A liquid dairy product packaging bag and its manufacturing method

Abstract

This invention discloses a liquid dairy product packaging bag, employing a three-layer composite structure, consisting of an outer layer, a middle structural layer, and an inner layer from the outside in. The outer layer materials include: low-density polyethylene, medium-density polyethylene, ethylene-α-olefin, titanium dioxide, and organically modified high-barrier zeolite molecular sieves; the mass ratio of low-density polyethylene, medium-density polyethylene, ethylene-α-olefin, titanium dioxide, and organically modified high-barrier zeolite molecular sieves is 20-40:5-15:2-10:5-15:1-5. The middle structural layer materials include: ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, and high-density polyethylene; the mass ratio of ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, and high-density polyethylene is 40-60:2-10:5-15. The inner layer materials include: low-density polyethylene, linear low-density polyethylene, and organically modified high-barrier zeolite molecular sieves. This invention also discloses a method for manufacturing the liquid dairy product packaging bag.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, and in particular to a liquid dairy product packaging bag and its manufacturing method. Background Technology

[0002] Liquid dairy products refer to liquid milk made primarily from cow's milk or sheep's milk and their processed products, with or without the addition of appropriate amounts of vitamins, minerals, and other excipients, and processed under conditions required by laws, regulations, and standards.

[0003] With the rapid development of my country's liquid milk industry, preservative-free liquid milk has become the most popular type in the current food industry, solving the problem of potential food additive hazards that people are worried about. However, this has brought about the challenge of how to effectively preserve liquid dairy products during packaging, transportation and storage.

[0004] Liquid dairy product packaging bags are an essential requirement for dairy product packaging. They protect food from damage caused by biological, chemical, and physical factors during its distribution from the factory to the consumer, and also maintain the stable quality of the food itself. Therefore, liquid dairy product packaging bags not only make it convenient for people in different regions to consume the product, reducing geographical limitations, but also ensure the taste and quality of the dairy products, allowing people to consume them at any time.

[0005] Existing liquid dairy product packaging bags are generally co-extruded high-barrier packaging films produced by a seven-layer co-extrusion method. Their structure is (PE + white masterbatch) / (PE + white masterbatch) / TIE / EVOH / TIE / (PE + black masterbatch) / (PE + black masterbatch). To ensure the film's applicability, white masterbatch (composed of titanium dioxide) is added to the outer and second-outermost layers, while black masterbatch (composed of carbon black) is added to the inner and second-innermost layers. This means that the black masterbatch in the inner layer comes into direct contact with the liquid milk after packaging, which not only affects the hygiene of the contents but also results in a large overall film thickness. Reducing the film thickness can easily lead to poor physical and mechanical properties, decreased barrier properties, and a higher leakage rate.

[0006] Zeolite molecular sieves, as an inorganic crystalline material, possess the structure and characteristics of crystals. Their surface forms a solid framework, and the molecular sieve crystals contain numerous cavities of a specific size, interconnected by pores of the same diameter. These internal pores function to adsorb molecules. Due to the cleanliness of the pores, the pore size distribution of molecular sieves is highly uniform, resulting in superior properties. Currently, zeolite molecular sieves are widely used in petrochemical, environmental protection, bioengineering, food industry, and pharmaceutical chemical fields.

[0007] Zeolite molecular sieves possess a regular molecular structure and high hydrothermal stability, making them suitable for use in liquid packaging bags. They offer excellent toughening effects and good thermal stability, effectively ensuring the hygiene of the contents. However, their strong hydrophilicity leads to poor barrier properties in the packaging bags, resulting in short shelf lives for liquid dairy products. Currently, existing technologies have not yet found a suitable application for zeolite molecular sieves in the packaging bag field. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by proposing a liquid dairy product packaging bag and its manufacturing method.

[0009] A packaging bag for liquid dairy products adopts a three-layer composite structure, consisting of an outer layer, a middle structural layer, and an inner layer from the outside to the inside.

[0010] The outer layer raw materials include: low-density polyethylene, medium-density polyethylene, ethylene-α-olefin, titanium dioxide, and organic high-barrier zeolite molecular sieve; the mass ratio of low-density polyethylene, medium-density polyethylene, ethylene-α-olefin, titanium dioxide, and organic high-barrier zeolite molecular sieve is 20-40:5-15:2-10:5-15:1-5.

[0011] The intermediate structural layer raw materials include: ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, and high-density polyethylene; the mass ratio of ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, and high-density polyethylene is 40-60:2-10:5-15.

[0012] The inner layer raw materials include: low-density polyethylene, linear low-density polyethylene, and organic high-barrier zeolite molecular sieve; the mass ratio of low-density polyethylene, linear low-density polyethylene, and organic high-barrier zeolite molecular sieve is 15-25:10-30:5-15.

[0013] Preferably, the organic high-barrier zeolite molecular sieve is made by grafting graphene oxide onto the surface of the organic zeolite molecular sieve, wherein the organic zeolite molecular sieve is a zeolite molecular sieve with a polymer film coating on its surface.

[0014] Preferably, the organic high-barrier zeolite molecular sieve is prepared by the following steps: adding the organic zeolite molecular sieve and graphene oxide into water, stirring at 60-80℃ for 2-6 hours, centrifuging, vacuum drying, adding to hydroiodic acid solution, stirring at 90-100℃ for 1-2 hours, centrifuging, washing with water until neutral, and drying to obtain the organic high-barrier zeolite molecular sieve.

[0015] Preferably, the mass ratio of organic zeolite molecular sieve to graphene oxide is 6-10:1-5, and the mass fraction of hydroiodic acid solution is 30-50%.

[0016] Preferably, the organic zeolite molecular sieve is prepared by the following steps: zeolite molecular sieve, polyimide, and dopamine are added to Tris-HCl solution and stirred for 2-5 hours, centrifuged, washed, and vacuum dried, then added to acetonitrile and dispersed evenly, 4-vinylpyridine is added and stirred for 1-2 hours, ethylene glycol dimethacrylate and azobisisobutyronitrile are added, and the mixture is stirred at 50-70°C for 10-15 hours under nitrogen protection, centrifuged, washed, and vacuum dried to obtain the organic zeolite molecular sieve.

[0017] Preferably, the mass ratio of zeolite molecular sieve, polyimide, dopamine, 4-vinylpyridine, ethylene glycol dimethacrylate, and azobisisobutyronitrile is 4-8:1-2:0.01-0.1:1-3:0.1-1:0.01-0.1.

[0018] Preferably, the total thickness of the packaging bag is 25-50 μm, and the thickness ratio of the outer layer, the middle structural layer, and the inner layer is 5-10:15-25:5-15.

[0019] The above-mentioned method for manufacturing liquid dairy product packaging bags includes the following steps: mixing the outer layer raw material, the middle structural layer raw material and the inner layer raw material evenly, and then adding them to the hoppers of the first extruder, the second extruder and the third extruder for preheating; extruding the outer layer raw material, the middle structural layer raw material and the inner layer raw material through the extruder die according to the thickness; and then guiding them through the stretching roller to the cooling roller for cooling to obtain the liquid dairy product packaging bag.

[0020] Preferably, the preheating temperature is 150-220℃ and the preheating time is 10-30min.

[0021] The technical effects of this invention are as follows:

[0022] This invention employs a three-layer co-extrusion process, which not only reduces the thickness of the packaging bag to below 50μm, but also improves its mechanical properties, increases its impact strength, enhances its dimensional stability, and provides better barrier performance, effectively extending the shelf life of liquid dairy product packaging bags.

[0023] This invention employs organic high-barrier zeolite molecular sieves in both the outer and inner layers. By grafting polyimide onto the surface of the zeolite molecular sieve and reacting it with ethylene glycol dimethacrylate in the presence of 4-vinylpyridine, the product is bonded to the zeolite molecular sieve to form a polymer film layer. This effectively enhances the barrier properties of the zeolite molecular sieve while maintaining its regular structure. Furthermore, due to the presence of amino and hydroxyl groups on its surface, it can combine with two-dimensional sheet graphene oxide. The sheet-like graphene oxide coating and bonding to the surface of the zeolite molecular sieve not only greatly enhances the hydrophobicity of the zeolite molecular sieve, but also the stacked nano-graphene structure effectively constructs surface roughness, synergistically forming a micro-nano-scale rough structure.

[0024] Organic high-barrier zeolite molecular sieves, when combined with low-density polyethylene and linear low-density polyethylene, exhibit extremely high affinity and good compatibility, giving the inner layer superhydrophobicity. When used in dairy product packaging bags, they not only possess excellent chemical stability and temperature resistance but also superior barrier properties.

[0025] The packaging bag obtained by this invention not only eliminates the need for color masterbatch in the inner layer that directly contacts milk, but also provides better barrier performance than a seven-layer co-extruded film, effectively extending the shelf life of milk. Furthermore, the organic high-barrier zeolite molecular sieve, with its surface polymerized with an organic layer and grafted with sheet-like graphene oxide, creates a flexible chain structure between the outer and inner layers, which can also be combined with the intermediate structural layer. This significantly reduces the thickness of the packaging bag while providing excellent impact resistance, effectively preventing it from breaking upon impact. Additionally, the organic high-barrier zeolite molecular sieve forms a superhydrophobic structure in the inner layer, greatly improving its sealing performance and expanding the bag's application adaptability, especially in the preservation of liquid milk. Attached Figure Description

[0026] Figure 1 This is a comparison chart of the barrier properties of the packaging bags obtained in Example 5 and Comparative Examples 1-3.

[0027] Figure 2 The chart shows the comparison of milk fat content at different time points for pasteurized milk sealed in packaging bags obtained in Example 5 and Comparative Examples 1-3. Detailed Implementation

[0028] The present invention will be further explained below with reference to specific embodiments.

[0029] Example 1

[0030] A packaging bag for liquid dairy products adopts a three-layer composite structure, consisting of an outer layer, a middle structural layer, and an inner layer from the outside to the inside.

[0031] The outer layer materials include: 20 kg of low-density polyethylene, 5 kg of medium-density polyethylene, 2 kg of ethylene-α-olefin, 5 kg of titanium dioxide, and 1 kg of organically modified high-barrier zeolite molecular sieve. The middle structural layer materials include: 40 kg of ethylene-vinyl alcohol copolymer, 2 kg of ethylene-vinyl acetate copolymer, and 5 kg of high-density polyethylene. The inner layer materials include: 15 kg of low-density polyethylene, 10 kg of linear low-density polyethylene, and 5 kg of organically modified high-barrier zeolite molecular sieve.

[0032] Organic high-barrier zeolite molecular sieves are prepared using the following steps:

[0033] i. Add 4 kg of zeolite molecular sieve, 1 kg of polyimide, and 0.01 kg of dopamine to 20 kg of Tris-HCl solution, stir at 1000 r / min for 2 h, centrifuge, wash alternately with water and ethanol, vacuum dry, add to 20 kg of acetonitrile and disperse evenly, add 1 kg of 4-vinylpyridine, stir at 1000 r / min for 1 h, add 0.1 kg of ethylene glycol dimethacrylate and 0.01 kg of azobisisobutyronitrile, stir at 50 °C for 10 h under nitrogen protection, centrifuge, wash alternately with water and ethanol, vacuum dry to obtain organic zeolite molecular sieve;

[0034] ii. Add 6 kg of organic zeolite molecular sieve and 1 kg of graphene oxide to 20 kg of water, stir at 60°C for 2 h, centrifuge, vacuum dry, add to 20 kg of 30% hydroiodic acid solution, stir at 90°C for 1 h, centrifuge, wash with water until neutral, and dry to obtain organic high-barrier zeolite molecular sieve.

[0035] The above-mentioned method for manufacturing liquid dairy product packaging bags includes the following steps: mixing the outer layer raw material, the middle structural layer raw material and the inner layer raw material evenly, and then adding them to the hoppers of the first extruder, the second extruder and the third extruder respectively, preheating at 150°C for 10 minutes, and then, according to the thickness, extruding the outer layer raw material, the middle structural layer raw material and the inner layer raw material through the extruder die, and then guiding them through the stretching roller to the cooling roller to cool and obtain the liquid dairy product packaging bag.

[0036] Example 2

[0037] A packaging bag for liquid dairy products adopts a three-layer composite structure, consisting of an outer layer, a middle structural layer, and an inner layer from the outside to the inside.

[0038] The outer layer materials include: 40 kg of low-density polyethylene, 15 kg of medium-density polyethylene, 10 kg of ethylene-α-olefin, 15 kg of titanium dioxide, and 5 kg of organically modified high-barrier zeolite molecular sieve. The middle structural layer materials include: 60 kg of ethylene-vinyl alcohol copolymer, 10 kg of ethylene-vinyl acetate copolymer, and 15 kg of high-density polyethylene. The inner layer materials include: 25 kg of low-density polyethylene, 30 kg of linear low-density polyethylene, and 15 kg of organically modified high-barrier zeolite molecular sieve.

[0039] Organic high-barrier zeolite molecular sieves are prepared using the following steps:

[0040] i. Add 8 kg of zeolite molecular sieve, 2 kg of polyimide, and 0.1 kg of dopamine to 50 kg of Tris-HCl solution, stir at 2000 r / min for 5 h, centrifuge, wash alternately with water and ethanol, vacuum dry, add to 50 kg of acetonitrile and disperse evenly, add 3 kg of 4-vinylpyridine, stir at 2000 r / min for 2 h, add 1 kg of ethylene glycol dimethacrylate and 0.1 kg of azobisisobutyronitrile, stir at 70 °C for 15 h under nitrogen protection, centrifuge, wash alternately with water and ethanol, vacuum dry to obtain organic zeolite molecular sieve;

[0041] ii. Add 10 kg of organic zeolite molecular sieve and 5 kg of graphene oxide to 50 kg of water, stir at 80 °C for 6 h, centrifuge, vacuum dry, add to 50 kg of 50% hydroiodic acid solution, stir at 100 °C for 2 h, centrifuge, wash with water until neutral, and dry to obtain organic high-barrier zeolite molecular sieve.

[0042] The above-mentioned method for manufacturing liquid dairy product packaging bags includes the following steps: mixing the outer layer raw material, the intermediate structural layer raw material and the inner layer raw material evenly, and then adding them to the hoppers of the first extruder, the second extruder and the third extruder respectively, preheating at 220°C for 30 minutes, and then, according to the thickness, extruding the outer layer raw material, the intermediate structural layer raw material and the inner layer raw material through the extruder die through co-flow extrusion, and then guiding them through the stretching roller to the cooling roller for cooling to obtain the liquid dairy product packaging bag.

[0043] Example 3

[0044] A packaging bag for liquid dairy products adopts a three-layer composite structure, consisting of an outer layer, a middle structural layer, and an inner layer from the outside to the inside.

[0045] The outer layer materials include: 25 kg of low-density polyethylene, 12 kg of medium-density polyethylene, 4 kg of ethylene-α-olefin, 12 kg of titanium dioxide, and 2 kg of organically modified high-barrier zeolite molecular sieve. The middle structural layer materials include: 55 kg of ethylene-vinyl alcohol copolymer, 4 kg of ethylene-vinyl acetate copolymer, and 12 kg of high-density polyethylene. The inner layer materials include: 18 kg of low-density polyethylene, 25 kg of linear low-density polyethylene, and 7 kg of organically modified high-barrier zeolite molecular sieve.

[0046] Organic high-barrier zeolite molecular sieves are prepared using the following steps:

[0047] i. Add 7 kg of zeolite molecular sieve, 1.3 kg of polyimide, and 0.08 kg of dopamine to 30 kg of Tris-HCl solution, stir at 1800 r / min for 3 h, centrifuge, wash alternately with water and ethanol, vacuum dry, add to 40 kg of acetonitrile and disperse evenly, add 1.5 kg of 4-vinylpyridine, stir at 1800 r / min for 80 min, add 0.8 kg of ethylene glycol dimethacrylate and 0.03 kg of azobisisobutyronitrile, stir at 65 °C for 11 h under nitrogen protection, centrifuge, wash alternately with water and ethanol, vacuum dry to obtain organic zeolite molecular sieve;

[0048] ii. Add 9 kg of organic zeolite molecular sieve and 2 kg of graphene oxide to 35 kg of water, stir at 65°C for 5 h, centrifuge, vacuum dry, add to 25 kg of 45% hydroiodic acid solution, stir at 93°C for 110 min, centrifuge, wash with water until neutral, and dry to obtain organic high-barrier zeolite molecular sieve.

[0049] The above-mentioned method for manufacturing liquid dairy product packaging bags includes the following steps: mixing the outer layer raw material, the middle structural layer raw material and the inner layer raw material evenly, and then adding them to the hoppers of the first extruder, the second extruder and the third extruder respectively, preheating at 170°C for 25 minutes, and then extruding the outer layer raw material, the middle structural layer raw material and the inner layer raw material through the extruder die according to the thickness, and then guiding them to the cooling roller through the stretching roller to cool and obtain the liquid dairy product packaging bag.

[0050] Example 4

[0051] A packaging bag for liquid dairy products adopts a three-layer composite structure, consisting of an outer layer, a middle structural layer, and an inner layer from the outside to the inside.

[0052] The outer layer materials include: 35 kg of low-density polyethylene, 8 kg of medium-density polyethylene, 8 kg of ethylene-α-olefin, 8 kg of titanium dioxide, and 4 kg of organically modified high-barrier zeolite molecular sieve. The middle structural layer materials include: 45 kg of ethylene-vinyl alcohol copolymer, 8 kg of ethylene-vinyl acetate copolymer, and 8 kg of high-density polyethylene. The inner layer materials include: 22 kg of low-density polyethylene, 15 kg of linear low-density polyethylene, and 13 kg of organically modified high-barrier zeolite molecular sieve.

[0053] Organic high-barrier zeolite molecular sieves are prepared using the following steps:

[0054] i. Add 5 kg of zeolite molecular sieve, 1.7 kg of polyimide, and 0.02 kg of dopamine to 40 kg of Tris-HCl solution, stir at 1200 r / min for 4 h, centrifuge, wash alternately with water and ethanol, vacuum dry, add to 30 kg of acetonitrile and disperse evenly, add 2.5 kg of 4-vinylpyridine, stir at 1200 r / min for 100 min, add 0.2 kg of ethylene glycol dimethacrylate and 0.07 kg of azobisisobutyronitrile, stir at 55 °C for 13 h under nitrogen protection, centrifuge, wash alternately with water and ethanol, vacuum dry to obtain organic zeolite molecular sieve;

[0055] ii. Add 7 kg of organic zeolite molecular sieve and 4 kg of graphene oxide to 25 kg of water, stir at 75°C for 3 h, centrifuge, vacuum dry, add to 45 kg of 35% hydroiodic acid solution, stir at 97°C for 70 min, centrifuge, wash with water until neutral, and dry to obtain organic high-barrier zeolite molecular sieve.

[0056] The above-mentioned method for manufacturing liquid dairy product packaging bags includes the following steps: mixing the outer layer raw material, the middle structural layer raw material and the inner layer raw material evenly, and then adding them to the hoppers of the first extruder, the second extruder and the third extruder respectively, preheating at 200°C for 15 minutes, and then, according to the thickness, extruding the outer layer raw material, the middle structural layer raw material and the inner layer raw material through the extruder die, and then guiding them through the stretching roller to the cooling roller to cool and obtain the liquid dairy product packaging bag.

[0057] Example 5

[0058] A packaging bag for liquid dairy products adopts a three-layer composite structure, consisting of an outer layer, a middle structural layer, and an inner layer from the outside to the inside.

[0059] The outer layer materials include: 30 kg of low-density polyethylene, 10 kg of medium-density polyethylene, 6 kg of ethylene-α-olefin, 10 kg of titanium dioxide, and 3 kg of organically modified high-barrier zeolite molecular sieve. The middle structural layer materials include: 50 kg of ethylene-vinyl alcohol copolymer, 6 kg of ethylene-vinyl acetate copolymer, and 10 kg of high-density polyethylene. The inner layer materials include: 20 kg of low-density polyethylene, 20 kg of linear low-density polyethylene, and 10 kg of organically modified high-barrier zeolite molecular sieve.

[0060] Organic high-barrier zeolite molecular sieves are prepared using the following steps:

[0061] i. Add 6 kg of zeolite molecular sieve, 1.5 kg of polyimide, and 0.05 kg of dopamine to 35 kg of Tris-HCl solution, stir at 1500 r / min for 3-4 h, centrifuge, wash alternately with water and ethanol, vacuum dry, add to 35 kg of acetonitrile and disperse evenly, add 2 kg of 4-vinylpyridine, stir at 1500 r / min for 90 min, add 0.5 kg of ethylene glycol dimethacrylate and 0.05 kg of azobisisobutyronitrile, stir at 60 °C for 12 h under nitrogen protection, centrifuge, wash alternately with water and ethanol, vacuum dry to obtain organic zeolite molecular sieve;

[0062] ii. Add 8 kg of organic zeolite molecular sieve and 3 kg of graphene oxide to 30 kg of water, stir at 70°C for 4 h, centrifuge, vacuum dry, add to 35 kg of 40% hydroiodic acid solution, stir at 95°C for 90 min, centrifuge, wash with water until neutral, and dry to obtain organic high-barrier zeolite molecular sieve.

[0063] The above-mentioned method for manufacturing liquid dairy product packaging bags includes the following steps: mixing the outer layer raw material, the intermediate structural layer raw material and the inner layer raw material evenly, and then adding them to the hoppers of the first extruder, the second extruder and the third extruder respectively, preheating at 180°C for 20 minutes, and then, according to the thickness, extruding the outer layer raw material, the intermediate structural layer raw material and the inner layer raw material through the extruder die, and then guiding them through the stretching roller to the cooling roller to cool and obtain the liquid dairy product packaging bag.

[0064] The total thickness of the packaging bag obtained in this embodiment is 36 μm, of which the outer layer thickness is 7 μm, the middle structural layer thickness is 21 μm, and the inner layer thickness is 8 μm.

[0065] Comparative Example 1

[0066] The ordinary 7-layer co-extruded film is used, and its structure is (PE + white masterbatch) / (PE + white masterbatch) / TIE / EVOH / TIE / (PE + black masterbatch) / (PE + black masterbatch).

[0067] The total thickness of the 7-layer co-extruded film used in this comparative example is 53 μm, of which the thickness of the first layer (PE + white masterbatch) is 12 μm, the thickness of the second layer (PE + white masterbatch) is 10 μm, the thickness of the third layer (TIE) is 3 μm, the thickness of the fourth layer (EVOH) is 3 μm, the thickness of the fifth layer (TIE) is 3 μm, the thickness of the sixth layer (PE + black masterbatch) is 10 μm, and the thickness of the seventh layer (PE + black masterbatch) is 12 μm.

[0068] Comparative Example 2

[0069] A packaging bag for liquid dairy products adopts a three-layer composite structure, consisting of an outer layer, a middle structural layer, and an inner layer from the outside to the inside.

[0070] The outer layer materials include: 30 kg of low-density polyethylene, 10 kg of medium-density polyethylene, 6 kg of ethylene-α-olefin, 10 kg of titanium dioxide, and 3 kg of biotite. The middle structural layer materials include: 50 kg of ethylene-vinyl alcohol copolymer, 6 kg of ethylene-vinyl acetate copolymer, and 10 kg of high-density polyethylene. The inner layer materials include: 20 kg of low-density polyethylene, 20 kg of linear low-density polyethylene, and 10 kg of biotite.

[0071] The above-mentioned method for manufacturing liquid dairy product packaging bags includes the following steps: mixing the outer layer raw material, the intermediate structural layer raw material and the inner layer raw material evenly, and then adding them to the hoppers of the first extruder, the second extruder and the third extruder respectively, preheating at 180°C for 20 minutes, and then, according to the thickness, extruding the outer layer raw material, the intermediate structural layer raw material and the inner layer raw material through the extruder die, and then guiding them through the stretching roller to the cooling roller to cool and obtain the liquid dairy product packaging bag.

[0072] The total thickness of the packaging bag obtained in this comparative example is 37 μm, of which the outer layer thickness is 8 μm, the middle structural layer thickness is 21 μm, and the inner layer thickness is 8 μm.

[0073] Comparative Example 3

[0074] A packaging bag for liquid dairy products adopts a three-layer composite structure, consisting of an outer layer, a middle structural layer, and an inner layer from the outside to the inside.

[0075] The outer layer materials include: 30 kg of low-density polyethylene, 10 kg of medium-density polyethylene, 6 kg of ethylene-α-olefin, 10 kg of titanium dioxide, and 3 kg of high-barrier zeolite molecular sieve. The middle structural layer materials include: 50 kg of ethylene-vinyl alcohol copolymer, 6 kg of ethylene-vinyl acetate copolymer, and 10 kg of high-density polyethylene. The inner layer materials include: 20 kg of low-density polyethylene, 20 kg of linear low-density polyethylene, and 10 kg of high-barrier zeolite molecular sieve.

[0076] The high-barrier zeolite molecular sieve is prepared by the following steps: 8 kg of zeolite molecular sieve and 3 kg of graphene oxide are added to 30 kg of water, stirred at 70°C for 4 h, centrifuged, vacuum dried, added to 35 kg of 40% hydroiodic acid solution, stirred at 95°C for 90 min, centrifuged, washed with water until neutral, and dried to obtain the high-barrier zeolite molecular sieve.

[0077] The above-mentioned method for manufacturing liquid dairy product packaging bags includes the following steps: mixing the outer layer raw material, the intermediate structural layer raw material and the inner layer raw material evenly, and then adding them to the hoppers of the first extruder, the second extruder and the third extruder respectively, preheating at 180°C for 20 minutes, and then, according to the thickness, extruding the outer layer raw material, the intermediate structural layer raw material and the inner layer raw material through the extruder die, and then guiding them through the stretching roller to the cooling roller to cool and obtain the liquid dairy product packaging bag.

[0078] The total thickness of the packaging bag obtained in this comparative example is 36 μm, of which the outer layer thickness is 7 μm, the middle structural layer thickness is 22 μm, and the inner layer thickness is 7 μm.

[0079] The mechanical properties of the packaging bags obtained in Example 5 and Comparative Examples 1-3 were measured as follows: tensile strength and elongation at break were tested according to GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for thin plastics and sheets"; dart impact strength was tested according to Method A in GB / T9639.1-2008 "Test methods for impact resistance of plastic films and sheets - Free-falling dart method - Part 1: Step method"; and drop tests were conducted according to GB / T4857.5-1992 "Packaging - Drop test method for transport packages".

[0080]

[0081] As can be seen from the table above, the three-layer co-extrusion method of this invention improves the mechanical properties of the packaging bag, increases its impact strength, and effectively extends the shelf life of liquid dairy product packaging bags.

[0082] The applicant believes this is because the surface of the organic high-barrier zeolite molecular sieve is polymerized with an organic material, and combined with the sheet-like graphene oxide grafted onto its surface, a flexible chain structure is formed between the outer and inner layers, and it can also be combined with the intermediate structural layer. While greatly reducing the thickness of the packaging bag, the packaging bag has extremely excellent impact resistance and effectively prevents the packaging bag from breaking due to impact.

[0083] Wettability is the tendency of one phase of a miscible fluid to spread or adhere to a solid surface; it is one of the most important properties of solid material surfaces. Wetting refers to the phenomenon of a liquid phase spreading along the surface of a solid phase when the liquid phase comes into contact with the solid phase. The wetting contact angle can be used as a physical quantity to characterize the degree of wetting and surface free energy of a product surface. The water contact angle of the inner surfaces of the packaging bags obtained in Example 5 and Comparative Examples 1-3 was measured using a contact angle measuring instrument. Three points were taken from the surface of each group of products for measurement, and the average value was calculated.

[0084] Group Contact angle, ° Example 5 164.7 Comparative Example 1 153.9 Comparative Example 2 151.4 Comparative Example 3 156.2

[0085] As shown in the table above, the inner surface of the packaging bag obtained in Example 5 has a larger water contact angle and lower surface energy, exhibiting superhydrophobic properties, which helps in the preservation of liquid dairy products.

[0086] The applicant believes this is because the surface of the mechanized zeolite molecular sieve contains amino and hydroxyl groups, which can combine with two-dimensional sheet graphene oxide. The sheet graphene oxide coating and bonding on the surface of the zeolite molecular sieve greatly enhances the hydrophobicity of the zeolite molecular sieve. Furthermore, the use of organic high-barrier zeolite molecular sieve in combination with low-density polyethylene and linear low-density polyethylene results in extremely high affinity and good compatibility, giving the inner layer superhydrophobicity.

[0087] The barrier properties of the packaging bags obtained in Example 5 and Comparative Examples 1-3 were measured, and the water vapor permeability and oxygen permeability were used to characterize the material barrier properties.

[0088] The water vapor transmission rate was tested according to the weight gain method in GB / T 1037-2021 "Determination of Water Vapor Transmission Performance of Plastic Films and Sheets - Cup Weight Gain and Weight Loss Method". The test temperature was 38℃, the humidity was 90%RH, the preheating time was 2h, the rotation interval was 10min, and 3 parallel tests were set up for each group.

[0089] The oxygen permeability test was conducted according to GB / T 1038.1-2022 "Test Methods for Gas Permeability of Plastic Films and Sheets - Part 1: Differential Pressure Method". The test temperature was 23℃, the humidity was 50%RH, and the vacuum time was 4 hours. Ensure the sample surface was free of contamination and scratches, and set up 3 parallel tests for each group.

[0090] like Figure 1 As shown, the water vapor transmission rate and oxygen transmission rate of the packaging bag obtained in Example 5 are both lower than those of the comparative example. The applicant believes this is because the present invention uses organic high-barrier zeolite molecular sieves in both the outer and inner layers. By grafting polyimide onto the surface of the zeolite molecular sieve and reacting it with ethylene glycol dimethacrylate in the presence of 4-vinylpyridine, the product is bonded to the zeolite molecular sieve to form a polymer film layer. While ensuring the regular structure of the zeolite molecular sieve, its barrier performance can be effectively enhanced. Furthermore, because its surface contains amino and hydroxyl groups, it can combine with two-dimensional sheet graphene oxide. The sheet graphene oxide coating and bonding to the surface of the zeolite molecular sieve greatly enhances the hydrophobicity of the zeolite molecular sieve. The use of organic high-barrier zeolite molecular sieves in combination with low-density polyethylene and linear low-density polyethylene results in extremely high affinity and good compatibility, giving the inner layer superhydrophobicity and excellent barrier performance when used in dairy product packaging bags.

[0091] Comparing Comparative Example 1 and Comparative Examples 2-3, it was found that when existing fillers (such as biotite) are used as molecular barrier agents and the number of film layers is changed, the barrier performance of the film will drop sharply. It is not as good as the existing seven-layer co-extruded high-barrier packaging film. This highlights that the packaging bag obtained in Example 5 can reduce the thickness of the film while improving the barrier performance.

[0092] During storage, milk fat undergoes oxidation and decomposition, producing off-flavor substances such as methyl ketones, which in turn denature whey proteins. Therefore, the applicant used the packaging bags obtained in Example 5 and Comparative Examples 1-3 to aseptically seal pasteurized milk and store it under room temperature and light conditions for 30 days. Samples were taken on days 0, 10, 20, and 30 to test the milk fat content.

[0093] like Figure 2 As shown, the results of milk fat content in each group correspond to the barrier performance of each group. The packaging bag obtained in Example 5 has the best barrier performance, and the milk fat content retention in the Example 5 group is the highest, which confirms that the packaging bag obtained by the present invention is more suitable for liquid dairy products.

[0094] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A liquid dairy product packaging bag, characterized in that, The packaging bag adopts a three-layer composite structure, and from outside to inside, it is an outer layer, an intermediate structure layer and an inner layer in sequence. The outer layer raw material comprises low-density polyethylene, medium-density polyethylene, ethylene-alpha olefin, titanium white powder and organic high-barrier zeolite molecular sieve, and the mass ratio of the low-density polyethylene, the medium-density polyethylene, the ethylene-alpha olefin, the titanium white powder and the organic high-barrier zeolite molecular sieve is 20-40:5-15:2-10:5-15:1-5. The intermediate structure layer raw material comprises ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer and high-density polyethylene, and the mass ratio of the ethylene-vinyl alcohol copolymer, the ethylene-vinyl acetate copolymer and the high-density polyethylene is 40-60:2-10:5-15. The inner layer raw material comprises low-density polyethylene, linear low-density polyethylene and organic high-barrier zeolite molecular sieve, and the mass ratio of the low-density polyethylene, the linear low-density polyethylene and the organic high-barrier zeolite molecular sieve is 15-25:10-30:5-15.

2. The liquid dairy product packaging bag of claim 1, wherein, The organic high-barrier zeolite molecular sieve is grafted and coated on the surface of the organic zeolite molecular sieve by graphene oxide, and the organic zeolite molecular sieve is coated with a polymer film layer on the surface of the zeolite molecular sieve.

3. A liquid milk product packaging bag according to claim 1 or 2, characterized in that The organic high-barrier zeolite molecular sieve is prepared by the following steps: the organic zeolite molecular sieve and graphene oxide are added to water, stirred at 60-80 DEG C for 2-6 h, centrifuged, vacuum dried, added to a hydroiodic acid solution, stirred at 90-100 DEG C for 1-2 h, centrifuged, washed with water until neutral, and dried to obtain the organic high-barrier zeolite molecular sieve.

4. The liquid dairy product packaging bag of claim 3, wherein, The mass ratio of the organic zeolite molecular sieve and graphene oxide is 6-10:1-5, and the mass fraction of the hydroiodic acid solution is 30-50%.

5. The liquid dairy product packaging bag of claim 2, wherein, The organic zeolite molecular sieve is prepared by the following steps: the zeolite molecular sieve, polyimide and dopamine are added to a Tris-HCl solution, stirred for 2-5 h, centrifuged, washed, vacuum dried, dispersed uniformly in acetonitrile, added with 4-vinylpyridine, stirred for 1-2 h, added with ethylene glycol dimethacrylate and azobisisobutyronitrile, stirred at 50-70 DEG C for 10-15 h under nitrogen protection, centrifuged, washed, vacuum dried to obtain the organic zeolite molecular sieve.

6. The liquid dairy product packaging bag of claim 5, wherein, The mass ratio of the zeolite molecular sieve, the polyimide, the dopamine, 4-vinylpyridine, ethylene glycol dimethacrylate and azobisisobutyronitrile is 4-8:1-2:0.01-0.1:1-3:0.1-1:0.01-0.

1.

7. The liquid dairy product packaging bag of claim 1, wherein, The total thickness of the packaging bag is 25-50 microns, and the thickness ratio of the outer layer, the intermediate structure layer and the inner layer is 5-10:15-25:5-15.

8. A method of manufacturing a liquid dairy product packaging bag according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: the outer layer raw material, the intermediate structure layer raw material and the inner layer raw material are respectively mixed uniformly, then respectively added to the hoppers of the first extruder, the second extruder and the third extruder for preheating, the outer layer raw material, the intermediate structure layer raw material and the inner layer raw material are co-cast extruded through the die of the extruder according to the thickness, then guided to the cooling roller through the drawing roller to obtain the liquid dairy product packaging bag.

9. The method of claim 8, wherein The preheating temperature is 150-220 DEG C, and the preheating time is 10-30 min.

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