High-barrier composite film and preparation method thereof

Abstract

The invention belongs to the technical field of co-extruded films, and particularly relates to a high-barrier composite film and a preparation method thereof. The composite film comprises an outer layer formed by blending LLDPE and HDPE, PA / EVOH / PA three barrier layers, an inner layer formed by blending ULDPE and mLLDPE and an adhesion layer, molecular monomers containing flexible polyethylene glycol chain segments and a thermal initiator are introduced into raw materials of all the layers, and the composite film is prepared through a high-temperature co-extrusion technology. By adding the flexible chain segment, the brittleness of the membrane material at low temperature can be reduced, the embrittlement resistance of the membrane material, especially the barrier layer, is improved, and the low-temperature resistance is further improved; the thermal initiator promotes free radical polymerization of functional groups of the molecular monomers, an interpenetrating network structure is formed between layers, and the mechanical strength is improved. Through cooperation of the formula and the process, the low temperature resistance and the mechanical strength of the membrane material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coextruded films, and more particularly, to a high-barrier composite film and a method for preparing the same. Background Art

[0002] Disposable storage containers have shown many advantages in the biopharmaceutical field and are gradually replacing traditional stainless steel or glass bioreactors. They are widely used in bioreaction processes at the experimental stage, pilot scale, and production scale, covering many sub-fields or scenarios such as microbial culture and cell culture in discontinuous or continuous processes, preparation of clinical samples in the process of process development, and GMP production of biological drugs. However, current disposable storage containers also have some defects. They are prone to becoming brittle and fragile in low-temperature environments, increasing the risk of product loss during cold chain handling (such as storage after freezing and transportation of bulk drug raw materials) compared to traditional stainless steel containers, which has become the main problem restricting the application of disposable storage containers in this field. Taking mRNA vaccines as an example, their storage temperature usually needs to be controlled below -20°C, or even -80°C, which requires the packaging film material to have both high barrier properties and low-temperature toughness, and be able to withstand accidental collisions or impacts during cold chain transportation. Most current high-barrier composite film materials focus on barrier properties and pay less attention to low-temperature freezing resistance.

[0003] The coextrusion process can utilize the complementary properties of each layer, which is a feasible solution to ensure the barrier properties, mechanical strength, and low-temperature resistance of composite film materials. For example, the commonly used basic film material structure with low-temperature resistance on the market is PA / TIE / PE / TIE / PA / TIE / PE. This structure combines the barrier property of nylon (PA) with the low-temperature toughness of polyethylene (PE) and is mainly used in the packaging of low-temperature meat products, fresh fish, and aquatic products. However, this structure uses the middle PA as the main barrier material and is difficult to meet the requirements of environments with higher barrier needs. As a high-performance barrier material, EVOH has a gas barrier property 100 times higher than that of PA, 10,000 times higher than that of PE and PP, and dozens of times higher than that of the commonly used barrier material PVDC. Since the EVOH molecule contains hydroxyl groups, it has strong hydrophilic and hygroscopic properties. After absorbing moisture, its barrier property will decrease. Therefore, the EVOH layer is usually wrapped in moisture-barrier materials such as polyolefins (such as PE, PP) or nylon through multi-layer coextrusion technology to isolate moisture. For example, taking a 7-layer coextruded film as an example, the commonly used structures currently are the symmetric structure such as PE / Tie / PA / EVOH / PA / Tie / PE and the asymmetric structure such as PA / EVOH / PA / Tie / PE / PE / PE. Although the PE / Tie / PA / EVOH / PA / Tie / PE structure has excellent comprehensive properties, the low-temperature brittleness of the EVOH layer limits its application in low-temperature environments.

[0004] Through blending modification, the impact resistance and low-temperature toughness of EVOH can be improved, and it can be further extended to a lower temperature range. Taking the Chinese patent application with the publication number CN1810502A as an example, it discloses a low-temperature high-shrinkage high-barrier film and its production method. The barrier film includes an outer layer and an inner layer, and the barrier layer is made of at least one layer of a mixture of one or several of polyamide, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol. When the three are blended, it can replace the non-environmentally friendly PVDC and the radiation cross-linking or chemical cross-linking methods of EVOH and PA. At 80-90°C, the shrinkage rate in at least one direction is ≥20%, 30%, 40%, the tensile strength is ≥30 MPa, and the elongation at break is ≥60% to meet the packaging requirements. In this application, the barrier layer is made of a mixture of one or several of polyamide, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol, and has excellent barrier properties and low-temperature high heat shrinkage rate. However, although there is a certain polarity similarity among polyamide, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol, PVA has a stronger polarity (multi-hydroxyl structure), and the intermolecular force difference with PA and EVOH is relatively large. The high barrier properties of EVOH and PVA both depend on high crystallinity, and high crystallinity will limit the movement of chain segments. Therefore, after mixing, there is a risk of increased brittleness due to limited movement of molecular chain segments at lower temperatures, and it still cannot well meet the application under freezing low-temperature conditions, and its tensile strength is about 40 MPa, and the mechanical strength is relatively low. Therefore, it is necessary to provide a high-barrier composite film resistant to low-temperature freezing. Summary of the Invention

[0005] An object of the present invention is to solve at least the above problems and / or defects. In order to solve the technical problems of the current high-barrier film material having insufficient resistance to freezing low temperature and low mechanical strength, the present invention provides a high-barrier composite film resistant to low-temperature freezing and its preparation method. The present invention adds a molecular monomer with a flexible chain segment to the film material. By introducing the flexible chain segment, the layers such as PA and EVOH in the barrier layer still maintain good chain segment movement ability at low temperature, and then through the free radical polymerization of the double bond at the end of the molecular monomer, an interpenetrating network structure is formed between the layers of the film material, enhancing the bonding strength between the layers of the material, improving the mechanical strength of the diaphragm, and at the same time endowing the film material with good mechanical strength and barrier ability.

[0006] The object of the present invention is achieved as follows: In the first aspect of the present invention, a high-barrier composite film is provided, which at least includes an outer layer, a barrier layer formed by co-extrusion of three layers of PA / EVOH / PA, an inner layer, and an adhesion layer provided between the barrier layer and the outer layer and the inner layer; the outer layer and the inner layer are polyethylene mixture layers; the raw material components of each layer further include a molecular monomer with a flexible chain segment and a thermal initiator.

[0007] In the present invention, the barrier layer includes an EVOH layer and PA layers on both sides; generally, EVOH has extremely high barrier properties against oxygen, but is highly sensitive to humidity and its barrier properties decrease under high humidity; PA provides certain moisture barrier properties and relatively high mechanical strength. Therefore, in the present invention, a PA / EVOH / PA three-layer barrier film structure is formed between the outer layer and the inner layer of polyethylene through a co-extrusion process, which can endow the film with high oxygen and water vapor barrier properties.

[0008] In one embodiment of the present invention, the raw material components of the outer layer are a mixture of LLDPE and HDPE, and the mass ratio of the two is (60~80):(20~40), so as to endow the outer side of the film with relatively high mechanical strength and puncture resistance to resist accidental collisions or impacts during transportation; the inner layer is a mixture of ULDPE and mLLDPE, and the mass ratio of the two is controlled at (70~90):(10~30), so as to endow the inner layer with better low-temperature resistance and heat-sealing strength to meet the applications in relatively extreme freezing environments; the adhesion layer uses maleic anhydride grafted polyethylene, so that the polar PA layer and the non-polar polyethylene mixture layer are co-extruded and matched to ensure the stability and functional synergy of each layer of the film.

[0009] By introducing molecular monomers with flexible chain segments and heat initiators into the film, the low-temperature resistance and mechanical strength of the film can be improved. Specifically, molecular monomers with flexible chain segments are introduced into each layer of the film. The introduction of the flexible chain segments enables each layer of the film, especially the barrier layer, to still maintain good chain segment movement ability at low temperatures, thereby ensuring the toughness of the film in the low-temperature frozen state; at the same time, when the film is co-extruded at high temperature, through the heat initiator, the double bonds at the ends of the molecular monomers undergo free radical polymerization reactions, and an interpenetrating "network structure" can be formed between and within the layers of the film, enhancing the bonding strength between the layers of the film and improving the mechanical strength of the film; in addition, the barrier properties of EVOH are greatly affected by humidity, and the tight bonding between layers helps to reduce interlayer defects and improve the barrier properties of the film.

[0010] In one embodiment of the present invention, the molecular monomer is one or a mixture of methoxypolyethylene glycol methacrylate and polyethylene glycol dimethacrylate, including flexible polyethylene glycol chain segments and methacrylate groups; among them, the weight average molecular weight of the molecular monomer is preferably controlled at 800~1500Da. Introducing it into the film at this molecular weight will not reduce the barrier properties of the film, but can improve the low-temperature resistance and mechanical strength of the film. Specifically, when the molecular weight of the molecular monomer is too large, it is easy to cause too low crosslinking density, and the density of the "network structure" formed after polymerization is low; when the molecular weight is too small, the crosslinking density is too large, and the film is prone to uneven thickness during co-extrusion, making it difficult to improve the mechanical strength of the film well.

[0011] In one embodiment of the present invention, the addition amount of the molecular monomer in the outer layer and the inner layer is 4-12 wt% of the resin mass; the addition amount of the molecular monomer in the adhesion layer is 5-15 wt% of the resin mass; in the PA / EVOH / PA three-layer barrier layer, the addition amount of the molecular monomer in the PA layer is 0.1-3.0 wt% of the resin mass; the addition amount of the molecular monomer in the EVOH layer is 0.1-1 wt% of the resin mass. Within the above-mentioned addition amount range, by increasing the addition amount of the molecular monomer, it helps to enhance the low-temperature resistance and mechanical strength of the film material. However, when the addition amount of the molecular monomer is too large, it is easy to possibly occur such situations as too rapid deterioration of the barrier performance and uneven film thickness.

[0012] In the second aspect of the present invention, a method for preparing a high-barrier composite film is provided, which includes proportioning according to the formulations of each layer of the high-barrier composite film, respectively putting the raw materials of each film layer into the hoppers of a plurality of screw extruders of a co-extrusion stream extension machine, the melt converges at the die head through a diverter, the melt is cast through a casting roll, and a molten film is extruded through a casting die head, cooled, and wound up to prepare a high-barrier composite film.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Using PA / / EVOH / PA as the middle barrier layer endows the film material with high barrier performance. Using PE as the outer layer and the inner layer, where the outer layer uses LLDPE and HDPE to endow the film material with better puncture resistance, impact strength and environmental stress cracking resistance; the inner layer uses ULDPE and mLLDPE to optimize the heat-sealing performance and flexibility; after co-extrusion into a film, the overall high barrier property and mechanical strength are achieved in balance. (2) By adding molecular monomers to the film material to introduce flexible chain segments, it helps to reduce the risk of brittle rupture of each layer of the film material, especially the middle barrier layer, under low-temperature freezing conditions, and improves the low-temperature resistance; in addition, in combination with the co-extrusion process, the ends of the molecular monomers undergo free radical polymerization reactions under the action of a thermal initiator to form a "network structure" within and between the film layers, which helps to enhance the bonding strength between the layers of the film material; the low-temperature resistance and mechanical strength of the film material are improved through the coordination of the formulation and the process. Description of the Drawings

[0014] Figure 1 It is a sectional view of one embodiment of the high-barrier composite film of the present invention; Markings in the figure: 10 - the first PE layer, 20 - the first adhesion layer, 30 - the first PA layer, 40 - the EVOH layer, 50 - the second PA layer, 60 - the second adhesion layer, 70 - the second PE layer. Detailed Embodiments

[0015] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts are within the scope of protection of the present application.

[0016] As used herein, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in multiple embodiments of the present application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein may be combined with other embodiments.

[0017] Please refer to Figure 1 , to solve the problem that the current high-barrier film material is not well applicable to low-temperature freezing conditions, a high-barrier composite film resistant to low temperatures is provided, which includes a first PE layer 10, a first adhesion layer 20, a first PA layer 30, an EVOH layer 40, a second PA layer 50, a second adhesion layer 60, and a second PE layer 70; the raw material components of the first PE layer 10 include: a mixture of LLDPE and HDPE, a molecular monomer with a flexible chain segment, and a thermal initiator; the raw material components of the first adhesion layer 20 and the second adhesion layer 60 include: maleic anhydride grafted polyethylene, a molecular monomer with a flexible chain segment, and a thermal initiator; the raw material components of the first PA layer 30 and the second PA layer 50 include: PA, a molecular monomer with a flexible chain segment, and a thermal initiator; the raw material components of the EVOH layer include: EVOH, a molecular monomer with a flexible chain segment, and a thermal initiator; the second PE layer 70 is used as the inner layer of the film material, and its raw material components include: a mixture of ULDPE and mLLDPE, a molecular monomer with a flexible chain segment, and a thermal initiator; wherein, the first PE layer 10 is used as the outer layer of the film material to resist external mechanical impacts; the second PE layer 70 is used as the inner layer of the film material to contact the contents such as drugs.

[0018] Specifically, in the raw material components of the outer layer, the mixture of LLDPE and HDPE includes 60 to 80 parts by mass of LLDPE and 20 to 40 parts by mass of HDPE; in the raw material components of the inner layer, the mixture of ULDPE and mLLDPE includes 70 to 90 parts by mass of ULDPE and 10 to 30 parts by mass of mLLDPE; among them, the melt index of LLDPE is controlled at 2.3 to 2.8 g / 10 min, and the density is 0.930 to 0.940; the melt index of HDPE is controlled at 1.0 - 1.4 g / 10 min, and the density is 0.958 - 0.962 g / cm³; the melt index of ULDPE is controlled at 0.6 - 1.2 g / 10 min, and the melting point is 0.880 - 0.905 g / cm³; the melt index of mLLDPE is controlled at 2.0 - 2.5 g / 10 min, and the density is 0.910 - 0.915 g / cm³. The molecular monomer with a flexible chain segment is one or a mixture of polyethylene glycol methacrylate and polyethylene glycol dimethacrylate, and its weight average molecular weight is controlled at 800 to 1500 Da, and it has a flexible polyethylene glycol chain segment and a methacrylate end group; here, by introducing a flexible polyethylene glycol chain segment, it helps to enhance the flexibility and anti-brittleness performance of the film material, especially the barrier layer, in a low-temperature environment, and thus enhance the low-temperature resistance performance of the film material; at the same time, under the action of the thermal initiator 2,3-dimethyl-2,3-diphenylbutane, the methacrylate end group undergoes free radical polymerization to form an interpenetrating network structure between the layers of the film material, and the film material can improve the bonding strength between the layers and further improve the mechanical strength of the film material.

[0019] A preparation method of a high-barrier composite film is carried out using a co-extrusion process. After melting and plasticizing the raw materials of each layer by multiple screw extruders respectively, they are injected into the same die head, and then through further processing, a high-performance composite film is prepared by utilizing the complementary properties of each layer. Specifically, it includes: formulating according to the formula of each layer of the above-mentioned high-barrier composite film, putting the raw materials of each film layer into the hoppers of multiple screw extruders of a co-extrusion flow extender respectively, the melt converges at the die orifice through a diverter, the melt is cast by a casting roller, and a molten film is extruded through a casting die head, cooled, and wound up to prepare a high-barrier composite film. Among them, for reference, the screw extrusion temperatures of the raw materials corresponding to the outer layer, the adhesion layer, the PA layer, the EVOH layer, and the inner layer are 210 - 230 °C; 200 - 220 °C; 240 - 260 °C; 200 - 215 °C; 200 - 220 °C respectively.

[0020] Example 1. A high-barrier composite film is prepared specifically through the following steps: Step 1. Weigh the raw materials corresponding to each layer in proportion. Among them, for the outer layer: by mass, it includes 40 parts of LLDPE, 20 parts of HDPE, 3 parts of polyethylene glycol methacrylate (950 Da), and 0.06 part of 2,3-dimethyl-2,3-diphenylbutane, and stir and mix them evenly; for each adhesion layer: by mass, it includes 16 parts of maleic anhydride grafted polyethylene, 2 parts of polyethylene glycol methacrylate, and 0.04 part of 2,3-dimethyl-2,3-diphenylbutane, and stir and mix them evenly; for each PA layer: by mass, it includes 28 parts of PA, 0.6 part of polyethylene glycol methacrylate, and 0.012 part of 2,3-dimethyl-2,3-diphenylbutane, and stir and mix them evenly; for the EVOH layer: by mass, it includes 20 parts of EVOH, 0.1 part of polyethylene glycol methacrylate, and 0.002 part of 2,3-dimethyl-2,3-diphenylbutane, and stir and mix them evenly; for the inner layer: by mass, it includes 50 parts of ULDPE, 10 parts of mLLDPE, 3 parts of polyethylene glycol methacrylate, and 0.06 part of 2,3-dimethyl-2,3-diphenylbutane, and stir and mix them evenly. Step 2. Put the raw materials of each film layer above into a co-extrusion screw extruder respectively for melt co-extrusion. The melts of each layer converge into a co-extrusion melt at the die orifice through a diverter. Among them, the extrusion temperature of the corresponding screw extruder for the outer layer is 220 °C; the extrusion temperature of the corresponding screw extruder for the adhesion layer is 210 °C; the process parameters of the corresponding screw extruder for the PA layer are: 250 °C; the process parameters of the corresponding screw extruder for the EVOH layer are: 215 °C; the process parameters of the corresponding screw extruder for the inner layer are 210 °C; the die head temperature is 230 °C; the co-extrusion melt is cast by a casting roller to obtain a molten film, cooled and shaped, and then wound to prepare the high-barrier composite film of the present invention.

[0021] Example 2. A high-barrier composite film is prepared through the following steps: Step 1. Weigh the raw materials corresponding to each layer in proportion. Among them, for the outer layer: by mass, it includes 42 parts of LLDPE, 18 parts of HDPE, 3 parts of polyethylene glycol dimethacrylate (950 Da), and 0.12 part of 2,3-dimethyl-2,3-diphenylbutane, and stir and mix them evenly; for each adhesion layer: by mass, it includes 16 parts of maleic anhydride grafted polyethylene, 2 parts of polyethylene glycol dimethacrylate, and 0.08 part of 2,3-dimethyl-2,3-diphenylbutane, and stir and mix them evenly; for each PA layer: by mass, it includes 28 parts of PA, 0.6 part of polyethylene glycol dimethacrylate, and 0.03 part of 2,3-dimethyl-2,3-diphenylbutane, and stir and mix them evenly; for the EVOH layer: by mass, it includes 20 parts of EVOH, 0.1 part of polyethylene glycol dimethacrylate, and 0.005 part of 2,3-dimethyl-2,3-diphenylbutane, and stir and mix them evenly; for the inner layer: by mass, it includes 50 parts of ULDPE, 10 parts of mLLDPE, 3 parts of polyethylene glycol dimethacrylate, and 0.012 part of 2,3-dimethyl-2,3-diphenylbutane, and stir and mix them evenly. Step 2. Put the raw materials of each film layer above into a co-extrusion screw extruder respectively for melt co-extrusion. The melts of each layer converge into a co-extrusion melt at the die orifice through a diverter. Among them, the extrusion temperature of the corresponding screw extruder for the outer layer is 220 °C; the extrusion temperature of the corresponding screw extruder for the adhesion layer is 210 °C; the process parameters of the corresponding screw extruder for the PA layer are: 250 °C; the process parameters of the corresponding screw extruder for the EVOH layer are: 215 °C; the process parameters of the corresponding screw extruder for the inner layer are 210 °C; the die head temperature is 230 °C; the co-extrusion melt is cast by a casting roller to obtain a molten film, cooled and shaped, and wound to prepare the high-barrier composite film of the present invention.

[0022] Example 3. Others are basically the same as Example 1, except that, by mass percentage, the mass ratio of LLDPE to HDPE in the outer layer is 70:30; the mass ratio of ULDPE to mLLDPE in the inner layer is 80:20.

[0023] Example 4. Others are basically the same as Example 1, except that, by mass percentage, the mass ratio of LLDPE to HDPE in the outer layer is 60:40; the mass ratio of ULDPE to mLLDPE in the inner layer is 90:10.

[0024] Example 5. Others are basically the same as Example 1, except that the weight-average molecular weight of the polyethylene glycol methacrylate is 1200.

[0025] Comparative Example 1, a high-barrier composite film, comprising an outer layer, a barrier layer formed by co-extruding three layers of PA / EVOH / PA, an inner layer, and adhesion layers disposed between the barrier layer and the outer layer and the inner layer; the outer layer and the inner layer are polyethylene mixture layers. It is specifically prepared through the following steps: Step 1, weigh the raw materials corresponding to each layer in proportion, wherein for the outer layer: by mass, it includes 40 parts of LLDPE and 20 parts of HDPE and stir and mix evenly; for each adhesion layer: by mass, it includes 16 parts of maleic anhydride grafted polyethylene; for each PA layer: by mass, it includes 28 parts of PA; for the EVOH layer: by mass, it includes 20 parts of EVOH; for the inner layer: by mass, it includes 50 parts of ULDPE, 10 parts of mLLDPE, and stir and mix evenly; Step 2, respectively put the above raw materials of each film layer into a co-extrusion screw extruder for melt co-extrusion, and the melts of each layer converge into a co-extrusion melt at the die orifice through a diverter; among them, the extrusion temperature of the corresponding screw extruder for the outer layer is 220 °C; the extrusion temperature of the corresponding screw extruder for the adhesion layer is 210 °C; the process parameters of the corresponding screw extruder for the PA layer are: 250 °C; the process parameters of the corresponding screw extruder for the EVOH layer are: 215 °C; the process parameters of the corresponding screw extruder for the inner layer are 210 °C; the die head temperature is 230 °C; the co-extrusion melt is cast by a casting roll to obtain a molten film, cooled and shaped, and wound to prepare the high-barrier composite film of this example.

[0026] Comparative Example 2, a high-barrier composite film, comprising an outer layer, an EVOH barrier layer, an inner layer, and adhesion layers disposed between the EVOH barrier layer and the outer layer and the inner layer; the outer layer and the inner layer are polyethylene mixture layers. It is specifically prepared through the following steps: Step 1, weigh the raw materials corresponding to each layer in proportion, wherein for the outer layer: by mass, it includes 40 parts of LLDPE and 20 parts of HDPE and stir and mix evenly; for each adhesion layer: by mass, it includes 16 parts of maleic anhydride grafted polyethylene; for the EVOH layer: by mass, it includes 20 parts of EVOH; for the inner layer: by mass, it includes 50 parts of ULDPE, 10 parts of mLLDPE, and stir and mix evenly; Step 2, respectively put the above raw materials of each film layer into a co-extrusion screw extruder for melt co-extrusion, and the melts of each layer converge into a co-extrusion melt at the die orifice through a diverter; among them, the extrusion temperature of the corresponding screw extruder for the outer layer is 220 °C; the extrusion temperature of the corresponding screw extruder for the adhesion layer is 210 °C; the process parameters of the corresponding screw extruder for the EVOH layer are: 215 °C; the process parameters of the corresponding screw extruder for the inner layer are 210 °C; the die head temperature is 230 °C; the co-extrusion melt is cast by a casting roll to obtain a molten film, cooled and shaped, and wound to prepare the high-barrier composite film of this example.

[0027] Comparative Example 3, other aspects are basically the same as those of Example 1, the difference is that the weight-average molecular weight of the polyethylene glycol methacrylate is adjusted to 2000.

[0028] Comparative Example 4, other aspects are basically the same as those of Example 1, except that the weight-average molecular weight of the polyethylene glycol methacrylate is adjusted to 300.

[0029] Comparative Example 5, other aspects are basically the same as those of Example 1, except that the outer layer raw material includes 60 parts of LLDPE, 3 parts of polyethylene glycol methacrylate (950 Da), and 0.06 part of 2,3-dimethyl-2,3-diphenylbutane; the inner layer raw material includes 60 parts of ULDPE, 3 parts of polyethylene glycol methacrylate, and 0.06 part of 2,3-dimethyl-2,3-diphenylbutane.

[0030] Verification Example 1, the barrier properties, mechanical properties, and heat-sealing properties of the high-barrier composite films of Examples 1-5 and Comparative Examples 1-5 were tested. The specific test methods are as follows: Barrier properties: Refer to GB / T1038-2022 and GB / T1037-2021; Mechanical properties: Refer to GB / T1040.3-2006 and GB / T229-2007; To measure the heat-sealing properties of the film material: Refer to GB / T12028-1991; The specific test results are shown in Table 1; Table 1

[0031] Verification Example 2, to make the beneficial effects of the technical solution of the present application clearer, the low-temperature resistance of the high-barrier composite films of Examples 1-5 and Comparative Examples 1-5 was detected. The specific detection standards and items are as follows: Impact embrittlement temperature detection: Refer to ASTM D746-24; Detection of change in cold resistance softness: Measure the softness of the film material at room temperature and record it as M1, and measure the softness at -40 °C low temperature and record it as M2; the change rate of cold resistance softness Q = ((M1 - M2) / M1) × 100%. The lower the change rate Q, the stronger the ability to maintain softness at low temperature; The specific test results are shown in Table 2; Table 2

[0032] 1) As can be seen from Tables 1 and 2 above, the high-barrier composite films of the embodiments of the present invention have strong barrier properties, and their barrier properties to oxygen and water vapor both meet the corresponding standards. Compared with the comparative examples without adding molecular monomers, the tensile strength, elongation at break, impact embrittlement temperature, etc. have all been significantly improved; it shows that the film material of the present invention has high barrier properties, high mechanical strength, and low-temperature resistance, and is expected to be applied to extreme low-temperature freezing working conditions.

[0033] 2) As can be seen from Tables 1 and 2 above, compared with Comparative Example 1, the mechanical strength and low-temperature resistance of the film material of the embodiment of the present invention are significantly improved. It shows that compared with the film material with a simple polyolefin outer layer and a three-layer co-extruded PA / EVOH / PA barrier layer, by introducing a molecular monomer with a flexible chain segment and coordinating with an initiator and a co-extrusion process, the overall mechanical strength and low-temperature resistance of the film material can be improved; the introduction of the flexible polyethylene glycol chain segment enables each layer of the film material, especially the barrier layer, to still maintain good segmental movement ability at low temperatures, thereby improving the film material's resistance to low-temperature freezing performance; at the same time, through a thermal initiator, a free radical polymerization reaction occurs at the ends of the molecular monomers, forming an interpenetrating "network structure" between and within each layer of the film material, which can enhance the bonding strength between each layer of the film material and improve the mechanical strength of the film material. In addition, the barrier performance of EVOH is greatly affected by humidity, and the tight layer bonding helps to reduce interlayer defects and improve the barrier performance of the film material.

[0034] 3) As can be seen from Tables 1 and 2 above, compared with Comparative Example 2, by setting the barrier layer to a three-layer co-extruded structure of PA / EVOH / PA, the barrier property is significantly improved compared with that of pure EVOH. Compared with a single EVOH layer, the PA / EVOH / PA structure can buffer low-temperature stress through the PA layer while maintaining high barrier performance, reducing the risk of low-temperature embrittlement of the EVOH layer.

[0035] 4) As can be seen from Tables 1 and 2 above, the mechanical strength of the film materials of Comparative Example 3 and Comparative Example 4 is significantly smaller than that of Example 1. It shows that when the molecular weight of the molecular monomer is too large or too small, it is not conducive to improving the mechanical strength of the film material; when the molecular weight of the molecular monomer is too large, the crosslinking density is too low, and the "network structure" formed after polymerization has a low density and is difficult to significantly improve the mechanical strength of the film material; while when the molecular weight is too small, the crosslinking density is too large, and the film material is prone to uneven thickness during co-extrusion.

[0036] 5) As can be seen from Tables 1 and 2 above, the mechanical strength, heat-sealing strength, and low-temperature resistance of the film material of Comparative Example 5 are lower. It shows that at a certain ratio, using a mixture of LLDPE and HDPE for the outer layer of the film material and a mixture of ULDPE and mLLDPE for the inner layer helps to enhance the mechanical strength, heat-sealing strength, and low-temperature resistance of the film material.

[0037] The above are only the preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-barrier composite film, characterized in that, It includes an outer layer, a barrier layer arranged in three layers of PA / EVOH / PA, an inner layer, and adhesion layers arranged between the barrier layer and the outer layer and the inner layer; the raw material components of the outer layer include a mixture of LLDPE and HDPE; the raw material components of the inner layer include a mixture of ULDPE and mLLDPE. This high-barrier composite film is prepared by a high-temperature co-extrusion process, and the raw material components of each layer also include molecular monomers and a thermal initiator; among them, at least the molecular monomers include flexible chain segments and functional groups that can undergo free radical polymerization under the action of this thermal initiator, and the initiation temperature of the thermal initiator is less than or equal to the processing temperature of the die head.

2. The high-barrier composite film according to claim 1, wherein The molecular monomers include one or a mixture of polyethylene glycol methacrylate and polyethylene glycol dimethacrylate; the thermal initiator is 2,3-dimethyl-2,3-diphenylbutane.

3. The high-barrier composite film according to claim 2, wherein, The weight-average molecular weight of the molecular monomers is controlled at 800~1500Da.

4. The high-barrier composite film according to claim 2, wherein By mass percentage, In the mixture of LLDPE and HDPE, the mass ratio of LLDPE to HDPE is (60~80):(20~40); in the mixture of ULDPE and mLLDPE, the mass ratio of ULDPE to mLLDPE is (70~90):(10~30).

5. The high-barrier composite film according to claim 2, wherein The addition amount of the molecular monomers in the outer layer and the inner layer is 4~12wt% of the resin mass; the addition amount of the molecular monomers in the adhesion layer is 5~15wt% of the resin mass; in the PA / EVOH / PA three-layer barrier layer, the addition amount of the molecular monomers in the PA layer is 0.1~3wt% of the resin mass; the addition amount of the molecular monomers in the EVOH layer is 0.1~1wt% of the resin mass.

6. The high-barrier composite film according to claim 5, wherein, In each layer of this high-barrier composite film, the addition amount of the thermal initiator is 0.5%~5wt% of the molecular monomer mass.

7. The high-barrier composite film according to claim 2, wherein, The melt index of LLDPE is controlled at 2.3~2.8g / 10min, and the density is 0.930~0.940g / cm³; the melt index of HDPE is controlled at 1.0 - 1.4g / 10min, and the density is 0.958 - 0.962g / cm³; the melt index of ULDPE is controlled at 0.6 - 1.2g / 10min, and the density is 0.880 - 0.905g / cm³; the melt index of mLLDPE is controlled at 2.0 - 2.5g / 10min, and the density is 0.910 - 0.915g / cm³.

8. A method for preparing a high-barrier composite film according to any one of claims 1-7, characterized in that According to the formulations of the outer layer, the PA / EVOH / PA three-layer barrier layer, the inner layer and the adhesion layer, ingredients are prepared. The melt converges at the die orifice through a diverter, the melt is cast through a casting roller, and a molten film is extruded through a casting die head, cooled, and wound up to prepare the high-barrier composite film.

9. The preparation method according to claim 8, characterized in that, The melting temperature of the mixture of LLDPE and HDPE in the outer layer is 210~230℃; the melting temperature of the mixture of ULDPE and mLLDPE in the inner layer is 200~220℃.

10. Use of a high-barrier composite film according to any one of claims 1-7, characterized in that, This high-barrier composite film is used to prepare disposable liquid bags for the storage and transportation of low-temperature liquids in the field of biopharmaceuticals.

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