Antibacterial nylon film for food packaging and method for preparing the same

Abstract

The application discloses an antibacterial and fresh-keeping nylon film for food packaging and a preparation method thereof. The nylon film is prepared from PA6 resin as a base body, two kinds of inorganic modified compounds, EVOH barrier agent and other additives, and is prepared through formula optimization, film layer structure design and combination of a magnetic driving linear synchronous stretching process. The core of the application lies in the design and application of the two kinds of inorganic modified compounds. The first kind is ZnO-Ag@PBSiO2, and the second kind is OMMT-HPBSi. The film preparation method adopts the magnetic driving linear synchronous stretching technology, realizes the synergistic improvement of the antibacterial, high-barrier and high-strength performance of the film through the regulation and control of the film material composition, crystallization and orientation structure, and simultaneously considers the good transparency and dimensional stability, and solves the technical problems that the traditional nylon film for food packaging has poor barrier property, poor antibacterial effect, unbalanced mechanical property and is easy to be damaged in high-speed processing, so that the food is easy to be oxidized, deteriorated, dampened and contaminated.

Description

Technical Field

[0001] This invention relates to the field of nylon film technology, specifically to an antibacterial and freshness-locking nylon film for food packaging and its preparation method. Background Technology

[0002] Biaxially oriented nylon (BOPA) film possesses excellent mechanical properties, transparency, and puncture resistance, as well as good toughness, oil resistance, and chemical resistance, making it widely used in various food packaging fields. With the upgrading and development of the food industry, especially for food categories with high preservation requirements such as fresh and cooked foods, higher demands are placed on the comprehensive performance of food packaging materials. These materials not only need to possess high strength and high barrier properties (blocking oxygen and water vapor to lock in freshness), but also long-lasting antibacterial properties to prevent food contamination by microorganisms. Simultaneously, they require good dimensional stability and strong processing adaptability to meet the needs of high-speed packaging production lines.

[0003] However, traditional BOPA films for food packaging have several technical shortcomings: First, their barrier properties are insufficient, allowing oxygen and water vapor to easily penetrate, leading to oxidation, spoilage, and moisture damage of the food inside, making it difficult to meet the requirements for long-term freshness preservation. Second, their antibacterial properties are lacking; most traditional BOPA films do not contain antibacterial components, resulting in poor antibacterial durability, easy bacterial migration into the food, and insufficient safety, failing to effectively guarantee food hygiene. Third, their mechanical properties are uneven, with significant differences in longitudinal and transverse tensile strength and a high heat shrinkage rate, making them prone to packaging deformation and damage, affecting the sealing and integrity of the food packaging. Fourth, their manufacturing processes are limited; traditional biaxial stretching often uses mechanical synchronous stretching, which has poor flexibility in adjusting the stretching ratio, making it difficult to accurately control the crystallization and orientation structure of the film, and resulting in low production efficiency and high energy consumption. In addition, existing film casting processes often use electrostatic bonding technology, which is prone to film puncture during high-speed production, limiting the speed of the production line and making it difficult to adapt to the needs of large-scale industrial production of food packaging.

[0004] Currently, although there are attempts in the industry to improve the performance of BOPA films used in food packaging by adding barrier agents or antibacterial agents, these efforts often result in improvements in a single property while leading to an imbalance in overall performance. For example, adding too many barrier agents can reduce the toughness of the film and make it brittle, while adding organic antibacterial agents poses a food safety risk. At the same time, existing modification technologies have not fully resolved the compatibility issues between nanomaterials and nylon 6 resin, which can easily lead to the aggregation of nanoparticles, affecting the transparency and mechanical properties of the film and failing to meet the requirements for food packaging. Summary of the Invention

[0005] The purpose of this invention is to provide an antibacterial and fresh-locking nylon film for food packaging and its preparation method. By innovatively introducing two functional inorganic modified compounds and leveraging their synergistic effect, the antibacterial, fresh-locking, and high-strength properties of the nylon film are synergistically improved. At the same time, a green, efficient, and stable preparation method is provided to meet the needs of various food fresh-locking packaging and the requirements of industrial production.

[0006] To achieve the above objectives, the solution of the present invention is: A nylon film for food packaging with antibacterial and freshness-locking properties, comprising, by weight, the following raw materials: 70-85 parts PA6 resin, 3-8 parts inorganic modified compound, 5-12 parts EVOH barrier agent, 4-9 parts composite toughening agent, 0.3-0.8 parts antioxidant, and 0.5-1.2 parts lubricant. The inorganic modified compound comprises nano zinc oxide-silver@polyboronsiloxane core-shell antibacterial and deodorizing agent (ZnO-Ag@PBSiO2) and modified organomontmorillonite-hyperbranched polyboronsiloxane hybrid (OMMT-HPBSi) in a mass ratio of 1-2:1. The composite toughening agent comprises maleic anhydride grafted polyolefin elastomer (POE-g-MAH) and nano calcium carbonate in a mass ratio of 2-4:1.

[0007] The PA6 resin has a relative viscosity of 2.4~2.8 and a moisture content of ≤0.05%. PA6 resin with these parameters has good melt processing performance and mechanical properties, which can provide excellent tensile strength and toughness for nylon films used in food packaging, while reducing defects such as bubbles and brittleness caused by moisture during processing, and ensuring the airtightness of food packaging.

[0008] The EVOH barrier agent has an ethylene content of 32% to 44%. EVOH (ethylene-vinyl alcohol copolymer) has excellent oxygen barrier properties. It works synergistically with the synthesized inorganic modified compounds to form a dual barrier system, which significantly improves the oxygen and water vapor barrier properties of the film, solving the problems of insufficient barrier properties and poor freshness retention of traditional food packaging films. At the same time, EVOH with this ethylene content has good compatibility with PA6 resin and will not cause a decrease in film toughness, ensuring that the film is not easily damaged during food packaging.

[0009] The composite toughening agent comprises maleic anhydride-grafted polyolefin elastomer (POE-g-MAH) and nano-calcium carbonate in a mass ratio of 2-4:1, wherein the nano-calcium carbonate has a particle size of 20 nm. Traditional single toughening agents either only improve toughness, resulting in a decrease in strength, or only improve strength but lack sufficient toughness, failing to meet the stretching and transportation requirements of food packaging. This invention uses a combination of elastomer and inorganic particles. POE-g-MAH can react with PA6 resin, improving compatibility and significantly enhancing the toughness and impact resistance of the film, preventing film brittleness. Nano-calcium carbonate can enhance the tensile strength and hardness of the film. The combination of the two can achieve a synergistic improvement in film strength and toughness, avoiding the performance imbalance caused by a single toughening agent. At the same time, nano-calcium carbonate can also help improve the barrier properties of the film, further enhancing the freshness-locking effect of food.

[0010] The antioxidant is antioxidant 1010 and / or antioxidant 1076. The antioxidant can prevent the film from undergoing oxidative degradation during high-temperature melting and processing, avoid yellowing of the film and decline in mechanical properties, improve product stability and service life, and ensure the safety of food packaging.

[0011] The lubricant is calcium stearate and / or ethylene bis-stearamide, which can improve the processing fluidity of the raw material, reduce the friction force on the raw material during extrusion and stretching, avoid defects such as scratches and roughness on the film surface, and facilitate the winding and cutting of the film, thus meeting the high-speed processing requirements of food packaging.

[0012] A method for preparing an antibacterial and freshness-locking nylon film for food packaging includes the following steps: Step 1, Raw material pretreatment: First, 70-85 parts of PA6 resin are vacuum dried at 80-100℃ for 4-6 hours with a vacuum degree of -0.08 to -0.09 MPa. Then, 3-8 parts of inorganic modifying compound, 5-12 parts of EVOH barrier agent, 4-9 parts of composite toughening agent, 0.3-0.8 parts of antioxidant and 0.5-1.2 parts of lubricant are added into a high-speed mixer in proportion and stirred for 10-15 minutes at 100-120℃ and 800-1000 r / min until uniformly mixed to obtain the mixed raw material. Step 2, Extrusion Granulation: The mixed raw materials are then fed into a twin-screw extruder for melt extrusion. The barrel temperature of the twin-screw extruder is 230℃, 235℃, 240℃, 245℃ and 250℃ from the feed section to the die head. The screw speed is 200~300 r / min. After melt extrusion, the material is pelletized by a pelletizer to a pellet size of 2~3 mm × 2~3 mm to obtain modified PA6 masterbatch. The modified PA6 masterbatch is then dried at 80℃ for 2~3 h. Step 3, casting: The modified PA6 masterbatch is then fed into a single-screw extruder for melt plasticization. The barrel temperature of the single-screw extruder is 230~245℃. After melt plasticization, the material is extruded through a T-die at an extrusion temperature of 240~250℃ and a die gap of 0.8~1.2 mm. The material is then cooled and shaped by a cooling roller at a temperature of 20~30℃ to obtain a sheet with a thickness of 0.8~1.2 mm. During the cooling process, an air knife bonding device is used with an air knife pressure of 0.3~0.5 MPa and a distance of 5~8 mm between the air knife and the surface of the cooling roller. High-speed, uniform airflow is used to press the sheet onto the surface of the cooling roller in a contactless and efficient manner. Step 4, Biaxial stretching: Then, a magnetically driven linear synchronous stretching device was used to stretch the thick sheet longitudinally and transversely. The longitudinal stretching temperature was 70~80℃, the stretching ratio was 2.5~3.5, and the stretching speed was 5~8 m / min. The transverse stretching temperature was 85~95℃, the stretching ratio was 3.0~4.0, and the stretching speed was 8~12 m / min. After stretching, heat setting was performed at a temperature of 120~140℃ for 3~5 s. After heat setting, the film was cooled to room temperature to obtain the thin film. Step 5: Roll up and cut: The heat-set film is then pulled by a traction machine with the traction speed matching the stretching speed and the traction tension being 50~80 N. During the traction process, an electrostatic eliminator is used to remove static electricity from the film surface. The film is then wound up by a winding machine with a winding speed of 10~15 m / min and a winding tension of 30~50 N. After winding, the film is cut to the specified size by a precision cutting machine to obtain the finished product.

[0013] In step 1, the inorganic modified compound includes a nano-zinc oxide-silver@polyborosiloxane core-shell antibacterial and deodorizing agent (ZnO-Ag@PBSiO2) and a modified organomontmorillonite-hyperbranched polyborosiloxane hybrid (OMMT-HPBSi) in a mass ratio of 1~2:1. ZnO-Ag@PBSiO2 provides long-lasting antibacterial and deodorizing functions; its core-shell structure prevents the migration and loss of internal antibacterial components, while maintaining antibacterial activity through a porous shell, ensuring food hygiene and safety. OMMT-HPBSi provides highly efficient barrier functions; its layered structure forms a dense barrier network with PA6 resin, blocking oxygen and water vapor penetration, enhancing the freshness-locking effect of food, and optimizing the interfacial bonding force within the film, improving mechanical properties and dimensional stability. Both compounds have excellent compatibility with PA6 resin and can be uniformly dispersed in the matrix, avoiding nanoparticle aggregation and ensuring the transparency and overall performance of the film.

[0014] The preparation method of ZnO-Ag@PBSiO2 is as follows: First, 0.2~1 g of nano zinc oxide is dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed until a uniform dispersion is formed. Then, silver nitrate solution is slowly added dropwise to the dispersion at a mass ratio of nano zinc oxide to silver nitrate of 5:1~10:1. After stirring evenly, the mixture is irradiated under ultraviolet light for 30~60 min to reduce silver nitrate with ultraviolet light assistance, thus obtaining ZnO-Ag composite particles. Subsequently, an alkaline catalyst, ammonia or sodium hydroxide, is added to the system to adjust the pH to 9~11. Ethyl borosilicate (BEOS) is slowly added dropwise, controlling the mass ratio of BEOS to ZnO-Ag composite particles to be 1:2~1:4. The mixture is stirred and reacted at 30~50℃ for 2~4 h to allow BEOS to undergo a hydrolysis-condensation reaction, coating the surface of the ZnO-Ag composite particles with a porous borosilicate oxide shell. After the reaction, the mixture is subjected to 5000~8000... The ZnO-Ag@PBSiO2 was obtained by centrifugation at a speed of r / min, washing with deionized water 3-5 times, and vacuum drying at 80-100℃ for 2-3 h. This core-shell structure can prevent the internal ZnO and Ag antibacterial components from migrating into the food, ensuring safety, and also allows microorganisms to fully contact the antibacterial components through the porous shell, maintaining long-lasting antibacterial activity. In subsequent film processing, the ZnO-Ag@PBSiO2 particles are encapsulated by a nylon matrix and EVOH. The two ends of this porous structure are sealed, forming a nanoscale non-permeable pore structure. This can effectively reduce the permeation rate of small molecules by extending the diffusion path of gas and water molecules, forming a physical shielding layer, and increasing adsorption sites, thereby helping to improve the barrier performance of the film and enhance the freshness-locking effect.

[0015] The preparation method of the OMMT-HPBSi is as follows: first, add organomontmorillonite to a mass fraction of 5 wt %~10 wt In a % hydrochloric acid solution, the mixture was stirred and activated at 60-80℃ for 2-3 h. After filtration and washing until neutral, the activated organomontmorillonite was obtained by vacuum drying. Then, using trimethylolpropane (TMP) as the core initiator, triethyl borate (TEB) as the boron source, and γ-glycidoxypropyltrimethoxysilane (KH-560) as the silicon source, anhydrous ethanol was added as a solvent at a mass ratio of TMP:TEB:KH-560 = 1:3-5:5-8. The mass of anhydrous ethanol was 3-5 times the total mass of TMP, TEB, and KH-560. Dibutyltin dilaurate (DBTDL) was used as a catalyst in the anhydrous ethanol solvent, with the mass of DBTDL being 0.5% of the total mass of TMP, TEB, and KH-560. wt %-1.0 wt The reaction mixture was stirred at 60-80℃ for 8-12 h. After the reaction, the solvent was removed by vacuum distillation at a vacuum degree of -0.07 to -0.08 MPa and a temperature of 70-80℃. The mixture was then vacuum dried at 80-100℃ for 2-3 h to obtain hyperbranched polyborosiloxane (HPBSi). This hyperbranched polyborosiloxane possesses a large number of active functional groups, which can form stable chemical bonds with organomontmorillonite sheets, while simultaneously improving compatibility with PA6 resin. Its branched structure can further optimize the barrier and mechanical properties of the film. The hyperbranched polyborosiloxane (HPBSi) was then dissolved in... N , N In dimethylformamide, HPBSi and N , N The mass ratio of dimethylformamide is 1:9 to 1:19. Activated organomontmorillonite is added, and the mass ratio of HPBSi to activated organomontmorillonite is 1:3 to 1:5. The mixture is stirred at 80 to 100 °C for 4 to 6 h to graft hyperbranched polyborosiloxane onto the surface of organomontmorillonite sheets. After the reaction, the mixture is centrifuged at 4000 to 6000 r / min for 15 to 30 min, washed, and vacuum dried to obtain OMMT-HPBSi. The layered structure of this hybrid can form a "labyrinthine" barrier channel in the PA6 matrix, significantly extending the permeation path of oxygen and water vapor and improving the barrier performance of the film. At the same time, the hyperbranched polyborosiloxane can improve the compatibility between organomontmorillonite and PA6 resin, avoid sheet aggregation, and further optimize the mechanical properties and transparency of the film.

[0016] The cooling process in step 4 is segmented cooling. The cooling temperature of the first segment is 80~90℃, the cooling temperature of the second segment is 40~50℃, and the cooling temperature of the third segment is 25~30℃.

[0017] During the winding process in step 5, an additive of 0.1% of the total mass of the nylon film can be added. wt %~0.3 wt % anti-stick masterbatch, which is a silica-based anti-stick masterbatch known in the art, mainly functions to reduce the surface adhesion of nylon film and improve the neatness and opening of winding.

[0018] After adopting the above technical solution, the antibacterial and freshness-locking nylon film for food packaging and its preparation method of the present invention have the following beneficial effects: 1. This invention innovatively introduces a composite system of nano zinc oxide-silver@polyboronsiloxane core-shell antibacterial and deodorizing agent (ZnO-Ag@PBSiO2) and modified organomontmorillonite-hyperbranched polyboronsiloxane hybrid (OMMT-HPBSi). The two play a synergistic role in "long-lasting antibacterial" and "high-efficiency barrier". Combined with EVOH barrier agent, composite toughening agent and other auxiliary agents, it achieves a comprehensive improvement in the film's antibacterial, high barrier (freshness lock), high strength, high transparency and dimensional stability. 2. The two functional inorganic modified compounds can achieve good compatibility with PA6 resin and other raw materials, avoiding problems such as decreased film transparency and deterioration of mechanical properties caused by nanoparticle aggregation. At the same time, the core-shell structure of ZnO-Ag@PBSiO2 can prevent the migration of antibacterial components and improve food safety, while the layered structure of OMMT-HPBSi can enhance the barrier effect and extend the shelf life of food. The introduction of hyperbranched polyborosiloxane (HPBSi) further optimizes the compatibility between the hybrid and the matrix, while improving the barrier and mechanical properties of the film. 3. The magnetically driven linear synchronous stretching equipment is used. Compared with the traditional mechanical stretching, the stretching ratio adjustment is more flexible and precise, which can significantly reduce the transverse and longitudinal shrinkage of the film and improve the dimensional stability of the product. The entire preparation process is clear and the parameters are controllable. It has high production efficiency and low energy consumption. No complex equipment modification is required. It can be directly adapted to existing industrial production lines, which is convenient for large-scale promotion and application and reduces the production cost of enterprises.

[0019] This invention discloses an antibacterial and freshness-locking nylon film for food packaging and its preparation method. Through formula optimization and film structure design, combined with advanced preparation technology, two inorganic modified compounds are introduced to exert a synergistic effect, resulting in a film with excellent comprehensive performance, especially suitable for high-end food packaging with high requirements for freshness preservation and antibacterial properties. Detailed Implementation

[0020] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0021] Example 1 1. Preparation of ZnO-Ag@PBSiO2 First, 0.2 g of nano-zinc oxide was dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed until a uniform dispersion was formed. Then, silver nitrate solution was slowly added dropwise to the dispersion at a mass ratio of nano-zinc oxide to silver nitrate of 8:1. After stirring evenly, the mixture was irradiated under ultraviolet light at a wavelength of 254 nm and a power of 300 W for 45 min to reduce silver nitrate with ultraviolet light assistance, thus obtaining ZnO-Ag composite particles. Subsequently, ammonia water was added to the system to adjust the pH to 10, and BEOS was slowly added dropwise, controlling the mass ratio of BEOS to ZnO-Ag composite particles to be 1:3. The mixture was stirred at 40 °C for 3 h to allow BEOS to undergo a hydrolysis-condensation reaction, coating the surface of the ZnO-Ag composite particles with a porous borosilicate oxide shell. After the reaction was completed, the mixture was centrifuged at 6000 r / min for 15 min, washed three times with deionized water, and finally vacuum dried at 90 °C for 2.5 h to obtain ZnO-Ag@PBSiO2.

[0022] 2. Preparation of OMMT-HPBSi First, add the organic montmorillonite to 8 wt In a % hydrochloric acid solution, the organomontmorillonite was activated by stirring at 70℃ for 2.5 h. Impurities on the surface of the organomontmorillonite were removed by acid washing to increase its specific surface area and reactivity. After filtration and washing with deionized water until neutral, it was vacuum dried at 80℃ for 5 h to obtain activated organomontmorillonite. Then, using TMP as the core initiator, TEB as the boron source, and KH-560 as the silicon source, at a mass ratio of TMP:TEB:KH-560 = 1:4:6, DBTDL was used as the catalyst in anhydrous ethanol solvent. The mass of anhydrous ethanol was 4 times the total mass of TMP, TEB, and KH-560, and the amount of DBTDL was 0.8 times the total mass of TMP, TEB, and KH-560. wt The reaction mixture was stirred at 70℃ for 10 h. After the reaction was completed, the solvent was removed by vacuum distillation (vacuum degree -0.075MPa, temperature 75℃), and then dried under vacuum at 90℃ for 2.5 h to obtain a pale yellow, transparent, viscous HPBSi. The HPBSi was then dissolved in... N , N In dimethylformamide, HPBSi and N , NThe mass ratio of dimethylformamide was 1:9, and activated organomontmorillonite was added. The mass ratio of HPBSi to activated organomontmorillonite was 1:4. The mixture was stirred at 90 °C for 5 h to graft hyperbranched polyborosiloxane onto the surface of organomontmorillonite sheets. After the reaction, the mixture was centrifuged at 4000 r / min for 30 min, and then ultrasonically washed twice with sufficient DMF, anhydrous ethanol, and deionized water. The final ultrasonic wash was performed once with anhydrous ethanol for 10 min each time. Finally, the mixture was dried at 70 °C under a vacuum of 0.08 MPa for 12 h to obtain OMMT-HPBSi.

[0023] 3. Preparation of antibacterial and freshness-locking nylon film for food packaging A method for preparing an antibacterial and freshness-locking nylon film for food packaging includes the following steps: Step 1, Raw material pretreatment: First, 75 parts of PA6 resin (relative viscosity 2.6, water content 0.04%) were vacuum dried at 90℃ for 5 h with a vacuum degree of -0.085 MPa. Then, 3 parts of ZnO-Ag@PBSiO2, 2 parts of OMMT-HPBSi, 8 parts of EVOH barrier agent, 4 parts of POE-g-MAH, 2 parts of nano-calcium carbonate with a particle size of 20 nm, 0.5 parts of antioxidant 1010 and 0.8 parts of calcium stearate were added to a high-speed mixer in proportion and stirred at 110℃ and 900 r / min for 12 min until uniformly mixed to obtain the mixed raw material. Step 2, Extrusion Granulation: The mixed raw materials were then fed into a twin-screw extruder for melt extrusion. The barrel temperature of the twin-screw extruder was 230℃, 235℃, 240℃, 245℃, and 250℃ from the feed section to the die head. The screw speed was 250 r / min. After melt extrusion, the material was pelletized by a pelletizer to a pellet size of 2.5 mm × 2.5 mm to obtain modified PA6 masterbatch. The modified PA6 masterbatch was then dried at 80℃ for 2.5 h. Step 3, casting: The modified PA6 masterbatch was then fed into a single-screw extruder for melt plasticization. The barrel temperature of the single-screw extruder was 238℃. After melt plasticization, the material was extruded through a T-die at an extrusion temperature of 245℃ and a die gap of 1.0 mm. The material was then cooled and shaped by cooling rollers at a temperature of 25℃, resulting in a sheet with a thickness of 1.0 mm. During the cooling process, an air knife bonding device was used with an air knife pressure of 0.4 MPa and a distance of 6 mm between the air knife and the surface of the cooling roller. Step 4, Biaxial stretching: Then, a magnetically driven linear synchronous stretching device was used to stretch the thick sheet longitudinally and transversely. The longitudinal stretching temperature was 75℃, the stretching ratio was 3.0, and the stretching speed was 6.5 m / min. The transverse stretching temperature was 90℃, the stretching ratio was 3.5, and the stretching speed was 10 m / min, with a stretching rate difference of 0.3 m / min. After stretching, heat setting was performed at 130℃ for 4 s. After heat setting, the film was cooled in stages (the first stage was cooled at 85℃, the second stage at 45℃, and the third stage at 28℃) to room temperature to obtain the film. Step 5: Roll up and cut: The heat-set film is then pulled by a traction machine with the traction speed matched to the stretching speed. The traction tension is 65 N and the traction speed is 10 m / min. During the traction process, an electrostatic eliminator is used to remove static electricity from the film surface. The film is then wound up by a winding machine with a winding speed of 12 m / min and a winding tension of 40 N. During winding, an anti-sticking masterbatch of 0.2% of the total mass of the nylon film is added. After winding, the film is cut to the specified size by a precision cutting machine to obtain the finished product.

[0024] Example 2 1. Preparation of ZnO-Ag@PBSiO2 First, 0.6 g of nano-zinc oxide was dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed until a uniform dispersion was formed. Then, silver nitrate solution was slowly added dropwise to the dispersion at a mass ratio of nano-zinc oxide to silver nitrate of 8:1. After stirring evenly, the mixture was irradiated under ultraviolet light at a wavelength of 254 nm and a power of 300 W for 45 min to reduce silver nitrate with ultraviolet light assistance, thus obtaining ZnO-Ag composite particles. Subsequently, ammonia water was added to the system to adjust the pH to 10, and BEOS was slowly added dropwise, controlling the mass ratio of BEOS to ZnO-Ag composite particles to be 1:3. The mixture was stirred at 40 °C for 3 h to allow BEOS to undergo a hydrolysis-condensation reaction, coating the surface of the ZnO-Ag composite particles with a porous borosilicate oxide shell. After the reaction was completed, the mixture was centrifuged at 6000 r / min for 15 min, washed three times with deionized water, and finally vacuum dried at 90 °C for 2.5 h to obtain ZnO-Ag@PBSiO2.

[0025] 2. Preparation of OMMT-HPBSi First, add the organic montmorillonite to 5 wt In a % hydrochloric acid solution, the organomontmorillonite was activated by stirring at 60℃ for 3.0 h. Impurities on the surface of the organomontmorillonite were removed by acid washing to increase its specific surface area and reactivity. After filtration and washing with deionized water until neutral, it was vacuum dried at 80℃ for 6 h to obtain activated organomontmorillonite. Then, using TMP as the core initiator, TEB as the boron source, and KH-560 as the silicon source, at a mass ratio of TMP : TEB : KH-560 = 1 : 3 : 5, in anhydrous ethanol solvent, with DBTDL as the catalyst, the mass of anhydrous ethanol being 3 times the total mass of TMP, TEB, and KH-560, and the amount of DBTDL being 0.5 times the total mass of TMP, TEB, and KH-560. wt The reaction mixture was stirred at 60℃ for 12 h. After the reaction was completed, the solvent was removed by vacuum distillation (vacuum degree -0.07 MPa, temperature 70℃), and then dried under vacuum at 80℃ for 3.0 h to obtain a pale yellow, transparent, viscous HPBSi. The HPBSi was then dissolved in... N , N In dimethylformamide, HPBSi and N , N The mass ratio of dimethylformamide was 1:15, and activated organomontmorillonite was added. The mass ratio of HPBSi to activated organomontmorillonite was 1:3. The mixture was stirred at 80 °C for 6 h to graft hyperbranched polyborosiloxane onto the surface of organomontmorillonite sheets. After the reaction, the mixture was centrifuged at 5000 r / min for 20 min, and then ultrasonically washed twice with sufficient DMF, anhydrous ethanol, and deionized water. The final ultrasonic wash was performed once with anhydrous ethanol for 10 min each time. Finally, the mixture was dried at 70 °C under a vacuum of 0.08 MPa for 12 h to obtain OMMT-HPBSi.

[0026] 3. Preparation of antibacterial and freshness-locking nylon film for food packaging A method for preparing an antibacterial and freshness-locking nylon film for food packaging includes the following steps: Step 1, Raw material pretreatment: First, 70 parts of PA6 resin (relative viscosity 2.4, water content 0.05%) were vacuum dried at 80℃ for 6 h with a vacuum degree of -0.08 MPa. Then, 3 parts of ZnO-Ag@PBSiO2, 1.5 parts of OMMT-HPBSi, 5 parts of EVOH barrier agent, 3 parts of POE-g-MAH, 1 part of nano-calcium carbonate with a particle size of 20 nm, 0.3 parts of antioxidant 1076 and 0.5 parts of ethylene bis-stearamide were added to a high-speed mixer in proportion and stirred at 100℃ and 800 r / min for 15 min until uniformly mixed to obtain the mixed raw material. Step 2, Extrusion Granulation: The mixed raw materials were then fed into a twin-screw extruder for melt extrusion. The barrel temperature of the twin-screw extruder was 230℃, 235℃, 240℃, 245℃, and 250℃ from the feed section to the die head. The screw speed was 200 r / min. After melt extrusion, the material was pelletized by a pelletizer to a pellet size of 2.0 mm × 2.0 mm to obtain modified PA6 masterbatch. The modified PA6 masterbatch was then dried at 80℃ for 3.0 h. Step 3, casting: The modified PA6 masterbatch was then fed into a single-screw extruder for melt plasticization. The barrel temperature of the single-screw extruder was 230℃. After melt plasticization, the material was extruded through a T-die at an extrusion temperature of 240℃ and a die gap of 0.8 mm. The material was then cooled and shaped by cooling rollers at a temperature of 20℃, resulting in a sheet with a thickness of 0.8 mm. During the cooling process, an air knife bonding device was used with an air knife pressure of 0.3 MPa and a distance of 5 mm between the air knife and the surface of the cooling roller. Step 4, Biaxial stretching: Then, a magnetically driven linear synchronous stretching device was used to stretch the thick sheet longitudinally and transversely. The longitudinal stretching temperature was 70℃, the stretching ratio was 2.5, and the stretching speed was 5.0 m / min. The transverse stretching temperature was 85℃, the stretching ratio was 3.0, and the stretching speed was 8 m / min, with a stretching rate difference of 0.2 m / min. After stretching, heat setting was performed at 120℃ for 5 s. After heat setting, the film was cooled in stages (the first stage was cooled at 80℃, the second stage at 40℃, and the third stage at 25℃) to room temperature to obtain the film. Step 5: Roll up and cut: The heat-set film is then pulled by a traction machine with the traction speed matched to the stretching speed. The traction tension is 50 N and the traction speed is 8 m / min. During the traction process, an electrostatic eliminator is used to remove static electricity from the film surface. The film is then wound up by a winding machine with a winding speed of 10 m / min and a winding tension of 30 N. During winding, 0.1% of anti-stick masterbatch (based on the total mass of the nylon film) is added. After winding, the film is cut to the specified size using a precision cutting machine to obtain the finished product.

[0027] Example 3 1. Preparation of ZnO-Ag@PBSiO2 First, 1g of nano-zinc oxide was dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed until a uniform dispersion was formed. Then, silver nitrate solution was slowly added dropwise to the dispersion at a mass ratio of nano-zinc oxide to silver nitrate of 8:1. After stirring evenly, the mixture was irradiated under ultraviolet light at a wavelength of 254 nm and a power of 300 W for 45 min to reduce silver nitrate with ultraviolet light assistance, thus obtaining ZnO-Ag composite particles. Subsequently, ammonia water was added to the system to adjust the pH to 10, and BEOS was slowly added dropwise, controlling the mass ratio of BEOS to ZnO-Ag composite particles to be 1:3. The mixture was stirred at 40℃ for 3 h to allow BEOS to undergo a hydrolysis-condensation reaction, coating the surface of the ZnO-Ag composite particles with a porous borosilicate oxide shell. After the reaction was completed, the mixture was centrifuged at 6000 r / min for 15 min, washed three times with deionized water, and finally vacuum dried at 90℃ for 2.5 h to obtain ZnO-Ag@PBSiO2.

[0028] 2. Preparation of OMMT-HPBSi First, add 10% organomontmorillonite. wt In a % hydrochloric acid solution, the organomontmorillonite was activated by stirring at 80℃ for 2.0 h. Impurities on the surface of the organomontmorillonite were removed by acid washing to increase its specific surface area and reactivity. After filtration and washing with deionized water until neutral, it was vacuum dried at 80℃ for 4 h to obtain activated organomontmorillonite. Then, using TMP as the core initiator, TEB as the boron source, and KH-560 as the silicon source, at a mass ratio of TMP : TEB : KH-560 = 1 : 5 : 8, in anhydrous ethanol solvent, with DBTDL as the catalyst, the mass of anhydrous ethanol was 5 times the total mass of TMP, TEB, and KH-560, and the amount of DBTDL was 1.0 times the total mass of TMP, TEB, and KH-560. wt The reaction mixture was stirred at 80℃ for 8 h. After the reaction was completed, the solvent was removed by vacuum distillation (vacuum degree -0.08MPa, temperature 80℃), and then dried under vacuum at 100℃ for 2.0 h to obtain a pale yellow, transparent, viscous HPBSi. The HPBSi was then dissolved in... N , N In dimethylformamide, HPBSi and N , NThe mass ratio of dimethylformamide was 1:19, and activated organomontmorillonite was added. The mass ratio of HPBSi to activated organomontmorillonite was 1:5. The mixture was stirred at 100℃ for 4 h to graft hyperbranched polyborosiloxane onto the surface of organomontmorillonite sheets. After the reaction, the mixture was centrifuged at 6000 r / min for 15 min, and then ultrasonically washed twice with sufficient DMF, anhydrous ethanol, and deionized water. The final ultrasonic wash was performed once with anhydrous ethanol, with each ultrasonic wash lasting 10 min. Finally, the mixture was dried at 70℃ under a vacuum of 0.08 MPa for 12 h to obtain OMMT-HPBSi.

[0029] 3. Preparation of antibacterial and freshness-locking nylon film for food packaging A method for preparing an antibacterial and freshness-locking nylon film for food packaging includes the following steps: Step 1, Raw material pretreatment: First, 85 parts of PA6 resin (relative viscosity 2.8, water content 0.03%) were vacuum dried at 100℃ for 4 h with a vacuum degree of -0.09 MPa. Then, 5.3 parts of ZnO-Ag@PBSiO2, 2.7 parts of OMMT-HPBSi, 12 parts of EVOH barrier agent, 7 parts of POE-g-MAH, 2 parts of nano-calcium carbonate with a particle size of 20 nm, 0.4 parts of antioxidant 1076, 0.4 parts of antioxidant 1010, 0.6 parts of ethylene bis-stearamide, and 0.6 parts of calcium stearate were added to a high-speed mixer in proportion and stirred at 120℃ and 1000 r / min for 10 min until uniformly mixed to obtain the mixed raw material. Step 2, Extrusion Granulation: The mixed raw materials were then fed into a twin-screw extruder for melt extrusion. The barrel temperature of the twin-screw extruder was 230℃, 235℃, 240℃, 245℃, and 250℃ from the feed section to the die head. The screw speed was 300 r / min. After melt extrusion, the material was pelletized by a pelletizer to a pellet size of 3.0 mm × 3.0 mm to obtain modified PA6 masterbatch. The modified PA6 masterbatch was then dried at 80℃ for 2.0 h. Step 3, casting: The modified PA6 masterbatch was then fed into a single-screw extruder for melt plasticization. The barrel temperature of the single-screw extruder was 245℃. After melt plasticization, the material was extruded through a T-die at an extrusion temperature of 250℃ and a die gap of 1.2 mm. The material was then cooled and shaped by cooling rollers at a temperature of 30℃, resulting in a sheet with a thickness of 1.2 mm. During the cooling process, an air knife bonding device was used with an air knife pressure of 0.5 MPa and a distance of 8 mm between the air knife and the surface of the cooling roller. Step 4, Biaxial stretching: Then, a magnetically driven linear synchronous stretching device was used to stretch the thick sheet longitudinally and transversely. The longitudinal stretching temperature was 80℃, the stretching ratio was 3.5, and the stretching speed was 8.0 m / min. The transverse stretching temperature was 95℃, the stretching ratio was 4.0, and the stretching speed was 12 m / min, with a stretching rate difference of 0.5 m / min. After stretching, heat setting was performed at 140℃ for 3 seconds. After heat setting, the sheet was cooled in stages (the first stage was cooled at 90℃, the second stage at 50℃, and the third stage at 30℃) to room temperature to obtain the film. Step 5: Roll up and cut: The heat-set film is then pulled by a traction machine with the traction speed matched to the stretching speed. The traction tension is 80 N and the traction speed is 12 m / min. During the traction process, an electrostatic eliminator is used to remove static electricity from the film surface. The film is then wound up by a winding machine with a winding speed of 15 m / min and a winding tension of 50 N. During winding, 0.3% of the total mass of the nylon film as anti-stick masterbatch is added. After winding, the film is cut to the specified size by a precision cutting machine to obtain the finished product.

[0030] Comparative Example 1 The difference from Example 1 is that in step 1 of the preparation method of the antibacterial and freshness-locking nylon film for food packaging in Comparative Example 1, OMMT-HPBSi is not added, and the amount of ZnO-Ag@PBSiO2 is replaced with 5 parts. The other steps are the same as in Example 1.

[0031] Comparative Example 2 The difference from Example 1 is that in step 1 of the preparation method of the antibacterial and freshness-locking nylon film for food packaging in Comparative Example 2, ZnO-Ag@PBSiO2 is not added, and the amount of OMMT-HPBSi is replaced with 5 parts. The other steps are the same as in Example 1.

[0032] The raw materials used in the above examples and comparative examples are all commercially available products. PA 6 resin was purchased from Evonik Specialty Chemicals; EVOH barrier agent was Kuraray EVAL™ SP521B (Japan); POE-g-MAH was Dow FUSABOND™ N598 (USA); KH-560 was purchased from Jiangxi Chenguang New Material Co., Ltd.; antioxidants 1010 and 1076 were purchased from Tianjin Lianlong New Material Co., Ltd.; the lubricants calcium stearate and ethylene bis-stearamide were purchased from Croda Chemicals (Shanghai) Co., Ltd.; and nano zinc oxide (particle size 30 mm) was used. The following materials were purchased: 1 nm (99.5% purity) from Lutai Nanomaterials; 99.9% silver nitrate from Jiangxi Copper; 99.5% trimethylolpropane (TMP) from Baichuan Chemical; 1 ethyl borosilicate (BEOS) from Intergol Chemicals, Inc.; 99.0% triethyl borate from Haiyakai Chemical; 99% dibutyltin dilaurate (DBTDL) from Shandong Yukang Chemical; and 1.30PS organomontmorillonite from Nanocor Nanomer, Inc., USA. N , N - Dimethylformamide (DMF) (99.9% purity) was purchased from BASF; nano-calcium carbonate (particle size 20 nm, specific surface area 20 m² / g) was selected from Guangxi Huana Triangle brand; anti-sticking masterbatch was purchased from Hubei Fusite Materials Technology Co., Ltd.

[0033] The equipment used in the above embodiments and comparative examples, such as high-speed mixers, twin-screw extruders, single-screw extruders, air knife bonding equipment, magnetically driven linear synchronous stretching equipment, heat setting equipment, traction machines, winding machines, and precision cutting machines, are all well-known in the art.

[0034] Performance testing: The performance of the nylon films for food packaging prepared in Examples 1-3 and Comparative Examples 1-2 was tested. The test standards and results are shown in Table 1 (wherein the antibacterial performance test was conducted using a bacterial strain concentration of 10). 6 CFU / mL, contact time 24 h).

[0035] Table 1. Performance of Nylon Film for Food Packaging

[0036] The beneficial effects of this invention can be seen from the above performance test data: 1. The nylon films prepared in Examples 1-3 have tensile strengths of 237-241 MPa, elongation at break of 367%-383%, and puncture resistance of 18.7-20.3 N / μm. Compared with Comparative Examples 1 and 2, which only added one of the inorganic modifying compounds, the mechanical strengths are significantly improved, indicating that the synergistic effect of the two compounds can effectively disperse stress, strengthen interfacial bonding, and significantly improve the mechanical properties of the film. 2. The oxygen and water vapor permeability of the nylon films prepared in Examples 1-3 and Comparative Example 2 (which only added OMMT-HPBSi) were much lower than those in Comparative Example 1 (without OMMT-HPBSi). This indicates that the dual barrier system formed by the two-dimensional nano barrier material and the EVOH barrier agent can effectively block the penetration of oxygen and water vapor and enhance the freshness-preserving effect of food. 3. The antibacterial rate of the nylon films prepared in Examples 1-3 and Comparative Example 1 all reached over 99%, indicating that the synthesized inorganic antibacterial agent can stably exert a long-lasting antibacterial effect and ensure food packaging safety.

[0037] 4. The haze of the nylon films prepared in Examples 1-3 was 2.6%-3.2%, all ≤3.5%, maintaining excellent transparency. This proves that the two inorganic modified compounds have excellent compatibility with PA6 resin, with no obvious agglomeration phenomenon, which can make the film dimensional stability better, effectively avoid packaging deformation, and meet the needs of high-speed packaging processing.

[0038] In summary, through formula optimization and process innovation, this invention achieves a comprehensive and synergistic improvement in the film's antibacterial, high barrier, high strength, high transparency, and dimensional stability properties, fully meeting the needs of various food freshness-locking packaging. Furthermore, the preparation process is suitable for large-scale industrial production and has good application value.

[0039] The above embodiments are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.

Claims

1. A nylon film for food packaging with antibacterial and freshness-locking properties, characterized in that: The raw materials, by weight, include the following amounts: 70-85 parts PA6 resin, 3-8 parts inorganic modifying compound, 5-12 parts EVOH barrier agent, 4-9 parts composite toughening agent, 0.3-0.8 parts antioxidant, and 0.5-1.2 parts lubricant. The inorganic modifying compound includes ZnO-Ag@PBSiO2 and OMMT-HPBSi in a mass ratio of 1-2:

1. The composite toughening agent includes POE-g-MAH and nano-calcium carbonate in a mass ratio of 2-4:

1.

2. The antibacterial and freshness-locking nylon film for food packaging according to claim 1, characterized in that: The PA6 resin has a relative viscosity of 2.4~2.8 and a water content of ≤0.05%.

3. The antibacterial and freshness-locking nylon film for food packaging according to claim 1, characterized in that: The EVOH barrier has an ethylene content of 32% to 44%.

4. The antibacterial and freshness-locking nylon film for food packaging according to claim 1, characterized in that: The composite toughening agent comprises POE-g-MAH and nano-calcium carbonate in a mass ratio of 2~4:1, wherein the nano-calcium carbonate has a particle size of 20 nm.

5. The antibacterial and freshness-locking nylon film for food packaging according to claim 1, characterized in that: The antioxidant is antioxidant 1010 and / or antioxidant 1076.

6. The antibacterial and freshness-locking nylon film for food packaging according to claim 1, characterized in that: The lubricant is calcium stearate and / or ethylene bis-stearamide.

7. A method for preparing an antibacterial and freshness-locking nylon film for food packaging as described in claim 1, characterized in that: Includes the following steps: Step 1, Raw material pretreatment: First, 70-85 parts of PA6 resin are vacuum dried at 80-100℃ for 4-6 h with a vacuum degree of -0.08 to -0.09 MPa. Then, 3-8 parts of inorganic modifying compound, 5-12 parts of EVOH barrier agent, 4-9 parts of composite toughening agent, 0.3-0.8 parts of antioxidant and 0.5-1.2 parts of lubricant are added into a high-speed mixer in proportion and stirred at 100-120℃ and 800-1000 r / min for 10-15 min until uniformly mixed to obtain the mixed raw material. Step 2, Extrusion Granulation: The mixed raw materials are then fed into a twin-screw extruder for melt extrusion. The barrel temperature of the twin-screw extruder is 230℃, 235℃, 240℃, 245℃ and 250℃ from the feed section to the die head. The screw speed is 200~300 r / min. After melt extrusion, the material is pelletized by a pelletizer to a pellet size of 2~3 mm × 2~3 mm to obtain modified PA6 masterbatch. The modified PA6 masterbatch is then dried at 80℃ for 2~3 h. Step 3, casting: The modified PA6 masterbatch is then fed into a single-screw extruder for melt plasticization. The barrel temperature of the single-screw extruder is 230~245℃. After melt plasticization, it is extruded through a T-die at an extrusion temperature of 240~250℃ and a die gap of 0.8~1.2mm. It is then cooled and shaped by cooling rollers at a temperature of 20~30℃ to obtain sheets with a thickness of 0.8~1.2mm. During the cooling process, an air knife bonding device is used with an air knife pressure of 0.3~0.5 MPa and a distance of 5~8 mm between the air knife and the surface of the cooling roller. Step 4, Biaxial stretching: Then, a magnetically driven linear synchronous stretching device was used to stretch the thick sheet longitudinally and transversely. The longitudinal stretching temperature was 70~80℃, the stretching ratio was 2.5~3.5, and the stretching speed was 5~8 m / min. The transverse stretching temperature was 85~95℃, the stretching ratio was 3.0~4.0, and the stretching speed was 8~12 m / min. After stretching, heat setting was performed at a temperature of 120~140℃ for 3~5 s. After heat setting, the film was cooled to room temperature to obtain the thin film. Step 5: Roll up and cut: The heat-set film is then pulled by a traction machine with the traction speed matching the stretching speed and the traction tension being 50~80N. During the traction process, an electrostatic eliminator is used to remove static electricity from the film surface. The film is then wound up by a winding machine with a winding speed of 10~15m / min and a winding tension of 30~50N. After winding, the film is cut to the specified size by a precision cutting machine to obtain the finished product.

8. The method for preparing an antibacterial and freshness-locking nylon film for food packaging according to claim 7, characterized in that: In step 1, the inorganic modified compound includes ZnO-Ag@PBSiO2 and OMMT-HPBSi in a mass ratio of 1~2:

1. The preparation method of ZnO-Ag@PBSiO2 is as follows: First, 0.2~1.0 g of nano zinc oxide is dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed until a uniform dispersion is formed. Then, silver nitrate solution is slowly added dropwise to the dispersion at a mass ratio of nano zinc oxide to silver nitrate of 5:1~10:

1. After stirring evenly, the mixture is irradiated under ultraviolet light for 30~60 min to reduce silver nitrate with ultraviolet light assistance, thereby obtaining ZnO-Ag composite particles. Subsequently, an alkaline catalyst, ammonia or sodium hydroxide, is added to the system to adjust the pH to 9~11. BEOS is then slowly added dropwise, controlling the mass ratio of BEOS to ZnO-Ag composite particles to be 1:2~1:

4. The mixture is stirred and reacted at 30~50℃ for 2~4 minutes. h, to induce a hydrolysis-condensation reaction of BEOS, coating the surface of ZnO-Ag composite particles with a porous borosilicate oxide shell. After the reaction, the particles are centrifuged at 5000-8000 r / min for 15-30 min, washed 3-5 times with deionized water, and vacuum dried at 80-100℃ for 2-3 h to obtain the ZnO-Ag@PBSiO2; the preparation method of OMMT-HPBSi is as follows: first, add organomontmorillonite to a mass fraction of 5 wt %~10 wt In a % hydrochloric acid solution, the mixture was stirred and activated at 60-80℃ for 2-3 h. After filtration and washing until neutral, the activated organomontmorillonite was obtained by vacuum drying. Then, using TMP as the core initiator, TEB as the boron source, and KH-560 as the silicon source, anhydrous ethanol was added as a solvent at a mass ratio of TMP:TEB:KH-560 = 1:3-5:5-8. The mass of anhydrous ethanol was 3-5 times the total mass of TMP, TEB, and KH-560. In the anhydrous ethanol solvent, DBTDL was used as a catalyst, with the mass of DBTDL being 0.5% of the total mass of TMP, TEB, and KH-560. wt %-1.0 wt The reaction mixture was stirred at 60-80℃ for 8-12 h. After the reaction, the solvent was removed by vacuum distillation at a vacuum degree of -0.07 to -0.08 MPa and a temperature of 70-80℃. The mixture was then dried under vacuum at 80-100℃ for 2-3 h to obtain HPBSi. The HPBSi was then dissolved in... N , N In dimethylformamide, HPBSi and N , N The mass ratio of dimethylformamide is 1:9 to 1:

19. Activated organomontmorillonite is added, and the mass ratio of HPBSi to activated organomontmorillonite is 1:3 to 1:

5. The mixture is stirred at 80 to 100 °C for 4 to 6 h to graft hyperbranched polyborosiloxane onto the surface of organomontmorillonite sheets. After the reaction is completed, the mixture is centrifuged at 4000 to 6000 r / min for 15 to 30 min, washed, and vacuum dried to obtain OMMT-HPBSi.

9. The method for preparing an antibacterial and freshness-locking nylon film for food packaging according to claim 7, characterized in that: The cooling process in step 4 is segmented cooling. The cooling temperature of the first segment is 80~90℃, the cooling temperature of the second segment is 40~50℃, and the cooling temperature of the third segment is 25~30℃.

10. The method for preparing an antibacterial and freshness-locking nylon film for food packaging according to claim 7, characterized in that: During the winding process in step 5, an additive of 0.1% of the nylon film mass can be added. wt %~0.3 wt % of anti-sticking masterbatch.

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