Bacteriostatic high-barrier cpp film and method for preparing the same

Abstract

The present application relates to the technical field of packaging materials, in particular to a bacteriostatic high-barrier CPP film and a preparation method thereof.The film comprises a heat-sealing layer, a core layer and a corona layer, and the total thickness of the film is 40-80 mu m.The heat-sealing layer is made of the following raw materials: 60-75 parts by weight of random copolymerized polypropylene, 15-25 parts by weight of linear low-density polyethylene, 3-8 parts by weight of maleic anhydride grafted polyethylene, 0.5-2.0 parts by weight of a composite antibacterial agent, 0.2-0.6 parts by weight of oleic acid amide, and 0.2-0.5 parts by weight of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester.In the present application, silver ions are loaded in the pore structure of mesoporous silica, and are coated with polydopamine and surface-modified with a silane coupling agent to form a silver ion slow-release composite antibacterial agent, which can effectively regulate the release rate of silver ions, stably disperse the antibacterial agent in the polypropylene matrix, improve the persistence of the antibacterial effect, reduce the migration amount of silver ions, and meet the requirements of safety standards.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, and more specifically, to antibacterial high-barrier CPP film and its preparation method. Background Technology

[0002] Polypropylene cast film (CPP film) is widely used in food packaging, medical packaging, and daily chemical product packaging due to its excellent transparency, heat resistance, heat-sealing performance, and processing adaptability. However, traditional CPP film only provides physical isolation and is insufficient to effectively inhibit the growth of microorganisms in the packaging environment, thus affecting the shelf life and safety of the product. Therefore, in recent years, the introduction of antibacterial fillers into CPP film to achieve active antibacterial activity has become a research hotspot. Among them, inorganic antibacterial systems, represented by silver ion antibacterial agents, are widely used due to their broad-spectrum antibacterial properties, heat resistance, and stability. At the same time, to extend shelf life, it is also necessary to introduce nanofillers or layered structural materials into the film system to improve the barrier properties against oxygen and water vapor, thereby achieving a synergistic enhancement of antibacterial and barrier functions.

[0003] However, existing technologies for introducing antibacterial agents into CPP films easily disrupt the crystalline and orientation structures of the polypropylene matrix, reducing the film's density and consequently lowering its gas barrier properties. Furthermore, antibacterial agents typically require high addition amounts, which not only reduces the film's heat-sealing strength and processing stability but also increases silver ion migration, posing safety risks. Therefore, to achieve a balance between long-lasting antibacterial properties and high barrier performance while ensuring the CPP film's processing and heat-sealing performance, this paper proposes an antibacterial high-barrier CPP film and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide an antibacterial high-barrier CPP film and its preparation method, in order to solve the problems mentioned in the background art, which are that introducing antibacterial agents into CPP films can easily damage the crystalline and orientation structures of the polypropylene matrix, reduce the density of the film, and thus reduce the gas barrier performance. In addition, antibacterial agents usually need to be added in high amounts, which not only reduces the heat-sealing strength and processing stability of the film, but also leads to an increase in the migration of silver ions, posing a safety risk.

[0005] To achieve the above objectives, the present invention provides an antibacterial high-barrier CPP film, which comprises, from the inside out, a heat-sealing layer, a core layer, and a corona layer; The heat-sealing layer is made from the following raw materials: 60-75 parts by weight of random copolymer polypropylene, 15-25 parts by weight of linear low-density polyethylene, 3-8 parts by weight of maleic anhydride grafted polyethylene, 0.5-2.0 parts by weight of composite antibacterial agent, 0.2-0.6 parts by weight of oleamide, and 0.2-0.5 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The composite antibacterial agent is prepared by loading silver ions into mesoporous silica channels, coating them with a polydopamine interface layer, and then further modifying them by surface coupling with γ-aminopropyltriethoxysilane.

[0006] Preferably, the preparation method of the composite antibacterial agent is as follows: S1.1 Add mesoporous silica to deionized water, wherein the mass ratio of mesoporous silica to deionized water is 1:20, and stir and disperse at 400-600 rpm for 30-60 min at 60-70℃ to obtain a dispersion system. S1.2 Add a 0.05-0.20 mol / L silver nitrate solution to the dispersion system to make the mass ratio of silver ions to mesoporous silica 1:10-20. Stir and react at 35-45℃ for 2-4 hours under light-protected conditions. Then adjust the pH to 8-9 with 0.5-1.5% ammonia water to allow silver ions to be adsorbed and deposited in the silica pores. After the reaction is complete, filter and dry at 80-100℃ for 6-8 hours to obtain silver ion-loaded mesoporous silica powder. S1.3. Silver ion-supported mesoporous silica powder was added to a Tris buffer solution with a concentration of 10 mmol / L and a pH of 8.5, followed by the addition of dopamine hydrochloride. The mixture was stirred at 300-500 rpm for 4-6 hours at room temperature. Under weakly alkaline conditions, dopamine underwent auto-oxidative polymerization, forming a polydopamine coating layer on the particle surface. Simultaneously, its reducing properties were used to reduce silver ions in situ to silver nanoparticles. After the reaction was completed, the mixture was filtered and washed 2-3 times with deionized water. It was then dried at 60-70℃ for 4-6 hours to obtain polydopamine-coated silver nanoparticle-supported mesoporous silica. S1.4 Add polydopamine-coated silver nanoparticles loaded with mesoporous silica to an ethanol-water mixed solvent, wherein the volume ratio of ethanol to deionized water is 4-6:1, and the mass ratio of polydopamine-coated silver nanoparticles loaded with mesoporous silica to the mixed solvent is 1:15-25. Stir and disperse at 400-600 rpm for 20-40 min to obtain a suspension. S1.5 Add anhydrous ethanol and γ-aminopropyltriethoxysilane to another reaction vessel, followed by deionized water, so that the molar ratio of γ-aminopropyltriethoxysilane to deionized water is 1:3-5. The amount of anhydrous ethanol added is 20-50 times the mass of γ-aminopropyltriethoxysilane. Adjust the pH to 4-5 with glacial acetic acid. Stir at 40-50℃ for 30-60 min to hydrolyze γ-aminopropyltriethoxysilane to generate silanol groups, and obtain a hydrolyzed silane solution. S1.6 Add the suspension to the hydrolyzed silane solution and stir at 400-500 rpm for 2-3 hours in a three-necked flask equipped with a reflux condenser at 80°C. This allows the hydrolyzed silanol groups to undergo a dehydration condensation reaction with the hydroxyl groups on the powder surface and the functional groups in the polydopamine layer, forming a stable chemical bond structure. After the reaction is complete, the mixture is filtered and washed 2-3 times with anhydrous ethanol to remove unreacted coupling agent. Then, it is vacuum dried at 40-60℃ to remove ethanol, and then heated to 60-80℃ for vacuum drying for 4-6 hours. After grinding and sieving, the composite antibacterial agent is obtained.

[0007] Preferably, in step S1.3, the amount of dopamine hydrochloride added is 5-10% of the mass of the silver ion-supported mesoporous silica powder.

[0008] Preferably, in S1.5, the amount of γ-aminopropyltriethoxysilane added is 1-3% of the mass of polydopamine-coated silver nanoparticles loaded with mesoporous silica.

[0009] Preferably, the core layer is made of the following raw materials: 70-85 parts by weight of homopolymer polypropylene, 2-5 parts by weight of nano-barrier agent, 2-6 parts by weight of maleic anhydride-grafted polypropylene, and 0.2-0.5 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The nano barrier agent is a premix of organic modified montmorillonite, graphene, and nano silica in a mass ratio of 3-5:2:2-4, which is then mixed in a high-speed mixer at 800-1200 rpm for 10-20 minutes to form a nanocomposite premix. Subsequently, it is melt-blended and granulated through a twin-screw extruder, thereby further exfoliating and dispersing the montmorillonite and graphene layers in polypropylene to form a multi-scale layered structure.

[0010] Preferably, the corona layer is made from the following raw materials: 85-95 parts by weight of random copolymer polypropylene, 2-5 parts by weight of calcium carbonate, and 0.2-0.5 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0011] Preferably, the heat-sealing layer has a thickness of 10-20 μm, the core layer has a thickness of 20-45 μm, and the corona layer has a thickness of 10-15 μm.

[0012] On the other hand, the present invention provides a method for preparing an antibacterial high-barrier CPP film, used for the antibacterial high-barrier CPP film described in any one of the above-mentioned methods, comprising the following steps: S2.1 Weigh the raw materials of the heat-sealing layer, core layer and corona layer according to the weight parts. Preheat and dry each layer of raw materials at 80-100℃ for 2-4 hours. Then place them in a high-speed mixer and mix at 500-800rpm for 5-10 minutes to obtain the mixture. S2.2 The mixture of heat-sealing layer, core layer and corona layer is added to three extruders for melt extrusion and cast into a film through a T-die; after extrusion through the die, it is cooled and shaped on a cooling roller at 40-60℃. S2.3. Perform corona treatment on the surface of the thin film corona layer; S2.4. Wind up at a traction speed of 30-80m / min to obtain an antibacterial high-barrier CPP film.

[0013] Preferably, in S2.2, the extruder temperature is controlled as follows: Zone 1 180-190℃, Zone 2 200-220℃, Zone 3 210-230℃, and Die head temperature 210-230℃.

[0014] Preferably, in step S2.3, the corona power is 1.5-2.5kW and the surface tension reaches 38-42mN / m.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: In the antibacterial high-barrier CPP film and its preparation method of the present invention, silver ions are loaded into the pore structure of mesoporous silica and then coated with polydopamine and surface modified with silane coupling agent to form a silver ion slow-release composite antibacterial agent. This can effectively control the release rate of silver ions, so that the antibacterial agent is stably dispersed in the polypropylene matrix, improve the persistence of antibacterial effect, and reduce the migration of silver ions, thus meeting the safety standards for contact materials.

[0016] In the antibacterial high-barrier CPP film and its preparation method of the present invention, a layered nano barrier structure formed by introducing organically modified montmorillonite, graphene and nano-silica into the core layer of the CPP film is formed, which creates a tortuous diffusion path in the polypropylene matrix, thereby extending the diffusion path of gas in the film and effectively improving the oxygen and water vapor barrier performance. Attached Figure Description

[0017] Figure 1 A schematic diagram of the three-layer structure of a high-barrier antibacterial CPP film; Figure 2 The graphs show the silver ion release kinetics in the films of Example 1 and Comparative Examples 1-4. Figure 3 The bar chart shows the oxygen and water vapor transmission rates of the thin films in Example 1 and Comparative Examples 1-4. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] The antibacterial high-barrier CPP film of the present invention comprises, from the inside out, a heat-sealing layer, a core layer, and a corona layer, with a total film thickness of 40-80 μm. The heat-sealing layer is made from the following raw materials: 60-75 parts by weight of random copolymer polypropylene, 15-25 parts by weight of linear low-density polyethylene, 3-8 parts by weight of maleic anhydride grafted polyethylene, 0.5-2.0 parts by weight of composite antibacterial agent, 0.2-0.6 parts by weight of oleamide, and 0.2-0.5 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The composite antibacterial agent is prepared by loading silver ions into mesoporous silica channels, coating them with a polydopamine interface layer, and then further modifying them by surface coupling with γ-aminopropyltriethoxysilane.

[0020] The random copolymer polypropylene (also known as random copolymer of polypropylene, YUNGSOX®PP 5003) was purchased from Dongguan Zhonghao New Materials Co., Ltd.

[0021] Linear low-density polyethylene (LLDPE UR754) was purchased from Dongguan Langfeng Plastic Raw Materials Co., Ltd.

[0022] Maleic anhydride-grafted polyethylene (99% purity) was purchased from Shanghai Koraman Reagent Co., Ltd.

[0023] Mesoporous silica (specific surface area 600m²) 2 (g, pore size 5nm) was purchased from Zhejiang Yamei Nanotechnology Co., Ltd.

[0024] Dopamine hydrochloride (CAS No.: 62-31-7, purity 99%) was purchased from Hangzhou Weibolai Biotechnology Co., Ltd.

[0025] γ-aminopropyltriethoxysilane (CAS No.: 919-30-2, purity 98%), oleamide (CAS No.: 301-02-0, purity 95%), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (CAS No.: 6683-19-8, purity 98%), and calcium carbonate (CAS No.: 471-34-1, purity 99%) were all purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0026] The homopolymer polypropylene (MOSTEN MA524) was purchased from Dongguan Suguang Plastic Raw Materials Co., Ltd.

[0027] Preparation method of organic modified montmorillonite: Montmorillonite is added to deionized water at a mass ratio of 1:20 and stirred and dispersed at 60-80℃ to fully swell and form a uniform suspension; then hexadecyltrimethylammonium bromide is added, with the addition amount being 30%-50% of the mass of montmorillonite, and an ion exchange reaction is carried out under continuous stirring, so that organic cations enter the interlayer of montmorillonite and replace the original inorganic cations, thereby increasing the interlayer spacing and endowing montmorillonite with organic affinity; after the reaction is completed, the mixture is filtered and separated, and repeatedly washed with deionized water until no bromide ions remain in the filtrate; finally, the solid product is dried at 80-100℃, pulverized and sieved to obtain organic modified montmorillonite.

[0028] Graphene (CAS No.: 1034343-98-0, purity 98%) was purchased from Anhui Kerun Nanotechnology Co., Ltd.

[0029] Example 1: A method for preparing an antibacterial high-barrier CPP film, comprising the following steps: S2.1 Weigh the raw materials for the heat-sealing layer, core layer and corona layer according to their respective weight parts; Heat-sealing layer raw materials: 68 parts by weight of random copolymer polypropylene, 20 parts by weight of linear low-density polyethylene, 5 parts by weight of maleic anhydride grafted polyethylene, 1.2 parts by weight of composite antibacterial agent, 0.4 parts by weight of oleamide, and 0.3 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Core layer raw materials: 76 parts by weight of homopolymer polypropylene, 3 parts by weight of nano barrier agent, 4 parts by weight of maleic anhydride-grafted polypropylene, and 0.3 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Corona layer raw materials: 90 parts by weight of random copolymer polypropylene, 4 parts by weight of calcium carbonate, and 0.3 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; Each layer of raw material was preheated and dried at 90℃ for 4 hours, and then placed in a high-speed mixer and mixed at 600rpm for 10 minutes to obtain a mixture. S2.2 The mixture of heat-sealing layer, core layer and corona layer is added to three extruders for melt extrusion. The extruder temperature is 185℃ in zone 1, 210℃ in zone 2 and 210℃ in zone 3, and the die temperature is 210℃. The three layers are co-extruded and cast into a film through a T-die. After extrusion through the die, the film is cooled and shaped on a 50℃ cooling roller. The heat-sealing layer has a thickness of 15μm, the core layer has a thickness of 30μm, and the corona layer has a thickness of 15μm. S2.3. The surface of the thin film corona layer is subjected to corona treatment with a corona power of 2.0kW and a surface tension of 40mN / m. S2.4. Wind up at a traction speed of 50m / min to obtain an antibacterial high-barrier CPP film.

[0030] The preparation method of the compound antibacterial agent is as follows: S1.1 Add mesoporous silica to deionized water, wherein the mass ratio of mesoporous silica to deionized water is 1:20, and stir and disperse at 500 rpm for 60 min at 65°C to obtain a dispersion system. S1.2 Add 0.1 mol / L silver nitrate solution to the dispersion system to make the mass ratio of silver ions to mesoporous silica 1:15. Stir and react at 40°C for 4 h under light-protected conditions. Then adjust the pH to 8.5 with 1.0% ammonia water. After the reaction is complete, filter and dry at 80°C for 8 h to obtain silver ion-supported mesoporous silica powder. S1.3. Silver ion-supported mesoporous silica powder was added to a Tris buffer solution with a concentration of 10 mmol / L and a pH of 8.5. Dopamine hydrochloride was then added in an amount equal to 8% of the mass of the silver ion-supported mesoporous silica powder. The mixture was stirred at 400 rpm for 6 hours at room temperature. After the reaction was completed, the mixture was filtered and washed three times with deionized water. It was then dried at 70°C for 6 hours to obtain polydopamine-coated silver nanoparticle-supported mesoporous silica. S1.4 Add polydopamine-coated silver nanoparticles loaded with mesoporous silica to an ethanol-water mixed solvent, wherein the volume ratio of ethanol to deionized water is 5:1 and the mass ratio of polydopamine-coated silver nanoparticles loaded with mesoporous silica to the mixed solvent is 1:20. Stir and disperse at 500 rpm for 40 min to obtain a suspension. S1.5. Add anhydrous ethanol and γ-aminopropyltriethoxysilane to another reaction vessel. The amount added is 2% of the mass of polydopamine-coated silver nanoparticles loaded with mesoporous silica. Then add deionized water to make the molar ratio of γ-aminopropyltriethoxysilane to deionized water 1:4. The amount of anhydrous ethanol added is 40 times the mass of γ-aminopropyltriethoxysilane. Adjust the pH to 5 with glacial acetic acid. Stir at 50°C for 60 min to obtain a hydrolyzed silane solution. S1.6. The suspension was added to the hydrolyzed silane solution and stirred at 500 rpm for 3 hours at 80°C in a three-necked flask equipped with a reflux condenser. After the reaction was completed, the mixture was filtered and washed three times with anhydrous ethanol to remove unreacted coupling agent. Then, the mixture was vacuum dried at 60°C to remove ethanol, and then heated to 80°C for vacuum drying for 6 hours. The mixture was then ground and sieved to obtain the composite antibacterial agent.

[0031] Example 2: Preparation method of antibacterial high-barrier CPP film, using the method of Example 1, except that the heat-sealing layer is made from the following raw materials: 68 parts by weight of random copolymer polypropylene, 20 parts by weight of linear low-density polyethylene, 5 parts by weight of maleic anhydride grafted polyethylene, 0.5 parts by weight of composite antibacterial agent, 0.4 parts by weight of oleamide, and 0.3 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0032] Example 3: Preparation method of antibacterial high-barrier CPP film, using the method of Example 1, except that the heat-sealing layer is made from the following raw materials: 68 parts by weight of random copolymer polypropylene, 20 parts by weight of linear low-density polyethylene, 5 parts by weight of maleic anhydride grafted polyethylene, 2.0 parts by weight of composite antibacterial agent, 0.4 parts by weight of oleamide, and 0.3 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0033] Example 4: Preparation method of antibacterial high-barrier CPP film, using the method of Example 1, except that the core layer is made of the following raw materials: 76 parts by weight of homopolymer polypropylene, 2 parts by weight of nano-barrier agent, 4 parts by weight of maleic anhydride-grafted polypropylene, and 0.3 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid].

[0034] Example 5: Preparation method of antibacterial high-barrier CPP film, using the method of Example 1, except that the core layer is made from the following raw materials: 76 parts by weight of homopolymer polypropylene, 5 parts by weight of nano-barrier agent, 4 parts by weight of maleic anhydride-grafted polypropylene, and 0.3 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0035] Example 6: Preparation method of antibacterial high barrier CPP film, using the method of Example 1, except that the heat-sealing layer thickness is 10 μm.

[0036] Example 7: Preparation method of antibacterial high barrier CPP film, using the method of Example 1, except that the heat-sealing layer thickness is 20 μm.

[0037] Example 8: Preparation method of antibacterial high-barrier CPP film, using the method of Example 1, except that the core layer thickness is 20 μm.

[0038] Example 9: Preparation method of antibacterial high barrier CPP film, using the method of Example 1, except that the core layer thickness is 45 μm.

[0039] Antibacterial performance (bacteriostatic rate) test procedure: Cut the film sample into 50mm×50mm specimens and sterilize; prepare a solution with a concentration of approximately 10... 5 -10 6 CFU / mL Escherichia coli suspension; 0.4 mL of bacterial suspension was added to the sample surface and covered with a sterile film, and cultured at 37℃ and relative humidity ≥90% for 24 h; bacteria were washed off with sterile physiological saline and plate culture was performed for counting; the inhibition rate % was calculated according to the formula = (BA) / A×100, where B is the number of colonies in the control sample and A is the number of colonies in the antibacterial sample.

[0040] Silver ion migration test procedure: Cut the film sample into 10cm×10cm pieces, immerse them in 4% acetic acid, and soak them at 37℃ for 10 days; at set time points of 0h, 1h, 3h, 6h, 12h, 24h, 48h, 72h, 7d, and 10d, take out a certain volume of the extract for detection, and simultaneously add an equal volume of fresh solution to maintain a constant system volume; use an atomic absorption spectrometer to determine the silver ion concentration in the solution, calculate the cumulative release of silver ions based on the detection results, and plot the kinetic curve of the cumulative release of silver ions over time; calculate the silver ion migration over 10 days.

[0041] Oxygen barrier performance (oxygen permeability) test procedure: Cut the film to the test size; fix the sample in the test chamber of the air permeability tester, introduce oxygen on one side and nitrogen on the other side, and test under conditions of 23℃ and 0%RH; record the amount of oxygen permeating per unit time (cm³). 3 / (m 2 ·24h).

[0042] Water vapor barrier performance (water vapor transmission rate) test procedure: Fix the membrane onto a permeation cup, add anhydrous calcium chloride desiccant to the cup, and place it at 38℃ and 90%RH; weigh the mass change of the permeation cup at regular intervals; calculate the permeability per unit area (g / (m²)). 2 ·24h).

[0043] Heat seal strength test procedure: Cut the film into 15mm×100mm pieces; Set the following parameters on the heat sealer: temperature 130-150℃, pressure 0.2-0.3MPa, time 1s for heat sealing; Perform a 180° peel test using an electronic tensile testing machine and record the maximum peel force (N / 15mm).

[0044] Table 1 Performance data of antibacterial high-barrier CPP films in Examples 1-9 ; The changes in the amount of compound antibacterial agent added (Examples 1-3) show that the antibacterial rate of the film increased from 95.4% to 99.2%, and further to 99.8%, showing an upward trend; at the same time, the silver ion migration increased from 0.009 mg / kg to 0.018 mg / kg, and further increased to 0.032 mg / kg. The results indicate that increasing the content of the composite antibacterial agent can enhance the antibacterial properties of the film, but it also leads to an increase in the migration of silver ions. This is mainly because the silver nanoparticles in the composite antibacterial agent slowly release Ag during use. + To exert antibacterial effects, as the content of antibacterial agent increases, the amount of silver ions that can be released in the film increases, thereby improving the antibacterial rate and slightly increasing the migration amount; however, since the present invention adopts a mesoporous silica-supported structure and forms a sustained-release structure through polydopamine surface coating, even at a higher addition amount, the silver ion migration amount remains at a low level, which can meet the safety requirements of contact materials.

[0045] Secondly, the changes in the amount of nano-barrier agent added (Examples 1, 4, and 5) show that the oxygen permeability decreased from 110 cm⁻¹. 3 / (m 2 • 24h) decreased to 72cm 3 / (m 2 •24h), further reduced to 60cm 3 / (m 2 •24h); Water vapor transmission rate also increased from 6.4 g / (m 2 • 24h) decreased to 4.6 g / (m 2 •24h), and further reduced to 3.9g / (m 2 The 24h result indicates a significant improvement in barrier performance. This is because the organic modified montmorillonite, graphene, and nano-silica in the nano-barrier agent can form a uniformly dispersed layered structure in the polypropylene matrix. This causes gas molecules to bypass a large number of layered structures when passing through the film, thus forming a tortuous diffusion path, increasing the gas diffusion resistance, and thereby reducing the oxygen and water vapor permeability.

[0046] Furthermore, the changes in heat-sealing layer thickness (Examples 1, 6, and 7) show that the heat-sealing strength increased from 31 N / 15 mm to 38 N / 15 mm, and further to 42 N / 15 mm, while the antibacterial rate and barrier properties changed relatively little. This phenomenon indicates that the heat-sealing layer thickness has a significant impact on the heat-sealing performance. The reason for this is that the heat-sealing layer is mainly composed of random copolymer polypropylene and linear low-density polyethylene, which can undergo fusion bonding during the heat-sealing process. When the heat-sealing layer thickness increases, the amount of molten material participating in the heat sealing increases, thereby forming a more stable molten interface and improving the sealing bond strength. Therefore, the heat-sealing strength is significantly improved.

[0047] Furthermore, the changes in core layer thickness (Examples 8, 1, and 9) show that the oxygen permeability increased from 96 cm⁻¹. 3 / (m 2 • 24h) decreased to 72cm 3 / (m 2 •24h), and further reduced to 64cm 3 / (m 2 •24h), while the water vapor transmission rate increased from 5.6 g / (m 2 • 24h) decreased to 4.6 g / (m 2 •24h), then reduced to 4.2g / (m 2 The result (24h) indicates that increasing the core layer thickness can further improve the barrier performance of the film. This is because the core layer contains nano-barrier agents. When the core layer thickness increases, the diffusion path of gas in the film is significantly extended, and the diffusion resistance increases accordingly, thereby effectively reducing the permeation rate of oxygen and water vapor.

[0048] Based on the above measurements, Example 1 achieved a good overall balance between antibacterial rate, silver ion migration, oxygen permeability, water vapor permeability, and heat sealing strength. It ensured antibacterial performance while also taking into account barrier performance, heat sealing performance, and contact safety. Therefore, Example 1 is considered the optimal example. Comparative Example 1: The method of Example 1 was used, except that no compound antibacterial agent was used.

[0049] Comparative Example 2: The method of Example 1 was used, except that polydopamine was not used for coating.

[0050] Comparative Example 3: The method of Example 1 was used, except that γ-aminopropyltriethoxysilane was not used for coupling.

[0051] Comparative Example 4: The method of Example 1 was used, except that only nano-silica was used as a nano-barrier.

[0052] Table 2 Performance data of antibacterial high-barrier CPP films of Examples 1 and Comparative Examples 1-4 ; First, comparing Example 1 with Comparative Example 1 shows that, without the addition of the composite antibacterial agent, the antibacterial rate of the film is 0, and the silver ion migration is also 0; at the same time, the oxygen permeability increases from 72 cm⁻¹. 3 / (m 2 (24h) rose slightly to 74cm 3 / (m 2 •24h), water vapor transmission rate increased from 4.6 g / (m 2 • 24h) rose to 4.8g / (m2 (24h), the heat seal strength changed from 38N / 15mm to 39N / 15mm, with no significant overall change; The results indicate that the CPP matrix material itself has almost no antibacterial ability. The antibacterial properties of the film mainly come from the composite antibacterial agent. The composite antibacterial agent has little effect on the barrier properties and heat-sealing properties of the film. Therefore, when no antibacterial agent is added, the film still maintains physical properties similar to those in Example 1, but the antibacterial properties are reduced.

[0053] Secondly, comparing Example 1 with Comparative Example 2, it can be found that without the use of polydopamine for coating, the antibacterial rate of the film decreased slightly from 99.2% to 98.6%, with no significant change. However, the silver ion migration increased from 0.018 mg / kg to 0.058 mg / kg, while the oxygen permeability, water vapor permeability, and heat sealing strength remained at a level similar to that of Example 1. This phenomenon indicates that the polydopamine coating structure has little impact on antibacterial properties, but plays an important regulatory role in the release behavior of silver ions. The reason is that polydopamine can form a dense coating layer on the surface of antibacterial particles, thereby slowing down the release rate of silver ions and achieving sustained-release antibacterial effect. When this coating layer is missing, silver ions are more likely to be released rapidly from the mesoporous silica carrier, resulting in a significant increase in migration.

[0054] Furthermore, comparing Example 1 with Comparative Example 3 shows that, without coupling modification using γ-aminopropyltriethoxysilane, the antibacterial rate slightly decreased from 99.2% to 98.8%, the silver ion migration increased from 0.018 mg / kg to 0.039 mg / kg, and the oxygen permeability increased from 72 cm⁻¹. 3 / (m 2 (24h) significantly increased to 90cm 3 / (m 2 •24h), water vapor transmission rate increased from 4.6 g / (m 2 The concentration of 24h increased to 5.4 g / (m 2 (24h), the heat seal strength also decreased from 38N / 15mm to 35N / 15mm; The main reason for this change is that silane coupling agents can form chemical bonds or interfacial bridges between antibacterial particles and polypropylene matrix, thereby improving the dispersibility and interfacial compatibility of fillers in polypropylene matrix. When no coupling modification is performed, antibacterial particles are prone to agglomeration in the matrix, resulting in the formation of micro-defects inside the material, making it easier for gases and water vapor to pass through, thus reducing barrier performance. At the same time, the reduced interfacial bonding force will also lead to a decrease in mechanical and heat-sealing properties.

[0055] Furthermore, comparing Example 1 with Comparative Example 4 reveals that when only nano-silica is used as the nano-barrier, the antibacterial rate and silver ion migration remain largely unchanged, but the oxygen permeability increases from 72 cm⁻¹. 3 / (m 2 • Increased to 145cm in 24 hours 3 / (m 2 •24h), water vapor transmission rate increased from 4.6 g / (m 2 The level rose to 7.2 g / (m²) over 24 hours. 2 •24h), while the heat seal strength remains essentially unchanged; The results indicate that the effect of single nano-silica on improving gas barrier performance is limited. This is because single particulate nanofillers are difficult to form an effective barrier structure in a polypropylene matrix. However, the organic modified montmorillonite, graphene and nano-silica composite system used in this invention can form a multi-scale layered structure, which makes gas molecules form a more tortuous transport path during diffusion, thereby reducing the permeation rate of oxygen and water vapor.

[0056] In summary, by comparing Example 1 with the comparative examples, it can be seen that the present invention, by constructing a composite antibacterial agent sustained-release system, using silane coupling modification, and constructing a multi-scale nano barrier structure, can improve the antibacterial and gas barrier properties of CPP film while ensuring a low silver ion migration amount, and maintain good heat-sealing performance, thereby obtaining a high-barrier antibacterial CPP film with excellent comprehensive performance.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. An antibacterial, high-barrier CPP film, characterized in that, From the inside out, it includes a heat-sealing layer, a core layer, and a corona layer; The heat-sealing layer is made from the following raw materials: 60-75 parts by weight of random copolymer polypropylene, 15-25 parts by weight of linear low-density polyethylene, 3-8 parts by weight of maleic anhydride grafted polyethylene, 0.5-2.0 parts by weight of composite antibacterial agent, 0.2-0.6 parts by weight of oleamide, and 0.2-0.5 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The composite antibacterial agent is prepared by loading silver ions into mesoporous silica channels, coating them with a polydopamine interface layer, and then further modifying them by surface coupling with γ-aminopropyltriethoxysilane.

2. The antibacterial high-barrier CPP film according to claim 1, characterized in that, The preparation method of the composite antibacterial agent is as follows: S1.1 Add mesoporous silica to deionized water, wherein the mass ratio of mesoporous silica to deionized water is 1:20, and stir and disperse at 400-600 rpm for 30-60 min at 60-70℃ to obtain a dispersion system. S1.2 Add a 0.05-0.20 mol / L silver nitrate solution to the dispersion system to make the mass ratio of silver ions to mesoporous silica 1:10-20. Stir and react at 35-45℃ for 2-4 hours under light-protected conditions. Then adjust the pH to 8-9 with 0.5-1.5% ammonia water. After the reaction is complete, filter and dry at 80-100℃ for 6-8 hours to obtain silver ion-supported mesoporous silica powder. S1.3 Add silver ion-supported mesoporous silica powder to a Tris buffer solution with a concentration of 10 mmol / L and a pH of 8.5, then add dopamine hydrochloride, and stir at 300-500 rpm for 4-6 h at room temperature. After the reaction is complete, filter and wash with deionized water 2-3 times, and dry at 60-70℃ for 4-6 h to obtain polydopamine-coated silver nanoparticle-supported mesoporous silica. S1.4 Add polydopamine-coated silver nanoparticles loaded with mesoporous silica to an ethanol-water mixed solvent, wherein the volume ratio of ethanol to deionized water is 4-6:1, and the mass ratio of polydopamine-coated silver nanoparticles loaded with mesoporous silica to the mixed solvent is 1:15-25. Stir and disperse at 400-600 rpm for 20-40 min to obtain a suspension. S1.5 Add anhydrous ethanol and γ-aminopropyltriethoxysilane to another reaction vessel, followed by deionized water, so that the molar ratio of γ-aminopropyltriethoxysilane to deionized water is 1:3-5. The amount of anhydrous ethanol added is 20-50 times the mass of γ-aminopropyltriethoxysilane. Adjust the pH to 4-5 with glacial acetic acid. Stir at 40-50℃ for 30-60 min to obtain a hydrolyzed silane solution. S1.6 Add the suspension to the hydrolyzed silane solution and stir at 400-500 rpm for 2-3 hours in a three-necked flask equipped with a reflux condenser at 80°C. After the reaction is complete, filter the solution and wash it 2-3 times with anhydrous ethanol to remove unreacted coupling agent. Then, vacuum dry the solution at 40-60°C to remove the ethanol, and then heat it to 60-80°C to vacuum dry for 4-6 hours. Grind and sieve the solution to obtain the composite antibacterial agent.

3. The antibacterial high-barrier CPP film according to claim 2, characterized in that, In step S1.3, the amount of dopamine hydrochloride added is 5-10% of the mass of the silver ion-supported mesoporous silica powder.

4. The antibacterial high-barrier CPP film according to claim 2, characterized in that, In S1.5, the amount of γ-aminopropyltriethoxysilane added is 1-3% of the mass of polydopamine-coated silver nanoparticles loaded with mesoporous silica.

5. The antibacterial high-barrier CPP film according to claim 1, characterized in that, The core layer is made of the following raw materials: 70-85 parts by weight of homopolymer polypropylene, 2-5 parts by weight of nano barrier agent, 2-6 parts by weight of maleic anhydride-grafted polypropylene, and 0.2-0.5 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The nano barrier agent is composed of organic modified montmorillonite, graphene and nano silica mixed in a mass ratio of 3-5:2:2-4.

6. The antibacterial high-barrier CPP film according to claim 1, characterized in that, The corona layer is made from the following raw materials: 85-95 parts by weight of random copolymer polypropylene, 2-5 parts by weight of calcium carbonate, and 0.2-0.5 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

7. The antibacterial high-barrier CPP film according to claim 1, characterized in that, The heat-sealing layer has a thickness of 10-20 μm, the core layer has a thickness of 20-45 μm, and the corona layer has a thickness of 10-15 μm.

8. A method for preparing an antibacterial high-barrier CPP film, used for preparing an antibacterial high-barrier CPP film as described in any one of claims 1-7, characterized in that, The preparation method is as follows: S2.1 Weigh the raw materials of the heat-sealing layer, core layer and corona layer according to the weight parts. Preheat and dry each layer of raw materials at 80-100℃ for 2-4 hours. Then place them in a high-speed mixer and mix at 500-800rpm for 5-10 minutes to obtain the mixture. S2.2 The mixture of heat-sealing layer, core layer and corona layer is added to three extruders for melt extrusion and cast into a film through a T-die; after extrusion through the die, it is cooled and shaped on a cooling roller at 40-60℃. S2.

3. Perform corona treatment on the surface of the thin film corona layer; S2.

4. Wind up at a traction speed of 30-80m / min to obtain an antibacterial high-barrier CPP film.

9. The method for preparing the antibacterial high-barrier CPP film according to claim 8, characterized in that, In S2.2, the extruder temperature is controlled as follows: Zone 1 180-190℃, Zone 2 200-220℃, Zone 3 210-230℃, and Die head temperature 210-230℃.

10. The method for preparing the antibacterial high-barrier CPP film according to claim 8, characterized in that, In S2.3, the corona power is 1.5-2.5kW and the surface tension reaches 38-42mN / m.

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