A high-barrier and high-temperature resistant food-grade film and its preparation method and application

Abstract

The present invention discloses a high-barrier and high-temperature-resistant food-grade film and its preparation method and application, belonging to the field of plastic films. It includes an outer film, an intermediate adhesive layer, and an inner film. The intermediate adhesive layer is a flexible enhanced slit-permeating dendritic polymer, and the flexible enhanced slit-permeating dendritic polymer is a dendritic polymer prepared by a divergent method and a convergent method using n-octyl α-cyanoacrylate as the initial core molecule, bio-based methacrylate as the main monomer, 3-mercaptopropyltriethoxysilane as the flexible chain segment monomer, diethylhydroxylamine as the enhancing monomer, BPO as the initiator, and DEVB as the crosslinking agent. The film prepared by the present invention has strong barrier properties and good flexibility.

Description

Technical Field

[0001] The present invention belongs to the field of plastic films, and relates to a high-barrier and high-temperature-resistant food-grade film, a preparation method thereof and an application thereof. Background Art

[0002] Food-grade films need to have both high-temperature resistance and high-barrier properties in food packaging to meet the safety and quality requirements of food during processing, storage and transportation, especially for vacuum packaging of high-temperature oil substances.

[0003] Currently, when improving the barrier performance of films, generally methods such as aluminizing, surface coating (nanomaterials, inorganic substances) are adopted. Although they can effectively improve the barrier property of the film, they will also significantly reduce the flexibility of the film. If the film has low flexibility, it cannot fit the food, affecting the tightness of food packaging, especially for vacuum packaging bags. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-barrier and high-temperature-resistant food-grade film, a preparation method thereof and an application thereof, which solves the problem that the flexibility of the film is significantly reduced when improving the barrier performance of the film.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A high-barrier and high-temperature-resistant food-grade film, comprising an outer film, an intermediate adhesive layer, and an inner film. The intermediate adhesive layer is a flexible-enhanced gap-permeating dendritic polymer. The flexible-enhanced gap-permeating dendritic polymer is a dendritic polymer prepared by a divergent method and a convergent method using n-octyl α-cyanoacrylate as the initial core molecule, bio-based methacrylate as the main monomer, 3-mercaptopropyltriethoxysilane as the flexible chain segment monomer, diethylhydroxylamine as the enhancing monomer, BPO as the initiator, and DEVB as the crosslinking agent;

[0007] Among them, the mass ratio of n-octyl α-cyanoacrylate is 10%, the mass ratio of bio-based methacrylate is 45%, the mass ratio of 3-mercaptopropyltriethoxysilane is 20%, the mass ratio of diethylhydroxylamine is 10%, the mass ratio of BPO is 5%, and the mass ratio of DEVB is 10%.

[0008] In the present invention, n-octyl α-cyanoacrylate is selected as the initial core molecule due to its property of rapid polymerization upon contact with water and surfaces having anions. This property enables it to rapidly and stably form a core structure at the initial stage of dendritic polymer formation, providing a solid foundation for subsequent polymerization reactions. As the initial core molecule, the cyano group and acrylic acid group in the structure of n-octyl α-cyanoacrylate provide high reactivity, enabling the rapid initiation of polymerization reactions under the action of the initiator BPO to form a stable polymerization core; the bio-based methacrylate is used as the main monomer and is connected to the core molecule through a free radical polymerization reaction to form the main chain of the polymer. Its bio-based source not only endows the polymer with environmental friendliness but also copolymerizes with other monomers through its methacrylate group, enhancing the overall properties of the polymer; 3-mercaptopropyltriethoxysilane is used as a flexible chain segment monomer. The thioether bond and siloxane bond in its structure provide good flexibility. During the polymerization process, these flexible chain segments are introduced into the polymer to form branched chains or pendant chains, thereby increasing the flexibility and permeability of the polymer; diethylhydroxylamine is used as a reinforcing monomer. The nitrogen-oxygen bond in its molecular structure can form hydrogen bonds or dipole-dipole interactions with other groups on the polymer chain, thereby enhancing the intermolecular forces between polymer molecules and improving the strength and hardness of the polymer.

[0009] Under the action of the BPO initiator, n-octyl α-cyanoacrylate first undergoes a free radical polymerization reaction to form a polymerization core. Subsequently, monomers such as bio-based methacrylate and 3-mercaptopropyltriethoxysilane are successively added to the reaction system and copolymerize with the core molecule or the polymer chains that have already formed; diethylhydroxylamine participates in the reaction as a reinforcing monomer and enhances the overall properties of the polymer through its intermolecular forces; finally, the DEVB crosslinking agent connects different polymer chains to form a three-dimensional network structure.

[0010] Due to the highly branched structure and abundant functional groups of the flexible enhanced gap-permeable dendritic polymer, its molecular chains can penetrate into the tiny gaps of the film. After forming a continuous covering layer on the film surface, the polymer branches can fill the gaps and form a dense barrier layer, effectively preventing the penetration of substances such as gases and liquids. In addition, the flexibility and permeability of the polymer molecular chains enable it to adapt to the tiny deformations of the film without being easily broken or detached, thus maintaining a long-term stable barrier effect.

[0011] The excellent flexibility of the flexible enhanced gap-permeating dendritic polymer is mainly due to the flexible segment monomers (3-mercaptopropyltriethoxysilane) in its molecular structure. These flexible segments form many pendant chains or branched chains in the polymer, enabling the polymer chains to bend and twist to a certain extent when subjected to external forces, thus maintaining the overall flexibility. At the same time, the addition of diethylhydroxylamine enhancing monomers increases the intermolecular interaction forces of the polymer, making the polymer have higher strength and hardness while maintaining flexibility; although the flexible enhanced gap-permeating dendritic polymer has high strength and hardness, its flexibility is not affected, which is mainly due to the reasonable ratio of flexible segment monomers and enhancing monomers in the polymer molecule and their interaction. The flexible segment monomers endow the polymer with good flexibility and elasticity, while the enhancing monomers maintain the overall mechanical properties of the polymer by increasing the intermolecular interaction forces. The balance between the two enables the polymer to still have good flexibility while maintaining high strength; therefore, due to the good flexibility of the intermediate adhesive layer of the present invention, after its branched chains penetrate into the gaps between the outer film and the inner film, it will not significantly reduce the flexibility of the outer film and the inner film, and thus will not significantly reduce the overall flexibility of the high-barrier heat-resistant food-grade film.

[0012] Furthermore, the flexible enhanced gap-permeating dendritic polymer is prepared by the following method:

[0013] S1. Under nitrogen protection, dissolve n-octyl α-cyanoacrylate in tetrahydrofuran to obtain an n-octyl α-cyanoacrylate solution. Add 20% by mass of a bio-based methacrylate to the n-octyl α-cyanoacrylate solution, then stir and heat to 60 °C and add 1% of a BPO initiator. React at 60 °C for 12 hours to obtain the first-generation dendritic polymer.

[0014] S2. Mix the bio-based methacrylate, 3-mercaptopropyltriethoxysilane, and diethylhydroxylamine in proportion to form a pre-polymerization system.

[0015] S3. Dissolve the remaining 4% of the initiator BPO in the bio-based methacrylate to obtain an initiator solution.

[0016] S4. Slowly add the pre-polymerization system obtained in step S2 to the first-generation dendritic polymer obtained in step S1. Stir and heat to 80 °C and then add the initiator solution obtained in step S3. Continue to stir and react for 6 hours to obtain a dendritic polymer.

[0017] S5. Add 5% by mass of a cross-linking agent DEVB to the dendritic polymer obtained in step S4. Continue to stir and react at 80 °C for 30 - 60 minutes to carry out the convergence of the network structure and obtain the flexible enhanced gap-permeating dendritic polymer.

[0018] The present invention employs a divergent method and a convergent method; Divergent method: Starting from the core of n-octyl α-cyanoacrylate, monomers such as bio-based methacrylate and 3-mercaptopropyltriethoxysilane are gradually added outward to form a dendritic structure. As the reaction proceeds, the polymer chains continuously grow and the branches gradually increase, forming a highly branched structure. Convergent method: On the basis of the divergent method, crosslinking agents are used to connect the polymer chains to form a complete three-dimensional network structure. This method helps to control the final morphology and properties of the polymer, ensuring that the polymer has excellent flexibility, strength, and barrier properties.

[0019] Further, the outer layer film comprises the following components in parts by weight: 60 parts of linear low density polyethylene, 5 parts of light stabilizer, 5 parts of slip agent, 5 parts of antistatic agent, and 30 parts of ethylene-vinyl acetate copolymer.

[0020] The outer layer film of the present invention combines the strength and toughness of LLDPE, the transparency and heat resistance of EVA, the light aging protection of the light stabilizer, the improvement of the processing performance of the slip agent, and the antistatic effect of the antistatic agent, forming a film material with excellent comprehensive properties, which is suitable for the complex environment of the outer layer.

[0021] Further, the inner layer film comprises the following components in parts by weight: 50 parts of high density polyethylene, 35 parts of ethylene-vinyl acetate copolymer, and 10 parts of nano-silica.

[0022] The inner layer film is in direct contact with food and needs to have good high temperature resistance. Therefore, nano-silica is added to the polyethylene film in the present invention, which helps to improve the high temperature resistance of the film.

[0023] Further, the light stabilizer is a hindered amine light stabilizer HALS, the slip agent is erucamide, and the antistatic agent is amide phosphate.

[0024] Further, the total thickness of the outer layer film, the middle adhesive layer, and the inner layer film is 0.28 mm, wherein the thickness of the outer layer film is 0.12 mm, the thickness of the inner layer film is 0.1 mm, and the thickness of the middle adhesive layer is 0.06 mm.

[0025] In the actual use process, the present invention optimizes the thickness of each layer.

[0026] The preparation method of a high barrier and high temperature resistant food-grade film described above comprises the following steps:

[0027] A. Prepare the outer layer film material: Melt and blend 60 parts of linear low density polyethylene, 5 parts of light stabilizer, 5 parts of slip agent, 5 parts of antistatic agent, and 30 parts of ethylene-vinyl acetate copolymer to obtain the outer layer film material;

[0028] B. Preparation of the inner layer film material: 50 parts of high-density polyethylene, 35 parts of ethylene-vinyl acetate copolymer, and 10 parts of nano-silica are melt-blended to obtain the inner layer film material;

[0029] C. Preparation of the intermediate adhesive layer material:

[0030] S1. Under nitrogen protection, n-octyl α-cyanoacrylate is dissolved in tetrahydrofuran to obtain an n-octyl α-cyanoacrylate solution. 20% by mass of a bio-based methacrylate is added to the n-octyl α-cyanoacrylate solution, and then the mixture is stirred and heated to 60 °C. After that, 1% of BPO initiator is added, and the reaction is carried out at 60 °C for 12 hours to obtain the first-generation dendritic polymer;

[0031] S2. The bio-based methacrylate, 3-mercaptopropyltriethoxysilane, and diethylhydroxylamine are mixed in proportion to form a prepolymerization system;

[0032] S3. The remaining 4% of the initiator BPO is dissolved in the bio-based methacrylate to obtain an initiator solution;

[0033] S4. The prepolymerization system obtained in step S2 is slowly added to the first-generation dendritic polymer obtained in step S1. After stirring and heating to 80 °C, the initiator solution obtained in step S3 is added, and the mixture is continuously stirred and reacted for 6 hours to obtain a dendritic polymer;

[0034] S5. 5% by mass of the crosslinking agent DEVB is added to the dendritic polymer obtained in step S4, and the reaction is continued at 80 °C with stirring for 30 - 60 minutes to carry out the convergence of the network structure, obtaining a flexible and enhanced gap-permeable dendritic polymer;

[0035] D. Using a multi-layer co-extrusion blown film machine to co-extrude and blow-mold the outer layer film material, the intermediate adhesive layer material, and the inner layer film material to obtain a high-barrier heat-resistant food-grade film with a three-layer structure. The high-barrier heat-resistant food-grade film includes an outer layer film, an intermediate adhesive layer, and an inner layer film.

[0036] Furthermore, the multi-layer co-extrusion blown film machine uses a GY-1600SB type multi-layer co-extrusion blown film machine.

[0037] Furthermore, the reaction time of S5 is 45 minutes.

[0038] The high-barrier heat-resistant food-grade film is used as a high-temperature oil-resistant vacuum bag in the food field.

[0039] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are:

[0040] 1. In a high-barrier and high-temperature resistant food-grade film, the gap-permeating dendritic polymer with enhanced flexibility has a highly branched structure and abundant functional groups. Its molecular chains can penetrate into the tiny gaps of the film. After forming a continuous covering layer on the film surface, the polymer branches can fill the gaps and form a dense barrier layer, effectively preventing the penetration of substances such as gases and liquids. Therefore, in the present invention, the gap-permeating dendritic polymer with enhanced flexibility is used as the intermediate adhesive layer, which can effectively improve the barrier properties of the outer film and the inner film, replacing the existing method of improving barrier properties by coating inorganic substances.

[0041] 2. In the gap-permeating dendritic polymer with enhanced flexibility in the present invention, the flexibility and permeability of the polymer molecular chains enable it to adapt to the tiny deformations of the film without being easily broken or detached, thus maintaining a long-term stable barrier effect.

[0042] 3. Since the intermediate adhesive layer of the present invention has good flexibility, after its branches penetrate into the gaps of the outer film and the inner film, it will not significantly reduce the flexibility of the outer film and the inner film, and thus will not significantly reduce the overall flexibility of the high-barrier and high-temperature resistant food-grade film.

[0043] 4. The present invention adopts a combination of the divergent method and the convergent method to prepare the gap-permeating dendritic polymer with enhanced flexibility, which helps to control the final morphology and properties of the polymer and ensure that the polymer has excellent flexibility and strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings, where:

[0045] Figure 1 is a SEM image of a high-barrier and high-temperature resistant food-grade film. DETAILED DESCRIPTION OF THE INVENTION

[0046] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following will further describe the present invention in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Usually, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0047] Accordingly, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0048] It should be noted that relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0049] The features and performance of the present invention will be further described in detail below in conjunction with embodiments.

[0050] Embodiment 1:

[0051] A high-barrier and high-temperature-resistant food-grade film provided by a preferred embodiment of the present invention includes an outer film, an intermediate adhesive layer, and an inner film. The intermediate adhesive layer is a flexible enhanced gap-permeable dendritic polymer, and the flexible enhanced gap-permeable dendritic polymer is a dendritic polymer prepared by a divergent method and a convergent method using n-octyl α-cyanoacrylate as the initial core molecule, bio-based methacrylate as the main monomer, 3-mercaptopropyltriethoxysilane as the flexible chain segment monomer, diethylhydroxylamine as the enhancing monomer, BPO as the initiator, and DEVB as the crosslinking agent.

[0052] Among them, the mass ratio of n-octyl α-cyanoacrylate is 10%, the mass ratio of bio-based methacrylate is 45%, the mass ratio of 3-mercaptopropyltriethoxysilane is 20%, the mass ratio of diethylhydroxylamine is 10%, the mass ratio of BPO is 5%, and the mass ratio of DEVB is 10%.

[0053] The flexible enhanced gap-permeable dendritic polymer is prepared by the following method:

[0054] S1. Under nitrogen protection, dissolve n-octyl α-cyanoacrylate in tetrahydrofuran to obtain an n-octyl α-cyanoacrylate solution. Add 20% by mass of bio-based methacrylate to the n-octyl α-cyanoacrylate solution, then stir and heat up to 60 °C, and add 1% of BPO initiator. After reacting at 60 °C for 12 hours, the first-generation dendritic polymer is formed;

[0055] S2. Mix bio-based methacrylate, 3-mercaptopropyltriethoxysilane and diethylhydroxylamine in proportion to form a prepolymerization system;

[0056] S3. Dissolve the remaining 4% of initiator BPO in bio-based methacrylate to obtain an initiator solution;

[0057] S4. Slowly add the prepolymerization system obtained in step S2 to the first-generation dendritic polymer obtained in step S1. Stir and heat to 80 °C, then add the initiator solution obtained in step S3, and continue to stir and react for 6 hours to obtain a dendritic polymer;

[0058] S5. Add 5% by mass of crosslinking agent DEVB to the dendritic polymer obtained in step S4, and continue to stir and react at 80 °C for 30 minutes to carry out the convergence of the network structure, obtaining a flexible and enhanced gap-permeable dendritic polymer.

[0059] The outer film comprises the following components in parts by weight: 60 parts of linear low-density polyethylene, 5 parts of light stabilizer, 5 parts of slip agent, 5 parts of antistatic agent, and 30 parts of ethylene-vinyl acetate copolymer.

[0060] The inner film comprises the following components in parts by weight: 50 parts of high-density polyethylene, 35 parts of ethylene-vinyl acetate copolymer, and 10 parts of nano-silica.

[0061] The light stabilizer is a hindered amine light stabilizer HALS, the slip agent is erucamide, and the antistatic agent is amide phosphate.

[0062] The total thickness of the outer film, the middle adhesive layer, and the inner film is 0.28 mm, wherein the thickness of the outer film is 0.12 mm, the thickness of the inner film is 0.1 mm, and the thickness of the middle adhesive layer is 0.06 mm.

[0063] The preparation method of the above-mentioned high-barrier and high-temperature-resistant food-grade film comprises the following steps:

[0064] A. Prepare the outer film material: Melt and blend 60 parts of linear low-density polyethylene, 5 parts of light stabilizer, 5 parts of slip agent, 5 parts of antistatic agent, and 30 parts of ethylene-vinyl acetate copolymer to obtain the outer film material;

[0065] B. Preparation of the inner layer film material: 50 parts of high-density polyethylene, 35 parts of ethylene-vinyl acetate copolymer, and 10 parts of nano-silica are melt-blended to obtain the inner layer film material;

[0066] C. Preparation of the intermediate adhesive layer material:

[0067] S1. Under nitrogen protection, n-octyl α-cyanoacrylate is dissolved in tetrahydrofuran to obtain an n-octyl α-cyanoacrylate solution. 20% by mass of a bio-based methacrylate is added to the n-octyl α-cyanoacrylate solution, and then the mixture is stirred and heated to 60 °C. After that, 1% of BPO initiator is added, and the reaction is carried out at 60 °C for 12 hours to obtain the first-generation dendritic polymer;

[0068] S2. The bio-based methacrylate, 3-mercaptopropyltriethoxysilane, and diethylhydroxylamine are mixed in proportion to form a prepolymerization system;

[0069] S3. The remaining 4% of the initiator BPO is dissolved in the bio-based methacrylate to obtain an initiator solution;

[0070] S4. The prepolymerization system obtained in step S2 is slowly added to the first-generation dendritic polymer obtained in step S1. After stirring and heating to 80 °C, the initiator solution obtained in step S3 is added, and the stirring reaction is continued for 6 hours to obtain a dendritic polymer;

[0071] S5. 5% by mass of the crosslinking agent DEVB is added to the dendritic polymer obtained in step S4, and the stirring reaction is continued at 80 °C for 30 minutes to carry out the convergence of the network structure, obtaining a flexible and enhanced gap-permeable dendritic polymer;

[0072] D. The outer layer film material, the intermediate adhesive layer material, and the inner layer film material are co-extruded and blown into shape by a multi-layer co-extrusion blown film machine to obtain a high-barrier and high-temperature-resistant food-grade film with a three-layer structure. The high-barrier and high-temperature-resistant food-grade film includes an outer layer film, an intermediate adhesive layer, and an inner layer film.

[0073] The multi-layer co-extrusion blown film machine used is a GY-1600SB type multi-layer co-extrusion blown film machine.

[0074] Figure 1 This is the SEM image of the outer surface of the high-barrier and high-temperature-resistant food-grade film prepared by the present invention. It can be clearly seen from the figure that there are fillers in the pores of the film, and the barrier performance is enhanced after there are fillers in the voids.

[0075] Example 2:

[0076] This example is based on Example 1. The difference between this example and Example 1 is that the reaction time in step S5 of this example is 45 minutes.

[0077] Example 3:

[0078] On the basis of Example 1, the difference between this example and Example 1 is that the reaction time in step S5 of this example is 60 minutes.

[0079] Comparative Example 1:

[0080] Based on Example 1, the difference between this comparative example and Example 1 is that in the comparative example, the mass ratio of n-octyl α-cyanoacrylate is 10%, the mass ratio of bio-based methacrylate is 45%, the mass ratio of 3-mercaptopropyltriethoxysilane is 10%, the mass ratio of diethylhydroxylamine is 10%, the mass ratio of BPO is 5%, and the mass ratio of DEVB is 10%.

[0081] Comparative Example 2:

[0082] Based on Example 1, the difference between this comparative example and Example 1 is that in the comparative example, the mass ratio of n-octyl α-cyanoacrylate is 10%, the mass ratio of bio-based methacrylate is 45%, the mass ratio of 3-mercaptopropyltriethoxysilane is 15%, the mass ratio of diethylhydroxylamine is 5%, the mass ratio of BPO is 5%, and the mass ratio of DEVB is 10%.

[0083] Comparative Example 3:

[0084] Based on Example 1, the difference between this comparative example and Example 1 is that: the high-barrier and high-temperature resistant food-grade film in this comparative example does not include an intermediate adhesive layer.

[0085] Comparative Example 4:

[0086] Based on Example 1, the difference between this comparative example and Example 1 is that: the intermediate adhesive layer in this comparative example does not include 3-mercaptopropyltriethoxysilane.

[0087] Comparative Example 5:

[0088] Based on Example 1, the difference between this comparative example and Example 1 is that: the intermediate adhesive layer in this comparative example does not include diethylhydroxylamine.

[0089] Comparative Example 6:

[0090] Based on Example 1, the difference between this comparative example and Example 1 is that: the intermediate adhesive layer in this comparative example does not include bio-based methacrylate.

[0091] Comparative Example 7:

[0092] Based on Example 1, the difference between this comparative example and Example 1 is that: the reaction time in step S5 of this comparative example is 65 minutes.

[0093] Comparative Example 8:

[0094] Based on Example 1, the difference between this comparative example and Example 1 is that: in this comparative example, the reaction time in step S5 is 25 minutes.

[0095] Test Example 1:

[0096] Detect the tensile strength, elongation at break, hardness, thermal weight loss temperature, and glass transition temperature (Tg) of the cured flexible enhanced slit-permeable dendritic polymer prepared in Examples 1-3 and Comparative Examples 1, 2, 4, 5, 6, 7, and 8; the test results are shown in Table 1.

[0097] The detection methods for the tensile strength, elongation at break, hardness, thermal weight loss temperature, and glass transition temperature of the cured flexible enhanced slit-permeable dendritic polymer are prior arts and will not be elaborated here.

[0098] Table 1 Performance detection of the cured flexible enhanced slit-permeable dendritic polymer

[0099] Tensile strength Hardness Thermogravimetric temperature Glass transition temperature (Tg) Example 1 30 MPa 60 Shore D >250°C 80°C Example 2 50 MPa 78 Shore D >250°C 90°C Example 3 55 MPa 80 Shore D >250°C 90°C Comparative Example 1 50 MPa 80 Shore D >250°C 80°C Comparative Example 2 20 MPa 50 Shore D >250°C 60°C Comparative Example 4 45 MPa 60 Shore D >250°C 60°C Comparative Example 5 15 MPa 40 Shore D >250°C 55°C Comparative Example 6 22 MPa 43 Shore D >250°C 56°C Comparative Example 7 55 MPa 82 Shore D >250°C 92°C Comparative Example 8 25 MPa 42 Shore D >250°C 50°C

[0100] Test Example 2:

[0101] Detect the porosity and elongation at break of the high-barrier high-temperature resistant food-grade films prepared in Examples 1-3 and Comparative Examples 1-8; the test results are shown in Table 2.

[0102] Table 2 Test results of the high-barrier high-temperature resistant food-grade films

[0103] Porosity Elongation at break Example 1 Less than 5% 500% Example 2 Less than 5% 600% Example 3 Less than 5% 450% Comparative Example 1 Less than 5% 400% Comparative Example 2 Less than 5% 650% Comparative Example 3 Greater than 5% 610% Comparative Example 4 Greater than 5% 200% Comparative Example 5 Less than 5% 550% Comparative Example 6 Less than 5% 500% Comparative Example 7 Less than 5% 300% Comparative Example 8 Less than 5% 450%

[0104] Combining the data in Table 1 and Table 2, Example 2 of the present invention is the best ratio, with its flexibility and mechanical strength maintained in balance, having both high mechanical strength and good flexibility; comparing Comparative Example 3 with Example 2, after adding the intermediate adhesive layer in the present invention, the overall flexibility of the film will indeed decrease, but the degree of decrease is small, indicating that the intermediate adhesive layer of the present invention has a small impact on the overall flexibility of the film. Combining with the porosity in Table 2 of the present invention, the porosity of the film of the present invention is less than 5%, indicating strong barrier properties; comparing Comparative Example 3 with Example 2, after adding the intermediate adhesive layer in the present invention, the porosity decreases, indicating that the intermediate adhesive layer of the present invention can significantly improve the barrier properties of the film.

[0105] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-barrier and high-temperature resistant food-grade film, comprising an outer film, an intermediate adhesive layer, and an inner film, characterized in that: The intermediate adhesive layer is a flexible enhanced slit-permeable dendritic polymer, and the flexible enhanced slit-permeable dendritic polymer is a dendritic polymer prepared by the divergent method and the convergent method using n-octyl α-cyanoacrylate as the initial core molecule, bio-based methacrylate as the main monomer, 3-mercaptopropyltriethoxysilane as the flexible chain segment monomer, diethylhydroxylamine as the enhancing monomer, BPO as the initiator, and DEVB as the crosslinking agent; Among them, the mass ratio of n-octyl α-cyanoacrylate is 10%, the mass ratio of bio-based methacrylate is 45%, the mass ratio of 3-mercaptopropyltriethoxysilane is 20%, the mass ratio of diethylhydroxylamine is 10%, the mass ratio of BPO is 5%, and the mass ratio of DEVB is 10%; The flexible enhanced slit-permeable dendritic polymer is prepared by the following method: S1. Under nitrogen protection, dissolve n-octyl α-cyanoacrylate in tetrahydrofuran to obtain an n-octyl α-cyanoacrylate solution. Add bio-based methacrylate with a mass ratio of 20% to the n-octyl α-cyanoacrylate solution, then stir and heat up to 60 °C and add 1% of the BPO initiator. React at 60 °C for 12 hours to obtain the first-generation dendritic polymer; S2. Mix bio-based methacrylate, 3-mercaptopropyltriethoxysilane, and diethylhydroxylamine in proportion to form a pre-polymerization system; S3. Dissolve the remaining 4% of the initiator BPO in bio-based methacrylate to obtain an initiator solution; S4. Slowly add the pre-polymerization system obtained in step S2 to the first-generation dendritic polymer obtained in step S1. Stir and heat up to 80 °C and then add the initiator solution obtained in step S3. Continue to stir and react for 6 hours to obtain a dendritic polymer; S5. Add crosslinking agent DEVB with a mass ratio of 5% to the dendritic polymer obtained in step S4, and continue to stir and react at 80 °C for 30 - 60 minutes to carry out the convergence of the network structure to obtain a flexible enhanced slit-permeable dendritic polymer.

2. The high-barrier and high-temperature resistant food-grade film according to claim 1, wherein: The outer film comprises the following components in parts by weight: 60 parts of linear low-density polyethylene, 5 parts of light stabilizer, 5 parts of slip agent, 5 parts of antistatic agent, and 30 parts of ethylene-vinyl acetate copolymer.

3. The high-barrier and high-temperature resistant food-grade film according to claim 1, characterized in that: The inner film comprises the following components in parts by weight: 50 parts of high-density polyethylene, 35 parts of ethylene-vinyl acetate copolymer, and 10 parts of nano-silica.

4. The high-barrier and high-temperature resistant food-grade film according to claim 2, wherein: The light stabilizer is a hindered amine light stabilizer HALS, the slip agent is erucamide, and the antistatic agent is amide phosphate.

5. A high-barrier and high-temperature resistant food-grade film according to claim 1, characterized in that: The total thickness of the outer film, the intermediate adhesive layer, and the inner film is 0.28 mm, wherein the thickness of the outer film is 0.12 mm, the thickness of the inner film is 0.1 mm, and the thickness of the intermediate adhesive layer is 0.06 mm.

6. The preparation method of a high-barrier and high-temperature resistant food-grade film according to any one of claims 1-5, characterized in that: Comprises the following steps: A. Prepare the outer film material: Melt and blend 60 parts of linear low-density polyethylene, 5 parts of light stabilizer, 5 parts of slip agent, 5 parts of antistatic agent, and 30 parts of ethylene-vinyl acetate copolymer to obtain the outer film material; B. Preparation of the inner layer film material: 50 parts of high-density polyethylene, 35 parts of ethylene-vinyl acetate copolymer, and 10 parts of nano-silica are melt-blended to obtain the inner layer film material; C. Preparation of the intermediate adhesive layer material: S1. Under nitrogen protection, n-octyl α-cyanoacrylate is dissolved in tetrahydrofuran to obtain an n-octyl α-cyanoacrylate solution. 20% by mass of bio-based methacrylate is added to the n-octyl α-cyanoacrylate solution, and then the mixture is stirred and heated to 60 °C. After that, 1% of BPO initiator is added, and the reaction is carried out at 60 °C for 12 hours to obtain the first-generation dendritic polymer; S2. Bio-based methacrylate, 3-mercaptopropyltriethoxysilane, and diethylhydroxylamine are mixed in proportion to form a prepolymerization system; S3. The remaining 4% of the initiator BPO is dissolved in bio-based methacrylate to obtain an initiator solution; S4. The prepolymerization system obtained in step S2 is slowly added to the first-generation dendritic polymer obtained in step S1. After stirring and heating to 80 °C, the initiator solution obtained in step S3 is added, and the stirring reaction is continued for 6 hours to obtain a dendritic polymer; S5. 5% by mass of crosslinking agent DEVB is added to the dendritic polymer obtained in step S4, and the stirring reaction is continued at 80 °C for 30 - 60 minutes for the convergence of the network structure to obtain a flexible enhanced gap-permeable dendritic polymer; D. Using a multi-layer coextrusion blown film machine to coextrude and blow-mold the outer layer film material, the intermediate adhesive layer material, and the inner layer film material to obtain a high-barrier high-temperature-resistant food-grade film with a three-layer structure. The high-barrier high-temperature-resistant food-grade film includes an outer layer film, an intermediate adhesive layer, and an inner layer film.

7. The preparation method of a high-barrier and high-temperature resistant food-grade film according to claim 6, characterized in that: The multi-layer coextrusion blown film machine adopts a GY-1600SB type multi-layer coextrusion blown film machine.

8. The preparation method of a high-barrier and high-temperature resistant food-grade film according to claim 6, characterized in that: The reaction time of step S5 is 45 minutes.

9. The application of a high-barrier and high-temperature resistant food-grade film according to claim 1, wherein: The high-barrier high-temperature-resistant food-grade film is used as a high-temperature oil-resistant vacuum bag in the food field.

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