High-barrier puncture-resistant flexible packaging film, preparation process and application

Abstract

The invention relates to the technical field of pet solid food packaging materials, and discloses a high-barrier puncture-resistant flexible packaging film, a preparation process and application, and the preparation process specifically comprises the following steps: carrying out nucleophilic addition reaction on an isocyanate functional group obtained by deblocking through a multifunctional connecting agent and a hydroxyl functional group enriched on the surface of a zinc-aluminum hydrotalcite nanosheet to obtain a high-barrier puncture-resistant flexible packaging film; anchoring molecules of a multifunctional connecting agent to the surface of the hydrotalcite to prepare methacrylic acid functionalized stable hydrotalcite; the preparation method comprises the following steps: under the action of a molten state and a free radical initiator, grafting methacrylic acid functionalized stable hydrotalcite to a main chain of polyethylene resin through a free radical addition reaction to prepare hydrotalcite modified polyethylene master batches; the high-barrier puncture-resistant flexible packaging film is prepared by taking hydrotalcite modified polyethylene master batch as a raw material of a functional layer in a three-layer co-extrusion film and adopting a three-layer co-extrusion blow molding process, meets the technical requirements of a pet solid food product packaging material on the aspects of barrier property and mechanical property, and can be used as a pet solid food packaging material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pet dry food packaging materials, and particularly relates to a high-barrier puncture-resistant soft packaging film, a preparation process and application. BACKGROUND

[0002] Pet dry food products are rich in high-fat and high-protein ingredients and add a variety of vitamins, and have characteristics such as hardness and sharp particle edges in form. Based on this, the top high-barrier packaging type with a material structure of nylon BOPA (providing puncture resistance and friction resistance) / aluminum foil Al (providing absolute barrier property) / high-temperature cooking grade cast polypropylene film RCPP (providing high strength and high-quality heat sealing property) has become the commercialized solution for pet dry food product packaging.

[0003] However, since BOPA, Al and RCPP are three completely different materials, they cannot be separated and recycled by conventional physical methods, and aluminum foil and nylon are relatively expensive materials, which makes the cost of the existing packaging structure much higher than that of emerging single-material packaging.

[0004] Research has found that the performance indicators of pet dry food product packaging materials usually require oxygen transmission less than 5 cm 3 / (m 2 ·24h·0.1MPa), water vapor transmission less than 2 g / (m 2 ·24h), and puncture force greater than 10 N. Accordingly, it is known that under the existing technical conditions, high-barrier non-aluminum materials combined with nitrogen charging processes can fully meet the commercial shelf life requirements without pursuing the absolute barrier level of aluminum foil. In the soft packaging industry, it is generally believed that materials with an oxygen transmission rate less than or equal to 5 cm 3 / (m 2 ·24h·0.1MPa) are called high-barrier materials, and materials with an oxygen transmission rate less than or equal to 1 cm 3 / (m 2 ·24h·0.1MPa) are called ultra-high barrier materials.

[0005] Based on this, the present application aims to provide an alternative solution for pet dry food product packaging that is different from the existing commercialized product packaging structure. SUMMARY

[0006] The application is based on a molecular design mechanism, and a new multifunctional linker is designed and synthesized, which realizes firm interfacial combination of inorganic two-dimensional nanofiller hydrotalcite and organic polymer matrix polyethylene through covalent bond, and a single-material polyethylene film product is prepared by adopting a multi-layer co-extrusion blow molding process, and the barrier property and mechanical strength of the product can meet the technical requirements of pet dry food product packaging materials, i.e., the product can be used to replace commercial product packaging structures.

[0007] To achieve the above object, the application adopts the following technical scheme: A preparation method of a high-barrier puncture-resistant soft packaging film, comprising the following steps: Step one: synthesis of sodium bisulfite-closed isocyanate type multifunctional linker; Step two: nucleophilic addition reaction of isocyanate functional groups obtained by deprotection of the multifunctional linker with hydroxyl functional groups enriched on the surface of zinc-aluminum hydrotalcite nanosheets, anchoring of the multifunctional linker molecules to the surface of the hydrotalcite, stretching of sulfonate ion functional groups in the multifunctional linker molecules to the outside of the hydrotalcite, prevention of re-aggregation of the hydrotalcite nanosheets by electrostatic repulsion and steric hindrance effect, and preparation of methacrylic acid functionalized stable hydrotalcite; Step three: initiation of macromolecular radicals in linear low-density polyethylene resin in a molten state by dicumyl peroxide, radical addition reaction of the macromolecular radicals with unsaturated double bonds on the surface of the methacrylic acid functionalized stable hydrotalcite, grafting of the hydrotalcite to the main chain of the linear low-density polyethylene resin in the form of a covalent bond, and preparation of hydrotalcite modified polyethylene masterbatch; The hydrotalcite modified polyethylene masterbatch is used as raw material of a functional layer in a three-layer co-extruded film, and a high-barrier puncture-resistant soft packaging film is prepared by adopting a three-layer co-extrusion blow molding process.

[0008] Preferably, the preparation method of the multifunctional linker is as follows: N-tert-butoxycarbonyl imidazole is used as a primary amine protection reagent of diethylenetriamine, and a di-primary amine protection type diethylenetriamine is prepared; Nucleophilic ring-opening addition reaction of 1 mole equivalent of secondary amine of the di-primary amine protection type diethylenetriamine with 1 mole equivalent of 1,3-propanesultone, and then neutralization reaction with sodium hydroxide, to prepare a di-primary amine protection type intermediate; Removal of the tert-butoxycarbonyl functional group of the di-primary amine protection type intermediate under the action of hydrochloric acid, to prepare an amino-terminated type intermediate; Based on the nucleophilic addition reaction mechanism, 1 mole equivalent of the amino-terminated type intermediate is reacted with 0.91-0.95 mole equivalent of a single-end sodium bisulfite-closed type hexamethylene diisocyanate, to prepare a mono-amino type intermediate; Based on the nucleophilic addition reaction mechanism, 1 molar equivalent of a monoamino intermediate reacts with 1 molar equivalent of isocyanoethyl methacrylate to generate a multifunctional linker.

[0009] Preferably, the preparation method of the di-primary amine protected diethylenetriamine is: N-tert-butyloxycarbonyl imidazole is added to toluene, diethylenetriamine is added, and the mixture is stirred at 60-70°C for reaction, cooled, filtered to remove the solid, removed the solvent, recrystallized and dried to obtain di-primary amine protected diethylenetriamine.

[0010] Preferably, the preparation method of the single-ended sodium bisulfite blocked hexamethylene diisocyanate is: Hexamethylene diisocyanate, sodium bisulfite and a phase transfer catalyst are added to acetone, stirred evenly, and reacted at 25-35° C. for 2 h. The molar ratio of hexamethylene diisocyanate to sodium bisulfite is controlled to be 1:(0.91-0.95). The solvent is removed by rotary evaporation to prepare single-ended sodium bisulfite-blocked hexamethylene diisocyanate.

[0011] Preferably, the preparation method of the zinc-aluminum hydrotalcite is: dissolving aluminum nitrate, zinc nitrate and urea in deionized water, refluxing under stirring for 12-36 hours, centrifuging, washing, and vacuum drying to obtain zinc-aluminum hydrotalcite; wherein the molar ratio of aluminum nitrate, zinc nitrate and urea is 1:2:7.

[0012] Preferably, the product structure of the high barrier and puncture-resistant flexible packaging film is the following layers arranged in sequence: Outer layer: The formula is 30-40wt% high-density polyethylene resin and 60-70wt% low-density polyethylene resin, with an amount of 30-50 parts by weight; Functional layer: The formula is 100wt% hydrotalcite modified polyethylene masterbatch, the dosage is 30-50 parts by weight; Inner layer: The formula is 35-45wt% metallocene polyethylene resin and 55-65wt% linear low-density polyethylene resin, and the amount is 10-30 parts by weight.

[0013] Preferably, the formula of the hydrotalcite-modified polyethylene masterbatch is: 95-99 wt% linear low-density polyethylene resin and 1-5 wt% methacrylic acid functionalized stabilized hydrotalcite.

[0014] Preferably, the formula of the methacrylic acid functionalized stable hydrotalcite is: 75-85 wt% zinc-aluminum hydrotalcite and 15-25 wt% multifunctional linker.

[0015] Preferably, the thickness of the high barrier and puncture-resistant flexible packaging film is 80-120 μm.

[0016] Preferably, the high-barrier puncture-resistant soft packaging film is used as a packaging material for pet dry food.

[0017] The present application has the following advantages: With diethylenetriamine as a skeleton raw material, firstly, two primary amine functional groups in the molecular structure of diethylenetriamine are protected, then a sulfonic acid functional group is introduced by using a secondary amine functional group in the molecular structure of diethylenetriamine and 1,3-propanesultone through a secondary amine-sultone ring-opening reaction, followed by an alkalization treatment by sodium hydroxide to generate a sulfonate ion functional group, then a deprotection treatment is performed on the two primary amines, an isocyanate functional group closed by sodium bisulfite is introduced by using a primary amine functional group and hexamethylene diisocyanate closed by sodium bisulfite through a primary amine-isocyanate addition reaction (the reaction is performed under the condition of controlling the molar ratio of the raw materials involved in the reaction, that is, the primary amine raw material is in excess), and finally a methacrylic acid functional group is introduced by using the remaining primary amine functional group and isocyanatoethyl methacrylate through a primary amine-isocyanate addition reaction, to prepare a multifunctional linker; The isocyanate functional group obtained by deprotection of the multifunctional linker reacts with the hydroxyl functional groups rich on the surface of the hydrotalcite to form a covalent bond, firmly anchoring the multifunctional linker molecules on the surface of the hydrotalcite, and then the sulfonate ion functional groups on the multifunctional linker molecules stretch out to the outside of the hydrotalcite, preventing the re-aggregation of the hydrotalcite nanosheets through electrostatic repulsion and steric hindrance effects, to prepare methacrylic acid functionalized stable hydrotalcite; Under the action of high temperature, a free radical initiator generates free radicals to abstract hydrogen atoms on the polyethylene molecular chain to generate macromolecular radicals, and then the methacrylic acid functionalized stable hydrotalcite is grafted onto the polyethylene main chain through a free radical addition reaction, to prepare hydrotalcite modified polyethylene masterbatch; The hydrotalcite modified polyethylene masterbatch is used as a functional layer raw material of a three-layer co-extrusion blow molding polyethylene composite film, and a three-layer co-extrusion blow molding process is adopted, to prepare a high-barrier puncture-resistant soft packaging film; The experimental results prove that the high-barrier puncture-resistant soft packaging film prepared by the present application meets the technical requirements of pet dry food product packaging materials in terms of barrier properties and mechanical properties, and its oxygen barrier performance reaches the technical standard of super-high barrier materials. DETAILED DESCRIPTION Example One:

[0018] The multifunctional linker is prepared, and the synthesis process is as follows: Step S1: N-tert-butoxycarbonylimidazole is used to protect the primary amine groups in diethylenetriamine, to obtain a double-primary amine protected diethylenetriamine; Step S2: introducing sulfonic acid group by nucleophilic ring-opening addition reaction of secondary amine group in the diamine-protected diethylenetriamine with sulfolane in 1,3-propanesultone, and neutralization reaction with sodium hydroxide, followed by removal of the protection of primary amine, to prepare the amino-terminated intermediate; Step S3: protecting one isocyanate group in hexamethylene diisocyanate with sodium bisulfite to obtain sodium bisulfite-terminated hexamethylene diisocyanate; The single-amino intermediate is prepared by nucleophilic addition reaction of the amino group in the amino-terminated intermediate with the isocyanate group in the sodium bisulfite-terminated hexamethylene diisocyanate; Step S4: preparing the multifunctional linker by nucleophilic addition reaction of the amino group in the single-amino intermediate with the isocyanate group in isocyanatoethyl methacrylate; The specific preparation steps of the multifunctional linker are as follows: First step: adding 3.4 g of imidazole and 25 mL of dichloromethane into a 250 mL three-necked flask, adding 10.91 g of di-tert-butyl dicarbonate dropwise at room temperature, magnetically stirring, stopping heating after refluxing for 2 h, cooling to room temperature, adding 50 mL of petroleum ether, precipitating solid under freezing, and preparing N-tert-butoxycarbonylimidazole by filtration; Adding 6.73 g of N-tert-butoxycarbonylimidazole and 10 mL of toluene into a 250 mL three-necked flask, adding 2.06 g of diethylenetriamine dropwise under ice bath, stirring at 65°C for 5 h, cooling, filtering out solid, removing solvent, recrystallizing, and obtaining diamine-protected diethylenetriamine after drying; Second step: adding 3.1 g of diamine-protected diethylenetriamine into 50 mL of isopropyl alcohol, mechanically stirring uniformly, adding 1.24 g of 1,3-propanesultone, stirring at 70°C for 4 h, adding 10 mL of deionized water solution containing 0.4 g of sodium hydroxide after the reaction is completed, continuing stirring at 70°C for 1 h, cooling to room temperature, filtering, washing, and drying at 60°C under vacuum for 6 h to prepare the diamine-protected intermediate; Adding 5 g of diamine-protected intermediate into 50 mL of 12% HCl solution (ethanol / water=1:1, v / v), oscillating and soaking at room temperature for 24 h, filtering, washing, and drying at 60°C under vacuum to constant weight to prepare the amino-terminated intermediate; Third step: adding 1.7 g of hexamethylene diisocyanate, 1.04 g of sodium bisulfite, and 0.03 g of catalyst tetrabutylammonium bromide into 30 mL of acetone, mechanically stirring uniformly, and constant-temperature reaction at 30°C for 2 h, and removing solvent by rotary evaporation to prepare sodium bisulfite-terminated hexamethylene diisocyanate; A 250 mL round bottom flask was charged with 2.5 g of the amino-terminated intermediate and 50 mL of acetone, stirred at room temperature for 30 min, 2.2 g of the monosodium bisulfite-terminated hexamethylene diisocyanate was added, and the reaction was continued to stir at room temperature for 24 h. After the reaction was completed, the solvent was removed by rotary evaporation to obtain the monoamino-terminated intermediate; Step 4: 4.81 g of the monoamino-terminated intermediate was dissolved in 60 mL of dichloromethane, 1.56 g of isocyanatoethyl methacrylate was added, and the reaction was stirred at room temperature for 24 h. The solvent was removed by rotary evaporation to obtain the multifunctional linker; The chemical structure of the multifunctional linker is as follows: ; The proton nuclear magnetic resonance spectrum of the multifunctional linker is as follows: 1 H NMR (DMSO-d6, 400 MHz) δ: 1.29-1.36 (m, 4H), 1.46-1.52 (m, 4H), 1.80 (s, 3H), 1.87-1.94 (m, 2H), 2.53-2.56 (t, 2H), 2.62-2.64 (t, 4H), 2.84-3.00 (m, 2H), 3.06-3.14 (m, 4H), 3.23-3.26 (m, 4H), 3.45-3.48 (m, 2H), 4.19-4.20 (t, 2H), 5.35-5.37 (t, 1H), 5.50-5.56 (d, 2H), 5.69-5.72 (m, 2H), 5.82-5.84 (t, 1H), 6.17-6.19 (t, 1H). Example 2:

[0019] The raw material formula for preparing the methacrylic acid functionalized stable hydrotalcite is: 80 wt% zinc aluminum hydrotalcite and 20 wt% multifunctional linker; In this embodiment, the specific formula of the methacrylic acid functionalized stable hydrotalcite is: 10 g of zinc aluminum hydrotalcite and 2 g of multifunctional linker; The specific experimental steps are as follows: The zinc aluminum hydrotalcite was dried in a vacuum drying oven at 100°C for 24 h. After drying, the zinc aluminum hydrotalcite and the multifunctional linker were added to 60 mL of anhydrous toluene, 2 drops of the catalyst dibutyltin dilaurate were added dropwise, and the system was sealed to exclude water vapor. The reaction was carried out under ultrasonic at 70°C for 2 h. After the reaction was completed, the solvent was removed by rotary evaporation, and the mixture was dried in a vacuum drying oven at 60°C for 8 h to obtain the methacrylic acid functionalized stable hydrotalcite; In this embodiment, a specific preparation method of zinc aluminum hydrotalcite is provided as follows: 1.875 g of aluminum nitrate [Al(NO3)3·9H2O], 2.97 g of zinc nitrate [Zn(NO3)2·6H2O] and 2.1 g of urea were dissolved in 500 mL of deionized water, refluxed under stirring for 24 h, centrifuged after reflux, washed, and vacuum dried at 60°C for 10 h to obtain zinc-aluminum hydrotalcite. Example 3:

[0020] (1) Preparation of hydrotalcite modified polyethylene masterbatch I, the raw material formula is: 97wt% linear low-density polyethylene resin (brand 6201XR); 3wt% methacrylate functionalized stabilized hydrotalcite; In the preparation process of melt grafting of hydrotalcite-modified polyethylene masterbatch I, the initiator used is dicumyl peroxide, and the amount of dicumyl peroxide used is 0.1wt% of the amount of linear low-density polyethylene resin; The preparation method of hydrotalcite-modified polyethylene masterbatch I comprises the following steps: Linear low-density polyethylene resin, methacrylate functionalized stabilized hydrotalcite and dicumyl peroxide were added to a high-speed mixer and stirred evenly. The mixed materials were placed in a twin-screw extruder for melt extrusion and granulation. The screw speed of the twin-screw extruder was 150 r / min, and the temperatures in zones 1-4 were 160° C., 170° C., 180° C. and 190° C. to obtain hydrotalcite-modified polyethylene masterbatch I.

[0021] (2) Preparation of hydrotalcite modified polyethylene masterbatch II, the formula of which is: 99wt% linear low-density polyethylene resin; 1wt% methacrylate functionalized stabilized hydrotalcite; The preparation method of hydrotalcite-modified polyethylene masterbatch II is the same as that of hydrotalcite-modified polyethylene masterbatch I.

[0022] (3) Preparation of hydrotalcite modified polyethylene masterbatch III, the formula of which is: 95wt% linear low-density polyethylene resin; 5wt% methacrylate functionalized stabilized hydrotalcite; The preparation method of hydrotalcite-modified polyethylene masterbatch III is the same as the preparation method of hydrotalcite-modified polyethylene masterbatch I. Example 4:

[0023] (1) Preparing flexible packaging film I, comprising the following steps: Step 1: Set the flexible packaging film I to a three-layer film structure, and the formula and dosage of each film layer are as follows: Outer layer: The formula is 30wt% high-density polyethylene resin and 70wt% low-density polyethylene resin, the amount is 40 parts by weight; Functional layer: The formula is 100wt% hydrotalcite modified polyethylene masterbatch I, the amount is 40 parts by weight; Inner layer: The formula is 40wt% metallocene polyethylene resin and 60wt% linear low-density polyethylene resin, the amount is 20 parts by weight; Step 2: The raw materials of each film layer in step 1 are respectively put into the hoppers of the three screw extruders of the three-layer co-extrusion film blowing unit, stirred and mixed, and the molten resin is merged at the head of the die through a splitter, extruded and blown through a die head, cooled, and wound to prepare a flexible packaging film I with a thickness of 100 μm; The process parameters of the screw extruder corresponding to the outer layer are set as follows: the temperatures of zones 1-3 are 130°C, 150°C, and 175°C, the flow channel temperature is 170°C, and the screw speed is 30 r / min; The process parameters of the screw extruder corresponding to the middle layer are set as follows: 1-3 zone temperatures are: 160°C, 170°C, 175°C, flow channel temperature is 170°C, and screw speed is 40r / min; The process parameters of the screw extruder corresponding to the inner layer are set as follows: 1-3 zone temperatures are: 120°C, 150°C, 170°C, flow channel temperature is 160°C, and screw speed is 30r / min; Among them, the brand of high-density polyethylene resin is MH602; the brand of linear low-density polyethylene resin is DFDA7042; the brand of low-density polyethylene resin is 2426H; and the brand of metallocene polyethylene resin is SP3010.

[0024] (2) Prepare flexible packaging film II, which differs from flexible packaging film I only in that hydrotalcite-modified polyethylene masterbatch II is used to replace hydrotalcite-modified polyethylene masterbatch I.

[0025] (3) Prepare flexible packaging film III, which differs from flexible packaging film I only in that hydrotalcite-modified polyethylene masterbatch III is used to replace hydrotalcite-modified polyethylene masterbatch I. Performance testing:

[0026] 1. Barrier performance: The flexible packaging film prepared by the present invention is made into an area of ​​40 cm 2 Circular samples; The oxygen barrier properties of the samples were tested according to GB / T 1038.1-2022 "Plastic Film and Sheeting Gas Permeability Test Method Part 1: Differential Pressure Method" and the oxygen permeation rate of the samples was recorded; The water resistance of the sample is tested according to GB / T 1037-2021 "Determination of water vapor transmission properties of plastic films and sheets - Cup method for gain and loss in weight", and the water vapor transmission amount of the sample is recorded, and the test conditions are temperature 23 DEG C, relative humidity 90%; II. Puncture resistance: the puncture resistance of the soft packaging film is tested according to GB / T 37841-2019 "Test method for puncture resistance of plastic films and sheets", and the specific test steps are as follows: 100mm*100mm sample is placed on a tensile testing machine, 5 samples are tested in each group, 4 points are selected on the periphery of each sample to test the thickness, and the average thickness of 5 samples is calculated, and the puncture speed is 50mm / min; III. Tensile strength: the longitudinal tensile strength of the soft packaging film is tested according to GB / T 1040.3-2006 "Test method for tensile properties of plastics - Part 3: test conditions for films and sheets" using a universal mechanical testing machine, the sample film is made into a long strip sample with a length of 150mm and a width of 20mm, the clamping distance is 50mm, and the test speed is 150mm / min; The above test results are shown in Table 1 below; Table 1 Performance test results of soft packaging film products

[0027] From the experimental results in Table 1, it can be seen that: The soft packaging film prepared in the application meets the performance index requirements of pet dry food product packaging materials in oxygen resistance, water resistance and puncture force (the technical requirements are as follows: oxygen transmission amount is less than 5cm 3 / (m 2 ·24h·0.1MPa), water vapor transmission amount is less than 2g / (m 2 ·24h), and puncture force is greater than 10N), which can be used as pet dry food packaging material.

Claims

1. A method for preparing a high barrier and puncture-resistant flexible packaging film, characterized in that: The following steps are involved: Step 1: Synthesize a sodium bisulfite-blocked isocyanate-type multifunctional linker, the chemical structure of which is: ； Step 2: The isocyanate functional groups obtained by deblocking the multifunctional linker react with the hydroxyl functional groups enriched on the surface of the zinc-aluminum hydrotalcite nanosheets through a nucleophilic addition reaction, anchoring the multifunctional linker molecules to the hydrotalcite surface. The sulfonate ion functional groups in the multifunctional linker molecules extend toward the exterior of the hydrotalcite, preventing the hydrotalcite nanosheets from reaggregating through electrostatic repulsion and steric hindrance, thereby producing a methacrylic acid-functionalized stable hydrotalcite. Step 3: Dicumyl peroxide triggers the molten linear low-density polyethylene resin to generate macromolecular free radicals, which react with the unsaturated double bonds on the surface of the methacrylic acid-functionalized stabilized hydrotalcite to covalently graft the hydrotalcite onto the main chain of the linear low-density polyethylene resin to produce a hydrotalcite-modified polyethylene masterbatch; A high-barrier and puncture-resistant flexible packaging film was produced by using hydrotalcite-modified polyethylene masterbatch as the raw material for the functional layer of a three-layer co-extrusion film and a three-layer co-extrusion blow molding process.

2. The method for preparing a high barrier and puncture-resistant flexible packaging film according to claim 1, characterized in that: The preparation method of the multifunctional linker is: Using N-tert-butyloxycarbonyl imidazole as the primary amine protecting reagent of diethylenetriamine, diethylenetriamine with double primary amine protection was prepared; One molar equivalent of the secondary amine of diethylenetriamine protected by bis-primary amine undergoes a nucleophilic ring-opening addition reaction with one molar equivalent of 1,3-propane sultone, followed by a neutralization reaction with sodium hydroxide to prepare a bis-primary amine protected intermediate; The tert-butyloxycarbonyl functional group of the di-primary amine-protected intermediate is removed under the action of hydrochloric acid to obtain an amino-terminated intermediate; Based on the nucleophilic addition reaction mechanism, 1 molar equivalent of the amino-terminated intermediate reacts with 0.91-0.95 molar equivalents of single-terminated sodium bisulfite-blocked hexamethylene diisocyanate to prepare a monoamino-terminated intermediate; Based on the nucleophilic addition reaction mechanism, 1 molar equivalent of a monoamino intermediate reacts with 1 molar equivalent of isocyanoethyl methacrylate to generate a multifunctional linker.

3. The method for preparing a high barrier and puncture-resistant flexible packaging film according to claim 2, characterized in that: The preparation method of the bis-primary amine protected diethylenetriamine is as follows: N-tert-butyloxycarbonyl imidazole is added to toluene, diethylenetriamine is added, and the mixture is stirred at 60-70°C for reaction, cooled, filtered to remove the solid, removed the solvent, recrystallized and dried to obtain di-primary amine protected diethylenetriamine.

4. The method for preparing a high barrier and puncture-resistant flexible packaging film according to claim 2, wherein: The preparation method of the single-ended sodium bisulfite blocked hexamethylene diisocyanate is as follows: Hexamethylene diisocyanate, sodium bisulfite and a phase transfer catalyst are added to acetone, stirred evenly, and reacted at 25-35° C. for 2 h. The molar ratio of hexamethylene diisocyanate to sodium bisulfite is controlled to be 1:(0.91-0.95). The solvent is removed by rotary evaporation to prepare single-ended sodium bisulfite-blocked hexamethylene diisocyanate.

5. The method for preparing a high barrier and puncture-resistant flexible packaging film according to claim 1, characterized in that: The preparation method of the zinc-aluminum hydrotalcite comprises: dissolving aluminum nitrate, zinc nitrate and urea in deionized water, refluxing under stirring for 12-36 hours, centrifuging, washing, and vacuum drying to obtain the zinc-aluminum hydrotalcite; wherein the molar ratio of aluminum nitrate, zinc nitrate and urea is 1:2:

7.

6. A high barrier and puncture-resistant flexible packaging film prepared according to the method according to any one of claims 1 to 5, characterized in that: The product structure of the high barrier and puncture-resistant flexible packaging film comprises the following layers arranged in sequence: Outer layer: The formula is 30-40wt% high-density polyethylene resin and 60-70wt% low-density polyethylene resin, with an amount of 30-50 parts by weight; Functional layer: The formula is 100wt% hydrotalcite modified polyethylene masterbatch, the dosage is 30-50 parts by weight; Inner layer: The formula is 35-45wt% metallocene polyethylene resin and 55-65wt% linear low-density polyethylene resin, and the amount is 10-30 parts by weight.

7. The high barrier and puncture-resistant flexible packaging film according to claim 6, characterized in that: The formula of the hydrotalcite-modified polyethylene masterbatch is: 95-99 wt% of linear low-density polyethylene resin and 1-5 wt% of methacrylic acid functionalized stabilized hydrotalcite.

8. The high barrier and puncture-resistant flexible packaging film according to claim 6, characterized in that: The formula of the methacrylic acid functionalized stable hydrotalcite is: 75-85 wt% of zinc-aluminum hydrotalcite and 15-25 wt% of a multifunctional linker.

9. The high barrier and puncture-resistant flexible packaging film according to claim 6, characterized in that: The thickness of the high-barrier and puncture-resistant flexible packaging film is 80-120 μm.

10. The high barrier and puncture-resistant flexible packaging film according to claim 6, characterized in that: The high-barrier, puncture-resistant flexible packaging film is used as a packaging material for pet dry food.

Images