High-toughness plastic packaging film material and method for preparing the same

Abstract

The application provides a high-toughness plastic packaging film material and a preparation method thereof, and belongs to the field of metallocene polyolefin plastics. The high-toughness plastic packaging film material is composed of the following chemical raw materials: 80-90 parts of metallocene polyethylene resin, 5-8 parts of supramolecular crosslinking agent, 6-10 parts of core-shell modifier, 3-5 parts of ethylene-vinyl acetate copolymer, 2-4 parts of nano calcium carbonate modified by stearic acid, 2-3 parts of polyolefin elastomer, 0.2-0.5 parts of bis(3,4-dimethyl dibenzylidene) sorbitol, 2-5 parts of thermotropic liquid crystal polymer, 0.4-0.7 parts of antioxidant, 0.8-1.2 parts of lubricant and 0.5-1.0 parts of antistatic agent. Through compatible design of toughening mechanism, synergistic balance of reinforcing mechanism and optimization of transparency guarantee, the application makes the components functionally complementary in the metallocene polyethylene resin matrix, and realizes the ultrahigh toughness, high strength and high transparency of the film material.

Description

Technical Field

[0001] This application relates to the field of metallocene polyolefin plastics technology, and in particular to a high-toughness plastic packaging film and its preparation method. Background Technology

[0002] Plastic packaging films are an important component of the modern packaging industry, widely used in food, daily chemicals, industrial products, and many other fields. With continuously increasing market demand, higher requirements are being placed on the comprehensive performance of packaging films, especially the simultaneous possession of ultra-high toughness (puncture and tear resistance), high strength (high tensile strength, high modulus), and high transparency. However, these performance indicators of materials often constrain each other, creating a "performance contradiction" where one's strengths are at odds with another's, making the development of a single film material possessing multiple excellent properties a significant technological challenge.

[0003] Currently, traditional methods for improving the mechanical properties of plastic packaging films are mainly divided into two categories, both of which have significant limitations: one is the elastomer toughening route, which improves the toughness and impact resistance of the film by adding flexible components such as ethylene-vinyl acetate copolymer (EVA) and polyolefin elastomer (POE). However, these elastomers have limited compatibility with matrix resins such as polyethylene and have low modulus. Adding large amounts will significantly sacrifice the rigidity and tensile strength of the material, and will also lead to increased haze and decreased transparency. The other is the rigid particle reinforcement route, which improves the strength, modulus and thermal stability of the material by adding inorganic nanoparticles such as nano-calcium carbonate and fibers. However, inorganic particles are prone to agglomerate in the polymer matrix to form stress concentration points, which leads to increased brittleness and decreased toughness of the material, and may also have a negative impact on transparency.

[0004] Existing technologies optimize performance through multi-component compounding. For example, Chinese invention patent CN107674340A discloses a composite film based on polyvinyl chloride (PVC), using liquid nitrile rubber (NBR) as a toughening agent and modified nano-calcium carbonate as rigid particles, attempting to simultaneously improve the toughness and strength of PVC film. However, from a performance balance perspective, this approach struggles to simultaneously achieve a balance between high transparency and high supramolecular-level toughness-strength, and the PVC system itself is unlikely to achieve excellent optical properties. In conclusion, neither single toughening or reinforcing methods, nor blending modification schemes using other resin systems such as PVC, can resolve the fundamental contradiction of the difficulty in synergistically improving toughness, strength, and transparency in high-performance packaging films. Summary of the Invention

[0005] This application provides a high-toughness plastic packaging film material and its preparation method to overcome the technical contradiction that existing high-performance plastic packaging films cannot simultaneously possess ultra-high toughness, high strength, and high transparency.

[0006] In a first aspect, this application provides a high-toughness plastic packaging film material, which, by weight, is composed of the following chemical raw materials: metallocene polyethylene resin: 80-90 parts, supramolecular crosslinking agent: 5-8 parts, core-shell modifier: 6-10 parts, ethylene-vinyl acetate copolymer: 3-5 parts, stearic acid modified nano-calcium carbonate: 2-4 parts, polyolefin elastomer: 2-3 parts, di(3,4-dimethyldibenzyl)sorbitol: 0.2-0.5 parts, thermotropic liquid crystal polymer: 2-5 parts, antioxidant: 0.4-0.7 parts, lubricant: 0.8-1.2 parts, antistatic agent: 0.5-1.0 parts;

[0007] The supramolecular crosslinking agent is a polycaprolactone polyol with end groups modified with ureidopyrimidinone bifunctional groups;

[0008] The core-shell modifier is a core-shell structured polymer with polymethyl methacrylate as the shell and an acrylate elastomer as the core. The surface of the core-shell modifier is pre-coated with polyethylene-grafted maleic anhydride polymer, and the coating mass of the polyethylene-grafted maleic anhydride polymer is 15% to 30% of the total mass of the core-shell modifier.

[0009] Optionally, the preparation method of the supramolecular crosslinking agent includes the following steps:

[0010] A1. Under inert gas protection, hydroxyl-terminated polycaprolactone polyol and 2,4-toluene diisocyanate are reacted at 60-80°C for 2-4 hours to obtain isocyanate-terminated polycaprolactone prepolymer.

[0011] A2. The isocyanate-terminated polycaprolactone prepolymer was reacted with 2-amino-4-hydroxy-6-methylpyrimidine at 40-60°C for 3-5 h to obtain the crude product;

[0012] A3. The crude product is precipitated in a non-solvent, filtered, and dried to obtain the polycaprolactone polyol with end groups modified with ureidopyrimidinone bifunctional groups.

[0013] Optionally, the molar ratio of the hydroxyl groups in the terminal hydroxyl polycaprolactone polyol to the isocyanate groups in the 2,4-toluene diisocyanate is 1:(2.0-2.2).

[0014] The molar ratio of the isocyanate group of the terminal isocyanate-based polycaprolactone prepolymer to the amino group of the 2-amino-4-hydroxy-6-methylpyrimidine is 1:(1.0 to 1.05).

[0015] Optionally, the preparation method of the core-shell modifier includes the following steps:

[0016] B1. Add a crosslinking agent and an initiator to the butyl acrylate monomer and perform emulsion polymerization at 75-85°C for 2.0-3.0 h to obtain an acrylate elastomer core emulsion;

[0017] B2. Add methyl methacrylate monomer to the acrylate elastomer core emulsion and continue the emulsion polymerization reaction at 80-85°C for 1.5-2.5 hours to polymerize the polymethyl methacrylate shell onto the surface of the acrylate elastomer core, thereby obtaining core-shell type modifier particles with polymethyl methacrylate as the shell and acrylate elastomer as the core.

[0018] B3. Disperse the core-shell modifier particles in xylene solvent to form a suspension; and dissolve the polyethylene-grafted maleic anhydride polymer in hot xylene solvent to form a coating solution;

[0019] B4. Under stirring conditions, the coating solution is added dropwise to the suspension, and the reaction is carried out at 70-80°C for 1.0-2.0 h to obtain the core-shell modifier.

[0020] Optionally, the crosslinking agent is divinylbenzene, and the added mass of divinylbenzene is 1.0 to 1.5% of the mass of the butyl acrylate monomer;

[0021] The initiator is potassium persulfate, and the mass of potassium persulfate added is 1.0 to 1.5% of the mass of the butyl acrylate monomer.

[0022] The mass ratio of the core layer to the shell layer of the core-shell modifier particles is (70-80):(30-20).

[0023] Optionally, the method for preparing the stearic acid-modified nano-calcium carbonate includes the following steps:

[0024] C1. Disperse nano-calcium carbonate in deionized water under high-speed stirring to form a suspension;

[0025] C2. Slowly add an ethanol solution of stearic acid to the suspension and react at 70-85°C for 1-2 hours to obtain the stearic acid-modified nano-calcium carbonate.

[0026] The amount of stearic acid added is 2.0 to 4.0% of the mass of the nano-calcium carbonate.

[0027] Optionally, the thermotropic liquid crystal polymer is a fully aromatic polyester liquid crystal polymer, which is obtained by copolymerization of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and 2-aminobenzothiazole-6-carboxylic acid via a polycondensation reaction.

[0028] The molar ratio of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and 2-aminobenzothiazole-6-carboxylic acid is (60-80):(20-40):(0.5-5).

[0029] Optionally, the antioxidant is composed of a hindered phenolic primary antioxidant and a phosphite secondary antioxidant, wherein the mass ratio of the hindered phenolic primary antioxidant to the phosphite secondary antioxidant is 1:(1.5-2.5).

[0030] The lubricant is composed of erucamide and polyethylene wax, wherein the mass ratio of erucamide to polyethylene wax is 1:(1-1.5).

[0031] The antistatic agent is glyceryl monostearate.

[0032] Secondly, this application provides a method for preparing the high-toughness plastic packaging film material according to any one of the first aspects, the method comprising the following steps:

[0033] S1. The metallocene polyethylene resin, the ethylene-vinyl acetate copolymer, the polyolefin elastomer, the di(3,4-dimethylbenzyl)sorbitol, the antioxidant, the lubricant and the antistatic agent are added to a high-speed mixer according to the formula ratio and mixed at 80-100°C for 5-10 minutes to obtain a premix.

[0034] S2. The premix, the supramolecular crosslinking agent, the core-shell modifier, the stearic acid-modified nano-calcium carbonate, and the thermotropic liquid crystal polymer are added to a twin-screw extruder, and then melt-blended and extruded to granulate to obtain masterbatch.

[0035] S3. Under the influence of an external electromagnetic field, the masterbatch is blow-molded to obtain the high-toughness plastic packaging film.

[0036] Optionally, the processing temperature of the twin-screw extruder is 160–200°C, and the screw speed is 200–400 rpm;

[0037] The applied electromagnetic field has a magnetic field strength of 0.5–1.5 T and an electric field strength of 500–1000 V / cm.

[0038] The blow molding process employs biaxial stretching, with a longitudinal stretching ratio of 2.5–3.5 and a transverse stretching ratio of 2.5–3.5. The die head temperature of the blow molding machine is 165–185°C.

[0039] The technical solutions provided in this application have the following advantages compared with the prior art:

[0040] This application provides a high-toughness plastic packaging film material, which, by weight, is composed of the following chemical raw materials: metallocene polyethylene resin: 80-90 parts, supramolecular crosslinking agent: 5-8 parts, core-shell modifier: 6-10 parts, ethylene-vinyl acetate copolymer: 3-5 parts, stearic acid-modified nano-calcium carbonate: 2-4 parts, polyolefin elastomer: 2-3 parts, di(3,4-dimethyldibenzyl)sorbitol: 0.2-0.5 parts, thermotropic liquid crystal polymer: 2-5 parts, antioxidant: 0.4-0.7 parts, lubricant: 0.8-1.2 parts, and antistatic agent: 0.5-1.0 parts. This application systematically solves the technical contradiction of achieving ultra-high toughness, high strength, and high transparency in high-performance plastic packaging films through precise component selection and multi-dimensional synergistic design. Its core logic lies in constructing a synergistic system that "increases toughness without compromising strength, enhances strength without weakening toughness, and optimizes performance without affecting transparency."

[0041] In terms of toughness enhancement, this application innovatively adopts a triple mechanism for synergistic toughening and avoids weakening of strength through compatibility design. The supramolecular crosslinking agent (polycaprolactone polyol with end-group modified ureidopyrimidinone bifunctional groups) relies on the reversible quadruple hydrogen bond network formed by the UPy bifunctional groups to efficiently dissipate energy through "dissociation-reconstruction" under external force, giving the membrane material ultra-high toughness. At the same time, its polycaprolactone segments have excellent compatibility with metallocene polyethylene (mPE) matrix, avoiding the embrittlement caused by traditional chemical crosslinking. The core-shell modifier uses acrylate elastomer as the core, which absorbs impact energy through deformation and shear yielding. Its surface is pre-coated with polyethylene grafted maleic anhydride (15% to 30% by mass) as an "interfacial bridge", which makes the elastomer core tightly bonded and uniformly dispersed with the mPE matrix, preventing agglomeration and the formation of weak points in strength. The polyolefin elastomer (POE) has excellent compatibility with mPE, improves the flexibility of the matrix by filling the gaps between molecular chains, and because the amount added is controllable (2 to 3 parts), it will not cause a decline in strength like the traditional method of adding large amounts of elastomer. The three mechanisms work synergistically to significantly improve toughness while maintaining the strength base by relying on good compatibility with the matrix.

[0042] Regarding strength enhancement, this application achieves a balance between strength improvement and toughness through a graded reinforcement strategy. Stearic acid-modified nano-calcium carbonate, after surface modification, exhibits significantly improved compatibility with mPE. It is uniformly dispersed at the nanoscale, forming a strong interfacial interaction with the matrix through its large specific surface area. This serves both as a "physical cross-linking point" to enhance rigidity and tensile strength and as an inducement of crazing to dissipate energy, achieving a synergistic "reinforcement-toughening" effect. Thermotropic liquid crystal polymer (TLCP) can form nanofibers in situ during processing, acting as a uniformly distributed "reinforcing skeleton" within the matrix. Its high modulus characteristics allow it to bear external loads, significantly improving tensile strength and modulus. Furthermore, the interfacially compatible components tightly bond with the matrix, avoiding the increased brittleness caused by traditional rigid particles. Meanwhile, mPE, as the main component (80-90 parts), with its regular molecular chains and controllable crystallization, provides a stable load-bearing substrate for the reinforcing components, ensuring the foundation of strength.

[0043] Regarding transparency assurance, this application employs a dual approach of crystallization optimization and dispersion control to ensure high transparency while enhancing toughness. Di(3,4-dimethyldibenzyl)sorbitol (DMDBS) acts as a nucleating agent, inducing the formation of numerous fine and uniform microcrystals in mPE. Because the microcrystal size is much smaller than the wavelength of visible light, light scattering is reduced, thus improving transparency. Simultaneously, ethylene-vinyl acetate copolymer (EVA) acts as a "compatibility medium," utilizing the bidirectional affinity between polar and non-polar segments to assist in the uniform dispersion of core-shell modifiers, nano-calcium carbonate, and other components, preventing light scattering caused by agglomeration. Furthermore, supramolecular crosslinking agents and POE, due to their excellent compatibility with mPE, do not form significant phase separation, further ensuring the transparent properties of the membrane material.

[0044] In summary, this application achieves a balance between ultra-high toughness, high strength, and high transparency by designing a compatible toughening mechanism, balancing enhancement strategies, and optimizing the structure to ensure transparency. This enables the components to complement each other and work synergistically in the mPE matrix, ultimately overcoming the performance contradictions of existing technologies. Attached Figure Description

[0045] 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.

[0046] 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.

[0047] Figure 1 This is a schematic flowchart illustrating a method for preparing a high-toughness plastic packaging film material according to an embodiment of this application. Detailed Implementation

[0048] 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.

[0049] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0050] This application provides a high-toughness plastic packaging film material, which, by weight, is composed of the following chemical raw materials: metallocene polyethylene resin: 80-90 parts, supramolecular crosslinking agent: 5-8 parts, core-shell modifier: 6-10 parts, ethylene-vinyl acetate copolymer: 3-5 parts, stearic acid modified nano-calcium carbonate: 2-4 parts, polyolefin elastomer: 2-3 parts, di(3,4-dimethyldibenzyl)sorbitol: 0.2-0.5 parts, thermotropic liquid crystal polymer: 2-5 parts, antioxidant: 0.4-0.7 parts, lubricant: 0.8-1.2 parts, antistatic agent: 0.5-1.0 parts;

[0051] The supramolecular crosslinking agent is a polycaprolactone polyol with end groups modified with ureidopyrimidinone bifunctional groups;

[0052] The core-shell modifier is a core-shell structured polymer with polymethyl methacrylate as the shell and an acrylate elastomer as the core. The surface of the core-shell modifier is pre-coated with polyethylene-grafted maleic anhydride polymer, and the coating mass of the polyethylene-grafted maleic anhydride polymer is 15% to 30% of the total mass of the core-shell modifier.

[0053] This application overcomes the technical contradiction of existing high-performance plastic packaging films simultaneously possessing ultra-high toughness, high strength, and high transparency by rationally designing the chemical composition of the plastic packaging film. The functions of each chemical component are as follows:

[0054] (1) Metallocene polyethylene resin (mPE, 80-90 parts): As the continuous phase and "skeleton" of the membrane material, mPE is the basis for carrying all other components. Its high molecular chain regularity and narrow molecular weight distribution not only endow the material with excellent basic mechanical properties (such as initial strength and flexibility) and processing fluidity, but also provide a "compatible platform" for the dispersion and action of various modified components through clear and controllable crystallization behavior. This ensures that other functional components can be stably embedded in the matrix without damaging the overall molding and processing properties of the material, making it the core carrier for realizing the comprehensive performance of the membrane material.

[0055] (2) Supramolecular crosslinking agent (5-8 parts): This component, namely polycaprolactone polyol (UPy-PCL) with end-group modified ureidopyrimidinone (UPy) bifunctional groups, is the core innovation of the membrane material's "high toughness". Its function is divided into two parts: On the one hand, the UPy end groups form quadruple hydrogen bonds to construct a high-strength and reversible dynamic physical crosslinking network. Under external impact or tension, these hydrogen bonds can quickly dissipate energy through "dissociation-reconstruction", avoiding brittle fracture caused by stress concentration, and endowing the material with excellent toughness, elasticity and potential self-healing ability; On the other hand, the polycaprolactone (PCL) segments have good flexibility and excellent compatibility with the amorphous region of mPE. They can act as "flexible spacer arms" for the UPy groups to prevent the crosslinking points from being too rigid and causing embrittlement, and can further fill the gaps between mPE molecular chains to help improve the flexibility of the matrix.

[0056] (3) Core-shell type modifier (6-10 parts): This component uses "polymethyl methacrylate (PMMA) as the shell and acrylate elastomer as the core" and is pre-coated with 15%-30% by mass of polyethylene grafted maleic anhydride (PE-g-MAH) on the surface, which is the key support for the impact resistance of the membrane material. Among them, the acrylate elastomer core is the "energy absorption core," which can quickly absorb and disperse external force energy through large deformation, shear yielding, and crazing effect when impacted; the PMMA shell acts as a "dispersion stabilizer," which can effectively isolate the elastomer core particles and prevent them from agglomerating during processing or storage, ensuring that the particles are uniformly dispersed in the mPE matrix at the nano / micro scale, becoming efficient stress dispersion points; while the PE-g-MAH pre-coating layer is the "interfacial bridge." The maleic anhydride (MAH) groups can form dipole-dipole interactions with the ester groups of the PMMA shell, and the PE segments can form molecular chain entanglements with the mPE matrix, completely solving the interfacial compatibility problem between the core-shell particles and the non-polar PE matrix, ensuring that stress can be efficiently transferred from the matrix to the elastomer core, and avoiding performance failure caused by interfacial debonding.

[0057] (4) Ethylene-vinyl acetate copolymer (EVA, 3-5 parts): EVA optimizes the overall component dispersibility of the membrane through a "two-way compatibility" effect. The vinyl acetate (VA) segments in the molecule are polar and can interact with polar components such as the PMMA shell of the core-shell modifier and the MAH group of PE-g-MAH; while the ethylene segments are completely compatible with the mPE matrix. This "polar-nonpolar dual structure" makes it a "transition layer" between different polar components, which can further weaken the interfacial tension between functional phases, assist PE-g-MAH in improving overall compatibility, and avoid performance fluctuations caused by uneven component dispersion.

[0058] (5) Stearic acid modified nano-calcium carbonate (2-4 parts): This component is a nanoscale supplement to improve the rigidity of the membrane material. The modification effect of stearic acid changes the surface of nano-calcium carbonate from hydrophilic to oleophobic, which greatly improves its compatibility with the non-polar mPE matrix, effectively inhibits the problem of easy agglomeration of nanoparticles, and achieves uniform dispersion at the nanoscale. With its huge specific surface area, the dispersed nano-calcium carbonate forms a strong interfacial interaction with the mPE matrix. It can not only act as a "physical cross-linking point" to restrict the movement of molecular chains and improve the stiffness, tensile strength and thermal stability of the material, but also assist the core-shell modifier in dissipating energy by inducing effects such as crazes and shear bands, while preventing the propagation of microcracks, thus taking into account both reinforcement and toughening effects.

[0059] (6) Polyolefin elastomer (POE, 2-3 parts): POE is a traditional and highly efficient polyolefin toughening agent with excellent compatibility with the mPE matrix. Through blending, it can form a "sea-island structure" or a bicontinuous phase. Its elastomer properties can directly fill the gaps between mPE molecular chains, reduce the intermolecular forces, and further improve the room temperature and low temperature flexibility and impact resistance of the membrane material without sacrificing strength. Together with the dynamic toughness of UPy-PCL and the energy absorption of the core-shell modifier, it forms a "triple toughening" system that comprehensively covers the toughness requirements under different stress conditions.

[0060] (7) Di(3,4-dimethyldibenzyl)sorbitol (DMDBS, 0.2-0.5 parts): As a highly efficient nucleating agent, DMDBS can self-assemble into a nanofiber network in the mPE melt, inducing the rapid formation of a large number of fine and uniform microcrystals in mPE through "heterogeneous nucleation". This optimization of the crystal structure brings multiple advantages: First, it significantly improves the crystallinity of mPE, enhancing the rigidity and tensile strength of the material; second, the microcrystal size is much smaller than the wavelength of visible light, greatly improving the transparency of the film material and meeting the appearance requirements of packaging films; third, the uniform microcrystalline structure provides a more stable "adhesion substrate" for functional components such as nano-calcium carbonate and core-shell particles, strengthening the bonding force between each component and the matrix.

[0061] (8) Thermotropic liquid crystal polymer (TLCP, 2-5 parts): TLCP is the core reinforcing component of the membrane material for "high strength and high modulus". During the membrane material processing (especially biaxial stretching), the TLCP molecular chains will be highly oriented under shear force, forming "microfibers" with a diameter of nanometers and a length of micrometers in situ, which are uniformly distributed in the mPE matrix like "steel bars" in concrete. These microfibers themselves have extremely high tensile modulus and strength, can efficiently bear external loads, and significantly improve the tensile strength, elastic modulus and heat resistance of the membrane material; at the same time, with the help of the interfacial compatibility of PE-g-MAH and EVA, the interfacial adhesion between TLCP microfibers and mPE matrix is ​​guaranteed, ensuring that stress can be effectively transferred from the matrix to the microfibers and avoiding the "reinforcing bars" from detaching from the matrix.

[0062] (9) Antioxidants, lubricants, and antistatic agents (total 1.7–2.9 parts): Antioxidants (0.4–0.7 parts): By capturing free radicals generated during processing and use, they inhibit the oxidative degradation of mPE and other polymer components, protect the delicate molecular structure such as the UPy hydrogen bond network and TLCP microfiber structure from damage, and extend the service life of the membrane material. Lubricants (0.8–1.2 parts): They can reduce the internal friction between mPE molecular chains and the external friction between the material and the processing equipment, improve melt flowability, ensure that the core-shell modifier, nano-calcium carbonate and other components can be evenly dispersed, and avoid material degradation caused by friction overheating during processing. Antistatic agents (0.5–1.0 parts): They accumulate on the surface of the membrane material through molecular migration, adsorb moisture in the air to form a conductive film, eliminate the accumulation of static electricity on the surface of the material, prevent dust attraction and film adhesion caused by static electricity during packaging, and improve ease of use.

[0063] This membrane formulation achieves a high degree of balance between rigidity, toughness, processability, and functionality through multi-scale, multi-mechanism component synergy. Its synergistic logic can be unfolded from four dimensions:

[0064] (1) Scale level: Layered reinforcement from molecular to macroscopic. At the molecular scale, the dynamic hydrogen bond network of UPy-PCL constructs the "first line of defense for toughness" and dissipates energy through the reversible change of intermolecular forces; the regular molecular chains of mPE provide a stable substrate for the adhesion and action of all functional components; at the nanoscale, the fine microcrystals induced by DMDBS optimize the matrix crystal structure and provide dispersion sites for nano-calcium carbonate; nano-calcium carbonate restricts the movement of molecular chains through interfacial interaction, which not only enhances rigidity but also helps to disperse stress, forming a "nanoscale reinforcement-crystallization optimization" synergy with the microcrystalline structure; at the micrometer scale, the elastomer core of the core-shell modifier acts as a "micrometer-level energy absorption station" and absorbs impact energy through deformation; the microfibers formed in situ by TLCP act as "micrometer-level reinforcing ribs" and bear tensile loads. The two improve mechanical properties from the two directions of "toughening" and "reinforcing" respectively, and both are tightly combined with the matrix through the interfacial interaction of PE-g-MAH and EVA.

[0065] (2) Functional level: The complementarity of multiple toughening and synergistic enhancement. In the direction of "toughening", the dynamic hydrogen bonds of UPy-PCL (molecular-level toughness), the elastomer core of the core-shell modifier (micron-level energy absorption), and the basic flexibility of POE (matrix-level toughening) form a "triple synergy", covering the toughness requirements of all scenarios from static tension to dynamic impact. In the direction of "enhancement", TLCP microfibers (main reinforcing ribs), nano calcium carbonate (nano reinforcing points), and DMDBS-induced microcrystals (crystallization enhancement) form a "three-level enhancement", which improves rigidity and strength from three dimensions: macro load bearing, micro molecular chain restriction, and matrix structure optimization. Moreover, the toughening and reinforcing components do not interfere with each other, but instead form a "rigid and flexible" balance through the action of interface compatibilizer.

[0066] (3) Interface level: A "bridge network" compatible with the whole system. PE-g-MAH and EVA jointly construct an "interface bridge network" covering all components: PE-g-MAH focuses on solving the interface problem between the core-shell modifier, TLCP and mPE matrix, and achieves strong adhesion through "group action + chain segment entanglement"; EVA fills the transition gap between polar components (such as PMMA shell, MAH group) and non-polar matrix, and weakens the interfacial tension. The two work together to ensure that all functional components (whether polar core-shell particles or rigid TLCP microfibers and nano calcium carbonate) can be uniformly dispersed and tightly bonded to the matrix, avoiding "component failure" caused by interfacial debonding, and allowing the function of each component to be fully utilized.

[0067] (4) Processing and performance aspects: Stable and controllable molding assurance. The DMDBS-optimized crystal structure improves the processing fluidity of mPE, and the lubricant further reduces melt friction. The two work together to ensure uniform dispersion and stable molding during multi-component blending. Antioxidants protect easily degradable components such as UPy-PCL and TLCP during processing, avoiding performance loss due to processing heat. Ultimately, under the synergistic system of "matrix support - functional complementarity - interface compatibility - processing assurance", all components enable the film material to simultaneously possess comprehensive properties such as high toughness, high strength, high transparency, good processability, and antistatic properties, which not only meet the impact resistance requirements of general packaging films, but also adapt to the requirements of special packaging for high strength and heat resistance.

[0068] In some embodiments, the preparation method of the supramolecular crosslinking agent includes the following steps:

[0069] A1. Under inert gas protection, hydroxyl-terminated polycaprolactone polyol and 2,4-toluene diisocyanate are reacted at 60-80°C for 2-4 hours to obtain isocyanate-terminated polycaprolactone prepolymer.

[0070] A2. The isocyanate-terminated polycaprolactone prepolymer was reacted with 2-amino-4-hydroxy-6-methylpyrimidine at 40-60°C for 3-5 h to obtain the crude product;

[0071] A3. The crude product is precipitated in a non-solvent, filtered, and dried to obtain the polycaprolactone polyol with end groups modified with ureidopyrimidinone bifunctional groups.

[0072] In some embodiments, the molar ratio of the hydroxyl groups of the terminal hydroxyl polycaprolactone polyol to the isocyanate groups of the 2,4-toluene diisocyanate is 1:(2.0 to 2.2).

[0073] The molar ratio of the isocyanate group of the terminal isocyanate-based polycaprolactone prepolymer to the amino group of the 2-amino-4-hydroxy-6-methylpyrimidine is 1:(1.0 to 1.05).

[0074] It should be noted that in step A1 (preparation of terminal isocyanate prepolymer), the role of inert gas (such as nitrogen) protection is to isolate oxygen and moisture, preventing the isocyanate group (-NCO) from reacting with water to form urea bonds, which would lead to cross-linking and aggregation of the molecular chain, affecting the efficiency of subsequent functional group modification. The reaction temperature is set at 60-80℃, which satisfies the reactivity of -NCO in 2,4-toluene diisocyanate (TDI) and hydroxyl group (-OH) in terminal hydroxyl polycaprolactone (PCL-OH) (too low a temperature results in a slow reaction rate, while too high a temperature can easily trigger TDI self-polymerization), and also ensures complete conversion of -OH through a reaction time of 2-4 hours (no residual hydroxyl group would lead to incomplete grafting of UPy groups in the subsequent process). The design of a hydroxyl to isocyanate molar ratio of 1:(2.0~2.2) ensures that both ends of the PCL molecular chain are capped with -NCO by excess TDI (forming "terminal isocyanate prepolymer"), avoiding the occurrence of single-end modified or unmodified PCL chains, and ensuring that the final product has a double UPy end group structure, providing sufficient hydrogen bond interaction sites for the formation of cross-linking network.

[0075] Step A2 (Introduction of UPy Group): The reaction temperature of 40-60℃ is lower than that of step A1 because the amino group (-NH2) in 2-amino-4-hydroxy-6-methylpyrimidine (UPy monomer precursor) has high reactivity with -NCO. The low temperature can reduce the aggregation of UPy monomer itself caused by the interaction between amino and hydroxyl groups. At the same time, the reaction time of 3-5 hours is sufficient for -NCO and -NH2 to react completely to form urea bonds, so that the UPy group is stably grafted onto the end group of the prepolymer. The isocyanate group to amino molar ratio of 1:(1.0-1.05) adopts a "slightly excess amino" design, which can ensure the complete reaction of -NCO (avoiding residual -NCO from causing side reactions in subsequent use) and remove the trace amount of unreacted UPy monomer precursor in subsequent purification without affecting the structural uniformity of the product.

[0076] Step A3 (Purification): The purpose of non-solvent precipitation (such as diethyl ether, n-hexane, etc., which have significantly different solubility from the product) is to separate unreacted TDI, UPy monomer precursors, and other small molecule impurities from the crude product. High-purity UPy-modified PCL is obtained through filtration and drying. Without purification, impurities will affect the hydrogen bonding efficiency of the UPy groups during membrane processing, leading to a decrease in dynamic network strength and weakening the material's toughness.

[0077] In some embodiments, the preparation method of the core-shell modifier includes the following steps:

[0078] B1. Add a crosslinking agent and an initiator to the butyl acrylate monomer and perform emulsion polymerization at 75-85°C for 2.0-3.0 h to obtain an acrylate elastomer core emulsion;

[0079] B2. Add methyl methacrylate monomer to the acrylate elastomer core emulsion and continue the emulsion polymerization reaction at 80-85°C for 1.5-2.5 hours to polymerize the polymethyl methacrylate shell onto the surface of the acrylate elastomer core, thereby obtaining core-shell type modifier particles with polymethyl methacrylate as the shell and acrylate elastomer as the core.

[0080] B3. Disperse the core-shell modifier particles in xylene solvent to form a suspension; and dissolve the polyethylene-grafted maleic anhydride polymer in hot xylene solvent to form a coating solution;

[0081] B4. Under stirring conditions, the coating solution is added dropwise to the suspension, and the reaction is carried out at 70-80°C for 1.0-2.0 h to obtain the core-shell modifier.

[0082] In some embodiments, the crosslinking agent is divinylbenzene, and the added mass of the divinylbenzene is 1.0 to 1.5% of the mass of the butyl acrylate monomer;

[0083] The initiator is potassium persulfate, and the mass of potassium persulfate added is 1.0 to 1.5% of the mass of the butyl acrylate monomer.

[0084] The mass ratio of the core layer to the shell layer of the core-shell modifier particles is (70-80):(30-20).

[0085] It should be noted that in step B1 (preparation of acrylate elastomer core): butyl acrylate (BA) is used as the monomer, divinylbenzene (DVB) as the crosslinking agent, and potassium persulfate (KPS) as the initiator. DVB, as the crosslinking agent, is added at 1.0–1.5% of the BA mass. This allows it to form a crosslinked network within the elastomer through double bond polymerization, giving the core layer good deformability (ensuring energy dissipation through shear yielding during impact), while also preventing excessive crosslinking from causing core layer embrittlement. KPS, as a water-soluble initiator, at an addition of 1.0–1.5%, can efficiently decompose at 75–85°C to generate free radicals, initiating BA polymerization. A reaction time of 2.0–3.0 hours ensures complete polymerization of BA to form a uniformly sized elastomer core emulsion (too large a particle size can lead to uneven subsequent shell coating, while too small a particle size results in low energy absorption efficiency).

[0086] Step B2 (PMMA Shell Coating): Methyl methacrylate (MMA) is added to the elastomer core emulsion, and polymerization continues at 80–85°C for 1.5–2.5 hours. Utilizing the principle of "seed emulsion polymerization," PMMA grows on the surface of the elastomer core to form a shell. This temperature is close to that of step B1, ensuring continuous polymerization. The PMMA shell acts as a "physical barrier," preventing the elastomer core from agglomerating due to high-temperature melting during subsequent processing. Simultaneously, its polar surface provides binding sites for subsequent PE-g-MAH coating. The core-shell mass ratio of (70–80):(30–20) is designed to balance performance through a "thick core, thin shell": 70–80% elastomer core ensures sufficient energy absorption capacity, while the 20–30% PMMA shell stabilizes the core particles without weakening the core's deformation efficiency due to excessive shell thickness.

[0087] Step B3 (Preparation of coating precursor solution): Core-shell particles are dispersed in xylene to form a suspension, while PE-g-MAH is dissolved in hot xylene (xylene is a good solvent for PE-g-MAH, and high temperature can accelerate dissolution) to form a coating solution. Xylene is chosen as the solvent because it has good compatibility with mPE, PMMA, and PE-g-MAH, and can be removed by subsequent heating and evaporation, leaving no residue in the product.

[0088] Step B4 (PE-g-MAH coating): The coating solution is added dropwise with stirring at 70–80℃, and the reaction is maintained at this temperature for 1.0–2.0 h. Utilizing the weak volatility of xylene and temperature-driven reaction, PE-g-MAH is uniformly adsorbed and coated onto the surface of the core-shell particles. This temperature ensures that PE-g-MAH is in a semi-molten state (facilitating spreading and coating) without causing deformation of the core-shell particles. The combination of stirring and dropwise addition prevents local agglomeration of PE-g-MAH, ensuring a uniform coating thickness. The core function of the PE-g-MAH coating layer is as an "interfacial bridge." A coating mass ratio of 15–30% allows for interaction between the MAH groups and the ester groups of the PMMA shell, as well as entanglement between the PE segments and the mPE matrix, while simultaneously preventing excessive coating thickness from reducing particle dispersibility.

[0089] In some embodiments, the method for preparing the stearic acid-modified nano-calcium carbonate includes the following steps:

[0090] C1. Disperse nano-calcium carbonate in deionized water under high-speed stirring to form a suspension;

[0091] C2. Slowly add an ethanol solution of stearic acid to the suspension and react at 70-85°C for 1-2 hours to obtain the stearic acid-modified nano-calcium carbonate.

[0092] The amount of stearic acid added is 2.0 to 4.0% of the mass of the nano-calcium carbonate.

[0093] It should be noted that in step C1 (preparation of suspension): nano-CaCO3 is dispersed in deionized water under high-speed stirring. High-speed stirring can break the hydrogen bond agglomeration of nano-CaCO3 formed by surface hydroxyl groups, forming a uniform suspension, which provides sufficient contact area for subsequent stearic acid modification (if the dispersion is uneven, some CaCO3 particles will not be modified and will still be easy to agglomerate).

[0094] Step C2 (Surface Modification Reaction): Stearic acid ethanol solution is slowly added dropwise to the suspension, and the reaction is carried out at 70–85°C for 1–2 hours. Ethanol, as a solvent, ensures uniform dispersion of stearic acid, and the slow dropwise addition avoids uneven modification caused by excessively high local concentrations of stearic acid. The temperature of 70–85°C accelerates the reaction between the carboxyl groups (-COOH) in stearic acid and the hydroxyl / calcium ions on the surface of nano-CaCO3 (forming calcium carboxylate salts for chemisorption), and also promotes ethanol evaporation through heating, causing the long alkyl chains of stearic acid to align oriented on the CaCO3 surface (forming an oleophobic layer). The key parameter is that the added stearic acid mass is 2.0–4.0% of the nano-CaCO3: if the addition is too low, a large number of hydrophilic groups remain on the CaCO3 surface, resulting in insufficient improvement in compatibility; if the addition is too high, stearic acid forms multilayer adsorption on the surface, leading to particle aggregation due to alkyl chain entanglement, thus losing the nano-effect.

[0095] In some embodiments, the thermotropic liquid crystal polymer is a fully aromatic polyester liquid crystal polymer, which is obtained by copolymerization of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and 2-aminobenzothiazole-6-carboxylic acid via a polycondensation reaction.

[0096] The molar ratio of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and 2-aminobenzothiazole-6-carboxylic acid is (60-80):(20-40):(0.5-5).

[0097] It should be noted that the core of the preparation of fully aromatic polyester TLCP is to control the liquid crystal cell structure by adjusting the monomer ratio, so as to ensure that it can be fiberized in situ during film processing and play the role of "nano-steel bar" reinforcement.

[0098] p-Hydroxybenzoic acid (PHB) and 6-hydroxy-2-naphthoic acid (HNA) are key monomers for forming the liquid crystal building blocks of the TLCP backbone: PHB provides a rigid benzene ring structure, while HNA further enhances the rigidity of the molecular chain and the stability of the liquid crystal phase through the naphthoic ring. The molar ratio of the two (60-80):(20-40) can be adjusted to allow the TLCP to exhibit a thermotropic liquid crystal phase within the temperature range of 160-200℃ (film processing temperature range) by adjusting the proportion of rigid segments (too high a temperature will cause the liquid crystal phase to disappear, while too low a temperature will result in high melt viscosity and difficulty in fiber formation). 2-Aminobenzothiazol-6-carboxylic acid (molar percentage 0.5-5%) acts as a "functional regulator." Its amino and thiazole rings can slightly disrupt the regularity of the liquid crystal building blocks through intermolecular hydrogen bonds, preventing excessive orientation of the TLCP molecular chain that could lead to film embrittlement. At the same time, it enhances the interfacial interaction between TLCP and PE-g-MAH (anhydride groups), ensuring a tight bond between the microfibers and the mPE matrix. Polycondensation reaction removes small molecules (such as water) to form a high-strength aromatic polyester backbone, providing TLCP microfibers with excellent mechanical strength and heat resistance.

[0099] In some embodiments, the antioxidant is composed of a hindered phenolic primary antioxidant and a phosphite secondary antioxidant, wherein the mass ratio of the hindered phenolic primary antioxidant to the phosphite secondary antioxidant is 1:(1.5-2.5).

[0100] The lubricant is composed of erucamide and polyethylene wax, wherein the mass ratio of erucamide to polyethylene wax is 1:(1-1.5).

[0101] The antistatic agent is glyceryl monostearate.

[0102] It should be noted that the antioxidants are hindered phenols and phosphites in a ratio of 1:(1.5–2.5): the hindered phenols, as the primary antioxidants, terminate the oxidation chain reaction by capturing free radicals generated during processing and use; the phosphites, as secondary antioxidants, decompose hydroperoxides produced by polymer oxidation (which the primary antioxidants cannot remove), forming a "synergistic antioxidant system." A slightly excessive amount of secondary antioxidants can prevent the primary antioxidants from becoming ineffective due to the accumulation of hydroperoxides, thus extending the membrane's lifespan (if the primary antioxidants are excessive, they are prone to discoloration due to oxidation, affecting the membrane's transparency).

[0103] The lubricant is erucamide:polyethylene wax = 1:(1~1.5): Erucamide is an internal lubricant that can penetrate between polymer molecular chains to reduce inter-chain friction; polyethylene wax is an external lubricant that can form a lubricating film on the surface of the material and processing equipment (such as screws and dies) to reduce interfacial friction. The synergistic effect of the two can comprehensively improve melt flowability and ensure uniform dispersion of each component; the slightly excessive amount of polyethylene wax can avoid excessive migration of erucamide to the surface after film forming, which would result in excessive slippage (affecting subsequent printing and other processing).

[0104] The antistatic agent is glyceryl monostearate: This component was chosen because its molecule contains both hydrophilic hydroxyl groups (which can adsorb moisture in the air to form a conductive layer and eliminate static electricity) and hydrophobic long alkyl chains (which have good compatibility with mPE and are not easy to migrate or be lost), which is suitable for the antistatic requirements of non-polar PE systems and will not affect the mechanical properties and transparency of the membrane material.

[0105] Figure 1 This is a schematic flowchart illustrating a method for preparing a high-toughness plastic packaging film material according to an embodiment of this application.

[0106] Based on a general inventive concept, such as Figure 1 As shown, this application provides a method for preparing the high-toughness plastic packaging film material according to any one of the above claims, the method comprising the following steps:

[0107] S1. The metallocene polyethylene resin, the ethylene-vinyl acetate copolymer, the polyolefin elastomer, the di(3,4-dimethylbenzyl)sorbitol, the antioxidant, the lubricant and the antistatic agent are added to a high-speed mixer according to the formula ratio and mixed at 80-100°C for 5-10 minutes to obtain a premix.

[0108] S2. The premix, the supramolecular crosslinking agent, the core-shell modifier, the stearic acid-modified nano-calcium carbonate, and the thermotropic liquid crystal polymer are added to a twin-screw extruder, and then melt-blended and extruded to granulate to obtain masterbatch.

[0109] S3. Under the influence of an external electromagnetic field, the masterbatch is blow-molded to obtain the high-toughness plastic packaging film.

[0110] In some embodiments, the processing temperature of the twin-screw extruder is 160–200°C, and the screw speed is 200–400 rpm;

[0111] The applied electromagnetic field has a magnetic field strength of 0.5–1.5 T and an electric field strength of 500–1000 V / cm.

[0112] The blow molding process employs biaxial stretching, with a longitudinal stretching ratio of 2.5–3.5 and a transverse stretching ratio of 2.5–3.5. The die head temperature of the blow molding machine is 165–185°C.

[0113] It should be noted that in step S1 (premix preparation): mPE, EVA, POE, DMDBS and various additives are mixed at 80-100℃ for 5-10 minutes. The core objective is to achieve "preliminary uniform dispersion" with low energy consumption, laying the foundation for subsequent melt blending.

[0114] The temperature of 80-100℃ is set as the "softening temperature range" of mPE (120-130℃ below its melting point). At this temperature, the mPE particles soften slightly and the fluidity is improved, which makes it easier for components such as EVA (VA segment polarity) and POE (elastomer) to adhere evenly to its surface. At the same time, this temperature can promote the initial dispersion of DMDBS (nucleating agent) (avoiding DMDBS agglomeration at high temperatures later) and will not cause the volatilization and failure of auxiliary agents (such as antioxidants).

[0115] A mixing time of 5 to 10 minutes balances "dispersion efficiency" and "energy consumption cost": if the time is too short, EVA, POE and other materials will not mix evenly with mPE, which may easily lead to phase separation in subsequent processing; if the time is too long, local overheating may cause decomposition of auxiliary agents or slight degradation of mPE.

[0116] Step S2 (Twin-screw extrusion granulation): The premixed material is melt-blended and granulated with supramolecular crosslinking agent, core-shell modifier, modified nano-CaCO3, and TLCP through a twin-screw extruder. This is a key step to achieve "uniform dispersion of each component at the nanoscale" and directly determines the microstructure and mechanical properties of the membrane material.

[0117] Processing temperature 160~200℃: This range covers the melting temperatures of mPE (melting point 120~130℃), EVA (melting point 80~100℃), and POE (melting point 60~80℃), while also satisfying the processing stability of supramolecular crosslinking agents (UPy groups are stable at this temperature and will not cause structural damage due to hydrogen bond dissociation) and TLCP (which presents a thermotropic liquid crystal phase, facilitating subsequent fiber formation). If the temperature is too low, the melt viscosity will be high, and it will be difficult to disperse core-shell particles, nano-CaCO3, etc.; if the temperature is too high, it will lead to mPE degradation, UPy group oxidation, and even the disappearance of the TLCP liquid crystal phase.

[0118] Screw speed of 200–400 rpm: High speed, through strong shear force, disperses core-shell modifiers (micron-sized), nano-CaCO3 (nano-sized), etc., into the mPE matrix, avoiding agglomeration; at the same time, shear force can promote the initial orientation of TLCP, preparing for "in-situ fiber formation" in subsequent molding. Too low a speed results in insufficient shear force, leading to uneven component dispersion; too high a speed can easily cause excessive shear heat, leading to local temperature exceeding the limit and triggering material degradation.

[0119] The purpose of extrusion granulation is to transform the uniformly mixed melt into masterbatch with uniform particle size, which facilitates stable feeding during subsequent blow molding (avoiding component segregation caused by directly feeding powder).

[0120] Step S3 (blow molding): Under the action of an external electromagnetic field, the film is formed by biaxial stretching blow molding. The core objective is to maximize the role of each functional component by “external force-induced microstructure orientation”, so as to give the film material a balance of high strength and high toughness.

[0121] An external electromagnetic field (magnetic field 0.5–1.5T, electric field 500–1000V / cm) is applied: The magnetic field induces the oriented alignment of TLCP molecular chains (aromatic rigid segments) with magnetic anisotropy along the magnetic field direction, while the electric field promotes the uniform distribution of core-shell particles and nano-CaCO3 in the matrix through polarization (avoiding stress concentration caused by particle agglomeration during stretching). The intensity of the electromagnetic field needs to be precisely controlled: too strong a field will cause over-orientation of TLCP, increasing the brittleness of the film material along the orientation direction; too weak a field will fail to achieve effective orientation, resulting in insufficient TLCP reinforcement.

[0122] Biaxial stretching (2.5–3.5 longitudinally, 2.5–3.5 transversely): A balanced ratio of longitudinal stretching (along the extrusion direction of the membrane) and transverse stretching (perpendicular to the extrusion direction) (2.5–3.5) allows the mPE molecular chains to achieve orientation in both directions (improving the overall strength of the membrane and avoiding excessive anisotropy caused by uniaxial stretching). Simultaneously, during stretching, TLCP "fiberizes in situ" under the combined action of shear force and electromagnetic field (forming a nanoscale microfiber network), while the core-shell modifier is further dispersed during stretching. The micro-deformation of its elastic core layer due to stretching provides toughness support for the membrane. If the stretch ratio is too low, the molecular chains and TLCP will not be sufficiently oriented, resulting in low membrane strength; if it is too high, it will lead to excessive stretching and breakage of the molecular chains, or destruction of the core-shell particles, thus weakening the toughness.

[0123] Die head temperature 165~185℃: This temperature is slightly lower than the extruder processing temperature, which can ensure that the masterbatch melt has good fluidity in the die head (avoiding molding instability due to excessive viscosity), and also allow the melt to cool down quickly after leaving the die head (facilitating the fixation of TLCP microfiber structure and avoiding orientation relaxation), while ensuring that the microcrystalline structure formed by DMDBS-induced mPE is uniform (improving the transparency and rigidity of the film material).

[0124] In summary, this application, focusing on the research and development of high-toughness plastic packaging film materials, systematically breaks through the technical bottleneck of existing high-performance packaging films that "difficulty in simultaneously achieving high toughness, high strength, and high transparency" through full-chain innovation in material formulation, functional component design, and preparation process. It forms a solution that combines technological innovation with practical application, and its core advantages are reflected in the following four aspects:

[0125] (1) The synergy and precision of the formulation design have constructed a multi-scale and multi-functional component synergy system. Using metallocene polyethylene (mPE) as a stable "skeleton", the balance of "rigidity-toughness-transparency" is achieved through the scientific ratio of differentiated functional components: the dynamic hydrogen bond network of supramolecular crosslinking agent (UPy-PCL), the elastic nuclear energy absorption of core-shell modifier, and the matrix toughening of polyolefin elastomer (POE) form a "triple toughening mechanism" to cover the toughness requirements under different stress scenarios; the in-situ fiber-forming reinforcement of thermotropic liquid crystal polymer (TLCP), the nanoscale reinforcement of stearic acid modified nano calcium carbonate, and the microcrystalline optimization induced by di(3,4-dimethyldibenzyl)sorbitol (DMDBS) construct a "three-level reinforcement system" to comprehensively improve strength from macroscopic load bearing to microscopic structural strengthening; at the same time, the fine microcrystals induced by DMDBS, because their size is smaller than the wavelength of visible light, combined with the uniform dispersion of each component, greatly improve the transparency of the film material, solving the problem of decreased transparency caused by traditional reinforcement and toughening modification. In addition, the ethylene-vinyl acetate copolymer (EVA) and polyethylene grafted maleic anhydride (PE-g-MAH) form a fully compatible "interfacial bridge network", which completely eliminates the interfacial barrier between polar components and non-polar mPE matrix, ensuring that each functional component plays an efficient role and avoiding performance fluctuations caused by uneven dispersion.

[0126] (2) The innovativeness and high efficiency of functional components break through the performance limitations of traditional modified materials. The supramolecular crosslinking agent (UPy-PCL) is the core innovation. Through the reversible hydrogen bond network formed by the terminal ureidopyrimidinone (UPy), it endows the membrane material with excellent toughness and has potential self-healing ability. Compared with traditional chemical crosslinking agents, it is easier to control and less likely to cause material embrittlement. The core-shell type modifier, through the three-layer structure design of "acrylate elastomer core-PMMA shell-PE-g-MAH coating layer", not only solves the problem of elastomer particle dispersion, but also achieves strong bonding with the mPE matrix through the interface coating layer. The energy absorption efficiency is much higher than that of ordinary elastomer modifiers. Fatty acid modified nano-calcium carbonate achieves uniform nanoscale dispersion through surface modification, enhancing rigidity while assisting in energy dissipation, achieving a synergistic effect of "reinforcement-toughening" and avoiding the drawbacks of easy agglomeration of traditional nanoparticles; All-aromatic polyester liquid crystal polymer (TLCP) can form nanoscale microfibers in situ during processing through specific monomer ratio control, which is like "nano-steel bars" for efficient reinforcement. Furthermore, the introduction of trace amounts of functional monomers (2-aminobenzothiazole-6-carboxylic acid) balances the contradiction between orientation reinforcement and material brittleness, making it easier to integrate with the matrix and reduce interface defects compared to traditional fiber reinforcement.

[0127] (3) The scientific nature and controllability of the preparation process ensure the stability and uniformity of the membrane material performance. The preparation process of each functional component is controlled by precise parameter regulation to achieve structural control: the supramolecular crosslinking agent is protected by inert gas, optimized molar ratio and purified to ensure efficient grafting of UPy bifunctional groups and high purity; the core-shell modifier is combined with seed emulsion polymerization and solution coating to achieve uniform and controllable core-shell structure and coating layer; the stearic acid modified nano-calcium carbonate is modified by high-speed dispersion and temperature control to ensure sufficient surface modification and uniform particle dispersion; the TLCP is optimized by monomer ratio to ensure that it presents a stable thermotropic liquid crystal phase within the membrane material processing temperature range, which is convenient for in-situ fiber formation. The overall preparation of the membrane material adopts the process of "premixing-melt blending granulation-electromagnetic field assisted biaxial stretching blow molding". In the premixing stage, the components are initially dispersed by temperature control. The twin-screw extrusion ensures that the components are uniformly mixed at the nanoscale by temperature and speed control. The electromagnetic field assisted biaxial stretching induces TLCP orientation through magnetic field and promotes particle dispersion through electric field. With the balanced longitudinal and transverse stretching ratio, the mPE molecular chains and TLCP microfibers achieve biaxial ordered orientation, which further improves the overall performance of the membrane material. Moreover, the parameters of the whole process are controllable, which facilitates the quality stability in industrial production.

[0128] (4) Wide range of applications and practicality, taking into account both general and special packaging needs. With its comprehensive properties of "high toughness, high strength and high transparency", this film material can meet the requirements of general packaging such as food and daily necessities for impact resistance, easy molding and clear appearance, and can also meet the requirements of special packaging such as electronic components and precision instruments for high strength, puncture resistance and antistatic (achieved through antistatic agents). At the same time, the scientific ratio of antioxidants, lubricants and other auxiliary agents in the formula ensures that the film material is not easily oxidized and degraded during processing and long-term use, thus extending its service life. Moreover, its good processing fluidity is compatible with existing blow molding equipment, without the need for large-scale production line modification, which lowers the threshold for industrial application and has extremely high practical value and market potential.

[0129] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0130] Example 1

[0131] This embodiment provides a high-toughness plastic packaging film material, which, by weight, is composed of the following chemical raw materials: metallocene polyethylene resin (mPE, purchased from ExxonMobil Saudi Arabia, grade CB1001): 85 parts; supramolecular crosslinking agent: 6.5 parts; core-shell modifier: 8 parts; ethylene-vinyl acetate copolymer (EVA, VA content 18%, CAS No. 24937-78-8): 4 parts; stearic acid modified nano-calcium carbonate: 3 parts; polyolefin elastomer (CAS No. 25087-34-7, purchased from Jiangsu Runfeng Synthetic Technology Co., Ltd.): 2.5 parts; di(3,4-dimethyldibenzyl)sorbitol (DMDBS, CAS No. 135861-56-2, purchased from... Shanghai Aladdin Biochemical Technology Co., Ltd.: 0.35 parts; Thermotropic liquid crystal polymer: 3.5 parts; Antioxidant (a composite system of hindered phenolic primary antioxidant 1010 and phosphite secondary antioxidant 168, primary antioxidant 1010 CAS No. 6683-19-8, secondary antioxidant 168 CAS No. 31570-04-4, mass ratio 1:2): 0.55 parts; Lubricant (a composite system of erucamide and polyethylene wax, erucamide CAS No. 112-84-5, polyethylene wax CAS No. 9002-88-4, mass ratio 1:1.25): 1.0 part; Antistatic agent (glyceryl monostearate, CAS No. 31566-31-1, purchased from Sinopharm Chemical Reagent Co., Ltd.): 0.75 parts.

[0132] The preparation method of the supramolecular crosslinking agent is as follows: A1. Under nitrogen (inert gas) protection, hydroxyl-terminated polycaprolactone polyol (OH-PCL-OH hydroxyl-terminated polycaprolactone, CAS No. 24980-41-4) and 2,4-toluene diisocyanate (CAS No. 584-84-9) are added to a four-necked reactor, stirring is started, the reaction temperature is controlled at 70℃, and the reaction is maintained for 3 hours to obtain isocyanate-terminated polycaprolactone prepolymer; wherein, the molar ratio of the hydroxyl groups of the hydroxyl-terminated polycaprolactone polyol to the isocyanate groups of the 2,4-toluene diisocyanate is 1:2; A2. 2-amino-4-hydroxy-6-methylpyrimidine (CAS No. 584-84-9) is added to the above reactor. (No. 3977-29-5), adjust the reaction temperature to 50℃, and continue stirring for 4 hours to obtain the crude product; wherein, the molar ratio of the isocyanate group of the terminal isocyanate group of polycaprolactone prepolymer to the amino group of 2-amino-4-hydroxy-6-methylpyrimidine is 1:1.1; A3, slowly add the crude product after reaction to n-hexane while stirring until a white solid precipitate is formed. After standing for 1 hour, filter. The obtained solid is washed 3 times with n-hexane, each time with an amount of 5 times the mass of the solid. Then, place the washed solid in a vacuum drying oven and vacuum dry at 60℃ for 8 hours to obtain polycaprolactone polyol (supramolecular crosslinking agent) with ureidopyrimidinone bifunctional group at the end.

[0133] The preparation method of the core-shell modifier includes: B1, adding butyl acrylate monomer (CAS No. 141-32-2), crosslinking agent divinylbenzene (CAS No. 1321-74-0), and initiator potassium persulfate sequentially to a four-necked reactor containing deionized water and sodium dodecyl sulfate (CAS: 151-21-3). Nitrogen gas is then introduced to purge air from the reactor at a flow rate of 0.5 L / min for 30 min. Afterward, stirring is started and the temperature is raised to 80°C. The emulsion polymerization reaction is maintained at this temperature for 2.5 h to obtain an acrylate elastomer core emulsion; wherein, divinyl... The mass of benzene added was 1.25% of the mass of butyl acrylate monomer, and the mass of potassium persulfate added was 1.25% of the mass of butyl acrylate monomer; B2, keeping the nitrogen atmosphere and stirring rate constant in the reactor, the reaction temperature was raised to 82℃, and methyl methacrylate monomer (CAS No. 80-62-6, purchased from Sinopharm Chemical Reagent Co., Ltd.) was slowly added dropwise to the above elastomer core emulsion at a dropping rate of 0.5 mL / min. After the addition was completed, the emulsion polymerization reaction was continued at the temperature for 2 hours, so that polymethyl methacrylate polymerized on the surface of the acrylate elastomer core to form a shell layer, resulting in... Core-shell modifier particles with polymethyl methacrylate as the shell and acrylate elastomer as the core; wherein the mass ratio of the core layer (acrylate elastomer) to the shell layer (polymethyl methacrylate) is 75:25; B3, the above core-shell modifier particles are collected by centrifugation (8000 rpm, centrifugation time 15 min), washed 3 times with deionized water, dispersed in xylene solvent, and ultrasonically treated for 20 min (ultrasonic power 300 W) to form a suspension with a mass concentration of 15%; at the same time, polyethylene grafted with maleic anhydride polymer (CAS No. 9006) is... -26-2 (grafting rate 1.2%) was added to hot xylene solvent at 80℃ and stirred until completely dissolved to form a coating solution with a mass concentration of 10%; B4. Under the condition of stirring speed of 300 rpm, the above coating solution was slowly added dropwise to the suspension for 30 min. After the addition was completed, the system temperature was controlled at 75℃ and the reaction was kept at this temperature for 1.5 h. After the reaction was completed, the mixture was centrifuged (speed 8000 rpm, centrifugation time 15 min), the solid product was collected, washed twice with xylene, and vacuum dried at 60℃ for 6 h to obtain the core-shell modifier.

[0134] The preparation method of the stearic acid modified nano-calcium carbonate includes: C1, adding nano-calcium carbonate (average particle size 50 nm, CAS number 471-34-1) to a high-speed stirred tank containing deionized water, turning on high-speed stirring at a stirring rate of 1500 rpm for 30 min to uniformly disperse the nano-calcium carbonate and form a suspension with a mass concentration of 10%; C2, dissolving stearic acid (CAS number 57-11-4) in ethanol to prepare a stearic acid ethanol solution with a mass concentration of 5%; under stirring conditions, slowly adding the stearic acid ethanol solution dropwise to the above suspension at a dropping rate of 1 mL / min, and after the addition is complete, raising the system temperature to 80℃ and maintaining the temperature for 1.5 h, centrifuging after the reaction is completed (speed 8000 rpm, centrifugation time 15 min), collecting the solid product, washing it three times with deionized water, and drying it in a forced-air conditioner at 60℃ for 4 h to obtain the stearic acid modified nano-calcium carbonate; wherein, the mass of stearic acid added is 3.0% of the mass of nano-calcium carbonate.

[0135] The preparation method of the thermotropic liquid crystal polymer (TLCP) is as follows: D1, p-hydroxybenzoic acid (CAS No. 99-96-7), 6-hydroxy-2-naphthoic acid (CAS No. 16712-64-4), and 2-aminobenzothiazol-6-carboxylic acid (CAS No. 93-85-6) are added to a four-necked reactor in a molar ratio of 70:30:2.75. Acetic anhydride (1.2 times the total mass of monomers) is then added as an acylating agent, and sodium acetate (0.5% of the total mass of monomers) is added as a catalyst. Nitrogen gas is then introduced to purge the reactor. Air and nitrogen flow rate were 0.3 L / min. Stirring was started and the temperature was raised to 280℃ at a rate of 5℃ / min. The temperature was maintained at 280℃ for 4 hours for polycondensation reaction. Acetic acid and unreacted acetic anhydride generated during the reaction were continuously discharged. D2. After the reaction was completed, heating was stopped. When the system temperature dropped to 150℃, the product was taken out and crushed into particles with a particle size of 1-3 mm. The particles were then placed in a vacuum drying oven and vacuum treated at 200℃ for 2 hours to remove residual small molecules, thus obtaining a fully aromatic polyester liquid crystal polymer (TLCP).

[0136] Meanwhile, this embodiment provides a method for preparing the above-mentioned high-toughness plastic packaging film material, including the following steps:

[0137] S1. According to the above proportions, add metallocene polyethylene resin, ethylene-vinyl acetate copolymer, polyolefin elastomer, di(3,4-dimethyldibenzyl)sorbitol, antioxidant, lubricant and antistatic agent into a high-speed mixer. Set the stirring speed of the high-speed mixer to 1500 rpm, the heating temperature to 90℃, and the mixing time to 7.5 min. After mixing, discharge the material to obtain the premix.

[0138] S2. The above premix, supramolecular crosslinking agent, core-shell modifier, stearic acid-modified nano-calcium carbonate, and thermotropic liquid crystal polymer are added to the feed hopper of a twin-screw extruder. The processing temperature of the twin-screw extruder is set to 180°C and the screw speed is 300 rpm. After melt blending and screw shearing dispersion in the twin-screw extruder, the material is extruded through the extruder die head and cut into masterbatch with a particle size of 2-3 mm by a pelletizer. The temperature distribution of each section of the twin-screw extruder is as follows: feeding section 160°C, compression section 170°C, melting section 180°C, homogenization section 180°C, and die head 175°C.

[0139] S3. Add the above masterbatch into the hopper of the blown film machine, turn on the blown film machine, set the die temperature of the blown film machine to 175℃, and simultaneously apply an external electromagnetic field at the die outlet of the blown film machine, setting the magnetic field strength to 1.0T and the electric field strength to 750V / cm; after the masterbatch melts and plasticizes in the blown film machine, it is extruded through the die to form a tubular film preform, and then the tubular film preform is bi-directionally stretched, setting the longitudinal stretch ratio to 3.0 and the transverse stretch ratio to 3.0. After stretching, it is cooled by a cooling air ring (cooling air temperature 25℃), pulled by a traction machine (traction speed 8m / min), and wound by a winding machine to obtain the high-toughness plastic packaging film material.

[0140] Example 2

[0141] This embodiment provides a high-toughness plastic packaging film material, which, by weight, is composed of the following chemical raw materials: metallocene polyethylene resin (mPE): 80 parts; supramolecular crosslinking agent: 5 parts; core-shell modifier: 6 parts; ethylene-vinyl acetate copolymer (EVA, VA content 15%): 3 parts; stearic acid modified nano-calcium carbonate: 2 parts; polyolefin elastomer: 2 parts; di(3,4-dimethyldibenzyl)sorbitol (DMDBS): 0.2 parts; thermotropic liquid crystal polymer (TLCP): 2 parts; antioxidant (a composite system of hindered phenolic primary antioxidant 1010 and phosphite auxiliary antioxidant 168, with a mass ratio of 1:1.5): 0.4 parts; lubricant (a composite system of erucamide and polyethylene wax, with a mass ratio of 1:1): 0.8 parts; antistatic agent (glyceryl monostearate): 0.5 parts.

[0142] The preparation method of the supramolecular crosslinking agent is as follows: A1. Under nitrogen (inert gas) protection, hydroxyl-terminated polycaprolactone polyol and 2,4-toluene diisocyanate are added to a four-necked reactor, stirring is started, the reaction temperature is controlled at 60°C, and the reaction is maintained at this temperature for 2 hours to obtain isocyanate-terminated polycaprolactone prepolymer; wherein, the molar ratio of the hydroxyl groups of the hydroxyl-terminated polycaprolactone polyol to the isocyanate groups of the 2,4-toluene diisocyanate is 1:2.0; A2. 2-Amino-4-hydroxy-6-methylpyrimidine is added to the above reactor, the reaction temperature is adjusted to 40°C, and the reaction is continued with stirring for 3 hours. The crude product was obtained; wherein the molar ratio of the isocyanate group of the isocyanate-terminated polycaprolactone prepolymer to the amino group of 2-amino-4-hydroxy-6-methylpyrimidine was 1:1.0; A3, the crude product after reaction was slowly added dropwise to n-hexane while stirring until a white solid precipitate was formed. After standing for 1 hour, the precipitate was filtered. The obtained solid was washed three times with n-hexane, each time with an amount of 4 times the mass of the solid. The washed solid was then placed in a vacuum drying oven and vacuum dried at 55°C for 7 hours to obtain polycaprolactone polyol (supramolecular crosslinking agent) with ureidopyrimidinone bifunctional groups at the end.

[0143] The preparation method of the core-shell modifier includes: B1, adding butyl acrylate monomer, crosslinking agent divinylbenzene, and initiator potassium persulfate sequentially to a four-necked reactor containing deionized water and sodium dodecyl sulfate; purging the reactor with nitrogen gas at a flow rate of 0.4 L / min for 30 min; then starting stirring and heating to 75°C; maintaining the temperature for 2.0 h to obtain an acrylate elastomer core emulsion; wherein the mass of divinylbenzene added is 1.0% of the mass of butyl acrylate monomer, and the mass of potassium persulfate... The mass of potassium acrylate added is 1.0% of the mass of butyl acrylate monomer; B2, keeping the nitrogen atmosphere and stirring rate constant in the reactor, raise the reaction temperature to 80℃, and slowly add methyl methacrylate monomer dropwise to the above elastomer core emulsion at a dropping rate of 0.4 mL / min. After the addition is complete, continue the emulsion polymerization reaction at the temperature for 1.5 h, so that polymethyl methacrylate polymerizes on the surface of the acrylate elastomer core to form a shell, obtaining core-shell type modifier particles with polymethyl methacrylate as the shell and acrylate elastomer as the core; In step B, the mass ratio of the core layer (acrylate elastomer) to the shell layer (polymethyl methacrylate) is 80:20. Step B3 involves collecting the core-shell modifier particles by centrifugation (7000 rpm, 12 min), washing them three times with deionized water, dispersing them in xylene solvent, and sonicating them for 15 min (280 W) to form a suspension with a mass concentration of 12%. Simultaneously, the polyethylene-grafted maleic anhydride polymer is added to hot xylene solvent at 75°C and stirred until completely dissolved. A coating solution with a mass concentration of 8% was formed; B4. Under the condition of stirring speed of 250 rpm, the above coating solution was slowly added dropwise to the suspension for 25 min. After the addition was completed, the system temperature was controlled at 70℃ and the reaction was kept at this temperature for 1.0 h. After the reaction was completed, the mixture was centrifuged (7000 rpm, centrifugation time 12 min), the solid product was collected, washed twice with xylene, and vacuum dried at 55℃ for 5 h to obtain the core-shell modifier (polyethylene grafted with maleic anhydride with a mass ratio of 15%).

[0144] The preparation method of the stearic acid modified nano-calcium carbonate includes: C1, adding nano-calcium carbonate (average particle size 40 nm) to a high-speed stirred tank containing deionized water, turning on high-speed stirring at a stirring rate of 1200 rpm for 25 min to uniformly disperse the nano-calcium carbonate and form a suspension with a mass concentration of 8%; C2, dissolving stearic acid in ethanol to prepare a stearic acid ethanol solution with a mass concentration of 4%; under stirring conditions, slowly adding the stearic acid ethanol solution dropwise to the above suspension at a dropping rate of 0.8 mL / min, and after the addition is complete, raising the system temperature to 70°C and maintaining the temperature for 1.0 h; after the reaction is completed, centrifuging (7000 rpm, centrifugation time 12 min), collecting the solid product, washing it three times with deionized water, and drying it in a forced-air conditioner at 55°C for 3 h to obtain the stearic acid modified nano-calcium carbonate; wherein, the mass of stearic acid added is 2.0% of the mass of nano-calcium carbonate.

[0145] The preparation method of the thermotropic liquid crystal polymer (TLCP) is as follows: D1, p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and 2-aminobenzothiazole-6-carboxylic acid are added to a four-necked reactor in a molar ratio of 60:40:0.5. Acetic anhydride (1.1 times the total mass of monomers) is then added as an acylating agent, and sodium acetate (0.4% of the total mass of monomers) is added as a catalyst. Nitrogen gas is introduced to purge air from the reactor at a flow rate of 0.2 L / min. Stirring is then started. The temperature was increased to 260℃ at a rate of 4℃ / min, and held at this temperature for 3 hours for polycondensation. During the reaction, acetic acid and unreacted acetic anhydride were continuously discharged. D2. After the reaction was completed, heating was stopped, and the product was removed when the system temperature dropped to 140℃. The product was then crushed into particles with a particle size of 1-2 mm. The particles were then placed in a vacuum drying oven and vacuum-treated at 180℃ for 1.5 hours to remove residual small molecules, thus obtaining a fully aromatic polyester liquid crystal polymer (TLCP).

[0146] Meanwhile, this embodiment provides a method for preparing the above-mentioned high-toughness plastic packaging film material, including the following steps: S1, according to the above proportions, metallocene polyethylene resin, ethylene-vinyl acetate copolymer, polyolefin elastomer, di(3,4-dimethyldibenzyl)sorbitol, antioxidant, lubricant and antistatic agent are added to a high-speed mixer, the stirring speed of the high-speed mixer is set to 1200 rpm, the heating temperature is set to 80°C, the mixing time is set to 5 min, and the material is discharged after mixing to obtain a premix;

[0147] S2. The above premix, supramolecular crosslinking agent, core-shell modifier, stearic acid-modified nano-calcium carbonate, and thermotropic liquid crystal polymer are added to the feed hopper of a twin-screw extruder. The processing temperature of the twin-screw extruder is set to 160℃ and the screw speed is 200rpm. After melt blending and screw shearing dispersion in the twin-screw extruder, the material is extruded through the extruder die head and cut into masterbatch with a particle size of 2-3mm by a pelletizer. The temperature distribution of each section of the twin-screw extruder is as follows: feeding section 150℃, compression section 155℃, melting section 160℃, homogenization section 160℃, and die head 155℃.

[0148] S3. Add the above masterbatch into the hopper of the blown film machine, turn on the blown film machine, set the die temperature of the blown film machine to 165℃, and simultaneously apply an external electromagnetic field at the die outlet of the blown film machine, setting the magnetic field strength to 0.5T and the electric field strength to 500V / cm; after the masterbatch melts and plasticizes in the blown film machine, it is extruded through the die to form a tubular film preform, and then the tubular film preform is bi-directionally stretched, setting the longitudinal stretch ratio to 2.5 and the transverse stretch ratio to 2.5. After stretching, it is cooled by a cooling air ring (cooling air temperature 22℃), pulled by a traction machine (traction speed 6m / min), and wound by a winding machine to obtain the high-toughness plastic packaging film material.

[0149] Example 3

[0150] This embodiment provides a high-toughness plastic packaging film material, which, by weight, is composed of the following chemical raw materials: metallocene polyethylene resin (mPE): 90 parts; supramolecular crosslinking agent: 8 parts; core-shell modifier: 10 parts; ethylene-vinyl acetate copolymer (EVA, VA content 22%): 5 parts; stearic acid modified nano-calcium carbonate: 4 parts; polyolefin elastomer: 3 parts; di(3,4-dimethyldibenzyl)sorbitol (DMDBS): 0.5 parts; thermotropic liquid crystal polymer (TLCP): 5 parts; antioxidant (a composite system of hindered phenolic primary antioxidant 1010 and phosphite auxiliary antioxidant 168, with a mass ratio of 1:2.5): 0.7 parts; lubricant (a composite system of erucamide and polyethylene wax, with a mass ratio of 1:1.5): 1.2 parts; antistatic agent (glyceryl monostearate): 1.0 part.

[0151] The preparation method of the supramolecular crosslinking agent is as follows: A1. Under nitrogen (inert gas) protection, hydroxyl-terminated polycaprolactone polyol and 2,4-toluene diisocyanate are added to a four-necked reactor, stirring is started, the reaction temperature is controlled at 80℃, and the reaction is maintained for 4 hours to obtain isocyanate-terminated polycaprolactone prepolymer; wherein, the molar ratio of the hydroxyl groups of the hydroxyl-terminated polycaprolactone polyol to the isocyanate groups of 2,4-toluene diisocyanate is 1:2.2; A2. 2-Amino-4-hydroxy-6-methylpyrimidine is added to the above reactor, the reaction temperature is adjusted to 60℃, and the reaction is continued with stirring for 5 hours. A crude product was obtained; wherein the molar ratio of the isocyanate group of the isocyanate-terminated polycaprolactone prepolymer to the amino group of 2-amino-4-hydroxy-6-methylpyrimidine was 1:1.05; A3. The crude product after the reaction was slowly added dropwise to n-hexane while stirring until a white solid precipitate was formed. After standing for 1.5 h, the precipitate was filtered. The obtained solid was washed four times with n-hexane, each time with an amount of 6 times the mass of the solid. The washed solid was then placed in a vacuum drying oven and dried under vacuum at 70 °C for 9 h to obtain polycaprolactone polyol (supramolecular crosslinking agent) with ureidopyrimidinone bifunctional groups at the end.

[0152] The preparation method of the core-shell modifier includes: B1, adding butyl acrylate monomer, crosslinking agent divinylbenzene, and initiator potassium persulfate sequentially to a four-necked reactor containing deionized water and sodium dodecyl sulfate; purging the reactor with nitrogen gas at a flow rate of 0.7 L / min for 40 min; then stirring and heating to 85°C; maintaining the temperature for 3.0 h to obtain an acrylate elastomer core emulsion; wherein the mass of divinylbenzene added is 1.5% of the mass of butyl acrylate monomer, and the mass of potassium persulfate is... The mass of potassium acrylate added is 1.5% of the mass of butyl acrylate monomer; B2, keeping the nitrogen atmosphere and stirring rate constant in the reactor, raise the reaction temperature to 85℃, and slowly add methyl methacrylate monomer dropwise to the above elastomer core emulsion at a dropping rate of 0.7 mL / min. After the addition is complete, continue the emulsion polymerization reaction at this temperature for 2.5 h, allowing polymethyl methacrylate to polymerize on the surface of the acrylate elastomer core to form a shell, thus obtaining core-shell type modifier particles with polymethyl methacrylate as the shell and acrylate elastomer as the core; The mass ratio of the core layer (acrylate elastomer) to the shell layer (polymethyl methacrylate) is 70:30; B3. The above core-shell modifier particles are collected by centrifugation (9000 rpm, 20 min), washed four times with deionized water, dispersed in xylene solvent, and ultrasonically treated for 30 min (ultrasonic power 350 W) to form a suspension with a mass concentration of 18%; at the same time, polyethylene grafted maleic anhydride polymer is added to hot xylene solvent at 85°C and stirred until completely dissolved to form... A coating solution with a mass concentration of 12% was prepared. B4. Under a stirring speed of 400 rpm, the above coating solution was slowly added dropwise to the suspension over a period of 40 min. After the addition was complete, the system temperature was controlled at 80℃, and the reaction was maintained at this temperature for 2.0 h. After the reaction was completed, the mixture was centrifuged (9000 rpm, centrifugation time 20 min), and the solid product was collected. The solid product was washed three times with xylene and then vacuum dried at 70℃ for 7 h to obtain the core-shell modifier (polyethylene grafted with maleic anhydride, mass percentage 30%).

[0153] The preparation method of the stearic acid modified nano-calcium carbonate includes: C1, adding nano-calcium carbonate (average particle size 60 nm) to a high-speed stirred tank containing deionized water, turning on high-speed stirring at a stirring rate of 1800 rpm for 40 min to uniformly disperse the nano-calcium carbonate and form a suspension with a mass concentration of 12%; C2, dissolving stearic acid in ethanol to prepare a stearic acid ethanol solution with a mass concentration of 7%; under stirring conditions, slowly adding the stearic acid ethanol solution dropwise to the above suspension at a dropping rate of 1.5 mL / min, and after the addition is complete, raising the system temperature to 85℃ and maintaining the temperature for 2.0 h; after the reaction is completed, centrifuging (9000 rpm, centrifugation time 20 min), collecting the solid product, washing it 4 times with deionized water, and drying it at 70℃ for 5 h to obtain the stearic acid modified nano-calcium carbonate; wherein, the mass of stearic acid added is 4.0% of the mass of nano-calcium carbonate.

[0154] The preparation method of the thermotropic liquid crystal polymer (TLCP) is as follows: D1, p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and 2-aminobenzothiazole-6-carboxylic acid are added to a four-necked reactor in a molar ratio of 80:20:5. Acetic anhydride (1.4 times the total mass of monomers) is then added as an acylating agent, and sodium acetate (0.7% of the total mass of monomers) is added as a catalyst. Nitrogen gas is introduced to purge air from the reactor at a flow rate of 0.5 L / min. Stirring is then started. The temperature was increased to 300℃ at a rate of 7℃ / min, and held at this temperature for 5 hours for polycondensation. During the reaction, the acetic acid and unreacted acetic anhydride generated in the reaction were continuously discharged. D2. After the reaction was completed, the heating was stopped, and when the system temperature dropped to 170℃, the product was taken out and crushed into particles with a particle size of 2-3 mm. The particles were then placed in a vacuum drying oven and vacuum treated at 220℃ for 3 hours to remove residual small molecules, thus obtaining a fully aromatic polyester liquid crystal polymer (TLCP).

[0155] Meanwhile, this embodiment provides a method for preparing the above-mentioned high-toughness plastic packaging film material, including the following steps:

[0156] S1. According to the above proportions, add metallocene polyethylene resin, ethylene-vinyl acetate copolymer, polyolefin elastomer, di(3,4-dimethylbenzyl)sorbitol, antioxidant, lubricant and antistatic agent into a high-speed mixer. Set the stirring speed of the high-speed mixer to 1800 rpm, the heating temperature to 100℃, and the mixing time to 10 min. After mixing, discharge the material to obtain the premix.

[0157] S2. The above premix, supramolecular crosslinking agent, core-shell modifier, stearic acid-modified nano-calcium carbonate, and thermotropic liquid crystal polymer are added to the feed hopper of a twin-screw extruder. The processing temperature of the twin-screw extruder is set to 200℃ and the screw speed is 400rpm. After melt blending and screw shearing dispersion in the twin-screw extruder, the material is extruded through the extruder die head and cut into masterbatch with a particle size of 2-3mm by a pelletizer. The temperature distribution of each section of the twin-screw extruder is as follows: feeding section 170℃, compression section 180℃, melting section 200℃, homogenization section 200℃, and die head 190℃.

[0158] S3. Add the above masterbatch into the hopper of the blown film machine, turn on the blown film machine, set the die temperature of the blown film machine to 185℃, and simultaneously apply an external electromagnetic field at the die outlet of the blown film machine, setting the magnetic field strength to 1.5T and the electric field strength to 1000V / cm; after the masterbatch melts and plasticizes in the blown film machine, it is extruded through the die to form a tubular film preform, and then the tubular film preform is bi-directionally stretched, setting the longitudinal stretch ratio to 3.5 and the transverse stretch ratio to 3.5. After stretching, it is cooled by a cooling air ring (cooling air temperature 30℃), pulled by a traction machine (traction speed 10m / min), and wound by a winding machine to obtain the high-toughness plastic packaging film material.

[0159] Comparative Example 1

[0160] This comparative example is modified from the one disclosed in Example 1 as follows:

[0161] The chemical composition of high-toughness plastic packaging film does not contain supramolecular crosslinking agents.

[0162] Comparative Example 2

[0163] This comparative example is modified from the one disclosed in Example 1 as follows:

[0164] The chemical composition of high-toughness plastic packaging film does not contain core-shell modifiers.

[0165] Comparative Example 3

[0166] This comparative example is modified from the one disclosed in Example 1 as follows:

[0167] The surface of the core-shell modifier in the chemical composition of the high-toughness plastic packaging film is not pre-coated with polyethylene-grafted maleic anhydride polymer.

[0168] Comparative Example 4

[0169] This comparative example is modified from the one disclosed in Example 1 as follows:

[0170] The chemical composition of high-toughness plastic packaging film does not contain stearic acid-modified nano-calcium carbonate.

[0171] Comparative Example 5

[0172] This comparative example is modified from the one disclosed in Example 1 as follows:

[0173] The chemical composition of high-toughness plastic packaging film does not contain di(3,4-dimethyldibenzyl)sorbitol.

[0174] Comparative Example 6

[0175] This comparative example is modified from the one disclosed in Example 1 as follows:

[0176] The chemical composition of high-toughness plastic packaging film does not contain thermotropic liquid crystal polymers.

[0177] The high-toughness plastic packaging films obtained in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests, and the results are shown in Table 1. The performance test methods are as follows:

[0178] Tensile property standard: ASTM D882;

[0179] Elastic modulus: ASTM D882;

[0180] Notched impact strength standard for cantilever beams: ASTM D256;

[0181] Puncture strength standard: ASTM F1306;

[0182] Haze standard: ASTM D1003.

[0183] Table 1. Performance of high-toughness plastic packaging film materials in Examples 1-3 and Comparative Examples 1-6

[0184]

[0185] As shown in Table 1, the high-toughness plastic packaging films of Examples 1-3 exhibit excellent comprehensive performance, demonstrating the synergistic advantages of high strength, high toughness, and low haze: tensile strength is 50.2-65.4 MPa, elastic modulus is 1154.1-1401.2 MPa, elongation at break is 481.5-553.1%, and impact strength is 70.1-91.4 kJ / m. 2 The puncture force is 155.3–194.6 N, and the haze is only 4.4–6.1%.

[0186] Comparative Example 1, lacking a supramolecular crosslinking agent, lost the dynamic reversible energy dissipation network constructed by UPy quadruple hydrogen bonds. Under external force, it could not absorb energy through hydrogen bond dissociation and reconstruction, resulting in a significant decrease in toughness indicators such as impact strength and elongation at break. Comparative Example 2, lacking the core "energy absorber" of a core-shell modifier, could not disperse impact stress through elastic core deformation and the induction of crazing, causing a sharp drop in toughness and exhibiting brittle fracture. Comparative Example 3, with core-shell particles not coated with PE-g-MAH, had poor compatibility with the PE matrix and weak interfacial adhesion, making the particles prone to detachment from the matrix under stress. Adhesion leads to crack formation, significantly weakening toughness; Comparative Example 4, lacking nano-calcium carbonate, loses its reinforcing effect of restricting molecular chain movement through large specific surface area and interfacial interaction, resulting in a decrease in rigidity (modulus) and strength; Comparative Example 5, lacking nucleating agent DMDBS, cannot form fine and uniform microcrystals in mPE, which reduces rigidity due to coarse grains and exacerbates haze and deteriorates transparency due to light scattering by crystals; Comparative Example 6, lacking TLCP, loses its role in forming a "microfiber-reinforced skeleton" during processing, losing the strength support similar to "steel bars," resulting in a significant decline in tensile strength and modulus.

[0187] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to. In the description of this application, the terms "comprising," "including," etc., mean "including but not limited to."

[0188] 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 high-toughness plastic packaging film material, characterized in that, The high-toughness plastic packaging film material, by weight, is composed of the following chemical raw materials. Composition: Metallocene polyethylene resin: 80-90 parts, supramolecular crosslinking agent: 5-8 parts, core-shell modifier: 6-10 parts, ethylene-vinyl acetate copolymer: 3-5 parts, stearic acid modified nano-calcium carbonate: 2-4 parts, polyolefin elastomer: 2-3 parts, di(3,4-dimethyldibenzyl)sorbitol: 0.2-0.5 parts, thermotropic liquid crystal polymer: 2-5 parts, antioxidant: 0.4-0.7 parts, lubricant: 0.8-1.2 parts, antistatic agent: 0.5-1.0 parts; The supramolecular crosslinking agent is a polycaprolactone polyol with end groups modified with ureidopyrimidinone bifunctional groups; The core-shell modifier is a core-shell structured polymer with polymethyl methacrylate as the shell and an acrylic elastomer as the core. The surface of the core-shell modifier is pre-coated with polyethylene-grafted maleic anhydride polymer, and the coating mass of the polyethylene-grafted maleic anhydride polymer is 15% to 30% of the total mass of the core-shell modifier. The thermotropic liquid crystal polymer is a fully aromatic polyester liquid crystal polymer, which is obtained by copolymerization of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and 2-aminobenzothiazole-6-carboxylic acid via a polycondensation reaction. The molar ratio of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and 2-aminobenzothiazole-6-carboxylic acid is (60-80):(20-40):(0.5-5).

2. The high-toughness plastic packaging film material according to claim 1, characterized in that, The preparation method of the supramolecular crosslinking agent includes the following steps: A1. Under inert gas protection, hydroxyl-terminated polycaprolactone polyol and 2,4-toluene diisocyanate are reacted at 60-80°C for 2-4 hours to obtain isocyanate-terminated polycaprolactone prepolymer. A2. The isocyanate-terminated polycaprolactone prepolymer was reacted with 2-amino-4-hydroxy-6-methylpyrimidine at 40-60°C for 3-5 h to obtain the crude product; A3. The crude product is precipitated in a non-solvent, filtered, and dried to obtain the polycaprolactone polyol with end groups modified with ureidopyrimidinone bifunctional groups.

3. The high-toughness plastic packaging film material according to claim 2, characterized in that, The molar ratio of the hydroxyl groups in the terminally hydroxyl polycaprolactone polyol to the isocyanate groups in the 2,4-toluene diisocyanate is 1:(2.0-2.2). The molar ratio of the isocyanate group of the terminal isocyanate-based polycaprolactone prepolymer to the amino group of the 2-amino-4-hydroxy-6-methylpyrimidine is 1:(1.0 to 1.05).

4. The high-toughness plastic packaging film material according to claim 1, characterized in that, The preparation method of the core-shell modifier includes the following steps: B1. Add a crosslinking agent and an initiator to the butyl acrylate monomer and perform emulsion polymerization at 75-85°C for 2.0-3.0 h to obtain an acrylate elastomer core emulsion; B2. Add methyl methacrylate monomer to the acrylate elastomer core emulsion and continue the emulsion polymerization reaction at 80-85°C for 1.5-2.5 hours to polymerize the polymethyl methacrylate shell onto the surface of the acrylate elastomer core, thereby obtaining core-shell type modifier particles with polymethyl methacrylate as the shell and acrylate elastomer as the core. B3. Disperse the core-shell modifier particles in xylene solvent to form a suspension; and dissolve the polyethylene-grafted maleic anhydride polymer in hot xylene solvent to form a coating solution; B4. Under stirring conditions, the coating solution is added dropwise to the suspension, and the reaction is carried out at 70-80°C for 1.0-2.0 h to obtain the core-shell modifier.

5. The high-toughness plastic packaging film material according to claim 4, characterized in that, The crosslinking agent is divinylbenzene, and the added mass of divinylbenzene is 1.0 to 1.5% of the mass of the butyl acrylate monomer. The initiator is potassium persulfate, and the mass of potassium persulfate added is 1.0 to 1.5% of the mass of the butyl acrylate monomer. The mass ratio of the core layer to the shell layer of the core-shell modifier particles is (70-80):(30-20).

6. The high-toughness plastic packaging film material according to claim 1, characterized in that, The preparation method of the stearic acid modified nano-calcium carbonate includes the following steps: C1. Disperse nano-calcium carbonate in deionized water under high-speed stirring to form a suspension; C2. Slowly add an ethanol solution of stearic acid to the suspension and react at 70-85°C for 1-2 hours to obtain the stearic acid-modified nano-calcium carbonate. The amount of stearic acid added is 2.0 to 4.0% of the mass of the nano-calcium carbonate.

7. The high-toughness plastic packaging film material according to claim 1, characterized in that, The antioxidant is composed of a hindered phenolic primary antioxidant and a phosphite secondary antioxidant, wherein the mass ratio of the hindered phenolic primary antioxidant to the phosphite secondary antioxidant is 1:(1.5-2.5). The lubricant is composed of erucamide and polyethylene wax, wherein the mass ratio of erucamide to polyethylene wax is 1:(1-1.5). The antistatic agent is glyceryl monostearate.

8. A method for preparing a high-toughness plastic packaging film material according to any one of claims 1 to 7, characterized in that, The method includes the following steps: S1. The metallocene polyethylene resin, the ethylene-vinyl acetate copolymer, the polyolefin elastomer, the di(3,4-dimethylbenzyl)sorbitol, the antioxidant, the lubricant and the antistatic agent are added to a high-speed mixer according to the formula ratio and mixed at 80-100°C for 5-10 minutes to obtain a premix. S2. The premix, the supramolecular crosslinking agent, the core-shell modifier, the stearic acid-modified nano-calcium carbonate, and the thermotropic liquid crystal polymer are added to a twin-screw extruder, and then melt-blended and extruded to granulate to obtain masterbatch. S3. Under the influence of an external electromagnetic field, the masterbatch is blow-molded to obtain the high-toughness plastic packaging film.

9. The method for preparing the high-toughness plastic packaging film material according to claim 8, characterized in that, The processing temperature of the twin-screw extruder is 160–200℃, and the screw speed is 200–400 rpm; The applied electromagnetic field has a magnetic field strength of 0.5–1.5 T and an electric field strength of 500–1000 V / cm. The blow molding process employs biaxial stretching, with a longitudinal stretching ratio of 2.5–3.5 and a transverse stretching ratio of 2.5–3.

5. The die head temperature of the blow molding machine is 165–185°C.

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