A high-barrier packaging film and its preparation method

Abstract

This application relates to the field of packaging materials, and specifically discloses a high-barrier packaging film and a preparation method thereof. A high-barrier packaging film includes an outer layer, an intermediate layer, and an inner layer; both the outer layer and the inner layer are water-proof layers; the intermediate layer is made of raw materials comprising the following parts by weight: 10-15 parts of aromatic dicarboxylic acid; 60-75 parts of aliphatic diamine; 45-55 parts of aliphatic dicarboxylic acid; the preparation method is: respectively feeding the raw materials of the outer layer, the intermediate layer, and the inner layer into an extruder for melt processing, and then feeding the melt of the raw materials of the outer layer, the intermediate layer, and the inner layer into a casting machine or a blow molding machine for coextrusion into a film and cooling to obtain a high-barrier packaging film. The high-barrier packaging film of this application can solve the problem that the goods in the packaging bag deteriorate due to oxygen and water vapor.

Description

Technical Field

[0001] The present application relates to the technical field of packaging materials, and more specifically, to a high-barrier packaging film and a preparation method thereof. Background Art

[0002] In our environment, there are substances such as oxygen, carbon dioxide, and water vapor. They are both necessary conditions for human survival and common factors causing damage and deterioration of many substances. In particular, the presence of oxygen and water vapor is an important factor that cannot be ignored in the storage of many commodities, such as processed foods, grains, and dried fruits. There are numerous cases where commodities deteriorate due to components such as oxygen, carbon dioxide, and water vapor.

[0003] For example, dried foods may lose their brittleness due to water absorption and softening; fried foods may develop a "rancid" smell due to oxidation; oxygen is a necessary condition for the survival of many aerobic bacteria, and the presence of oxygen may lead to the rapid reproduction of bacteria, which is a common cause of food spoilage. The spoilage of processed meat due to bacterial reproduction is a typical case in this regard.

[0004] In order to avoid the occurrence of the above problems, it is urgent to develop a packaging material with good barrier properties to form an independent space that can be isolated from the external environment inside the packaging bag and reduce the impact of external oxygen and water vapor on the commodities inside the packaging bag. Summary of the Invention

[0005] In order to solve the problem of deterioration of commodities inside the packaging bag due to oxygen and water vapor, the present application provides a high-barrier packaging film and a preparation method thereof.

[0006] In the first aspect, the present application provides a high-barrier packaging film, adopting the following technical solution:

[0007] A high-barrier packaging film includes an outer layer, an intermediate layer, and an inner layer; both the outer layer and the inner layer are water-proof layers; the intermediate layer is made of raw materials including the following parts by weight: 10-15 parts of aromatic dicarboxylic acid; 60-75 parts of aliphatic diamine; 45-55 parts of aliphatic dicarboxylic acid.

[0008] By adopting the above technical solution, the modified polyamide is prepared by reacting the above raw materials. Among them, the aromatic dicarboxylic acid contains a rigid planar structure, which can make the molecular chains of the modified polyamide stack more closely, reduce the free volume in the structure of the modified polyamide, and reduce the possibility of small molecule gases passing through the intermediate layer. In addition, the rigid planar structure in the aromatic dicarboxylic acid also enhances the rigidity of the molecular chains of the modified polyamide, restricts the movement of the molecular chains of the modified polyamide, makes it difficult to form gas channels inside the polyamide, enhances the barrier performance of the modified polyamide, and the intermediate layer made of the modified polyamide has good barrier performance. The outer layer and the inner layer are both waterproof layers, and the two waterproof layers and the intermediate layer together produce a packaging film with better barrier performance, solving the problem that the goods in the packaging bag deteriorate due to oxygen and water vapor.

[0009] Preferably, the aromatic dicarboxylic acid is one or more of terephthalic acid, 2-methyl terephthalic acid, naphthol dicarboxylic acid, hydroxyquinoline dicarboxylic acid, and fluorinated benzene dicarboxylic acid.

[0010] Preferably, the aromatic dicarboxylic acid is hydroxyquinoline dicarboxylic acid and / or naphthol dicarboxylic acid.

[0011] By adopting the above technical solution, both hydroxyquinoline dicarboxylic acid and naphthol dicarboxylic acid contain hydroxyl groups, introducing active hydrogen atoms onto the main chain of the modified polyamide. The active hydrogen atoms can form hydrogen bonds with the polar groups on the main chain, increasing the intermolecular force, increasing the packing density of the modified polyamide, and reducing the free volume of the modified polyamide. In addition, the hydrogen bond effect can also induce the crystallization of the modified polyamide, further improving the barrier performance of the modified polyamide, and thus enhancing the barrier performance of the packaging film.

[0012] Preferably, the aromatic dicarboxylic acid is fluorinated benzene dicarboxylic acid.

[0013] By adopting the above technical solution, fluorinated benzene dicarboxylic acid introduces fluorine atoms into the modified polyamide. Fluorine is the element with the highest electronegativity, and the fluorocarbon bond has very good stability. The introduction of fluorine atoms reduces the surface energy of the modified polyamide, improves the hydrophobic effect of the intermediate layer, and improves the water vapor barrier performance of the packaging film.

[0014] Preferably, the raw materials of the intermediate layer further include 4-6 parts by weight of nanocellulose.

[0015] By adopting the above technical solution, nanocellulose has the following functions: First, nanocellulose contains a large number of hydroxyl groups, which can crosslink with the modified polyamide through hydrogen bond interaction, improving the crosslinking degree of the modified polyamide, and thus enhancing the density of the structure of the modified polyamide. Second, nanocellulose itself also has good oxygen barrier performance. Adding nanocellulose to the raw materials of the intermediate layer can improve the barrier performance of the intermediate layer, and thus enhance the barrier performance of the packaging film.

[0016] Preferably, the raw materials of the intermediate layer further include 2-4 parts by weight of a modifier; the modifier is dioctadecyl hydroxypropyl dicarboxylate and / or glycerol monolaurate.

[0017] By adopting the above technical solution, the modifier is grafted onto the modified polyamide through a hydroxyl group, introducing a hydrophobic long chain into the modified polyamide. The hydrophobic long chains are arranged on the surface of the modified polyamide, improving the water vapor barrier property of the intermediate layer.

[0018] Preferably, the raw materials of the water barrier layer include polylactic acid and polyethylene glycol, and the mass ratio of polyethylene glycol to polylactic acid is (8-12):100.

[0019] By adopting the above technical solution, the hydroxyl group of polyethylene glycol reacts with the carboxyl group in polylactic acid, introducing a flexible polyethylene glycol segment into the polylactic acid molecular chain, improving the toughness of polylactic acid; polylactic acid has good barrier properties to water vapor and oxygen. Using polylactic acid and polyethylene glycol as raw materials can produce a water barrier layer with better toughness and barrier properties.

[0020] Preferably, the raw materials of the water barrier layer further include a hydroxyl-terminated hyperbranched polyester, and the mass ratio of the hydroxyl-terminated hyperbranched polyester to polylactic acid is (5-8):100.

[0021] By adopting the above technical solution, the hydroxyl-terminated hyperbranched polyester contains multiple branches. On the one hand, the hydroxyl-terminated hyperbranched polyester physically cross-links with polylactic acid molecules and polyethylene glycol molecules through multiple branches, improving the toughness of the water barrier layer. On the other hand, the hydroxyl-terminated hyperbranched polyester cross-links with the modified polyamide through hydrogen bonds, further improving the adhesion performance between the outer layer, the intermediate layer, and the inner layer, reducing the possibility of gas molecules passing through the packaging film through the interlayer voids, and improving the barrier performance of the packaging film.

[0022] Preferably, the raw materials of the water barrier layer further include nano-silica, and the mass ratio of nano-silica to polylactic acid is (2-3):100.

[0023] By adopting the above technical solution, the hydroxyl-terminated hyperbranched polyester physically cross-links with polylactic acid. There is a hydrogen bond interaction between nano-silica and the hydroxyl-terminated hyperbranched polyester. The hydroxyl-terminated hyperbranched polyester improves the compatibility between nano-silica and polylactic acid, making nano-silica evenly dispersed in polylactic acid. The evenly dispersed nano-silica as a filler improves the barrier performance of polylactic acid and also improves the toughness of polylactic acid.

[0024] Second, the present application provides a method for preparing a high-barrier packaging film, adopting the following technical solution:

[0025] A method for preparing a high-barrier packaging film, comprising the following steps:

[0026] The outer layer raw materials, middle layer raw materials, and inner layer raw materials are respectively put into an extruder for melting and processing, and the melt of the outer layer raw materials, middle layer raw materials, and inner layer raw materials is sent into a casting machine or a blow molding machine for coextrusion into a film and cooling to obtain a high-barrier packaging film.

[0027] In summary, the present application has the following beneficial effects:

[0028] 1. The present application uses aromatic dicarboxylic acids as raw materials to prepare modified polyamides, introducing a rigid planar structure into the modified polyamides. On the one hand, it makes the molecular chains of the modified polyamides stack more closely, reduces the free volume in the structure of the modified polyamides, and reduces the possibility of small molecule gases passing through the middle layer; on the other hand, it enhances the rigidity of the molecular chains of the modified polyamides, restricts the movement of the molecular chains of the modified polyamides, and makes it difficult to form gas channels inside the modified polyamides. The middle layer made of the modified polyamides has good barrier properties; the outer layer and the inner layer are both waterproof layers, and the two waterproof layers and the middle layer together produce a packaging film with better barrier properties, solving the problem of the goods in the packaging bag deteriorating due to oxygen and water vapor.

[0029] 2. In the present application, hydroxyquinoline dicarboxylic acid and / or naphthol dicarboxylic acid are preferably used. Both hydroxyquinoline dicarboxylic acid and naphthol dicarboxylic acid contain hydroxyl groups, and there is a hydrogen bond interaction between the hydroxyl groups and the polar groups on the main chain of the modified polyamide, improving the intermolecular force and packing density of the modified polyamide, and also being able to induce the crystallization of the modified polyamide, further enhancing the barrier properties of the modified polyamide, and thus improving the barrier properties of the packaging film.

[0030] 3. The packaging film of the present application is divided into an outer layer, a middle layer, and an inner layer, where the outer layer and the inner layer are both water barrier layers, and terminal hydroxyl hyperbranched polyester and polylactic acid are used as raw materials for the water barrier layers. The polylactic acid molecular chain contains a large number of hydrophobic ester groups, making it have good waterproof performance; on the one hand, the hyperbranched polyester physically entangles with the polylactic acid through a large number of branches, and on the other hand, it forms a hydrogen bond crosslinking with the polar groups on the modified polyamide of the middle layer through hydroxyl groups, improving the adhesion performance between the outer layer, the middle layer, and the inner layer, reducing the possibility of gas molecules passing through the gaps between the layers and passing through the packaging film, and enhancing the barrier properties of the packaging film. Specific Embodiments

[0031] The following further elaborates on the present application in conjunction with examples.

[0032] Unless otherwise specified, the specifications of the raw materials used in the following examples and comparative examples are shown in Table 1.

[0033] Table 1. Information on Raw Material Specifications

[0034] Raw materials Specifications Fluorobenzenedicarboxylic acid 3-Fluorophthalic acid Nanocellulose Model: CNF-H2 Polylactic acid Item number: REVODE701 Polyethylene glycol Model: PEG200 Nanosilica Item number: REOLOSIL QS-30-1

[0035] Preparation Example of Aromatic Dicarboxylic Acid

[0036] Preparation Example a

[0037] Hydroxyquinoline dicarboxylic acid was prepared according to the following steps:

[0038] 500 g of 5,7-dichloro-8-carboxyquinoline and 1200 ml of toluene were mixed to obtain a mixed solution. 180 g of anhydrous aluminum trichloride was added to the above mixed solution under an ice-water bath, and the temperature was raised to 50 °C. The reaction was carried out for 2 h, then the temperature was raised to 90 °C and kept warm for 12 h. After cooling to 25 °C, it was washed with 20% (mass fraction) dilute hydrochloric acid, filtered, and dried to obtain Substance A;

[0039] 300 g of Substance A was taken and added to 1000 ml of glacial acetic acid. After mixing and stirring for 1 h, the temperature was raised to 25 °C and the reaction was stirred for 8 h. It was washed with 20% (mass fraction) dilute hydrochloric acid, filtered by suction, and dried to obtain hydroxyquinoline dicarboxylic acid.

[0040] Preparation Example b

[0041] Naphthol dicarboxylic acid was prepared according to the following steps:

[0042] 500 g of 5,7-dichloro-8-carboxyquinoline and 1200 ml of toluene were mixed to obtain a mixed solution. 180 g of anhydrous aluminum trichloride was added to the above mixed solution under an ice-water bath, and the temperature was raised to 50 °C. The reaction was carried out for 2 h, then the temperature was raised to 90 °C and kept warm for 12 h. After cooling to 25 °C, it was washed with 20% (mass fraction) dilute hydrochloric acid, filtered, and dried to obtain Substance B;

[0043] 300 g of Substance B was taken and added to 1000 ml of glacial acetic acid. After mixing and stirring for 1 h, the temperature was raised to 25 °C and the reaction was stirred for 8 h. It was washed with 20% (mass fraction) dilute hydrochloric acid, filtered by suction, and dried to obtain naphthol dicarboxylic acid.

[0044] Preparation Example of Hydroxyl-Terminated Hyperbranched Polyester

[0045] Preparation Example A

[0046] The hydroxyl-terminated hyperbranched polyester was prepared according to the following steps:

[0047] Under nitrogen protection, 50 g of 2,2-bis(hydroxymethyl)propionic acid, 10 g of trimethylolpropane, and 0.18 g of p-toluenesulfonic acid were mixed and stirred. The temperature was raised to 130 °C and dehydrated by refluxing for 4 h. 100 g of 2,2-bis(hydroxymethyl)propionic acid and 0.85 g of p-toluenesulfonyl chloride were added, and nitrogen was continuously passed for protection. The reaction was carried out at 130 °C for 3 h. The nitrogen passing was stopped, and water was removed by reduced pressure distillation. 150 g of 2,2-bis(hydroxymethyl)propionic acid and 1.8 g of p-toluenesulfonyl chloride were added, nitrogen was passed for protection, and the reaction was continued at 130 °C for 3 h. After cooling to 25 °C, it was dissolved in 1000 g of acetone, filtered by suction, and dried to obtain the hydroxyl-terminated hyperbranched polyester.

[0048] Preparation Example of Intermediate Layer Raw Material

[0049] Preparation Example 1

[0050] The intermediate layer raw material was prepared according to the following steps:

[0051] 600 g of hexamethylenediamine was mixed and stirred with 1000 g of water, heated to 50 °C, 100 g of terephthalic acid and 450 g of malonic acid were added, 500 g of water was added additionally, mixed and stirred, 2 g of sodium dihydrogen phosphate dihydrate was added, the pH value was adjusted to 7, kept warm at 50 °C for 1 h, cooled to 25 °C, filtered by suction and dried to obtain a modified polyamide salt;

[0052] The modified polyamide salt was put into a reaction kettle, 100 g of distilled water was added, the air in the reaction kettle was replaced with nitrogen 3 times, then nitrogen was charged, the pressure in the reaction kettle was maintained at 0.3 MPa, heated to 220 °C, the pressure in the kettle rose to 2.2 MPa, reacted for 1 h, the gas was slowly released to reduce the pressure in the kettle to 0.1 MPa within 2 h, vacuum reacted for 1 h, cooled to 25 °C to obtain a modified polyamide prepolymer;

[0053] The modified polyamide prepolymer was crushed, dried, and then put into a reaction kettle, reacted under a vacuum of 10 Pa for 10 h to obtain the intermediate layer raw material.

[0054] Preparation Examples 2 - 3

[0055] The difference between the intermediate layer raw material and Preparation Example 1 is that the composition of the intermediate layer raw material is different, and the specific composition is shown in Table 2 below:

[0056] Table 2. Composition of Intermediate Layer Raw Material

[0057]

[0058] Preparation Example 4

[0059] The difference between the intermediate layer raw material and Preparation Example 3 is that the aromatic dicarboxylic acid is different. In this preparation example, terephthalic acid was replaced with hydroxyquinoline dicarboxylic acid prepared in Preparation Example a in equal mass.

[0060] Preparation Example 5

[0061] The difference between the intermediate layer raw material and Preparation Example 3 is that the aromatic dicarboxylic acid is different. In this preparation example, terephthalic acid was replaced with naphthol dicarboxylic acid prepared in Preparation Example b in equal mass.

[0062] Preparation Example 6

[0063] The difference between the intermediate layer raw material and Preparation Example 3 is that the aromatic dicarboxylic acid is different. In this preparation example, terephthalic acid was replaced with 3 - fluorophthalic acid in equal mass.

[0064] Preparation Example 7

[0065] The intermediate layer raw material, the difference from Preparation Example 6 is that: 40 g of nanocellulose is newly added to the intermediate layer raw material.

[0066] Preparation Example 8

[0067] The intermediate layer raw material, the difference from Preparation Example 6 is that: 60 g of nanocellulose is newly added to the intermediate layer raw material.

[0068] Preparation Example 9

[0069] The intermediate layer raw material, the difference from Preparation Example 8 is that: 20 g of modifier dipropylene glycol monostearate is newly added to the intermediate layer raw material.

[0070] Preparation Example 10

[0071] The intermediate layer raw material, the difference from Preparation Example 8 is that: 20 g of modifier monoglyceryl laurate is newly added to the intermediate layer raw material.

[0072] Preparation Example 11

[0073] The intermediate layer raw material, the difference from Preparation Example 8 is that: 40 g of modifier monoglyceryl laurate is newly added to the intermediate layer raw material.

[0074] Preparation Comparative Example of Intermediate Layer Raw Material

[0075] Preparation Comparative Example 1

[0076] The intermediate layer raw material, the difference from Preparation Example 1 is that: terephthalic acid is replaced with malonic acid in equal mass.

[0077] Examples

[0078] Example 1

[0079] A high-barrier packaging film is prepared according to the following steps:

[0080] Take 200 g of polylactic acid and 16 g of polyethylene glycol and put them into an extruder for melt processing to obtain an outer layer raw material melt;

[0081] Take 300 g of the intermediate layer raw material prepared in Preparation Example 1 and put it into an extruder for melt processing to obtain an intermediate layer raw material melt;

[0082] Take 200 g of polylactic acid and 16 g of polyethylene glycol and put them into an extruder for melt processing to obtain an inner layer raw material melt;

[0083] Feed the outer layer raw material, the intermediate layer raw material, and the inner layer raw material melt into a casting machine for coextrusion into a film and cooling to obtain a high-barrier packaging film.

[0084] Examples 2 - 11

[0085] A high-barrier packaging film, the difference from Example 1 lies in: the selection of the raw materials for the middle layer is different, and the specific selection is shown in Table 3 below:

[0086] Table 3. Selection of Raw Materials for the Middle Layer

[0087]

[0088]

[0089] Example 12

[0090] A high-barrier packaging film, the difference from Example 11 lies in: both the outer layer and the inner layer are water-proof layers, and the selection of the raw materials for the water-proof layers is different. In this example, 10 g of the hydroxyl-terminated hyperbranched polyester prepared from Preparation Example A is newly added to the raw materials for the water-proof layer.

[0091] Example 13

[0092] A high-barrier packaging film, the difference from Example 11 lies in: both the outer layer and the inner layer are water-proof layers, and the selection of the raw materials for the water-proof layers is different. In this example, 16 g of the hydroxyl-terminated hyperbranched polyester prepared from Preparation Example A is newly added to the raw materials for the water-proof layer.

[0093] Example 14

[0094] A high-barrier packaging film, the difference from Example 13 lies in: the selection of the raw materials for the water-proof layer is different. In this example, 4 g of nano-silica is newly added to the raw materials for the water-proof layer.

[0095] Example 15

[0096] A high-barrier packaging film, the difference from Example 13 lies in: the selection of the raw materials for the water-proof layer is different. In this example, 6 g of nano-silica is newly added to the raw materials for the water-proof layer.

[0097] Example 16

[0098] A high-barrier packaging film, the difference from Example 15 lies in: the dosage of polyethylene glycol in the raw materials for the water-proof layer is different. In this example, 24 g of polyethylene glycol is added to the raw materials for the water-proof layer.

[0099] Comparative Example

[0100] Comparative Example 1

[0101] A high-barrier packaging film, the difference from Example 1 lies in: the selection of the raw materials for the middle layer is different. In this comparative example, the raw materials for the middle layer prepared in Comparative Example 1 are selected.

[0102] Performance Detection

[0103] Detection Method

[0104] The total migration amount in the high-barrier packaging films prepared in Examples 1-16 and Comparative Example 1 was detected in accordance with GB 4806.7-2016 "National Food Safety Standard - Plastic Materials and Products for Food Contact" to characterize the safety performance of the high-barrier packaging films;

[0105] The oxygen transmission rate of the high-barrier packaging films prepared in Examples 1-16 and Comparative Example 1 was tested in accordance with GB / T 1038-2000 to characterize the oxygen barrier performance of the high-barrier packaging films;

[0106] The water vapor transmission rate of the high-barrier packaging films prepared in Examples 1-16 and Comparative Example 1 was tested in accordance with GB / T 1037-88 to characterize the water vapor barrier performance of the high-barrier packaging films;

[0107] The elongation at break of the high-barrier packaging films prepared in Examples 1-16 and Comparative Example 1 was tested in accordance with GB / T 1040.1-2006 to characterize the toughness of the high-barrier packaging films. The higher the elongation at break, the better the toughness. The specific test results are shown in Table 4.

[0108] Test Results

[0109] Table 4. Performance Test of High-Barrier Packaging Films

[0110]

[0111]

[0112] As can be seen from Table 4, the oxygen transmission rate of the high-barrier packaging film prepared in the examples of this application is ≤ 0.67 cm 3 / m 2 ·24 h·bar, the water vapor transmission rate is ≤ 0.563 g / m 2 ·24 h, and the elongation at break is ≥ 148%. It can be seen that the gas barrier performance and mechanical properties of a high-barrier packaging film of this application are better;

[0113] In addition, the total migration amount of the high-barrier packaging film prepared in the examples of this application is ≤ 3.87 mg / dm 2 , meeting the requirement in GB4806.7-2016 that the total migration amount is not higher than 10 mg / dm 2 and meeting the safety requirements of plastic materials for food contact.

[0114] Combining Example 1 and Comparative Example 1 and Table 4, it can be seen that the oxygen transmission rate of the high-barrier packaging film prepared in Example 1 is 0.66 cm 3 / m 2 ·24 h·bar, which is much lower than that of Comparative Example 1. The water vapor transmission rate of Example 1 is 0.563 g / m 2·24h is also much lower than that of Comparative Example 1. This may be because: Example 1 selects the intermediate layer raw material prepared in Preparation Example 1, while Preparation Example 1 selects aromatic dibasic acid as the raw material for the intermediate layer. The raw material for the intermediate layer is modified polyamide. The aromatic dibasic acid contains a rigid planar structure, which can make the molecular chains of the modified polyamide stack more tightly, reduce the free volume in the modified polyamide structure, and reduce the possibility of small molecular gases passing through the intermediate layer; in addition, the rigid planar structure also enhances the rigidity of the modified polyamide molecular chain, restricts the movement of the modified polyamide molecular chain, makes it difficult to form a gas channel inside the modified polyamide, improves the barrier performance of the intermediate layer, and then improves the barrier performance of the high barrier packaging film.

[0115] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A high-barrier packaging film, characterized in that: It includes an outer layer, an intermediate layer and an inner layer; both the outer layer and the inner layer are water-proof layers; the intermediate layer is made of raw materials comprising the following parts by weight: 10-15 parts of aromatic diacid; 60-75 parts of aliphatic diamine; 45-55 parts of aliphatic diacid, and the aromatic diacid is one of hydroxyquinoline diacid, naphthol diacid and fluorinated benzene diacid.

2. The high-barrier packaging film according to claim 1, characterized in that: The raw materials of the intermediate layer further include 4-6 parts by weight of nanocellulose.

3. The high-barrier packaging film according to claim 1, characterized in that: The raw materials of the intermediate layer further include 2-4 parts by weight of a modifier; the modifier is dioxypropyl octadecanoate and / or monoglyceride laurate.

4. The high-barrier packaging film according to claim 1, characterized in that: The raw materials of the water-proof layer include polylactic acid and polyethylene glycol, and the mass ratio of polyethylene glycol to polylactic acid is (8-12):

100.

5. The high-barrier packaging film according to claim 4, characterized in that: The raw materials of the water-proof layer further include hydroxyl-terminated hyperbranched polyester, and the mass ratio of the hydroxyl-terminated hyperbranched polyester to polylactic acid is (5-8):

100.

6. The high-barrier packaging film according to claim 5, characterized in that: The raw materials of the water-proof layer further include nano-silica, and the mass ratio of the nano-silica to polylactic acid is (2-3):

100.

7. A method for preparing the high-barrier packaging film according to any one of claims 1-6, characterized in that It includes the following steps: Put the raw materials of the outer layer, the raw materials of the intermediate layer and the raw materials of the inner layer into an extruder for melt processing respectively, and then send the melt of the raw materials of the outer layer, the intermediate layer and the inner layer into a casting machine or a blow molding machine for co-extrusion into a film and cooling to obtain a high-barrier packaging film.

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