Fresh-keeping packaging film for chilled livestock and poultry meat and preparation process of fresh-keeping packaging film

Abstract

The invention belongs to the field of packaging materials, and discloses a chilled fresh livestock and poultry meat fresh-keeping packaging film and a preparation technology thereof.The packaging film sequentially comprises a polyethylene terephthalate (PET) film layer, a polyamide (PA) film layer, a polyimide and silicon dioxide aerogel composite heat insulation film layer and a polyethylene (PE) antibacterial film layer from outside to inside; according to the chilled fresh livestock and poultry meat fresh-keeping packaging film and the preparation technology thereof, by optimizing the structure and composition of the packaging film, the packaging film is endowed with excellent heat insulation, antibacterial and barrier properties, so that the fresh-keeping period of chilled fresh livestock and poultry meat is prolonged, and the quality of the chilled fresh livestock and poultry meat is kept.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, specifically to a preservation packaging film for chilled fresh livestock and poultry meat and its preparation process. Background Art

[0002] Fresh chilled meat and poultry are widely loved by consumers for their tender taste and rich nutrition. However, during storage and transportation, fresh chilled meat and poultry are susceptible to microbial contamination, oxygen oxidation, moisture loss, and temperature fluctuations, leading to meat deterioration and a shortened shelf life. Traditional packaging films are insufficient to simultaneously meet the multiple preservation requirements of fresh chilled meat and poultry, including heat insulation, antibacterial properties, and high barrier properties.

[0003] Currently, common packaging films on the market, such as ordinary polyethylene film, have poor antibacterial properties and cannot effectively inhibit microbial growth; some packaging films with simple heat insulation functions have limited heat insulation effects and are difficult to maintain the preservation temperature of chilled meat in environments with large temperature fluctuations; while packaging films with better barrier properties are expensive and have complex manufacturing processes. Therefore, developing a chilled meat preservation packaging film that can comprehensively solve the above problems is of great practical significance. Summary of the Invention

[0004] The purpose of this invention is to provide a preservation packaging film for chilled fresh meat and poultry and its preparation process. By optimizing the structure and composition of the packaging film, the packaging film is endowed with excellent heat insulation, antibacterial and barrier properties, thereby extending the shelf life of chilled fresh meat and poultry and maintaining its quality.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The technical solution provided by the present invention is: a chilled fresh meat preservation packaging film, wherein the packaging film comprises, from the outside to the inside, a polyethylene terephthalate (PET) film layer, a polyamide (PA) film layer, a polyimide and silica aerogel composite heat insulation film layer, and a polyethylene (PE) antibacterial film layer.

[0006] Polyethylene terephthalate (PET) film: Prepared by drying polyethylene terephthalate chips at 160-180℃ for 3-5 hours to remove moisture; then melt-extruded at 270-290℃ through a T-die, followed by rapid cooling on a cooling roller at 30-50℃. The film is then longitudinally stretched at 90-110℃ with a stretch ratio of 3-5 times, and finally transversely stretched at 100-120℃ with a stretch ratio of 3-6 times, yielding a polyethylene terephthalate (PET) film with a thickness of 15-25 μm. This PET film possesses good mechanical strength and gloss, providing support and protection for packaging films.

[0007] Polyethylene (PE) antibacterial film layer: made from the following components by weight percentage: 50% low-density polyethylene 1810D, 23% linear low-density polyethylene 7042, 10.5% low-density polyethylene 1802, 6% chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch, 3% anti-fogging surfactant masterbatch, 2% antioxidant 1010, 0.3% titanate coupling agent NDZ-201, 0.2% lecithin dispersant, 3% ethoxylated fatty amine antistatic agent, and 2% erucamide opening slip agent. The chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch is prepared by the following method: chitosan oligosaccharide is dissolved in a 1-3% acetic acid solution as a reaction solvent, p-toluenesulfonic acid is used as a catalyst at 0.5-1% of the chitosan oligosaccharide mass, octadecyl dimethyl benzyl ammonium chloride is added, and the reaction is carried out at 40-60℃ for 4-8 hours. Then, the masterbatch with a particle size of 50-200μm and a degree of substitution of 50-70% is prepared by spray drying. The polyethylene antibacterial film layer can effectively inhibit the growth of microorganisms and prevent chilled fresh meat from being contaminated by bacteria. It also has anti-fogging, antistatic, and slip-resistant functions, which facilitates packaging operations.

[0008] Polyimide and silica aerogel composite thermal insulation film: prepared by freeze-drying method. The silica aerogel is prepared through the following steps: using tetraethyl orthosilicate as the silicon source, ethanol as the solvent, and deionized water and ammonia (25-28% by mass) as catalysts, the mixture is homogeneously mixed at a volume ratio of tetraethyl orthosilicate:ethanol:deionized water:ammonia of 1:5-8:2-4:0.1-0.3. After gelling at room temperature for 24-48 hours, the gel is placed in an ethanol solution and stirred at 200-300 r / min for solvent exchange. Each exchange lasts 2-4 hours, repeated 3-5 times until the moisture content in the gel is below 5% (by mass), indicating that solvent exchange is complete. The gel is then freeze-dried at -50℃ to -30℃ for 24-48 hours to obtain a silica aerogel with a specific surface area of ​​600-800 m² / g and a density of 0.1-0.3 g / cm³. A 10-20% (mass fraction) polyimide precursor solution using N,N-dimethylformamide as a solvent is mixed with prepared silica aerogel particles at a mass ratio of 1:0.3-0.5. After uniform dispersion under ultrasonic power of 300-500W and ultrasonic time of 15-25 minutes, the mixture is cast onto polyethylene terephthalate (PET) film using a blade coating method at a flow rate of 3-5 mm / s. The solvent is removed by freeze-drying, and then imidized at 250-350℃ to form a composite heat-insulating film. This composite heat-insulating film layer can effectively block heat transfer, maintain a low-temperature environment inside the packaging, and is beneficial for the preservation of chilled fresh meat.

[0009] A polyvinylidene chloride (PVDC) barrier layer with a thickness of 8-12 μm is provided between the polyamide (PA) film layer and the polyimide and silica aerogel composite heat insulation film layer to enhance the packaging film's barrier performance against oxygen, water vapor and odors, thereby further extending the shelf life of chilled fresh meat.

[0010] The inner surface of the polyethylene (PE) antibacterial film is coated with an ε-polylysine / sodium alginate composite coating with a thickness of 2-5 μm. The composite coating is formed by interlayer electrostatic interaction and is used to achieve the slow-release and controlled release of antibacterial components, so as to continuously exert antibacterial effects.

[0011] A method for preparing a chilled fresh meat preservation packaging film as described in any of the above claims includes the following steps: S1: Preparation of polyethylene terephthalate (PET) film: Polyethylene terephthalate chips are dried at 160-180℃ for 3-5 hours to remove moisture; then melt-extruded at 270-290℃, extruded through a T-die, and rapidly cooled on a cooling roller at 30-50℃. Then, longitudinally stretched at 90-110℃ using a longitudinal stretching machine with a stretching ratio of 3-5 times, and finally transversely stretched at 100-120℃ using a transverse stretching machine with a stretching ratio of 3-6 times, to obtain a polyethylene terephthalate (PET) film with a thickness of 15-25μm.

[0012] S2: Preparation of polyethylene antibacterial film layer: 50% low-density polyethylene 1810D, 23% linear low-density polyethylene 7042, and 10.5% low-density polyethylene 1802 are added to a high-speed mixer, followed by 6% chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch, 3% anti-fogging surfactant masterbatch, 2% antioxidant 1010, 0.3% titanate coupling agent NDZ-201, 0.2% lecithin dispersant, 3% ethoxylated fatty amine antistatic agent, and 2% erucamide opening slip agent. The mixture is stirred at 80-100℃ and 500-800r / min for 10-15 minutes. Then, it is melt-blended in a twin-screw extruder at 170-210℃ and blow-molded to form a polyethylene antibacterial film layer with a thickness of 40-60μm.

[0013] S3: Preparation of polyimide and silica aerogel composite heat insulation film: A polyimide precursor solution with a concentration of 10-20% (mass fraction) and N,N-dimethylformamide as solvent is mixed with the prepared silica aerogel particles at a mass ratio of 1:0.3-0.5. After uniform dispersion under ultrasonic power of 300-500W and ultrasonic time of 15-25 minutes, the mixture is cast onto polyethylene terephthalate (PET) film by a scraping method at a casting speed of 3-5 mm / s. The solvent is removed by freeze drying, and then imidized at 250-350℃ to form a composite heat insulation film.

[0014] S4: Multilayer film lamination: A dry lamination process is adopted, using polyurethane adhesives with an adhesive coating amount of 3-5 g / m². The polyethylene terephthalate (PET) film layer, polyamide (PA) film layer, polyvinylidene chloride (PVDC) barrier layer, polyimide and silica aerogel composite heat insulation film layer, and polyethylene (PE) antibacterial film layer are laminated sequentially. After lamination, curing is carried out at a temperature of 50-70℃ for 12-24 hours. Specifically, before lamination, the surfaces of each film layer are subjected to corona treatment with a voltage of 15-25 kV and a treatment time of 1-3 seconds. The PET film layer and PA film layer are first laminated at a lamination temperature of 60-85℃ and a lamination pressure of 0.6-1.2 MPa for 3-5 minutes. After cooling to room temperature, the PVDC barrier layer is then laminated to the laminated film layer under the same conditions, and so on, until all film layers are laminated.

[0015] S5: ε-polylysine / sodium alginate composite coating: Prepare ε-polylysine into a 1-3% aqueous solution and sodium alginate into a 0.5-2% aqueous solution. Apply the coating alternately to the inner surface of the polyethylene (PE) antibacterial film layer by layer-by-layer impregnation to form an ε-polylysine / sodium alginate composite coating with a thickness of 2-5μm. Dry at 50-70℃.

[0016] S6: Bag forming: The composite multilayer film is formed into a bag-shaped structure through a three-sided heat sealing process. The heat sealing temperature is 160-190℃, the heat sealing pressure is 0.3-0.6MPa, and the heat sealing width is 5-10mm.

[0017] The beneficial effects of this technical solution are: (1) The chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch in the polyethylene antibacterial film layer and the ε-polylysine and sodium alginate composite coating on the inner surface can effectively inhibit the growth and reproduction of various bacteria, such as Escherichia coli and Staphylococcus aureus, reduce microbial contamination of chilled livestock and poultry meat during storage, and extend the shelf life.

[0018] (2) The composite heat insulation film layer of polyimide and silica aerogel utilizes the porous network structure of silica aerogel and the excellent properties of polyimide to effectively block the entry of external heat, maintain the low temperature environment inside the packaging, and ensure that chilled meat is stored at a suitable temperature.

[0019] (3) The polyvinylidene chloride (PVDC) barrier layer works synergistically with other film layers to significantly enhance the packaging film’s ability to block oxygen, water vapor and odors, prevent the fresh meat from oxidizing and deteriorating, losing moisture and absorbing odors, and maintain the freshness and taste of the meat.

[0020] (4) The packaging film also has functions such as anti-fogging, anti-static and smooth opening, which facilitates packaging operation and use, and improves packaging efficiency and user experience. Attached Figure Description

[0021] Figure 1 This is a data table for Example 1 of the present invention, which describes a chilled fresh meat preservation packaging film and its preparation process. Figure 2 This is a data table for Example 2 of the present invention, which describes a chilled fresh meat preservation packaging film and its preparation process. Figure 3 This is a data table for Example 3 of the present invention, which describes a chilled fresh meat preservation packaging film and its preparation process. Figure 4 This is a data table for Example 4 of the present invention, which describes a chilled fresh meat preservation packaging film and its preparation process. Figure 5 This is a data table for Example 5 of the present invention, which describes a chilled fresh meat preservation packaging film and its preparation process. Figure 6 This is a data table for Example 6 of the present invention, which describes a chilled fresh meat preservation packaging film and its preparation process. Figure 7 This is a table showing the data differences among various embodiments of the chilled fresh meat preservation packaging film and its preparation process proposed in this invention. Detailed Implementation

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] The specific implementation process is as follows: Example 1: Please see Figure 1 and Figure 7 The present invention provides a technical solution: a chilled fresh meat preservation packaging film, comprising the following steps: S1: Polyethylene terephthalate (PET) chips are dried at 160°C for 5 hours to remove moisture; then melt-extruded at 270°C, extruded through a T-die, and rapidly cooled on a cooling roller at 30°C. The chips are then longitudinally stretched at 90°C with a stretching ratio of 3 times, and finally transversely stretched at 100°C with a stretching ratio of 3 times to obtain a polyethylene terephthalate (PET) film with a thickness of 15 μm. S2: Add 50g of low-density polyethylene 1810D, 23g of linear low-density polyethylene 7042, and 10.5g of low-density polyethylene 1802 to a high-speed mixer, then sequentially add 6g of chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch (made by dissolving chitosan oligosaccharide in 1% acetic acid solution, using p-toluenesulfonic acid as a catalyst, with the amount being 0.5% of the mass of chitosan oligosaccharide, adding octadecyl dimethyl benzyl ammonium chloride, reacting at 40℃ for 8 hours, and then spray drying), replacing... The following ingredients were mixed at 80°C and 500 r / min for 15 minutes: 50% (50%), 3g antifogging surfactant masterbatch, 2g antioxidant 1010, 0.3g titanate coupling agent NDZ-201, 0.2g lecithin dispersant, 3g ethoxylated fatty amine antistatic agent, and 2g erucamide opening slip agent. The mixture was then melt-blended at 170°C using a twin-screw extruder and blow-molded to form a 40μm thick polyethylene antibacterial film. S3: Using tetraethyl orthosilicate as the silicon source, ethanol as the solvent, and deionized water and 25% ammonia as catalysts, a mixture of tetraethyl orthosilicate:ethanol:deionized water:ammonia in a volume ratio of 1:5:2:0.1 was prepared and gelled at room temperature for 48 hours. The gel was then placed in an ethanol solution and stirred at 200 rpm for solvent exchange. Each exchange lasted 4 hours, repeated three times, until the water content in the gel was below 5% (mass fraction), indicating that solvent exchange was complete. Finally, the gel was freeze-dried at -50°C for 48 hours. A silica aerogel with a specific surface area of ​​600 m² / g and a density of 0.1 g / cm³ was prepared. A polyimide precursor solution with a concentration of 10% (mass fraction) and N,N-dimethylformamide as solvent was mixed with the prepared silica aerogel particles at a mass ratio of 1:0.3. After being dispersed evenly under ultrasonic power of 300 W and ultrasonic time of 25 minutes, the mixture was cast onto a PET film at a casting speed of 3 mm / s using a scraping method. The solvent was removed by freeze drying, and then imidized at 250 °C to form a composite heat insulation film. S4: A dry lamination process is adopted, using polyurethane adhesive with an adhesive application rate of 3g / m². The PET film layer, polyamide (PA) film layer, 8μm thick polyvinylidene chloride (PVDC) barrier layer, polyimide and silica aerogel composite heat insulation film layer, and polyethylene (PE) antibacterial film layer are laminated sequentially. Before lamination, the surfaces of each film layer are subjected to corona treatment at a voltage of 15kV for 3 seconds. The PET film layer and PA film layer are first laminated at a lamination temperature of 60℃ and a lamination pressure of 0.6MPa for 5 minutes. After cooling to room temperature, the PVDC barrier layer is then laminated to the laminated film layer under the same conditions, and so on, until all film layers are laminated. After lamination, the film is cured at 50℃ for 24 hours. S5: Prepare a 1% aqueous solution of ε-polylysine and a 0.5% aqueous solution of sodium alginate. Apply the ε-polylysine and sodium alginate composite coating with a thickness of 2μm by layer-by-layer impregnation on the inner surface of the polyethylene (PE) antibacterial film layer and dry it at 50℃. S6: The composite multilayer film is made into a bag-like structure by a three-sided heat sealing process. The heat sealing temperature is 160℃, the heat sealing pressure is 0.3MPa, and the heat sealing width is 5mm. This embodiment adopts a conservative approach in parameter selection, successfully preparing a basic chilled fresh meat preservation packaging film through mild reaction conditions and low process parameters. Although the PET film layer has relatively low mechanical strength, it can provide basic support and protection for the packaging. In the polyethylene antibacterial film layer, the chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch is prepared under relatively mild conditions with a substitution degree of 50%, which has a certain inhibitory effect on common bacteria such as Escherichia coli and Staphylococcus aureus. Combined with the ε-polylysine and sodium alginate composite coating, it achieves dual antibacterial properties, which can effectively reduce microbial contamination of chilled fresh meat during short-term storage. The polyimide and silica aerogel composite heat insulation film, through basic raw material ratio and preparation process, forms a structure with preliminary heat insulation ability, which can slow down the entry of external heat to a certain extent and maintain the low temperature environment inside the packaging; the polyvinylidene chloride (PVDC) barrier layer works in synergy with other film layers to have a certain barrier effect on oxygen, water vapor and odor, reducing the risk of oxidation and deterioration, moisture loss and cross-contamination of chilled fresh meat. In addition, the packaging film also has functions such as anti-fogging, anti-static, and smooth opening, which facilitates packaging operations. This embodiment is suitable for scenarios with low requirements for packaging performance and short storage periods, such as short-term sales packaging in small farmers' markets, to achieve basic preservation functions at a lower cost.

[0024] Example 2: Please see Figure 1 and Figure 7 The present invention provides a technical solution: a chilled fresh meat preservation packaging film, comprising the following steps: S1: Polyethylene terephthalate (PET) chips are dried at 180°C for 3 hours to remove moisture; then melt-extruded at 290°C, extruded through a T-die, and rapidly cooled on a cooling roller at 50°C. The chips are then stretched longitudinally at 110°C using a longitudinal stretching machine with a stretching ratio of 5 times, and finally stretched transversely at 120°C using a transverse stretching machine with a stretching ratio of 6 times, to obtain a polyethylene terephthalate (PET) film with a thickness of 25 μm. S2: Add 50g of low-density polyethylene 1810D, 23g of linear low-density polyethylene 7042, and 10.5g of low-density polyethylene 1802 to a high-speed mixer, then add 6g of chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch (made by dissolving chitosan oligosaccharide in 3% acetic acid solution, using p-toluenesulfonic acid as a catalyst, the amount of which is 1% of the mass of chitosan oligosaccharide, adding octadecyl dimethyl benzyl ammonium chloride, reacting at 60℃ for 4 hours, and then spray drying, with a substitution degree of 70%), 3g of anti-fogging surfactant masterbatch, 2g of antioxidant 1010, 0.3g of titanate coupling agent NDZ-201, 0.2g of lecithin dispersant, 3g of ethoxylated fatty amine antistatic agent, and 2g of erucamide opening slip agent. Mix at 100℃ and 800r / min for 10 minutes, then melt-blend at 210℃ using a twin-screw extruder, and blow-mold to produce a polyethylene antibacterial film layer with a thickness of 60μm. S3: Using tetraethyl orthosilicate as the silicon source, ethanol as the solvent, and deionized water and 28% ammonia as catalysts, a mixture of tetraethyl orthosilicate:ethanol:deionized water:ammonia in a volume ratio of 1:8:4:0.3 was prepared and gelled at room temperature for 24 hours. The gel was then placed in an ethanol solution and stirred at 300 rpm for solvent exchange. Each exchange lasted 2 hours, repeated 5 times, until the water content in the gel was below 5% (mass fraction), indicating that solvent exchange was complete. Finally, the gel was freeze-dried at -30°C for 24 hours. A silica aerogel with a specific surface area of ​​800 m² / g and a density of 0.3 g / cm³ was prepared. A polyimide precursor solution with a concentration of 20% (mass fraction) and N,N-dimethylformamide as solvent was mixed with the prepared silica aerogel particles at a mass ratio of 1:0.5. After being dispersed evenly under ultrasonic power of 500 W and ultrasonic time of 15 minutes, the mixture was cast onto a PET film at a casting speed of 5 mm / s using a scraping method. The solvent was removed by freeze drying, and then imidized at 350℃ to form a composite heat insulation film. S4: A dry lamination process is adopted, using polyurethane adhesive with an adhesive application rate of 5g / m². The PET film layer, polyamide (PA) film layer, 12μm thick polyvinylidene chloride (PVDC) barrier layer, polyimide and silica aerogel composite heat insulation film layer, and polyethylene (PE) antibacterial film layer are laminated sequentially. Before lamination, the surfaces of each film layer are subjected to corona treatment at a voltage of 25kV for 1s. The PET film layer and PA film layer are first laminated at a lamination temperature of 85℃ and a lamination pressure of 1.2MPa for 3 minutes. After cooling to room temperature, the PVDC barrier layer is then laminated to the laminated film layer under the same conditions, and so on, until all film layers are laminated. After lamination, the film is cured at 70℃ for 12 hours. S5: Prepare a 3% aqueous solution of ε-polylysine and a 2% aqueous solution of sodium alginate. Apply the coating alternately to the inner surface of the polyethylene (PE) antibacterial film layer by layer impregnation to form a 5μm thick composite coating of ε-polylysine and sodium alginate. Dry at 70℃. S6: The composite multilayer film is made into a bag-like structure by a three-sided heat sealing process. The heat sealing temperature is 190℃, the heat sealing pressure is 0.6MPa, and the heat sealing width is 10mm. Example 2 uses a combination of upper limit parameters to achieve a high level of performance in the packaging film; the PET film layer obtains excellent mechanical strength through higher drying temperature, melt extrusion temperature and larger stretch ratio, and can withstand greater external forces, providing more reliable physical protection for chilled meat during transportation and storage. In the polyethylene antibacterial film layer, the chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch has a substitution degree of up to 70% under more intense reaction conditions, which greatly enhances the antibacterial performance. At the same time, the high concentration of ε-polylysine and sodium alginate composite coating achieves efficient and controlled release of antibacterial components, significantly prolonging the antibacterial effect and effectively addressing the microbial challenges faced by high-end chilled products during long-term storage. The polyimide and silica aerogel composite heat insulation film layer utilizes high proportion of raw materials, short gelation time and rapid solvent exchange processes to produce silica aerogel with a specific surface area of ​​800m² / g and a density of 0.3g / cm³. Combined with a high concentration of polyimide precursor solution, it has excellent heat insulation performance and can maintain a stable low temperature inside the packaging under large temperature fluctuations, ensuring the quality of chilled fresh meat. The thicker PVDC barrier layer and optimized composite process further enhance the barrier capabilities against oxygen, moisture, and odors, almost completely isolating the product from adverse external factors. This packaging film is suitable for the long-term storage and long-distance transportation of high-end chilled meat and poultry, such as for export chilled products, ensuring product quality and freshness in all aspects.

[0025] Example 3: Please see Figure 1 and Figure 7 The present invention provides a technical solution: a chilled fresh meat preservation packaging film, comprising the following steps: S1: Parameters are the same as in Example 1; S2: When preparing the chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch, the concentration of acetic acid solution is 2%, the amount of catalyst is 0.8% of the mass of chitosan oligosaccharide, the reaction temperature is 50℃, the reaction time is 6 hours, and the remaining steps are the same as in Example 1; S3: In the preparation of silica aerogel, the ethanol solvent was exchanged 4 times, with each exchange lasting 3 hours. The other parameters were the same as in Example 1. S4: Composite temperature 75℃, composite pressure 0.9MPa, adhesive coating amount 4g / m², other parameters are the same as in Example 1; S5-S6: Parameters are the same as in Example 1; Example 3 optimized intermediate parameters to achieve a balanced and stable overall performance of the packaging film; the PET film layer is the same as in Example 1, meeting the mechanical strength requirements of conventional packaging; in the polyethylene antibacterial film layer, the chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch achieves a substitution degree of 60% under appropriate reaction conditions, exhibiting stable and efficient antibacterial performance, effectively inhibiting the growth of common spoilage bacteria; the reasonable combination of other additives enables the film layer to synergistically perform anti-fogging, antistatic, and other functions, ensuring smooth packaging operations; The composite thermal insulation film of polyimide and silica aerogel is made more uniform in pore structure by optimizing parameters such as solvent exchange number and time, which improves thermal insulation performance while ensuring the stability of the preparation process; the appropriate ratio of polyimide precursor solution and aerogel particles ensures the balance between flexibility and thermal insulation of the composite film. The appropriate PVDC barrier layer thickness and composite process parameters reduce production costs and energy consumption while ensuring good barrier performance. This packaging film is suitable for industrial mass production, has stable product performance, and can be widely used in the conventional packaging of various chilled fresh meats and poultry. It has good economic benefits and production feasibility while ensuring quality.

[0026] Example 4: Please see Figure 1 and Figure 7 The present invention provides a technical solution: a chilled fresh meat preservation packaging film, comprising the following steps: S1: Parameters are the same as in Example 2; S2: Parameters are the same as in Example 2; S3: The concentration of the polyimide precursor solution is 15%, the mass ratio of polyimide precursor to silica aerogel particles is 1:0.4, the ultrasonic power is 400W, the casting speed is 4mm / s, and the other parameters are the same as in Example 2. S4: Parameters are the same as in Example 2; S5-S6: Parameters are the same as in Example 2; Example 4, based on Example 2, adjusts the parameters of the polyimide and silica aerogel composite heat insulation film layer, focusing on improving the flexibility and uniformity of the packaging film; the PET film layer and polyethylene antibacterial film layer have the same performance as in Example 2, providing reliable physical protection and strong antibacterial ability; Regarding the composite thermal insulation film layer, adjusting the concentration of the polyimide precursor solution and the mass ratio of aerogel particles, along with optimized ultrasonic power, ultrasonic time, and casting speed, reduces aerogel particle agglomeration, resulting in a more uniform and dense composite film layer structure. This not only enhances the flexibility of the film layer, enabling it to adapt to the needs of irregularly shaped and complex packaging structures, such as curved packaging boxes and convex / concave packaging, but also further improves the stability of thermal insulation performance, ensuring that it can still effectively block heat transfer under different packaging shapes. The other film layers and composite processes are the same as in Example 2, maintaining high barrier properties and strong antibacterial properties. Therefore, this packaging film is suitable for chilled fresh meat products with special requirements for packaging flexibility, such as high-end chilled gift boxes with customized packaging, which can meet both aesthetic requirements and ensure product freshness.

[0027] Example 5: Please see Figure 1 and Figure 7 The present invention provides a technical solution: a chilled fresh meat preservation packaging film, comprising the following steps: S1: Drying temperature 170℃, drying time 4 hours, longitudinal stretching ratio 4 times, transverse stretching ratio 4 times, to obtain a PET film layer with a thickness of 20μm; S2: Lecithin dispersant is omitted; other parameters are the same as in Example 1. S3: In the preparation of silica aerogel, the volume ratio of ammonia to water is 0.2, and the other parameters are the same as in Example 1; S4: Use starch-based adhesive instead of polyurethane adhesive, with a coating amount of 5g / m², a curing temperature of 60℃ after lamination, and a curing time of 18 hours. Other parameters are the same as in Example 1. S5-S6: Parameters are the same as in Example 1; Example 5 focuses on low-cost process optimization, reducing production costs while ensuring the basic performance of the packaging film; the PET film layer reduces energy consumption while meeting basic strength requirements by adjusting parameters such as drying and stretching; the polyethylene antibacterial film layer omits lecithin dispersant, reducing raw material costs to a certain extent, and the combination of antibacterial agent masterbatch and other additives can still provide basic antibacterial and anti-fogging functions, which can meet the microbial protection needs of short-term storage of chilled fresh meat. The composite thermal insulation film of polyimide and silica aerogel, by adjusting parameters such as the ammonia-water ratio, reduces costs while maintaining a certain level of thermal insulation performance, and can cope with temperature changes in normal environments. The use of starch-based adhesives instead of polyurethane adhesives not only reduces material costs but also meets environmental protection requirements. Although the bonding strength is slightly reduced, effective bonding between the film layers can still be guaranteed by optimizing the composite process parameters. The thinner PVDC barrier layer and simplified lamination and heat-sealing process further control costs; this packaging film is suitable for cost-sensitive low-end markets, such as bulk packaging for small processing enterprises, providing basic preservation functions at an affordable price to meet diverse market demands.

[0028] Example 6: Please see Figure 1 and Figure 7 The present invention provides a technical solution: a chilled fresh meat preservation packaging film, comprising the following steps: S1: Parameters are the same as in Example 1; S2: The amount of antioxidant 1010 is increased to 3g, and the other parameters are the same as in Example 2; S3: The freeze-drying cooling rate is -40℃ / h (the midpoint between -50℃ and -30℃ in the claims), and the other parameters are the same as in Example 2; S4: The curing time after lamination is extended to 36 hours, and the other parameters are the same as in Example 2; S5-S6: Parameters are the same as in Example 2; Example 6 mainly optimizes the adaptability to extreme conditions and improves the preservation ability of the packaging film in harsh environments; the PET film layer is the same as in Example 1, providing basic physical protection; the polyethylene antibacterial film layer increases the amount of antioxidants, significantly enhancing the antioxidant performance. In easily oxidized environments such as high temperature and high humidity, it can effectively slow down the oxidation rate of chilled fresh meat and poultry, and maintain the color and nutritional components of the meat. The polyimide and silica aerogel composite insulation film layer, by controlling the freeze-drying cooling rate, makes the aerogel pore structure more delicate, improves the stability of the insulation performance under extreme temperature fluctuations (±10℃), and ensures that the internal temperature of the packaging is always maintained within the range suitable for the storage of chilled fresh meat. Extending the curing time after multilayer film lamination enhances the bonding strength between film layers, making it less prone to delamination under frequent handling and compression during long-distance transportation. This packaging film is suitable for long-distance transportation, high temperature and high humidity environments, such as transportation in tropical regions and intercontinental cold chain transportation, providing reliable quality and safety assurance for chilled fresh meat and poultry in complex environments.

[0029] Please see Figure 1-7 All embodiments exhibit excellent antibacterial capabilities, with embodiments 2, 4, and 6 showing antibacterial rates ≥96% against Escherichia coli and Staphylococcus aureus. Compared to the single antibacterial method in the prior art, this technology utilizes a dual antibacterial system of chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch and ε-polylysine / sodium alginate composite coating. This not only significantly improves the antibacterial rate but also achieves sustained and controlled release of antibacterial components, extending the antibacterial effect by 3-5 times and ensuring the microbial safety of chilled fresh meat for a longer period. In the heat insulation tests of Examples 2, 4, and 6, the temperature difference between the inside and outside of the packaging film reached 12°C within 24 hours, far exceeding that of traditional heat insulation packaging films. The unique structure and preparation process of the polyimide and silica aerogel composite heat insulation film layer enable it to effectively block heat transfer, maintain a low temperature environment inside the packaging, reduce the risk of meat spoilage caused by temperature fluctuations, and provide more stable storage conditions for chilled fresh meat. Examples 2, 4, and 6 show oxygen permeability as low as 5 cm³ / (m²・24h・0.1 MPa) and water vapor permeability as low as 8 g / (m²・24h). Compared with existing packaging films, their ability to block oxygen, water vapor, and odors is significantly improved. The polyvinylidene chloride (PVDC) barrier layer works synergistically with other film layers to almost completely isolate external adverse factors, prevent the oxidation and deterioration of chilled fresh meat, moisture loss, and cross-contamination of odors, greatly extend the shelf life of the product, and maintain the freshness and taste of the meat. Existing packaging films have limited functionality and cannot simultaneously meet the diverse performance requirements of chilled meat. In contrast, the packaging film of this technology, through scientific film layer design and raw material ratio, integrates multiple functions such as antibacterial, heat insulation, high barrier properties, anti-fogging, antistatic properties, and smooth opening. Data from various embodiments shows that while ensuring the core preservation function, the packaging film also possesses excellent operability and practicality. For example, the anti-fogging function prevents fogging inside the packaging from affecting product display, while the antistatic and smooth opening functions facilitate packaging operations, improving packaging efficiency and user experience—features unmatched by existing technologies. This technology, through setting up multiple embodiments and adjusting process parameters and raw material ratios, enables the packaging film to be precisely adapted to different application scenarios. Embodiment 1 achieves basic preservation functions at a low cost, suitable for short-term storage and ordinary transportation; Embodiment 2 has excellent performance and is suitable for high-end chilled products and long-term storage; Embodiment 3 has balanced overall performance and is suitable for industrial mass production; Embodiment 4 meets the needs of irregularly shaped packaging; Embodiment 5 is suitable for the cost-sensitive low-end market; and Embodiment 6 can cope with extreme environments such as long-distance transportation and high temperature and humidity. In contrast, existing packaging films often have fixed functions and are difficult to meet diverse needs. The flexibility and adaptability of this technology significantly broaden the application fields of packaging films. From the cost data, each embodiment achieves an optimized balance between cost and performance while improving performance. Embodiment 5 reduces the cost to 0.9 yuan / m² by simplifying the process, reducing additives, and changing the adhesive, thus meeting the strict cost requirements of the low-end market while ensuring basic preservation functions. Although Embodiments 2 and 6 have higher costs (2.0 yuan / m²), their superior performance provides reliable protection for high-end and extreme environment applications. This flexible adjustment of cost and performance makes this technology competitive at different market levels, representing a significant improvement over existing technologies that are either too expensive or have poor performance.

[0030] The above descriptions are merely embodiments of the present invention. Commonly known technical solutions or characteristics in the solutions are not described in detail here. It should be noted that those skilled in the art can make several modifications and improvements without departing from the technical solutions of the present invention. These modifications and improvements should also be considered within the scope of protection of the present invention, and they will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A preservation packaging film for chilled fresh livestock and poultry meat, characterized in that, The packaging film, from the outside to the inside, comprises a polyethylene terephthalate (PET) film layer, a polyamide (PA) film layer, a polyimide and silica aerogel composite heat insulation film layer, and a polyethylene (PE) antibacterial film layer. The polyethylene terephthalate (PET) film is prepared by the following method: polyethylene terephthalate chips are dried at 160-180℃ for 3-5 hours to remove moisture; then melt-extruded at 270-290℃, extruded through a T-die, and rapidly cooled on a cooling roller at 30-50℃; then longitudinally stretched at 90-110℃ using a longitudinal stretching machine with a stretching ratio of 3-5 times; finally, transversely stretched at 100-120℃ using a transverse stretching machine with a stretching ratio of 3-6 times, to obtain a polyethylene terephthalate (PET) film with a thickness of 15-25μm. The polyethylene (PE) antibacterial film layer is made of the following components by weight percentage: 50% low-density polyethylene 1810D, 23% linear low-density polyethylene 7042, 10.5% low-density polyethylene 1802, 6% chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch, 3% anti-fogging surfactant masterbatch, 2% antioxidant 1010, 0.3% titanate coupling agent NDZ-201, 0.2% lecithin dispersant, 3% ethoxylated fatty amine antistatic agent, and 2% erucamide opening slip agent; The chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch is prepared by the following method: chitosan oligosaccharide is dissolved in 1-3% acetic acid solution as a reaction solvent, p-toluenesulfonic acid is used as a catalyst at an amount of 0.5-1% of the mass of chitosan oligosaccharide, octadecyl dimethyl benzyl ammonium chloride is added, and the reaction is carried out at 40-60℃ for 4-8 hours. Then, the masterbatch with a particle size of 50-200μm and a degree of substitution of 50-70% is prepared by spray drying.

2. The chilled fresh meat preservation packaging film according to claim 1, characterized in that, The polyimide-silica aerogel composite heat insulation film was prepared by freeze-drying. The silica aerogel is prepared by the following steps: using tetraethyl orthosilicate as the silicon source, ethanol as the solvent, and deionized water and ammonia water with a mass fraction of 25-28% as catalysts, the mixture is stirred at a volume ratio of tetraethyl orthosilicate:ethanol:deionized water:ammonia water of 1:5-8:2-4:0.1-0.3 until homogeneous. After gelling at room temperature for 24-48 hours, the gel is placed in an ethanol solution and stirred at a speed of 200-300 r / min to perform solvent exchange. Each exchange lasts for 2-4 hours and is repeated 3-5 times until the water content in the gel is less than 5% by mass, which is considered as the solvent exchange is complete. Each exchange lasts for 2-4 hours. Then, the gel is freeze-dried at -50℃ to -30℃ for 24-48 hours to obtain a silica aerogel with a specific surface area of ​​600-800 m² / g and a density of 0.1-0.3 g / cm³. A polyimide precursor solution with a mass concentration of 10-20% and N,N-dimethylformamide as solvent is mixed with the prepared silica aerogel particles at a mass ratio of 1:0.3-0.

5. After being dispersed evenly under ultrasonic power of 300-500W and ultrasonic time of 15-25 minutes, the mixture is cast onto polyethylene terephthalate (PET) film by a scraping method at a casting speed of 3-5 mm / s. The solvent is removed by freeze drying, and then imidized at 250-350℃ to form a composite heat insulation film.

3. The chilled fresh meat preservation packaging film according to claim 1 or 2, characterized in that, A polyvinylidene chloride (PVDC) barrier layer with a thickness of 8-12 μm is provided between the polyamide (PA) film layer and the polyimide and silica aerogel composite heat insulation film layer.

4. The chilled fresh meat preservation packaging film according to claim 1 or 2, characterized in that, The inner surface of the polyethylene (PE) antibacterial film is coated with a composite coating of ε-polylysine and sodium alginate with a thickness of 2-5 μm, which is formed by interlayer electrostatic interaction.

5. A method for preparing a chilled fresh meat preservation packaging film as described in any one of claims 1-4, characterized in that, The following steps are involved: S1: Polyethylene terephthalate (PET) chips are dried at 160-180℃ for 3-5 hours to remove moisture; then melt-extruded at 270-290℃, extruded through a T-die, and rapidly cooled on cooling rollers at 30-50℃. The chips are then longitudinally stretched at 90-110℃ using a longitudinal stretching machine with a stretch ratio of 3-5 times. Finally, they are transversely stretched at 100-120℃ using a transverse stretching machine with a stretch ratio of 3-6 times, yielding a polyethylene terephthalate (PET) film with a thickness of 15-25 μm. S2: Add 50% low-density polyethylene 1810D, 23% linear low-density polyethylene 7042, and 10.5% low-density polyethylene 1802 to a high-speed mixer, then add 6% chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch, 3% anti-fogging surfactant masterbatch, 2% antioxidant 1010, 0.3% titanate coupling agent NDZ-201, 0.2% lecithin dispersant, 3% ethoxylated fatty amine antistatic agent, and 2% erucamide opening slip agent in sequence. Mix at 80-100℃ and 500-800r / min for 10-15 minutes. Then melt-blend the mixture through a twin-screw extruder at 170-210℃ and blow-mold it to form a polyethylene antibacterial film layer with a thickness of 40-60μm. S3: A polyimide precursor solution with a mass concentration of 10-20% and N,N-dimethylformamide as solvent is mixed with the prepared silica aerogel particles at a mass ratio of 1:0.3-0.

5. After being ultrasonically dispersed evenly, the mixture is cast onto a polyethylene terephthalate (PET) film. The solvent is removed by freeze-drying, and then imidized at 250-350℃ to form a composite heat insulation film. S4: A dry lamination process is adopted, using polyurethane adhesives with an adhesive application rate of 3-5 g / m². The polyethylene terephthalate (PET) film layer, polyamide (PA) film layer, polyvinylidene chloride (PVDC) barrier layer, polyimide and silica aerogel composite heat insulation film layer, and polyethylene (PE) antibacterial film layer are laminated sequentially. After lamination, curing is carried out at a temperature of 50-70℃ for 12-24 hours. Specifically, before lamination, the surfaces of each film layer are subjected to corona treatment with a voltage of 15-25 kV and a treatment time of 1-3 seconds. The PET film layer and PA film layer are first laminated at a lamination temperature of 60-85℃ and a lamination pressure of 0.6-1.2 MPa for 3-5 minutes. After cooling to room temperature, the PVDC barrier layer is then laminated to the laminated film layer under the same conditions, and so on, until all film layers are laminated. S5: Prepare an aqueous solution of 1-3% ε-polylysine and an aqueous solution of 0.5-2% sodium alginate. Apply the solutions alternately to the inner surface of the polyethylene (PE) antibacterial film layer by layer-by-layer impregnation to form an ε-polylysine / sodium alginate composite coating with a thickness of 2-5 μm. Dry the coating at 50-70℃. S6: The composite multilayer film is made into a bag-like structure through a three-sided heat sealing process. The heat sealing temperature is 160-190℃, the heat sealing pressure is 0.3-0.6MPa, and the heat sealing width is 5-10mm.

6. The preparation method according to claim 5, characterized in that, The preparation process of the chitosan oligosaccharide-quaternary ammonium salt antibacterial agent masterbatch is as follows: chitosan oligosaccharide is dissolved in 1-3% acetic acid solution, octadecyl dimethyl benzyl ammonium chloride is added, and the mixture is reacted at 40-60℃ for 4-8 hours. Then, the masterbatch with a particle size of 50-200μm is prepared by spray drying.

7. The preparation method according to claim 5 or 6, characterized in that, In the preparation of the polyimide and silica aerogel composite heat insulation film, the silica aerogel particles are subjected to surface amination treatment to enhance the interfacial bonding force with the polyimide matrix, and the pore structure is controlled by a cooling rate of -50℃ to -30℃ during the freeze-drying process.

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