Multi-layer co-extruded film, preparation method thereof, bag body and application of multi-layer co-extruded film and bag body

Abstract

The invention relates to the technical field of co-extruded films, and provides a multi-layer co-extruded film, a preparation method thereof, a bag body and application of the multi-layer co-extruded film and the preparation method. The multi-layer co-extruded film comprises an outer surface layer, an inner surface layer and a middle layer, the middle layer comprises a blocking layer and a flexible supporting layer, the flexible supporting layer comprises at least two flexible layers which are directly connected, and each flexible layer comprises random copolymer containing ethylene structural units and unsaturated carboxylic ester structural units and optional polyolefin. The Shore hardness H of the single flexible layer is not higher than 90 Shore A, and the ratio of the Shore hardness H of the single flexible layer to the Shore hardness of the barrier layer is 0.5-0.8. The co-extrusion film can tolerate folding and twisting, has high stability and reliability, and is suitable for being used as a freezing and thawing bag or a biological feed liquid bag and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of co-extruded films, and in particular to a multi-layer co-extruded film, a method for preparing the co-extruded film, a bag, and the use of the multi-layer co-extruded film or the bag in preparing freeze-thaw bags or biological liquid bags. Background Art

[0002] Multilayer co-extruded film is a barrier material with at least three layers of materials, including at least one barrier layer (generally EVOH or PA), an outer layer and an inner layer. It can be used as disposable reaction bags, liquid storage bags, freeze-thaw bags, food packaging materials, etc.

[0003] When bags made of multi-layer co-extruded films are used as reaction bags, liquid storage bags, etc., they are often placed in cylindrical rigid containers. Under the combined action of the internal liquid pressure and the outer container, the bag body will tend to expand in a cylindrical shape. When preparing the bag body, in order to facilitate welding, a square bottom surface is usually adopted, resulting in a complete match between the bag body and the cylindrical peripheral container, especially the corner areas cannot fully adapt to the corners of the container, so there will be folding and twisting. In addition, the bottom corner areas, welding line areas and the installation areas of external devices are susceptible to greater pressure, which makes the above-mentioned areas more prone to breakage, leakage, etc., affecting the reliability of the bag body. Therefore, there is an urgent need to develop a multi-layer co-extruded film that can withstand folding and twisting. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a multi-layer co-extruded film and a preparation method thereof, a bag body and their applications, wherein the multi-layer co-extruded film can withstand folding and twisting and has high stability and reliability.

[0005] In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a multi-layer co-extruded film, which includes an outer surface layer, an inner surface layer and an intermediate layer, the intermediate layer includes a barrier layer and a flexible support layer, the flexible support layer includes at least two directly connected flexible layers, the flexible layer includes a random copolymer containing ethylene structural units and unsaturated carboxylic acid ester structural units and an optional polyolefin, and the Shore hardness H of a single flexible layer is not higher than 90 Shore A, and the hardness of the flexible layer is not higher than the hardness of the barrier layer.

[0006] In the present invention, “the Shore hardness H of a single flexible layer is not higher than 90 Shore A” means that the hardness of each flexible layer is not higher than 90 Shore A.

[0007] Compared with a whole flexible layer, a small amount of sliding can occur between the multiple flexible layers in the flexible support layer described in the present invention, which allows a single flexible layer to adopt a relatively high hardness setting (not higher than 90 Shore A). In addition, the copolymer of the flexible layer contains ester-grafted polyolefin segments, and the side chains are used to form a looser intermolecular arrangement structure, thereby making the flexible layer have better softness.

[0008] When the bag is used as a freeze-thaw bag, the liquid in the bag will freeze and expand at low temperatures, becoming a rigid structure, which is prone to generating greater internal stress. On the one hand, it squeezes the film layer outward, and on the other hand, it will also form ice crystals inside the bag, which is more likely to cause damage to the inside of the film. In the present invention, when the single-layer flexible layer has a high hardness (such as 80-90 Shore A), the multi-layer co-extruded film has good puncture resistance and is suitable for making freeze-thaw bags to avoid damage caused by ice crystals in the freeze-thaw bag. However, its hardness should generally not exceed that of the barrier layer.

[0009] At the same time, even if the multi-layer flexible layers prepared by multi-layer extrusion contain defects, the areas where the defects appear in different flexible layers are generally different. Therefore, during the folding and twisting process, the locations where damage is most likely to occur will be different, making the multi-layer co-extruded film less likely to be damaged in the face of folding and twisting, etc., which can improve the quality stability and reliability of the multi-layer co-extruded film.

[0010] The flexible support layer may be entirely located on one side of the barrier layer (for example, entirely on the inside or entirely on the outside), or may be partially located on the inside of the barrier layer and partially located on the outside of the barrier layer. In the case where the multi-layer co-extruded film includes multiple barrier layers, a flexible support layer may also be included between two adjacent groups of barrier layers.

[0011] In the present invention, the hardness can be obtained by testing with a Shore durometer, and the Shore hardness obtained is respectively Shore A or Shore D according to the overall hardness.

[0012] As a further improvement of the present invention, the multi-layer co-extruded film satisfies 45D≤H / n≤175D; wherein D is the total thickness of the flexible layer, in mm; H is the Shore hardness of a single flexible layer, in Shore A; and n is the total number of flexible layers. In this case, the folding and twisting resistance can be further improved.

[0013] It should be noted that, in this solution, for each flexible layer, the hardness of any flexible layer needs to meet the above requirements.

[0014] As a further improvement of the present invention, the total number n of flexible layers is 2 to 8;

[0015] The thickness of a single flexible layer is 10 to 70 μm, and the total thickness of the flexible layer is not greater than 350 μm;

[0016] The Shore hardness H of the single flexible layer is 30 to 90 Shore A.

[0017] In the present invention, the total number of flexible layers is calculated as the total number of flexible layers included in the portion of the multi-layer co-extruded film that serves as the flexible support layer (comprising at least two flexible layers). When the total number of flexible layers n is 2 to 8 and a single flexible layer meets these conditions, the mechanical properties of the flexible support layer can be improved, further enhancing the folding and twisting resistance of the multi-layer co-extruded film. If the hardness of the flexible support layer is too low, the overall strength of the multi-layer co-extruded film will be insufficient, which is not conducive to improving the folding and twisting resistance of the product.

[0018] The flexible layer can be composed of conventional materials in the art. As a further improvement of the present invention, the unsaturated carboxylate structural units include acrylic acid ester structural units and / or vinyl ester structural units. Preferably, the random copolymer containing vinyl structural units and unsaturated carboxylate structural units includes at least one of ethylene-vinyl acetate copolymer, ethylene-vinyl propionate copolymer, ethylene-vinyl butyrate copolymer, and ethylene-methacrylate copolymer. In this case, the puncture resistance of the bag during freeze-thaw cycles can be further improved.

[0019] In the present invention, "unsaturated carboxylate structural unit" refers to a structural unit in which an unsaturated carboxylate monomer is embedded in the main chain or side chain of a polymer after polymerization; "unsaturated carboxylate monomer" refers to a polymerizable compound having a carboxylate group and a carbon-carbon double bond.

[0020] As a further improvement of the present invention, in the flexible layer, the content of the unsaturated carboxylic acid ester structural units in the random copolymer is 9 to 28 mol%. In this case, the flexibility of the flexible layer can be increased, the puncture resistance of the bag during freeze-thaw cycles can be further improved, and the water and steam resistance of the bag can be improved.

[0021] As a further improvement of the present invention, the polyolefin comprises at least one of very low-density polyethylene, low-density polyethylene, and polypropylene. Adding the polyolefin to the flexible layer can improve the toughness and tensile strength of the film. The polyolefin content is generally 5-50% of the weight of the flexible layer. Excessive addition can lead to a certain decrease in folding and rubbing resistance and sealing performance.

[0022] As a further improvement of the present invention, the flexible supporting layer includes a first flexible supporting layer arranged between the barrier layer and the inner surface layer and / or a second flexible supporting layer arranged between the barrier layer and the outer surface layer. That is, the flexible supporting layer can be located between the barrier layer and the inner surface layer or between the barrier layer and the outer surface layer or simultaneously exist between the barrier layer and the inner surface layer and between the barrier layer and the outer surface layer.

[0023] A first flexible support layer is provided between the barrier layer and the inner surface layer, which reduces the impact of the barrier layer on the inner surface layer, thereby improving the water and steam resistance of the multilayer co-extruded film. This allows the multilayer co-extruded film to withstand steam sterilization when used in a biomaterial liquid bag, thereby increasing the lifespan of the biomaterial liquid bag. Furthermore, the first flexible support layer, being located between the barrier layer and the inner surface layer, allows the film on the outside of the barrier layer (which may include an outer surface layer and optional functional layers, such as a flexible support layer and / or an adhesive layer, etc.) to have a higher hardness (no higher than 60 Shore D) to improve the puncture resistance of the product, making it suitable for use in freeze-thaw bags and preventing damage to the bag during the freeze-thaw process that would affect its normal use. In a preferred embodiment, the Shore D hardness of the outer surface layer is 40-60 Shore D. In this case, the film on the outside of the barrier layer can have a higher hardness, allowing the film as a whole to have both appropriate softness and hardness, further improving the puncture resistance of the multilayer co-extruded film and making it more suitable for use in freeze-thaw bags.

[0024] The presence of the second flexible support layer can further enhance the softness and bending resistance of the overall structure, improve the bonding strength between the barrier layer and the outer layer, improve the twisting and folding resistance of the multi-layer co-extruded film, and further reduce the water and vapor penetration rate, thereby improving the water and steam resistance.

[0025] As a further improvement of the present invention, the hardness of the flexible supporting layer adjacent to the barrier layer is higher than the hardness of the flexible layer adjacent to the flexible layer on the side away from the barrier layer. The flexible supporting layer may be the first flexible supporting layer or the second flexible supporting layer. In this case, the flexible supporting layer and the barrier layer can be more closely bonded together, preventing delamination.

[0026] As a further improvement of the present invention, the hardness of the flexible layer adjacent to the inner surface layer in the first flexible supporting layer is greater than the hardness of the flexible layer adjacent to the first flexible layer on the side away from the inner surface layer. In this case, the barrier layer, the flexible supporting layer, and the inner surface layer can be more closely bonded together, preventing delamination.

[0027] Taking the first flexible supporting layer including three flexible layers as an example, in the first flexible supporting layer, the hardness of the flexible layer adjacent to the inner surface layer is greater than the hardness of the flexible layer adjacent to the flexible layer on the side away from the inner surface layer, and the hardness of the flexible layer adjacent to the barrier layer is higher than the hardness of the flexible layer adjacent to the flexible layer on the side away from the barrier layer, which means that the hardness of the middle flexible layer is lower than the hardness of the flexible layers on both sides of it.

[0028] As a further improvement of the present invention, in the flexible layer adjacent to the inner surface layer, the content of the unsaturated carboxylate structural units in the random copolymer is 9 to 22 mol%. When the content of the unsaturated carboxylate structural units is within this range, the radiation resistance and anti-curling properties can be further improved.

[0029] As a further improvement of the present invention, the multilayer co-extruded film further comprises a first adhesive layer positioned between the barrier layer and the flexible support layer. The first adhesive layer comprises a random copolymer containing ethylene structural units and unsaturated carboxylic acid ester structural units, and maleic anhydride grafted polyethylene (Tie), and the hardness of the first adhesive layer is between the hardness of the barrier layer and the hardness of the flexible support layer. Studies have found that a large difference in softness between layers can easily cause the layers of the co-extruded film to affect each other when bent or rubbed, potentially causing the film to break. By using a first adhesive layer and controlling the hardness of the first adhesive layer to be between the barrier layer and the flexible support layer, the problems caused by the large difference in softness between the layers can be reduced, making the co-extruded film less prone to breakage and more stable. At the same time, the barrier layer and the flexible support layer can be more closely bonded together to avoid delamination.

[0030] As a further improvement of the present invention, the multilayer co-extruded film further includes a second tie layer positioned between the barrier layer and the outer skin layer. The second tie layer comprises a random copolymer containing ethylene structural units and unsaturated carboxylic acid ester structural units, and maleic anhydride-grafted polyethylene. The second tie layer can improve adhesion between the barrier layer and the outer skin layer, thereby preventing delamination.

[0031] As a further improvement of the present invention, the multi-layer co-extruded film comprises at least two barrier layers and a third adhesive layer located between the two barrier layers. In this case, the barrier properties and puncture resistance of the multi-layer co-extruded film can be further improved.

[0032] During the research process, the inventors of the present invention found that when the multi-layer co-extruded film is faced with radiation sterilization and other situations, problems such as adhesion or curling may occur. As a further improvement of the present invention, in the first adhesive layer, the second adhesive layer or the third adhesive layer, the mass proportion of the maleic anhydride grafted polyethylene is independently 50 to 95%. Preferably, in the first adhesive layer, the second adhesive layer or the third adhesive layer, the random copolymer containing ethylene structural units and unsaturated carboxylic ester structural units is independently 30 to 60 Shore A. In this case, the tolerance to radiation can be improved and the anti-curling performance of the film can be improved.

[0033] As a further improvement of the present invention, the barrier layer is ethylene-vinyl alcohol copolymer (such as EVOH) and has a Shore hardness of not less than 70 Shore A, or the barrier layer is polyamide (PA) and has a Shore hardness of not less than 90 Shore A. In addition to employing multiple flexible layers, the addition of a barrier layer with greater hardness can enhance the barrier effect of the multi-layer co-extruded film while also improving its mechanical strength.

[0034] The inner surface layer may be made of conventional materials in the art, such as a copolymer of ethylene and unsaturated carboxylic acid ester monomers (such as EVA), and its thickness is not particularly limited, such as 10-90 μm.

[0035] The outer layer material can be a conventional material in the art, such as a copolymer of ethylene and unsaturated carboxylic acid ester monomers (such as EVA) and / or polyester (such as PET), etc. Its thickness is not particularly limited, for example, it can be 5-30 μm.

[0036] A second aspect of the present invention provides a method for preparing the multilayer co-extruded film as described above, comprising the following steps:

[0037] S1. Prepare raw materials according to mass ratio;

[0038] S2. Co-extruding the above raw materials to form a multilayer film precursor;

[0039] S3, cooling the multilayer film precursor to obtain a multilayer co-extruded film;

[0040] In step S2, the extrusion temperature of the barrier layer is 1.1 to 1.5 times its melting point, and the extrusion temperatures T1 and T2 of the flexible layer meet the following relationship: 5°C ≤ T2 - T1 ≤ 30°C. Processing the barrier layer at a higher temperature and the flexible layer at a relatively lower temperature not only maintains good uniformity and processability of the barrier layer, reducing defects, but also improves overall molding performance and enhances the processability of the outer layer. Controlling the die head temperature close to or slightly above the extrusion temperature of the barrier layer improves the reliability of the interlayer composite.

[0041] As a further improvement of the present invention, the multilayer co-extruded film further comprises a first adhesive layer positioned between the barrier layer and the flexible support layer. The extrusion temperature of the first adhesive layer is no lower than that of the flexible layer, and no higher than that of the barrier layer. Processing the first adhesive layer at a temperature slightly higher than that of the flexible layer allows the adhesive layer to better bond the flexible layer to the barrier layer, improving the integrity, uniformity, and flexibility of the overall film.

[0042] As a further improvement of the present invention, in steps S2 and S3, the multilayer film precursor is pulled at a speed of 6 to 20 m / min. In this case, controlling the pulling speed can improve the flexibility of the multilayer co-extruded film, achieve a more ordered arrangement of molecules in the film along the stretching direction, and enhance the film's mechanical properties along the thickness direction. Too low a pulling speed can lead to uneven film cooling, adversely affecting both the overall mechanical and barrier properties. Too high a pulling speed can result in excessive horizontal orientation of the film, leading to a decrease in overall film softness.

[0043] As a further improvement of the present invention, the multilayer co-extruded film comprises at least two barrier layers and a third adhesive layer located between the two barrier layers, and the extrusion temperature of the third adhesive layer is 0.8 to 0.95 times the extrusion temperature of the barrier layer.

[0044] A third aspect of the present invention provides a bag comprising the multi-layer co-extruded film described above.

[0045] A fourth aspect of the present invention provides use of the multi-layer co-extruded film or the bag as described above in the preparation of freeze-thaw bags or biological fluid bags.

[0046] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0047] The multi-layer co-extruded film provided by the present invention includes a flexible support layer containing multiple flexible layers, which can allow a single flexible layer to adopt a relatively high hardness setting (not higher than 90 Shore A), and the copolymer of the flexible layer adopts an ester-grafted polyolefin segment, and utilizes the branched chain to form a looser intermolecular arrangement structure, thereby making the flexible layer have better softness, which can improve the overall softness of the multi-layer co-extruded film, balance the overall hardness, and at the same time improve the overall puncture resistance and distortion resistance. It is suitable for preparing liquid storage bags, reaction bags, freeze-thaw bags, etc., and the bag body has high stability and is not easy to be damaged.

[0048] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Herein, unless otherwise specified, data ranges include endpoints. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the co-extruded film structure in Example 1-1 of the present invention. DETAILED DESCRIPTION

[0050] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0051] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0052] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0053] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0054] The present invention will be described in detail below with reference to specific embodiments. These embodiments are intended to help you understand the present invention but are not intended to limit it.

[0055] Unless otherwise specified, in the following examples, the Shore hardness of EVOH is 77 Shore D and the melting point is 195°C; the content, melting point and hardness of the vinyl ester structural unit in the ethylene-vinyl acetate copolymer EVA and the content, melting point and hardness of the propylene ester structural unit in the ethylene-propylene acetate copolymer EMA are also shown in the following table.

[0056]

[0057] The hardness in the following examples was obtained by directly extruding the corresponding materials at the corresponding extrusion temperatures and then measuring them using a durometer. If conditions permit, the hardness of the corresponding extruded layer can also be measured after separating or removing other layers from the co-extruded film using physical or chemical methods.

[0058] Example 1 and Comparative Example 1

[0059] This embodiment is used to illustrate a multi-layer co-extruded film and a preparation method thereof according to the present invention.

[0060] In Example 1, the multilayer co-extruded film includes an outer surface layer, an inner surface layer, and an intermediate layer. The intermediate layer includes a barrier layer and a flexible support layer disposed between the barrier layer and the inner surface layer. The flexible support layer includes at least two directly connected flexible layers. The multilayer co-extruded film further includes a first adhesive layer located between the barrier layer and the flexible support layer, and a second adhesive layer located between the barrier layer and the outer surface layer. The method for preparing the multilayer co-extruded film includes: preparing raw materials according to a mass ratio; co-extruding the raw materials to form a multilayer film precursor; and cooling the multilayer film precursor to obtain a multilayer co-extruded film. The moving speed of the multilayer film precursor under traction is 12 m / min. In the first adhesive layer, the second adhesive layer, or the third adhesive layer, the mass proportion of maleic anhydride grafted polyethylene is independently 80%. The material composition, thickness, and extrusion temperature of each layer in the multilayer co-extruded film are shown in Table 1.

[0061] Table 2 shows the results of the type of polymer in the flexible layer, the number of flexible layers, the thickness of a single flexible layer, and H / (n*D).

[0062] Different from Example 1, in Comparative Example 1, the flexible supporting layer contains only one flexible layer. The type of polymer in the flexible layer, the number of flexible layers, the thickness of the flexible layer, and the results of H / (n*D) are shown in Table 2.

[0063] The obtained multilayer co-extruded film was subjected to performance tests using the following test methods. The test results of mechanical properties are shown in Table 2, and the results of rubbing resistance, puncture resistance, and barrier properties are shown in Table 3.

[0064] (1) Mechanical properties

[0065] The mechanical properties of the multilayer co-extruded film include (1) maximum load, (2) tensile length, and (3) tensile strength; the mechanical properties are determined according to ISO 527, wherein the sample width is 5 mm, the tensile speed is 300 mm / min, and the gauge length is 30 mm.

[0066] (2) Rub resistance

[0067] Cut the sample into a 280mm x 200mm square and secure it to the rubbing tester using 10-12mm wide double-sided tape. After 700 or 3500 rubs, remove the film and cut a 200mm x 150mm section from the middle of the film and lay it flat on white A4 paper. Apply turpentine to the film sample several times with a brush and let it sit for 1 minute. Remove the film from the paper and count the number of leaks that penetrated through the sample onto the white paper. For each example, test 10 samples and determine the average number of leaks.

[0068] (3) Puncture resistance

[0069] The puncture force of the prepared sample was measured according to ASTM F1306 at a test speed of 100 mm / min. The average of three measurements was taken.

[0070] (4) Barrier properties

[0071] The oxygen permeation rate and carbon dioxide permeation rate were measured according to the method in ASTM D1434, with the ambient temperature set to room temperature and the pressure set to 0.1 mPa.

[0072] Since the number of leakage points before and after rubbing is basically consistent with the trend of barrier performance changes before and after rubbing, barrier performance verification is no longer performed on other examples and comparative examples except Example 1.

[0073] Table 1

[0074]

[0075] Note: “ / ” indicates not measured

[0076] Table 2

[0077]

[0078]

[0079] Table 3

[0080]

[0081]

[0082] Note: \ indicates not determined.

[0083] It should be noted that in Example 1, only the flexible layer is adjusted, and the other layers remain unchanged.

[0084] It can be seen from the above data that in the comparative example 1 group, since one flexible layer is used, the multi-layer co-extruded film prepared has a single flexible layer whose thickness is too large, which affects the tensile length and puncture resistance. It also causes a significant increase in the number of leakage points of the film after rubbing, that is, the rubbing resistance of the film is significantly reduced.

[0085] When other conditions are the same but the composition of the flexible layer is different, if the Shore hardness H of a single flexible layer is higher than 90 Shore A, although it may improve puncture resistance in some cases, the overall softness and rubbing resistance will be significantly reduced, and it will be easily damaged when folded and twisted. The barrier performance before rubbing is mainly related to the thickness and material, and has little to do with the layer arrangement. A small number of layers and a large H / (n*D) will slightly reduce the barrier properties before rubbing. When H / (n*D) is within the range of 45 to 175, the film's rubbing resistance, puncture resistance, barrier performance, and mechanical properties are all good, and can meet the needs of high-reliability applications such as freeze-thaw bags and biological fluid bags. When it is not within the range, the film is too soft or too hard, resulting in a decrease in rubbing resistance and barrier performance. Specifically, when the H / (n*D) value is greater than 175 in Comparative Example 1-1, Example 1-10, and Example 1-13, it is clearly seen that they have a higher average number of leakage points, indicating that their folding resistance is worse and the sealing performance is significantly lost after rubbing. In Examples 1-14 and 1-18, it can be seen that when the H / (n*D) value is less than 45, their puncture resistance and strength are also significantly reduced, resulting in a weakening of their rubbing resistance.

[0086] Example 2 group

[0087] The method described in Example 1-1 was used for operation, except that at least one of the total thickness D of the flexible layer and the arrangement of the flexible layer was different, as shown in Table 4.

[0088] The performance test results of the multi-layer co-extruded film are shown in Table 4.

[0089] Among them, continuous arrangement refers to AAABBB, represented by L, and alternating arrangement refers to ABABAB, represented by J; "2*50+2*90L" can be understood as two flexible layers with a thickness of 50μm and two flexible layers with a thickness of 90μm are arranged continuously from the outside to the inside; "3*30+3*50J" can be understood as three flexible layers with a thickness of 30μm and three flexible layers with a thickness of 50μm are arranged alternately from the outside to the inside.

[0090] Table 4

[0091]

[0092] The above data show that when the total thickness D of the flexible layer increases while the number of layers n remains constant, H / (n*D) decreases, which improves the maximum load, tensile strength, and puncture resistance of the film, but is detrimental to tensile properties and also leads to a slight decrease in rub resistance. When the individual layer thicknesses are too high or the total thickness is too large, as in Examples 2-6, although the tensile strength and puncture resistance of the film are slightly improved, it is detrimental to tensile properties and also leads to a slight decrease in rub resistance.

[0093] Examples 2-8 to 2-16 show that different thicknesses can be used in this solution, but the overall thickness of each flexible layer should be within the range of 10 to 70 μm. If the thickness of some layers is too low or some layers are too high (as in Examples 2-15 and 2-16), the strength of the system will be low and the rubbing resistance will be affected.

[0094] Example 3 group

[0095] The method described in Example 1-1 was followed, except that the flexible layer was made of a different material. The performance test results of the multi-layer co-extruded film are shown in Table 5.

[0096] Example 3-1: Among the 6 flexible layers, the material of the middle four flexible layers is EVA1, and the material of the flexible layers on both sides is EVA4.

[0097] Example 3-2: Among the 6 flexible layers, the material of the three flexible layers close to the inner surface layer is EVA1, and the material of the three flexible layers close to the outer surface layer is EVA4.

[0098] Example 3-3: From the inside to the outside, the flexible layers composed of EVA1 and EVA4 are arranged alternately.

[0099] Example 3-4: Among the 6 flexible layers, the material of the flexible layer close to the inner surface layer is EVA1, and the materials of the other 5 flexible layers are EVA4.

[0100] Example 3-5: Among the 6 flexible layers, the material of the three flexible layers close to the inner surface layer is EVA5, and the material of the three flexible layers close to the outer surface layer is EVA4.

[0101] Example 3-6: From the inside to the outside, the flexible layers composed of EVA1 and EVA4 are arranged alternately.

[0102] Example 3-7: Among the 6 flexible layers, the material of the three flexible layers close to the inner surface layer is EMA1, and the material of the three flexible layers close to the outer surface layer is EMA3.

[0103] Example 3-8: Among the 6 flexible layers, the material of the three flexible layers close to the inner surface layer is EMA2, and the material of the three flexible layers close to the outer surface layer is EMA3.

[0104] Table 5

[0105]

[0106] The above data demonstrates that flexible layers made with EVA1 and EVA4, when used alternately or in a soft-inner-hard-outer configuration, perform better overall than those made with only EVA1, EMA3+EMA1, or EMA3+EMA2. This demonstrates that a higher hardness can be used in the flexible layer near the inner surface, improving puncture resistance without significantly impacting softness. For example, Example 3-2 outperforms Example 1 in tensile strength, rubbing resistance, and puncture force, demonstrating that a design with a softer inner flexible layer and a harder outer flexible layer can significantly improve the overall performance of the membrane.

[0107] Example 4 Group

[0108] The operation was carried out according to the method described in Example 3-2, except that the material of the three flexible layers close to the outer surface layer also contained polyolefin. The specific composition (content by mass) and performance test results of the prepared multilayer co-extruded film are shown in Tables 6-1 and 6-2.

[0109] Table 6-1

[0110] Serial number composition Maximum load (N) Stretched length (mm) Tensile strength (MPa) Example 1-1 100% EVA1 19.0 423.3 23.3 Example 4-1 95%EVA1+5%VLDPE 19.4 426.0 23.3 Example 4-2 75% EVA1+25% VLDPE 20.3 419.7 25.0 Example 4-3 50% EVA1+50% VLDPE 20.0 411.0 24.2 Example 4-4 40% EVA1+60% VLDPE 17.5 381.5 21.0 Examples 4-5 95% EVA1+5% LDPE 19.1 420.3 23.8 Examples 4-6 75% EVA1+25% LDPE 20.6 411.4 25.0 Examples 4-7 50% EVA1+50% LDPE 20.2 393.8 23.7 Examples 4-8 40% EVA1+60% LDPE 18.0 352.1 20.8 Examples 4-9 75% EMA3 + 25% VLDPE 19.5 360.1 19.5 Examples 4-10 50% EMA3 + 50% VLDPE 19.2 363.9 19.0

[0111] Table 6-2

[0112]

[0113]

[0114] The above data demonstrates that as the polyolefin content increases, the overall performance of the film generally increases and then decreases. When the polyolefin content exceeds 50%, the overall performance of the film decreases. Compared to LDPE, the addition of VLDPE improves the film's tensile strength and rubbing resistance, but exhibits slightly lower puncture resistance. In both Examples 4-4 and 4-8, it can be seen that excessive addition of polyolefin can lead to a decrease in the softness and folding resistance of the flexible layer.

[0115] Example 5 Group

[0116] The method described in Example 1-1 was followed, except that the barrier layer was designed differently. The performance test results of the prepared multi-layer co-extruded film are shown in Table 7.

[0117] Example 5-1: PA is used instead of EVOH.

[0118] Example 5-2: The multi-layer co-extruded film includes two barrier layers (made of EVOH) and a bonding layer located between the two barrier layers.

[0119] Example 5-3: The operation is carried out in the same manner as Example 5-2, except that a "third adhesive layer + flexible layer + third adhesive layer" structure is provided between the two barrier layers, and the positions of the remaining five flexible layers remain unchanged.

[0120] Example 5-4: The operation is carried out in the manner of Example 5-3, except that a "third adhesive layer + 4 flexible layers + third adhesive layer" structure is provided between the two barrier layers, and a single flexible layer is provided between the barrier layer and the inner surface layer and between the barrier layer and the outer surface layer.

[0121] In the above solution, the thickness and number of the flexible layers remain unchanged from those in Example 1, that is, 6 flexible layers are provided, each with a thickness of 40 μm.

[0122] In this embodiment, the extrusion temperature of the third adhesive layer is 200° C. In general, the extrusion temperature of the third adhesive layer is controlled to be 0.8 to 0.95 times the extrusion temperature of the barrier layer.

[0123] Table 7

[0124]

[0125] From the above data, it can be seen that when the barrier layer is made of PA material, it is beneficial to improve the maximum load, tensile strength, puncture resistance and oxygen barrier performance of the film, while other properties are reduced.

[0126] When a multilayer co-extruded film includes two barrier layers, it can improve the film's maximum load, tensile strength, puncture resistance, and barrier properties. When only one adhesive layer is included in the two barrier layers, it is not conducive to improving the film's flex resistance. However, when a flexible layer is placed between them, the film's flex resistance can be maintained. When a continuous flexible layer is placed between the barrier layer and the inner surface layer, it can improve other properties besides tensile strength.

[0127] Example 6

[0128] The method described in Example 1-1 was followed, except that the relative positions of the layers in the multilayer co-extruded film were different. The performance test results of the prepared multilayer co-extruded film are shown in Table 8.

[0129] Example 6-1: From inside to outside, it is the inner surface layer, the adhesive layer, the barrier layer, the adhesive layer, the 6-layer flexible layer (ie, the second flexible supporting layer) and the outer surface layer.

[0130] Example 6-2: From inside to outside, it is the inner surface layer, three 40μm flexible layers (i.e., the first flexible supporting layer), the adhesive layer, the barrier layer, the adhesive layer, three 40μm flexible layers (i.e., the second flexible supporting layer) and the outer surface layer.

[0131] Example 6-3: From inside to outside, it is the inner surface layer, three 50μm flexible layers (i.e., the first flexible support layer), the adhesive layer, the barrier layer, the adhesive layer, three 30μm flexible layers (i.e., the second flexible support layer) and the outer surface layer.

[0132] Example 6-4: The operation is carried out in the same manner as Example 6-3, except that the material of the three flexible layers close to the inner surface is EVA1, and the material of the three flexible layers close to the outer surface is EVA4.

[0133] Table 8

[0134]

[0135] It can be seen from the above data that the flexible layers are all located outside the barrier layer, which is beneficial to improving the tensile length, but is not conducive to improving the rubbing resistance, puncture resistance and barrier performance.

[0136] When flexible layers with the same hardness are distributed on both sides of the barrier layer, it is not conducive to improving the overall performance of the film. However, when the hardness of the inner flexible layer is lower than that of the outer flexible layer, it is conducive to improving the overall performance of the film.

[0137] Example 7 Group

[0138] The operation was carried out according to the method described in Example 1-1, except that the extrusion temperature of each layer was adjusted as follows:

[0139] Example 7-1, based on Example 1-1, the extrusion temperature of the barrier layer was adjusted to 230°C.

[0140] Example 7-2, based on Example 1-1, the extrusion temperature of the barrier layer was adjusted to 200°C.

[0141] Example 7-3, based on Example 1-1, the extrusion temperature of the adhesive layer is adjusted to 195°C.

[0142] Example 7-4, based on Example 1-1, the extrusion temperature of the flexible support layer is adjusted to 210°C, and the temperature of the adhesive layer is adjusted to 215°C.

[0143] Example 7-5, based on Example 7-4, the extrusion temperature of the barrier layer was adjusted to 240°C.

[0144] Example 7-6, based on Example 7-4, the extrusion temperature of the barrier layer was adjusted to 250°C.

[0145] Example 7-7, based on Example 7-4, the temperature of the adhesive layer is adjusted to 210°C.

[0146] The experimental results in Example 7 are shown in Table 9.

[0147] Table 9

[0148]

[0149] In the above scheme, the flexible layer should generally have a lower extrusion temperature than the barrier layer. The difference between its extrusion temperature and the barrier layer's extrusion temperature is preferably within the range of 5-30°C. Excessively high temperature differences can lead to poor interlayer bonding, impacting strength and rubbing resistance. The adhesive layer temperature should generally be higher than that of the flexible layer, which helps improve the adhesive layer's bond between the barrier and flexible layers, thereby optimizing the overall mechanical properties of the film material.

[0150] It should be noted that, in this article, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the opposite order according to the functions involved. For example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0151] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-layer co-extruded film, characterized in that: The multilayer co-extruded film includes an outer layer, an inner layer and an intermediate layer, the intermediate layer includes a barrier layer and a flexible support layer, the flexible support layer includes at least two directly connected flexible layers, the flexible layer includes a random copolymer containing ethylene structural units and unsaturated carboxylic acid ester structural units and an optional polyolefin, and the Shore hardness H of the single flexible layer is not higher than 90 Shore A, and the Shore hardness of the flexible layer is not higher than the Shore hardness of the barrier layer.

2. The multi-layer co-extruded film according to claim 1, characterized in that The multi-layer co-extruded film satisfies 45D≤H / n≤175D; Where D is the total thickness of the flexible layer, in mm; H is the Shore hardness of the single flexible layer, in Shore A; n is the total number of flexible layers, in layers.

3. The multi-layer co-extruded film according to claim 2, characterized in that The total number of layers n of the flexible layer is 2 to 8; The thickness of a single flexible layer is 10 to 70 μm, and the total thickness of the flexible layer is not greater than 350 μm; The Shore hardness H of the single flexible layer is 30 to 90 Shore A.

4. The multi-layer co-extruded film according to claim 1, characterized in that The unsaturated carboxylic acid ester structural units include acrylic acid ester structural units and / or vinyl ester structural units.

5. The multi-layer co-extruded film according to claim 4, characterized in that The random copolymer containing ethylene structural units and unsaturated carboxylic acid ester structural units includes at least one of ethylene-vinyl acetate copolymer, ethylene-vinyl propionate copolymer, ethylene-vinyl butyrate copolymer and ethylene-methacrylate copolymer.

6. The multi-layer co-extruded film according to claim 1, characterized in that In the flexible layer, the content of the unsaturated carboxylic acid ester structural unit in the random copolymer is 9 to 28 mol%.

7. The multi-layer co-extruded film according to claim 1, characterized in that The polyolefin includes at least one of very low density polyethylene, low density polyethylene and polypropylene, and the mass of the polyolefin accounts for 5 to 50% of the mass of the flexible layer.

8. The multi-layer co-extruded film according to any one of claims 1 to 7, characterized in that: The flexible supporting layer includes a first flexible supporting layer disposed between the barrier layer and the inner surface layer and / or a second flexible supporting layer disposed between the barrier layer and the outer surface layer.

9. The multi-layer co-extruded film according to claim 8, characterized in that: In the first flexible supporting layer, the hardness of the flexible layer adjacent to the inner surface layer is greater than the hardness of the flexible layer adjacent to the flexible layer on a side away from the inner surface layer.

10. The multi-layer co-extruded film according to claim 8, characterized in that In the flexible layer adjacent to the inner surface layer, the content of the unsaturated carboxylic acid ester structural unit in the random copolymer is 9 to 22 mol%.

11. The multi-layer co-extruded film according to claim 1, characterized in that The multilayer co-extruded film further comprises a first bonding layer between the barrier layer and the flexible support layer, wherein the first bonding layer comprises a random copolymer containing ethylene structural units and unsaturated carboxylic acid ester structural units and maleic anhydride grafted polyethylene, and the hardness of the first bonding layer is between the hardness of the barrier layer and the hardness of the flexible support layer.

12. The multi-layer co-extruded film according to claim 1, characterized in that The multi-layer co-extruded film further comprises a second tie layer located between the barrier layer and the outer layer, wherein the second tie layer comprises a random copolymer containing ethylene structural units and unsaturated carboxylic acid ester structural units and maleic anhydride grafted polyethylene.

13. The multi-layer co-extruded film according to claim 1, characterized in that The multi-layer co-extruded film comprises at least two barrier layers and a third bonding layer located between the two barrier layers. The third bonding layer comprises a random copolymer containing ethylene structural units and unsaturated carboxylic acid ester structural units and maleic anhydride grafted polyethylene.

14. The multi-layer co-extruded film according to any one of claims 11 to 13, characterized in that In the first adhesive layer, the second adhesive layer or the third adhesive layer, the mass proportion of the maleic anhydride grafted polyethylene is independently 50 to 95%.

15. The multi-layer co-extruded film according to claim 14, characterized in that In the first tie layer, the second tie layer or the third tie layer, the random copolymer containing ethylene structural units and unsaturated carboxylic acid ester structural units has a Shore A hardness of 30 to 60 Shore A, respectively, independently.

16. The multi-layer co-extruded film according to claim 1, characterized in that The barrier layer is ethylene-vinyl alcohol copolymer, and the Shore hardness of the barrier layer is not less than 70 Shore A, or The barrier layer is made of polyamide, and the Shore hardness of the barrier layer is not less than 90 Shore A.

17. The method for preparing a multi-layer co-extruded film according to any one of claims 1 to 16, characterized in that: The steps include: S1. Prepare raw materials according to mass ratio; S2. Co-extruding the above raw materials to form a multilayer film precursor; S3, cooling the multilayer film precursor to obtain a multilayer co-extruded film; In step S2, the extrusion temperature of the barrier layer is 1.1 to 1.3 times the melting point of the barrier layer, and the extrusion temperature T1 of the flexible layer and the extrusion temperature T2 of the barrier layer have the following relationship: 5°C ≤ T2-T1 ≤ 30°C.

18. The method for preparing a multi-layer co-extruded film according to claim 17, wherein: The multi-layer co-extruded film further comprises a first bonding layer located between the barrier layer and the flexible support layer, wherein the extrusion temperature of the first bonding layer is not lower than the extrusion temperature of the flexible layer and is not higher than the extrusion temperature of the barrier layer.

19. The method for preparing a multi-layer co-extruded film according to claim 17, wherein: In steps S2 and S3, the multilayer film precursor moves at a speed of 6 to 20 m / min under traction.

20. The method for preparing a multi-layer co-extruded film according to claim 17, wherein: The multi-layer co-extruded film comprises at least two barrier layers and a third bonding layer located between the two barrier layers. The extrusion temperature of the third bonding layer is 0.8 to 0.95 times the extrusion temperature of the barrier layers.

21. A bag, characterized in that: The bag comprises the multilayer co-extruded film according to any one of claims 1 to 20.

22. Use of the multi-layer co-extruded film according to any one of claims 1 to 16 or the bag according to claim 21 in the preparation of freeze-thaw bags or biological liquid bags.

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