A continuous vacuum nitrogen filling process and its application in food packaging bags

Abstract

The application belongs to the technical field of packaging bags, and particularly relates to a continuous vacuum nitrogen filling process and application thereof in food packaging bags. The continuous vacuum nitrogen filling process comprises the following steps: S1, instant vacuum cavity degassing; S2, instant nitrogen filling; S3, low vacuum degree instant sealing; and S4, vacuum nitrogen filling sterilization. The self-made packaging bag can adapt to the continuous vacuum nitrogen filling process, has high mechanical strength, good toughness and high temperature resistance, is not easy to be damaged in the process flow, has good oxygen and water vapor barrier properties, can prolong the product shelf life, reduce the product peroxide value, and thus improve the product qualification rate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of packaging bags, and particularly relates to a continuous vacuum nitrogen filling process and application thereof in food packaging bags. BACKGROUND

[0002] In recent years, with the significant improvement of people's living standards, consumers' demand for convenient, healthy and delicious snack foods is increasing, which puts forward higher requirements for food packaging technology. Although the traditional vacuum packaging technology can effectively isolate oxygen and prolong the shelf life of food, the high pressure in the sterilization process often leads to serious loss of food flavor, and it is difficult to maintain the original shape and appearance of the raw materials, which affects the overall appearance and consumer experience of the product. In addition, vacuum packaging may also cause changes in the structure of food tissue, affecting the taste.

[0003] On the other hand, the nitrogen filling packaging technology replaces the air in the packaging bag to reduce the oxygen content, thereby slowing down the oxidation and deterioration process of the food. However, this technology faces many challenges in practical application, such as the difficulty in completely removing the air and oxygen molecules in the packaging bag, which limits the preservation effect; at the same time, the requirement for sterilization technology is high, the operation is complex, and there is a safety risk, which limits its wide application in more types of food. At present, nitrogen filling packaging is mainly limited to puffed products such as potato chips and potato chips, which have less effect on shape retention and taste, and in other foods such as egg products that require better flavor and shape preservation, the application effect is not ideal.

[0004] Therefore, the application provides a continuous vacuum nitrogen filling process, and a packaging bag suitable for the continuous vacuum nitrogen filling process is prepared, providing a more efficient, safe and flexible packaging solution for food packaging bags. SUMMARY

[0005] The application aims to provide a continuous vacuum nitrogen filling process and its application in food packaging bags, which can adapt to the continuous vacuum nitrogen filling process by using self-made packaging bags, not only having high mechanical strength, good toughness and high temperature resistance, but also being not easy to be damaged in the process flow, and having good oxygen and water vapor barrier properties, which can prolong the shelf life of the product, reduce the peroxide value of the product, and thus improve the product yield.

[0006] The continuous vacuum nitrogen filling process comprises the following steps:

[0007] S1, instant vacuum cavity degassing: placing the product to be packaged in the vacuum cavity and pumping to a vacuum degree of-0.09 MPa or lower;

[0008] S2, instant nitrogen filling: keeping the sealing state of the vacuum cavity, instant filling of pure nitrogen into the vacuum cavity to a vacuum degree of 0.1 MPa, and the nitrogen filling time is less than or equal to 5s;

[0009] S3, low vacuum degree transient sealing: after filling nitrogen, the vacuum degree of the vacuum chamber is reduced to -0.02 to -0.04 MPa, and the bag is quickly sealed before air and pollutants enter the bag;

[0010] S4, vacuum nitrogen sterilization: while maintaining the vacuum nitrogen environment, the product is sterilized.

[0011] Preferably, the specific conditions of the sealing are: sealing temperature is 150-200℃, sealing pressure is 0.3-0.5MPa, and sealing time is 1-3s.

[0012] Preferably, the specific conditions of the sterilization treatment are: heating rate is 5-10℃ / min, sterilization temperature is 121-135℃, pressure increasing rate is 0.5-1.0bar / min, and sterilization time is 15-60min.

[0013] The packaging bag is composed of two side bags and a bottom film; the structure of the two side bags is consistent, and the inside to the outside is a first support layer, a first barrier layer, and a second support layer; the structure of the bottom film is a third support layer, a second barrier layer, and a fourth support layer from the inside to the outside.

[0014] The preparation raw materials and preparation methods of the first support layer and the third support layer are consistent.

[0015] Preferably, the preparation raw materials of the first barrier layer include AL; the preparation raw materials of the second support layer include PET; and the preparation raw materials of the second barrier layer include PA.

[0016] Preferably, the AL is an aluminum barrier film, which is commercially available, provided by Wuxi Color Printing Factory, and has a thickness of 13μm.

[0017] Preferably, the intrinsic viscosity of the PET is 0.78-0.85d l / g, and the density is 1.2-1.6g / cm 3 .

[0018] In some preferred embodiments, the PET is purchased from Changzhou Huarun, PET CR-8816.

[0019] Preferably, the tensile modulus of the PA is 1500-2000MPa, and the notched impact strength at -30℃ is 14-18kJ / m2.

[0020] In some preferred embodiments, the PA is purchased from Plastic Crown Technology, PA66 A3ST.

[0021] Preferably, the fourth support layer is OPET, which is purchased from Klocke, C#12.

[0022] The preparation raw material of the first support layer comprises, by weight parts, polyethylene 100 parts, polyamide 15-25 parts, compatibility agent 10-20 parts, inorganic modifier 15-25 parts, lubricant 0.1-0.5 parts, antioxidant 0.1-0.2 parts.

[0023] The packaging bag is composed of two side bags and a bottom film. The side bags are PE-based material / AL / PET, and the bottom film is PE-based material / PA / OPET. The PE-based material of the side bags provides the necessary flexibility and strength, directly contacting the contents to ensure safety and non-toxicity. The AL layer in the middle plays an excellent oxygen barrier performance, effectively preventing oxygen from entering the inside of the packaging bag, prolonging the shelf life of the product. The PET layer as the outer layer not only provides additional structural support and strength, but also forms a good adhesion with the AL layer, ensuring the overall stability of the packaging bag. In terms of the bottom film, the PE-based material also provides the necessary strength and flexibility, and the PA layer further enhances the water vapor barrier performance, reducing the possibility of water vapor entering the packaging bag. The outermost OPET layer, after orientation treatment, has higher strength and rigidity, ensuring that the packaging bag has enough support force at the bottom and is not easily deformed or damaged. Such a multi-layer structure design not only makes the packaging bag have excellent adaptability and stability in the continuous vacuum nitrogen filling process, but also greatly improves the barrier performance to oxygen and water vapor, effectively prolonging the shelf life of the product, reducing the peroxide value of the product, and significantly improving the product's pass rate, providing consumers with a safer and higher-quality product experience.

[0024] Preferably, the polyethylene includes linear low-density polyethylene and metallocene polyethylene.

[0025] Preferably, the mass ratio of the linear low-density polyethylene and the metallocene polyethylene is (1-3):1; further preferably, 2:1.

[0026] Preferably, the linear low-density polyethylene has a melt index of 1-5 g / 10 min at 190℃, a density of 0.9-0.94 g / cm 3 , and a tear strength of 130-150 kN / m.

[0027] In some preferred embodiments, the linear low-density polyethylene is purchased from SABI C, 318B.

[0028] Preferably, the metallocene polyethylene has a melt index of 0.5-2 g / 10 min at 190℃, a flexural modulus of 100-150 MPa, a tensile strength of 45-65 MPa, and an elongation at break ≥600%.

[0029] In some preferred embodiments, the metallocene polyethylene is purchased from Exxon Mobil, MPE 1012HJ.

[0030] By selecting specific linear low-density polyethylene and metallocene polyethylene, the mechanical properties of the first support layer can be significantly improved, thereby enhancing the strength and toughness of the entire packaging bag. This may be because linear low-density polyethylene has high strength, high toughness, and good heat resistance, while metallocene polyethylene exhibits high durability, tensile strength, and excellent optical quality through precise control of the molecular structure by metallocene catalyst. The combination of the two not only achieves performance complementation but also optimizes the molecular structure, forming a more tightly ordered material system. In addition, the addition of metallocene polyethylene also improves the processing performance of the composite material, making the packaging bag more easily shaped and demolded during the manufacturing process, and its addition can reduce the temperature required for heat sealing while maintaining high heat sealing strength, which helps to maintain the integrity of the packaging bag while reducing energy consumption and improving production efficiency. However, using polyethylene as the raw material for the first support layer has limited improvement in mechanical properties, and its heat resistance is relatively poor, which may affect the heat sealing strength of the vacuum bag.

[0031] The raw material of the polyamide is consistent with the raw material PA for preparing the second barrier layer.

[0032] By selecting polyamide and polyethylene for blending modification, not only can the mechanical properties of the first support layer be significantly improved, but also the high-temperature resistance can be improved, and certain barrier effects can be achieved, thereby improving the overall performance of the packaging bag. This may be because polyamide and polyethylene are blended, on the one hand, promoting the formation of intermolecular hydrogen bonds and other forces, which helps to disperse stress, enhance the strength of the blend, and thus improve the strength of the packaging bag. On the other hand, the entanglement degree and stability of the molecular chain are optimized, so that the blend exhibits higher strength and toughness when stressed, and the heat resistance is improved. In addition, PA has certain barrier properties, combined with the close arrangement of PE molecular chains, effectively preventing the penetration of gases or chemicals, and improving the barrier effect of the vacuum bag. However, the compatibility between PA and PE is poor, which affects the mechanical properties of the packaging bag. And the affinity between the polyethylene-based material of the support layer and the materials of the first and second barrier layers is also poor, which may delaminate during long-term use, affecting the performance of the vacuum bag.

[0033] Preferably, the compatibilizer includes one or more of maleic anhydride grafted EVA and maleic anhydride grafted LDPE; further preferably, maleic anhydride grafted EVA and maleic anhydride grafted LDPE.

[0034] Preferably, the mass ratio of the maleic anhydride grafted EVA and the maleic anhydride grafted LDPE is 1:(2-4); further preferably, 1:3.

[0035] Preferably, the melt index of the maleic anhydride grafted EVA at 190℃ is 2-4 g / 10 min, the maleic anhydride grafting rate is 1%-1.2%, and the VA content is 25%-30%.

[0036] Preferably, the melt index of the maleic anhydride grafted LDPE at 190℃ is 5-7 g / 10 min, the maleic anhydride grafting rate is 1%-1.3%.

[0037] In some preferred embodiments, the maleic anhydride grafted EVA and the maleic anhydride grafted LDPE are purchased from Dongguan Shenghao Plastic Raw Material Co., Ltd.

[0038] By selecting specific compatibilizers, not only can the compatibility between polyethylene and polyamide be improved, but also the affinity between the barrier layer (AL or PA) and the support layer polyethylene-based material can be improved, avoiding interlayer separation under high temperature and high pressure, which affects the heat seal strength. This may be because the synergistic effect of the two compatibilizers not only reduces the polarity difference between PE and PA, but also promotes the chemical bonding between them. Thermodynamically, they act as surfactants, reducing interfacial tension and increasing interfacial layer thickness, promoting the reduction of dispersed particle size, thus forming a macroscopically uniform, microscopically phase-separated thermodynamic stable phase structure. In addition, the maleic anhydride grafted compatibilizer can also promote the interpenetration and interweaving between PE and PA molecular chains, forming a blurred interface and enhancing the adhesion between the barrier layer and the support layer. Meanwhile, the hydrogen bonding that may occur between the anhydride groups and the amide groups further enhances their mutual interaction. These synergistic mechanisms collectively enhance the morphological stability of the composite material, making it less likely to separate between the barrier layer and the support layer under high temperature and high pressure, thus ensuring the stability of the heat seal strength.

[0039] Preferably, the inorganic modifier is modified montmorillonite.

[0040] By selecting montmorillonite as the inorganic modifier, the mechanical properties, dimensional stability, and high temperature resistance of the first support layer can be significantly improved, thereby enhancing the overall performance of the packaging bag. This may be because montmorillonite, as a layered silicate mineral, has excellent adsorption properties and ion exchange capacity. It can uniformly disperse between PE molecular chains, forming effective physical crosslinking points, thereby improving the mechanical properties of the material such as tensile strength, bending strength, and impact strength. At the same time, the layered structure of montmorillonite can effectively prevent the thermal motion of PE molecular chains, improving the thermal stability and dimensional stability of the material. However, montmorillonite has poor dispersibility in PE-based materials and tends to agglomerate, affecting its modification effect on PE-based materials.

[0041] The preparation method of the modified montmorillonite includes the following steps:

[0042] A1, after the montmorillonite is crushed through a 200-400 mesh sieve and dispersed in 80wt% ethanol water solution for 1-3h under ultrasonic, a silane coupling agent is added, the pH value of the system is adjusted to 8-9, and the system is reacted for 2-4h at 60-80℃, then cooled to room temperature, separated by filtration, washed with deionized water until neutral, and dried at 60-70℃ under vacuum to obtain the silane coupling agent modified montmorillonite;

[0043] A2, the silane coupling agent modified montmorillonite is mixed with water, stirred and heated to 80-90℃, a long-chain fatty acid is added, and the system is reacted for 8-10h, then separated by filtration, washed with deionized water until neutral, and dried at 60-70℃ under vacuum to obtain the modified montmorillonite.

[0044] Preferably, the montmorillonite is sodium-based montmorillonite with an ion exchange capacity of 140-150meq / 100g and an aspect ratio of 200-400.

[0045] In some preferred embodiments, the montmorillonite is purchased from Jiangsu Xianfeng Nanometer Material Science and Technology.

[0046] Preferably, the mass ratio of the montmorillonite to 80wt% ethanol water solution is 1:(10-20).

[0047] Preferably, the silane coupling agent is γ-aminopropyl triethoxysilane and γ-methacryloyloxypropyl trimethoxysilane.

[0048] Preferably, the mass ratio of the γ-aminopropyl triethoxysilane to the γ-methacryloyloxypropyl trimethoxysilane is 1:(0.5-2); further preferably, 1:1.

[0049] Preferably, the silane coupling agent is added in an amount of 5%-10% of the mass of the montmorillonite.

[0050] Preferably, the mass ratio of the silane coupling agent modified montmorillonite to water is 1:(40-50).

[0051] Preferably, the long-chain fatty acid includes one or more of oleic acid, linolenic acid, and palmitic acid; further preferably, linolenic acid.

[0052] Preferably, the long-chain fatty acid is added in an amount of 3-5 times the mass of the silane coupling agent modified montmorillonite.

[0053] The dispersibility and compatibility of the montmorillonite in the PE-based material can be improved by grafting a silane coupling agent on the surface of the montmorillonite first and then modifying the montmorillonite with linolenic acid again, so that the performance of the packaging bag is further improved. This may be because the silane coupling agent can form a covalent bond with the hydroxyl groups on the surface of the montmorillonite through hydrolysis and condensation reaction, so as to be firmly grafted on the montmorillonite, which not only changes the hydrophilicity of the montmorillonite, but also increases the interlayer spacing thereof, thereby providing favorable conditions for the further intercalation of the polymer chain. The introduction of linolenic acid further modifies the surface of the modified montmorillonite, thereby enhancing the interaction between the montmorillonite and the PE molecules. The functional groups in the linolenic acid molecules have a strong interaction with the surface of the montmorillonite modified by the silane coupling agent, which not only improves the binding force between the two, but also further improves the compatibility of the montmorillonite with the PE. Through this double modification, the dispersibility of the montmorillonite in the PE matrix is significantly improved, and the agglomeration phenomenon is effectively inhibited. Moreover, the silane coupling agent and linolenic acid selected in the present application are non-toxic and harmless, and are suitable for application fields such as food packaging bags which have high safety requirements.

[0054] Preferably, the lubricant is one or more of paraffin, calcium stearate, barium stearate, ethylene bis-stearamide, pentaerythritol stearate; further preferably, pentaerythritol stearate and ethylene bis-stearamide.

[0055] Preferably, the mass ratio of pentaerythritol stearate and ethylene bis-stearamide is 1:(1-3); further preferably, 1:2.

[0056] Preferably, the antioxidant comprises one or more of antioxidant 1010, antioxidant 168, antioxidant 1076; further preferably, antioxidant 1010 and antioxidant 168.

[0057] Preferably, the mass ratio of antioxidant 1010 and antioxidant 168 is (1-2):1; further preferably, 3:2.

[0058] The preparation method of the packaging bag comprises the following steps:

[0059] B1, preparation of the bag body: adding the first support layer raw material into a film blowing machine and blowing film forming at 190-220°C; adding the second support layer raw material into the film blowing machine and blowing film forming at 180-230°C; compounding the first support layer, the first barrier layer and the second support layer by dry compounding technology, thereby obtaining the bag body;

[0060] B2, preparation of the bottom film: the raw materials of the third support layer, the second barrier layer and the fourth support layer are added into the multi-layer co-extrusion film blowing machine according to the proportion of the formula, the temperature of the third support layer is set to 190-220 DEG C, the temperature of the second barrier layer is set to 240-260 DEG C, the temperature of the second barrier layer is set to 250-280 DEG C, the screw rotation speed is adjusted to 30-60 rpm, the pulling speed is 5-15 m / nib, the winding tension is 0.5-1.0 N / mm2, and the bottom film is obtained after cooling and shaping;

[0061] B3, the two bag bodies are combined with the bottom film, and the packaging bag is obtained.

[0062] Preferably, the thickness of the first support layer is 50-100 μm; the thickness of the first barrier layer is 13 μm; and the thickness of the second support layer is 12-20 μm.

[0063] The specific operation process of the dry composite technology is referred to the paper "Composite Process Research of Hot Aluminum Composite Material" published by Liao Shuai.

[0064] Preferably, the thickness of the third support layer is 50-70 μm; the thickness of the second barrier layer is 15-25 μm; and the thickness of the fourth support layer is 12-20 μm.

[0065] Compared with the prior art, the application has the following advantages and beneficial effects:

[0066] 1. The application provides a continuous vacuum nitrogen filling process, through the self-made packaging bag, the packaging bag can adapt to the continuous vacuum nitrogen filling process, has high mechanical strength, good toughness and high temperature resistance, is not easy to be damaged in the process flow, has good oxygen and water vapor barrier properties, can prolong the shelf life of the product, reduce the peroxide value of the product, and thus improve the product qualification rate.

[0067] 2. The application can significantly improve the mechanical properties of the first support layer by selecting specific linear low-density polyethylene and metallocene polyethylene, thereby enhancing the strength and toughness of the entire packaging bag.

[0068] 3. The application can significantly improve the mechanical properties of the first support layer by selecting polyamide and polyethylene for blending modification, can improve the high temperature resistance of the first support layer, and has certain barrier effect, thereby improving the overall performance of the packaging bag.

[0069] 4. The application can improve the compatibility between polyethylene and polyamide, and can improve the affinity between the barrier layer (AL or PA) and the support layer polyethylene-based material, avoid layer separation under high temperature and high pressure, and affect the heat sealing strength.

[0070] 5. The application can significantly improve the mechanical properties, dimensional stability and high temperature resistance of the first supporting layer by selecting montmorillonite as an inorganic modifier, thereby enhancing the overall performance of the packaging bag; and the dispersibility and compatibility of the montmorillonite in the PE-based material can be improved by first grafting a silane coupling agent on the surface of the montmorillonite for primary modification and then using linolenic acid for secondary modification, thereby further improving the performance of the packaging bag. DETAILED DESCRIPTION

[0071] The technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0072] The raw materials used in the application are commercially available, and specifically:

[0073] AL is an aluminum barrier film, commercially available, provided by Wuxi Color Printing Factory, and has a thickness of 13 μm.

[0074] PET has a specific viscosity of 0.78-0.85 d l / g and a density of 1.2-1.6 g / cm 3 , and is commercially available from Changzhou Hualun, PET CR-8816.

[0075] PA has a tensile modulus of 1500-2000 MPa and a notched impact strength at -30℃ of 14-18 kJ / m2, and is commercially available from Plastic Crown Technology, PA66 A3ST.

[0076] OPET is commercially available from Kolon Specially, C#12.

[0077] Linear low-density polyethylene has a melt index at 190℃ of 1-5 g / 10 min, a density of 0.9-0.94 g / cm 3 , and a tear strength of 130-150 kN / m, and is commercially available from SABIC, 318B.

[0078] Metallocene polyethylene has a melt index at 190℃ of 0.5-2 g / 10 min, a flexural modulus of 100-150 MPa, a tensile strength of 45-65 MPa, and an elongation at break of ≥600%, and is commercially available from Exxon Mobil, MPE 1012HJ.

[0079] The melt index of the maleic anhydride grafted EVA at 190℃ is 2-4 g / 10 min, the maleic anhydride grafting rate is 1%-1.2%, and the VA content is 25%-30%; the melt index of the maleic anhydride grafted LDPE at 190℃ is 5-7 g / 10 min, the maleic anhydride grafting rate is 1%-1.3%; purchased from Dongguan Shenghao Plastic Raw Material Co., Ltd.

[0080] The montmorillonite is sodium-based montmorillonite, the ion exchange capacity is 140-150 meq / 100 g, and the aspect ratio is 200-400, purchased from Jiangsu Xianfeng Nanometer Material Science and Technology.

[0081] Example 1

[0082] The embodiment provides a continuous vacuum nitrogen filling process, and the steps are as follows:

[0083] S1, degassing in a transient vacuum cavity: placing the product to be packaged in the vacuum cavity, and pumping to a vacuum degree of-0.08 MPa;

[0084] S2, instantaneous nitrogen filling: keeping the sealing state of the vacuum cavity, instantaneously filling pure nitrogen into the vacuum cavity to a vacuum degree of 0.1 MPa, and the nitrogen filling time is 5 s;

[0085] S3, low vacuum degree instantaneous sealing: after the nitrogen is filled, the vacuum degree of the vacuum cavity is reduced to-0.03 MPa, and the bag is quickly sealed before air and pollutants enter the bag;

[0086] S4, vacuum nitrogen filling sterilization: while keeping the vacuum nitrogen filling environment, the product is subjected to sterilization treatment.

[0087] The specific conditions of the sealing are as follows: the sealing temperature is 180℃, the sealing pressure is 0.4 MPa, and the sealing time is 2 s.

[0088] The specific conditions of the sterilization treatment are as follows: the temperature rising rate is 8℃ / min, the sterilization temperature is 128℃, the pressure rising rate is 0.8 bar / min, and the sterilization time is 40 min.

[0089] The packaging bag is composed of two side bag bodies and a bottom film; the two side bag bodies are consistent in structure, and sequentially from the inside to the outside are a first support layer, a first barrier layer, and a second support layer; the structure of the bottom film sequentially from the inside to the outside is a third support layer, a second barrier layer, and a fourth support layer.

[0090] The preparation raw materials and preparation methods of the first support layer and the third support layer are consistent.

[0091] The preparation raw material of the first barrier layer is AL; the preparation raw material of the second support layer is PET; the preparation raw material of the second barrier layer is PA; and the fourth support layer is OPET.

[0092] The preparation raw material of the first support layer is polyethylene 100 parts, polyamide 20 parts, compatibilizer 15 parts, inorganic modifier 20 parts, lubricant 0.3 parts, and antioxidant 0.15 parts by weight.

[0093] The polyethylene is linear low density polyethylene and metallocene polyethylene, and the mass ratio is 2:1.

[0094] The raw material of the polyamide is consistent with the preparation raw material PA of the second barrier layer.

[0095] The compatibilizer is maleic anhydride grafted EVA and maleic anhydride grafted LDPE, and the mass ratio is 1:3.

[0096] The inorganic modifier is modified montmorillonite.

[0097] The preparation method of the modified montmorillonite includes the following steps:

[0098] A1, after the montmorillonite is crushed through a 300 mesh sieve and ultrasonically dispersed in 80wt% ethanol water solution for 2h, silane coupling agent is added, the pH value of the system is adjusted to 9, and after reaction at 70℃ for 3h, it is cooled to room temperature, filtered and separated, washed with deionized water until neutral, and vacuum dried at 65℃ to obtain silane coupling agent modified montmorillonite;

[0099] A2, the silane coupling agent modified montmorillonite is mixed with water, stirred and heated to 85℃, long chain fatty acid is added, and after reaction for 9h, it is filtered and separated, washed with deionized water until neutral, and vacuum dried at 65℃ to obtain modified montmorillonite.

[0100] The mass ratio of the montmorillonite and 80wt% ethanol water solution is 1:15.

[0101] The silane coupling agent is γ-aminopropyl triethoxysilane and γ-methacryloyloxypropyl trimethoxysilane, and the mass ratio is 1:1.

[0102] The addition amount of the silane coupling agent is 8% of the mass of the montmorillonite.

[0103] In A2, the mass ratio of the silane coupling agent modified montmorillonite and water is 1:50.

[0104] The long chain fatty acid is linolenic acid, and the addition amount is 4 times the mass of the silane coupling agent modified montmorillonite.

[0105] The lubricant is pentaerythritol stearate and ethylene bis stearic acid amide, and the mass ratio is 1:2.

[0106] The antioxidant is antioxidant 1010 and antioxidant 168, and the mass ratio is 3:2.

[0107] The method for preparing the packaging bag includes the following steps:

[0108] B1. Preparation of the bag body: The raw material of the first support layer is added to the blown film machine and blown film is formed at 210°C; the raw material of the second support layer is added to the blown film machine and blown film is formed at 220°C; the first support layer, the first barrier layer and the second support layer are composited by dry composite technology to obtain the bag body.

[0109] B2. Preparation of the base film: According to the formula ratio, the raw materials of the third support layer, the second barrier layer and the fourth support layer are added to the multi-layer co-extrusion blown film machine. The temperature of the third support layer is set to 205℃, the temperature of the second barrier layer is set to 250℃ and the temperature of the third barrier layer is set to 270℃. The screw speed is adjusted to 50rpm, the traction speed is 10m / minb, and the winding tension is 0.8N / mm2. After cooling and shaping, the film is obtained.

[0110] B3. Combine the two layers of the bag body with the bottom film to obtain the packaging bag.

[0111] The thickness of the first support layer is 70 μm; the thickness of the first barrier layer is 13 μm; and the thickness of the second support layer is 16 μm.

[0112] For the specific operation process of the dry composite technology, please refer to the paper "Research on Composite Process of Tropical Aluminum Composite Materials" published by Liao Shuai.

[0113] The thickness of the third support layer is 60 μm; the thickness of the second barrier layer is 20 μm; and the thickness of the fourth support layer is 16 μm.

[0114] Example 2

[0115] The difference between this embodiment and Embodiment 1 is that the raw materials for preparing the first support layer, by weight, are 100 parts of polyethylene, 18 parts of polyamide, 13 parts of compatibilizer, 22 parts of inorganic modifier, 0.3 parts of lubricant, and 0.15 parts of antioxidant.

[0116] Comparative Example 1

[0117] The difference between this comparative example and Example 1 is that the polyethylene described is linear low-density polyethylene.

[0118] Comparative Example 2

[0119] The difference between this comparative example and Example 1 is that the raw materials for preparing the first support layer, by weight, are 100 parts of polyethylene, 10 parts of polyamide, 15 parts of compatibilizer, 20 parts of inorganic modifier, 0.3 parts of lubricant, and 0.15 parts of antioxidant.

[0120] Comparative Example 3

[0121] The difference between the present comparative example and Example 1 is that the raw material for preparing the first support layer is 100 parts by weight of polyethylene, 20 parts by weight of polyamide, 5 parts by weight of a compatibilizer, 20 parts by weight of an inorganic modifier, 0.3 parts by weight of a lubricant, and 0.15 parts by weight of an antioxidant.

[0122] Comparative Example 4

[0123] The difference between the present comparative example and Example 1 is that the compatibilizer is maleic anhydride grafted EVA.

[0124] Comparative Example 5

[0125] The difference between the present comparative example and Example 1 is that the inorganic modifier is montmorillonite.

[0126] Comparative Example 6

[0127] The difference between the present comparative example and Example 1 is that the preparation method of the modified montmorillonite is as follows: after the montmorillonite is crushed to pass through a 300-mesh sieve, it is ultrasonically dispersed in 80 wt% ethanol aqueous solution for 2 h, then a silane coupling agent is added, the pH value of the system is adjusted to 9, and the system is reacted at 70°C for 3 h, then cooled to room temperature, separated by filtration, washed with deionized water until neutral, and vacuum dried at 65°C to obtain the modified montmorillonite.

[0128] Performance test

[0129] The tensile strength and elongation at break are tested according to GB / T 1040.3-2006, and the units are MPa and %, respectively; the oxygen transmission coefficient of the material is tested according to GB / T 19789-2021, and the unit is cm 3 ·m / (m 2 ·d·Pa); the water vapor transmission coefficient of the material is tested according to GB 1037-70, and the unit is g·m / (m 2 ·d·Pa); the heat seal strength of the material is tested according to QB / T 2358-1998, and the unit is MPa; the heat resistance of the packaging bag at 150°C is tested according to GB / T 21302-2007, and no deformation, delamination, or rupture is qualified. The results are shown in Table 1.

[0130] Table 1 Test results

[0131]

[0132]

[0133] The packaging bag prepared by the embodiments 1-2 of the application has high mechanical strength, good toughness and high temperature resistance, is not easy to be damaged in the process flow, has good oxygen and water vapor barrier properties, can prolong the product shelf life, reduce the product peroxide value, and thus improve the product pass rate. The packaging bag prepared by Comparative Example 1 without adding metallocene polyethylene, Comparative Example 2 with less polyamide, Comparative Example 3 with less compatibilizer, Comparative Example 4 without adding maleic anhydride grafted LDPE, Comparative Example 5 without modifying the montmorillonite, and Comparative Example 6 without secondary modification of the montmorillonite has low tensile strength, elongation at break and heat sealing strength, high oxygen transmission coefficient and water vapor transmission coefficient, and poor heat resistance. Therefore, the packaging bag prepared by the raw materials and method described in the application has high mechanical strength, good toughness and high temperature resistance, is not easy to be damaged in the vacuum nitrogen filling process flow described in the application, has good oxygen and water vapor barrier properties, can prolong the product shelf life, reduce the product peroxide value, and thus improve the product pass rate.

[0134] The above is the preferred embodiment of the application. It should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the application. These improvements and refinements should also be considered within the scope of the application.

Claims

1. A continuous vacuum nitrogen-charging process, characterized by, The process comprises the following steps: S1, degassing of the transient vacuum chamber: the product to be packaged is placed in the vacuum chamber, and the vacuum degree is drawn to below -0.09 MPa; S2, transient nitrogen filling: the vacuum chamber is kept sealed, and pure nitrogen is filled into the vacuum chamber to a vacuum degree of 0.1 MPa, and the nitrogen filling time is ≤5 s; S3, low vacuum degree transient sealing: after the nitrogen is filled, the vacuum degree of the vacuum chamber is reduced to -0.02 to -0.04 MPa, and the sealing is rapidly performed before air and pollutants enter the packaging bag; S4, vacuum nitrogen filling sterilization: while keeping the vacuum nitrogen filling environment, the product is subjected to sterilization treatment, and the specific conditions are: the temperature rising rate is 5-10°C / min, the sterilization temperature is 121-135°C, the pressure rising rate is 0.5-1.0 bar / min, and the sterilization time is 15-60 min; The packaging bag is composed of two side bag bodies and a bottom film; the two side bag bodies are consistent in structure, and from the inside to the outside, they are a first support layer, a first barrier layer, and a second support layer; and the structure of the bottom film is a third support layer, a second barrier layer, and a fourth support layer from the inside to the outside; The preparation raw materials and the preparation method of the first support layer and the third support layer are consistent; the preparation raw materials of the second support layer include PET; The preparation raw materials of the first barrier layer include AL; and the preparation raw materials of the second barrier layer include PA; The preparation raw materials of the first support layer include, by weight, 100 parts of polyethylene, 15-25 parts of polyamide, 10-20 parts of a compatibilizer, 15-25 parts of an inorganic modifier, 0.1-0.5 parts of a lubricant, and 0.1-0.2 parts of an antioxidant; Polyethylene includes linear low density polyethylene and metallocene polyethylene; linear low density polyethylene has a melt index of 1-5 g / 10 min at 190°C, a density of 0.9-0.94 g / cm 3 , and a tear strength of 130-150 kN / m; metallocene polyethylene has a melt index of 0.5-2 g / 10 min at 190°C, a flexural modulus of 100-150 MPa, a tensile strength of 45-65 MPa, and an elongation at break of ≥600%. The fourth support layer is OPET; The inorganic modifier is modified montmorillonite, and the preparation method comprises the following steps: A1, after the montmorillonite is crushed through a 200-400 mesh sieve and ultrasonically dispersed in 80wt% ethanol water solution for 1-3 h, a silane coupling agent is added, the pH value of the system is adjusted to 8-9, and after reaction at 60-80°C for 2-4 h, the system is cooled to room temperature, filtered and separated, washed with deionized water until neutral, and vacuum dried at 60-70°C to obtain the silane coupling agent modified montmorillonite; A2, the silane coupling agent modified montmorillonite is mixed with water, stirred and heated to 80-90°C, a long-chain fatty acid is added, and after reaction for 8-10 h, the system is filtered and separated, washed with deionized water until neutral, and vacuum dried at 60-70°C to obtain the modified montmorillonite.

2. The continuous vacuum nitrogen charging process according to claim 1, characterized in that, The specific conditions of the sealing are: the sealing temperature is 150-200°C, the sealing pressure is 0.3-0.5 MPa, and the sealing time is 1-3 s.

3. The continuous vacuum nitrogen charging process according to claim 1, characterized in that, The compatibilizer includes one or more of maleic anhydride grafted EVA and maleic anhydride grafted LDPE.

4. Application of the continuous vacuum nitrogen filling process according to any one of claims 1-3 in a food packaging bag.

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