 70-90°C to obtain the organic modified montmorillonite.

[0011] Optionally, the mass ratio of the hexadecyltriphenyl quaternary phosphonium salt to the sodium montmorillonite is 1:(2~3).

[0012] Secondly, embodiments of this application provide a method for preparing a retort-resistant packaging film material as described in any one of the first aspects, the method comprising the following steps: S1. Random copolymer polypropylene, cyclic olefin copolymer, hyperbranched polyester with epoxy groups at the end, epoxy-modified nano silica, maleic anhydride grafted polyolefin, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, polyamide elastomer, organic modified montmorillonite, organosilicon composite masterbatch, antioxidant and lubricant are mixed at 500-1500 rpm for 10-30 min to obtain a mixture. S2. The mixture is fed into a twin-screw extruder for melt blending and extrusion, followed by extrusion granulation to obtain composite granules; S3. The composite granules are melt-extruded into a film using a casting extruder, and then drawn and wound to obtain the retort-resistant packaging film material.

[0013] Optionally, the barrel temperature of the twin-screw extruder is set as follows: feeding section 170-190℃, melting section 190-210℃, homogenization section 200-220℃, die head temperature 210-230℃, and screw speed 100-250 rpm.

[0014] Optionally, the barrel temperature of the cast extruder is 200-220°C, the die temperature is 210-230°C, and the cast roll temperature is 30-60°C.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: (1) The improved resistance to boiling stems from the in-situ chemical cross-linking network constructed by the reactive components during melt processing. The epoxy groups carried by the terminal epoxy hyperbranched polyester (HBPE-EP) and the ethylene-methyl acrylate-glycidyl methacrylate terpolymer (E-MA-GMA) undergo ring-opening addition reactions with the anhydride groups of maleic anhydride-grafted polyolefin (MAH-g-PO) and the terminal amino groups of polyamide elastomer (TPAE) in the molten state, forming a stable ester bond and CN bond cross-linking structure. This network structure effectively inhibits the slippage and swelling of molecular chains under high-temperature boiling conditions of 121℃, maintaining the dimensional stability and structural integrity of the membrane. The quaternary phosphonium salt intercalating agent in organically modified montmorillonite (OMMT) remains stable at the processing temperature, ensuring that the layered silicate sheet structure does not collapse and continues to play a physical barrier role.

[0016] (2) Barrier performance is achieved through the synergistic effect of multiple physical barriers. After the quaternary phosphonium salt intercalation, the interlayer spacing of the OMMT nanosheets increases, forming a labyrinth effect of parallel or staggered arrangement in the membrane material, forcing water vapor and oxygen molecules to diffuse around it, and significantly extending the permeation path. The rigid particles of epoxy-modified nano-silica also form tortuous channels in the matrix, synergistically extending the diffusion path with the OMMT sheets. Cyclic olefin copolymers (COC) inherently have high water and oxygen barrier properties, and their rigid cyclic molecular chain structure further reduces the gas permeability coefficient. The combination of these three factors significantly improves the barrier efficiency.

[0017] (3) The improvement in mechanical properties stems from a toughening and strengthening mechanism that combines rigidity and flexibility. The rigid particles of nano-silica provide mechanical reinforcement, increasing the tensile strength and elastic modulus of the membrane; the soft segments of the polyamide elastomer endow the membrane with flexibility and impact resistance, while the hard segments provide polarity barrier and strength support; the flexible main chain of E-MA-GMA forms a stress buffer region in the crosslinking network, absorbing impact energy. OMMT nanosheets, as heterogeneous nucleating agents, refine the size of PPR spherulites, improve crystallization uniformity, and reduce optical scattering, maintaining high transparency while enhancing mechanical properties. The crosslinking network anchors the rigid particles, elastomers, and montmorillonite sheets in the matrix through chemical bonds, ensuring interfacial bonding strength, allowing multiple strengthening and toughening mechanisms to work synergistically without phase separation or aggregation. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic flowchart illustrating the method for preparing the retort-resistant packaging film material provided in this application embodiment; Figure 2 FTIR spectra of the membrane material and each pure component provided in Example 1 of this application; Figure 3 XPS C1s high-resolution spectra of the membrane materials provided in Example 1 and Comparative Example 2 of this application. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0023] This application provides a retortible packaging film material, which, by weight, is composed of the following chemical raw materials: random copolymer polypropylene: 30-50 parts, cyclic olefin copolymer: 5-10 parts, hyperbranched polyester with epoxy groups at the end: 3-5 parts, epoxy-modified nano-silica: 1-2 parts, maleic anhydride-grafted polyolefin: 8-12 parts, ethylene-methyl acrylate-glycidyl methacrylate terpolymer: 3-6 parts, polyamide elastomer: 3-5 parts, organically modified montmorillonite: 1-2 parts, organosilicon composite masterbatch: 1-3 parts, antioxidant: 0.2-0.5 parts, lubricant: 0.2-0.5 parts.

[0024] It should be noted that this application has rationally designed the chemical composition of the retort-resistant packaging film material, which together constructs a composite material system that can withstand high temperature and high humidity retort environments.

[0025] Random copolymer polypropylene (PPR, 30-50 parts) is the continuous phase of the membrane matrix and is the core skeleton material of the packaging film. The non-polar structure of PPR results in poor heat resistance and barrier properties, and its interfacial compatibility with polar additives in the system is extremely poor. It is necessary to rely on compatibilizers and reactive additives to achieve multiphase interfacial bonding, so as to provide the membrane material with basic mechanical properties and molding processability.

[0026] Cyclic olefin copolymers (COC, 5-10 parts) are barrier-modifying functional components. Their molecular chains contain a rigid cyclic structure, have a high glass transition temperature, and extremely low gas permeability, which can significantly improve the water and oxygen barrier properties of membrane materials and extend the shelf life of food. COC and PPR have significant differences in polarity and solubility parameters, and direct blending is prone to phase separation. Therefore, a compatibilizing system is needed to achieve uniform dispersion and fully exert the barrier-enhancing effect.

[0027] Terminally epoxy-based hyperbranched polyester (HBPE-EP, 3-5 parts) is a multifunctional reactive crosslinking agent. Its three-dimensional dendritic structure exhibits low viscosity and high reactivity, with numerous terminal epoxy groups serving as core reaction sites. Under melt processing conditions, based on the epoxy ring-opening addition reaction mechanism, it can undergo in-situ chemical reactions with maleic anhydride groups and terminal amino / carboxyl groups of polyamide to construct a stable covalent crosslinking network. This structure effectively inhibits molecular chain slippage and swelling under high-temperature cooking (121℃), fundamentally improving the film's cooking resistance and interfacial bonding strength.

[0028] Epoxy-modified nano-silica (1-2 parts) is an inorganic reinforcing barrier agent, surface-grafted with KH-560 silane coupling agent, resulting in surface-bonded active epoxy groups. Based on nano-reinforcement theory and tortuous path barrier mechanism, the high specific surface area and high rigidity of nano-silica can improve the mechanical strength and dimensional stability of the membrane material; its surface epoxy groups can participate in the epoxy-anhydride crosslinking reaction of the system, realizing chemical bonding between the inorganic phase and the organic matrix, and preventing nanoparticle aggregation. At the same time, nanoparticles can construct tortuous gas permeation channels, extending the diffusion paths of water vapor and oxygen, and synergistically enhancing barrier performance.

[0029] Maleic anhydride-grafted polyolefin (MAH-g-PO, 8–12 parts) serves as the core reactive compatibilizer, suitable for the compatibility requirements of multiphase systems. Its polyolefin backbone is structurally similar to the PPR matrix, enabling physical entanglement of molecular chains and reducing interfacial tension. The active maleic anhydride groups on the side chains can undergo two key reactions: first, an anhydride-epoxy ring-opening reaction with the epoxy groups of HBPE-EP and E-MA-GMA to construct a crosslinked network; second, an amidation reaction with the terminal amino groups of TPAE, resolving the phase separation problem between nonpolar PPR and polar polyamide, thus serving as a core bridge for compatibility in multi-component systems.

[0030] Ethylene-methyl acrylate-glycidyl methacrylate terpolymer (E-MA-GMA, 3-6 parts) is a reactive toughening and compatibilizing agent. The flexible segments of ethylene-methyl acrylate are compatible with the polyolefin matrix, absorbing impact stress through the energy-dissipating mechanism of polymer flexibility, thereby improving the toughness and puncture resistance of the membrane material. The GMA side chain contains highly active epoxy sites, which can undergo cross-linking reactions with MAH-g-PO anhydride groups and TPAE polar end groups in the molten state, helping to increase the cross-linking density of the system, alleviating thermal stress during high-temperature cooking, and preventing brittle cracking of the membrane material.

[0031] Polyamide elastomer (TPAE, 3-5 parts) is an oil-resistant and toughening functional component, composed of block copolymers of polyamide hard segments and flexible soft segments. Based on the polar adsorption and hydrogen bonding mechanism, the polyamide hard segments impart oil and organic solvent resistance and auxiliary barrier properties to the membrane material, while the soft segments provide elastic recovery, improving the membrane material's bending resistance and low-temperature toughness. Its terminal amino and carboxyl groups can undergo covalent grafting reactions with epoxy groups within the system, achieving a strong bond with the PPR matrix, preventing phase separation, and adapting to the stress changes caused by thermal expansion and contraction during cooking.

[0032] Organically modified montmorillonite (1-2 parts) is a highly efficient barrier modifier. After intercalation modification with hexadecyltriphenyl quaternary phosphonium salt, the interlayer spacing of montmorillonite increases, and the surface changes from hydrophilic to hydrophobic, adapting to the compatibility characteristics of polyolefin matrices. Based on the layered labyrinth barrier mechanism, its nanosheets are arranged in an interlaced manner within the membrane, significantly extending the gas permeation path. The quaternary phosphonium salt modified structure has a thermal stability temperature of 210℃, can withstand processing temperatures without collapsing, and ensures long-term stable barrier performance. Simultaneously, it can act as a heterogeneous nucleating agent, refining PPR spherulites and improving the transparency and mechanical uniformity of the membrane material.

[0033] The organosilicon composite masterbatch (1-3 parts) is a surface processing modifier. During processing, the organosilicon components spontaneously migrate to the film surface, forming a lubricating thin layer, reducing the coefficient of friction between the melt and the equipment, and preventing sticking to rollers and surface scratches. At the same time, it can improve the film's opening properties, anti-blocking properties, and surface hydrophobicity, optimizing the subsequent bag making and filling processing performance.

[0034] Antioxidant (0.2-0.5 parts) is a thermo-oxidative stabilizing agent that ensures the structural and performance stability of the membrane material during processing and long-term use.

[0035] Lubricant (0.2-0.5 parts, such as zinc stearate, EBS, polyethylene wax, etc.) is a rheology processing aid. Lubricant can improve the uniformity of melt flow and ensure the uniformity of film thickness and surface finish of cast film.

[0036] In some embodiments, the preparation method of the hyperbranched polyester with epoxy groups at the end includes the following steps: S101. Under inert gas protection, the hydroxyl-terminated hyperbranched polyester is stirred and kept at a constant temperature of 60°C. The catalyst boron trifluoride diethyl ether is added. Epichlorohydrin is added in a constant pressure dropping funnel. Under nitrogen protection, epichlorohydrin is added dropwise at a rate of 5 drops / second. After the addition is complete, the reaction is kept at a constant temperature for 3 hours to carry out the ring-opening reaction. S102. After the reaction is complete, cool down to 30°C and add saturated sodium hydroxide solution to a constant pressure dropping funnel at a rate of 5 drops / second. After the addition is complete, keep the temperature constant for 4 hours to carry out the closed-loop reaction and obtain the reaction solution. S103. The reaction solution is post-treated to obtain a hyperbranched polyester with epoxy groups at the end.

[0037] In some embodiments, the mass of boron trifluoride ether is 0.5% to 1.5% of the mass of the hydroxyl-terminated hyperbranched polyester; The molar ratio of hydroxyl-terminated hyperbranched polyester to epichlorohydrin is 1:1.2; The molar ratio of epichlorohydrin to sodium hydroxide is 1:1.2.

[0038] The terminal hydroxyl groups of the hyperbranched polyester act as nucleophiles, attacking the epoxy ring of epichlorohydrin under the activation of the Lewis acid catalyst boron trifluoride diethyl ether, resulting in an SN2 ring-opening reaction to generate a chloroalcohol intermediate. The chloroalcohol intermediate then undergoes deHClation under alkaline conditions to form an epoxy group.

[0039] In some embodiments, the epoxy-modified nano-silica is KH-560 modified nano-silica.

[0040] In some embodiments, the mass ratio of nano-silica to KH-560 is 1:(0.5 to 0.8).

[0041] The surface of nano-SiO2 is rich in silanol groups, which undergo hydrolysis and condensation reactions with the methoxysilane groups of KH-560 to form Si-O-Si covalent bonds, grafting epoxy-containing organic segments onto the SiO2 surface.

[0042] In some embodiments, the preparation method of organically modified montmorillonite includes the following steps: S201. Disperse sodium montmorillonite in deionized water to obtain a suspension; S202. Add hexadecyltriphenyl quaternary phosphonium salt to the suspension, adjust the pH to 6-8, and stir the reaction at 75-85℃ for 2-4 hours to obtain the second reaction solution; S203. The second reaction solution is filtered and washed with deionized water until no halogen ions are detected. Then it is vacuum dried at 70-90℃ to obtain organic modified montmorillonite.

[0043] In some embodiments, the mass ratio of hexadecyltriphenyl quaternary phosphonium salt to sodium montmorillonite is 1:(2~3).

[0044] Sodium-based montmorillonite has exchangeable Na between its layers. + Hexadecyltriphenylphosphine bromide (C 16 TPPB is a cationic surfactant whose quaternary phosphonium cation reacts with interlayer Na + An ion exchange reaction occurs, allowing it to enter the interlayer of montmorillonite. Long-chain alkyl groups (C... 16 This increases the interlayer spacing, and the triphenyl structure stabilizes the positive charge through the conjugation effect, thus improving thermal stability.

[0045] Figure 1This is a schematic flowchart illustrating the preparation method of the retort-resistant packaging film material provided in the embodiments of this application.

[0046] Based on a general inventive concept, such as Figure 1 As shown in the embodiments of this application, a method for preparing a retort-resistant packaging film material according to any one of the above-mentioned methods is provided, the method comprising the following steps: S1. Random copolymer polypropylene, cyclic olefin copolymer, hyperbranched polyester with epoxy groups at the end, epoxy-modified nano silica, maleic anhydride grafted polyolefin, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, polyamide elastomer, organic modified montmorillonite, organosilicon composite masterbatch, antioxidant and lubricant are mixed at 500-1500 rpm for 10-30 min to obtain a mixture. S2. The mixture is fed into a twin-screw extruder for melt blending and extrusion, followed by extrusion granulation to obtain composite granules; S3. The composite granules are melt-extruded into a film using a casting extruder, and then drawn and wound to obtain a packaging film material resistant to boiling.

[0047] In some embodiments, the barrel temperature of the twin-screw extruder is set as follows: 170-190°C in the feeding section, 190-210°C in the melting section, 200-220°C in the homogenization section, 210-230°C in the die head, and the screw speed is 100-250 rpm.

[0048] In some embodiments, the barrel temperature of the cast extruder is 200–220°C, the die temperature is 210–230°C, and the cast roll temperature is 30–60°C.

[0049] S1 High-speed premixing step: Mix at 500-1500 rpm for 10-30 minutes. Based on the principle of fluid shear dispersion, achieve macroscopic uniform dispersion of resin, inorganic filler, various reactive additives and processing aids, avoid local filler agglomeration and additive segregation, and lay a uniform mixing foundation for subsequent melt interface reaction. Under room temperature mixing conditions, all raw materials are in the thermally stable range, with no thermal decomposition, and the physicochemical structure of each component remains stable.

[0050] The S2 twin-screw melt extrusion granulation process involves the following steps: The feeding section (170–190°C) only preheats and conveys the material to prevent premature melting, adhesion, and bridging; the melting section (190–210°C) fully plasticizes the resin; the homogenization section (200–220°C) utilizes the screw's shearing action to enhance the micro-dispersion of each phase, while simultaneously triggering in-situ grafting crosslinking reactions between epoxy, anhydride, and amino groups; the die head (210–230°C) is below the thermal decomposition temperature of the organically modified montmorillonite and epoxy additives, ensuring that each additive undergoes only controlled chemical reactions without thermal degradation; the low-speed shearing of the screw (100–250 rpm) avoids localized overheating, guaranteeing the stable existence of all components, and resulting in a uniformly structured composite granule through extrusion granulation, thus fixing the crosslinked and compatible system structure.

[0051] S3 Casting Film Forming Steps: The barrel is set at 200-220℃ and the die at 210-230℃, within the thermal stability window of each raw material. This ensures that the composite granules are fully melted and flowed to form the film without causing thermal decomposition of additives or thermal oxidative aging of the matrix. The cross-linked network formed in the early stage can be stably retained. The casting roller at a low temperature of 30-60℃ quickly cools and shapes the film, inhibiting the excessive crystallization of PPR. This preserves the high transparency of the film material and locks in the multiphase uniform dispersion structure and chemical bonding interface, ultimately resulting in a retort-resistant packaging film material with stable composition and uniform structure.

[0052] Therefore, the design principle of this application is based on a synergistic strategy of multi-component reactive compatibilization and nano-reinforcement, and constructs a retort-resistant packaging film material through melt blending.

[0053] The core chemical mechanism is as follows: During melt processing, the epoxy groups of terminally epoxy-terminated hyperbranched polyester (HBPE-EP) and E-MA-GMA undergo in-situ ring-opening addition reactions with the anhydride groups of maleic anhydride-grafted polyolefins and the terminal amino groups of polyamide elastomers, forming a mildly chemically cross-linked network that inhibits chain slippage and swelling during high-temperature cooking. Quaternary phosphonium salt-modified montmorillonite, after cation exchange, exhibits increased interlayer spacing, and its layers create a labyrinth effect within the membrane material, extending the water vapor permeation path.

[0054] The physical synergy is as follows: after being grafted with KH-560, the epoxy-modified nano-silica has epoxy groups on its surface, which participate in the cross-linking reaction and chemically bond with the matrix to avoid agglomeration. At the same time, it synergistically enhances the barrier properties with montmorillonite; the cyclic olefin copolymer provides high barrier properties, and the organosilicon masterbatch improves the smoothness of processing.

[0055] The system completes the reaction at low temperature and is mildly chemically cross-linked. The degree of cross-linking is controlled to prevent macroscopic gelation, ensuring that the composite material still has thermoplasticity. It can be successfully extruded by twin screws and cast into films, taking into account both thermal stability and structural integrity. Ultimately, it achieves packaging film material that is resistant to 121℃ cooking, has high barrier properties, and high transparency.

[0056] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0057] The raw material source information for the examples and comparative examples is shown in Table 1.

[0058] Table 1. Raw material source information for the examples and comparative examples. Hyperbranched polyesters with terminal epoxy groups are prepared by the following method: Under nitrogen protection, the hydroxyl-terminated hyperbranched polyester was stirred and kept at a constant temperature of 60°C. Boron trifluoride diethyl ether catalyst, accounting for 1.0% of the mass of the hydroxyl-terminated hyperbranched polyester, was added. Epichlorohydrin was added in a constant-pressure dropping funnel at a molar ratio of 1:1.2. Under nitrogen protection, epichlorohydrin was added dropwise at a rate of 5 drops / second. After the addition was complete, the reaction was kept at a constant temperature for 3 hours to initiate the ring-opening reaction. After the reaction was completed, the temperature was lowered to 30°C, and a saturated sodium hydroxide solution containing 1.2 times the amount of epichlorohydrin was added in a constant-pressure dropping funnel at a rate of 5 drops / second. After the addition was complete, the reaction was kept at a constant temperature for 4 hours to initiate the ring-closing reaction, yielding a reaction solution. The reaction solution was then post-treated to obtain a hyperbranched polyester with epoxy groups at the end of its epoxy groups, with an epoxy value of 0.32 mol / 100 g.

[0059] Epoxy-modified nano-silica was prepared by the following method: Nano-silica with a particle size of 20 nm was dispersed in a mixed solvent of ethanol and water at a volume ratio of 8:2. The pH was adjusted to 4.5 with glacial acetic acid. γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560) was added under stirring, with a mass ratio of nano-silica to KH-560 of 1:0.65. The mixture was refluxed at 80 °C for 6 h to obtain the first reaction solution. The first reaction solution was centrifuged and washed four times with anhydrous ethanol, and then vacuum dried at 70 °C for 18 h to obtain epoxy-modified nano-silica with a grafting rate of 2.1 mmol / g.

[0060] Organically modified montmorillonite was prepared by the following method: Sodium-based montmorillonite was dispersed in deionized water to prepare a suspension with a mass concentration of 3.5%. Hexadecyltriphenyl quaternary phosphonium salt (hexadecyltriphenyl phosphonium bromide) was added to the suspension at a mass ratio of 1:2.5 to sodium-based montmorillonite. The pH was adjusted to 7, and the mixture was stirred at 80°C for 3 hours to obtain a second reaction solution. The second reaction solution was filtered and washed with deionized water until no bromide ions were detected by silver nitrate solution. Then, it was vacuum dried at 80°C to obtain organically modified montmorillonite with an average interlayer spacing of 3.2 nm.

[0061] Example 1 This embodiment provides a retortible packaging film material, the raw material composition of which, by mass parts, is: 40 parts random copolymer polypropylene, 8 parts cyclic olefin copolymer, 4 parts hyperbranched polyester with epoxy groups at the end, 1.5 parts epoxy-modified nano silica, 10 parts maleic anhydride grafted polyolefin, 5 parts ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 4 parts polyamide elastomer, 1.5 parts organic modified montmorillonite, 2 parts organosilicon composite masterbatch, 0.3 parts antioxidant 1010, and 0.3 parts lubricant (zinc stearate).

[0062] This embodiment also provides a method for preparing a retort-resistant packaging film material, including the following steps: S1. Add 40 parts of random copolymer polypropylene, 8 parts of cyclic olefin copolymer, 4 parts of hyperbranched polyester with epoxy groups at the end, 1.5 parts of epoxy-modified nano silica, 10 parts of maleic anhydride grafted polyolefin, 5 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 4 parts of polyamide elastomer, 1.5 parts of organic modified montmorillonite, 2 parts of organosilicon composite masterbatch, 0.3 parts of antioxidant and 0.3 parts of lubricant to a high-speed mixer and stir at 1000 rpm at room temperature for 15 min to obtain a mixture. S2. The mixture is fed into a twin-screw extruder for melt blending and extrusion. The barrel temperature of the twin-screw extruder is set as follows: feeding section 180℃, melting section 200℃, homogenization section 210℃, die head temperature 220℃, screw speed 200rpm, and extrusion granulation to obtain composite granules. S3. The composite granules are melt-extruded into a film using a casting extruder. The barrel temperature of the casting extruder is 210℃, the die temperature is 220℃, and the casting roller temperature is 40℃. After traction and winding, a 60μm thick retort-resistant packaging film is obtained.

[0063] Example 2 This embodiment provides a retortible packaging film material, the raw material composition of which, by mass parts, is: 35 parts random copolymer polypropylene, 6 parts cyclic olefin copolymer, 3.5 parts hyperbranched polyester with epoxy groups at the end, 1.2 parts epoxy-modified nano silica, 9 parts maleic anhydride grafted polyolefin, 4 parts ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 3.5 parts polyamide elastomer, 1.2 parts organic modified montmorillonite, 1.5 parts organosilicon composite masterbatch, 0.25 parts antioxidant 168, and 0.25 parts lubricant (EBS).

[0064] This embodiment also provides a method for preparing a retort-resistant packaging film material, including the following steps: S1. Add 35 parts of random copolymer polypropylene, 6 parts of cyclic olefin copolymer, 3.5 parts of hyperbranched polyester with epoxy groups at the end, 1.2 parts of epoxy-modified nano silica, 9 parts of maleic anhydride-grafted polyolefin, 4 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 3.5 parts of polyamide elastomer, 1.2 parts of organic modified montmorillonite, 1.5 parts of organosilicon composite masterbatch, 0.25 parts of antioxidant and 0.25 parts of lubricant to a high-speed mixer and stir at 800 rpm at room temperature for 20 min to obtain a mixture. S2. The mixture is fed into a twin-screw extruder for melt blending and extrusion. The barrel temperature of the twin-screw extruder is set as follows: feeding section 170℃, melting section 190℃, homogenization section 200℃, die head temperature 210℃, screw speed 150rpm, and extrusion granulation to obtain composite granules. S3. The composite granules are melt-extruded into a film using a casting extruder. The barrel temperature of the casting extruder is 200℃, the die temperature is 210℃, and the casting roller temperature is 35℃. After traction and winding, a 50μm thick retort-resistant packaging film is obtained.

[0065] Example 3 This embodiment provides a retortible packaging film material, the raw material composition of which, by mass parts, is: 45 parts random copolymer polypropylene, 9 parts cyclic olefin copolymer, 4.5 parts hyperbranched polyester with epoxy groups at the end, 1.8 parts epoxy-modified nano silica, 11 parts maleic anhydride grafted polyolefin, 5.5 parts ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 4.5 parts polyamide elastomer, 1.8 parts organically modified montmorillonite, 2.5 parts organosilicon composite masterbatch, 0.4 parts antioxidant 168, and 0.4 parts lubricant (polyethylene wax).

[0066] The preparation methods for hyperbranched polyesters with epoxy-terminated ends, epoxy-modified nano-silica, and organically modified montmorillonite are the same as in Example 1.

[0067] This embodiment also provides a method for preparing a retort-resistant packaging film material, including the following steps: S1. Add 45 parts of random copolymer polypropylene, 9 parts of cyclic olefin copolymer, 4.5 parts of hyperbranched polyester with epoxy groups at the end, 1.8 parts of epoxy-modified nano silica, 11 parts of maleic anhydride-grafted polyolefin, 5.5 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 4.5 parts of polyamide elastomer, 1.8 parts of organic modified montmorillonite, 2.5 parts of organosilicon composite masterbatch, 0.4 parts of antioxidant and 0.4 parts of lubricant to a high-speed mixer and stir at 1200 rpm at room temperature for 12 min to obtain a mixture. S2. The mixture is fed into a twin-screw extruder for melt blending and extrusion. The barrel temperature of the twin-screw extruder is set as follows: feeding section 185℃, melting section 205℃, homogenization section 215℃, die head temperature 225℃, screw speed 240rpm, and extrusion granulation to obtain composite granules. S3. The composite granules are melt-extruded into a film using a casting extruder. The barrel temperature of the casting extruder is 215℃, the die temperature is 225℃, and the casting roller temperature is 50℃. After traction and winding, a retort-resistant packaging film with a thickness of 70μm is obtained.

[0068] Comparative Example 1 This comparative example is modified from the one disclosed in Example 1 as follows: The raw material composition of the retortible packaging film does not contain cyclic olefin copolymers.

[0069] Comparative Example 2 This comparative example is modified from the one disclosed in Example 1 as follows: The raw material composition of the retortible packaging film does not contain hyperbranched polyester with epoxy groups at the end.

[0070] Comparative Example 3 This comparative example is modified from the one disclosed in Example 1 as follows: The raw materials of the retortible packaging film do not contain epoxy-modified nano-silica.

[0071] Comparative Example 4 This comparative example is modified from the one disclosed in Example 1 as follows: The epoxy-modified nano-silica in the raw material composition of the retortible packaging film material is replaced with nano-silica.

[0072] Comparative Example 5 This comparative example is based on the disclosure in Example 1, with the following modifications: The raw material composition of the retortible packaging film does not contain ethylene-methyl acrylate-glycidyl methacrylate terpolymer.

[0073] Comparative Example 6 This comparative example is based on the disclosure in Example 1, with the following modifications: The raw materials of the retortible packaging film do not contain polyamide elastomers.

[0074] Comparative Example 7 This comparative example is based on the disclosure in Example 1, with the following modifications: The raw material composition of the retortible packaging film does not contain organically modified montmorillonite.

[0075] The packaging films obtained in Examples 1-3 and Comparative Examples 1-7 were subjected to performance tests. The performance test results are shown in Table 2. The performance test methods are as follows: Retort resistance: The membrane material was prepared into 20cm×20cm samples, with 3 parallel samples per group. The samples were placed in a high-temperature and high-pressure retort and retorted for 30 minutes at 121℃±2℃ and 0.12MPa±0.01MPa. After retort, the samples were removed and allowed to cool naturally to room temperature. The tensile strength of the membrane material before and after retort was tested, and the retention rate was calculated: Retort strength retention rate (%) = (Tensile strength after retort / Tensile strength before retort) × 100%.

[0076] Oxygen permeability: Tested according to the method provided in GB / T 19789-2005; Water vapor transmission rate: Tested according to the method provided in GB / T 26253-2010; Tensile strength and elongation at break: Tested according to the methods provided in GB / T 1040.3-2006.

[0077] Table 2 Performance of Packaging Films in Examples 1-3 and Comparative Examples 1-7 As shown in Table 2, the packaging films of each embodiment exhibit excellent and stable comprehensive performance in terms of retort strength retention, barrier properties, and mechanical properties. Examples 1-3 show retort strength retention rates as high as 93.5%-95.1% and oxygen permeability as low as 1.18-1.31 cm⁻¹. 3 / (m 2 (24h·0.1MPa), water vapor transmission rate is 2.08~2.24g / (m²). 2 The tensile strength reached 44.3-49.5 MPa and the elongation at break was 315%-425% after 24 hours, with all indicators showing excellent synergy.

[0078] The performance comparisons of Comparative Examples 1–7 reveal the functional contributions of each component. The absence of COC (Comparative Example 1) significantly increased oxygen and water vapor permeability, indicating that COC is a key contributing component to barrier performance. The absence of terminally epoxy-based hyperbranched polyester (Comparative Example 2) drastically reduced the cooking strength retention to 65.8%, while tensile strength and elongation at break also decreased significantly, proving that this component is the core of constructing the cooking-resistant crosslinking network. Replacing epoxy-modified nano-silica with ordinary unmodified nano-silica (Comparative Example 4) reduced the cooking strength retention to 63.4% and increased the oxygen permeability to 4.35%, a deterioration even exceeding that of Comparative Example 2. This indicates that unmodified nano-silica, due to agglomeration and interfacial defects, actually degrades performance, highlighting the technical necessity of KH-560 epoxy modification. The absence of E-MA-GMA (Comparative Example 5) or TPAE (Comparative Example 6) both resulted in a significant decrease in cooking strength retention and elongation at break, indicating that both are indispensable in the synergistic compatibilization and toughening of the crosslinking network. The absence of organically modified montmorillonite (Comparative Example 7) significantly degraded the barrier properties, confirming the physical barrier contribution of the montmorillonite sheets. The above comparisons clearly demonstrate that the components, through the synergistic effects of chemical cross-linking network construction, interfacial compatibilization, and physical barrier properties, jointly achieve a synergistic improvement in the retort resistance, barrier properties, and mechanical properties of the packaging film.

[0079] Figure 2 The FTIR spectra of the membrane material and each pure component provided in Example 1 of this application are shown.

[0080] Depend on Figure 2 It can be seen that the anhydride bimodal peaks of pure MAH-g-PO are ~1852 and ~1780 cm⁻¹. -1 The membrane material of Example 1 almost completely disappeared; the membrane material of Example 1 was at ~1730 cm. -1 A new strong absorption peak appears, which is attributed to the ester carbonyl group formed by the reaction of epoxy with acid anhydride; the characteristic epoxy peaks of terminal epoxy hyperbranched polyesters (~908, ~835 cm⁻¹) -1 The strength of the membrane material is reduced by about 70%, which proves that a large number of epoxy groups are consumed through ring opening.

[0081] Figure 3 XPS C1s high-resolution spectra of the membrane materials provided in Example 1 and Comparative Example 2 of this application.

[0082] Depend on Figure 3It can be seen that Comparative Example 2 only shows two peaks at ~284.8 eV and ~286.5 eV, which are attributed to CC / CH and CO, respectively, and there is no significant signal at ~288.1 eV. Example 1 shows a new and obvious absorption peak at ~288.1 eV, which is attributed to the ester carbonyl group (OC=O) formed by the reaction of epoxy group and acid anhydride group. The CO peak intensity at ~286.5 eV in Example 1 is significantly enhanced and the peak shape is broadened compared with Comparative Example 2, proving that additional COC ether bonds and C-OH structures are formed after the epoxy ring is opened. The CC / CH main peak at ~284.8 eV in Example 1 is slightly weaker and broader, proving that some nonpolar carbon is introduced into the polar interface layer due to interfacial chemical reactions, and the chemical environment tends to be heterogeneous.

[0083] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A packaging film material resistant to boiling and steaming, characterized in that, The packaging film material, by weight, is composed of the following chemical raw materials. Composition: Random copolymer polypropylene: 30-50 parts, cyclic olefin copolymer: 5-10 parts, hyperbranched polyester with epoxy groups at the end: 3-5 parts, epoxy-modified nano-silica: 1-2 parts, maleic anhydride-grafted polyolefin: 8-12 parts, ethylene-methyl acrylate-glycidyl methacrylate terpolymer: 3-6 parts, polyamide elastomer: 3-5 parts, organically modified montmorillonite: 1-2 parts, organosilicon composite masterbatch: 1-3 parts, antioxidant: 0.2-0.5 parts, lubricant: 0.2-0.5 parts.

2. The retort-resistant packaging film material according to claim 1, characterized in that, The preparation method of the hyperbranched polyester with epoxy groups at the end includes the following steps: S101. Under inert gas protection, the hydroxyl-terminated hyperbranched polyester is stirred and kept at a constant temperature of 60°C. The catalyst boron trifluoride diethyl ether is added. Epichlorohydrin is added in a constant pressure dropping funnel. Under nitrogen protection, epichlorohydrin is added dropwise at a rate of 5 drops / second. After the addition is complete, the reaction is kept at a constant temperature for 3 hours to carry out the ring-opening reaction. S102. After the reaction is complete, cool down to 30°C and add saturated sodium hydroxide solution to a constant pressure dropping funnel at a rate of 5 drops / second. After the addition is complete, keep the temperature constant for 4 hours to carry out the closed-loop reaction and obtain the reaction solution. S103. The reaction solution is post-treated to obtain the hyperbranched polyester with epoxy groups at the end.

3. The retort-resistant packaging film material according to claim 2, characterized in that, The mass of the boron trifluoride ether is 0.5% to 1.5% of the mass of the hydroxyl-terminated hyperbranched polyester. The molar ratio of the hydroxyl-terminated hyperbranched polyester to the epichlorohydrin is 1:1.2; The molar ratio of epichlorohydrin to sodium hydroxide is 1:1.

2.

4. The retort-resistant packaging film material according to claim 1, characterized in that, The epoxy-modified nano-silica is KH-560 modified nano-silica.

5. The retort-resistant packaging film material according to claim 4, characterized in that, The mass ratio of the nano-silica to the KH-560 is 1:(0.5~0.8).

6. The retort-resistant packaging film material according to claim 1, characterized in that, The preparation method of the organically modified montmorillonite includes the following steps: S201. Disperse sodium montmorillonite in deionized water to obtain a suspension; S202. Add hexadecyltriphenyl quaternary phosphonium salt to the suspension, adjust the pH to 6-8, and stir the reaction at 75-85°C for 2-4 hours to obtain the second reaction solution; S203. The second reaction solution is filtered and washed with deionized water until no halogen ions are detected. Then it is vacuum dried at 70-90°C to obtain the organic modified montmorillonite.

7. The retort-resistant packaging film material according to claim 6, characterized in that, The mass ratio of the hexadecyltriphenyl quaternary phosphonium salt to the sodium montmorillonite is 1:(2~3).

8. A method for preparing a retort-resistant packaging film material according to any one of claims 1 to 7, characterized in that, The method includes the following steps: S1. Random copolymer polypropylene, cyclic olefin copolymer, hyperbranched polyester with epoxy groups at the end, epoxy-modified nano silica, maleic anhydride grafted polyolefin, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, polyamide elastomer, organic modified montmorillonite, organosilicon composite masterbatch, antioxidant and lubricant are mixed at 500-1500 rpm for 10-30 min to obtain a mixture. S2. The mixture is fed into a twin-screw extruder for melt blending and extrusion, followed by extrusion granulation to obtain composite granules; S3. The composite granules are melt-extruded into a film using a casting extruder, and then drawn and wound to obtain the retort-resistant packaging film material.

9. The method for preparing the retort-resistant packaging film material according to claim 8, characterized in that, The barrel temperature of the twin-screw extruder is set as follows: feeding section 170-190℃, melting section 190-210℃, homogenization section 200-220℃, die head temperature 210-230℃, and screw speed 100-250 rpm.

10. The method for preparing the retort-resistant packaging film material according to claim 8, characterized in that, The barrel temperature of the cast extruder is 200-220℃, the die temperature is 210-230℃, and the cast roll temperature is 30-60℃.

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