PE shrink film and preparation method thereof

Abstract

The invention relates to the technical field of shrink films, and discloses a PE shrink film and a preparation method thereof. The prepared PE shrink film is composed of an inner layer, a middle layer and an outer layer, the thickness of the inner layer is the same as that of the outer layer, and the thickness of the middle layer is larger than that of the inner layer and that of the outer layer; the composite reinforcing agent is introduced into the raw materials of each layer of the shrink film, so that the matrix has excellent antibacterial property and mildew-proof property on the basis of keeping good mechanical property and toughness.

Description

Technical Field

[0001] This invention relates to the field of shrink film technology, specifically to a PE shrink film and its preparation method. Background Technology

[0002] Polyethylene (PE) shrink film, widely used as an outer packaging material for food, pharmaceuticals, daily chemical products, and industrial goods, is favored for its excellent cost-effectiveness, good transparency, and processability. Especially in logistics and bulk packaging, PE shrink film shrinks under heat to tightly wrap goods, forming stable and aesthetically pleasing packaging units, effectively preventing goods from scattering and enhancing brand image. However, with increasingly sophisticated market demands and more complex application environments, traditional PE shrink film has revealed several key technical bottlenecks after long-term use, which urgently need to be addressed: insufficient mechanical properties and lack of antibacterial and anti-mildew functions.

[0003] To address the aforementioned issues, the industry typically employs blending modification methods. For example: (1) This is often achieved by adding elastomers (such as POE and EVA), but this usually comes at the cost of sacrificing the tensile strength, rigidity, and transparency of the material, and may increase the viscosity of the film, affecting subsequent processing and user experience; (2) Directly adding small-molecule organic antibacterial agents presents problems such as easy migration, poor durability, and potential odor generation; while ordinary inorganic antibacterial agents have poor interfacial compatibility with the polymer matrix, making them difficult to disperse evenly and prone to forming stress concentration points, which in turn leads to a decline in mechanical properties. Therefore, the market urgently needs a new type of PE shrink film that can synergistically achieve high strength, high toughness, broad-spectrum efficiency, and long-lasting antibacterial and antifungal functions. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a PE shrink film and its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A PE shrink film is composed of an inner layer, a middle layer and an outer layer, wherein the inner layer and the outer layer have the same thickness and the thickness ratio of the inner layer, the outer layer and the middle layer is 1:1:1.3-1.6;

[0007] The inner and outer layers comprise the following raw materials in parts by weight: 35-45 parts of linear low-density polyethylene, 20-30 parts of ethylene-polypropylene copolymer, 10-20 parts of linear high-density polyethylene, 4-6 parts of composite reinforcing agent, and 3-6 parts of polyethylene wax.

[0008] The intermediate layer comprises the following raw materials in parts by weight: 40-60 parts of linear low-density polyethylene, 25-35 parts of metallocene linear low-density polyethylene, 15-25 parts of linear high-density polyethylene, 4-9 parts of composite reinforcing agent, and 6-10 parts of polyethylene wax.

[0009] The composite reinforcing agent is prepared by the following steps:

[0010] Step A1: Heat p-carboxybenzaldehyde in propionic acid and stir until reflux at 140°C. Then add pyrrole propionic acid solution dropwise over 30 min and continue reflux for 3 h. Cool to room temperature, add anhydrous ethanol, seal and refrigerate for 24 h. Filter, wash and recrystallize to obtain porphyrin ligand.

[0011] Further, in step A1, the ratio of carboxybenzaldehyde, propionic acid, pyrrole propionic acid solution and anhydrous ethanol is 10-20g:150mL:15-20mL:150mL.

[0012] Furthermore, the pyrrole propionic acid solution described in step A1 is prepared by mixing pyrrole and propionic acid in a volume ratio of 1-2:2;

[0013] Step A2: Add the porphyrin ligand to DMF and heat to 165°C under reflux. Then add zinc acetate and maintain the temperature while stirring for 2 hours. Cool to room temperature, add distilled water and refrigerate at 4°C overnight. Filter and dry to obtain zinc metal porphyrin ligand.

[0014] Furthermore, in step A2, the ratio of porphyrin ligand, DMF, zinc acetate, and distilled water is 0.2-0.6 g: 50 mL: 0.5-1.5 g: 50 mL;

[0015] Step A3: Disperse carboxylated nano-silica in DMF, then add zinc metal porphyrin ligand, zirconium tetrachloride and 4-hydroxybenzoic acid in sequence, ultrasonically disperse for 30 min, then transfer to a high-pressure reactor and react at 120℃ for 48 h. After filtration, washing, acetone activation and drying, PCN@SiO2 material (porphyrin metal-organic framework supported SiO2 material) is obtained.

[0016] Furthermore, in step A3, the ratio of carboxylated nano-silica, DMF, zinc metal porphyrin ligand, zirconium tetrachloride, 4-hydroxybenzoic acid, and acetone is 0.05-0.2g:20mL:0.05-0.1g:0.075-0.1g:2.7g;

[0017] Step A4: Under nitrogen atmosphere, mix and stir the epoxidized quaternary ammonium salt and tetrabutylammonium bromide in DMF until homogeneous, then add PCN@SiO2 material and stir until homogeneous. Stir at 90°C for 4-6 hours. After the reaction is complete, filter, wash and dry to obtain the composite reinforcing agent.

[0018] Further, the epoxidized quaternary ammonium salt described in step A4 is prepared by the following steps: epichlorohydrin is stirred evenly in methanol and heated to 65°C in an oil bath, then dodecyl dimethyl tertiary amine is slowly added and stirred for 6-10 hours, cooled to room temperature, and then distilled under reduced pressure and washed to obtain the epoxidized quaternary ammonium salt.

[0019] Furthermore, the ratio of epichlorohydrin, methanol, and dodecyl dimethyl tertiary amine in the epoxidized quaternary ammonium salt is 30-50 mL: 150 mL: 1.5 g;

[0020] Furthermore, in step A4, the ratio of the amount of epoxidized quaternary ammonium salt, tetrabutylammonium bromide, DMF, and PCN@SiO2 material is 0.2-0.3 mol: 0.01-0.015 mol: 100 mL: 3-6 g.

[0021] A method for preparing a PE shrink film includes the following steps:

[0022] Step S1: Weigh the raw materials according to the weight parts, mix linear low-density polyethylene, ethylene-polypropylene copolymer, linear high-density polyethylene, composite reinforcing agent and polyethylene wax evenly to obtain inner layer premix and outer layer premix respectively; mix linear low-density polyethylene, metallocene linear low-density polyethylene, linear high-density polyethylene, composite reinforcing agent and polyethylene wax evenly to obtain middle layer premix.

[0023] Step S2: The inner layer premix, the middle layer premix and the outer layer premix are respectively fed to the extruder of the three-layer co-extrusion blown film unit. After extrusion, blowing, cooling, traction and winding, PE shrink film is obtained.

[0024] The beneficial effects of this invention are:

[0025] The PE shrink film prepared by this invention consists of an inner layer, a middle layer and an outer layer. The inner and outer layers have the same thickness, while the middle layer has a greater thickness than the inner and outer layers. A composite reinforcing agent is introduced into the raw materials of each layer of the shrink film. Its presence enables the matrix to maintain good mechanical properties and toughness, as well as excellent antibacterial and antifungal properties.

[0026] The composite reinforcing agent used in this invention significantly improves the antibacterial rate and antifungal properties of the matrix. This is due to the introduction of porphyrin COF, cationic quaternary ammonium salt structure, and metal ions (Zn) into the composite reinforcing agent. 2+ and Zr 4+These antibacterial mechanisms work synergistically to enhance the antibacterial and antifungal properties of the matrix. Specifically, under visible light (especially natural light) irradiation, porphyrin COF absorbs light energy and enters an excited state. It then transfers this energy to generate a large amount of highly reactive reactive oxygen species, possessing extremely strong oxidizing power. This oxidative damage can attack bacterial cell membranes, proteins, enzymes, and genetic material, leading to the disintegration of bacterial and fungal cell structures, metabolic disorders, and ultimately, death. Quaternary ammonium salt structures carry a positive charge, while bacterial cell membranes typically carry a negative charge. After the quaternary ammonium salt structure adsorbs onto the bacterial surface, the long-chain alkyl groups can insert into and disrupt the lipid bilayer structure of the bacterial cell membrane and cell wall, thereby killing bacteria and fungi. Furthermore, the metal ions complexed in porphyrin COF, upon contact with bacteria, can disrupt the permeability and integrity of the bacterial cell membrane, thus killing bacteria and fungi and enhancing the antibacterial and antifungal effects of the matrix.

[0027] Rigid silica is also introduced into the composite reinforcing agent. The surface modification treatment of silica improves its dispersibility in the matrix. The improved dispersibility allows the stress to be effectively transferred from the relatively soft PE matrix to the rigid silica particles when the matrix is ​​stretched. These uniformly dispersed hard particles hinder the free movement and slippage of PE molecular chain segments, thereby improving the tensile strength of the matrix. The COF and grafts on the silica surface can tightly entangle with the long molecular chains of PE in the matrix, thereby establishing numerous "anchoring points" between the composite reinforcing agent and the PE matrix. This entanglement greatly enhances the interfacial bonding force. When subjected to external force, the stress must first overcome these strong anchoring effects before the molecular chains can slip or break, which greatly improves the tensile strength and toughness of the matrix. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The carboxylated silica used in the following examples was prepared by the following steps: 0.01 mol of silane coupling agent KH550 and 0.01 mol of succinic anhydride were added to 50 mL of DMF and stirred for 3 h. Then, 3 g of silica and 20 mL of DMF were added and stirred evenly. Then, 5 mL of water was added and stirred for another 5 h. After filtration, washing and drying, carboxylated silica was obtained.

[0030] Example 1: Epoxidized quaternary ammonium salts were prepared by the following steps:

[0031] 30 mL of epichlorohydrin was stirred evenly in 150 mL of methanol and heated to 65 °C in an oil bath. Then, 1.5 g of dodecyl dimethyl tertiary amine was slowly added and stirring was continued for 6 h. After cooling to room temperature, the mixture was distilled under reduced pressure and washed to obtain the epoxidized quaternary ammonium salt.

[0032] The composite reinforcing agent is prepared by the following steps:

[0033] Step A1: Heat 10g of p-carboxybenzaldehyde in 150mL of propionic acid and stir until reflux at 140℃. Then, add 15mL of pyrrole propionic acid solution dropwise over 30min and continue reflux for 3h. Cool to room temperature, add 150mL of anhydrous ethanol, seal and refrigerate for 24h. Filter, wash, and recrystallize to obtain the porphyrin ligand. The pyrrole propionic acid solution is prepared by mixing pyrrole and propionic acid in a volume ratio of 1:2.

[0034] Step A2: Add 0.2g of porphyrin ligand to 50mL of DMF and heat to 165℃ under reflux. Then add 0.5g of zinc acetate and maintain the temperature while stirring for 2 hours. Cool to room temperature, add 50mL of distilled water and refrigerate at 4℃ overnight. Filter and dry to obtain zinc metal porphyrin ligand.

[0035] Step A3: Disperse 0.05g of carboxylated nano-silica in 20mL of DMF, then add 0.05g of zinc metal porphyrin ligand, 0.075g of zirconium tetrachloride and 2.7g of 4-hydroxybenzoic acid in sequence, and ultrasonically disperse for 30min. Then transfer to a high-pressure reactor and react at 120℃ for 48h. After filtration, washing, acetone activation and drying, PCN@SiO2 material (porphyrin metal-organic framework supported SiO2 material) is obtained.

[0036] Step A4: Under nitrogen atmosphere, mix 0.2 mol of epoxidized quaternary ammonium salt and 0.01 mol of tetrabutylammonium bromide in 100 mL of LDM and stir until homogeneous. Then add 3 g of PCN@SiO2 material and stir until homogeneous. Stir at 90 °C for 4 h. After the reaction is complete, filter, wash and dry to obtain the composite reinforcing agent.

[0037] Example 2: Epoxidized quaternary ammonium salts were prepared by the following steps:

[0038] 40 mL of epichlorohydrin was stirred evenly in 150 mL of methanol and heated to 65 °C in an oil bath. Then, 1.5 g of dodecyl dimethyl tertiary amine was slowly added and stirring was continued for 8 h. After cooling to room temperature, the mixture was distilled under reduced pressure and washed to obtain the epoxidized quaternary ammonium salt.

[0039] The composite reinforcing agent is prepared by the following steps:

[0040] Step A1: Heat 15g of p-carboxybenzaldehyde in 150mL of propionic acid and stir until reflux at 140℃. Then, add 17mL of pyrrole propionic acid solution dropwise over 30min and continue reflux for 3h. Cool to room temperature, add 150mL of anhydrous ethanol, seal and refrigerate for 24h. Filter, wash, and recrystallize to obtain the porphyrin ligand. The pyrrole propionic acid solution is prepared by mixing pyrrole and propionic acid in a volume ratio of 1.5:2.

[0041] Step A2: Add 0.4g of porphyrin ligand to 50mL of DMF and heat to 165℃ under reflux. Then add 1g of zinc acetate and maintain the temperature while stirring for 2 hours. Cool to room temperature, add 50mL of distilled water and refrigerate at 4℃ overnight. Filter and dry to obtain zinc metal porphyrin ligand.

[0042] Step A3: Disperse 0.1g of carboxylated nano-silica in 20mL of DMF, then add 0.075g of zinc metal porphyrin ligand, 0.09g of zirconium tetrachloride and 2.7g of 4-hydroxybenzoic acid in sequence, and ultrasonically disperse for 30min. Then transfer to a high-pressure reactor and react at 120℃ for 48h. After filtration, washing, acetone activation and drying, PCN@SiO2 material (porphyrin metal-organic framework supported SiO2 material) is obtained.

[0043] Step A4: Under nitrogen atmosphere, mix 0.25 mol of epoxidized quaternary ammonium salt and 0.013 mol of tetrabutylammonium bromide in 100 mL of DMF and stir until homogeneous. Then add 4.5 g of PCN@SiO2 material and stir until homogeneous. Stir at 90 °C for 5 h. After the reaction is complete, filter, wash and dry to obtain the composite reinforcing agent.

[0044] Example 3: Epoxidized quaternary ammonium salts were prepared by the following steps:

[0045] 50 mL of epichlorohydrin was stirred evenly in 150 mL of methanol and heated to 65 °C in an oil bath. Then, 1.5 g of dodecyl dimethyl tertiary amine was slowly added and stirring was continued for 10 h. After cooling to room temperature, the mixture was distilled under reduced pressure and washed to obtain the epoxidized quaternary ammonium salt.

[0046] The composite reinforcing agent is prepared by the following steps:

[0047] Step A1: Heat 20g of p-carboxybenzaldehyde in 150mL of propionic acid and stir until reflux at 140℃. Then, add 20mL of pyrrole propionic acid solution dropwise over 30min and continue reflux for 3h. Cool to room temperature, add 150mL of anhydrous ethanol, seal and refrigerate for 24h. Filter, wash, and recrystallize to obtain the porphyrin ligand. The pyrrole propionic acid solution is prepared by mixing pyrrole and propionic acid in a volume ratio of 2:2.

[0048] Step A2: Add 0.6g of porphyrin ligand to 50mL of DMF and heat to 165℃ under reflux. Then add 1.5g of zinc acetate and maintain the temperature while stirring for 2 hours. Cool to room temperature, add 50mL of distilled water and refrigerate at 4℃ overnight. Filter and dry to obtain zinc metal porphyrin ligand.

[0049] Step A3: Disperse 0.2g of carboxylated nano-silica in 20mL of DMF, then add 0.1g of zinc metal porphyrin ligand, 0.1g of zirconium tetrachloride and 2.7g of 4-hydroxybenzoic acid in sequence, and ultrasonically disperse for 30min. Then transfer to a high-pressure reactor and react at 120℃ for 48h. After filtration, washing, acetone activation and drying, PCN@SiO2 material (porphyrin metal-organic framework supported SiO2 material) is obtained.

[0050] Step A4: Under nitrogen atmosphere, mix 0.3 mol of epoxidized quaternary ammonium salt and 0.015 mol of tetrabutylammonium bromide in 100 mL of LDM and stir until homogeneous. Then add 6 g of PCN@SiO2 material and stir until homogeneous. Stir at 90 °C for 6 h. After the reaction is complete, filter, wash and dry to obtain the composite reinforcing agent.

[0051] Example 4: A method for preparing a PE shrink film includes the following steps:

[0052] The inner and outer layers comprise the following raw materials in parts by weight: 35 parts of linear low-density polyethylene, 20 parts of ethylene-polypropylene copolymer, 10 parts of linear high-density polyethylene, 4 parts of the composite reinforcing agent prepared in Example 1, and 3 parts of polyethylene wax.

[0053] The intermediate layer comprises the following raw materials in parts by weight: 40 parts of linear low-density polyethylene, 25 parts of metallocene linear low-density polyethylene, 15 parts of linear high-density polyethylene, 4 parts of the composite reinforcing agent prepared in Example 1, and 6 parts of polyethylene wax.

[0054] Step S1: Weigh the raw materials according to the weight parts, mix linear low-density polyethylene, ethylene-polypropylene copolymer, linear high-density polyethylene, the composite reinforcing agent prepared in Example 1 and polyethylene wax evenly to obtain inner layer premix and outer layer premix respectively; mix linear low-density polyethylene, metallocene linear low-density polyethylene, linear high-density polyethylene, the composite reinforcing agent prepared in Example 1 and polyethylene wax evenly to obtain middle layer premix.

[0055] Step S2: The inner layer premix, the middle layer premix, and the outer layer premix are respectively fed to the extruder of the three-layer co-extrusion blown film unit. After extrusion, blowing, cooling, traction, and winding, a PE shrink film is obtained. The inner and outer layers have the same thickness, and the thickness ratio of the inner layer, the outer layer, and the middle layer is 1:1:1.3.

[0056] Example 5: A method for preparing a PE shrink film includes the following steps:

[0057] The inner and outer layers comprise the following raw materials in parts by weight: 40 parts of linear low-density polyethylene, 25 parts of ethylene-polypropylene copolymer, 15 parts of linear high-density polyethylene, 5 parts of the composite reinforcing agent prepared in Example 2, and 4.5 parts of polyethylene wax.

[0058] The intermediate layer comprises the following raw materials in parts by weight: 50 parts of linear low-density polyethylene, 30 parts of metallocene linear low-density polyethylene, 20 parts of linear high-density polyethylene, 7 parts of the composite reinforcing agent prepared in Example 2, and 8 parts of polyethylene wax.

[0059] Step S1: Weigh the raw materials according to the weight parts, mix linear low-density polyethylene, ethylene-polypropylene copolymer, linear high-density polyethylene, the composite reinforcing agent prepared in Example 2 and polyethylene wax evenly to obtain inner layer premix and outer layer premix respectively; mix linear low-density polyethylene, metallocene linear low-density polyethylene, linear high-density polyethylene, the composite reinforcing agent prepared in Example 2 and polyethylene wax evenly to obtain middle layer premix.

[0060] Step S2: The inner layer premix, the middle layer premix and the outer layer premix are respectively fed to the extruder of the three-layer co-extrusion blown film unit. After extrusion, blowing, cooling, traction and winding, PE shrink film is obtained. The inner layer and the outer layer have the same thickness, and the thickness ratio of the inner layer, the outer layer and the middle layer is 1:1:1.45.

[0061] Example 6: A method for preparing a PE shrink film includes the following steps:

[0062] The inner and outer layers comprise the following raw materials in parts by weight: 45 parts of linear low-density polyethylene, 30 parts of ethylene-polypropylene copolymer, 20 parts of linear high-density polyethylene, 6 parts of the composite reinforcing agent prepared in Example 3, and 6 parts of polyethylene wax.

[0063] The intermediate layer comprises the following raw materials in parts by weight: 60 parts of linear low-density polyethylene, 35 parts of metallocene linear low-density polyethylene, 25 parts of linear high-density polyethylene, 9 parts of the composite reinforcing agent prepared in Example 3, and 10 parts of polyethylene wax.

[0064] Step S1: Weigh the raw materials according to the weight parts, mix linear low-density polyethylene, ethylene-polypropylene copolymer, linear high-density polyethylene, the composite reinforcing agent prepared in Example 3 and polyethylene wax evenly to obtain inner layer premix and outer layer premix respectively; mix linear low-density polyethylene, metallocene linear low-density polyethylene, linear high-density polyethylene, the composite reinforcing agent prepared in Example 3 and polyethylene wax evenly to obtain middle layer premix.

[0065] Step S2: The inner layer premix, the middle layer premix and the outer layer premix are respectively fed to the extruder of the three-layer co-extrusion blown film unit. After extrusion, blowing, cooling, traction and winding, PE shrink film is obtained. The inner layer and the outer layer have the same thickness, and the thickness ratio of the inner layer, the outer layer and the middle layer is 1:1:1.6.

[0066] Comparative Example 1: This comparative example is a PE shrink film. The difference between it and Example 6 is that a quaternary ammonium salt antibacterial agent is used instead of the composite reinforcing agent prepared in Example 3. All other aspects are the same.

[0067] Comparative Example 2: This comparative example is a PE shrink film. The difference between it and Example 6 is that nano-silver is used instead of the composite reinforcing agent prepared in Example 3. All other aspects are the same.

[0068] Comparative Example 3: This comparative example is a PE shrink film. The difference between it and Example 6 is that silica is used instead of the composite reinforcing agent prepared in Example 3. All other aspects are the same.

[0069] The performance of the PE shrink films prepared in Examples 4-6 and Comparative Examples 1-3 was tested:

[0070] Antibacterial performance test: The test methods and detection means of QB / T 2591-2003 "Test Methods for Antibacterial Performance and Antibacterial Effect" were adopted. Among them, the antibacterial rate ≥99% is considered to have strong antibacterial effect; the antibacterial rate ≥90% is considered to have antibacterial effect; the mold growth grade of 0 represents strong antifungal effect; the mold growth grade of I represents antifungal effect.

[0071] Mechanical property testing: The tensile strength (≥10MPa) and nominal strain at break (≥200%) of the specimens were tested according to the GB / T 4456-2008 standard for polyethylene blown films for packaging.

[0072] The test results are shown in Table 1:

[0073] Table 1: Performance Test Results

[0074]

[0075] As can be seen from Table 1, the PE shrink film prepared by this invention not only has excellent mechanical properties, but also excellent antibacterial and antifungal properties.

[0076] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the scope defined by the inventive concept, they should all fall within the protection scope of the present invention.

Claims

1. A PE shrink film, characterized in that, It consists of an inner layer, a middle layer, and an outer layer, wherein the inner layer and the outer layer have the same thickness, and the thickness ratio of the inner layer, the outer layer, and the middle layer is 1:1:1.3-1.6; The inner and outer layers comprise the following raw materials in parts by weight: 35-45 parts of linear low-density polyethylene, 20-30 parts of ethylene-polypropylene copolymer, 10-20 parts of linear high-density polyethylene, 4-6 parts of composite reinforcing agent, and 3-6 parts of polyethylene wax. The intermediate layer comprises the following raw materials in parts by weight: 40-60 parts of linear low-density polyethylene, 25-35 parts of metallocene linear low-density polyethylene, 15-25 parts of linear high-density polyethylene, 4-9 parts of composite reinforcing agent, and 6-10 parts of polyethylene wax. The composite reinforcing agent is prepared by grafting an epoxide quaternary ammonium salt onto the surface of PCN@SiO2 material. The PCN@SiO2 material is prepared by synthesizing PCN on the surface of carboxylated nano-silica using zinc metal porphyrin ligand, zirconium tetrachloride, and 4-hydroxybenzoic acid as raw materials. The zinc metal porphyrin ligand is prepared by reacting porphyrin ligand with zinc acetate. The porphyrin ligand is prepared by reacting p-carboxybenzaldehyde with pyrrole. The epoxide quaternary ammonium salt is prepared by reacting epichlorohydrin with dodecyl dimethyl tertiary amine.

2. The PE shrink film according to claim 1, characterized in that, The composite reinforcing agent is prepared by the following steps: Step A1: Heat p-carboxybenzaldehyde in propionic acid and stir until reflux at 140°C. Then add pyrrole propionic acid solution dropwise over 30 min and continue reflux for 3 h. Cool to room temperature, add anhydrous ethanol, seal and refrigerate for 24 h. Filter, wash and recrystallize to obtain porphyrin ligand. Step A2: Add the porphyrin ligand to DMF and heat to 165°C under reflux. Then add zinc acetate and maintain the temperature while stirring for 2 hours. Cool to room temperature, add distilled water and refrigerate at 4°C overnight. Filter and dry to obtain zinc metal porphyrin ligand. Step A3: Disperse carboxylated nano-silica in DMF, then add zinc metal porphyrin ligand, zirconium tetrachloride and 4-hydroxybenzoic acid in sequence, ultrasonically disperse for 30 min, then transfer to high pressure reactor, react at 120℃ for 48 h, filter, wash, activate with acetone, dry, and obtain PCN@SiO2 material; Step A4: Under nitrogen atmosphere, mix and stir the epoxidized quaternary ammonium salt and tetrabutylammonium bromide in DMF until homogeneous, then add PCN@SiO2 material and stir until homogeneous. Stir at 90°C for 4-6 hours. After the reaction is complete, filter, wash and dry to obtain the composite reinforcing agent.

3. The PE shrink film according to claim 2, characterized in that, In step A1, the ratio of carboxybenzaldehyde, propionic acid, pyrrole propionic acid solution and anhydrous ethanol is 10-20g:150mL:15-20mL:150mL. The pyrrole propionic acid solution is prepared by mixing pyrrole and propionic acid in a volume ratio of 1-2:

2.

4. A PE shrink film according to claim 2, characterized in that, In step A2, the ratio of porphyrin ligand, DMF, zinc acetate, and distilled water is 0.2-0.6 g: 50 mL: 0.5-1.5 g: 50 mL.

5. A PE shrink film according to claim 2, characterized in that, In step A3, the ratio of carboxylated nano-silica, DMF, zinc metal porphyrin ligand, zirconium tetrachloride, 4-hydroxybenzoic acid and acetone is 0.05-0.2g:20mL:0.05-0.1g:0.075-0.1g:2.7g.

6. A PE shrink film according to claim 2, characterized in that, The epoxidized quaternary ammonium salt described in step A4 is prepared by the following steps: Epichlorohydrin was stirred evenly in methanol and heated to 65°C in an oil bath. Dodecyl dimethyl tertiary amine was then slowly added and stirring continued for 6-10 hours. The mixture was cooled to room temperature, and then distilled under reduced pressure and washed to obtain the epoxidized quaternary ammonium salt.

7. A PE shrink film according to claim 6, characterized in that, The ratio of epichlorohydrin, methanol, and dodecyl dimethyl tertiary amine in the epoxidized quaternary ammonium salt is 30-50 mL: 150 mL: 1.5 g.

8. A PE shrink film according to claim 2, characterized in that, In step A4, the ratio of epoxidized quaternary ammonium salt, tetrabutylammonium bromide, DMF, and PCN@SiO2 material is 0.2-0.3 mol: 0.01-0.015 mol: 100 mL: 3-6 g.

9. A method for preparing the PE shrink film according to any one of claims 1-8, characterized in that, Includes the following steps: Step S1: Weigh the raw materials according to the weight parts, mix linear low-density polyethylene, ethylene-polypropylene copolymer, linear high-density polyethylene, composite reinforcing agent and polyethylene wax evenly to obtain inner layer premix and outer layer premix respectively; mix linear low-density polyethylene, metallocene linear low-density polyethylene, linear high-density polyethylene, composite reinforcing agent and polyethylene wax evenly to obtain middle layer premix. Step S2: The inner layer premix, the middle layer premix and the outer layer premix are respectively fed to the extruder of the three-layer co-extrusion blown film unit. After extrusion, blowing, cooling, traction and winding, PE shrink film is obtained.

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