An antibacterial nylon coated film for vacuum packaging and its application

Abstract

This invention discloses an antibacterial nylon coated film for vacuum packaging and its applications. The film consists of a polyamide substrate layer and a coating layer. The coating layer is prepared using a coating solution containing polyvinyl alcohol, citric acid, and an antibacterial agent. The polyamide substrate layer is a three-layer co-extruded biaxially oriented structure. The antibacterial agent is formed by crosslinking chitosan oligosaccharide with an oxidically modified coating shell, exhibiting high stability, antibacterial properties, and good mechanical properties. This film is suitable for packaging in the food, medical, health product, and cosmetic industries, effectively extending product shelf life and ensuring product safety.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, and in particular to an antibacterial nylon coated film for vacuum packaging and its application. Background Technology

[0002] Vacuum packaging technology, as a core means of extending shelf life and ensuring product quality in the modern food industry, has always focused on optimizing barrier properties and expanding functionality through material innovation. Polyamide coated film, as a new generation of high-performance packaging substrate, effectively solves the technical bottlenecks of traditional polyethylene / polypropylene materials in oxygen barrier properties and puncture resistance by combining biaxially oriented nylon film with a functional coating.

[0003] CN115286905A discloses a food packaging film with antibacterial properties and its preparation method, comprising 30-40 parts starch, 55-75 parts biodegradable polyester, 8-16 parts plasticizer, 3-6 parts compatibilizer, 2-4 parts nickel and copper modified cobalt-based metal-organic framework, 2-4 parts lubricant, and 4-6 parts zinc and indium co-doped TiO2. By utilizing the interactions between the components, the strength and antibacterial properties of the packaging film are significantly improved; however, the antibacterial stability of the packaging film prepared by this method is poor.

[0004] CN107163572A discloses a high surface energy long-chain polyamide transparent film, its preparation method, and its applications. The raw material of this invention comprises a long-chain polyamide material, wherein the main chain contains ≥10 methylene groups between adjacent amide groups. The prepared film possesses excellent mechanical properties, good dimensional stability, oil resistance, and gas barrier properties. Furthermore, it exhibits ideal printability without the need for surface treatment processes such as corona treatment, while maintaining high transparency. However, when applied to the packaging industry, especially food packaging, the film prepared by this invention is prone to bacterial growth, leading to food spoilage. Summary of the Invention

[0005] In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is to improve the antibacterial and mechanical properties of antibacterial nylon coated films used for vacuum packaging.

[0006] To achieve the above objectives, the present invention provides an antibacterial nylon coated film for vacuum packaging, comprising: a polyamide substrate layer and a coating layer; the coating layer is formed by coating the surface of the polyamide substrate layer with a polyvinyl alcohol coating solution; the polyvinyl alcohol coating solution is prepared from polyvinyl alcohol, citric acid and an antibacterial agent; the polyamide substrate layer is composed of three co-extruded biaxially oriented polyamide films; the antibacterial agent is formed by ultrasonic-assisted compounding of a coating agent modified by oxyacetic acid oxidation with chitosan oligosaccharide in an ethanol aqueous solution.

[0007] Preferably, the method for preparing the antibacterial agent includes the following steps, in parts by weight:

[0008] S1: Dissolve 15-30 parts of coating agent in 150-250 parts of water at 60-75℃, stir well, and use for the next step; the coating agent is any one of pectin, starch and sodium alginate;

[0009] S2: Take 15-20 parts of the product obtained in the previous step and add 150-250 parts of peracetic acid. Adjust the pH to 4.0-5.0 with acetic acid. In a water bath under light-protected conditions, stir magnetically at 40-60 rpm and ultrasonically at 60-80 W for 2-3 hours. Add 150-300 parts of ethanol to remove the peracetic acid. Centrifuge, separate the precipitate, dialyze for 4-6 hours, wash 1-3 times, and freeze-dry for 48-72 hours for use in the next step.

[0010] S3: Dissolve 20-40 parts of chitosan oligosaccharide and 10-15 parts of the product obtained in step S2 in 400-700 parts of ethanol aqueous solution, stir at 35-40℃ for 2-3 hours, sonicate at 60-80W for 0.5-1 hours, and then freeze-dry for 48-72 hours to obtain the antibacterial agent.

[0011] Preferably, the method for preparing the antibacterial agent includes the following steps, in parts by weight:

[0012] S1: Add 15-20 parts urea and 5-15 parts sodium hydroxide to 50-120 parts water, stir until completely dissolved, and pre-freeze for 2-4 hours to obtain a pre-cooled alkaline solution; separately add 15-30 parts microcrystalline cellulose to 150-250 parts water and stir evenly; add the mixture of microcrystalline cellulose and water to the pre-cooled alkaline solution at -5~-10℃, and add the coagulant after 30-60 minutes for the next step;

[0013] S2: Take 15-20 parts of the product obtained in the previous step and add 150-250 parts of peracetic acid. Adjust the pH to 4.0-5.0 with acetic acid. In a water bath under light-protected conditions, stir magnetically at 40-60 rpm and ultrasonically at 60-80 W for 2-3 hours. Add 150-300 parts of ethanol to remove the peracetic acid. Centrifuge, separate the precipitate, dialyze for 4-6 hours, wash 1-3 times, and freeze-dry for 48-72 hours for use in the next step.

[0014] S3: Dissolve 20-40 parts of chitosan oligosaccharide and 10-15 parts of the product obtained in step S2 in 400-700 parts of ethanol aqueous solution, stir at 35-40℃ for 2-3 hours, sonicate at 60-80W for 0.5-1 hours, and then freeze-dry for 48-72 hours to obtain the antibacterial agent.

[0015] Preferably, the concentration of peracetic acid is 0.5%-2wt%.

[0016] Preferably, the water bath temperature is 35-40℃.

[0017] Preferably, the coagulant is epichlorohydrin.

[0018] Preferably, the concentration of ethanol in step S3 is 20-40 wt%.

[0019] A method for preparing an antibacterial nylon coated film for vacuum packaging includes the following steps, in parts by weight:

[0020] Step 1: Mix 97-99 parts of polyamide, 0.5-1.5 parts of opening agent, and 0.5-1 parts of slip agent, melt-blend, extrude, and granulate using a twin-screw extruder, and dry the resulting masterbatch A for later use;

[0021] Step 2: Mix 60-90 parts of copolyamide, 3-13 parts of zinc oxide, 0.5-1 part of antioxidant, 0.5-1.5 parts of opening agent, and 0.5-1.5 parts of slip agent, melt-blend, extrude, and granulate using a twin-screw extruder, and dry the resulting masterbatch B for later use;

[0022] Step 3: Feed the masterbatch A obtained in Step 1 into extruder 1 to make the outer layer; feed 90-100 parts of polyamide into extruder 2 to make the middle layer; feed 50-70 parts of masterbatch B obtained in Step 2, 10-20 parts of dendritic polyamide amine, and 3-8 parts of maleic anhydride into extruder 3 to make the inner layer; the extruder temperature and T-die temperature of the outer and middle layers are controlled between 220-240℃, and the extruder temperature and T-die temperature of the inner layer are controlled between 140-180℃.

[0023] Step 4: Dissolve 8-15 parts of polyvinyl alcohol in 50-100 parts of water, heat and stir at 90-100℃ until the polyvinyl alcohol is completely dissolved, then cool to 55-60℃ to obtain a polyvinyl alcohol solution for later use.

[0024] Step 5: Add 1-4 parts citric acid and 2-8 parts antibacterial agent to the solution obtained in step 4, stir and sonicate until homogeneous to prepare polyvinyl alcohol coating solution;

[0025] Step Six: Using the LISIM synchronous stretching method, the extruded and rapidly cooled castings from each layer in Step Three are humidified and cleaned in a 60-80℃ hot water bath. After removing the surface moisture with hot air, the polyvinyl alcohol coating liquid prepared in Step Five is coated onto the inner layer surface. Then, biaxial stretching is performed at a stretching temperature of 60-100℃ and a setting temperature of 125-190℃, with a stretching ratio of 3.2×3.2-3.8×3.8, to obtain an antibacterial nylon coated film for vacuum packaging.

[0026] The present invention also provides the application of the above-mentioned vacuum-packed antibacterial nylon coated film in the fields of food, medical and health products, cosmetics and skin care product packaging.

[0027] Technical concept:

[0028] Vacuum-packed foods (especially bamboo shoots and pastries) face the dual challenges of microbial contamination and packaging damage during storage. While polyamide possesses high tensile strength and puncture resistance, making it suitable for packaging bamboo shoots with their sharp edges, it lacks antibacterial properties. Pastries, containing oils and sugars, are susceptible to mold contamination, and conventional nylon films cannot inhibit microbial growth. Polyvinyl alcohol (PVA) coating solution, as a raw material for preparing coated films, has good compatibility with nylon films due to its numerous hydroxyl groups in its molecular chain. Furthermore, the resulting film is flexible and transparent, making it suitable as a carrier for antibacterial agents. Adding antibacterial agents not only imparts antibacterial activity to the packaging film—such as chitosan oligosaccharides and nano-zinc oxide—which can disrupt microbial cell membranes or inhibit enzyme activity, but also enhances interfacial bonding through hydrogen bonding between PVA and polyamide, improving overall mechanical properties. In addition, the barrier properties of polyvinyl alcohol can help polyamide improve its ability to block oxygen and water vapor, delaying food oxidation and moisture absorption. This design, which involves coating a polyvinyl alcohol solution containing antibacterial agents onto a polyamide substrate, utilizes the mechanical advantages of nylon and achieves synergistic enhancement of antibacterial function, high barrier performance and mechanical properties through the polyvinyl alcohol coating layer, specifically addressing the puncture resistance and antibacterial requirements of food packaging.

[0029] In the preparation of the modified antibacterial formulation, the raw materials and their functions are as follows:

[0030] Urea, as a hydrogen bond disruptor, works synergistically with sodium hydroxide to form a urea-water-chitosan complex, thereby reducing the intermolecular hydrogen bond forces of chitosan and promoting the dissolution of chitosan in alkaline solutions.

[0031] Sodium hydroxide provides a strongly alkaline environment, which disrupts the crystalline structure of chitosan and causes it to dissolve.

[0032] Epichlorohydrin acts as a coagulant to link chitosan molecular chains into a network structure, thereby enhancing the mechanical strength and stability of the gel.

[0033] Peracetic acid, as an oxidizing agent, modifies and oxidizes the hydroxyl functional group molecules contained in the coating shell into aldehyde functional groups through its strong oxidizing properties.

[0034] Acetic acid can react with excess peracetic acid to produce acetic acid and water, thereby removing excess peracetic acid.

[0035] Ethanol reduces solvent polarity, promoting the precipitation of antibacterial agents and facilitating subsequent separation.

[0036] Chitosan oligosaccharides enhance the stability and sustained-release properties of antibacterial agents by forming covalent crosslinks between amino groups and aldehyde groups contained in the oxidized coating agent.

[0037] The beneficial effects of this invention are:

[0038] 1. Compared with the prior art, the present invention chemically crosslinks chitosan oligosaccharide with an oxidized and modified coating agent to form an antibacterial system with high stability and sustained-release properties, which effectively solves the problems of poor antibacterial effect and poor stability of existing packaging materials, and improves the mechanical properties of the coated film.

[0039] 2. Compared to existing technologies, this invention employs a three-layer co-extruded biaxially oriented polyamide substrate structure, with a polyvinyl alcohol coating liquid containing an antibacterial agent applied to the surface. The polyamide substrate itself possesses high tensile strength and puncture resistance. Simultaneously, the barrier properties of polyvinyl alcohol further enhance the film's ability to block oxygen and water vapor. Detailed Implementation

[0040] The parameters and sources of the specific chemical substances used.

[0041] Polyamide, specifically Nylon 66, model: A3WG6, manufactured by BASF, Germany.

[0042] Copolymer polyamide, PA6T / 66-GF35, product name: BK083, DuPont, USA.

[0043] Dendritic polyamide amine, PAMAM G1.0, product number: XK8466, Hubei Xinkang Pharmaceutical Chemical Co., Ltd.

[0044] Organosilicon oil, model: BY16-201, Dow Corning.

[0045] Polyvinyl alcohol, model: BP-22, Kuraray Co., Ltd., Japan.

[0046] Zinc oxide, particle size, 15 nm.

[0047] Talc powder, particle size: 325 mesh.

[0048] Corn starch, Guangrao Lifeng Biotechnology Co., Ltd.

[0049] Example 1

[0050] A method for preparing an antibacterial nylon coated film for vacuum packaging includes the following steps:

[0051] Step 1: Mix 98kg of polyamide, 1kg of talc powder, and 1kg of silicone oil, melt-blend, extrude, and granulate using a twin-screw extruder, and dry the resulting masterbatch A for later use.

[0052] Step 2: Mix 75kg of copolyamide, 7kg of zinc oxide, 1kg of antioxidant 1010, 1kg of talc, and 1kg of silicone oil. Then, melt-blend, extrude, and granulate the mixture using a twin-screw extruder. Dry the resulting masterbatch B for later use.

[0053] Step 3: Feed masterbatch A into extruder 1 to make the outer layer; feed 100 kg of polyamide into extruder 2 to make the middle layer; feed 65 kg of masterbatch B, 15 kg of dendritic polyamide amine, and 3 kg of maleic anhydride into extruder 3 to make the inner layer; the extruder temperature and T-die temperature of the outer and middle layers are controlled at 240℃, and the extruder temperature and T-die temperature of the inner layer are controlled at 150℃.

[0054] Step 4: Dissolve 10 kg of polyvinyl alcohol in 70 L of water, heat and stir at 90 °C until the polyvinyl alcohol is completely dissolved, then cool to 55 °C to obtain a polyvinyl alcohol solution for later use.

[0055] Step 5: Add 2 kg of citric acid and 6 kg of antibacterial agent to the solution obtained in Step 4, and sonicate at 150 rpm and 100 W for 0.5 h to prepare polyvinyl alcohol coating solution;

[0056] Step Six: Using the LISIM synchronous stretching method, the extruded and rapidly cooled cast sheets from each layer in Step Three are humidified and cleaned in a 75°C hot water bath. After removing moisture from the surface of the cast sheets with hot air, a 1μm thick polyvinyl alcohol coating solution prepared in Step Five is coated onto the inner layer surface. Then, biaxial stretching is performed at a stretching temperature of 90°C and a setting temperature of 180°C, with a stretching ratio of 3.5×3.5, to obtain a 20μm thick antibacterial nylon coated film for vacuum packaging.

[0057] The preparation method of the antibacterial agent includes the following steps:

[0058] S1: Add 15g urea and 10g sodium hydroxide to 90mL of water, stir at 200rpm for 1h, and pre-freeze for 3h to obtain a pre-cooled alkaline solution; separately add 20g microcrystalline cellulose to 200mL of water, stir at 200rpm for 1h; add the mixed solution of microcrystalline cellulose and water to the pre-cooled alkaline solution at -5℃, and after 45 min, add 3g epichlorohydrin and continue stirring for 5 min, for use in the next step;

[0059] S2: Take 15g of the mixture obtained in the previous step and add 200mL of 0.5wt% peracetic acid. Adjust the pH to 4.0 with 15wt% acetic acid. Under light-protected conditions, stir magnetically at 40rpm and ultrasonically at 60W for 2h in a 35℃ water bath. Add 200mL of 35wt% ethanol to remove the peracetic acid. Centrifuge, separate the precipitate, dialyze for 6h, wash 3 times, freeze dry for 48h, and use it for the next step.

[0060] S3: Dissolve 30g of chitosan oligosaccharide and 12g of the product obtained in step S2 in a 3wt% acetic acid aqueous solution, adjust the pH to 4.0, stir at 40℃ for 2h, sonicate at 80W for 0.5h, and then freeze-dry for 48h to obtain the antibacterial agent.

[0061] Example 2

[0062] The only difference between the preparation methods of Example 2 and Example 1 in this application is the different antibacterial agents.

[0063] The preparation method of the antibacterial agent described in this embodiment includes the following steps:

[0064] S1: Dissolve 20g of pectin in 180mL of water at 70℃ and stir at 200rpm for 1h for the next step;

[0065] S2: Take 15g of the mixture obtained in the previous step and add 200mL of 0.5wt% peracetic acid. Adjust the pH to 4.0 with 15wt% acetic acid. Under light-protected conditions, stir magnetically at 40rpm and ultrasonically at 60W for 2h in a 35℃ water bath. Add 200mL of 35wt% ethanol to remove the peracetic acid. Centrifuge, separate the precipitate, dialyze for 6h, wash 3 times, freeze dry for 48h, and use it for the next step.

[0066] S3: Dissolve 30g of chitosan oligosaccharide and 12g of the product obtained in step S2 in a 3wt% acetic acid aqueous solution, adjust the pH to 4.0, stir at 40℃ for 2h, sonicate at 80w for 0.5h, and then freeze-dry for 48h to obtain the antibacterial agent.

[0067] Example 3

[0068] The only difference between the preparation methods of Example 3 and Example 1 in this application is the different antibacterial agents.

[0069] The preparation method of the antibacterial agent described in this embodiment includes the following steps:

[0070] S1: Dissolve 20g of corn starch in 180mL of water at 70℃ and stir at 200rpm for 1h for the next step;

[0071] S2: Take 15g of the mixture obtained in the previous step and add 200mL of 0.5wt% peracetic acid. Adjust the pH to 4.0 with 15wt% acetic acid. Under light-protected conditions, stir for 2 hours in a 35℃ water bath with magnetic force at 40rpm and ultrasonication at 60W. Add 200mL of 35wt% ethanol to remove the peracetic acid. Centrifuge, separate the precipitate, dialyze for 6 hours, wash 3 times, freeze dry for 48 hours, and use for the next step.

[0072] S3: Dissolve 30g of chitosan oligosaccharide and 12g of the product obtained in step S2 in 3wt% acetic acid aqueous solution, adjust the pH to 4.0, stir at 40℃ for 2h, sonicate at 80w for 0.5h, and then freeze dry for 48h to obtain the antibacterial agent.

[0073] Example 4

[0074] The only difference between the preparation methods of Example 4 and Example 1 in this application is the different antibacterial agents.

[0075] The preparation method of the antibacterial agent described in this embodiment includes the following steps:

[0076] S1: Dissolve 20g of sodium alginate in 180mL of water at 70℃ and stir at 200rpm for 1h for the next step;

[0077] S2: Take 15g of the mixture obtained in the previous step and add 200mL of 0.5wt% peracetic acid. Adjust the pH to 4.0 with 15wt% acetic acid. Under light-protected conditions, stir magnetically at 40rpm and ultrasonically at 60W for 2h in a 35℃ water bath. Add 200mL of 35wt% ethanol to remove the peracetic acid. Centrifuge, separate the precipitate, dialyze for 6h, wash 3 times, freeze dry for 48h, and use it for the next step.

[0078] S3: Dissolve 30g of chitosan oligosaccharide and 12g of the product obtained in step S2 in 3wt% acetic acid aqueous solution, adjust the pH to 4.0, stir at 40℃ for 2h, sonicate at 80w for 0.5h, and then freeze dry for 48h to obtain the antibacterial agent.

[0079] Comparative Example 1

[0080] The only difference between the preparation methods of Comparative Example 1 and Example 1 is the antibacterial agent.

[0081] The preparation method of the antibacterial agent described in this comparative example includes the following steps:

[0082] S1: Dissolve 20g of β-cyclodextrin in 180mL of water at 70℃ and stir at 200rpm for 1h for the next step;

[0083] S2: Take 15g of the mixture obtained in the previous step and add 200mL of 0.5wt% peracetic acid. Adjust the pH to 4.0 with 15wt% acetic acid. Under light-protected conditions, stir magnetically at 40rpm and ultrasonically at 60W for 2h in a 35℃ water bath. Add 200mL of 35wt% ethanol to remove the peracetic acid. Centrifuge, separate the precipitate, dialyze for 6h, wash 3 times, freeze-dry for 48h, and use it for the next step.

[0084] S3: Dissolve 30g of chitosan oligosaccharide and 12g of the product obtained in step S2 in 3wt% acetic acid aqueous solution, adjust the pH to 4.0, stir at 40℃ for 2h, sonicate at 80w for 0.5h, and then freeze dry for 48h to obtain the antibacterial agent.

[0085] Comparative Example 2

[0086] The difference in the preparation methods of Comparative Example 2 and Example 1 lies in the different antibacterial agents.

[0087] The antibacterial agent described in this comparative example is chitosan oligosaccharide.

[0088] Test Example 1

[0089] Antimicrobial performance testing: The antimicrobial performance of the vacuum-packed antimicrobial nylon coated film was measured using the plate count method, specifically testing the antimicrobial activity of the food packaging film against *Escherichia coli* (CGMCC 1.12883, commercially available, China General Microbiological Culture Collection Center) and *Staphylococcus aureus* (CGMCC 1.12409, commercially available, China General Microbiological Culture Collection Center). The antimicrobial nylon coated films for vacuum packaging prepared in Examples 1-4 and Comparative Examples 1-2 were cut into circular samples with a diameter of 10 mm and placed at the bottom of the wells of a 24-well plate. Subsequently, 100 μL of diluted bacterial suspension (approximately 10 μL) was dropped into each well. 5 The bacterial suspension (CFU / mL) was uniformly dispersed on the membrane surface. The 24-well plate was then placed in a bacterial incubator and incubated at 37°C for 6 hours. Each sample was then removed and immersed in a test tube containing 10 mL of PBS solution. All test tubes were then placed in a water bath shaker (150 rpm) and shaken for 10 minutes. Subsequently, 60 μL of the diluted bacterial suspension was spread onto nutrient agar plates and incubated at 35°C for 24 hours. The number of viable colonies was counted, and the experiment was repeated three times. The test results are shown in Table 1.

[0090] Table 1 Antibacterial Performance Test

[0091] Experimental group Escherichia coli inhibition rate / % Staphylococcus aureus inhibition rate / % Example 1 98.8 97.4 Example 2 96.4 95.6 Example 3 94.4 95.8 Example 4 92.3 94.1 Comparative Example 1 80.4 81.8 Comparative Example 2 68.5 67.4

[0092] Test Example 2

[0093] Mechanical property testing: Refer to GB / T 1040.1-2022 "Determination of tensile properties of plastics – Part 2: Test conditions for molded and extruded plastics". Tensile strength was measured using a universal tensile testing machine at room temperature, with a tensile speed of 50 mm / min. Each sample was measured five times, and the average value was taken.

[0094] Oxygen permeability test: The samples were tested using the differential pressure method, and the test procedure was carried out according to GB / T 1038.1-2022 "Test methods for gas permeability of plastic films and sheets - Part 1: Differential pressure method". The test results are shown in Table 2:

[0095] Table 2 Mechanical Performance Tests

[0096] Experimental group Tensile strength / MPa <![CDATA[Oxygen permeability rate cm 3 / (m²·24h·0.1MPa)]]> Example 1 251.3 1.0 Example 2 231.5 3.3 Example 3 225.6 3.6 Example 4 218.3 3.5 Comparative Example 1 201.6 4.2 Comparative Example 2 182.7 4.9

[0097] By observing and comparing the test data in Tables 1 and 2, it can be found that the antibacterial effect and mechanical properties of the coated film prepared in Example 1 are the best.

[0098] Comparing the test data of Examples 1-4 and Comparative Example 1, it was found that Example 1 had better tensile strength and oxygen permeability, possibly due to the use of a different coating shell. The coating shell can encapsulate the material, reducing damage to the film material from external temperature, ultraviolet radiation, and air, thus improving the stability of the encapsulated material. The coating agent used in Example 1 was microcrystalline cellulose. Besides containing the hydroxyl functional groups found in Examples 2-4 that can be oxidized to aldehyde groups, microcrystalline cellulose also has high crystallinity and a dense hydroxyl network. When blended with polyamide and other raw materials, its nanoscale fiber network can form a physically entangled structure within the film. Simultaneously, the hydrogen bond network formed by the hydroxyl groups and the matrix polar groups enhances the interfacial bonding force, restricting polymer chain slippage and thus improving the mechanical properties of the food packaging film. In contrast, the substances used in Examples 2-4 only contain hydroxyl functional groups and do not possess the fibrous skeleton structure of microcrystalline cellulose itself, therefore exhibiting poorer tensile strength.

[0099] Comparing Example 1 with Comparative Example 2, it can be found that the antibacterial effect of Example 1 is better. This may be because Example 1 uses an oxidizing agent to oxidize the coating material, followed by chemical cross-linking, which increases the stability of the coating material and thus enhances its antibacterial effect. Simultaneously, the antibacterial agent and zinc oxide also have a synergistic effect, improving the antibacterial effect of the coating film. In contrast, Comparative Example 2 only mixes the coating material with other raw materials to prepare the coating film, resulting in poorer antibacterial stability. Comparing Example 1 with Examples 2-4, it can be found that the difference in antibacterial effect values ​​is not significant. This may be because all examples involve coating, and the chemical properties of the coating film are relatively stable, leading to a small difference in antibacterial effect. The difference may be due to the different coating agents used. The coating agent used in Example 1 is microcrystalline cellulose, which has a better network structure than pectin, starch, and sodium alginate, thus improving the stability of the antibacterial agent. Compared with Comparative Example 1, Example 1 showed a better antibacterial effect. This may be because microcrystalline cellulose has a rigid linear polymer chain structure, which can form a more regular three-dimensional network in the polymer, improving the stability of the antibacterial agent. Simultaneously, the coexistence of crystalline and amorphous regions in microcrystalline cellulose enhances the mechanical strength of the polymer and reduces the loss of antibacterial agents under the influence of the external environment. While β-cyclodextrin has a cyclic cavity structure, the inclusion effect of the cavity is a physical adsorption, resulting in relatively weak binding force. In the polymer system, the antibacterial agent is easily released rapidly due to swelling and other effects, making it difficult to maintain a long-lasting antibacterial effect.

Claims

1. An antibacterial nylon coated film for vacuum packaging, characterized in that, include: The product comprises a polyamide substrate layer and a coating layer; the coating layer is formed by coating the surface of the polyamide substrate layer with a polyvinyl alcohol coating solution; the polyvinyl alcohol coating solution is prepared from polyvinyl alcohol, citric acid and an antibacterial agent; the polyamide substrate layer is composed of three co-extruded biaxially oriented polyamide films; the antibacterial agent is formed by ultrasonic-assisted compounding of a coating agent modified by oxyacetic acid oxidation with chitosan oligosaccharide in an ethanol aqueous solution; The method for preparing the antibacterial agent includes the following steps: S1: Add 15g urea and 10g sodium hydroxide to 90mL of water, stir at 200rpm for 1h, and pre-freeze for 3h to obtain a pre-cooled alkaline solution; separately add 20g microcrystalline cellulose to 200mL of water, stir at 200rpm for 1h; add the mixed solution of microcrystalline cellulose and water to the pre-cooled alkaline solution at -5℃, and after 45 min, add 3g epichlorohydrin and continue stirring for 5 min, for use in the next step; S2: Take 15g of the mixture obtained in the previous step and add 200mL of 0.5wt% peracetic acid. Adjust the pH to 4.0 with 15wt% acetic acid. Under light-protected conditions, stir magnetically at 40rpm and ultrasonically at 60W for 2h in a 35℃ water bath. Add 200mL of 35wt% ethanol to remove the peracetic acid. Centrifuge, separate the precipitate, dialyze for 6h, wash 3 times, freeze dry for 48h, and use it for the next step. S3: Dissolve 30g of chitosan oligosaccharide and 12g of the product obtained in step S2 in a 3wt% acetic acid aqueous solution, adjust the pH to 4.0, stir at 40℃ for 2h, sonicate at 80W for 0.5h, and then freeze-dry for 48h to obtain the antibacterial agent.

2. The method for preparing the antibacterial nylon coated film for vacuum packaging as described in claim 1, characterized in that, The steps include the following, in parts by weight: Step 1: Mix 97-99 parts of polyamide, 0.5-1.5 parts of opening agent, and 0.5-1 parts of slip agent in a certain proportion, melt-blend, extrude, and granulate using a twin-screw extruder, and dry the resulting masterbatch A for later use. Step 2: Mix 60-90 parts of copolyamide, 3-13 parts of zinc oxide, 0.5-1 part of antioxidant, 0.5-1.5 parts of opening agent, and 0.5-1.5 parts of slip agent in a certain proportion, melt-blend, extrude, and granulate using a twin-screw extruder, and dry the resulting masterbatch B for later use. Step 3: Feed the masterbatch A obtained in Step 1 into extruder 1 to make the outer layer; feed 90-100 parts of polyamide into extruder 2 to make the middle layer; feed 50-70 parts of masterbatch B obtained in Step 2, 10-20 parts of dendritic polyamide amine, and 3-8 parts of maleic anhydride into extruder 3 in proportion to make the inner layer; the extruder temperature and T-die temperature of the outer and middle layers are controlled between 220-240℃, and the extruder temperature and T-die temperature of the inner layer are controlled between 140-180℃. Step 4: Dissolve 8-15 parts of polyvinyl alcohol in 50-100 parts of water, heat and stir at 90-100℃ until the polyvinyl alcohol is completely dissolved, then cool to 55-60℃ to obtain a polyvinyl alcohol solution for later use. Step 5: Add 1-4 parts citric acid and 2-8 parts antibacterial agent to the solution obtained in step 4, stir and sonicate until homogeneous to prepare polyvinyl alcohol coating solution; Step Six: Using the LISIM synchronous stretching method, the extruded and rapidly cooled castings from each layer in Step Three are humidified and cleaned in a 60-80℃ hot water bath. After removing the surface moisture with hot air, the polyvinyl alcohol coating liquid prepared in Step Five is coated onto the inner layer surface. Then, biaxial stretching is performed at a stretching temperature of 60-100℃ and a setting temperature of 125-190℃, with a stretching ratio of 3.2×3.2-3.8×3.8, to obtain an antibacterial nylon coated film for vacuum packaging.

3. The method for preparing the antibacterial nylon coated film for vacuum packaging as described in claim 2, characterized in that, The steps include the following, in parts by weight: Step 1: Mix 98kg of polyamide, 1kg of talc powder, and 1kg of silicone oil, melt-blend, extrude, and granulate using a twin-screw extruder, and dry the resulting masterbatch A for later use. Step 2: Mix 75kg of copolyamide, 7kg of zinc oxide, 1kg of antioxidant 1010, 1kg of talc, and 1kg of silicone oil. Then, melt-blend, extrude, and granulate the mixture using a twin-screw extruder. Dry the resulting masterbatch B for later use. Step 3: Feed masterbatch A into extruder 1 to make the outer layer; feed 100 kg of polyamide into extruder 2 to make the middle layer; feed 65 kg of masterbatch B, 15 kg of dendritic polyamide amine, and 3 kg of maleic anhydride into extruder 3 to make the inner layer; the extruder temperature and T-die temperature of the outer and middle layers are controlled at 240℃, and the extruder temperature and T-die temperature of the inner layer are controlled at 150℃. Step 4: Dissolve 10 kg of polyvinyl alcohol in 70 L of water, heat and stir at 90 °C until the polyvinyl alcohol is completely dissolved, then cool to 55 °C to obtain a polyvinyl alcohol solution for later use. Step 5: Add 2 kg of citric acid and 6 kg of antibacterial agent to the solution obtained in Step 4, and sonicate at 150 rpm and 100 W for 0.5 h to prepare polyvinyl alcohol coating solution; Step Six: Using the LISIM synchronous stretching method, the layers from Step Three are extruded and rapidly cooled into cast sheets. After being humidified and cleaned in a 75°C hot water bath, and the surface moisture is removed with hot air, a 1μm thick polyvinyl alcohol coating solution prepared in Step Five is coated onto the inner layer surface. Then, biaxial stretching is performed at a stretching temperature of 90°C, a setting temperature of 180°C, and a stretching ratio of 3.5×3.5 to obtain a 20μm thick antibacterial nylon coated film for vacuum packaging. The preparation method of the antibacterial agent includes the following steps: S1: Add 15g urea and 10g sodium hydroxide to 90mL of water, stir at 200rpm for 1h, and pre-freeze for 3h to obtain a pre-cooled alkaline solution; separately add 20g microcrystalline cellulose to 200mL of water, stir at 200rpm for 1h; add the mixed solution of microcrystalline cellulose and water to the pre-cooled alkaline solution at -5℃, and after 45 min, add 3g epichlorohydrin and continue stirring for 5 min, for use in the next step; S2: Take 15g of the mixture obtained in the previous step and add 200mL of 0.5wt% peracetic acid. Adjust the pH to 4.0 with 15wt% acetic acid. Under light-protected conditions, stir magnetically at 40rpm and ultrasonically at 60W for 2h in a 35℃ water bath. Add 200mL of 35wt% ethanol to remove the peracetic acid. Centrifuge, separate the precipitate, dialyze for 6h, wash 3 times, freeze dry for 48h, and use it for the next step. S3: Dissolve 30g of chitosan oligosaccharide and 12g of the product obtained in step S2 in a 3wt% acetic acid aqueous solution, adjust the pH to 4.0, stir at 40℃ for 2h, sonicate at 80W for 0.5h, and then freeze-dry for 48h to obtain the antibacterial agent.

4. The application of the antibacterial nylon coated film for vacuum packaging as described in claim 1 in the fields of food, medical or cosmetic packaging.