Low-temperature-resistant food packaging composite bag and preparation method thereof

Abstract

The invention discloses a low-temperature-resistant food packaging composite bag and a preparation method thereof, and relates to the technical field of plastics. The packaging film comprises a base material layer, a barrier layer and a heat sealing layer which are arranged in sequence. Wherein the base material layer is a biaxially oriented polypropylene film; the barrier layer is an ethylene-vinyl alcohol copolymer film; the heat sealing layer is prepared from the following raw materials in parts by mass: 100 to 150 parts of low-density polyethylene particles, 1.5 to 2 parts of synergist, 0.1 to 0.2 part of antioxidant 1010, 0.5 to 1 part of calcium stearate, 15 to 20 parts of polyolefin elastomer and 2 to 5 parts of modified nano calcium carbonate; the synergist is prepared from stearoyl chloride, triethylamine and epsilon-polylysine; the modified nano calcium carbonate is prepared from nano calcium carbonate and stearic acid. Due to the introduction of the synergist and the modified nano calcium carbonate, the elongation at break, the tensile strength, the barrier capacity, the low temperature resistance and the antibacterial property of the food packaging bag are effectively improved. Therefore, the method has a wider application prospect.

Description

Technical Field

[0001] This invention relates to the field of plastics technology, specifically to a low-temperature resistant food packaging composite bag and its preparation method. Background Technology

[0002] Plastic packaging bags are packaging bags made from plastic and used in the production and daily life of various products. They are widely used in daily life and industrial production. Food packaging bags commonly use food-grade materials such as polyethylene, polypropylene, and polyester. With their advantages of being lightweight, easy to process, cost-effective, and having good sealing properties, they can provide basic protection for various foods such as snacks, fresh produce, cooked food, and grains and oils, meeting core requirements such as moisture protection, dust protection, and portability.

[0003] However, food packaging bags still have performance shortcomings in practical applications: First, their barrier properties are poor. Conventional plastic packaging bags have limited efficiency in blocking water vapor, leading to food softening due to moisture and fresh products losing freshness due to moisture loss, significantly shortening their shelf life. Second, the tensile strength and elongation at break of the packaging bags are insufficient, making them prone to tearing and breaking during transportation, stacking, manual handling, or mechanical repackaging. Third, their low-temperature resistance is poor. Commonly used materials such as polyethylene become brittle and lose toughness in low-temperature environments, making the packaging bags susceptible to cracking from minor impacts during handling and thawing when used for low-temperature food storage. Fourth, they lack antibacterial function. Food packaging can easily become a carrier for bacteria and mold growth in humid and high-temperature circulation environments. Therefore, the elongation at break, tensile strength, barrier capacity, low-temperature resistance, and antibacterial properties of existing food packaging bags still need improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a low-temperature resistant food packaging composite bag and its preparation method, thereby solving the following technical problems: Existing food packaging bags still suffer from poor elongation at break, tensile strength, barrier properties, low-temperature resistance, and antibacterial properties.

[0005] The objective of this invention can be achieved through the following technical solutions: A low-temperature resistant food packaging composite bag includes a substrate layer, a barrier layer, and a heat-sealing layer arranged sequentially. The substrate layer is a 25μm thick biaxially oriented polypropylene film; The barrier layer is a 5μm thick ethylene-vinyl alcohol copolymer film; The heat-sealing layer comprises the following raw materials in parts by weight: 100-150 parts of low-density polyethylene granules, 1.5-2 parts of synergist, 0.1-0.2 parts of antioxidant 1010, 0.5-1 parts of calcium stearate, 15-20 parts of polyolefin elastomer, and 2-5 parts of modified nano calcium carbonate. The synergist was prepared from stearoyl chloride, triethylamine, and ε-polylysine. The modified nano-calcium carbonate is prepared from nano-calcium carbonate and stearic acid.

[0006] Preferably, the synergist is prepared by the following method: A1: Under a nitrogen atmosphere, stearoyl chloride and triethylamine are added to anhydrous dimethyl sulfoxide and stirred for 30-50 min to obtain a stearoyl chloride solution; A2: Add deionized water 1 to anhydrous dimethyl sulfoxide and stir well. Then add ε-polylysine and stir at 50°C for 30-50 min. Subsequently, remove the deionized water by vacuum rotary evaporation at 60°C. Add anhydrous magnesium sulfate and stir for 10-15 min, then filter. Stir the filtrate at 60°C under a nitrogen atmosphere for 30-50 min, then add stearoyl chloride solution and stir at 60°C for 4-5 h. After cooling, pour into deionized water 2 and stir for 10-20 min. After standing for 2-6 h, centrifuge and wash the precipitate 3-5 times with deionized water, then wash twice with a mixture of ethanol and water. Finally, vacuum dry at 40°C for 24-30 h to obtain the synergist.

[0007] Preferably, the ratio of anhydrous dimethyl sulfoxide, stearyl chloride, and triethylamine in A1 is 100-120 mL: 15 g: 8 mL.

[0008] Preferably, the ratio of anhydrous dimethyl sulfoxide, deionized water 1, ε-polylysine, anhydrous magnesium sulfate, stearoyl chloride solution, and deionized water 2 in A2 is 140-150mL: 60-100mL: 10g: 5-7g: 105mL: 1000mL.

[0009] Preferably, the modified nano-calcium carbonate is prepared as follows: Stearic acid was added to nano-calcium carbonate and stirred at 80°C for 30-40 min, followed by vacuum drying at 60°C for 2-3 h to obtain modified nano-calcium carbonate.

[0010] Preferably, the mass ratio of the nano-calcium carbonate to stearic acid is 4-5:0.1.

[0011] Preferably, the heat-sealing layer is prepared as follows: B1: Low-density polyethylene particles, synergist, antioxidant 1010, calcium stearate, polyolefin elastomer, and modified nano calcium carbonate are premixed for 5-7 min, then mixed at 1000 r / min at 80℃ for 10-15 min, then extruded, and finally cooled with water, pelletized, and vacuum dried at 80℃ for 2-4 h to obtain composite masterbatch. B2: The composite masterbatch is blown into a film to obtain a heat-sealing layer with a thickness of 20 μm.

[0012] Preferably, in the extrusion process described in B1, the screw diameter of the twin-screw extruder is 45 mm, the length-to-diameter ratio is 40:1, the temperature of the feeding zone is 120°C, the temperature of the compression zone is 140°C, the temperature of the metering zone is 150-160°C, the die head temperature is 150°C, the screw speed is 200 r / min, and the feeding rate is 10 kg / h. In the blown film processing described in B2, the die diameter of the blown film machine is 50mm, the temperature of the feeding zone is 130℃, the temperature of the plasticizing zone is 150℃, the die temperature is 140℃, the blow-up ratio is 2-3:1, and the traction speed is 3-7m / min.

[0013] A method for preparing a low-temperature resistant food packaging composite bag includes the following steps: S1: Add polypropylene glycol to a nitrogen atmosphere reactor and heat to 45-50℃. Then add dibutyltin dilaurate and stir well. Then add 4,4'-methylenebis(phenyl isocyanate) and stir at 1000-1200 r / min for 15-20 min. After reacting at 45-50℃ for 10-12 min, cool under a nitrogen atmosphere to obtain the adhesive. S2: The substrate layer, barrier layer, and heat-sealing layer are laminated in a dry laminating machine with adhesive at a temperature of 80℃, a pressure of 0.35MPa, and a speed of 30m / min. After lamination, the layers are cured at 60-65℃ for 24-48 hours, then cut, and finally heat-sealed at a temperature of 125-130℃, a pressure of 0.4MPa, and a duration of 1-2 seconds to obtain a low-temperature resistant food packaging composite bag.

[0014] Preferably, the mass ratio of polypropylene glycol, dibutyltin dilaurate, and 4,4'-methylenebis(phenyl isocyanate) in S1 is 95-100:0.1-0.2:18-20.

[0015] The beneficial effects of this invention are: This invention provides a low-temperature resistant food packaging composite bag and its preparation method. The invention effectively improves the elongation at break, tensile strength, barrier properties, low-temperature resistance, and antibacterial properties of the food packaging bag through the following method.

[0016] (1) In this invention, the ε-polylysine in the synergist can exert antibacterial effects by disrupting bacterial cell membranes and inhibiting metabolism; at the same time, the long-chain alkyl group introduced by stearylation can significantly improve the compatibility of the synergist with low-density polyethylene and polyolefin elastomers, effectively preventing the aggregation of antibacterial components and ensuring that they are uniformly dispersed in the film at the molecular and nanoscale levels, achieving a stable and long-lasting antibacterial effect. The stearoyl group of the synergist can form a strong interfacial bond with the polyolefin substrate, reducing the gaps and interfacial defects between components; and the synergist can improve the compatibility of nano-calcium carbonate with organic substrates, making the nano-calcium carbonate more uniformly dispersed. The two work together to enhance the film structure, and the uniformly dispersed synergist chain segments and nano-calcium carbonate together densify the film structure, significantly improving the tensile strength. The synergist can alleviate the damage to the toughness of the film caused by the aggregation of nano-calcium carbonate; at the same time, its long-chain stearoyl alkyl group can assist the polyolefin elastomer in exerting a toughening effect, avoiding the decrease in elongation caused by interfacial separation during stretching. The strong hydrophobicity of the stearoyl long-chain alkyl group in the synergist reduces the contact and penetration of water molecules with the film surface. Furthermore, the uniformly dispersed synergist segments form micro-barrier nodes, extending the diffusion path of gases and water vapor. This synergistic effect with the filling and densification of nano-calcium carbonate, and further enhances the overall barrier capability of the composite bag by combining with the core barrier function of the ethylene-vinyl alcohol copolymer barrier layer. In addition, the synergist's good compatibility reduces interfacial defects within the film at low temperatures, preventing stress concentration caused by the agglomeration of unmodified components and reducing the risk of brittle fracture at low temperatures. Simultaneously, its uniform dispersion provides structural support for the polyolefin elastomer to perform its core low-temperature resistance function, improving the film's performance stability at low temperatures. Moreover, the strong interfacial bonding between the stearoyl group and the polyolefin substrate optimizes the heat-sealing uniformity of the heat-sealing layer, improving heat-sealing strength and stability at low temperatures.

[0017] (2) After modification with stearic acid, the surface of the modified nano-calcium carbonate of this invention changes from hydrophilic to hydrophobic, forming a tight interfacial bond with low-density polyethylene and polyolefin elastomers, ensuring that it is uniformly dispersed in the substrate without obvious agglomeration. The nanoscale size of nano-calcium carbonate can effectively disperse stress, while the strong interfacial effect brought about by stearic acid modification can realize the effective transfer of stress between the filler and the substrate, avoiding the strength reduction caused by internal defects formed by agglomeration when unmodified, and effectively improving the tensile strength of the film. Under low temperature environment, the interfacial bonding force between polymer substrate and filler is easily weakened. The strong interfacial effect between modified nano-calcium carbonate and low-density polyethylene and polyolefin elastomers can stabilize the internal structure of the heat-sealing layer and reduce the risk of stress cracking at low temperature. At the same time, the uniform dispersion and non-agglomeration of modified nano-calcium carbonate provides structural protection for the low-temperature toughness of polyolefin elastomers, reduces internal defects, and further improves the low-temperature resistance of the heat-sealing layer. In addition, the uniform dispersion of modified nano-calcium carbonate can avoid heat-sealing defects caused by agglomerates during the heat-sealing process. Combined with the optimization of the compatibility of the heat-sealing layer by the synergist, it can improve the interfacial bonding stability between the heat-sealing layer and the adhesive, and indirectly ensure the integrity of the interlayer structure of the composite bag at low temperatures.

[0018] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the following information pertains to some of the raw materials used in the following embodiments and comparative examples of this invention: The low-density polyethylene was purchased from Wuxi Zhuomao Plastics Co., Ltd., model: HD7000F; the polyolefin elastomer was purchased from Airefu (Shanghai) New Material Technology Co., Ltd., item number: ENGAGE 8200.

[0021] Example 1: A method for preparing a low-temperature resistant food packaging composite bag is as follows: S1: Under a nitrogen atmosphere, add 15g of stearoyl chloride and 8mL of triethylamine to 100mL of anhydrous dimethyl sulfoxide and stir for 30min to obtain a stearoyl chloride solution. S2: Add 60 mL of deionized water to 140 mL of anhydrous dimethyl sulfoxide and stir until homogeneous. Then add 10 g of ε-polylysine and stir at 50 °C for 30 min. Subsequently, remove the deionized water by vacuum rotary evaporation at 60 °C. Add 5 g of anhydrous magnesium sulfate and stir for 10 min, then filter. Stir the filtrate at 60 °C under a nitrogen atmosphere for 30 min, then add 105 mL of stearoyl chloride solution at 1 mL / min and stir at 500 r / min at 60 °C for 4 h. After cooling, pour into 1000 mL of deionized water and stir for 10 min. After standing for 2 h, centrifuge and wash the precipitate three times with deionized water, then wash twice with a mixture of ethanol and water. Finally, vacuum dry at 40 °C for 24 h to obtain the synergist. S3: Add 0.1g of stearic acid to 4g of nano-calcium carbonate and stir at 80℃ for 30min, then vacuum dry at 60℃ for 2h to obtain modified nano-calcium carbonate; S4: 100g of low-density polyethylene granules, 1.5g of synergist, 0.1g of antioxidant 1010, 0.5g of calcium stearate, 15g of polyolefin elastomer, and 2g of modified nano-calcium carbonate are premixed at 500r / min for 5min, then mixed at 1000r / min for 10min at 80℃. After that, the mixture is extruded using a twin-screw extruder with a screw diameter of 45mm and a length-to-diameter ratio of 40:1. The temperature of the feeding zone is 120℃, the temperature of the compression zone is 140℃, the temperature of the metering zone is 150℃, the temperature of the die head is 150℃, the screw speed is 200r / min, and the feeding rate is 10kg / h. Finally, the mixture is water-cooled, pelletized, and vacuum-dried at 80℃ for 2h to obtain composite masterbatch. S5: Add the composite masterbatch into a blown film machine with a die diameter of 50mm, and perform blown film treatment with a feeding zone temperature of 130℃, a plasticizing zone temperature of 150℃, a die temperature of 140℃, a blow-up ratio of 2:1, and a traction speed of 3m / min to obtain a heat-sealing layer with a thickness of 20μm. S6: Add 95g of polypropylene glycol to a nitrogen atmosphere reactor and heat to 45℃. Then add 0.1g of dibutyltin dilaurate and stir evenly. Then add 18g of 4,4'-methylenebis(phenyl isocyanate) and stir at 1000r / min for 15min. After reacting at 45℃ for 10min, cool under a nitrogen atmosphere to obtain the adhesive. S7: The substrate layer, barrier layer (intermediate layer), and heat-sealing layer are laminated in a dry laminating machine with adhesive at a temperature of 80℃, a pressure of 0.35MPa, and a speed of 30m / min. After lamination, the material is cured at 60℃ for 24 hours, then cut, and finally heat-sealed at a temperature of 125℃, a pressure of 0.4MPa, and a duration of 1s to obtain a low-temperature resistant food packaging composite bag.

[0022] The substrate layer is a 25μm thick biaxially oriented polypropylene film; the barrier layer is a 5μm thick ethylene-vinyl alcohol copolymer film; and the adhesive coating amount is 2.5g / m². 2 .

[0023] Example 2: A method for preparing a low-temperature resistant food packaging composite bag is as follows: S1: Under a nitrogen atmosphere, 15g of stearoyl chloride and 8mL of triethylamine were added to 110mL of anhydrous dimethyl sulfoxide and stirred for 40min to obtain a stearoyl chloride solution. S2: Add 80 mL of deionized water to 145 mL of anhydrous dimethyl sulfoxide and stir until homogeneous. Then add 10 g of ε-polylysine and stir at 50 °C for 40 min. Subsequently, remove the deionized water by vacuum rotary evaporation at 60 °C. Add 6 g of anhydrous magnesium sulfate and stir for 13 min, then filter. Stir the filtrate at 60 °C under a nitrogen atmosphere for 40 min, then add 105 mL of stearoyl chloride solution at 1 mL / min and stir at 500 r / min at 60 °C for 4.5 h. After cooling, pour into 1000 mL of deionized water and stir for 15 min. After standing for 4 h, centrifuge and wash the precipitate 4 times with deionized water, then wash twice with a mixture of ethanol and water. Finally, vacuum dry at 40 °C for 27 h to obtain the synergist. S3: Add 0.1g of stearic acid to 4.5g of nano-calcium carbonate and stir at 80℃ for 35min, then vacuum dry at 60℃ for 2.5h to obtain modified nano-calcium carbonate; S4: 125g of low-density polyethylene granules, 1.8g of synergist, 0.15g of antioxidant 1010, 0.8g of calcium stearate, 18g of polyolefin elastomer, and 4g of modified nano-calcium carbonate are premixed at 500r / min for 6min, then mixed at 1000r / min for 13min at 80℃. After that, the mixture is extruded using a twin-screw extruder with a screw diameter of 45mm and a length-to-diameter ratio of 40:1. The feeding zone temperature is 120℃, the compression zone temperature is 140℃, the metering zone temperature is 155℃, the die head temperature is 150℃, the screw speed is 200r / min, and the feeding rate is 10kg / h. Finally, the mixture is water-cooled, pelletized, and vacuum-dried at 80℃ for 3h to obtain the composite masterbatch. S5: Add the composite masterbatch into a blown film machine with a die diameter of 50mm, and perform blown film treatment with a feeding zone temperature of 130℃, a plasticizing zone temperature of 150℃, a die temperature of 140℃, a blow-up ratio of 2.5:1, and a traction speed of 5m / min to obtain a heat-sealing layer with a thickness of 20μm. S6: Add 98g of polypropylene glycol to a nitrogen atmosphere reactor and heat to 48℃. Then add 0.5g of dibutyltin dilaurate and stir evenly. Then add 19g of 4,4'-methylenebis(phenyl isocyanate) and stir at 1100r / min for 18min. After reacting at 48℃ for 11min, cool under a nitrogen atmosphere to obtain the adhesive. S7: The substrate layer, barrier layer (intermediate layer), and heat-sealing layer are laminated in a dry laminating machine with adhesive at a temperature of 80℃, a pressure of 0.35MPa, and a speed of 30m / min. After lamination, the material is cured at 63℃ for 36 hours, then cut, and finally heat-sealed at a temperature of 128℃, a pressure of 0.4MPa, and a duration of 1.5s to obtain a low-temperature resistant food packaging composite bag.

[0024] The substrate layer is a 25μm thick biaxially oriented polypropylene film; the barrier layer is a 5μm thick ethylene-vinyl alcohol copolymer film; and the adhesive coating weight is 2.8g / m². 2 .

[0025] Example 3: A method for preparing a low-temperature resistant food packaging composite bag is as follows: S1: Under a nitrogen atmosphere, 15g of stearoyl chloride and 8mL of triethylamine were added to 120mL of anhydrous dimethyl sulfoxide and stirred for 50min to obtain a stearoyl chloride solution. S2: Add 100 mL of deionized water to 150 mL of anhydrous dimethyl sulfoxide and stir until homogeneous. Then add 10 g of ε-polylysine and stir at 50 °C for 50 min. Subsequently, remove the deionized water by vacuum rotary evaporation at 60 °C. Add 7 g of anhydrous magnesium sulfate and stir for 15 min, then filter. Stir the filtrate at 60 °C under a nitrogen atmosphere for 50 min, then add 105 mL of stearoyl chloride solution at 1 mL / min and stir at 500 r / min at 60 °C for 5 h. After cooling, pour into 1000 mL of deionized water and stir for 20 min. After standing for 6 h, centrifuge and wash the precipitate 5 times with deionized water, then wash twice with a mixture of ethanol and water. Finally, vacuum dry at 40 °C for 30 h to obtain the synergist. S3: Add 0.1g stearic acid to 5g of nano calcium carbonate and stir at 80℃ for 40min, then vacuum dry at 60℃ for 3h to obtain modified nano calcium carbonate; S4: 150g of low-density polyethylene granules, 2g of synergist, 0.2g of antioxidant 1010, 1g of calcium stearate, 20g of polyolefin elastomer, and 5g of modified nano-calcium carbonate are premixed at 500r / min for 7min, then mixed at 1000r / min for 15min at 80℃. After that, the mixture is extruded using a twin-screw extruder with a screw diameter of 45mm and a length-to-diameter ratio of 40:1. The temperature of the feeding zone is 120℃, the temperature of the compression zone is 140℃, the temperature of the metering zone is 160℃, the temperature of the die head is 150℃, the screw speed is 200r / min, and the feeding rate is 10kg / h. Finally, the mixture is water-cooled, pelletized, and vacuum-dried at 80℃ for 4h to obtain the composite masterbatch. S5: Add the composite masterbatch to a blown film machine with a die diameter of 50mm, and perform blown film treatment with a feeding zone temperature of 130℃, a plasticizing zone temperature of 150℃, a die temperature of 140℃, a blow-up ratio of 3:1, and a traction speed of 7m / min to obtain a heat-sealing layer with a thickness of 20μm. S6: Add 100g of polypropylene glycol to a nitrogen atmosphere reactor and heat to 50℃. Then add 0.2g of dibutyltin dilaurate and stir evenly. Then add 20g of 4,4'-methylenebis(phenyl isocyanate) and stir at 1200r / min for 20min. After reacting at 50℃ for 12min, cool under a nitrogen atmosphere to obtain the adhesive. S7: The substrate layer, barrier layer (intermediate layer), and heat-sealing layer are laminated in a dry laminating machine with adhesive at a temperature of 80℃, a pressure of 0.35MPa, and a speed of 30m / min. After lamination, the material is cured at 65℃ for 48 hours, then cut, and finally heat-sealed at a temperature of 130℃, a pressure of 0.4MPa, and a duration of 2 seconds to obtain a low-temperature resistant food packaging composite bag.

[0026] The substrate layer is a 25μm thick biaxially oriented polypropylene film; the barrier layer is a 5μm thick ethylene-vinyl alcohol copolymer film; and the adhesive coating amount is 3g / m². 2 .

[0027] Comparative Example 1: Compared with Example 1, this comparative example only did not add a "synergist" in the preparation process of S4. All other steps and parameters were the same, and will not be repeated here. The final result was a low-temperature resistant food packaging composite bag.

[0028] Comparative Example 2: Compared with Example 1, this comparative example only replaces the "modified nano calcium carbonate" added in the preparation process of S4 with "nano calcium carbonate". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a low-temperature resistant food packaging composite bag is obtained.

[0029] Comparative Example 3: Compared with Example 1, this comparative example only did not add "modified nano-calcium carbonate" in the preparation process of S4. All other steps and parameters were the same, and will not be repeated here. The final result was a low-temperature resistant food packaging composite bag.

[0030] Performance testing: Determination of elongation at break: Referring to GB / T 1040.3-2006 standard, the elongation at break (%) of the low-temperature resistant food packaging composite bags prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention was determined at a tensile rate of 2 mm / min. The test results are shown in Table 1. Determination of tensile strength: Referring to GB / T 1040.3-2006 standard, the tensile strength (MPa) of the low-temperature resistant food packaging composite bags prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention was determined at a tensile rate of 2 mm / min. The test results are shown in Table 1. Determination of barrier properties: The water vapor transmission rate (g / (m³)) of the low-temperature resistant food packaging composite bags prepared in Examples 1-3 and Comparative Examples 1-3 of this invention was determined using a water vapor transmission rate tester (WB-11-A, Changzhou Dedu Precision Instruments Co., Ltd.). 2 The test results (24h) are shown in Table 1. Low temperature resistance test: Referring to GB / T 1040.3-2006 standard, the elongation at break (%) of the low-temperature resistant food packaging composite bags prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention at a tensile rate of 2 mm / min was determined. The test results are shown in Table 1. Determination of antibacterial activity: Referring to GB / T 31402-2023 standard, a 5×10⁻⁶ coating was applied to the surface of the sterilized sample. 5 CFU / mL bacterial suspensions (Bacteria 1: Escherichia coli ATCC 8739, Bacteria 2: Staphylococcus aureus ATCC 6538P) were cultured at 35°C and 95% humidity for 24 h. Then, the bacterial solution was eluted with phosphate buffer containing 0.05% Tween-80 at 200 rpm for 10 min. The eluent was spread on a culture medium and cultured for 48 h. Colony counts were then performed, and the antibacterial activity value was calculated. The antibacterial activity values ​​of the low-temperature resistant food packaging composite bags prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were determined according to the above method. The test results are shown in Table 1.

[0031] Table 1: Performance test results of Examples 1-3 and Comparative Examples 1-3

[0032] Data Analysis: As can be seen from Table 1, the low-temperature resistant food packaging composite bags prepared in the embodiments of the present invention simultaneously possess excellent elongation at break, tensile strength, barrier properties, low-temperature resistance, and antibacterial properties.

[0033] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A low temperature resistant food packaging composite bag, characterized by, The base material layer, the barrier layer and the heat-sealing layer are sequentially arranged; The base material layer is a biaxially stretched polypropylene film; The barrier layer is an ethylene-vinyl alcohol copolymer film; The heat-sealing layer comprises the following raw materials in parts by mass: low-density polyethylene particles 100-150 parts, synergist 1.5-2 parts, antioxidant 1010 0.1-0.2 parts, calcium stearate 0.5-1 part, polyolefin elastomer 15-20 parts, and modified nano calcium carbonate 2-5 parts; The synergist is prepared from stearoyl chloride, triethylamine and ε-polylysine; The modified nano calcium carbonate is prepared from nano calcium carbonate and stearic acid.

2. The cryogenic food packaging bag of claim 1, wherein, The preparation method of the synergist is as follows: A1: under a nitrogen atmosphere, stearoyl chloride, triethylamine and anhydrous dimethyl sulfoxide are added and stirred for 30-50 min to obtain a stearoyl chloride solution; A2: deionized water 1 is added to anhydrous dimethyl sulfoxide and stirred, then ε-polylysine is added and stirred at 50℃ for 30-50 min, then deionized water is removed by rotary evaporation, anhydrous magnesium sulfate is added and stirred for 10-15 min, then filtered, the filtrate is stirred at 60℃ under a nitrogen atmosphere for 30-50 min, then the stearoyl chloride solution is added and stirred at 60℃ for 4-5 h, then cooled and poured into deionized water 2 and stirred for 10-20 min, then centrifuged, washed and dried to obtain the synergist.

3. The cryogenic food packaging bag of claim 2, wherein, The amount ratio of the anhydrous dimethyl sulfoxide, stearoyl chloride and triethylamine in A1 is 100-120 mL: 15 g: 8 mL.

4. The cryogenic food packaging bag of claim 2, wherein The amount ratio of the anhydrous dimethyl sulfoxide, deionized water 1, ε-polylysine, anhydrous magnesium sulfate, stearoyl chloride solution and deionized water 2 in A2 is 140-150 mL: 60-100 mL: 10 g: 5-7 g: 105 mL: 1000 mL.

5. The cryogenic food packaging bag of claim 1, wherein The preparation method of the modified nano calcium carbonate is as follows: Stearic acid is added to nano calcium carbonate and stirred at 80℃ for 30-40 min, then vacuum dried at 60℃ for 2-3 h to obtain the modified nano calcium carbonate.

6. The cryogenic food packaging bag of claim 5, wherein, The mass ratio of the nano calcium carbonate and stearic acid is 4-5: 0.

1.

7. The cryogenic food packaging bag of claim 1, wherein The preparation method of the heat-sealing layer is as follows: B1: the low-density polyethylene particles, synergist, antioxidant 1010, calcium stearate, polyolefin elastomer and modified nano calcium carbonate are premixed for 5-7 min, then mixed at 80℃ for 10-15 min, then extruded, then water-cooled, pelletized and dried to obtain a composite master batch; B2: the composite master batch is blown into a film to obtain the heat-sealing layer.

8. The cryogenic food packaging bag of claim 7, wherein, In B1, the screw diameter of the double-screw extruder during the extrusion is 45 mm, the length-diameter ratio is 40:1, the feeding zone temperature is 120℃, the compression zone temperature is 140℃, the metering zone temperature is 150-160℃, the die head temperature is 150℃, the screw rotation speed is 200 r / min, and the feeding rate is 10 kg / h; In B2, the die head diameter of the film blowing machine during the film blowing is 50 mm, the feeding zone temperature is 130℃, the plasticizing zone temperature is 150℃, the die head temperature is 140℃, the blow-up ratio is 2-3:1, and the pulling speed is 3-7 m / min.

9. A process for the production of a low temperature resistant food packaging composite bag according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: S1: add polyoxypropylene diol into a nitrogen atmosphere reaction kettle and heat to 45-50℃, then add dibutyl tin dilaurate and stir, then add 4,4'-methylene bis(phenyl isocyanate) and stir for 15-20min, react for 10-12min at 45-50℃, then cool under nitrogen atmosphere to obtain an adhesive; S2: the substrate layer, the barrier layer, and the heat-seal layer are subjected to a compounding treatment in a dry compounding machine using the adhesive at a temperature of 80℃, a pressure of 0.35MPa, and a vehicle speed of 30m / min, then aged at 60-65℃ for 24-48h, then cut, and then subjected to a heat-seal bag making treatment to obtain a low-temperature resistant food packaging composite bag.

10. The method of producing a low-temperature resistant food packaging composite bag according to claim 9, characterized by, The mass ratio of the polyoxypropylene diol, the dibutyl tin dilaurate, and the 4,4'-methylene bis(phenyl isocyanate) in S1 is 95-100:0.1-0.2:18-20.

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