High-barrier composite coating liquid and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a high-barrier composite coating liquid and a preparation method thereof. Aiming at the problems of poor barrier property and limited application scene of a PE (polyethylene) film in the prior art, the invention provides the high-barrier composite coating liquid and the preparation method thereof, and the high-barrier composite coating liquid comprises the following components in parts by mass: 25-35 parts of deionized water, 45-65 parts of low-polymerization-degree PVA (polyvinyl alcohol) emulsion, 10-25 parts of low-polymerization-degree ethylene maleic anhydride homopolymer and 0.5-2 parts of flow improver. The composite coating liquid provided by the invention is coated on the surface of a PE film, so that the problem of poor barrier property of a PE film made of a single material can be effectively solved, and the PE film can partially replace composite films such as PET / PE, PA / PE, KPET / PE or PET / PA / PE of a three-layer structure, BOPP / PA / PE and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a high-barrier composite coating liquid and a preparation method thereof. Background Art

[0002] Although plastic films or composite films have been widely used to package food and non-food materials, plastics generally have poor barrier properties to gases such as oxygen, aroma or water vapor. When packaging food, it is even more important to have barrier properties to gases such as oxygen and water vapor. Oxygen and moisture in the environment can easily cause food oxidation, resulting in browning, rancidity, taste change and odor, and mold formation, which makes it impossible to extend the shelf life of food. Spoiled food can also cause harm to the body.

[0003] At present, most of the high-barrier packaging bags on the market are composite materials, such as PET / PE, PA / PE, KPET / PE or three-layer structure PET / PA / PE, BOPP / PA / PE, etc., but they are difficult to recycle after use, and the raw materials and manufacturing costs are also high. PE film is the simplest macromolecular organic compound with low price and high toughness and strength. It is the most widely used macromolecular material in the world today, but its barrier properties to gases such as oxygen are poor, so it is usually coated. The most widely used coating types are PVDC, PVA, etc. as barrier coatings, but PVDC can maintain high barrier properties under high temperature and high humidity, but the subsequent recycling and treatment is not environmentally friendly. Chlorine-containing compounds will produce dioxins and other damage to the environment and human health when burned. In addition, some coatings such as PVDC coatings have poor adhesion and need to be processed by two processes of primer and topcoat. The PVA molecular chain is symmetrical and regular, and it mainly relies on the combination of intermolecular hydrogen bonds to reduce the intermolecular gaps and hinder oxygen penetration, but the hydrogen bond energy is weak and its stability is poor. In high temperature and high humidity environments, the barrier properties are greatly reduced, and the use scenarios are limited.

[0004] For example, a Chinese invention patent application discloses a high-barrier modified PVA / acrylic composite coating liquid and its preparation method [application number: 202211151469.6]. The invention application contains the following components in weight percentage: 10-30% aqueous acrylic emulsion; 2-10% PVA resin; 1-5% low molecular weight hydroxyl-containing polyolefin; 1-5% cross-linking agent; 2-8% cosolvent; 50%-80% deionized water. The preparation steps include: (a) first adding deionized water to a container, then adding PVA resin and stirring continuously, heating to completely dissolve PVA; (b) adding low molecular weight hydroxyl-containing polyolefin resin to the cosolvent and stirring to dissolve, adding the cross-linking agent to react at 70-80°C, then adding the dissolved PVA solution to continue the reaction and then cooling to room temperature to obtain a modified PVA resin liquid; (c) adding the aqueous acrylic emulsion to the modified PVA resin liquid, mixing evenly to obtain a high-barrier modified PVA / acrylic composite coating liquid.

[0005] This invention application uses water-based acrylic emulsion and PVA resin as the main materials of the coating liquid, but it can be seen from its performance test that the coating liquid is mainly suitable for PET film and BOPP film, and cannot be well applied to PE film. Summary of the invention

[0006] The object of the present invention is to provide a high-barrier composite coating liquid in view of the above problems.

[0007] Another object of the present invention is to provide a method for preparing a high-barrier composite coating liquid in view of the above problems.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A high-barrier composite coating liquid comprises 25-35 parts by weight of deionized water, 45-65 parts by weight of a low-polymerization degree PVA emulsion, 10-25 parts by weight of a low-polymerization degree ethylene maleic anhydride homopolymer and 0.5-2 parts by weight of a flow improver.

[0010] The high-barrier composite coating liquid mentioned above includes 31 parts by weight of deionized water, 48 parts by weight of low-polymerization degree PVA emulsion, 20 parts by weight of low-polymerization degree ethylene maleic anhydride homopolymer and 1 part by weight of flow improver.

[0011] In the above-mentioned high-barrier composite coating liquid, the low-polymerization degree PVA emulsion comprises 6-12 parts by weight of PVA resin, 70-90 parts by weight of solvent, 0.1-1 parts by weight of defoaming agent and 0.5-2 parts by weight of surfactant.

[0012] In the above-mentioned high-barrier composite coating liquid, the low-polymerization degree PVA emulsion includes 10 parts by weight of PVA resin, 80 parts by weight of solvent, 0.5 parts by weight of defoaming agent and 1 part by weight of surfactant.

[0013] In the above-mentioned high-barrier composite coating solution, the solvent is deionized water.

[0014] In the above-mentioned high-barrier composite coating liquid, the surfactant is a mixture of hexadecyltrimethylammonium bromide and PEG2000 in a mass ratio of 1:1.

[0015] In the above-mentioned high-barrier composite coating liquid, the molecular weight of the PVA resin is 10,000-120,000.

[0016] In the above-mentioned high-barrier composite coating liquid, the low-polymerization degree ethylene maleic anhydride homopolymer is a 1:1 homopolymer of ethylene and maleic anhydride, and has a molecular weight of 8,000-80,000.

[0017] In the above-mentioned high-barrier composite coating liquid, the flow improver includes at least one of polyethylene wax, polyether silicone oil and polyacrylic acid.

[0018] A method for preparing the above-mentioned high-barrier composite coating liquid comprises the following steps:

[0019] Step 1: First, add deionized water and flow improver into low-polymerization PVA emulsion, stir evenly, and heat to 75-80°C to obtain a mixed solution;

[0020] Step 2: adding a low-polymerization degree ethylene maleic anhydride homopolymer to the mixed solution prepared in step 1 while stirring to obtain a composite coating solution;

[0021] Step 3: Place the corona treated PE film in the unwinding position, pump the composite coating liquid prepared in step 2 into the coating storage tank for coating, and then sequentially pass through a first oven at 0°C, a second oven at 95°C, a third oven at 85°C, and a fourth oven at 90°C for drying to obtain a PE film coated with a composite coating.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] 1. The composite coating liquid provided by the present invention is coated on the surface of the PE film, which can effectively solve the problem of poor barrier properties of the PE film of a single material, so that the PE material film can partially replace the application of composite films such as PET / PE, PA / PE, KPET / PE or three-layer structure PET / PA / PE, BOPP / PA / PE, etc.

[0024] 2. The present invention uses a composite of PVA and ethylene maleic anhydride homopolymer, and part of the maleic anhydride can react with the hydroxyl group to form a monoester with relatively high bond energy, and the partially hydrolyzed carboxyl group and the hydroxyl group can form a hydrogen bond, so that a dense cross-linked molecular film is formed through the combined action of intermolecular forces, chemical bonds and hydrogen bonds, which not only does not increase the free space between molecules, but also does not deteriorate the barrier properties of PVA, and can also improve the instability of PVA. In addition, the corona-exposed PE substrate has polar groups, and the hydroxyl and carboxyl groups in the coating liquid can also form bonds with the corona-exposed substrate, greatly improving the peel strength of the coating and the substrate.

[0025] 3. The present invention uses a mixture of hexadecyltrimethylammonium bromide and PEG2000 as a surfactant, which can further promote the esterification degree between PVA and ethylene maleic anhydride homopolymer, and further ensure the barrier property of the PE film after coating. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with specific implementation methods.

[0027] Example 1

[0028] This embodiment provides a high-barrier composite coating liquid and a preparation method thereof, wherein the high-barrier composite coating liquid comprises 31 parts by weight of deionized water, 48 parts by weight of low-polymerization degree PVA emulsion, 20 parts by weight of low-polymerization degree ethylene maleic anhydride homopolymer, and 1 part by weight of flow improver. The low-polymerization degree PVA emulsion comprises 10 parts by weight of PVA resin, 80 parts by weight of solvent, 0.5 parts by weight of defoamer, and 1 part by weight of surfactant.

[0029] Among them, the surfactant is a mixture of hexadecyltrimethylammonium bromide and PEG2000 in a mass ratio of 1:1; the molecular weight of the PVA resin is 50,000; the low-polymerization degree ethylene maleic anhydride homopolymer is a 1:1 homopolymer of ethylene and maleic anhydride, and the molecular weight is 45,000; the flow improver includes polyacrylic acid; the defoamer is DP-281 type pva defoamer produced by Guangdong Tianfeng Defoamer Co., Ltd.

[0030] The above composite coating liquid is prepared and applied by the following steps:

[0031] Step 1: first add deionized water and flow improver into low polymerization degree PVA emulsion, stir evenly, and heat to 78°C to obtain a mixed solution;

[0032] Step 2: adding a low-polymerization degree ethylene maleic anhydride homopolymer to the mixed solution prepared in step 1 while stirring to obtain a composite coating solution;

[0033] Step 3: Place the corona treated PE film in the unwinding position, pump the composite coating liquid prepared in step 2 into the coating storage tank for coating, and then sequentially pass through a first oven at 0°C, a second oven at 95°C, a third oven at 85°C, and a fourth oven at 90°C for drying to obtain a PE film coated with a composite coating.

[0034] Example 2

[0035] This embodiment provides a high-barrier composite coating liquid and a preparation method thereof, wherein the high-barrier composite coating liquid comprises 25 parts by weight of deionized water, 65 parts by weight of low-polymerization degree PVA emulsion, 25 parts by weight of low-polymerization degree ethylene maleic anhydride homopolymer, and 2 parts by weight of flow improver. The low-polymerization degree PVA emulsion comprises 6 parts by weight of PVA resin, 90 parts by weight of deionized water, 1 part by weight of defoamer, and 2 parts by weight of surfactant.

[0036] Among them, the surfactant is a mixture of hexadecyltrimethylammonium bromide and PEG2000 in a mass ratio of 1:1; the molecular weight of the PVA resin is 10,000; the low-polymerization degree ethylene maleic anhydride homopolymer is a 1:1 homopolymer of ethylene and maleic anhydride, and the molecular weight is 8,000; the flow improver includes polyethylene wax and polyether silicone oil mixed in a volume ratio of one to one; the defoamer is DP-281 type pva defoamer produced by Guangdong Tianfeng Defoamer Co., Ltd.

[0037] The above composite coating liquid is prepared and applied by the following steps:

[0038] Step 1: first add deionized water and flow improver into low polymerization degree PVA emulsion, stir evenly, and heat to 75°C to obtain a mixed solution;

[0039] Step 2: adding a low-polymerization degree ethylene maleic anhydride homopolymer to the mixed solution prepared in step 1 while stirring to obtain a composite coating solution;

[0040] Step 3: Place the corona treated PE film in the unwinding position, pump the composite coating liquid prepared in step 2 into the coating storage tank for coating, and then sequentially pass through a first oven at 0°C, a second oven at 95°C, a third oven at 85°C, and a fourth oven at 90°C for drying to obtain a PE film coated with a composite coating.

[0041] Example 3

[0042] This embodiment provides a high-barrier composite coating liquid and a preparation method thereof, wherein the high-barrier composite coating liquid comprises 35 parts by weight of deionized water, 45 parts by weight of low-polymerization degree PVA emulsion, 10 parts by weight of low-polymerization degree ethylene maleic anhydride homopolymer, and 0.5 parts by weight of flow improver. The low-polymerization degree PVA emulsion comprises 12 parts by weight of PVA resin, 70 parts by weight of deionized water, 0.1 parts by weight of defoamer, and 0.5 parts by weight of surfactant.

[0043] Among them, the surfactant is a mixture of hexadecyltrimethylammonium bromide and PEG2000 in a mass ratio of 1:1; the molecular weight of the PVA resin is 120,000; the low-polymerization degree ethylene maleic anhydride homopolymer is a 1:1 homopolymer of ethylene and maleic anhydride, and the molecular weight is 80,000; the flow improver includes polyether silicone oil; the defoamer is DP-281 type pva defoamer produced by Guangdong Tianfeng Defoamer Co., Ltd.

[0044] The above composite coating liquid is prepared and applied by the following steps:

[0045] Step 1: first add deionized water and flow improver into low polymerization degree PVA emulsion, stir evenly, and heat to 80°C to obtain a mixed solution;

[0046] Step 2: adding a low-polymerization degree ethylene maleic anhydride homopolymer to the mixed solution prepared in step 1 while stirring to obtain a composite coating solution;

[0047] Step 3: Place the corona treated PE film in the unwinding position, pump the composite coating liquid prepared in step 2 into the coating storage tank for coating, and then sequentially pass through a first oven at 0°C, a second oven at 95°C, a third oven at 85°C, and a fourth oven at 90°C for drying to obtain a PE film coated with a composite coating.

[0048] Comparative Example 1

[0049] This comparative example provides a coating liquid and a preparation method thereof, wherein the coating liquid comprises 31 parts by weight of deionized water, 48 parts by weight of a low-polymerization degree PVA emulsion, and 1 part of a flow improver. The low-polymerization degree PVA emulsion comprises 10 parts by weight of a PVA resin, 80 parts by weight of a solvent, 0.5 parts by weight of a defoaming agent, and 1 part by weight of a surfactant.

[0050] Among them, the surfactant is a mixture of hexadecyltrimethylammonium bromide and PEG2000 in a mass ratio of 1:1; the molecular weight of the PVA resin is 50,000; the flow improver includes polyacrylic acid; and the defoamer is DP-281 type PVA defoamer produced by Guangdong Tianfeng Defoamer Co., Ltd.

[0051] The above composite coating liquid is prepared and applied by the following steps:

[0052] Step 1: first add deionized water and flow improver into low polymerization degree PVA emulsion, stir evenly, and heat to 78°C to obtain a composite coating solution;

[0053] Step 2: Place the corona treated PE film in the unwinding position, pump the composite coating liquid prepared in step 1 into the coating storage tank for coating, and then sequentially pass through a first oven at 0°C, a second oven at 95°C, a third oven at 85°C, and a fourth oven at 90°C for drying to obtain a PE film coated with a composite coating.

[0054] Comparative Example 2

[0055] This comparative example provides a coating liquid and a preparation method thereof. The coating liquid comprises 31 parts by weight of deionized water, 20 parts by weight of a low-polymerization degree ethylene maleic anhydride homopolymer, and 1 part by weight of a flow improver.

[0056] Among them, the surfactant is a mixture of hexadecyltrimethylammonium bromide and PEG2000 in a mass ratio of 1:1; the low-polymerization degree ethylene maleic anhydride homopolymer is a 1:1 homopolymer of ethylene and maleic anhydride, and has a molecular weight of 45,000; the flow improver includes polyacrylic acid; the defoamer is DP-281 type pva defoamer produced by Guangdong Tianfeng Defoamer Co., Ltd.

[0057] The above composite coating liquid is prepared and applied by the following steps:

[0058] Step 1: First, add deionized water and flow improver, mix and stir evenly, and heat to 78°C to obtain a mixed solution;

[0059] Step 2: adding a low-polymerization degree ethylene maleic anhydride homopolymer to the mixed solution prepared in step 1 while stirring to obtain a composite coating solution;

[0060] Step 3: Place the corona treated PE film in the unwinding position, pump the composite coating liquid prepared in step 2 into the coating storage tank for coating, and then sequentially pass through a first oven at 0°C, a second oven at 95°C, a third oven at 85°C, and a fourth oven at 90°C for drying to obtain a PE film coated with a composite coating.

[0061] Comparative Example 3

[0062] This comparative example provides a coating liquid and a preparation method thereof, wherein the coating liquid comprises 31 parts by weight of deionized water, 48 parts by weight of a low-polymerization degree PVA emulsion, 20 parts by weight of a low-polymerization degree ethylene maleic anhydride homopolymer, and 1 part of a flow improver. The low-polymerization degree PVA emulsion comprises 10 parts by weight of a PVA resin, 80 parts by weight of a solvent, 0.5 parts by weight of a defoaming agent, and 1 part by weight of a surfactant.

[0063] Among them, the surfactant is hexadecyltrimethylammonium bromide; the molecular weight of the PVA resin is 50,000; the low-polymerization degree ethylene maleic anhydride homopolymer is a 1:1 homopolymer of ethylene and maleic anhydride, and the molecular weight is 45,000; the flow improver includes polyacrylic acid; the defoamer is DP-281 type PVA defoamer produced by Guangdong Tianfeng Defoamer Co., Ltd.

[0064] The above composite coating liquid is prepared and applied by the following steps:

[0065] Step 1: first add deionized water and flow improver into low polymerization degree PVA emulsion, stir evenly, and heat to 78°C to obtain a mixed solution;

[0066] Step 2: adding a low-polymerization degree ethylene maleic anhydride homopolymer to the mixed solution prepared in step 1 while stirring to obtain a composite coating solution;

[0067] Step 3: Place the corona treated PE film in the unwinding position, pump the composite coating liquid prepared in step 2 into the coating storage tank for coating, and then sequentially pass through a first oven at 0°C, a second oven at 95°C, a third oven at 85°C, and a fourth oven at 90°C for drying to obtain a PE film coated with a composite coating.

[0068] Comparative Example 4

[0069] This comparative example provides a coating liquid and a preparation method thereof, wherein the coating liquid comprises 31 parts by weight of deionized water, 48 parts by weight of a low-polymerization degree PVA emulsion, 20 parts by weight of a low-polymerization degree ethylene maleic anhydride homopolymer, and 1 part of a flow improver. The low-polymerization degree PVA emulsion comprises 10 parts by weight of a PVA resin, 80 parts by weight of a solvent, 0.5 parts by weight of a defoaming agent, and 1 part by weight of a surfactant.

[0070] Among them, the surfactant is PEG2000; the molecular weight of the PVA resin is 50,000; the low-polymerization degree ethylene maleic anhydride homopolymer is a 1:1 homopolymer of ethylene and maleic anhydride, and the molecular weight is 45,000; the flow improver includes polyacrylic acid; the defoamer is DP-281 type PVA defoamer produced by Guangdong Tianfeng Defoamer Co., Ltd.

[0071] The above composite coating liquid is prepared and applied by the following steps:

[0072] Step 1: first add deionized water and flow improver into low polymerization degree PVA emulsion, stir evenly, and heat to 78°C to obtain a mixed solution;

[0073] Step 2: adding a low-polymerization degree ethylene maleic anhydride homopolymer to the mixed solution prepared in step 1 while stirring to obtain a composite coating solution;

[0074] Step 3: Place the corona treated PE film in the unwinding position, pump the composite coating liquid prepared in step 2 into the coating storage tank for coating, and then sequentially pass through a first oven at 0°C, a second oven at 95°C, a third oven at 85°C, and a fourth oven at 90°C for drying to obtain a PE film coated with a composite coating.

[0075] Comparative Example 5

[0076] This comparative example provides a coating liquid and a preparation method thereof, wherein the coating liquid comprises 31 parts by weight of deionized water, 48 parts by weight of a low-polymerization degree PVA emulsion, 20 parts by weight of a low-polymerization degree ethylene maleic anhydride homopolymer, and 1 part of a flow improver. The low-polymerization degree PVA emulsion comprises 10 parts by weight of a PVA resin, 80 parts by weight of a solvent, and 0.5 parts by weight of a defoamer.

[0077] Among them, the molecular weight of PVA resin is 50,000; the low-polymerization degree ethylene maleic anhydride homopolymer is a 1:1 homopolymer of ethylene and maleic anhydride, and the molecular weight is 45,000; the flow improver includes polyacrylic acid; the defoamer is DP-281 type PVA defoamer produced by Guangdong Tianfeng Defoamer Co., Ltd.

[0078] The above composite coating liquid is prepared and applied by the following steps:

[0079] Step 1: first add deionized water and flow improver into low polymerization degree PVA emulsion, stir evenly, and heat to 78°C to obtain a mixed solution;

[0080] Step 2: adding a low-polymerization degree ethylene maleic anhydride homopolymer to the mixed solution prepared in step 1 while stirring to obtain a composite coating solution;

[0081] Step 3: Place the corona treated PE film in the unwinding position, pump the composite coating liquid prepared in step 2 into the coating storage tank for coating, and then sequentially pass through a first oven at 0°C, a second oven at 95°C, a third oven at 85°C, and a fourth oven at 90°C for drying to obtain a PE film coated with a composite coating.

[0082] Application Example 1

[0083] A PE film 1 was prepared by the preparation method described in Example 1;

[0084] A PE film 2 was prepared by the preparation method described in Comparative Example 1;

[0085] A PE film 3 was prepared by the preparation method described in Comparative Example 2;

[0086] A PE film 4 was prepared by the preparation method described in Comparative Example 3;

[0087] A PE film 5 was prepared by the preparation method described in Comparative Example 4;

[0088] A PE film 6 was prepared by the preparation method described in Comparative Example 5;

[0089] The PE film with a thickness of 90 μm is PE film 7;

[0090] The coating thickness of the above PE films is the same, and the PE substrates are all 90 μm PE films. The oxygen permeability and water vapor permeability of PE films 1-7 were measured respectively, the oxygen permeability was tested according to GB / T 1038-2022 Plastic film and sheet gas permeability test method, and the water vapor permeability was tested according to GB / T 1037-2021.

[0091] The following table shows the classification of water vapor transmission levels:

[0092]

[0093] The following table shows the oxygen permeability level classification

[0094]

[0095] The results are shown in the following table:

[0096] Experimental Group Water vapor transmission rate grade Oxygen permeability level PE film 1 Level 1 Level 1 PE film 2 Level 1 Level 2 PE film 3 Level 3 Level 3 PE film 4 Level 1 Level 1 PE film 5 Level 1 Level 1 PE film 6 Level 1 Level 1 PE film 7 Level 3 Level 4

[0097] Result analysis: It can be seen from the above experimental data that PE film 1 has obvious advantages in barrier properties compared with PE films 2-7, so the expected purpose of the present invention is achieved.

[0098] Application Example 2

[0099] The PE films 1-6 prepared in Application Example 1 were boiled in a water bath at 80°C for 30 minutes, wiped dry, and subjected to a 3 M tape peeling test 20 times to observe the shedding of the surface coating. The results are shown in the following table:

[0100]

[0101]

[0102] Result analysis: It can be seen from the above experimental data that PE film 1 has obvious advantages in coating peel strength compared with PE films 2-6, so the expected purpose of the present invention is achieved.

[0103] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A high barrier composite coating liquid, characterized in that: The invention comprises 25-35 parts by weight of deionized water, 45-65 parts by weight of low-polymerization degree PVA emulsion, 10-25 parts by weight of low-polymerization degree ethylene maleic anhydride homopolymer and 0.5-2 parts by weight of flow improver.

2. A high barrier composite coating liquid as claimed in claim 1, characterized in that: The invention comprises 31 parts by weight of deionized water, 48 parts by weight of low-polymerization degree PVA emulsion, 20 parts by weight of low-polymerization degree ethylene maleic anhydride homopolymer and 1 part by weight of flow improver.

3. A high barrier composite coating liquid as claimed in claim 1, characterized in that: The low-polymerization degree PVA emulsion comprises 6-12 parts by weight of PVA resin, 70-90 parts by weight of solvent, 0.1-1 parts by weight of defoaming agent and 0.5-2 parts by weight of surfactant.

4. A high barrier composite coating liquid as claimed in claim 3, characterized in that: The low-polymerization degree PVA emulsion comprises 10 parts by weight of PVA resin, 80 parts by weight of solvent, 0.5 parts by weight of defoaming agent and 1 part by weight of surfactant.

5. A high barrier composite coating liquid as claimed in claim 3, characterized in that: The solvent is deionized water.

6. A high barrier composite coating liquid as claimed in claim 3, characterized in that: The surfactant is prepared by mixing hexadecyltrimethylammonium bromide and PEG2000 in a mass ratio of 1:

1.

7. A high barrier composite coating liquid as claimed in claim 3, characterized in that: The molecular weight of the PVA resin is 10,000-120,000.

8. The high barrier composite coating liquid according to claim 1, characterized in that: The low-polymerization-degree ethylene-maleic anhydride homopolymer is a 1:1 homopolymer of ethylene and maleic anhydride, and has a molecular weight of 8,000-80,000.

9. A high barrier composite coating liquid as claimed in claim 1, characterized in that: The flow improver includes at least one of polyethylene wax, polyether silicone oil and polyacrylic acid.

10. A method for preparing a high barrier composite coating liquid as claimed in any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: First, add deionized water and flow improver into low-polymerization PVA emulsion, stir evenly, and heat to 75-80°C to obtain a mixed solution; Step 2: adding a low-polymerization degree ethylene maleic anhydride homopolymer to the mixed solution prepared in step 1 while stirring to obtain a composite coating solution; Step 3: Place the corona treated PE film in the unwinding position, pump the composite coating liquid prepared in step 2 into the coating storage tank for coating, and then sequentially pass through a first oven at 0°C, a second oven at 95°C, a third oven at 85°C, and a fourth oven at 90°C for drying to obtain a PE film coated with a composite coating.

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