Fresh-keeping packaging film capable of inhibiting browning and preparation method of fresh-keeping packaging film

Abstract

The invention belongs to the technical field of fresh keeping of agricultural products, and particularly relates to a fresh-keeping packaging film capable of inhibiting browning and a preparation method of the fresh-keeping packaging film. The fresh-keeping packaging film sequentially comprises a first PE layer, a second PE layer, a third PA layer, a fourth PA layer and a fifth PE-EVA-POE layer from the first layer to the fifth layer from outside to inside, the first PE layer comprises the following raw materials in parts by weight: 25-40 parts of low-density polyethylene, 15-30 parts of linear low-density polyethylene, 30-60 parts of high-density polyethylene and 2-5 parts of a modified nano material; the modified nano material is prepared by mixing nano titanium dioxide, nano silicon dioxide and nano zinc oxide and then sequentially reacting with a silane coupling agent KH570 and a hyperbranched polymer. The prepared fresh-keeping packaging film has an excellent fruit browning prevention effect and is high in puncture resistance and good in low-temperature resistance effect.

Description

Technical Field

[0001] The invention belongs to the technical field of agricultural product preservation, and in particular relates to a fresh-keeping packaging film capable of inhibiting browning and a preparation method thereof. Background Art

[0002] Agricultural product fresh-keeping packaging film is a commonly used packaging material, usually used to extend the shelf life of fruits or other products. It protects the contents by blocking oxygen, moisture, light and odor, and also has heat sealing function.

[0003] The purpose of using agricultural product fresh-keeping packaging film is to effectively protect the integrity of agricultural products, extend their shelf life, and maintain their quality and appearance. However, the following problems still need to be solved in the prior art: 1. Agricultural products (especially fruits and vegetables) are easily squeezed or collided by external forces during transportation, storage and sales, resulting in packaging damage. If the packaging film does not have good puncture resistance, it may cause agricultural products to be exposed to the external environment and accelerate decay. 2. Consumers usually have high requirements for the appearance of agricultural products, and browning will significantly reduce the attractiveness of the products and affect sales. By reducing browning, the aging process of fruits can be delayed, keeping them fresh for longer. 3. Agricultural products contain a lot of water. If the water vapor permeability of the packaging film is too high, it will cause water loss, causing the products to wilt, dry up and other problems. Excessive water vapor permeability may lead to poor humidity inside the package, which may promote the growth of microorganisms and accelerate corruption.

[0004] Chinese patent CN202411118536.3 discloses a low-temperature-resistant, puncture-resistant antibacterial composite film and its application in food packaging. It adopts a 7-layer co-extrusion blown film process, and the materials include nylon, PE, EVOH, etc. Among them, PA is arranged in the outermost layer of the composite film, and the puncture-resistant PA is easy to absorb moisture, and its toughness deteriorates at low temperatures. The EVOH layer has the function of blocking water vapor, but EVOH is not resistant to low temperatures. At low temperatures, EVOH becomes more brittle and its impact resistance deteriorates. The thickness of the PA layer in the inner layer of the composite film prepared by this method is relatively small. The thorns of special fruits (such as lychees) after vacuum packaging stored under low temperature conditions pierce the PA layer of the inner layer and the EVOH layer with moisture barrier properties, which greatly reduces the barrier effect of the composite film. In addition, EVOH molecules contain hydroxyl groups, so they have strong hydrophilicity and hygroscopicity. After EVOH absorbs moisture, its barrier properties will decrease.

[0005] Therefore, there is an urgent need for a fresh-keeping packaging film that inhibits browning and a preparation method thereof. Summary of the invention

[0006] The purpose of the present invention is to provide a fresh-keeping packaging film capable of inhibiting browning and a preparation method thereof.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A fresh-keeping packaging film for inhibiting browning, wherein the fresh-keeping packaging film comprises, from the first layer to the fifth layer from the outside to the inside, a first PE layer, a second PE layer, a third PA layer, a fourth PA layer and a fifth PE-EVA-POE layer;

[0009] The first PE layer comprises the following raw materials in parts by weight: 25-40 parts of low-density polyethylene, 15-30 parts of linear low-density polyethylene, 30-60 parts of high-density polyethylene and 2-5 parts of modified nanomaterials; the modified nanomaterials are prepared by mixing nano titanium dioxide, nano silicon dioxide and nano zinc oxide in a weight ratio of 1: (1.3-1.4): (0.5-0.7), and then reacting with a silane coupling agent KH570 and a hyperbranched polymer in sequence.

[0010] Furthermore, the preparation method of the hyperbranched polymer comprises the following steps: mixing hydrolyzed polymaleic anhydride, diisopropanolamine, 3,5-diaminobenzoic acid, triethanolamine, n-propyl titanate, and N,N-dimethylformamide, heating to 127-130° C., and reacting for 22-25 hours to obtain a hyperbranched polymer; wherein the weight ratio of hydrolyzed polymaleic anhydride, 3,5-diaminobenzoic acid, diisopropanolamine, triethanolamine, n-propyl titanate, and N,N-dimethylformamide is 1:

[0011] (3-5):(1-2):(2-3):(0.2-0.3):(6-8).

[0012] The invention can improve the puncture resistance of the fresh-keeping packaging film by adding modified nanomaterials in the first PE layer. The modified nano titanium dioxide, nano silicon dioxide and nano zinc oxide in a specific ratio can form better compatibility with the components in the first PE layer, thereby improving the puncture resistance.

[0013] Furthermore, the second PE layer comprises the following raw materials in parts by weight: 30-50 parts of low-density polyethylene, 20-40 parts of linear low-density polyethylene and 10-50 parts of high-density polyethylene.

[0014] Furthermore, the raw materials used for the third PA layer and the fourth PA layer are both polyamide 6.

[0015] Furthermore, the fifth PE-EVA-POE layer comprises the following raw materials in parts by weight: 30-55 parts of low-density polyethylene, 15-30 parts of linear low-density polyethylene, 15-30 parts of polyethylene-vinyl acetate, 10-15 parts of polyolefin elastomer, and 4-7 parts of anti-browning material.

[0016] Furthermore, the preparation method of the anti-browning material comprises the following steps:

[0017] (1) Mix montmorillonite and diatomaceous earth in a weight ratio of 1:(1.2-1.5), stir evenly, place in deionized water, heat at 90-95° C. for 10-15 minutes, filter, and retain the filter residue; dry the filter residue to a water content of less than 8%, and then grind it to less than 800 mesh to obtain an adsorption material.

[0018] (2) Prepare a tea polyphenol aqueous solution with a concentration of 5-8 g / L, mix the adsorption material and the tea polyphenol aqueous solution in a weight ratio of 1:(18-20), rotate at 40-50 r / min, stir for 4-5 hours, centrifuge, and dry the precipitate obtained by centrifugation to obtain an anti-browning material.

[0019] The present invention can improve the anti-browning effect of the fresh-keeping packaging film by adding an anti-browning material to the fifth PE-EVA-POE layer. The present invention can load more tea polyphenols by using montmorillonite and diatomaceous earth, and utilize the antioxidant and enzyme inhibition properties of tea polyphenols. Tea polyphenols will be slowly released from the adsorption material into the food environment. Montmorillonite and diatomaceous earth can protect tea polyphenols from external conditions, extend their active life, and improve the anti-browning effect. The present invention can reduce the water vapor transmission rate by adding modified nanomaterials and anti-browning materials at the same time.

[0020] Furthermore, the raw materials of the fifth PE-EVA-POE layer also include: 4-5 parts of a lubricant; and 6-8 parts of a heat sealant.

[0021] Furthermore, the melt extrusion temperatures of the first layer to the fifth layer are 195-210°C; 195-210°C; 230-240°C; 230-240°C; 185-200°C, respectively.

[0022] Furthermore, the thicknesses of the first to fifth layers are 20-35 μm, 20-30 μm, 15-30 μm, 15-30 μm, and 30-40 μm, respectively.

[0023] The present invention also provides a method for preparing the browning-inhibiting fresh-keeping packaging film, comprising the following steps: placing the raw materials of each layer in different extruders for melting and plasticization, and performing composite co-extrusion at the die head, and blowing film forming to obtain the packaging film.

[0024] The present invention also provides a fresh-keeping packaging film bag prepared by the fresh-keeping packaging film inhibiting browning.

[0025] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0026] 1. The present invention breaks through the traditional formula in the 5-layer co-extrusion, and changes the existing technology of only sandwiching a layer of PA in the middle or the surface layer to PA in the third and fourth layers, thereby increasing the flexibility of the co-extruded film and improving the puncture resistance. The fifth layer uses three main raw materials and has good tearing performance and good low-temperature heat sealing performance. The PA layer is designed inside to avoid moisture absorption, and the comprehensive fresh-keeping performance is significantly improved. The tearing performance is improved. Due to the design of double-layer PA, the moisture barrier effect is obvious, that is, the water vapor transmission rate is significantly reduced.

[0027] 2. The present invention removes branches from fresh citrus or lychees after harvesting, vacuum packs single fruits in packaging bags, stores them in liquid nitrogen at -80°C for 30 days, and takes them out after thawing in ice water at 0°C for 30 minutes. The fruits maintain good freshness and the puncture resistance of the packaging film is not significantly reduced. However, when the commercially available PE packaging bags determined by the present invention are placed under the same low-temperature conditions, the fruits turn brown significantly, the puncture resistance of the packaging film is significantly reduced, and the packaging film is not resistant to low temperatures.

[0028] Compared with commercial packaging, this packaging film has an inhibitory effect on the browning of the fruit peel when used at room temperature. Through the anti-browning effect test, the total color difference is compared with the fresh fruit peel, and the ΔE value does not exceed 10.

[0029] 3. The present invention can improve the puncture resistance of the fresh-keeping packaging film by adding modified nanomaterials into the first PE layer.

[0030] 4. The present invention can improve the anti-browning effect of the fresh-keeping packaging film by adding an anti-browning material in the fifth PE-EVA-POE layer.

[0031] 5. The present invention adds modified nanomaterials and anti-browning materials at the same time, which can reduce the water vapor transmission rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a picture of the changes in the fruit peel in the experiment to inhibit browning of the fruit peel. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The raw materials used in the following examples of the present invention are all commercially available products:

[0035] Low-density polyethylene: CNOOC Shell Petrochemical Co., Ltd., 2420T

[0036] Linear low-density polyethylene: ExxonMobil Chemical Company, LL1002BU

[0037] High-density polyethylene: ExxonMobil Chemical Company, H1003

[0038] Polyamide 6: CNOOC Shell Petrochemical Co., Ltd. N6-011

[0039] Polyethylene vinyl acetate: CNOOC Shell Petrochemical Co., Ltd. 2409X

[0040] Polyolefin elastomer: Dow Chemical Company (China), POE5401

[0041] Nano titanium dioxide: particle size 10-20nm, specific surface area 30-100m2 / g; Beijing Dekedaojin Technology Co., Ltd.

[0042] Nano-silicon dioxide: average particle size is 10nm, average specific surface area is 380m 2 / g, purchased from Jinlei Technology, model JL-S iO2-N10.

[0043] Nano zinc oxide: particle size 30-50nm, specific surface area 15-30m 2 / g; Zhejiang Zhiti Nano New Materials Co., Ltd.

[0044] Montmorillonite: Xianfeng Nano, model PGW.

[0045] Diatomite: Jilin Yuantong Mining Co., Ltd., model TL-301.

[0046] Hydrolyzed polymaleic anhydride: Shandong Haizhou Bioengineering Co., Ltd., molecular weight 400.

[0047] Example 1

[0048] A fresh-keeping packaging film for inhibiting browning, wherein the fresh-keeping packaging film comprises, from the first layer to the fifth layer from the outside to the inside, a first PE layer, a second PE layer, a third PA layer, a fourth PA layer and a fifth PE-EVA-POE layer;

[0049] The first PE layer comprises the following raw materials in parts by weight: 30 parts of low-density polyethylene, 20 parts of linear low-density polyethylene, 40 parts of high-density polyethylene and 3 parts of modified nanomaterials.

[0050] The preparation method of the modified nanomaterial comprises the following steps:

[0051] (1) Mix nano titanium dioxide, nano silicon dioxide and nano zinc oxide to obtain a nano material; wherein the weight ratio of nano titanium dioxide, nano silicon dioxide and nano zinc oxide is 1:1.3:0.6.

[0052] (2) mixing the nanomaterial, the silane coupling agent KH570 and the ethanol aqueous solution with a volume fraction of 45%, adjusting the pH to 4.5 with acetic acid, stirring and reacting at 47° C. for 7 hours, filtering, and drying to obtain a pre-modified nanomaterial; the weight ratio of the nanomaterial, the silane coupling agent KH570 and the ethanol aqueous solution with a volume fraction of 45% is 1:0.1:7;

[0053] (3) mixing hydrolyzed polymaleic anhydride, diisopropanolamine, 3,5-diaminobenzoic acid, triethanolamine, n-propyl titanate, and N,N-dimethylformamide, heating to 128° C., and reacting for 23 hours to obtain a hyperbranched polymer; the weight ratio of hydrolyzed polymaleic anhydride, 3,5-diaminobenzoic acid, diisopropanolamine, triethanolamine, n-propyl titanate, and N,N-dimethylformamide is 1:4:1.4:2.5:0.25:7;

[0054] (4) Under a nitrogen atmosphere, N,N-dimethylformamide, pre-modified nanomaterial, hyperbranched polymer and azobisisobutyronitrile were mixed, stirred for 25 minutes, and then reacted at 65°C for 16 hours. The weight ratio of N,N-dimethylformamide, pre-modified nanomaterial, hyperbranched polymer and azobisisobutyronitrile was 6:2.5:1:0.02. The mixture was filtered and dried to obtain a modified nanomaterial.

[0055] The second PE layer includes the following raw materials in parts by weight: 40 parts of low-density polyethylene, 30 parts of linear low-density polyethylene and 25 parts of high-density polyethylene.

[0056] The raw materials used for the third PA layer and the fourth PA layer are both polyamide 6.

[0057] The fifth PE-EVA-POE layer includes the following raw materials in parts by weight: 42 parts of low-density polyethylene, 23 parts of linear low-density polyethylene, 27 parts of polyethylene-vinyl acetate, 12 parts of polyolefin elastomer, and 6 parts of anti-browning material.

[0058] The preparation method of the anti-browning material comprises the following steps:

[0059] (1) Mix montmorillonite and diatomaceous earth in a weight ratio of 1:1.4, stir evenly, place in deionized water, heat at 92°C for 12 minutes, filter, and retain the filter residue; dry the filter residue to a water content of less than 8%, and then grind it to less than 800 mesh to obtain an adsorption material.

[0060] (2) A tea polyphenol aqueous solution with a concentration of 6 g / L was prepared, and the adsorption material and the tea polyphenol aqueous solution were mixed in a weight ratio of 1:19, the rotation speed was 45 r / min, the stirring was performed for 5 h, and the centrifugation was performed. The precipitate obtained by centrifugation was dried to obtain an anti-browning material.

[0061] The method for preparing the browning-inhibiting fresh-keeping packaging film comprises the following steps: placing the raw materials of each layer in different extruders for melting and plasticization, the melting and extrusion temperatures of the first to fifth layers are 200°C, 198°C, 233°C, 235°C, and 190°C, respectively; and compounding and co-extruding in the die head, the thicknesses of the first to fifth layers are 30μm, 25μm, 20μm, 18μm, and 34μm, respectively. Film blowing molding, the blowing ratio is 2.2:1, and the cooling water temperature is 25°C, to obtain the packaging film.

[0062] Example 2

[0063] A fresh-keeping packaging film for inhibiting browning, wherein the fresh-keeping packaging film comprises, from the first layer to the fifth layer from the outside to the inside, a first PE layer, a second PE layer, a third PA layer, a fourth PA layer and a fifth PE-EVA-POE layer;

[0064] The first PE layer comprises the following raw materials in parts by weight: 28 parts of low-density polyethylene, 20 parts of linear low-density polyethylene, 35 parts of high-density polyethylene and 5 parts of modified nanomaterials.

[0065] The preparation method of the modified nanomaterial comprises the following steps:

[0066] (1) Nano titanium dioxide, nano silicon dioxide and nano zinc oxide are mixed to obtain a nano material; wherein the weight ratio of nano titanium dioxide, nano silicon dioxide and nano zinc oxide is 1:1.3:0.7.

[0067] (2) mixing the nanomaterial, the silane coupling agent KH570 and the ethanol aqueous solution with a volume fraction of 50%, adjusting the pH to 4 with acetic acid, stirring and reacting at 50° C. for 6 hours, filtering, and drying to obtain a pre-modified nanomaterial; the weight ratio of the nanomaterial, the silane coupling agent KH570 and the ethanol aqueous solution with a volume fraction of 50% is 1:0.1:7;

[0068] (3) mixing hydrolyzed polymaleic anhydride, diisopropanolamine, 3,5-diaminobenzoic acid, triethanolamine, n-propyl titanate, and N,N-dimethylformamide, heating to 127° C., and reacting for 25 hours to obtain a hyperbranched polymer; the weight ratio of hydrolyzed polymaleic anhydride, 3,5-diaminobenzoic acid, diisopropanolamine, triethanolamine, n-propyl titanate, and N,N-dimethylformamide is 1:3:1:2:0.3:8;

[0069] (4) Under a nitrogen atmosphere, N,N-dimethylformamide, pre-modified nanomaterial, hyperbranched polymer and azobisisobutyronitrile were mixed, stirred for 30 minutes, and reacted at 70°C for 15 hours. The weight ratio of N,N-dimethylformamide, pre-modified nanomaterial, hyperbranched polymer and azobisisobutyronitrile was 5:2:1:0.03. The mixture was filtered and dried to obtain a modified nanomaterial.

[0070] The second PE layer includes the following raw materials in parts by weight: 42 parts of low-density polyethylene, 36 parts of linear low-density polyethylene and 38 parts of high-density polyethylene.

[0071] The raw materials used for the third PA layer and the fourth PA layer are both polyamide 6.

[0072] The fifth PE-EVA-POE layer includes the following raw materials in parts by weight: 44 parts of low-density polyethylene, 22 parts of linear low-density polyethylene, 19 parts of polyethylene-vinyl acetate, 15 parts of polyolefin elastomer, and 7 parts of anti-browning material.

[0073] The preparation method of the anti-browning material comprises the following steps:

[0074] (1) Mix montmorillonite and diatomaceous earth in a weight ratio of 1:1.2, stir evenly, place in deionized water, heat at 95°C for 10 minutes, filter, and retain the filter residue; dry the filter residue to a water content of less than 8%, and then grind it to less than 800 mesh to obtain an adsorption material.

[0075] (2) preparing a tea polyphenol aqueous solution with a concentration of 5-8 g / L, mixing the adsorption material and the tea polyphenol aqueous solution at a weight ratio of 1:20, rotating at 50 r / min, stirring for 5 h, centrifuging, and drying the precipitate obtained by centrifugation to obtain an anti-browning material.

[0076] The method for preparing the browning-inhibiting fresh-keeping packaging film comprises the following steps: placing the raw materials of each layer in different extruders for melting and plasticization, the melting and extrusion temperatures of the first to fifth layers are 200°C, 198°C, 233°C, 235°C, and 190°C, respectively; and compounding and co-extruding in the die head, the thicknesses of the first to fifth layers are 30μm, 25μm, 20μm, 18μm, and 34μm, respectively. Film blowing molding, the blowing ratio is 2.2:1, and the cooling water temperature is 25°C, to obtain the packaging film.

[0077] Comparative Example 1

[0078] The difference between this comparative example and Example 1 is that no modified nanomaterial is added to the first PE layer.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 1 is that the weight ratio of nano titanium dioxide, nano silicon dioxide and nano zinc oxide is 1:1:1.

[0081] Comparative Example 3

[0082] The difference between this comparative example and Example 1 is that the preparation method of the modified nanomaterial is different.

[0083] (1) Mix nano titanium dioxide, nano silicon dioxide and nano zinc oxide to obtain a nano material; wherein the weight ratio of nano titanium dioxide, nano silicon dioxide and nano zinc oxide is 1:1.3:0.6.

[0084] (2) The nanomaterial, the silane coupling agent KH570 and the ethanol aqueous solution with a volume fraction of 45% are mixed, the pH is adjusted to 4.5 with acetic acid, the mixture is stirred and reacted at 47° C. for 7 hours, filtered, and dried to obtain a modified nanomaterial; the weight ratio of the nanomaterial, the silane coupling agent KH570 and the ethanol aqueous solution with a volume fraction of 45% is 1:0.1:7.

[0085] Comparative Example 4

[0086] The difference between this comparative example and Example 1 is that no anti-browning material is added to the fifth PE-EVA-POE layer.

[0087] Comparative Example 5

[0088] The difference between this comparative example and Example 1 is: commercially available product. Brand: Guangdong Huicheng Packaging Co., Ltd. Five-layer co-extruded LDPE film, model PE-X, thickness 110 μm*width 730 mm.

[0089] Performance Testing

[0090] 1. The heat sealing strength of the packaging films of Example 1 and Comparative Example 5 was compared under the test conditions of 0.2 MPa and 1 s. The results are shown in Table 1.

[0091] Table 1 Heat seal strength test results (unit: N)

[0092] 115℃ 120℃ 125℃ 130℃ 135℃ 140℃ Example 1 0 4.5 20.6 23.2 24.5 26.5 Comparative Example 5 0 0 2.0 19.9 21.0 21.1

[0093] 2. Determine the performance parameters of the packaging films of Examples 1-2 and Comparative Examples 1-5. The results are shown in

[0094] Table 2.

[0095]

[0096]

[0097] As shown in Table 1, the fresh-keeping packaging films of Examples 1-2 have excellent comprehensive performance. They have good low-temperature heat-sealing performance, and the heat-sealing temperature of 120°C is 4.5N higher than that of commercially available products. The puncture resistance of Example 1 reaches 4.7N; the impact strength reaches 159kJ / m 2 The nominal strain after stretching exceeds 460%.

[0098] In Comparative Example 1, the first PE layer does not contain modified nanomaterials. It can be seen that the puncture resistance of the fresh-keeping packaging film is reduced, and the tensile strength and impact strength are reduced.

[0099] In Comparative Example 2, the weight ratio of nano-titanium dioxide, nano-silicon dioxide and nano-zinc oxide was changed. From the results, it can be seen that the puncture resistance of the fresh-keeping packaging film is reduced and the water vapor transmission rate is increased.

[0100] In Comparative Example 3, the preparation method of the modified nanomaterial is different. From the results, it can be seen that the puncture resistance of the fresh-keeping packaging film is reduced.

[0101] In Comparative Example 4, the fifth PE-EVA-POE layer does not have any anti-browning material added, and the water vapor transmission rate becomes higher.

[0102] Figure 1 This is a picture of the changes in the fruit skin during the experiment to inhibit the browning of the fruit skin. Figure 1 It can be seen that the packaging film of Example 1 of the present invention has a better anti-browning effect.

[0103] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A fresh-keeping packaging film for inhibiting browning, characterized in that: The first to fifth layers of the fresh-keeping packaging film from the outside to the inside sequentially include: a first PE layer, a second PE layer, a third PA layer, a fourth PA layer and a fifth PE-EVA-POE layer; The first PE layer comprises the following raw materials in parts by weight: 25-40 parts of low-density polyethylene, 15-30 parts of linear low-density polyethylene, 30-60 parts of high-density polyethylene and 2-5 parts of modified nanomaterials; the modified nanomaterials are prepared by mixing nano titanium dioxide, nano silicon dioxide and nano zinc oxide, and reacting with silane coupling agent KH570 and hyperbranched polymer in sequence.

2. The browning-inhibiting fresh-keeping packaging film according to claim 1, characterized in that: The preparation method of the hyperbranched polymer comprises the following steps: mixing hydrolyzed polymaleic anhydride, diisopropanolamine, 3,5-diaminobenzoic acid, triethanolamine, n-propyl titanate and N,N-dimethylformamide, heating to 127-130° C., reacting for 22-25 hours, and obtaining a hyperbranched polymer; wherein the weight ratio of the hydrolyzed polymaleic anhydride, 3,5-diaminobenzoic acid, diisopropanolamine, triethanolamine, n-propyl titanate and N,N-dimethylformamide is 1:(3-5):(1-2):(2-3):(0.2-0.3):(6-8).

3. The browning-inhibiting fresh-keeping packaging film according to claim 1, characterized in that: The second PE layer comprises the following raw materials in parts by weight: 30-50 parts of low-density polyethylene, 20-40 parts of linear low-density polyethylene and 10-50 parts of high-density polyethylene.

4. The browning-inhibiting fresh-keeping packaging film according to claim 1, characterized in that: The raw materials used for the third PA layer and the fourth PA layer are both polyamide 6.

5. The browning-inhibiting fresh-keeping packaging film according to claim 1, characterized in that: The fifth PE-EVA-POE layer comprises the following raw materials in parts by weight: 30-55 parts of low-density polyethylene, 15-30 parts of linear low-density polyethylene, 15-30 parts of polyethylene-vinyl acetate, 10-15 parts of polyolefin elastomer and 4-7 parts of anti-browning material.

6. The browning-inhibiting fresh-keeping packaging film according to claim 5, characterized in that: The preparation method of the anti-browning material comprises the following steps: (1) Mix montmorillonite and diatomaceous earth, stir them evenly, place them in deionized water, heat them at 90-95° C. for 10-15 minutes, filter them, and retain the filter residue; dry the filter residue, and then grind it to obtain an adsorption material. (2) Prepare a tea polyphenol aqueous solution with a concentration of 5-8 g / L, mix the adsorption material and the tea polyphenol aqueous solution in a weight ratio of 1:(18-20), rotate at 40-50 r / min, stir for 4-5 hours, centrifuge, and dry the precipitate obtained by centrifugation to obtain an anti-browning material.

7. The browning-inhibiting fresh-keeping packaging film according to claim 5, characterized in that: The raw materials of the fifth PE-EVA-POE layer also include: 4-5 parts of a lubricant; and 6-8 parts of a heat sealant.

8. The browning-inhibiting fresh-keeping packaging film according to claim 1, characterized in that: The melt extrusion temperatures of the first to fifth layers are 195-210°C; 195-210°C; 230-240℃；230-240℃；185-200℃。 9. A method for preparing the browning-inhibiting fresh-keeping packaging film according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: placing raw materials of each layer in different extruders for melting and plasticization respectively, and compounding and co-extruding at the die head, and blowing film to form, so as to obtain the packaging film.

10. A fresh-keeping packaging film bag prepared from the fresh-keeping packaging film with browning inhibition according to any one of claims 1 to 8.

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