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

Abstract

The application relates to the technical field of pet dry food packaging materials, and discloses a high-barrier puncture-resistant soft packaging film, a preparation process and application, which specifically are as follows: isocyanate functional groups obtained by deblocking of a multifunctional linking agent are subjected to nucleophilic addition reaction with hydroxyl functional groups enriched on the surface of zinc-aluminum hydrotalcite nanosheets, the multifunctional linking agent molecules are anchored to the surface of the hydrotalcite, and methacrylic acid functionalized stable hydrotalcite is prepared; under the action of a melt state and a free radical initiator, the methacrylic acid functionalized stable hydrotalcite is grafted to a polyethylene resin main chain through a free radical addition reaction, and hydrotalcite modified polyethylene masterbatch is prepared; the hydrotalcite modified polyethylene masterbatch is used as raw material of a functional layer in a three-layer co-extrusion film, a three-layer co-extrusion blow molding process is adopted, and the high-barrier puncture-resistant soft packaging film is prepared, which meets the technical requirements of pet dry food product packaging materials in barrier properties and mechanical properties and can be used as pet dry food packaging materials.

Description

Technical Field

[0001] This invention relates to the field of pet dry food packaging materials technology, and in particular to a high-barrier, puncture-resistant flexible packaging film, its preparation process, and its application. Background Technology

[0002] Pet dry food products are rich in fat and protein and contain multiple vitamins. They are also characterized by their hard texture and sharp edges. Based on this, the top-tier high-barrier packaging type, which uses a material structure of nylon BOPA (providing puncture resistance and abrasion resistance), aluminum foil Al (providing absolute barrier properties), and high-temperature retort-grade cast polypropylene film RCPP (providing high strength and high-quality heat-sealing properties), has become the commercial solution for pet dry food packaging.

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

[0004] Research has found that the performance indicators for packaging materials for dry pet food products typically require an oxygen permeability of less than 5cm. 3 / (m 2 • 24h • 0.1MPa), water vapor transmission rate less than 2g / (m 2 • 24h), piercing force greater than 10N;

[0005] Therefore, it can be concluded that under the current technological conditions, the commercial shelf life requirements can be fully met by using high-barrier non-aluminum materials combined with nitrogen filling process, without the need to pursue the absolute barrier level of aluminum foil.

[0006] In the flexible packaging industry, it is generally considered that an oxygen permeability of less than or equal to 5 cm is acceptable. 3 / (m 2 Materials with an oxygen permeability of 0.1 MPa (24h) are called high-barrier materials; oxygen permeability is less than or equal to 1 cm³. 3 / (m 2 Materials with a strength of 0.1 MPa (24h) are called ultra-high barrier materials.

[0007] Based on this, the present invention aims to provide an alternative solution that differs from the existing commercial product packaging structure, specifically for the application scenario of pet dry food product packaging. Summary of the Invention

[0008] Based on molecular design principles, this invention designs and synthesizes a novel multifunctional binder that achieves a strong interfacial bond between inorganic two-dimensional nanofiller hydrotalcite and organic polymer matrix polyethylene through covalent bonds. A single-material polyethylene film product is then produced using a multilayer co-extrusion blow molding process. The barrier properties and mechanical strength of this product meet the technical requirements for pet dry food packaging materials, and it can be used to replace commercial product packaging structures.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing a high-barrier, puncture-resistant flexible packaging film includes the following steps:

[0011] Step 1: Synthesize sodium bisulfite-blocked isocyanate-type multifunctional linker;

[0012] Step 2: The isocyanate functional groups obtained by unsealing with the multifunctional linker undergo a nucleophilic addition reaction with the hydroxyl functional groups enriched on the surface of the zinc-aluminum hydrotalcite nanosheets, anchoring the multifunctional linker molecules to the surface of the hydrotalcite. The sulfonate ion functional groups in the multifunctional linker molecules extend outward from the hydrotalcite, preventing the hydrotalcite nanosheets from re-aggregating through electrostatic repulsion and steric hindrance, thus obtaining methacrylic acid functionalized stable hydrotalcite.

[0013] Step 3: Dicumyl peroxide initiates the generation of macromolecular free radicals in the molten linear low-density polyethylene resin. These macromolecular free radicals undergo a free radical addition reaction with the unsaturated double bonds on the surface of methacrylic acid functionalized stabilized hydrotalcite, thereby grafting hydrotalcite onto the main chain of linear low-density polyethylene resin in the form of covalent bonds to obtain hydrotalcite modified polyethylene masterbatch.

[0014] Using hydrotalcite-modified polyethylene masterbatch as the raw material for the functional layer in a three-layer co-extruded film, a high-barrier, puncture-resistant flexible packaging film is produced by adopting a three-layer co-extrusion blow molding process.

[0015] Preferably, the preparation method of the multifunctional binder is as follows:

[0016] Using N-tert-butoxycarbonylimidazolium as the primary amine protecting agent of diethylenetriamine, a bis-primary amine protected diethylenetriamine was prepared.

[0017] A nucleophilic ring-opening addition reaction was carried out between a 1 molar equivalent of the secondary amine of a bis-primary amine protected diethylenetriamine and a 1 molar equivalent of 1,3-propanesulfonic acid lactone, followed by a neutralization reaction with sodium hydroxide to obtain a bis-primary amine protected intermediate.

[0018] The tert-butoxycarbonyl functional group of the bis-primary amine protected intermediate was removed under hydrochloric acid acidification to obtain an amino-terminated intermediate.

[0019] Based on the nucleophilic addition reaction mechanism, a monoamino intermediate was prepared by reacting 1 molar equivalent of an amino-terminated intermediate with 0.91-0.95 molar equivalents of a monoamino-terminated sodium bisulfite-blocked hexamethylene diisocyanate.

[0020] Based on the nucleophilic addition reaction mechanism, 1 molar equivalent of a monoamino intermediate reacts with 1 molar equivalent of isocyanate methacrylate to generate a multifunctional linker.

[0021] Preferably, the preparation method of the bis-primary amine protected diethylenetriamine is as follows:

[0022] N-tert-butoxycarbonylimidazolium was added to toluene, followed by diethylenetriamine. The mixture was stirred and reacted at 60-70°C. After cooling, the solid was filtered off, the solvent was removed, and the mixture was recrystallized and dried to obtain diethylenetriamine protected by primary amine.

[0023] Preferably, the preparation method of the single-terminated sodium bisulfite-blocked hexamethylene diisocyanate is as follows:

[0024] Hexamethylene diisocyanate, sodium bisulfite, and a phase transfer catalyst were added to acetone, stirred, and reacted at 25-35°C for 2 hours. The molar ratio of hexamethylene diisocyanate to sodium bisulfite was controlled to be 1:(0.91-0.95). The solvent was removed by rotary evaporation to obtain hexamethylene diisocyanate with a single end blocked by sodium bisulfite.

[0025] Preferably, the zinc-aluminum hydrotalcite is prepared by dissolving aluminum nitrate, zinc nitrate and urea in deionized water, refluxing under stirring conditions 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.

[0026] Preferably, the product structure of the high-barrier puncture-resistant flexible packaging film comprises the following layers arranged sequentially:

[0027] Outer layer: The formula consists of 30-40 wt% high-density polyethylene resin and 60-70 wt% low-density polyethylene resin, with a dosage of 30-50 parts by weight;

[0028] Functional layer: The formulation is 100wt% hydrotalcite modified polyethylene masterbatch, and the dosage is 30-50 parts by weight;

[0029] Inner layer: The formulation consists of 35-45 wt% metallocene polyethylene resin and 55-65 wt% linear low-density polyethylene resin, with a dosage of 10-30 parts by weight.

[0030] Preferably, the formulation of the hydrotalcite-modified polyethylene masterbatch is: 95-99 wt% linear low-density polyethylene resin and 1-5 wt% methacrylic acid functionalized stabilized hydrotalcite.

[0031] Preferably, the formulation of the methacrylic acid functionalized stabilized hydrotalcite is: 75-85 wt% zinc aluminum hydrotalcite and 15-25 wt% multifunctional binder.

[0032] Preferably, the thickness of the high-barrier, puncture-resistant flexible packaging film is 80-120 μm.

[0033] Preferably, the high-barrier, puncture-resistant flexible packaging film is used as a pet dry food packaging material.

[0034] The beneficial effects of this invention are as follows:

[0035] Using diethylenetriamine as the backbone raw material, the two primary amine functional groups in the diethylenetriamine molecule are first protected. Then, a sulfonic acid functional group is introduced by reacting the secondary amine functional group in the diethylenetriamine molecule with 1,3-propanesulfonate lactone through a secondary amine-sulfonate lactone ring-opening reaction. Subsequently, the sulfonate ion functional group is generated by alkalization with sodium hydroxide. After deprotection of the two primary amines, an isocyanate functional group blocked by sodium bisulfite is introduced by reacting one primary amine functional group with hexamethylene diisocyanate blocked at one end with sodium bisulfite through a primary amine-isocyanate addition reaction (this reaction is carried out under the condition of controlling the molar ratio of the reactants, i.e., the primary amine is provided in excess). Finally, a methacrylic acid functional group is introduced by reacting the remaining primary amine functional group with isocyanoethyl methacrylate through a primary amine-isocyanate addition reaction, thus preparing a multifunctional linker.

[0036] The isocyanate functional groups obtained by unsealing the multifunctional linker react with the hydroxyl functional groups abundant on the surface of the hydrotalcite to form covalent bonds, firmly anchoring the multifunctional linker molecules to the surface of the hydrotalcite. Then, the sulfonate ion functional groups on the multifunctional linker molecules extend to the outside of the hydrotalcite. Through electrostatic repulsion and steric hindrance, the re-aggregation of hydrotalcite nanosheets is prevented, thus preparing methacrylic acid functionalized stable hydrotalcite.

[0037] Under high temperature, a free radical initiator generates free radicals that capture hydrogen atoms from the polyethylene molecular chain to generate macromolecular free radicals. Subsequently, methacrylic acid functionalized stabilized hydrotalcite is grafted onto the polyethylene main chain through a free radical addition reaction to obtain hydrotalcite modified polyethylene masterbatch.

[0038] Hydrotalcite-modified polyethylene masterbatch was used as the functional layer raw material for three-layer co-extrusion blow molding polyethylene composite film. A high-barrier, puncture-resistant flexible packaging film was prepared by using a three-layer co-extrusion blow molding process.

[0039] Experimental results demonstrate that the high-barrier, puncture-resistant flexible packaging film prepared by this invention meets the technical requirements for barrier performance and mechanical properties of pet dry food packaging materials, and its oxygen barrier performance also reaches the technical standards of ultra-high barrier materials. Detailed Implementation Example 1:

[0040] The synthesis process for preparing multifunctional linkers is as follows:

[0041] Step S1: The primary amine group in diethylenetriamine is protected with N-tert-butoxycarbonylimidazolium to obtain diethylenetriamine with bisprimary amine protection;

[0042] Step S2: A sulfonic acid group is introduced by a nucleophilic ring-opening addition reaction between the secondary amine group in the bis-primary amine-protected diethylenetriamine and the sulfonate lactone in 1,3-propanesulfonic acid lactone, followed by a neutralization reaction with sodium hydroxide, and then the protection of the primary amine is removed to obtain an amino-terminated intermediate.

[0043] Step S3: Use sodium bisulfite to protect one isocyanate group of hexamethylene diisocyanate to obtain sodium bisulfite-blocked hexamethylene diisocyanate.

[0044] A monoamino intermediate was prepared by nucleophilic addition of the amino group in the amino-terminated intermediate to the isocyanate group in the monoamino-terminated sodium bisulfite-blocked hexamethylene diisocyanate.

[0045] Step S4: A multifunctional linker is prepared by nucleophilic addition reaction between the amino group in the monoamino intermediate and the isocyanate group in isocyanate methacrylate.

[0046] The specific preparation steps for multifunctional linkers are as follows:

[0047] Step 1: Add 3.4g imidazole and 25mL dichloromethane to a 250mL three-necked flask, add 10.91g ditert-butyl dicarbonate dropwise at room temperature, stir magnetically, reflux for 2h, stop heating, cool to room temperature, concentrate the solvent, add 50mL petroleum ether, precipitate solid under freezing, filter, and obtain N-tert-butyloxycarbonyl imidazole.

[0048] 6.73 g of N-tert-butyloxycarbonylimidazolium and 10 mL of toluene were added sequentially to a 250 mL three-necked flask. 2.06 g of diethylenetriamine was added dropwise under ice bath conditions. The mixture was stirred at 65 °C for 5 h. After cooling, the solid was filtered off, the solvent was removed, and the mixture was recrystallized and dried to obtain diethylenetriamine protected by primary amine.

[0049] Step 2: Add 3.1g of diethylenetriamine protected by primary amine to 50mL of isopropanol, stir mechanically until homogeneous, add 1.24g of 1,3-propanesulfonic acid lactone, stir and react at 70℃ for 4h. After the reaction is complete, add 10mL of deionized water containing 0.4g of sodium hydroxide, stir and react at 70℃ for another 1h, cool to room temperature, filter, wash, and vacuum dry at 60℃ for 6h to obtain the diethylenetriamine protected intermediate.

[0050] 5g of the bis-primary amine protected intermediate was added to 50mL of 12% HCl solution (ethanol / water = 1:1, v / v), and shaken and soaked at room temperature for 24h. After soaking, the intermediate was filtered, washed, and dried under vacuum at 60℃ to constant weight to obtain the amino-terminated intermediate.

[0051] Step 3: Add 1.7g hexamethylene diisocyanate, 1.04g sodium bisulfite and 0.03g tetrabutylammonium bromide catalyst to 30mL acetone, stir mechanically until uniform, react at 30℃ for 2h, remove solvent by rotary evaporation to obtain single-end sodium bisulfite-blocked hexamethylene diisocyanate.

[0052] Add 2.5 g of amino-terminated intermediate and 50 mL of acetone to a 250 mL round-bottom flask, stir at room temperature for 30 min, add 2.2 g of sodium bisulfite-terminated hexamethylene diisocyanate, and continue stirring at room temperature for 24 h. After the reaction is complete, remove the solvent by rotary evaporation to obtain the monoamino intermediate.

[0053] Step 4: Dissolve 4.81g of monoamino intermediate in 60mL of dichloromethane, add 1.56g of isocyanate methacrylate, stir and react at room temperature for 24h, remove the solvent by rotary evaporation to prepare a multifunctional linker.

[0054] The chemical structural formula of the multifunctional linker is:

[0055] ;

[0056] The proton NMR spectrum characterization of the multifunctional linker is as follows:

[0057] 1H NMR (DMSO-d6, 400MHz) 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),3.06-3.1 4(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:

[0058] The raw material formulation for preparing methacrylic acid-functionalized stabilized hydrotalcite is: 80 wt% zinc-aluminum hydrotalcite and 20 wt% multifunctional binder.

[0059] In this embodiment, the specific formulation of the methacrylic acid functionalized stabilized hydrotalcite is: 10g zinc aluminum hydrotalcite and 2g multifunctional binder;

[0060] The specific experimental steps are as follows:

[0061] Zinc-aluminum hydrotalcite was dried in a vacuum drying oven at 100℃ for 24 hours. After drying, zinc-aluminum hydrotalcite and a multifunctional linker were added to 60 mL of anhydrous toluene, and 2 drops of dibutyltin dilaurate catalyst were added. The mixture was sealed to prevent moisture from entering, and the mixture was ultrasonically reacted at 70℃ for 2 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and the mixture was dried in a vacuum drying oven at 60℃ for 8 hours to obtain methacrylic acid functionalized stabilized hydrotalcite.

[0062] This embodiment provides a specific method for preparing zinc-aluminum hydrotalcite as follows:

[0063] 1.875 g aluminum nitrate [Al(NO3)3·9H2O], 2.97 g zinc nitrate [Zn(NO3)2·6H2O] and 2.1 g urea were dissolved in 500 mL of deionized water and refluxed for 24 h under stirring. After reflux, the mixture was centrifuged, washed, and vacuum dried at 60 °C for 10 h to obtain zinc-aluminum hydrotalcite. Example 3:

[0064] (1) Preparation of hydrotalcite-modified polyethylene masterbatch I, the raw material formula is as follows:

[0065] 97wt% linear low-density polyethylene resin (grade 6201XR);

[0066] 3wt% functionalized and stabilized hydrotalcite with methacrylic acid;

[0067] In the preparation of hydrotalcite-modified polyethylene masterbatch I, dicumyl peroxide was used as the initiator during melt grafting, and the amount of dicumyl peroxide was 0.1 wt% of the linear low-density polyethylene resin.

[0068] The preparation method of hydrotalcite-modified polyethylene masterbatch I includes the following steps:

[0069] Linear low-density polyethylene resin, methacrylic acid functionalized stabilized hydrotalcite, and diisopropylbenzene peroxide were added to a high-speed mixer and stirred until homogeneous. The mixed material was then placed in a twin-screw extruder for melt extrusion granulation. The screw speed of the twin-screw extruder was 150 r / min, and the temperatures of zones 1-4 were 160℃, 170℃, 180℃, and 190℃, respectively, to obtain hydrotalcite-modified polyethylene masterbatch I.

[0070] (2) Prepare hydrotalcite-modified polyethylene masterbatch II, the formulation of which is as follows:

[0071] 99wt% linear low-density polyethylene resin;

[0072] 1wt% functionalized and stabilized hydrotalcite with methacrylic acid;

[0073] The preparation method of hydrotalcite-modified polyethylene masterbatch II is the same as that of hydrotalcite-modified polyethylene masterbatch I.

[0074] (3) Prepare hydrotalcite-modified polyethylene masterbatch III, the formulation of which is as follows:

[0075] 95wt% linear low-density polyethylene resin;

[0076] 5wt% functionalized and stabilized hydrotalcite with methacrylic acid;

[0077] The preparation method of hydrotalcite-modified polyethylene masterbatch III is the same as that of hydrotalcite-modified polyethylene masterbatch I. Example 4:

[0078] (1) Preparation of flexible packaging film I, including the following steps:

[0079] Step 1: Set up flexible packaging film I as a three-layer film structure. The formulation and dosage of each layer are as follows:

[0080] Outer layer: The formula consists of 30 wt% high-density polyethylene resin and 70 wt% low-density polyethylene resin, with a dosage of 40 parts by weight;

[0081] Functional layer: The formulation is 100wt% hydrotalcite modified polyethylene masterbatch I, with a dosage of 40 parts by weight;

[0082] Inner layer: The formula consists of 40 wt% metallocene polyethylene resin and 60 wt% linear low-density polyethylene resin, with a dosage of 20 parts by weight.

[0083] Step 2: The raw materials for each film layer in Step 1 are respectively fed into the hoppers of the three screw extruders of the three-layer co-extrusion film blow molding unit. After stirring and mixing, the molten resin is combined at the die head through the distributor, extruded and blow-molded through the die head, cooled and wound up to prepare a flexible packaging film I with a thickness of 100μm.

[0084] The process parameters for the screw extruder corresponding to the outer layer are set as follows: zone 1-3 temperatures are 130℃, 150℃, and 175℃, the runner temperature is 170℃, and the screw speed is 30r / min.

[0085] The process parameters for the screw extruder corresponding to the intermediate layer are set as follows: zone 1-3 temperatures are 160℃, 170℃, and 175℃, the runner temperature is 170℃, and the screw speed is 40r / min.

[0086] The process parameters for the screw extruder corresponding to the inner layer are set as follows: zone 1-3 temperatures are 120℃, 150℃, and 170℃, the runner temperature is 160℃, and the screw speed is 30r / min.

[0087] Among them, the high-density polyethylene resin is designated as MH602; the linear low-density polyethylene resin is designated as DFDA7042; the low-density polyethylene resin is designated as 2426H; and the metallocene polyethylene resin is designated as SP3010.

[0088] (2) Prepare flexible packaging film II, which differs from flexible packaging film I only in that: hydrotalcite-modified polyethylene masterbatch II is used instead of hydrotalcite-modified polyethylene masterbatch I.

[0089] (3) Prepare flexible packaging film III, which differs from flexible packaging film I only in that: hydrotalcite-modified polyethylene masterbatch III is used instead of hydrotalcite-modified polyethylene masterbatch I.

[0090] Performance testing:

[0091] I. Barrier Properties: The flexible packaging film prepared according to this invention is made into a film with an area of ​​40cm². 2 Circular sample;

[0092] The oxygen barrier properties of the samples were tested according to GB / T 1038.1-2022 "Test methods for gas permeability of plastic films and sheets - Part 1: Differential pressure method", and the oxygen permeation of the samples was recorded.

[0093] The water resistance of the samples was tested according to GB / T 1037-2021 "Determination of Water Vapor Permeability of Plastic Films and Sheets - Cup Method for Weight Gain and Loss". The water vapor permeation of the samples was recorded. The test conditions were 23℃ and 90% relative humidity.

[0094] II. Puncture Resistance: The puncture resistance of flexible packaging film was tested according to GB / T 37841-2019 "Test Method for Puncture Resistance of Plastic Films and Sheets". The specific test steps are as follows: Place a 100mm×100mm sample on a tensile testing machine. Test 5 samples in each group. Select 4 points around the perimeter of each sample to test the thickness. Calculate the average thickness of the 5 samples. The puncture speed is 50mm / min.

[0095] III. Tensile Strength: The longitudinal tensile strength of the flexible packaging film was tested using a universal testing machine according to GB / T 1040.3-2006 "Test of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets". The sample film was made into a strip with a length of 150 mm and a width of 20 mm, with a clamping distance of 50 mm and a testing speed of 150 mm / min.

[0096] The test results are shown in Table 1 below;

[0097] Table 1 Performance test results of flexible packaging film products

[0098]

[0099] The experimental results in Table 1 show that:

[0100] The flexible packaging film prepared by this invention meets the performance requirements for pet dry food packaging materials in terms of oxygen barrier, water barrier, and puncture resistance (specifically, oxygen permeability is less than 5 cm). 3 / (m 2 • 24h • 0.1MPa), water vapor transmission rate less than 2g / (m 2 •24h), puncture force greater than 10N), can be used as packaging material for pet dry food.

Claims

1. A method for preparing a high-barrier, puncture-resistant flexible packaging film, characterized in that, Includes the following steps: Step 1: Synthesize a sodium bisulfite-blocked isocyanate-type multifunctional linker. The chemical structural formula of this multifunctional linker is as follows: ； Step 2: The isocyanate functional groups obtained by unsealing with the multifunctional linker undergo a nucleophilic addition reaction with the hydroxyl functional groups enriched on the surface of the zinc-aluminum hydrotalcite nanosheets, anchoring the multifunctional linker molecules to the surface of the hydrotalcite. The sulfonate ion functional groups in the multifunctional linker molecules extend outward from the hydrotalcite, preventing the hydrotalcite nanosheets from re-aggregating through electrostatic repulsion and steric hindrance, thus obtaining methacrylic acid functionalized stable hydrotalcite. Step 3: Dicumyl peroxide initiates the generation of macromolecular free radicals in the molten linear low-density polyethylene resin. These macromolecular free radicals undergo a free radical addition reaction with the unsaturated double bonds on the surface of methacrylic acid functionalized stabilized hydrotalcite, thereby grafting hydrotalcite onto the main chain of linear low-density polyethylene resin in the form of covalent bonds to obtain hydrotalcite modified polyethylene masterbatch. Using hydrotalcite-modified polyethylene masterbatch as the raw material for the functional layer in a three-layer co-extruded film, a high-barrier, puncture-resistant flexible packaging film is produced by adopting a three-layer co-extrusion blow molding process.

2. The method for preparing a high-barrier, puncture-resistant flexible packaging film according to claim 1, characterized in that, The preparation method of the multifunctional binder is as follows: Using N-tert-butoxycarbonylimidazolium as the primary amine protecting agent of diethylenetriamine, a bis-primary amine protected diethylenetriamine was prepared. A nucleophilic ring-opening addition reaction was carried out between a 1 molar equivalent of the secondary amine of a bis-primary amine protected diethylenetriamine and a 1 molar equivalent of 1,3-propanesulfonic acid lactone, followed by a neutralization reaction with sodium hydroxide to obtain a bis-primary amine protected intermediate. The tert-butoxycarbonyl functional group of the bis-primary amine protected intermediate was removed under hydrochloric acid acidification to obtain an amino-terminated intermediate. Based on the nucleophilic addition reaction mechanism, a monoamino intermediate was prepared by reacting 1 molar equivalent of an amino-terminated intermediate with 0.91-0.95 molar equivalents of a monoamino-terminated sodium bisulfite-blocked hexamethylene diisocyanate. Based on the nucleophilic addition reaction mechanism, 1 molar equivalent of a monoamino intermediate reacts with 1 molar equivalent of isocyanate methacrylate to generate a multifunctional linker.

3. The method for preparing a high-barrier, 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-butoxycarbonylimidazolium was added to toluene, followed by diethylenetriamine. The mixture was stirred and reacted at 60-70°C. After cooling, the solid was filtered off, the solvent was removed, and the mixture was recrystallized and dried to obtain diethylenetriamine protected by primary amine.

4. The method for preparing a high-barrier, puncture-resistant flexible packaging film according to claim 2, characterized in that, The preparation method of the single-terminated sodium bisulfite-blocked hexamethylene diisocyanate is as follows: Hexamethylene diisocyanate, sodium bisulfite, and a phase transfer catalyst were added to acetone, stirred, and reacted at 25-35°C for 2 hours. The molar ratio of hexamethylene diisocyanate to sodium bisulfite was controlled to be 1:(0.91-0.95). The solvent was removed by rotary evaporation to obtain hexamethylene diisocyanate with a single end blocked by sodium bisulfite.

5. The method for preparing a high-barrier, puncture-resistant flexible packaging film according to claim 1, characterized in that, The method for preparing the zinc-aluminum hydrotalcite is as follows: aluminum nitrate, zinc nitrate and urea are dissolved in deionized water, refluxed for 12-36 hours under stirring, centrifuged, washed and vacuum dried to obtain zinc-aluminum hydrotalcite; wherein the molar ratio of aluminum nitrate, zinc nitrate and urea is 1:2:

7.

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

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

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

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

Images