Preparation method of high-barrier aluminum oxide composite film for food packaging

Abstract

The invention discloses a preparation method of a high-barrier aluminum oxide composite film for food packaging, and relates to the technical field of food packaging materials. The high-barrier aluminum oxide composite film for food packaging comprises the following raw materials in parts by weight: a barrier layer: 60-90 parts of modified nano aluminum oxide and 20-30 parts of a silane coupling agent KH-560; the functional layer is prepared from the following components in parts by weight: 18 to 28 parts of nano silver, 16 to 22 parts of compound antioxidant and 4 to 10 parts of nano titanium dioxide; the heat sealing layer is prepared from 22 to 32 parts of modified polylactic acid, 2 to 6 parts of graphene quantum dots, 12 to 16 parts of methyl methacrylate-butadiene-styrene copolymer, 3 to 6 parts of dodecyl trimethyl ammonium chloride, 10 to 14 parts of resorcinol tetraphenyl diphosphate and 7 to 17 parts of stearic acid intercalation modified nano montmorillonite. The high-barrier aluminum oxide composite film for food packaging is prepared by modifying nano aluminum oxide and polylactic acid, the barrier ability to gas, water vapor and ultraviolet rays is greatly improved, and the high-barrier aluminum oxide composite film is oil-resistant and antistatic. The product is high in mechanical strength, high in processing adaptability, capable of adapting to complex scenes, environment-friendly and safe.

Description

Technical Field

[0001] The invention relates to the technical field of food packaging materials, in particular to a method for preparing a high-barrier alumina composite film for food packaging. Background Art

[0002] In the field of food packaging, high-barrier composite films are the core materials for extending food shelf life and ensuring quality. Traditional packaging films generally have two major bottlenecks:

[0003] First, the barrier layer's performance is limited. For example, nano-alumina's high surface energy leads to particle agglomeration, resulting in weak interfacial bonding with the organic substrate. This makes the barrier layer susceptible to cracking when bent or subjected to stress, allowing small molecules like oxygen and water vapor to penetrate, causing food to oxidize and deteriorate due to moisture. For example, aluminum foil-based composite films can crack easily in frozen environments, leading to air leaks in meat packaging and shortening its shelf life.

[0004] Second, the heat-seal layer has a limited function: While traditional PLA heat-seal layers are biodegradable, they lack oil resistance and are easily corroded by grease at high temperatures, leading to package damage. They also have poor anti-static properties, making them susceptible to static electricity and dust attraction on automated packaging lines, impacting production efficiency and package cleanliness. For example, in packaging greasy baked goods, traditional PLA heat-seal layers often crack due to grease penetration.

[0005] In addition, insufficient functional integration is also a pain point in the industry: existing composite films are difficult to simultaneously achieve multiple functions such as high barrier, antistatic, high and low temperature resistance, and environmentally friendly recycling. Especially in high-end food packaging, higher requirements are placed on the comprehensive performance of materials.

[0006] To address the above problems, the present invention has developed a new composite film with high barrier, strong toughness, antistatic and environmental adaptability through directional modification of nano-alumina and polylactic acid, combined with multi-layer composite process optimization, filling the gap in traditional materials in multifunctional integration and long-term stability. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the present invention provides a method for preparing a high-barrier alumina composite film for food packaging, which solves the above-mentioned problems.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] A high-barrier alumina composite film for food packaging comprises the following raw materials in parts by weight:

[0010] Barrier layer: 60-90 parts modified nano-alumina, 20-30 parts silane coupling agent KH-560;

[0011] Functional layer: 18-28 parts of nano silver, 16-22 parts of compound antioxidant, 4-10 parts of nano titanium dioxide;

[0012] Heat sealing layer: 22-32 parts of modified polylactic acid, 2-6 parts of graphene quantum dots, 12-16 parts of methyl methacrylate-butadiene-styrene copolymer, 3-6 parts of dodecyltrimethylammonium chloride, 10-14 parts of resorcinol tetraphenyl diphosphate, and 7-17 parts of stearic acid intercalated modified nano-montmorillonite.

[0013] Furthermore, the modified nano-alumina is prepared in the following steps:

[0014] A1. Add deionized water to a beaker, then slowly pour concentrated sulfuric acid into it and stir evenly. Continue adding nano-alumina powder while stirring. Place the beaker in an ultrasonic cleaner for ultrasonic dispersion. Transfer the suspension to a reactor, heat to 80°C, and stir for 3 hours. After the reaction, cool to room temperature, transfer the suspension to a centrifuge tube, and centrifuge. Discard the supernatant, wash the precipitate with deionized water, and then dry it in a vacuum drying oven for 12 hours to obtain hydroxylated alumina.

[0015] A2. Add an ethanol-water mixture to a three-necked flask, slowly add γ-aminopropyltriethoxysilane dropwise while stirring at room temperature, and continue stirring for 1 hour after the addition is completed; add the hydroxylated alumina powder to the above hydrolyzate, raise the temperature to 80°C, and stir to react for 4 hours; after the reaction is completed, wait for the solution to cool to room temperature and transfer it to a centrifuge tube, centrifuge, and wash the precipitate with anhydrous ethanol. After each washing, centrifuge and transfer the precipitate to a vacuum drying oven and dry it for 8 hours to obtain silane-coated alumina;

[0016] A3. Add xylene and silane-coated alumina powder into a four-necked flask, introduce nitrogen protection, stir and heat to 110°C; dissolve dodecafluoroheptyl methacrylate and dibenzoyl peroxide in xylene, and add them dropwise to the above reaction system through a constant pressure dropping funnel. After the addition is complete, continue stirring and react for 5 hours; after the reaction is completed, cool to room temperature, slowly pour into excess acetone to precipitate the product, collect the solid product by suction filtration through a sand core funnel, wash with acetone, and then transfer to a vacuum drying oven to dry for 8 hours to obtain fluorine-modified alumina.

[0017] Furthermore, in step A1, the ratio of deionized water, concentrated sulfuric acid, and nano-alumina powder is 300 mL: 5 mL: 25 g; the ultrasonic cleaning machine is set to a frequency of 40 kHz for ultrasonic dispersion for 40 minutes; the stirring speed in the reactor is 400 r / min; the centrifugal speed is 8000 r / min, and the centrifugation is carried out for 10 minutes; the precipitate is washed three times with deionized water and dried at 60°C;

[0018] Furthermore, in step A2, the ratio of the ethanol-water mixture, γ-aminopropyltriethoxysilane, and hydroxylated alumina powder is 300 mL: 5 mL: 25 g; the volume ratio of ethanol to water is 7:3; the stirring speed of the hydrolyzate is 200 r / min, the speed during heating and stirring is 500 r / min, the centrifugal speed is 8000 r / min, and the centrifugation is 10 minutes; the precipitate is washed three times with anhydrous ethanol; and the drying temperature is 80°C.

[0019] Furthermore, in step A3, the ratio of xylene to silane-coated alumina powder is 200 mL:25 g, and the stirring speed is 300 r / min; the ratio of dodecafluoroheptyl methacrylate, dibenzoyl peroxide, and xylene is 8 g:0.5 g:30 mL; the solution addition rate is 1 mL / min; the solid product is washed three times with acetone, and the drying temperature is 60°C.

[0020] In the A1 hydroxylation step, concentrated sulfuric acid etching generates -OH groups on the surface of the aluminum oxide. The polar groups enhance the chemical reaction activity with the silane coupling agent, solving the problem of particle agglomeration. In the A2 silane coupling step, γ-aminopropyltriethoxysilane hydrolyzes to generate Si-OH, which condenses with the -OH on the surface of the aluminum oxide to form a Si-O-Al covalent bond. At the same time, the amino group on the other end provides a reaction site for subsequent fluorocarbon grafting, realizing "inorganic-organic" interface bridging. In the A3 fluorocarbon grafting step, dodecafluoroheptyl methacrylate reacts with the double bond through the amino group to graft -C8F on the surface of the aluminum oxide. 17 The fluorocarbon chain forms a low surface energy hydrophobic layer, improving compatibility with PET while enhancing the ability to block ultraviolet and near-infrared light.

[0021] Furthermore, the modified polylactic acid is specifically prepared in the following steps:

[0022] B1. Add dichloromethane and polylactic acid particles to a three-necked flask, stir at room temperature until completely dissolved, then add phosphotungstic acid catalyst, raise the temperature to 45°C and keep stirring, slowly add hydrogen peroxide solution dropwise through a constant pressure dropping funnel, raise the temperature to 65°C after the addition is complete, and stir and react for 5 hours; after the reaction is completed, cool to room temperature, transfer to a separatory funnel, add saturated salt water, shake and wash, and then stand to separate, collect the lower organic phase, wash with saturated salt water, and then transfer the organic phase to a rotary evaporator, remove dichloromethane by vacuum distillation, and transfer the residue to a vacuum drying oven and dry for 4 hours to obtain epoxy-modified polylactic acid;

[0023] B2. Sodium alginate was added to deionized water and stirred at room temperature until completely dissolved to prepare a sodium alginate aqueous solution; poly (N-isopropylacrylamide) solution and dodecyltrimethylammonium chloride were separately taken, and deionized water was added and mixed uniformly; tetrahydrofuran and epoxy-modified polylactic acid were added to a four-necked flask, stirred at room temperature to dissolve, and the sodium alginate aqueous solution was slowly poured into the tetrahydrofuran solution of epoxy-modified polylactic acid, and a high-speed shear emulsifier was used to form a stable oil-water emulsion; a mixed solution of poly (N-isopropylacrylamide) and dodecyltrimethylammonium chloride was added to the emulsion, and stirring was continued for 5 minutes; calcium chloride solution was slowly added dropwise by a peristaltic pump, and stirring was continued for 2 hours after the addition was complete to fully cross-link the microcapsules, and the emulsion was transferred to a centrifuge tube for centrifugation, the supernatant was discarded, the precipitate was washed with deionized water, and then transferred to a vacuum drying oven for drying for 10 hours to obtain antistatic microcapsule-modified polylactic acid.

[0024] Furthermore, in step B1, the ratio of dichloromethane, polylactic acid particles, phosphotungstic acid, and hydrogen peroxide solution is 200 mL: 60 g: 0.8 g: 35 mL; the initial stirring speed is 300 r / min; the mass fraction of the hydrogen peroxide solution is 35%; the dropping speed is 1 mL / min, and the stirring speed during the dropwise addition is 500 r / min; the vacuum distillation temperature is 40° C.; and the drying temperature is 60° C.

[0025] Furthermore, in the B2 step, the ratio of sodium alginate and deionized water is 20 g:647 mL; the ratio of poly N-isopropylacrylamide solution, dodecyltrimethylammonium chloride, and deionized water is 12 mL:10 g:50 mL; the mass fraction of poly N-isopropylacrylamide solution is 15%; the ratio of tetrahydrofuran and epoxy-modified polylactic acid is 100 mL:50 g; the stirring speed is 300 r / min; the emulsification speed is 10000 r / min, and the emulsification is 10 min; the concentration of calcium chloride solution is 0.2 mol / L, the amount is 15 mL, and the dropping speed is 5 mL / min; the centrifugal speed is 10000 r / min, and the centrifugation is 10 min; the precipitate is washed 3 times with deionized water, and the drying temperature is 40°C.

[0026] In the B1 epoxidation step, hydrogen peroxide epoxidizes the double bonds of the polylactic acid molecular chain under the catalysis of phosphotungstic acid, introducing epoxy groups. This increases polarity and allows them to hydrogen-bond with the functional layer of nanosilver. The ester structure also resists grease corrosion and improves oil resistance. In the B2 microcapsule loading step, sodium alginate and poly (N-isopropylacrylamide) form thermosensitive microcapsules, which encapsulate dodecyltrimethylammonium chloride and are fixed to the polylactic acid matrix via calcium ion crosslinking. Temperature changes during the packaging process trigger the release of antistatic agents from the microcapsules, which are evenly distributed on the membrane surface, reducing surface resistance. Simultaneously, the quaternary ammonium salt structure destroys microbial cell membranes, achieving antibacterial properties.

[0027] Furthermore, the compound antioxidant is a hindered phenol antioxidant 1010 and a phosphite antioxidant 168 compounded in a mass ratio of 1:1; the mass ratio of stearic acid to nano-montmorillonite in the stearic acid intercalated modified nano-montmorillonite is 1:3.

[0028] The preparation method of high-barrier alumina composite film for food packaging specifically comprises the following steps:

[0029] S1. Raw material pretreatment

[0030] Outer layer preparation:

[0031] Polyethylene terephthalate (PET) film was selected as the outer substrate and corona treated to increase the surface tension;

[0032] Barrier layer raw material mixing:

[0033] The modified nano-alumina and the modified silane coupling agent were placed in a stirring kettle, and then an ethanol-acetone mixed solvent was added and stirred evenly to prepare a slurry with a solid content of 20%;

[0034] Heat sealing layer raw material preparation:

[0035] Weigh modified polylactic acid, graphene quantum dots, methyl methacrylate-butadiene-styrene copolymer, dodecyltrimethylammonium chloride, resorcinol tetraphenyl diphosphate, and stearic acid intercalated modified nano-montmorillonite according to weight, put all the raw materials into a high-speed mixer, and stir and mix them evenly;

[0036] Preparation of functional layer raw materials:

[0037] Nano-silver particles, compound antioxidants and nano-titanium dioxide are mixed, and ethyl acetate is added as a solvent to prepare a functional layer coating with a solid content of 15%. During the mixing process, ultrasonic dispersion is performed to ensure uniform dispersion;

[0038] S2. Preparation of each layer

[0039] Barrier coating:

[0040] The prepared barrier layer slurry was coated on the pretreated PET outer layer film using a gravure coater, with the wet film thickness controlled to be 30 μm. After coating, the film was sent to a drying oven for drying to fully evaporate the solvent, thereby forming a barrier layer and obtaining a PET / Al2O3 composite outer layer.

[0041] Heat seal layer extrusion:

[0042] The prepared heat-sealing layer raw material is put into a twin-screw extruder, and the temperature gradient and screw speed are set. The raw material undergoes the processes of conveying, melting, mixing, and homogenization in the extruder in sequence, and is finally extruded from the die head to form a heat-sealing layer film. The extruded film is cooled and shaped by a cooling roller;

[0043] Functional layer coating:

[0044] The functional layer coating is evenly coated on a 10 μm thick polyethylene (PE) film using gravure printing to form a functional layer / PE composite film;

[0045] S3, three-layer composite

[0046] First, a solvent-free polyurethane adhesive is applied to the coating roller of the composite equipment. Then, the three layers of film are fed into the composite roller in sequence for composite. After the composite is completed, the composite film is sent to the aging chamber for aging for 24 hours to fully solidify the adhesive and form a high-barrier alumina composite film for food packaging.

[0047] Furthermore, in the S1 step, the thickness of the polyethylene terephthalate film of the outer layer is 20-30 μm, and the surface tension after corona is 56 mN / m; the mass ratio of the barrier layer modified nano-alumina to the modified silane coupling agent is 3:1, the volume ratio of the ethanol-acetone mixed solvent is 5:3, the stirring speed is 300-500 r / min, and the stirring time is 30-60 min; the stirring speed of the heat sealing layer raw material in the high-speed mixer is 800-1200 r / min, and the stirring time is 15-20 min; the functional layer raw material is ultrasonically dispersed for 20-30 min.

[0048] Furthermore, in the step S2, when the barrier layer is coated, the wet film thickness is controlled to be 30-40 μm, the coating speed is 5-10 m / min, the line number of the anilox roller is 300-400 lines / inch, and the film is dried at 120°C for 5 minutes; the temperature of the twin-screw extruder for extruding the heat-sealing layer is: 130-140°C in zone 1, 150-160°C in zone 2, 170-180°C in zone 3, 190-200°C in zone 4, and 210-220°C in zone 5, the screw speed is 250-350 r / min, the thickness of the heat-sealing layer film extruded from the die head is 25 μm, and the cooling water temperature is controlled at 5-10°C; the coating amount of the functional layer coating is , drying temperature is 80-100℃, drying time is 3-5min;

[0049] Furthermore, in the step S3, the coating amount is controlled to The composite conditions are 120℃, 0.8MPa pressure, the composite speed is controlled at 10-15m / min, and the composite film is matured at 40-50℃.

[0050] The present invention provides a method for preparing a high-barrier alumina composite film for food packaging, which has the following beneficial effects:

[0051] 1. Powerful protection, comprehensively extending the food shelf life: Through a special modification process, the barrier properties of the composite film are enhanced to effectively block the intrusion of oxygen, water vapor and ultraviolet rays, significantly inhibiting food oxidation, moisture and light deterioration, greatly extending the shelf life of meat, baked goods, etc., and reducing food waste caused by packaging failure. It is especially suitable for the protection needs of long-shelf-life or high-value-added foods.

[0052] 2. Tough and durable, adaptable to diverse packaging and transportation scenarios: The composite film has high strength puncture resistance and flexibility, can withstand the impact of food particles and transportation bumps, and is not easily damaged; at the same time, it can adapt to high and low temperature environments such as from freezing to steaming. The heat seal layer is firm and reliable, and is not easily cracked by oil penetration or temperature changes, ensuring the integrity of the packaging throughout its life cycle. It is suitable for a variety of categories such as quick-frozen foods and ready-to-heat foods.

[0053] 3. Functional integration to enhance packaging intelligence and safety: The heat-sealing layer is given antistatic function through modification technology, reducing the problem of electrostatic adsorption in automated production and improving packaging efficiency. At the same time, the material meets food contact safety standards, has no risk of harmful substance migration, and some components have antibacterial properties, further ensuring food hygiene and safety. It is suitable for scenarios with high safety requirements such as infant food and fresh food.

[0054] 4. Environmental compatibility, helping the transition to sustainable packaging: The use of recyclable design and halogen-free modification technology reduces the burden of packaging waste on the environment, in line with the trend of green packaging. The process is adapted to existing production lines and can achieve the production of high-performance composite films without large-scale equipment modifications, taking into account both economic and environmental benefits, helping food companies upgrade to sustainable packaging. DETAILED DESCRIPTION

[0055] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0056] Example 1: Preparation of a high-barrier alumina composite film for food packaging. The specific steps are as follows:

[0057] S1. Raw material pretreatment

[0058] Preparation of outer layer ingredients:

[0059] A polyethylene terephthalate film with a thickness of 20 μm was selected as the outer substrate and subjected to corona treatment to achieve a surface tension of 56 mN / m;

[0060] Barrier layer raw material mixing:

[0061] 60 parts of modified nano-alumina and 20 parts of modified silane coupling agent were put into a stirred tank, followed by the addition of 320 parts of a 5:3 volume ratio ethanol-acetone mixed solvent, and stirred evenly to prepare a slurry with a solid content of 20%. During the stirring process, the speed was controlled at 300 r / min and the stirring time was 30 min.

[0062] Heat sealing layer raw material preparation:

[0063] Weigh 22 parts of modified polylactic acid, 2 parts of graphene quantum dots, 12 parts of methyl methacrylate-butadiene-styrene copolymer, 3 parts of dodecyltrimethylammonium chloride, 10 parts of resorcinol tetraphenyl diphosphate, and 7 parts of stearic acid intercalated modified nano-montmorillonite according to the following weight parts, put all the raw materials into a high-speed mixer, and mix at a speed of 800 r / min for 15 minutes to uniformly disperse the components;

[0064] Preparation of functional layer raw materials:

[0065] 18 parts of nano-silver particles, 16 parts of compound antioxidant and 4 parts of nano-titanium dioxide were mixed, and 342 parts of ethyl acetate was added as a solvent to prepare a functional layer coating with a solid content of 10%. During the mixing process, ultrasonic dispersion was performed at a frequency of 40 kHz for 20 minutes to ensure uniform dispersion.

[0066] S2. Preparation of each layer

[0067] Barrier coating:

[0068] The prepared barrier layer slurry was coated on the pretreated PET outer film using a gravure coater, with a wet film thickness of 30 μm. During the coating process, the coating speed of the coater was adjusted to 5 m / min and the line count of the anilox roller was adjusted to 300 lines / inch. After coating, the film was sent to a drying oven and dried at 120°C for 5 minutes to fully evaporate the solvent and form a barrier layer, thereby obtaining a PET / Al2O3 composite outer layer.

[0069] Heat seal layer extrusion:

[0070] The prepared heat-sealing layer raw material was put into a twin-screw extruder, and the temperature gradient was set as follows: 130°C in zone 1, 150°C in zone 2, 170°C in zone 3, 190°C in zone 4, and 210°C in zone 5. The screw speed was 250 r / min. The raw material was sequentially conveyed, melted, mixed, and homogenized in the extruder before being extruded from the die to form a heat-sealing layer film with a thickness of 25 μm. The extruded film was cooled and shaped by a cooling roller, and the cooling water temperature was controlled at 5°C.

[0071] Functional layer coating:

[0072] The functional layer coating is evenly coated on a polyethylene film with a thickness of 10 μm by gravure printing. During the coating process, the coating amount is controlled to be , the drying temperature is 80°C, the drying time is 3 minutes, the solvent is evaporated, and a functional layer / PE composite film is obtained;

[0073] S3, three-layer composite

[0074] First, apply solvent-free polyurethane adhesive on the coating roller of the composite equipment, and the coating amount is controlled to Then, the three layers of film are fed into the composite roller in turn and composited at 120°C and 0.8MPa pressure. During the composite process, the composite speed is controlled at 10m / min. After the composite is completed, the composite film is sent to the aging chamber and aged at 40°C for 24h to fully solidify the adhesive to form a high-barrier alumina composite film for food packaging.

[0075] Example 2: Preparation of a high-barrier alumina composite film for food packaging. The specific steps are as follows:

[0076] S1. Raw material pretreatment

[0077] Preparation of outer layer ingredients:

[0078] A polyethylene terephthalate film with a thickness of 30 μm was selected as the outer substrate and subjected to corona treatment to achieve a surface tension of 56 mN / m;

[0079] Barrier layer raw material mixing:

[0080] 90 parts of modified nano-alumina and 30 parts of modified silane coupling agent were put into a stirred tank, followed by the addition of 480 parts of a 5:3 ethanol-acetone mixed solvent, and stirred evenly to prepare a slurry with a solid content of 20%. The stirring speed was controlled at 500 r / min and the stirring time was 60 min.

[0081] Heat sealing layer raw material preparation:

[0082] According to the following weight parts, 32 parts of modified polylactic acid, 6 parts of graphene quantum dots, 16 parts of methyl methacrylate-butadiene-styrene copolymer, 6 parts of dodecyltrimethylammonium chloride, 14 parts of resorcinol tetraphenyl diphosphate, and 17 parts of stearic acid intercalated modified nano-montmorillonite were weighed and all the raw materials were put into a high-speed mixer and mixed at a speed of 1200 r / min for 20 min to uniformly disperse the components;

[0083] Preparation of functional layer raw materials:

[0084] 28 parts of nano-silver particles, 22 parts of compound antioxidant and 10 parts of nano-titanium dioxide were mixed, and 340 parts of ethyl acetate was added as a solvent to prepare a functional layer coating with a solid content of 15%. During the mixing process, ultrasonic dispersion was performed at a frequency of 40 kHz for 30 minutes to ensure uniform dispersion.

[0085] S2. Preparation of each layer

[0086] Barrier coating:

[0087] The prepared barrier layer slurry was coated on the pretreated PET outer film using a gravure coater, with a wet film thickness of 30 μm. During the coating process, the coating speed of the coater was adjusted to 10 m / min and the line count of the anilox roller was adjusted to 400 lines / inch. After coating, the film was sent to a drying oven and dried at 120°C for 5 minutes to fully evaporate the solvent and form a barrier layer, thereby obtaining a PET / Al2O3 composite outer layer.

[0088] Heat seal layer extrusion:

[0089] The prepared heat-sealing layer raw material was put into a twin-screw extruder, and the temperature gradient was set as follows: 140°C in zone 1, 160°C in zone 2, 180°C in zone 3, 200°C in zone 4, and 220°C in zone 5. The screw speed was 350 r / min. The raw material was sequentially conveyed, melted, mixed, and homogenized in the extruder before being extruded from the die to form a heat-sealing layer film with a thickness of 25 μm. The extruded film was cooled and shaped by a cooling roller, and the cooling water temperature was controlled at 10°C.

[0090] Functional layer coating:

[0091] The functional layer coating is evenly coated on a polyethylene film with a thickness of 10 μm by gravure printing. During the coating process, the coating amount is controlled to be , the drying temperature is 100°C, the drying time is 5 minutes, the solvent is evaporated, and a functional layer / PE composite film is obtained;

[0092] S3, three-layer composite

[0093] First, apply solvent-free polyurethane adhesive on the coating roller of the composite equipment, and the coating amount is controlled to 5g / Then, the three layers of film are fed into the composite roller in turn and composited at 120°C and 0.8MPa pressure. During the composite process, the composite speed is controlled at 15m / min. After the composite is completed, the composite film is sent to the aging chamber and aged at 50°C for 24 hours to fully solidify the adhesive to form a high-barrier alumina composite film for food packaging.

[0094] Example 3: Preparation of a high-barrier alumina composite film for food packaging. The specific steps are as follows:

[0095] S1. Raw material pretreatment

[0096] Preparation of outer layer ingredients:

[0097] A polyethylene terephthalate film with a thickness of 25 μm was selected as the outer substrate and subjected to corona treatment to achieve a surface tension of 56 mN / m;

[0098] Barrier layer raw material mixing:

[0099] 75 parts of modified nano-alumina and 25 parts of modified silane coupling agent were put into a stirred tank, followed by the addition of 400 parts of a 5:3 volume ratio ethanol-acetone mixed solvent, and stirred evenly to prepare a slurry with a solid content of 20%. During the stirring process, the speed was controlled at 400 r / min and the stirring time was 45 min.

[0100] Heat sealing layer raw material preparation:

[0101] Weigh 27 parts of modified polylactic acid, 4 parts of graphene quantum dots, 14 parts of methyl methacrylate-butadiene-styrene copolymer, 4 parts of dodecyltrimethylammonium chloride, 12 parts of resorcinol tetraphenyl diphosphate, and 12 parts of stearic acid intercalated modified nano-montmorillonite according to the following weight parts, put all the raw materials into a high-speed mixer, and mix at a speed of 1000 r / min for 17 minutes to uniformly disperse the components;

[0102] Preparation of functional layer raw materials:

[0103] 23 parts of nano-silver particles, 19 parts of compound antioxidant and 7 parts of nano-titanium dioxide were mixed, and 359 parts of ethyl acetate was added as a solvent to prepare a functional layer coating with a solid content of 12%. During the mixing process, ultrasonic dispersion was performed at a frequency of 40kHz for 25 minutes to ensure uniform dispersion.

[0104] S2. Preparation of each layer

[0105] Barrier coating:

[0106] The prepared barrier layer slurry was coated on the pretreated PET outer film using a gravure coater, with a wet film thickness of 35 μm. During the coating process, the coating speed of the coater was adjusted to 7 m / min, and the line count of the anilox roller was adjusted to 350 lines / inch. After coating, the film was sent to a drying oven and dried at 120°C for 5 minutes to fully evaporate the solvent and form a barrier layer, thereby obtaining a PET / Al2O3 composite outer layer.

[0107] Heat seal layer extrusion:

[0108] The prepared heat-sealing layer raw material was put into a twin-screw extruder, and the temperature gradient was set as follows: 135°C in zone 1, 155°C in zone 2, 175°C in zone 3, 195°C in zone 4, and 215°C in zone 5. The screw speed was 300 r / min. The raw material was sequentially conveyed, melted, mixed, and homogenized in the extruder before being extruded from the die to form a heat-sealing layer film with a thickness of 25 μm. The extruded film was cooled and shaped by a cooling roller, and the cooling water temperature was controlled at 7°C.

[0109] Functional layer coating:

[0110] The functional layer coating is evenly coated on a polyethylene film with a thickness of 10 μm by gravure printing. During the coating process, the coating amount is controlled to be , the drying temperature is 90°C, the drying time is 4 minutes, the solvent is evaporated, and a functional layer / PE composite film is obtained;

[0111] S3, three-layer composite

[0112] First, apply solvent-free polyurethane adhesive on the coating roller of the composite equipment, and the coating amount is controlled to Then, the three layers of film are fed into the composite roller in turn and composited at 120°C and 0.8MPa pressure. During the composite process, the composite speed is controlled at 12m / min. After the composite is completed, the composite film is sent to the aging room and aged at 5°C for 24 hours to fully solidify the adhesive to form a high-barrier alumina composite film for food packaging.

[0113] Example 4, preparing modified alumina, the specific steps are as follows:

[0114] A1. Add 300 mL of deionized water to a beaker, then slowly pour in 5 mL of concentrated sulfuric acid and stir evenly. Continue to add 25 g of nano-alumina powder while stirring. Place the beaker in an ultrasonic cleaner and set the frequency to 40 kHz for ultrasonic dispersion for 40 minutes. Then transfer the suspension to a reactor, heat it to 80°C and stir at 400 r / min for 3 hours. After the reaction is completed, cool it to room temperature, transfer it to a centrifuge tube, and centrifuge it at 8000 r / min for 10 minutes. Discard the supernatant, wash the precipitate with deionized water three times, and then dry it in a vacuum drying oven at 60°C for 12 hours to obtain hydroxylated alumina.

[0115] A2. Add 300 mL of an ethanol-water mixture with a volume ratio of 7:3 to a three-necked flask, slowly add 5 mL of γ-aminopropyltriethoxysilane dropwise at room temperature and 200 r / min stirring, and continue stirring for 1 hour after the addition is completed; add 25 g of hydroxylated alumina powder to the above hydrolyzate, raise the temperature to 80 ° C and maintain the stirring speed at 500 r / min for 4 hours; after the reaction, wait for the solution to cool to room temperature and transfer it to a centrifuge tube, centrifuge at 8000 r / min for 10 minutes, wash the precipitate with anhydrous ethanol 3 times, centrifuge after each washing, transfer the precipitate to a vacuum drying oven, and dry it at 80 ° C for 8 hours to obtain silane-coated alumina;

[0116] A3. Add 200 mL of xylene and 25 g of silane-coated alumina powder to a four-necked flask, introduce nitrogen protection, stir at 300 r / min and heat to 110°C; dissolve 8 g of dodecafluoroheptyl methacrylate and 0.5 g of dibenzoyl peroxide in 30 mL of xylene, and add them dropwise to the above reaction system through a constant pressure dropping funnel at a dropping speed of 1 mL / min. After the addition is complete, maintain the speed of 300 r / min and continue stirring for 5 hours; after the reaction is completed, cool to room temperature, slowly pour into excess acetone to precipitate the product, collect the solid product by filtration through a sand core funnel, wash with acetone 3 times, and then transfer to a vacuum drying oven and dry at 60°C for 8 hours to obtain fluorine-modified alumina.

[0117] Example 5, preparing modified polylactic acid, the specific steps are as follows:

[0118] B1. Add 200 mL of dichloromethane and 60 g of polylactic acid particles to a three-necked flask, stir at 300 r / min at room temperature until completely dissolved, then add 0.8 g of phosphotungstic acid catalyst, raise the temperature to 45 ° C and keep stirring, slowly add 35 mL of 35% hydrogen peroxide solution by mass at a dropping speed of 1 mL / min through a constant pressure dropping funnel, raise the temperature to 65 ° C after the addition is complete, maintain a speed of 500 r / min and react for 5 hours; after the reaction is completed, cool to room temperature, transfer to a separatory funnel, add saturated salt water, shake and wash, and then stand to separate, collect the lower organic phase, wash with saturated salt water, and then transfer the organic phase to a rotary evaporator, remove dichloromethane by reduced pressure distillation at 40 ° C, transfer the residue to a vacuum drying oven, and dry it at 60 ° C for 4 hours to obtain epoxy-modified polylactic acid;

[0119] B2. Add 20g of sodium alginate to 647mL of deionized water and stir at room temperature until completely dissolved to prepare a sodium alginate aqueous solution; take another 12mL of 15% mass fraction poly N-isopropylacrylamide solution and 10g of dodecyltrimethylammonium chloride, add 50mL of deionized water and mix evenly; add 100mL of tetrahydrofuran and 50g of epoxy-modified polylactic acid into a four-necked flask, stir at room temperature to dissolve, slowly pour the sodium alginate aqueous solution into the tetrahydrofuran solution of epoxy-modified polylactic acid, use a high-speed shear emulsifier, emulsify at a speed of 10000r / min for 10min, and form a flask. to form a stable oil-water emulsion; add a mixture of poly (N-isopropylacrylamide) and dodecyltrimethylammonium chloride to the emulsion and continue stirring for 5 minutes; slowly add 15 mL of 0.2 mol / L calcium chloride solution at a dropping speed of 5 mL / min through a peristaltic pump, and continue stirring for 2 hours after the addition is completed to allow the microcapsules to be fully cross-linked and formed. The emulsion is transferred to a centrifuge tube and centrifuged at 10,000 r / min for 10 minutes. The supernatant is discarded, and the precipitate is washed three times with deionized water and then transferred to a vacuum drying oven and dried at 40°C for 10 hours to obtain antistatic microcapsule modified polylactic acid.

[0120] Comparative Example 1: Preparation of a high-barrier alumina composite film for food packaging, the specific steps are as follows:

[0121] The remaining steps remained unchanged, except that the modified nano-alumina in Example 2 was replaced by nano-alumina without any treatment to prepare a high-barrier alumina composite film for food packaging.

[0122] Comparative Example 2: Preparation of a high-barrier alumina composite film for food packaging, the specific steps are as follows:

[0123] The remaining steps remained unchanged, except that the modified polylactic acid in Example 2 was replaced by polylactic acid without any treatment to prepare a high-barrier alumina composite film for food packaging.

[0124] Performance Testing

[0125]

[0126] Barrier Performance: The oxygen and water vapor transmission rates of Examples 1-3 were significantly lower than those of the comparative examples. In particular, the transmittance of Comparative Example 1, which exhibits barrier layer defects due to particle agglomeration, increased by 6-20 times, demonstrating the critical role of nano-alumina modification in maintaining barrier layer continuity. UV rejection rates were all >99%, demonstrating the highly effective UV shielding properties of fluorine-modified alumina.

[0127] Mechanical strength: The puncture resistance of the examples reached 25-28N, an increase of 33%-56% compared with Comparative Example 1, indicating that the interfacial modification enhanced the interlayer bonding strength; Comparative Example 2 had poor oil resistance and the heat seal layer was easily corroded by grease, so the mechanical properties did not decrease significantly, but there were potential risks in actual applications.

[0128] Antistatic and oil resistance: Example Surface resistance , meeting antistatic standards for food packaging. Comparative Example 2, due to the lack of antistatic microcapsules in the unmodified PLA, had a 17-fold increase in surface resistivity, making it susceptible to dust absorption. The oil resistance test for Comparative Example 2 showed an 8.2% mass change, confirming that traditional PLA heat seals are susceptible to oil penetration. Modified PLA, through epoxidation and microcapsule loading, significantly improves oil resistance and stability.

[0129] Environmental adaptability: The low-temperature brittle temperature of the embodiment is lower than -25°C, which is suitable for quick-frozen food packaging; the comparative example 1 has weak interface bonding of alumina, is prone to cracking at low temperatures, and the brittle temperature rises to -15°C, which limits the cold chain application scenario.

[0130] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. High barrier alumina composite film for food packaging, characterized by: Contains the following raw materials in parts by weight: Barrier layer: 60-90 parts modified nano-alumina, 20-30 parts silane coupling agent KH-560; Functional layer: 18-28 parts of nano-silver, 16-22 parts of compound antioxidant, 4-10 parts of nano-titanium dioxide; Heat sealing layer: 22-32 parts of modified polylactic acid, 2-6 parts of graphene quantum dots, 12-16 parts of methyl methacrylate-butadiene-styrene copolymer, 3-6 parts of dodecyltrimethylammonium chloride, 10-14 parts of resorcinol tetraphenyl diphosphate, and 7-17 parts of stearic acid intercalated modified nano-montmorillonite.

2. The high-barrier alumina composite film for food packaging according to claim 1, characterized in that: The modified nano-alumina is prepared in the following specific steps: A1. Add deionized water to a beaker, then slowly pour concentrated sulfuric acid into it and stir evenly. Continue adding nano-alumina powder while stirring. Place the beaker in an ultrasonic cleaner for ultrasonic dispersion. Transfer the suspension to a reactor, heat to 80°C, and stir for 3 hours. After the reaction, cool to room temperature, transfer the suspension to a centrifuge tube, and centrifuge. Discard the supernatant, wash the precipitate with deionized water, and then dry it in a vacuum drying oven for 12 hours to obtain hydroxylated alumina. A2. Add an ethanol-water mixture to a three-necked flask, slowly add γ-aminopropyltriethoxysilane dropwise while stirring at room temperature, and continue stirring for 1 hour after the addition is completed; add the hydroxylated alumina powder to the above hydrolyzate, raise the temperature to 80°C, and stir to react for 4 hours; after the reaction is completed, wait for the solution to cool to room temperature and transfer it to a centrifuge tube, centrifuge, and wash the precipitate with anhydrous ethanol. After each washing, centrifuge and transfer the precipitate to a vacuum drying oven and dry it for 8 hours to obtain silane-coated alumina; A3. Add xylene and silane-coated alumina powder into a four-necked flask, introduce nitrogen protection, stir and heat to 110°C; dissolve dodecafluoroheptyl methacrylate and dibenzoyl peroxide in xylene, and add them dropwise to the above reaction system through a constant pressure dropping funnel. After the addition is complete, continue stirring and react for 5 hours; after the reaction is completed, cool to room temperature, slowly pour into excess acetone to precipitate the product, collect the solid product by suction filtration through a sand core funnel, wash with acetone, and then transfer to a vacuum drying oven to dry for 8 hours to obtain fluorine-modified alumina.

3. The high-barrier alumina composite film for food packaging according to claim 2, characterized in that: In step A1, the ratio of deionized water, concentrated sulfuric acid, and nano-alumina powder is 300 mL: 5 mL: 25 g; the ultrasonic cleaning machine is set to a frequency of 40 kHz for ultrasonic dispersion for 40 minutes; the stirring speed in the reactor is 400 r / min; the centrifugal speed is 8000 r / min, and the centrifugation is carried out for 10 minutes; the precipitate is washed three times with deionized water and dried at 60°C; In step A2, the ratio of the ethanol-water mixture, γ-aminopropyltriethoxysilane, and hydroxylated alumina powder is 300 mL:5 mL:25 g; the volume ratio of ethanol to water is 7:3; the hydrolyzate is stirred at a speed of 200 r / min, the speed during heating and stirring is 500 r / min, the centrifugal speed is 8000 r / min, and the centrifugation is performed for 10 minutes; the precipitate is washed three times with anhydrous ethanol; and the drying temperature is 80°C.

4. The high-barrier alumina composite film for food packaging according to claim 2, wherein: In step A3, the ratio of xylene to silane-coated alumina powder is 200 mL:25 g, and the stirring speed is 300 r / min; the ratio of dodecafluoroheptyl methacrylate, dibenzoyl peroxide, and xylene is 8 g:0.5 g:30 mL; the solution dropwise addition rate is 1 mL / min; the solid product is washed three times with acetone, and the drying temperature is 60°C.

5. The high-barrier alumina composite film for food packaging according to claim 1, wherein: The modified polylactic acid is specifically prepared in the following steps: B1. Add dichloromethane and polylactic acid particles to a three-necked flask, stir at room temperature until completely dissolved, then add phosphotungstic acid catalyst, raise the temperature to 45°C and keep stirring, slowly add hydrogen peroxide solution dropwise through a constant pressure dropping funnel, raise the temperature to 65°C after the addition is complete, and stir and react for 5 hours; after the reaction is completed, cool to room temperature, transfer to a separatory funnel, add saturated salt water, shake and wash, and then stand to separate, collect the lower organic phase, wash with saturated salt water, and then transfer the organic phase to a rotary evaporator, remove dichloromethane by vacuum distillation, and transfer the residue to a vacuum drying oven and dry for 4 hours to obtain epoxy-modified polylactic acid; B2. Sodium alginate was added to deionized water and stirred at room temperature until completely dissolved to prepare a sodium alginate aqueous solution; poly (N-isopropylacrylamide) solution and dodecyltrimethylammonium chloride were separately taken, and deionized water was added and mixed uniformly; tetrahydrofuran and epoxy-modified polylactic acid were added to a four-necked flask, stirred at room temperature to dissolve, and the sodium alginate aqueous solution was slowly poured into the tetrahydrofuran solution of epoxy-modified polylactic acid, and a high-speed shear emulsifier was used to form a stable oil-water emulsion; a mixed solution of poly (N-isopropylacrylamide) and dodecyltrimethylammonium chloride was added to the emulsion, and stirring was continued for 5 minutes; calcium chloride solution was slowly added dropwise by a peristaltic pump, and stirring was continued for 2 hours after the addition was complete to fully cross-link the microcapsules, and the emulsion was transferred to a centrifuge tube for centrifugation, the supernatant was discarded, the precipitate was washed with deionized water, and then transferred to a vacuum drying oven for drying for 10 hours to obtain antistatic microcapsule-modified polylactic acid.

6. The high-barrier alumina composite film for food packaging according to claim 5, characterized in that: In step B1, the ratio of dichloromethane, polylactic acid particles, phosphotungstic acid, and hydrogen peroxide solution is 200 mL: 60 g: 0.8 g: 35 mL; the initial stirring speed is 300 r / min; the mass fraction of the hydrogen peroxide solution is 35%; the dropping speed is 1 mL / min, and the stirring speed during the dropwise addition is 500 r / min; the vacuum distillation temperature is 40° C.; and the drying temperature is 60° C. In step B2, the ratio of sodium alginate and deionized water is 20 g:647 mL; the ratio of poly (N-isopropylacrylamide) solution, dodecyltrimethylammonium chloride, and deionized water is 12 mL:10 g:50 mL; the mass fraction of poly (N-isopropylacrylamide) solution is 15%; the ratio of tetrahydrofuran and epoxy-modified polylactic acid is 100 mL:50 g; the stirring speed is 300 r / min; the emulsification speed is 10,000 r / min, and the emulsification time is 10 min; the concentration of calcium chloride solution is 0.2 mol / L, the amount is 15 mL, and the dropping speed is 5 mL / min; the centrifugal speed is 10,000 r / min, and the centrifugation time is 10 min; the precipitate is washed three times with deionized water, and the drying temperature is 40°C.

7. The high-barrier alumina composite film for food packaging according to claim 1, wherein: The compound antioxidant is a hindered phenol antioxidant 1010 and a phosphite antioxidant 168 compounded in a mass ratio of 1:1; the mass ratio of stearic acid to nano-montmorillonite in the stearic acid intercalated modified nano-montmorillonite is 1:

3.

8. A method for preparing a high-barrier alumina composite film for food packaging, characterized in that: The specific steps include: S1. Raw material pretreatment Outer layer preparation: Polyethylene terephthalate film is selected as the outer substrate and corona treated to increase the surface tension; Barrier layer raw material mixing: The modified nano-alumina and the modified silane coupling agent were placed in a stirred tank, and then an ethanol-acetone mixed solvent was added and stirred evenly to prepare a slurry with a solid content of 20%; Heat sealing layer raw material preparation: Weigh modified polylactic acid, graphene quantum dots, methyl methacrylate-butadiene-styrene copolymer, dodecyltrimethylammonium chloride, resorcinol tetraphenyl diphosphate, and stearic acid intercalated modified nano-montmorillonite according to weight, put all the raw materials into a high-speed mixer, and stir and mix them evenly; Preparation of functional layer raw materials: Nano-silver particles, compound antioxidants and nano-titanium dioxide are mixed, and ethyl acetate is added as a solvent to prepare a functional layer coating with a solid content of 15%. During the mixing process, ultrasonic dispersion is performed to ensure uniform dispersion; S2. Preparation of each layer Barrier coating: The prepared barrier layer slurry was coated on the pretreated PET outer film using a gravure coater, with the wet film thickness controlled to be 30 μm. After coating, the film was sent to a drying oven for drying to fully evaporate the solvent to form a barrier layer, thereby obtaining a polyethylene terephthalate / Al2O3 composite outer layer. Heat seal layer extrusion: The prepared heat-sealing layer raw material is put into a twin-screw extruder, and the temperature gradient and screw speed are set. The raw material undergoes the processes of conveying, melting, mixing, and homogenization in the extruder in sequence, and is finally extruded from the die head to form a heat-sealing layer film. The extruded film is cooled and shaped by a cooling roller; Functional layer coating: The functional layer coating is evenly coated on a polyethylene film with a thickness of 10 μm by gravure printing to form a functional layer / polyethylene composite film; S3, three-layer composite First, a solvent-free polyurethane adhesive is applied to the coating roller of the composite equipment. Then, the three layers of film are fed into the composite roller in sequence for composite. After the composite is completed, the composite film is sent to the aging chamber for aging for 24 hours to fully solidify the adhesive and form a high-barrier alumina composite film for food packaging.

9. The method for preparing a high-barrier alumina composite film for food packaging according to claim 8, wherein: In step S1, the thickness of the polyethylene terephthalate film of the outer layer is 20-30 μm, and the surface tension after corona treatment is 56 mN / m; the mass ratio of the modified nano-alumina to the modified silane coupling agent in the barrier layer is 3:1, the volume ratio of the ethanol-acetone mixed solvent is 5:3, the stirring speed is 300-500 r / min, and the stirring time is 30-60 min; the stirring speed of the heat sealing layer raw material in the high-speed mixer is 800-1200 r / min, and the stirring time is 15-20 min; The functional layer raw materials are ultrasonically dispersed for 20-30 minutes.

10. The method for preparing a high-barrier alumina composite film for food packaging according to claim 8, wherein: In the step S2, when the barrier layer is coated, the wet film thickness is controlled to be 30-40 μm, the coating speed is 5-10 m / min, the line number of the anilox roller is 300-400 lines / inch, and the film is dried at 120°C for 5 minutes; the temperature of the twin-screw extruder for extruding the heat-sealing layer is: 130-140°C in zone 1, 150-160°C in zone 2, 170-180°C in zone 3, 190-200°C in zone 4, and 210-220°C in zone 5, the screw speed is 250-350 r / min, the thickness of the heat-sealing layer film extruded from the die head is 25 μm, and the cooling water temperature is controlled at 5-10°C; the coating amount of the functional layer coating is , drying temperature is 80-100℃, drying time is 3-5min; In the step S3, the coating amount is controlled to be The composite conditions are 120℃, 0.8MPa pressure, the composite speed is controlled at 10-15m / min, and the composite film is matured at 40-50℃.

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