A puncture-resistant composite film

Abstract

The application discloses a kind of puncture-resistant composite films, belong to composite film technical field, PA11, metallocene polyethylene, composite powder, nano aluminum powder and silane coupling agent KH560 are mixed after extrusion with double screw extruder, granulation, obtain intermediate layer masterbatch;Modified PA6 and PA6 are mixed after extrusion, granulation, obtain upper layer masterbatch;With PA11 as lower layer masterbatch, upper layer masterbatch, intermediate layer masterbatch and lower layer masterbatch are extruded into cast sheet by three-layer structure die at 220-230 DEG C;After cast sheet is treated by humidification, it is prepared into puncture-resistant composite film including upper layer, intermediate layer and lower layer by the way of two-way stretching;-NH- in PA11 can form hydrogen bond with hydroxyl in the surface modified cellulose of composite powder, play the role of physical crosslinking, help to improve the strength and puncture resistance of intermediate layer;Nano aluminum powder and metallocene polyethylene also help to improve the puncture resistance of composite film.

Description

Technical Field

[0001] This invention belongs to the field of composite film technology, and specifically relates to a puncture-resistant composite film. Background Technology

[0002] Packaging film mainly refers to films used for packaging goods, including polyethylene film, biaxially oriented polyester film, biaxially oriented polypropylene film, and cast polypropylene film, etc.

[0003] Packaging films need sufficient mechanical strength and durability to withstand the pressure and impact during packaging and transportation. In the food packaging sector, packaging films must also ensure food safety, preventing the migration of harmful substances and ensuring that the quality, taste, and nutritional value of the food are not affected. Food packaging films should also have good barrier properties against gases, moisture, and light to maintain the freshness and quality of the food, and possess good sealing properties to effectively prevent contact between the food and outside air, avoiding oxidation, moisture intrusion, and contamination. These performance requirements aim to protect food safety and quality, providing excellent packaging protection and a superior user experience.

[0004] Chinese patent announcement CN106739340B discloses a high-barrier packaging film that does not roll up after high-temperature sterilization. It provides barrier properties through an EVOH layer and puncture resistance through a PA layer. PA food packaging film has good oil resistance and high-temperature retortability, making it suitable for packaging foods containing large amounts of oil. However, its puncture resistance is still poor for foods with hard shells. Summary of the Invention

[0005] The purpose of this invention is to provide a puncture-resistant composite film to solve the problem of poor puncture resistance in existing PA food packaging films.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A puncture-resistant composite film includes an upper layer, an intermediate layer, and a lower layer, wherein the lower layer is for contact with food, the intermediate layer is a puncture-resistant layer, and the upper layer is for printing information.

[0008] The puncture-resistant composite film is prepared by the following steps:

[0009] Step 1: At 20-30℃, microcrystalline cellulose and a 60-65% sulfuric acid solution are added to a reaction vessel and stirred. The mixture is then ultrasonically dispersed for 20-30 minutes, and stirred for another 50-60 minutes at 45-50℃. The mixture is then diluted with deionized water at 0-4℃ to obtain a diluted solution. The pH of the diluted solution is adjusted to 8 with sodium hydroxide solution, and then centrifuged at 10000-12000 r / min for 5-10 minutes. The precipitate is washed 3-5 times with deionized water and dispersed in deionized water to obtain a dispersion with a solid content of 10 wt%. The dispersion is then transferred to a 1 kDa dialysis bag and dialyzed in deionized water for 4-6 days. After completing the above dialysis purification, the mixture is freeze-dried to obtain modified cellulose powder.

[0010] Step 2: Mix silane coupling agent and deionized water at a mass ratio of 1:99, adjust the pH to 4-5 with 0.05 mol / L oxalic acid solution to obtain silane coupling agent solution; add silane coupling agent solution, acetone and silicon nitride whiskers to reaction vessel and stir to mix, then ultrasonically disperse for 10-20 min, keep warm at 30-40℃ for 18-24 h, filter out the material, wash with anhydrous ethanol to remove acetone and then vacuum dry to obtain modified silicon nitride whiskers;

[0011] Step 3: Dissolve the modified cellulose powder in a 5% acetic acid solution, then add the modified silicon nitride whiskers, ultrasonically disperse at 30-40℃ for 1.5-2 hours, freeze dry to obtain the composite powder;

[0012] Step 4: Add PA11, metallocene polyethylene, composite powder, nano aluminum powder and silane coupling agent KH560 to a high-speed mixer and mix for 20-30 minutes at 60-65℃. Then transfer to a twin-screw extruder and extrude at 220-230℃ to granulate and obtain intermediate layer masterbatch.

[0013] Step 5: Add the upper layer masterbatch, middle layer masterbatch and lower layer masterbatch into the upper layer extruder, middle layer extruder and lower layer extruder respectively, and extrude them into cast sheets through a three-layer die at 220-230℃.

[0014] Step 6: Immerse the casting in deionized water at a temperature of 50-55℃ for 60±5s to complete the moisture conditioning treatment of the casting. Then, prepare the moisture-conditioned casting into a puncture-resistant composite film consisting of an upper layer, a middle layer and a lower layer by biaxial stretching.

[0015] Furthermore, in step one, the ratio of microcrystalline cellulose, sulfuric acid solution, and deionized water is 1g:17-18g:170-180mL.

[0016] Furthermore, in step two, the ratio of silane coupling agent solution, acetone, and silicon nitride whiskers is 1 mL: 69 mL: 1.5-2 g.

[0017] Furthermore, in step two, the silane coupling agent is either silane coupling agent KH550 or silane coupling agent KH560.

[0018] Furthermore, in step three, the ratio of modified cellulose powder, acetic acid solution, and modified silicon nitride whiskers is 1g:100mL:0.6-0.8g.

[0019] Furthermore, in step four, the ratio of PA11, metallocene polyethylene, modified cellulose powder, nano aluminum powder, and silane coupling agent KH560 is 50g: 25-30g: 2-3g: 1.5-2g: 35-50mg.

[0020] Furthermore, the thickness ratio of the upper layer, middle layer, and lower layer is 5:6:4.

[0021] Furthermore, sulfonated polyether ether ketone is prepared via the following steps:

[0022] Step S1: Add polyether ether ketone and 98% concentrated sulfuric acid to a polytetrafluoroethylene reactor. Stir at 60-65℃ for 50-60 minutes. Cool the reaction solution to 0℃ using the cooling device of the polytetrafluoroethylene reactor and dilute it with deionized water at 0-4℃ to precipitate the solid in the reactants. After the mass of the precipitated solid is constant, collect the precipitated solid. Wash the solid with deionized water until the pH of the final washing solution is neutral. Then, vacuum dry the solid at 45-60℃ to obtain sulfonated polyether ether ketone.

[0023] Step S2: Grind sulfonated polyether ether ketone and PA6 into powder and add them to the reaction vessel. Then add N,N-dimethylformamide to the reaction vessel and stir for 15-20 min. Add dicyclohexylcarbodiimide particles and reflux at 100℃ for 25-30 h. Filter to remove the dicyclohexylcarbodiimide particles to obtain the reaction solution. Filter the reaction solution at 70-80℃. Wash the filter cake with anhydrous ethanol 3-5 times, then vacuum dry at 45-60℃ and pulverize to obtain modified PA6. Mix the modified PA6 and 5 times the mass of PA6 at 60-65℃ for 20-30 min, then transfer to a twin-screw extruder and extrude at 220-230℃ to granulate and obtain the upper masterbatch.

[0024] Furthermore, the ratio of polyetheretherketone to concentrated sulfuric acid is 1g:46g.

[0025] Furthermore, the ratio of sulfonated polyether ether ketone, PA6, N,N-dimethylformamide and dicyclohexylcarbodiimide particles is 3g:3g:200mL:50g.

[0026] Furthermore, the lower layer masterbatch is PA11.

[0027] The beneficial effects of this invention are:

[0028] The puncture-resistant composite film of the present invention comprises an upper layer, a middle layer and a lower layer, wherein the lower layer is made of PA11 and is used for contact with food. PA11 has good dimensional stability, low water absorption, good oil resistance and is easy to process. The puncture strength of the composite film is much greater than that of ordinary PA film.

[0029] The intermediate layer is a puncture-resistant layer. First, modified cellulose powder is prepared by acid hydrolysis of microcrystalline cellulose. This modified cellulose powder is dissolved in acetic acid solution and then freeze-dried again, allowing it to coat the surface of modified silicon nitride whiskers. The silicon nitride whiskers, after treatment with a silane coupling agent, exhibit good dispersibility and interfacial affinity, thereby increasing the adhesion between them and the surface-attached modified cellulose powder. This results in a rough-surfaced composite powder, whose rough surface increases the interfacial area, acting as an anchoring agent and increasing the mechanical strength and stability of the intermediate layer. PA11 contains amide groups, where the -NH- groups can form hydrogen bonds with the hydroxyl groups in the modified cellulose on the composite powder surface, acting as a physical cross-linking agent. This further restricts the movement of molecular chains in PA11, contributing to improved strength and puncture resistance of the intermediate layer. Nano-aluminum powder is also added to the intermediate layer, helping to synergistically reduce oxygen and water vapor permeability and further improve puncture resistance. Metallocene polyethylene, with its long-branched structure, helps increase the toughness of the intermediate layer after composite formation, contributing to improved strength and puncture resistance of the composite film.

[0030] The main material of the upper layer is PA6, which helps to ensure the printability of the film surface. After polyetheretherketone is treated with concentrated sulfuric acid azeotropically, sulfonic acid groups are grafted onto the benzene ring. Under the dehydration of dicyclohexylcarbodiimide particles, the sulfonic acid groups on the sulfonated polyetheretherketone and the imine bonds in PA6 are dehydrated and grafted to obtain modified PA6, which helps to increase the compatibility between polyetheretherketone and PA6. The composite of sulfonated polyetheretherketone helps to increase the retort resistance and dimensional stability of the upper layer. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] This embodiment provides a puncture-resistant composite film, including the following implementation steps:

[0034] Step 1: Add 2 kg of polyether ether ketone and 92 kg of 98% concentrated sulfuric acid to a polytetrafluoroethylene (PTFE) reactor. Stir at 60°C for 50 min. Cool the reaction solution to 0°C using the PTFE reactor's cooling device and dilute with 0°C deionized water to precipitate the solids in the reactants. Once the mass of the precipitated solids is constant, collect the precipitated solids. Wash the solids with deionized water until the pH of the final washing solution is neutral. Then, vacuum dry the solids at 45°C to obtain sulfonated polyether ether ketones.

[0035] Step 2: Grind 1.5 kg of sulfonated polyether ether ketone and 1.5 kg of PA6 into powder and add them to the reaction vessel. Then add 100 L of N,N-dimethylformamide to the reaction vessel and stir for 15 min. Add 25 kg of dicyclohexylcarbodiimide particles and reflux at 100 °C for 25 h. Filter to remove the dicyclohexylcarbodiimide particles to obtain the reaction solution. Filter the reaction solution at 70 °C. Wash the filter cake three times with anhydrous ethanol, then vacuum dry at 45 °C and pulverize to obtain modified PA6. Mix 2 kg of modified PA6 and 10 kg of PA6 at 60 °C for 20 min, then transfer to a twin-screw extruder and extrude at 220 °C to granulate and obtain the upper masterbatch.

[0036] Step 3: At 20℃, 100 kg of microcrystalline cellulose and 1700 kg of 60% sulfuric acid solution were added to a reaction vessel and stirred. The mixture was then ultrasonically dispersed for 20 min, and stirred for another 50 min at 45℃. The mixture was then diluted with 17000 L of deionized water at 0℃ to obtain a diluted solution. The pH of the diluted solution was adjusted to 8 with sodium hydroxide solution, and then centrifuged at 10000 r / min for 5 min. The precipitate was washed three times with deionized water and dispersed in deionized water to obtain a dispersion with a solid content of 10 wt%. The dispersion was then transferred to a 1 kDa dialysis bag and dialyzed in deionized water for 4 days. Finally, the mixture was freeze-dried to obtain modified cellulose powder.

[0037] Step 4: Mix silane coupling agent KH550 and deionized water at a mass ratio of 1:99, adjust the pH to 4 with 0.05 mol / L oxalic acid solution to obtain a silane coupling agent solution; add 10 kg of silane coupling agent solution, 690 L of acetone and 15 kg of silicon nitride whiskers to a reaction vessel and stir to mix, then ultrasonically disperse for 10 min, keep warm at 30℃ for 18 h, filter out the material, wash with anhydrous ethanol to remove acetone and vacuum dry to obtain modified silicon nitride whiskers; dissolve 10 kg of modified cellulose powder in 1000 L of 5% acetic acid solution, then add 6 kg of modified silicon nitride whiskers, ultrasonically disperse at 30℃ for 1.5 h, freeze dry to obtain composite powder.

[0038] Step 5: Add 50kg PA11, 25kg metallocene polyethylene, 2kg composite powder, 1.5kg nano aluminum powder and 35g silane coupling agent KH560 to a high-speed mixer and mix at 60℃ for 20min. Then transfer to a twin-screw extruder and extrude at 220℃ to granulate and obtain intermediate layer masterbatch.

[0039] Step Six: Using PA11 as the lower masterbatch, the upper masterbatch, middle masterbatch, and lower masterbatch are added to the upper extruder, middle extruder, and lower extruder, respectively, and extruded into a cast sheet through a three-layer die at 220°C. The cast sheet is then immersed in deionized water at 50°C for 60±5s to complete the moisture conditioning treatment. The moisture-conditioned cast sheet is then biaxially stretched at 230°C to prepare a puncture-resistant composite film consisting of an upper layer, a middle layer, and a lower layer.

[0040] Example 2

[0041] This embodiment provides a puncture-resistant composite film, including the following implementation steps:

[0042] Step 1: Add 2 kg of polyether ether ketone and 92 kg of 98% concentrated sulfuric acid to a polytetrafluoroethylene (PTFE) reactor. Stir at 62°C for 55 min. Cool the reaction solution to 0°C using the PTFE reactor's cooling device and dilute with 2°C deionized water to precipitate the solids in the reactants. Once the mass of the precipitated solids is constant, collect the precipitated solids. Wash the solids with deionized water until the pH of the final washing solution is neutral. Then, vacuum dry the solids at 55°C to obtain sulfonated polyether ether ketones.

[0043] Step 2: Grind 1.5 kg of sulfonated polyether ether ketone and 1.5 kg of PA6 into powder and add them to the reactor. Then add 100 L of N,N-dimethylformamide to the reactor and stir for 18 min. Add 25 kg of dicyclohexylcarbodiimide particles and reflux at 100 °C for 28 h. Filter to remove the dicyclohexylcarbodiimide particles to obtain the reaction solution. Filter the reaction solution at 75 °C. Wash the filter cake four times with anhydrous ethanol, then vacuum dry at 55 °C and pulverize to obtain modified PA6. Mix 2 kg of modified PA6 and 10 kg of PA6 at 62 °C for 25 min, then transfer to a twin-screw extruder and extrude at 225 °C to granulate and obtain the upper masterbatch.

[0044] Step 3: At 25℃, 100 kg of microcrystalline cellulose and 1750 kg of 62% sulfuric acid solution were added to a reaction vessel and stirred. The mixture was then ultrasonically dispersed for 25 min, and stirred for another 55 min at 48℃. The mixture was then diluted with 17500 L of deionized water at 2℃ to obtain a diluted solution. The pH of the diluted solution was adjusted to 8 with sodium hydroxide solution, and then centrifuged at 11000 r / min for 8 min. The precipitate was washed four times with deionized water and dispersed in deionized water to obtain a dispersion with a solid content of 10 wt%. The dispersion was then transferred to a 1 kDa dialysis bag and dialyzed in deionized water for 5 days. Finally, the mixture was freeze-dried to obtain modified cellulose powder.

[0045] Step 4: Mix silane coupling agent KH560 and deionized water at a mass ratio of 1:99, adjust the pH to 4.5 with 0.05 mol / L oxalic acid solution to obtain a silane coupling agent solution; add 10 kg of silane coupling agent solution, 690 L of acetone and 18 kg of silicon nitride whiskers to a reaction vessel and stir to mix, then ultrasonically disperse for 15 min, keep warm at 35℃ for 21 h, filter out the material, wash with anhydrous ethanol to remove acetone and vacuum dry to obtain modified silicon nitride whiskers; dissolve 10 kg of modified cellulose powder in 1000 L of 5% acetic acid solution, then add 7 kg of modified silicon nitride whiskers, ultrasonically disperse at 35℃ for 1.8 h, freeze dry to obtain composite powder.

[0046] Step 5: Add 50kg PA11, 28kg metallocene polyethylene, 2.5kg composite powder, 1.8kg nano aluminum powder and 40g silane coupling agent KH560 to a high-speed mixer and mix at 62℃ for 25min. Then transfer to a twin-screw extruder and extrude at 225℃ to granulate and obtain intermediate layer masterbatch.

[0047] Step Six: Using PA11 as the lower masterbatch, the upper masterbatch, middle masterbatch, and lower masterbatch are added to the upper extruder, middle extruder, and lower extruder, respectively, and extruded into a cast sheet through a three-layer die at 225°C. The cast sheet is then immersed in deionized water at 52°C for 60±5s to complete the moisture conditioning treatment. The moisture-conditioned cast sheet is then biaxially stretched at 230°C to prepare a puncture-resistant composite film consisting of an upper layer, a middle layer, and a lower layer.

[0048] Example 3

[0049] This embodiment provides a puncture-resistant composite film, including the following implementation steps:

[0050] Step 1: Add 2 kg of polyether ether ketone and 92 kg of 98% concentrated sulfuric acid to a polytetrafluoroethylene (PTFE) reactor. Stir at 65°C for 60 min. Cool the reaction solution to 0°C using the PTFE reactor's cooling device and dilute with 4°C deionized water to precipitate the solids from the reactants. Once the mass of the precipitated solids is constant, collect the precipitated solids. Wash the solids with deionized water until the pH of the final washing solution is neutral. Then, vacuum dry the solids at 60°C to obtain sulfonated polyether ether ketones.

[0051] Step 2: Grind 1.5 kg of sulfonated polyether ether ketone and 1.5 kg of PA6 into powder and add them to the reactor. Then add 100 L of N,N-dimethylformamide to the reactor and stir for 20 min. Add 25 kg of dicyclohexylcarbodiimide particles and reflux at 100 °C for 30 h. Filter to remove the dicyclohexylcarbodiimide particles to obtain the reaction solution. Filter the reaction solution at 80 °C. Wash the filter cake 5 times with anhydrous ethanol, then vacuum dry at 60 °C and pulverize to obtain modified PA6. Mix 2 kg of modified PA6 and 10 kg of PA6 at 65 °C for 30 min, then transfer to a twin-screw extruder and extrude at 230 °C to granulate and obtain the upper masterbatch.

[0052] Step 3: At 30℃, 100 kg of microcrystalline cellulose and 1800 kg of 65% sulfuric acid solution were added to a reaction vessel and stirred. The mixture was then ultrasonically dispersed for 30 min, stirred for another 60 min at 50℃, and then diluted with 18000 L of deionized water at 4℃ to obtain a diluted solution. The pH of the diluted solution was adjusted to 8 with sodium hydroxide solution, and then centrifuged at 12000 r / min for 10 min. The precipitate was washed 5 times with deionized water and dispersed in deionized water to obtain a dispersion with a solid content of 10 wt%. The dispersion was then transferred to a 1 kDa dialysis bag and dialyzed in deionized water for 6 days. Finally, the mixture was freeze-dried to obtain modified cellulose powder.

[0053] Step 4: Mix silane coupling agent KH550 and deionized water at a mass ratio of 1:99, adjust the pH to 5 with 0.05 mol / L oxalic acid solution to obtain a silane coupling agent solution; add 10 kg of silane coupling agent solution, 690 L of acetone and 20 kg of silicon nitride whiskers to a reaction vessel and stir to mix, then ultrasonically disperse for 20 min, keep warm at 40℃ for 24 h, filter out the material, wash with anhydrous ethanol to remove acetone and vacuum dry to obtain modified silicon nitride whiskers; dissolve 10 kg of modified cellulose powder in 1000 L of 5% acetic acid solution, then add 8 kg of modified silicon nitride whiskers, ultrasonically disperse at 40℃ for 2 h, freeze dry to obtain composite powder.

[0054] Step 5: Add 50kg PA11, 30kg metallocene polyethylene, 3kg composite powder, 2kg nano aluminum powder and 50g silane coupling agent KH560 to a high-speed mixer and mix at 65℃ for 30 minutes. Then transfer to a twin-screw extruder and extrude at 230℃ to granulate and obtain intermediate layer masterbatch.

[0055] Step Six: Using PA11 as the lower masterbatch, the upper masterbatch, middle masterbatch, and lower masterbatch are added to the upper extruder, middle extruder, and lower extruder, respectively, and extruded into a cast sheet through a three-layer die at 230°C. The cast sheet is then immersed in deionized water at 55°C for 60±5s to complete the moisture conditioning treatment. The moisture-conditioned cast sheet is then biaxially stretched at 230°C to prepare a puncture-resistant composite film comprising an upper layer, middle layer, and lower layer.

[0056] Comparative Example 1: Based on Example 3, step five did not add the composite powder prepared in step four, while the remaining steps remained unchanged, and a composite film was prepared.

[0057] Comparative Example 2: Based on Example 3, metallocene polyethylene was not added in step five, while the remaining steps remained unchanged, and a composite film was prepared.

[0058] Comparative Example 3: Based on Example 3, step five was performed without adding nano-aluminum powder, while the remaining steps remained unchanged, and a composite film was prepared.

[0059] Comparative Example 4: Based on Example 3, no modified PA6 was added in step two, and the remaining steps remained unchanged to prepare a composite film.

[0060] Comparative Example 5: Based on Example 3, in step two, the sulfonated polyether ether ketone prepared in step one was not used. Instead, polyether ether ketone and PA6 were directly melt-extruded at a mass ratio of 1:1 to prepare modified PA6, which replaced the modified PA6 in step two. The remaining steps remained unchanged, and a composite film was prepared.

[0061] Comparative Example 6: A food-grade puncture-resistant vacuum bag with a film thickness of 0.15mm produced by Henan Zhongsu Printing Co., Ltd. was selected and cut into a film.

[0062] The polyetheretherketone (PEEK) used in the examples and comparative examples was Evonik Degussa L4000G, PA11 was purchased from Arkema, PA6 was purchased from BASF, metallocene polyethylene was ExxonMobil 3518CB, nano-aluminum powder was flake aluminum powder (particle size 3-5μm, flake thickness 20-30nm) produced by Hunan Jinhao New Material Technology Co., Ltd., and silicon nitride whiskers were purchased from Suzhou Beike Nanotechnology Co., Ltd.

[0063] Performance tests were conducted on Examples 1-3 and Comparative Examples 1-5 according to the standard GB / T10004-2008 Plastic Composite Films and Bags for Packaging (dry lamination and extrusion lamination). In order to prepare samples of the same specifications, the thickness of the composite film in Examples 1-3 and Comparative Examples 1-5 was 0.15 mm, with the upper layer thickness being 0.05 mm, the middle layer thickness being 0.06 mm, and the lower layer thickness being 0.04 mm.

[0064] Test the tensile strength, elongation at break, puncture strength, oxygen permeability, water vapor permeability and retort resistance of different composite films; among which, the tensile strength and elongation at break are determined according to GB / T1040.3-2006, the length of the specimen is 150 mm, the width is 15 mm, and the test speed is 200 mm / min; the puncture resistance is referred to GB / T 37841-2019. When testing, the composite films in Examples 1-3 and Comparative Examples 1-5 and the film in Comparative Example 6 are prepared into specimens with a specification of 100 mm×100 mm, then the specimens are fixed on the clamping ring, and a steel needle with a spherical tip diameter of 1 mm and a radius of 0.5 mm is used to pierce from the lower layer to the upper layer at a speed of 50 mm / min, read the maximum load penetrating the specimen, and take the average value of five groups; the oxygen permeability is tested according to GB / T1038.1-2022; the water vapor permeability is tested according to GB / T 1037-2021; when testing the retort resistance, different composite films are prepared into packaging bags with a size of 180 mm×120 mm, 50 g of borax snails are packed in the bag, vacuumed for 5 s and then heat-sealed, and the packaged borax snails are placed in a retort pot and cooked at 121 °C for 30 min to complete the cooking test. Each group is repeated 3 times, and observe whether there are obvious deformations, interlayer peeling, heat-sealing part peeling and other abnormal phenomena in the packaging. If there are no abnormal phenomena, it is judged as qualified and marked as "√", otherwise marked as "×". The results are shown in Table 1:

[0065] Table 1

[0066]

[0067]

[0068] As can be seen from Table 1, the mechanical properties, barrier properties and retort resistance of the specimens in Examples 1-3 are better; the composite powder, metallocene polyethylene and nano-aluminum powder all help to improve the tensile strength and puncture strength of the composite film, and help to reduce the oxygen permeability and water vapor permeability of the composite film. Comparative Examples 4-5 show that the modified PA6 prepared from sulfonated polyether ether ketone and PA6 helps to improve the retort resistance of the composite film, but has little effect on the mechanical properties.

[0069] The puncture-resistant composite films prepared in Examples 1-3 were cut into strips. 5g of each strip was weighed and mixed with 50mL of ethyl acetate, then added to a flask. The mixture was extracted using an ultrasonic extractor (Wuxi Woxin Instrument Manufacturing Co., Ltd.) at 25°C for 30min. The first extract was collected by filtration. The remaining strips in the flask were extracted a second time with 40mL of ethyl acetate under the same conditions. The second extract was collected by filtration. The remaining strips in the flask were extracted a third time with 20mL of ethyl acetate under the same conditions. The three extracts were combined and concentrated to 2mL using a dry nitrogen blower (Langma Technology). The solution was filtered through a 0.22μm needle filter and the residual DMF (N,N-dimethylformamide) was detected using a gas chromatograph (Agilent 8890, 0V-1301 capillary column). The results are shown in Table 2.

[0070] Table 2

[0071]

[0072] According to the ICH classification of commonly used organic solvents and residue limits, the limit for DMF residue in 10g of pharmaceutical product is 880ppm. The DMF residue in Examples 1-3 is within the safe limit.

[0073] The safety of the puncture-resistant composite films in Examples 1-3 was tested according to GB4806.7-2016 "National Food Safety Standard - Plastic Materials and Articles for Food Contact", GB31604.2-2016 "National Food Safety Standard - Determination of Potassium Permanganate Consumption in Food Contact Materials and Articles", GB31604.8-2021 "National Food Safety Standard - Determination of Total Migration in Food Contact Materials and Articles", and GB31604.9-2016 "National Food Safety Standard - Determination of Heavy Metals in Food Simulators of Food Contact Materials and Articles". The results are shown in Table 3.

[0074] Table 3

[0075]

[0076] As can be seen from Table 3, the puncture-resistant composite films tested in Examples 1-3 meet the requirements of standard GB4806.7-2016 "National Food Safety Standard for Plastic Materials and Products for Food Contact".

[0077] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0078] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A puncture-resistant composite film, characterized in that, The composite film has a three-layer structure, including an upper layer, a middle layer and a lower layer, and the thickness ratio of the upper layer, the middle layer and the lower layer is 5:6:4; The raw material in the lower layer is a lower layer masterbatch, and the raw material in the lower layer masterbatch is PA11; The intermediate layer raw material is an intermediate layer masterbatch, which includes the following components by mass: 5000 parts PA11, 2500-3000 parts metallocene polyethylene, 200-300 parts composite powder, 150-200 parts nano aluminum powder, and 3.5-5 parts silane coupling agent KH560. The raw material of the upper layer is the upper layer masterbatch, and the raw material of the upper layer masterbatch includes, by mass parts: 1 part of modified PA6 and 5 parts of PA6; The composite powder is prepared by the following steps: Step 1: Mix microcrystalline cellulose and sulfuric acid solution in a reaction vessel and ultrasonically disperse. Stir at 45-50℃ for 50-60 min. Dilute with deionized water at 0-4℃ and adjust the pH to 8 with sodium hydroxide solution. Centrifuge, wash the precipitate and disperse it with deionized water to form a dispersion with a solid content of 10 wt%. Dialyze the dispersion in deionized water using a 1 kDa dialysis bag for 4-6 days. Dry to obtain modified cellulose powder. Step 2: Mix silane coupling agent and deionized water at a mass ratio of 1:99, adjust the pH to 4-5 with 0.05 mol / L oxalic acid solution to obtain silane coupling agent solution; add silane coupling agent solution, acetone and silicon nitride whiskers to reaction vessel and stir to mix, then ultrasonically disperse for 10-20 min, keep warm at 30-40℃ for 18-24 h, filter out the material, wash with anhydrous ethanol to remove acetone and then vacuum dry to obtain modified silicon nitride whiskers; Step 3: Dissolve the modified cellulose powder in a 5% acetic acid solution, then add the modified silicon nitride whiskers, ultrasonically disperse at 30-40℃ for 1.5-2 hours, and freeze-dry to obtain the composite powder; the ratio of modified cellulose powder, acetic acid solution and modified silicon nitride whiskers is 1g:100mL:0.6-0.8g. The modified PA6 is prepared by the following steps: Sulfonated polyether ether ketone and PA6 were ground into powder and added to a reaction vessel. N,N-dimethylformamide was then added and stirred for 15-20 minutes. Dicyclohexylcarbodiimide particles were added and refluxed at 100°C for 25-30 hours. The reaction solution was obtained by filtration and then filtered at 70-80°C. The filter cake was washed, dried, and pulverized to obtain modified PA6.

2. The puncture-resistant composite film according to claim 1, characterized in that, In step one, the ratio of microcrystalline cellulose, sulfuric acid solution, and deionized water is 1g:17-18g:170-180mL; the mass fraction of the sulfuric acid solution is 60-65%.

3. The puncture-resistant composite film according to claim 1, characterized in that, In step two, the ratio of silane coupling agent solution, acetone, and silicon nitride whiskers is 1 mL: 69 mL: 1.5-2 g; the silane coupling agent is silane coupling agent KH550 or silane coupling agent KH560.

4. The puncture-resistant composite film according to claim 1, characterized in that, The upper masterbatch is prepared through the following steps: Modified PA6 and PA6 are mixed and extruded at 220-230℃ to granulate, thus obtaining the upper masterbatch.

5. The puncture-resistant composite film according to claim 1, characterized in that, The intermediate layer masterbatch is prepared through the following steps: PA11, metallocene polyethylene, composite powder, nano aluminum powder and silane coupling agent KH560 are mixed at 60-65℃ for 20-30 minutes, and then extruded using a twin-screw extruder at 220-230℃ to granulate and obtain intermediate layer masterbatch.

6. The puncture-resistant composite film according to claim 1, characterized in that, The ratio of sulfonated polyether ether ketone, PA6, N,N-dimethylformamide and dicyclohexylcarbodiimide particles is 3g:3g:200mL:50g.

7. The puncture-resistant composite film according to claim 1, characterized in that, The sulfonated polyether ether ketone is prepared by the following steps: Polyether ether ketone and 98% concentrated sulfuric acid were added to a polytetrafluoroethylene reactor and stirred at 60-65°C for 50-60 minutes. The reaction solution was cooled to 0°C using the cooling device of the polytetrafluoroethylene reactor and diluted with deionized water at 0-4°C. The precipitated solid was collected and washed with deionized water until the pH of the final washing solution was neutral. The solid was then vacuum dried at 45-60°C to obtain sulfonated polyether ether ketone.

8. The puncture-resistant composite film according to claim 7, characterized in that, The ratio of polyetheretherketone to concentrated sulfuric acid is 1g:46g.

9. The puncture-resistant composite film according to claim 1, characterized in that, Prepared by the following steps: Step 1: Add the upper layer masterbatch, middle layer masterbatch and lower layer masterbatch to the upper layer extruder, middle layer extruder and lower layer extruder respectively, and extrude them into cast sheets through a three-layer die at 220-230℃. Step 2: Immerse the casting in deionized water at a temperature of 50-55℃ for 60±5s to complete the moisture conditioning treatment of the casting. Then, prepare the moisture-conditioned casting into a puncture-resistant composite film consisting of an upper layer, a middle layer and a lower layer by biaxial stretching.

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