PA-EVOH multi-layer co-extrusion film, preparation method thereof and composite film

Abstract

The invention relates to the technical field of film packaging, in particular to a PA-EVOH multi-layer co-extrusion film, a preparation method thereof and a composite film. The PA-EVOH multi-layer co-extrusion film comprises a first functional surface layer, a first secondary surface layer, a core layer, a second secondary surface layer and a second functional surface layer, the thickness of the core layer is 13%-40% of the total thickness of the film layer, the melting point of the adopted PA resin is 215-225 DEG C, the melting point of the EVOH resin is 164-183 DEG C, and the ethylene content is 32-44 mol%. The PA-EVOH multi-layer co-extrusion film and the composite film thereof have high barrier property and thermal stability, and good transparency and apparent quality, and can be used for pasteurization or poaching sterilization food packaging. The invention further provides a preparation method which is used for manufacturing the PA-EVOH multi-layer co-extrusion film, the film layer structure and the film layer thickness proportion are optimized, and better physical comprehensive performance and processing performance are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of film packaging, and in particular to a PA-EVOH multi-layer co-extruded film and a preparation method thereof and a composite film. Background Art

[0002] In the field of food packaging, in order to ensure the freshness and safety of food, packaging films need to have good barrier properties and thermal stability.

[0003] Traditional polyolefin films such as polypropylene films and polyethylene films have good transparency and mechanical properties, but their barrier properties are poor, especially the barrier properties to oxygen and water vapor, and cannot effectively prevent food from oxidizing and spoiling and losing its original flavor. Barrier films made of metal materials such as aluminum foil have excellent barrier properties, but they also have defects such as high cost and environmental pollution.

[0004] In addition, existing packaging films also have deficiencies in thermal stability and are prone to shrinkage and deformation under high temperature conditions, affecting the appearance and sealing of the packaging.

[0005] On June 5, 2013, Chinese patent CN103129832B disclosed a moisture-proof, oxygen-proof and aroma-preserving packaging film with anti-fog function, including a co-extruded blown film with a moisture-proof layer and an oxygen-proof layer, which has aroma retention and low haze and can be used for packaging frozen meat, fresh meat and other foods. However, the moisture-proof, oxygen-proof and aroma-preserving packaging film with anti-fog function has not yet taken into account both low oxygen permeability and high thermal stability. It can be seen that how to develop a new type of packaging film material with both excellent barrier properties and thermal stability to meet the needs of food packaging is still a problem that technicians in this field need to solve. Summary of the invention

[0006] In order to solve the technical problem of how to develop a new type of packaging film material with excellent barrier properties and thermal stability, the present invention provides a PA-EVOH multilayer co-extruded film, the film layer structure includes a first functional surface layer, a first surface layer, a core layer, a second surface layer and a second functional surface layer arranged in sequence from top to bottom; Wherein, the thickness of the core layer is 13% to 40% of the total thickness of the film layer; Measured by weight percentage, the first functional surface layer and the second functional surface layer each include 90% to 97% of PA resin and 3% to 10% of functional masterbatch; Calculated by weight percentage, the first surface layer and the second surface layer are both 100% PA resin; By weight percentage, the core layer is 100% EVOH resin; The PA resin has a melting point of 215°C to 225°C; The EVOH resin has a melting point of 164°C to 183°C and an ethylene content of 32 mol% to 44 mol%; The functional masterbatch includes PA resin, anti-blocking agent, lubricant and other additives; The other auxiliary agents are any one or any combination of antioxidants, compatibilizers, chain extenders and antistatic agents.

[0007] In one embodiment, the ratio of PA resin, antiblocking agent, lubricant and other additives in the functional masterbatch is (90~97): (1~7): (1~6): (0.01~5) by weight percentage.

[0008] In one embodiment, the anti-blocking agent is any one or any combination of silicon dioxide, talc, calcium carbonate and glass beads; the lubricating agent is any one or any combination of PE wax, erucamide and oleamide.

[0009] In one embodiment, the total thickness of the PA-EVOH multi-layer co-extruded film is 10 μm to 30 μm; wherein the thickness of the first functional surface layer and the second functional surface layer are both 6% to 20% of the total thickness of the film layer; the thickness of the first surface layer and the second surface layer are both 5% to 25% of the total thickness of the film layer.

[0010] In one embodiment, the oxygen permeability of the PA-EVOH multilayer co-extruded film at 23°C and 50% RH is 0.5 cc / m 2 ·day ~ 5 cc / m 2 ·day.

[0011] In one embodiment, the PA-EVOH multi-layer co-extruded film is heated at (160±2)°C for 5 min, and its longitudinal heat shrinkage is less than 2.5%, and its transverse heat shrinkage is less than 2.0%.

[0012] The present invention also provides a preparation method for producing the PA-EVOH multilayer co-extruded film as described above, comprising the following steps: The raw materials of the first functional surface layer, the first surface layer, the core layer, the second surface layer and the second functional surface layer are respectively put into extruder 1, extruder 2, extruder 3, extruder 4 and extruder 5, and after melt extrusion, flow out through a T-die to form a molten thick sheet; Passing through a casting roller to form a thick casting sheet; Performing synchronous biaxial stretching on the cast thick sheet; The stretched film is subjected to heat setting treatment, cooled, and rolled up to obtain the PA-EVOH multi-layer co-extruded film.

[0013] In one embodiment, the melt extrusion temperature T 挤出 Set to T m <T 挤出 <T d ; Casting roller temperature T 流延辊 Set to 28℃<T 流延辊 <40℃; stretching temperature T 拉伸 Set to T g <T 拉伸 <T m ; Heat setting temperature T 定型 Set to T max <T 定型 <T m ; wherein the T m is the melting point of PA resin, the T d is the decomposition temperature of PA resin, the T g is the glass transition temperature of PA resin, the T max It is the maximum crystallization rate temperature of PA resin.

[0014] In one embodiment, when the cast thick sheet is subjected to synchronous biaxial stretching, the stretching ratio is (2.8-3.5)×(2.8-3.5).

[0015] The present invention also provides a composite film, comprising the PA-EVOH multi-layer co-extruded film as described above and any one or any combination of PP, PE and PET.

[0016] The PA-EVOH multi-layer co-extruded film provided by the present invention comprises a five-layer film structure, which is a first functional surface layer, a first surface layer, a core layer, a second surface layer and a second functional surface layer arranged in sequence from top to bottom. PA resin and EVOH resin are used as main raw materials, and the melting point of the PA resin is 215°C to 225°C, the melting point of the EVOH resin is 164°C to 183°C, and the ethylene content is 32 mol% to 44 mol%. The materials are highly compatible with each other, and the obtained film product has stable and balanced performance, high apparent quality, and both excellent barrier performance and thermal stability. The film is suitable for the packaging of jelly, sauce, milk powder and the like in a pasteurized manner that requires high gas barrier properties and aroma and taste preservation, and the packaging of pickled vegetables, seafood, meat products and the like in a boiling sterilization manner.

[0017] Specifically, the oxygen permeability of the PA-EVOH multilayer co-extruded film at 23°C and 50%RH is 0.5 cc / m 2 ·day ~ 5 cc / m 2·day, after being compounded with PE film and then boiled in water, it can still maintain high barrier properties and effectively prevent oxygen penetration; after being heated at (160 ± 2)℃ for 5 min, the longitudinal heat shrinkage rate of the film is less than 2.5%, and the transverse heat shrinkage rate is less than 2.0%, which has good thermal stability.

[0018] In addition, the PA-EVOH multi-layer co-extruded film also has lower haze, higher tensile strength, good film transparency, and higher load-bearing capacity and durability.

[0019] The preparation method for manufacturing PA-EVOH multilayer co-extruded film provided by the present invention specially designs the setting rules of process parameters of each processing step, including: melt extrusion temperature T 挤出 Set to T m <T 挤出 <T d , casting roll temperature T 流延辊 Set to 28℃<T 流延辊 <40℃, stretching temperature T 拉伸 Set to T g <T 拉伸 <T m , heat setting temperature T 定型 Set to T max <T 定型 <T m ; Among them, T m is the melting point of PA resin, T d is the decomposition temperature of PA resin, T g is the glass transition temperature of PA resin, T max It is the maximum crystallization rate temperature of PA resin.

[0020] Specifically, the casting roll temperature T 流延辊 Set to 28℃<T 流延辊 <40℃ is in accordance with 28℃<T 流延辊 <<T g The principle of polymer from T m The cooling rate from the above temperature to the temperature below determines the degree of crystallization, morphology, size, etc. of the polymer. 流延辊 <<T g When the cooling rate is fast, the relaxation process of macromolecular chain segment rearrangement lags behind the rate of temperature change. At this time, the polymer has low crystallinity, fine spherulites and loose volume, which is conducive to the subsequent stretching orientation process.

[0021] Furthermore, when the unstretched cast thick film is subjected to synchronous biaxial stretching, the stretching temperature should not be too high, because the slower crystallization rate during the stretching process is more conducive to stretching orientation, and it is also not easy to generate overly large crystals, which will affect the optical properties and other physical properties of the material; however, the stretching temperature should not be too low, because when stretching a polymer containing a crystalline phase, crystals will also be generated, and molecular orientation during the stretching process can also accelerate crystallization. If the stretching temperature is too low, it is not easy to improve the orientation uniformity. Therefore, the stretching temperature is set at T g <T 拉伸 <T m Better.

[0022] In order to improve mechanical properties, reduce thermal shrinkage of materials, and increase crystallization perfection, rapid crystallization is required during heat setting, so T is set. max <T 定型 <T m , and T 定型 >T 拉伸 For the best.

[0023] In summary, compared with the prior art, the PA-EVOH multilayer co-extruded film and its preparation method and composite film provided by the present invention have the following beneficial effects: (1) It has both excellent barrier properties and good thermal stability. Both the film and its composite film can be suitable for boiling. After boiling, they can still maintain excellent barrier properties and thermal stability. They are suitable for food packaging scenarios that use pasteurization, boiling sterilization, etc. (2) The film has good transparency, high tensile strength, high bearing capacity and durability; (3) Optimized film structure and film thickness ratio, with better comprehensive physical properties and processing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a schematic diagram of the film layer structure of the PA-EVOH multi-layer co-extruded film provided in Example 1 of the present invention.

[0026] Reference numerals: 10-first functional surface layer; 20-first surface layer; 30-core layer; 40-second surface layer; 50-second functional surface layer. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0029] Example 1 This embodiment provides a PA-EVOH multilayer co-extruded film, such as Figure 1 As shown, a film structure having a total of five layers, namely, a first functional surface layer 10, a first surface layer 20, a core layer 30, a second surface layer 40 and a second functional surface layer 50, is sequentially arranged from top to bottom, and the total thickness of the film layer is 15 μm, and is prepared according to the following steps: The raw materials of the first functional surface layer, the first surface layer, the core layer, the second surface layer and the second functional surface layer are respectively put into extruder 1, extruder 2, extruder 3, extruder 4 and extruder 5, and are melt-extruded at 235° C. to 260° C. and then flow out through a T-die to form a molten thick sheet; The casting roller forms a thick casting sheet, and the casting roller temperature is 30°C; The cast thick sheet is subjected to synchronous biaxial stretching at a stretching temperature of 160° C. and a stretching ratio of 3.0×3.0; The stretched film is heat-set at 180° C., cooled, and rolled up to obtain the PA-EVOH multi-layer co-extruded film.

[0030] In this embodiment, preferably, the raw materials of the first functional surface layer 10 and the second functional surface layer 50 are both 92% PA resin and 8% functional masterbatch in terms of weight percentage.

[0031] In this embodiment, preferably, the ratio of PA resin, anti-blocking agent, lubricant and other additives in the functional masterbatch is 91.8:6:2:0.2 by weight; wherein the anti-blocking agent is silicon dioxide, the lubricant is erucic acid amide, the other additives include antioxidants and antistatic agents, the antioxidant is obtained by mixing antioxidant 1010 and antioxidant 1070 in a ratio of 1:1 by weight, and the antistatic agent is graphene nanosheets; further, the ratio of the antioxidant to the antistatic agent in weight percentage is 1:1.

[0032] In this embodiment, preferably, the raw materials of the first surface layer 20 and the second surface layer 40 are both 100% PA resin in terms of weight percentage.

[0033] In this embodiment, preferably, the raw material of the core layer 30 is 100% EVOH resin by weight.

[0034] In this embodiment, preferably, the melting point of the PA resin is 220° C.; the melting point of the EVOH resin is 172° C., and in the ethylene-vinyl alcohol system, the ethylene content is 38 mol %.

[0035] In this embodiment, preferably, the thickness of the first functional surface layer 10 and the second functional surface layer 50 are both 20% of the total thickness of the film layer, that is, 3 μm; the thickness of the first surface layer 20 and the second surface layer 40 are both 22.5% of the total thickness of the film layer, that is, 3.375 μm; the thickness of the core layer 30 is 15% of the total thickness of the film layer, that is, 2.25 μm.

[0036] Example 2 This embodiment provides a PA-EVOH multilayer co-extruded film; wherein the total thickness of the film layer is 15 μm, the thickness of the first functional surface layer and the second functional surface layer are both 12.5% ​​of the total thickness of the film layer, i.e., 1.875 μm; the thickness of the first surface layer and the second surface layer are both 25% of the total thickness of the film layer, i.e., 3.75 μm; the thickness of the core layer is 25% of the total thickness of the film layer, i.e., 3.75 μm. The remaining raw materials, proportions, preparation steps and process parameters are consistent with those of Example 1.

[0037] Example 3 This embodiment provides a PA-EVOH multilayer co-extruded film; wherein the total thickness of the film layer is 15 μm, the thickness of the first functional surface layer and the second functional surface layer are both 11% of the total thickness of the film layer, i.e., 1.65 μm; the thickness of the first surface layer and the second surface layer are both 20% of the total thickness of the film layer, i.e., 3 μm; the thickness of the core layer is 38% of the total thickness of the film layer, i.e., 5.7 μm. The remaining raw materials, proportions, preparation steps and process parameters are consistent with those in Example 1.

[0038] Example 4 This embodiment provides a PA-EVOH multilayer co-extruded film, wherein when the film is formed into a cast thick sheet by a casting roller, the casting roller temperature is 40° C. The remaining raw materials, proportions, preparation steps and process parameters are the same as those in Example 1.

[0039] Example 5 This embodiment provides a PA-EVOH multilayer co-extruded film; wherein the melting point of the EVOH resin is 183° C., and in the ethylene-vinyl alcohol system, the ethylene content is 32 mol %. The remaining raw materials, proportions, preparation steps and process parameters are consistent with those in Example 1.

[0040] Comparative Example 1 This comparative example is a commercially available 15 μm BOPA film, which is a three-layer co-extruded biaxially stretched film consisting of a first surface layer, a core layer, and a second surface layer, wherein the first surface layer and the second surface layer are both PA layers with functional masterbatch added, and the core layer is 100% PA resin.

[0041] Comparative Example 2 This comparative example provides a PA-EVOH multilayer co-extruded film, which is different from Example 1 of the present invention in that: the thickness of the core layer is 50% of the total thickness of the film layer, that is, 7.5 μm, and the thickness of the first functional surface layer and the second functional surface layer are correspondingly adjusted to 10% of the total thickness of the film layer, that is, 1.5 μm, and the thickness of the first surface layer and the second surface layer are both 15% of the total thickness of the film layer, that is, 2.25 μm. The remaining raw materials, proportions, preparation steps and process parameters are consistent with those of Example 1.

[0042] Comparative Example 3 This comparative example provides a PA-EVOH multilayer co-extruded film, which is different from Example 1 of the present invention in that: the thickness of the core layer is 10% of the total thickness of the film layer, that is, 1.5 μm, and the thickness of the first functional surface layer and the second functional surface layer are correspondingly adjusted to 25% of the total thickness of the film layer, that is, 3.75 μm; the thickness of the first surface layer and the second surface layer are both 20% of the total thickness of the film layer, that is, 3 μm. The remaining raw materials, proportions, preparation steps and process parameters are consistent with those of Example 1.

[0043] Comparative Example 4 This comparative example provides a PA-EVOH multilayer co-extruded film, which is different from Example 1 of the present invention in that when the film is formed into a cast thick sheet by a casting roller, the casting roller temperature is 50° C. The remaining raw materials, proportions, preparation steps and process parameters are the same as those in Example 1.

[0044] Comparative Example 5 This comparative example provides a PA-EVOH multilayer co-extruded film, which is different from Example 1 of the present invention in that the melting point of the PA resin is 210° C. The remaining raw materials, proportions, preparation steps and process parameters are the same as those of Example 1.

[0045] Comparative Example 6 This comparative example provides a PA-EVOH multilayer co-extruded film, which is different from Example 1 of the present invention in that the PA resin has a melting point of 240°C, and is melt-extruded at 235°C to 275°C and flows out through a T-die to form a molten thick sheet. The remaining raw materials, proportions, preparation steps and process parameters are the same as those of Example 1.

[0046] Comparative Example 7 This comparative example provides a PA-EVOH multilayer coextruded film, which is different from Example 1 of the present invention in that the melting point of the EVOH resin is 188° C., and the ethylene content in the ethylene-vinyl alcohol system is 29 mol%. The remaining raw materials, proportions, preparation steps and process parameters are consistent with those in Example 1.

[0047] The PA-EVOH multilayer co-extruded films prepared in the above Examples 1 to 5 and Comparative Examples 2 to 7 and the BOPA film provided in Comparative Example 1 were subjected to performance tests, and the test results are summarized in Table 1.

[0048] The oxygen permeability of the film was tested according to ASTM F1927 standard, and the oxygen permeability of the pure PA-EVOH multilayer co-extruded film and the film composited with PE film and then boiled in water were tested respectively; The compounding steps are as follows: compounding PA-EVOH with PE film by glue, and after ripening, standby; The test method is as follows: use an octagonal mold to cut 3 parallel samples of the film, place them in a dryer filled with anhydrous calcium chloride or other desiccant to adjust the sample state for no less than 48 hours, then put each parallel sample into the test chamber, use the isobaric method-continuous flow technology, and detect the number of oxygen molecules passing through the sensor according to the current size; The test parameters are: test environment temperature is 23℃, humidity is 50%RH; The boiling conditions were: 85°C, 30 min.

[0049] The haze of the film is tested according to GB / T 2410-2008 “Determination of light transmittance and haze of transparent plastics”.

[0050] The film heat shrinkage rate is measured according to GB / T 12027-2004 "Test method for dimensional change rate of plastic film and sheeting upon heating", including the longitudinal heat shrinkage rate and the transverse heat shrinkage rate. The heating temperature was (160 ± 2)°C and the heating time was 5 min.

[0051] The tensile strength of the film is measured in accordance with GB / T 20218-2021 "Biaxially oriented polyamide (nylon) film", including longitudinal tensile strength and transverse tensile strength.

[0052] The film stretchability was evaluated during the stretching process.

[0053] Table 1 PA-EVOH multilayer co-extruded film and BOPA film performance test table

[0054] According to Table 1, the oxygen transmission rate of the PA-EVOH multilayer co-extruded films prepared in Examples 1 to 5 of the present invention at 23°C and 50%RH is 0.5 cc / m 2 ·day ~ 5 cc / m 2 ·day, with high barrier performance, the oxygen permeability of the film in Example 3 is only 0.54 cc / m 2 ·day, excellent barrier properties; after the simple film was laminated with the PE film and then boiled, the oxygen transmission rate of the composite film was slightly improved, but still within 5 cc / m 2 ·days, it still has high oxygen barrier performance; the oxygen permeability of the commercially available BOPA film provided in Comparative Example 1 under the same conditions is 29 cc / m 2 ·day, which is much higher than the oxygen permeability of the PA-EVOH multilayer co-extruded film and its composite film after boiling in water provided by the embodiment of the present invention. It can be seen that the PA-EVOH multilayer co-extruded film has excellent barrier properties, can effectively prevent oxygen penetration, and can still maintain its barrier properties well after compounding and boiling.

[0055] According to Table 1, the PA-EVOH multilayer co-extruded films prepared in Examples 1 to 5 of the present invention have low thermal shrinkage, with longitudinal thermal shrinkage below 2.5% and transverse thermal shrinkage below 2.0%, and have good thermal stability; the oxygen permeability of the single film of Comparative Example 2 is 0.51 cc / m 2 ·day, the barrier performance is excellent, but the thermal stability is poor, the longitudinal heat shrinkage rate reaches 3.0%, and the film appearance performance is also poor. During the stretching orientation, the film forming property is poor, the film is easy to break, and the film appearance quality is poor; Comparative Example 3 reduces the thickness of the EVOH core layer, and the thermal stability, film formability and appearance quality all meet the requirements. After heating, the longitudinal heat shrinkage rate and the transverse heat shrinkage rate are 1.3% and 1.0% respectively, which are equivalent to the embodiments of the present invention, but its oxygen permeability is higher than that of the embodiments of the present invention, and the oxygen permeability of the pure film is 3.98 cc / m 2 ·day, the barrier performance is obviously inferior to that of the embodiment of the present invention, and the oxygen transmission rate increases to 5.02 cc / m after composite boiling 2·day, the barrier performance decreased significantly. It can be seen that although increasing the thickness of the EVOH core layer can improve the barrier property of the film, it will further affect the apparent quality of the film product due to the impact on the film processing performance, resulting in it being unable to meet the comprehensive performance requirements of film packaging products.

[0056] Further analysis of the performance test data of Example 4 and Comparative Example 4 also verifies that, during the film processing, the setting of process parameters will have a significant impact on the apparent quality of the film. In Comparative Example 4, when the casting roller forms a thick film, the casting roller temperature is 50°C, which fails to meet T 流延辊 <<T g Under the conditions, the film product obtained has multiple film breakages during the stretching process, affecting the apparent quality of the film; in Example 4, the temperature of the casting roll is 40°C, and various performance parameters such as oxygen permeability and heat shrinkage are slightly better than those of Comparative Example 4, but there is a risk of film breakage during the stretching process, and the processing difficulty is higher than that of Example 1.

[0057] In Comparative Examples 5 and 6, the melting points of PA resin are 210°C and 240°C, respectively, and the apparent performance of the film products obtained in these two examples is poor; the film surface of Comparative Example 5 is poor, which is because the viscosity of EVOH resin is relatively large at this temperature, which is incompatible with the viscosity of PA resin, resulting in poor film surface; the film thickness and performance of Comparative Example 6 are uneven, which is because with the increase of temperature and the shearing effect of the screw, the melt fluidity will improve, and the temperature is high, the flow rate of EVOH resin is fast, and after merging with PA resin in the distribution area, the flow rates of the two are inconsistent, resulting in uneven product thickness, and the barrier property of the area with smaller EVOH resin thickness is poor, which leads to uneven product performance.

[0058] In Comparative Example 7, the ethylene content is 29 mol%, and the obtained film product has high barrier properties. The oxygen permeability is 1.4 cc / m at 23°C and 50% RH. 2 ·day, but its processing performance is poor, the film is easy to break during the stretching process, the film appearance quality is poor, and it cannot meet the film packaging requirements.

[0059] In addition, according to Table 1, the PA-EVOH multilayer co-extruded films prepared in Examples 1 to 5 of the present invention also have a low film haze, which is all below 4.8, ensuring high barrier properties of the film while also having good transparency; at the same time, they also have high tensile strength, with both longitudinal and transverse tensile strengths being above 190 MPa, and the film has high load-bearing capacity and durability.

[0060] Although this article uses more such as first functional surface layer, first surface layer, core layer, second surface layer, second functional surface layer, functional masterbatch, multi-layer coextrusion, melt extrusion, melt thick sheet, cast thick sheet, synchronous biaxial stretching, heat setting treatment, T 挤出 , T流延辊 , T 拉伸 , T 定型 , oxygen permeability, oxygen permeability, heat shrinkage, thermal stability, barrier properties, transparency, film haze, load-bearing capacity, durability, simple film, composite film, physical comprehensive properties and film comprehensive properties, but does not exclude the possibility of using other terms. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitations is contrary to the spirit of the present invention.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A PA-EVOH multilayer co-extruded film, characterized in that: The membrane layer structure includes a first functional surface layer, a first surface layer, a core layer, a second surface layer and a second functional surface layer arranged in sequence from top to bottom; Wherein, the thickness of the core layer is 13% to 40% of the total thickness of the film layer; In terms of weight percentage, the first functional surface layer and the second functional surface layer each comprise 90% to 97% of PA resin and 3% to 10% of functional masterbatch; Calculated by weight percentage, the first surface layer and the second surface layer are both 100% PA resin; By weight percentage, the core layer is 100% EVOH resin; The PA resin has a melting point of 215°C to 225°C; The EVOH resin has a melting point of 164°C to 183°C and an ethylene content of 32 mol% to 44 mol%; The functional masterbatch includes PA resin, anti-blocking agent, lubricant and other additives; The other auxiliary agents are any one or any combination of antioxidants, compatibilizers, chain extenders and antistatic agents.

2. The PA-EVOH multilayer coextruded film according to claim 1, characterized in that: Calculated by weight percentage, the ratio of PA resin, anti-blocking agent, lubricant and other additives in the functional masterbatch is (90~97): (1~7): (1~6): (0.01~5).

3. The PA-EVOH multilayer co-extruded film according to claim 1, characterized in that: The opening agent is any one or any combination of silicon dioxide, talcum powder, calcium carbonate and glass microspheres; The lubricant is any one or any combination of PE wax, erucamide and oleamide.

4. The PA-EVOH multilayer coextruded film according to claim 1, characterized in that: The total thickness of the PA-EVOH multi-layer co-extruded film layer is 10 μm to 30 μm; Wherein, the thickness of the first functional surface layer and the second functional surface layer are both 6% to 20% of the total thickness of the film layer; The thickness of the first surface layer and the second surface layer is 5% to 25% of the total thickness of the film layer.

5. The PA-EVOH multilayer coextruded film according to claim 1, characterized in that: The oxygen transmission rate of the PA-EVOH multilayer coextruded film at 23°C and 50%RH is 0.5 cc / m 2 ·day ~ 5 cc / m 2 ·day.

6. The PA-EVOH multilayer coextruded film according to claim 1, characterized in that: The PA-EVOH multilayer co-extruded film is heated at (160±2)°C for 5 min, and its longitudinal heat shrinkage is less than 2.5%, and its transverse heat shrinkage is less than 2.0%.

7. A preparation method for producing the PA-EVOH multilayer co-extruded film according to any one of claims 1 to 6, characterized in that: The following steps are involved: The raw materials of the first functional surface layer, the first surface layer, the core layer, the second surface layer and the second functional surface layer are respectively put into extruder 1, extruder 2, extruder 3, extruder 4 and extruder 5, and after melt extrusion, flow out through a T-die to form a molten thick sheet; Passing through a casting roller to form a thick casting sheet; Performing synchronous biaxial stretching on the cast thick sheet; The stretched film is subjected to heat setting treatment, cooled, and rolled up to obtain the PA-EVOH multi-layer co-extruded film.

8. The preparation method according to claim 7, characterized in that: Melt extrusion temperature T 挤出 Set to T m <T 挤出 <T d ; Casting roll temperature T 流延辊 Set to 28℃<T 流延辊 <40℃; Stretching temperature T 拉伸 Set to T g <T 拉伸 <T m ; Heat setting temperature T 定型 Set to T max <T 定型 <T m ; Among them, the T m is the melting point of PA resin, the T d is the decomposition temperature of PA resin, the T g is the glass transition temperature of PA resin, the T max It is the maximum crystallization rate temperature of PA resin.

9. The preparation method according to claim 7, characterized in that: When the cast thick sheet is subjected to synchronous biaxial stretching, the stretching ratio is (2.8-3.5) × (2.8-3.5).

10. A composite film, characterized in that: It comprises the PA-EVOH multilayer co-extruded film as described in any one of claims 1 to 6 and any one or several of PP, PE and PET.

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