High-barrier composite film

Abstract

The invention discloses a high-barrier composite film, and relates to the technical field of film materials. Comprising the following raw materials: 20 to 30 parts of a functional copolymer, 40 to 60 parts of an ethylene-vinyl alcohol copolymer, 5 to 8 parts of cellulose nanocrystals, 2 to 4 parts of a compatilizer, 0.5 to 1 part of an antioxidant, 0.8 to 1.2 parts of a lubricant, 3 to 5 parts of 1-allyl-3-vinyl imidazole chlorine salt and 1 to 2 parts of allyl-beta-cyclodextrin. The functional copolymer comprises a structural unit introduced by the following monomers: vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1, 1-difluoro-2-propylene-1-yl)-2 (1H)-quinoxalinone, and N-(4-cyano-3-trifluoromethylphenyl) methacrylamide. The film is good in mechanical property, good in barrier property, excellent in damp-heat aging resistance and long in service life.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane materials, and in particular to a high-barrier composite film. Background Art

[0002] In the packaging materials sector, high-barrier composite films are widely used in the food and pharmaceutical industries due to their effective barrier properties against oxygen, water vapor, odors, and other substances. Traditional high-barrier films often use aluminum foil, aluminized film, or ethylene-vinyl alcohol copolymer (EVOH) as a barrier layer. Aluminum foil easily bends, creating pinholes and resulting in barrier failure, while EVOH's barrier properties significantly decrease in high-humidity environments, making it difficult to meet the requirements of high-end applications.

[0003] Currently, high-barrier films are mostly based on polymers such as polyethylene (PE) and polypropylene (PP). While these films exhibit certain barrier properties, their effectiveness degrades significantly when exposed to extreme environments such as high humidity and high temperature. To enhance the performance of these films, inorganic barrier materials such as montmorillonite and silica are added. However, inorganic materials have poor dispersion in the polymer matrix and are prone to agglomeration. This agglomeration not only weakens the mechanical properties of the composite film, making it susceptible to breakage during packaging, but also creates permeation channels, severely impacting the overall barrier performance. Furthermore, the production process for existing high-barrier composite films is complex and expensive. Some preparation methods require the use of large amounts of organic solvents, which not only pollute the environment but also increase safety risks during production. Furthermore, the complex preparation process results in low production efficiency, making it difficult to meet the needs of large-scale industrial production.

[0004] To address the above-mentioned issues, a Chinese invention patent with authorization publication number CN117021633B discloses a high-barrier composite film and its preparation process, belonging to the technical field of packaging composite films. The key points of its technical solution include the following steps: heat-sealing film treatment: S1, corona treatment of the heat-sealing film to make the surface tension of the heat-sealing film ≥38 dynes; S2, coating the heat-sealing film after corona treatment with a barrier liquid, wherein the barrier liquid mainly comprises an aqueous solution of polyvinyl alcohol and a solution of an organosilicon-modified inorganic nanomaterial; S3, oven-drying the heat-sealing film obtained in step S2 to obtain a high-barrier heat-sealing film; unwinding film treatment: coating the unwinding film with a solvent-free adhesive; film bonding treatment: bonding the side of the high-barrier heat-sealing film coated with the barrier liquid with the side of the unwinding film coated with the adhesive to obtain a high-barrier composite film, which is then wound and aged. This method reduces the production cost of the composite packaging film while ensuring the barrier performance of the composite film. However, the moisture-heat aging resistance and mechanical properties of the high-barrier composite film still need to be further improved.

[0005] It can be seen that the development of a high-barrier composite film with good mechanical properties, good barrier properties, excellent resistance to moisture and heat aging, and long service life meets market demand, has broad market value and application prospects, and is of great significance to promoting the development of the field of high-barrier composite films. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a high-barrier composite film with good mechanical properties, good barrier properties, excellent resistance to moisture and heat aging, and long service life.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a high-barrier composite film, which is made of the following raw materials, by weight: 20-30 parts of a functional copolymer, 40-60 parts of an ethylene-vinyl alcohol copolymer, 5-8 parts of cellulose nanocrystals, 2-4 parts of a compatibilizer, 0.5-1 part of an antioxidant, 0.8-1.2 parts of a lubricant, 3-5 parts of 1-allyl-3-vinylimidazolium chloride, and 1-2 parts of allyl-β-cyclodextrin; the functional copolymer includes structural units introduced by the following monomers: vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxalinone, and N-(4-cyano-3-trifluoromethylphenyl)methacrylamide.

[0008] Preferably, the preparation method of the functional copolymer comprises the following steps: adding vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl)methacrylamide, and an initiator to a high boiling point solvent, stirring and reacting at 70-80° C. in an inert gas atmosphere for 3-5 hours, cooling to room temperature after the reaction, precipitating in water, washing the precipitated polymer with ethanol 3-6 times, and finally removing residual ethanol by rotary evaporation to obtain a functional copolymer.

[0009] Preferably, the mass ratio of the vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl)methacrylamide, initiator, and high boiling point solvent is 2:(0.8-1.2):0.5:(1-2):(0.05-0.07):(15-25).

[0010] Preferably, the initiator is azobisisobutyronitrile; the high boiling point solvent is at least one of N,N-dimethylformamide and N-methylpyrrolidone; and the inert gas is any one of nitrogen, helium, neon and argon.

[0011] Preferably, the ethylene-vinyl alcohol copolymer is SoarnolTM BX6804B EVOH.

[0012] Preferably, the cellulose nanocrystals have a length of 200 nm and an outer diameter of 10 nm.

[0013] Preferably, the compatibilizer is selected from PP-g-MAH with the brand name HW-501.

[0014] Preferably, the antioxidant is at least one of antioxidant 1010, antioxidant 168, and antioxidant 1076.

[0015] Preferably, the lubricant is at least one of butyl stearate and ethylene bisstearamide.

[0016] Another object of the present invention is to provide a method for preparing the high-barrier composite film, comprising the following steps: Step S1, after uniformly mixing the functional copolymer, ethylene-vinyl alcohol copolymer, cellulose nanocrystals, a compatibilizer, an antioxidant and a lubricant to obtain a mixture, the mixture is added into a twin-screw extruder for extrusion molding, and then subjected to biaxial stretching and heat setting in sequence to obtain a primary film; Step S2, soaking the nascent film in an aqueous solution of 1-allyl-3-vinylimidazole chloride at 50-60° C. for 20-30 hours, taking it out and then soaking it in an ethanol solution containing a photoinitiator and allyl-β-cyclodextrin, taking it out and irradiating it under ultraviolet light for 20-30 minutes, repeatedly washing it with water and ethanol, and finally drying it to obtain a high-barrier composite film.

[0017] Preferably, the extrusion molding temperature in step S1 is 200-220°C.

[0018] Preferably, the stretching temperature of the biaxial stretching in step S1 is 100-110° C., and the stretching ratio is 3-5.

[0019] Preferably, the heat setting temperature in step S1 is 120-130° C. and the time is 2-4 minutes.

[0020] Preferably, the mass percentage concentration of the aqueous solution of 1-allyl-3-vinylimidazolium chloride in step S2 is 5-8%.

[0021] Preferably, in the ethanol solution containing the photoinitiator and allyl-β-cyclodextrin in step S2, the mass ratio of the photoinitiator, allyl-β-cyclodextrin, and ethanol is 0.01:1:20.

[0022] Preferably, the photoinitiator is benzoin ethyl ether.

[0023] Preferably, the wavelength of the ultraviolet light is 220-260 nm.

[0024] Due to the application of the above technical solution, the present invention has the following beneficial effects: (1) The method for preparing the high-barrier composite film disclosed in the present invention has a simple process, convenient operation and control, high preparation efficiency and finished product qualification rate, is suitable for continuous large-scale production, and has high promotion and application value.

[0025] (2) The high barrier composite film disclosed in the present invention is made of the following raw materials, calculated by weight: 20-30 parts of functional copolymer, 40-60 parts of ethylene-vinyl alcohol copolymer, 5-8 parts of cellulose nanocrystals, 2-4 parts of compatibilizer, 0.5-1 part of antioxidant, 0.8-1.2 parts of lubricant, 3-5 parts of 1-allyl-3-vinyl imidazole chloride, and 1-2 parts of allyl-β-cyclodextrin; through the mutual coordination and joint action of the raw materials, the prepared film has good mechanical properties, good barrier properties, excellent resistance to moisture and heat aging, and long service life. The functional copolymer includes structural units introduced from the following monomers: vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, and N-(4-cyano-3-trifluoromethylphenyl)methacrylamide; the structural unit introduced from vinylidene chloride has excellent barrier properties and is the basic unit for providing high barrier properties; the polar group introduced from 2-acrylamido-2-methylpropanesulfonic acid can interact with polar molecules such as water molecules to hinder their penetration, while enhancing the interaction with other polar raw materials. The sulfonic acid groups on them can connect with 1-allyl-3-vinylimidazolium chloride through ion exchange and ion bonding, providing reaction sites for subsequent cross-linking and curing reactions. 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxalinone and N-(4-cyano-3-trifluoromethylphenyl)methacrylamide contain special functional groups, such as fluorine atoms and cyano groups. The fluorine atoms have a small radius and high electronegativity, which can form a dense electron cloud on the molecular surface, increasing the diffusion resistance of gas molecules and improving the barrier capacity for gases such as oxygen and carbon dioxide. The simultaneously introduced dichloro, amide, fluorine-containing quinoxalinone, cyano, and trifluoromethylphenyl groups, through the multiple effects of electronic, steric, and conjugated effects, give the film superior mechanical properties, barrier properties, and resistance to wet and heat aging.

[0026] (4) The high-barrier composite film disclosed in the present invention has cellulose nanocrystals with high crystallinity and a rigid rod-like structure, which can form a physical barrier in the film. Gas molecules need to bypass the particles when passing through, which greatly increases the tortuosity of the diffusion path. The abundant hydroxyl groups on its surface can form hydrogen bonds with other polymers, making the film structure denser and further improving the barrier performance. The hydrophobic cavity of allyl-β-cyclodextrin can encapsulate small molecular gases or odor molecules. The introduction of allyl groups allows it to polymerize with 1-allyl-3-vinyl imidazolium chloride to form an interpenetrating network structure, which is stable on the surface of the film and continuously exerts a selective barrier effect on specific substances, preventing the entry of external odors and the dissemination of internal fragrance, while further improving the mechanical properties and resistance to moisture and heat aging.

[0027] (5) The high-barrier composite film disclosed in the present invention has better mechanical properties, better barrier properties, better resistance to moisture and heat aging, and longer service life through the reasonable selection of preparation process steps and parameters. DETAILED DESCRIPTION

[0028] The following description is intended to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are merely examples, and those skilled in the art may conceive of other obvious variations.

[0029] Example 1 A high-barrier composite film is made from the following raw materials, measured in parts by weight: 20 parts of a functional copolymer, 40 parts of an ethylene-vinyl alcohol copolymer, 5 parts of cellulose nanocrystals, 2 parts of a compatibilizer, 0.5 parts of an antioxidant, 0.8 parts of a lubricant, 3 parts of 1-allyl-3-vinylimidazolium chloride, and 1 part of allyl-β-cyclodextrin; the functional copolymer includes structural units introduced by the following monomers: vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxalinone, and N-(4-cyano-3-trifluoromethylphenyl)methacrylamide.

[0030] The preparation method of the functional copolymer comprises the following steps: adding vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl) methacrylamide and an initiator to a high boiling point solvent, stirring and reacting at 70°C for 3 hours in an inert gas atmosphere, cooling to room temperature after the reaction is completed, precipitating in water, washing the precipitated polymer with ethanol for 3 times, and finally removing the precipitated polymer by rotary evaporation. The residual ethanol was used to obtain a functional copolymer; the mass ratio of vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl)methacrylamide, initiator, and high boiling point solvent was 2:0.8:0.5:1:0.05:15; the initiator was azobisisobutyronitrile; the high boiling point solvent was N,N-dimethylformamide; and the inert gas was nitrogen. The M of the obtained functional copolymer was measured by GPC test. n =14730g / mol,M W / M n =1.319; through elemental analysis and weight change calculation, the mass ratio of the structural units introduced by vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxalinone, and N-(4-cyano-3-trifluoromethylphenyl)methacrylamide in the functional copolymer is 1.97:0.8:0.49:0.98.

[0031] The ethylene-vinyl alcohol copolymer is Soarnol TM BX6804B EVOH; the cellulose nanocrystals have a length of 200 nm and an outer diameter of 10 nm; the compatibilizer is selected from PP-g-MAH with the brand HW-501; the antioxidant is antioxidant 1010; and the lubricant is butyl stearate.

[0032] A method for preparing the high-barrier composite film comprises the following steps: Step S1, after uniformly mixing the functional copolymer, ethylene-vinyl alcohol copolymer, cellulose nanocrystals, a compatibilizer, an antioxidant and a lubricant to obtain a mixture, the mixture is added into a twin-screw extruder for extrusion molding, and then subjected to biaxial stretching and heat setting in sequence to obtain a primary film; Step S2, soaking the primary film in an aqueous solution of 1-allyl-3-vinylimidazole chloride at 50°C for 20 hours, taking it out and then soaking it in an ethanol solution containing a photoinitiator and allyl-β-cyclodextrin, taking it out and irradiating it under ultraviolet light for 20 minutes, repeatedly washing it with water and ethanol, and finally drying it to obtain a high-barrier composite film.

[0033] The extrusion molding temperature in step S1 is 200°C; the stretching temperature of the biaxial stretching in step S1 is 100°C, and the stretching ratio is 4; the heat setting temperature in step S1 is 120°C, and the time is 2 minutes; the mass percentage concentration of the aqueous solution of 1-allyl-3-vinylimidazolium chloride in step S2 is 5%; the mass ratio of the photoinitiator, allyl-β-cyclodextrin, and ethanol in the ethanol solution containing the photoinitiator and allyl-β-cyclodextrin in step S2 is 0.01:1:20; the photoinitiator is benzoin ethyl ether; and the wavelength of the ultraviolet light is 220nm.

[0034] Example 2 A high-barrier composite film is made from the following raw materials, measured in parts by weight: 23 parts of a functional copolymer, 45 parts of an ethylene-vinyl alcohol copolymer, 6 parts of cellulose nanocrystals, 2.5 parts of a compatibilizer, 0.6 parts of an antioxidant, 0.9 parts of a lubricant, 3.5 parts of 1-allyl-3-vinylimidazolium chloride, and 1.2 parts of allyl-β-cyclodextrin; the functional copolymer includes structural units introduced by the following monomers: vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxalinone, and N-(4-cyano-3-trifluoromethylphenyl)methacrylamide.

[0035] The preparation method of the functional copolymer comprises the following steps: adding vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl) methacrylamide and an initiator to a high boiling point solvent, stirring and reacting at 73°C for 3.5 hours in an inert gas atmosphere, cooling to room temperature after the reaction is completed, precipitating in water, washing the precipitated polymer with ethanol 4 times, and finally removing it by rotary evaporation. The residual ethanol is used to obtain a functional copolymer; the mass ratio of the vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl)methacrylamide, initiator, and high boiling point solvent is 2:0.9:0.5:1.3:0.055:17; the initiator is azobisisobutyronitrile; the high boiling point solvent is N-methylpyrrolidone; and the inert gas is helium.

[0036] The ethylene-vinyl alcohol copolymer is Soarnol TM BX6804B EVOH; the cellulose nanocrystals have a length of 200 nm and an outer diameter of 10 nm; the compatibilizer is selected from PP-g-MAH with the brand HW-501; the antioxidant is antioxidant 168; and the lubricant is ethylene bisstearamide.

[0037] A method for preparing the high-barrier composite film comprises the following steps: Step S1, after uniformly mixing the functional copolymer, ethylene-vinyl alcohol copolymer, cellulose nanocrystals, a compatibilizer, an antioxidant and a lubricant to obtain a mixture, the mixture is added into a twin-screw extruder for extrusion molding, and then subjected to biaxial stretching and heat setting in sequence to obtain a primary film; Step S2, soaking the primary film in an aqueous solution of 1-allyl-3-vinylimidazole chloride at 53°C for 23 hours, taking it out and then soaking it in an ethanol solution containing a photoinitiator and allyl-β-cyclodextrin, taking it out and irradiating it under ultraviolet light for 23 minutes, repeatedly washing it with water and ethanol, and finally drying it to obtain a high-barrier composite film.

[0038] The extrusion molding temperature in step S1 is 205°C; the stretching temperature of the biaxial stretching in step S1 is 103°C, and the stretching ratio is 4; the heat setting temperature in step S1 is 123°C, and the time is 2.5 minutes; the mass percentage concentration of the aqueous solution of 1-allyl-3-vinylimidazolium chloride in step S2 is 6%; the mass ratio of the photoinitiator, allyl-β-cyclodextrin, and ethanol in the ethanol solution containing the photoinitiator and allyl-β-cyclodextrin in step S2 is 0.01:1:20; the photoinitiator is benzoin ethyl ether; and the wavelength of the ultraviolet light is 230nm.

[0039] Example 3 A high-barrier composite film is made from the following raw materials, measured in parts by weight: 25 parts of a functional copolymer, 50 parts of an ethylene-vinyl alcohol copolymer, 6.5 parts of cellulose nanocrystals, 3 parts of a compatibilizer, 0.75 parts of an antioxidant, 1 part of a lubricant, 4 parts of 1-allyl-3-vinylimidazolium chloride, and 1.5 parts of allyl-β-cyclodextrin; the functional copolymer includes structural units introduced by the following monomers: vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxalinone, and N-(4-cyano-3-trifluoromethylphenyl)methacrylamide.

[0040] The preparation method of the functional copolymer comprises the following steps: adding vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl) methacrylamide and an initiator to a high boiling point solvent, stirring and reacting at 75° C. for 4 hours in an inert gas atmosphere, cooling to room temperature after the reaction is completed, precipitating in water, washing the precipitated polymer with ethanol 5 times, and finally removing the precipitated polymer by rotary evaporation. The residual ethanol is used to obtain a functional copolymer; the mass ratio of the vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl)methacrylamide, initiator, and high boiling point solvent is 2:1:0.5:1.5:0.06:20; the initiator is azobisisobutyronitrile; the high boiling point solvent is N,N-dimethylformamide; and the inert gas is neon.

[0041] The ethylene-vinyl alcohol copolymer is Soarnol TM BX6804B EVOH; the cellulose nanocrystals have a length of 200 nm and an outer diameter of 10 nm; the compatibilizer is selected from PP-g-MAH with the brand HW-501; the antioxidant is antioxidant 1076; and the lubricant is butyl stearate.

[0042] A method for preparing the high-barrier composite film comprises the following steps: Step S1, after uniformly mixing the functional copolymer, ethylene-vinyl alcohol copolymer, cellulose nanocrystals, a compatibilizer, an antioxidant and a lubricant to obtain a mixture, the mixture is added into a twin-screw extruder for extrusion molding, and then subjected to biaxial stretching and heat setting in sequence to obtain a primary film; Step S2, soaking the primary film in an aqueous solution of 1-allyl-3-vinylimidazole chloride at 55°C for 25 hours, taking it out and then soaking it in an ethanol solution containing a photoinitiator and allyl-β-cyclodextrin, taking it out and irradiating it under ultraviolet light for 25 minutes, repeatedly washing it with water and ethanol, and finally drying it to obtain a high-barrier composite film.

[0043] The extrusion molding temperature in step S1 is 210°C; the stretching temperature of the biaxial stretching in step S1 is 105°C, and the stretching ratio is 4; the heat setting temperature in step S1 is 125°C, and the time is 3 minutes; the mass percentage concentration of the aqueous solution of 1-allyl-3-vinylimidazolium chloride in step S2 is 6.5%; the mass ratio of the photoinitiator, allyl-β-cyclodextrin, and ethanol in the ethanol solution containing the photoinitiator and allyl-β-cyclodextrin in step S2 is 0.01:1:20; the photoinitiator is benzoin ethyl ether; and the wavelength of the ultraviolet light is 240nm.

[0044] Example 4 A high-barrier composite film is made from the following raw materials, measured in parts by weight: 28 parts of a functional copolymer, 55 parts of an ethylene-vinyl alcohol copolymer, 7.5 parts of cellulose nanocrystals, 3.5 parts of a compatibilizer, 0.9 parts of an antioxidant, 1.1 parts of a lubricant, 4.5 parts of 1-allyl-3-vinylimidazolium chloride, and 1.8 parts of allyl-β-cyclodextrin; the functional copolymer includes structural units introduced by the following monomers: vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxalinone, and N-(4-cyano-3-trifluoromethylphenyl)methacrylamide.

[0045] The preparation method of the functional copolymer comprises the following steps: adding vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl)methacrylamide and an initiator to a high-boiling-point solvent, stirring and reacting at 78°C for 4.5 hours in an inert gas atmosphere, cooling to room temperature after the reaction, precipitating the polymer in water, washing the precipitated polymer with ethanol for 5 times, and finally removing the residual ethanol by rotary evaporation to obtain the functional copolymer. The mass ratio of the vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl)methacrylamide, initiator, and high-boiling-point solvent is 2:1.1:0.5:1.8:0.065:23; the initiator is azobisisobutyronitrile; the high-boiling-point solvent is a mixture of N,N-dimethylformamide and N-methylpyrrolidone in a mass ratio of 1:2; and the inert gas is nitrogen.

[0046] The ethylene-vinyl alcohol copolymer is Soarnol TM BX6804B EVOH; the cellulose nanocrystals have a length of 200 nm and an outer diameter of 10 nm; the compatibilizer is selected from PP-g-MAH with the brand HW-501; the antioxidant is a mixture of antioxidant 1010, antioxidant 168, and antioxidant 1076 in a mass ratio of 1:2:3; the lubricant is a mixture of butyl stearate and ethylene bisstearamide in a mass ratio of 1:3.

[0047] A method for preparing the high-barrier composite film comprises the following steps: Step S1, after uniformly mixing the functional copolymer, ethylene-vinyl alcohol copolymer, cellulose nanocrystals, a compatibilizer, an antioxidant and a lubricant to obtain a mixture, the mixture is added into a twin-screw extruder for extrusion molding, and then subjected to biaxial stretching and heat setting in sequence to obtain a primary film; Step S2, soaking the primary film in an aqueous solution of 1-allyl-3-vinylimidazole chloride at 58°C for 28 hours, taking it out and then soaking it in an ethanol solution containing a photoinitiator and allyl-β-cyclodextrin, taking it out and irradiating it under ultraviolet light for 28 minutes, repeatedly washing it with water and ethanol, and finally drying it to obtain a high-barrier composite film.

[0048] The extrusion molding temperature in step S1 is 215° C.; the stretching temperature of the biaxial stretching in step S1 is 108° C., and the stretching ratio is 4; the heat setting temperature in step S1 is 128° C., and the time is 3.5 minutes; the mass percentage concentration of the aqueous solution of 1-allyl-3-vinylimidazolium chloride in step S2 is 7.5%; the mass ratio of the photoinitiator, allyl-β-cyclodextrin, and ethanol in the ethanol solution containing the photoinitiator and allyl-β-cyclodextrin in step S2 is 0.01:1:20; the photoinitiator is benzoin ethyl ether; and the wavelength of the ultraviolet light is 250 nm.

[0049] Example 5 A high-barrier composite film is made from the following raw materials, measured in parts by weight: 30 parts of a functional copolymer, 60 parts of an ethylene-vinyl alcohol copolymer, 8 parts of cellulose nanocrystals, 4 parts of a compatibilizer, 1 part of an antioxidant, 1.2 parts of a lubricant, 5 parts of 1-allyl-3-vinylimidazolium chloride, and 2 parts of allyl-β-cyclodextrin; the functional copolymer includes structural units introduced by the following monomers: vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxalinone, and N-(4-cyano-3-trifluoromethylphenyl)methacrylamide.

[0050] The preparation method of the functional copolymer comprises the following steps: adding vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl) methacrylamide and an initiator to a high boiling point solvent, stirring and reacting at 80°C for 5 hours in an inert gas atmosphere, cooling to room temperature after the reaction is completed, precipitating in water, washing the precipitated polymer with ethanol for 6 times, and finally removing the precipitated polymer by rotary evaporation. The residual ethanol is used to obtain a functional copolymer; the mass ratio of the vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl)methacrylamide, initiator, and high boiling point solvent is 2:1.2:0.5:2:0.07:25; the initiator is azobisisobutyronitrile; the high boiling point solvent is N,N-dimethylformamide; and the inert gas is nitrogen.

[0051] The ethylene-vinyl alcohol copolymer is Soarnol TM BX6804B EVOH; the cellulose nanocrystals have a length of 200 nm and an outer diameter of 10 nm; the compatibilizer is selected from PP-g-MAH with the brand HW-501; the antioxidant is antioxidant 1010; and the lubricant is ethylene bisstearamide.

[0052] A method for preparing the high-barrier composite film comprises the following steps: Step S1, after uniformly mixing the functional copolymer, ethylene-vinyl alcohol copolymer, cellulose nanocrystals, a compatibilizer, an antioxidant and a lubricant to obtain a mixture, the mixture is added into a twin-screw extruder for extrusion molding, and then subjected to biaxial stretching and heat setting in sequence to obtain a primary film; Step S2, soaking the primary film in an aqueous solution of 1-allyl-3-vinylimidazole chloride at 60°C for 30 hours, taking it out and then soaking it in an ethanol solution containing a photoinitiator and allyl-β-cyclodextrin, taking it out and irradiating it under ultraviolet light for 30 minutes, repeatedly washing it with water and ethanol, and finally drying it to obtain a high-barrier composite film.

[0053] The extrusion molding temperature in step S1 is 220°C; the stretching temperature of the biaxial stretching in step S1 is 110°C, and the stretching ratio is 4; the heat setting temperature in step S1 is 130°C, and the time is 4 minutes; the mass percentage concentration of the aqueous solution of 1-allyl-3-vinylimidazolium chloride in step S2 is 8%; the mass ratio of the photoinitiator, allyl-β-cyclodextrin, and ethanol in the ethanol solution containing the photoinitiator and allyl-β-cyclodextrin in step S2 is 0.01:1:20; the photoinitiator is benzoin ethyl ether; and the wavelength of the ultraviolet light is 260nm.

[0054] Comparative Example 1 This example provides a high barrier composite film, which is basically the same as Example 1, except that an equal amount of ethylene-vinyl alcohol copolymer is used instead of the functional copolymer, and an equal amount of 1-allyl-3-vinylimidazolium chloride is used instead of allyl-β-cyclodextrin.

[0055] Comparative Example 2 This example provides a high barrier composite film, which is basically the same as Example 1, except that an equal amount of functional copolymer is used instead of ethylene-vinyl alcohol copolymer, and an equal amount of allyl-β-cyclodextrin is used instead of 1-allyl-3-vinylimidazole chloride.

[0056] To further illustrate the beneficial technical effects of the high-barrier composite films of various embodiments of the present invention, relevant performance tests were conducted on the films involved in each example. The test results are shown in Table 1. The test methods are as follows: Water vapor transmission rate was tested according to GB / T 1037-1988, "Plastic Film and Sheeting - Water Vapor Permeability - Test Method - Cup Method," and oxygen transmission rate was tested according to GB / T 1038-2000, "Plastic Film and Sheeting - Gas Permeability - Test Method - Pressure Differential Method." Tensile strength was tested according to GB / T 1040.3-2006, "Plastics - Determination of Tensile Properties - Part 3: Film and Sheeting - Test Conditions." For wet heat aging resistance, the composite film samples were conditioned at 85°C, 85% RH for 1000 hours, then the tensile strength was measured again after returning to room temperature. The tensile strength retention was calculated; a higher value indicates better wet heat aging resistance. The test samples were controlled to have a thickness of 20 μm.

[0057] Table 1 High barrier composite film performance test results project unit Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Water vapor transmission rate g / (m²·24h) 0.28 0.22 0.20 0.15 0.12 0.87 1.03 Oxygen transmission rate cm³ / (m²·24h·0.1MPa) 0.25 0.21 0.18 0.12 0.10 0.78 0.92 tensile strength MPa 130 133 135 140 142 98 104 Resistance to heat and humidity aging % 98.67 98.98 99.40 99.58 99.70 93.29 96.15 As can be seen from Table 1, the high-barrier composite films of the embodiments of the present invention have better barrier properties, mechanical properties, and resistance to moist heat aging than the comparative examples. The combined use of ethylene-vinyl alcohol copolymer, functional copolymer, 1-allyl-3-vinylimidazolium chloride, and allyl-β-cyclodextrin is beneficial to improving the above properties.

[0058] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high barrier composite film, characterized in that: The invention is prepared from the following raw materials in parts by weight: 20-30 parts of a functional copolymer, 40-60 parts of an ethylene-vinyl alcohol copolymer, 5-8 parts of cellulose nanocrystals, 2-4 parts of a compatibilizer, 0.5-1 part of an antioxidant, 0.8-1.2 parts of a lubricant, 3-5 parts of 1-allyl-3-vinylimidazolium chloride, and 1-2 parts of allyl-β-cyclodextrin; the functional copolymer includes structural units introduced by the following monomers: vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, and N-(4-cyano-3-trifluoromethylphenyl)methacrylamide.

2. The high barrier composite film according to claim 1, characterized in that: The preparation method of the functional copolymer comprises the following steps: adding vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl)methacrylamide and an initiator to a high-boiling-point solvent, stirring and reacting at 70-80° C. for 3-5 hours in an inert gas atmosphere, cooling to room temperature after the reaction is completed, precipitating the polymer in water, washing the precipitated polymer with ethanol for 3-6 times, and finally removing residual ethanol by rotary evaporation to obtain the functional copolymer.

3. The high barrier composite film according to claim 2, characterized in that: The mass ratio of the vinylidene chloride, 2-acrylamido-2-methylpropanesulfonic acid, 3-(1,1-difluoro-2-propene-1-yl)-2(1H)-quinoxalinone, N-(4-cyano-3-trifluoromethylphenyl)methacrylamide, initiator, and high boiling point solvent is 2:(0.8-1.2):0.5:(1-2):(0.05-0.07):(15-25).

4. The high barrier composite film according to claim 2, characterized in that: The initiator is azobisisobutyronitrile; the high boiling point solvent is at least one of N,N-dimethylformamide and N-methylpyrrolidone; and the inert gas is any one of nitrogen, helium, neon and argon.

5. The high barrier composite film according to claim 1, characterized in that: The ethylene-vinyl alcohol copolymer is Soarnol TM BX6804B EVOH; the cellulose nanocrystals have a length of 200 nm and an outer diameter of 10 nm.

6. The high barrier composite film according to claim 1, characterized in that: The compatibilizer is selected from PP-g-MAH with the brand name HW-501; the antioxidant is at least one of antioxidant 1010, antioxidant 168, and antioxidant 1076; and the lubricant is at least one of butyl stearate and ethylene bisstearamide.

7. A method for preparing a high barrier composite film according to any one of claims 1 to 6, characterized in that: The steps include: Step S1, after uniformly mixing the functional copolymer, ethylene-vinyl alcohol copolymer, cellulose nanocrystals, a compatibilizer, an antioxidant and a lubricant to obtain a mixture, the mixture is added into a twin-screw extruder for extrusion molding, and then subjected to biaxial stretching and heat setting in sequence to obtain a primary film; Step S2, soaking the nascent film in an aqueous solution of 1-allyl-3-vinylimidazole chloride at 50-60° C. for 20-30 hours, taking it out and then soaking it in an ethanol solution containing a photoinitiator and allyl-β-cyclodextrin, taking it out and irradiating it under ultraviolet light for 20-30 minutes, repeatedly washing it with water and ethanol, and finally drying it to obtain a high-barrier composite film.

8. The method for preparing a high barrier composite film according to claim 7, characterized in that: The extrusion molding temperature in step S1 is 200-220°C; the biaxial stretching temperature in step S1 is 100-110°C, and the stretching ratio is 3-5; the heat setting temperature in step S1 is 120-130°C, and the time is 2-4 minutes.

9. The method for preparing a high barrier composite film according to claim 7, wherein: The mass percentage concentration of the aqueous solution of 1-allyl-3-vinylimidazolium chloride described in step S2 is 5-8%; the mass ratio of photoinitiator, allyl-β-cyclodextrin and ethanol in the ethanol solution containing photoinitiator and allyl-β-cyclodextrin described in step S2 is 0.01:1:

20.

10. The method for preparing a high barrier composite film according to claim 7, wherein: The photoinitiator is benzoin ethyl ether; the wavelength of the ultraviolet light is 220-260nm.