Ultra-high barrier multi-layer co-extruded film for food packaging and preparation method thereof

Abstract

The present invention discloses an ultra-high barrier multilayer co-extruded film for food packaging and a preparation method thereof, and belongs to the field of multilayer film processing technology. The present invention is used to solve the technical problems that the barrier performance of the multilayer co-extruded film in the prior art is limited, the oxygen content in the packaging environment cannot be reduced, the food quality assurance time is short, and the mechanical properties of the existing multilayer co-extruded film need to be further improved. The ultra-high barrier multilayer co-extruded film for food packaging includes an upper surface layer, a core layer and a lower surface layer arranged in sequence from top to bottom, and the upper surface layer is composed of ethylene-vinyl alcohol copolymer, nylon 6, modified graphene and additives in a dosage ratio of 50g:18g:5g:1g. The multilayer co-extruded film prepared by the present invention has good mechanical properties while also having good oxygen barrier properties, and can have a stable fresh-keeping effect on spinach and beef.

Description

Technical Field

[0001] The present invention relates to the technical field of multilayer film processing, and in particular to an ultra-high barrier multilayer co-extruded film for food packaging and a preparation method thereof. Background Art

[0002] Ultra-high barrier multi-layer co-extruded film is a new type of packaging material. It is formed by stacking layers of different materials using a multi-layer co-extrusion film blown film machine. Multi-layer co-extruded film offers excellent oxygen and moisture resistance and barrier properties. In the food packaging industry, the use of high-quality multi-layer co-extruded film as a packaging material to protect food quality and extend its shelf life has become a significant industry trend.

[0003] Food packaging materials in the existing technology, such as polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC), all have limited barrier properties and are unable to effectively protect the quality of food for a long time. In addition, multi-layer co-extruded films are usually composed of multiple layers of films, and there are certain differences in the compatibility between the film layers. As a result, the mechanical properties of the multi-layer co-extruded films need to be further improved. Existing food packaging materials are mostly improved in terms of their barrier properties to oxygen and water vapor. However, small oxygen molecules always have the phenomenon of penetration, which cannot reduce the oxygen content in the packaging environment, resulting in the need for further improvement in the preservation performance of food materials.

[0004] In view of the technical defects in this aspect, a solution is now proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide an ultra-high barrier multi-layer co-extruded film for food packaging and a preparation method thereof, so as to solve the technical problems in the prior art that multi-layer co-extruded films have limited barrier properties, cannot reduce the oxygen content in the packaging environment, resulting in a short food quality assurance period, and the mechanical properties of the existing multi-layer co-extruded films need to be further improved.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] An ultra-high barrier multi-layer co-extruded film for food packaging, comprising an upper surface layer, a core layer, and a lower surface layer arranged in order from top to bottom, wherein the upper surface layer comprises ethylene-vinyl alcohol copolymer, nylon 6, modified graphene, and additives in a ratio of 50g:18g:5g:1g; the core layer comprises ethylene-vinyl alcohol copolymer, modified polypropylene, modified graphene, and additives in a ratio of 50g:17g:5g:1g; and the lower surface layer comprises polyvinylidene fluoride, modified polypropylene, modified composite microspheres, and additives in a ratio of 50g:20g:8g:1g.

[0008] The modified composite microspheres are prepared by the following steps:

[0009] A1, trimethoxysilyl methyl mercaptan, trimethoxysilane, tetramethoxysilane and anhydrous ethanol were added to a three-necked flask, stirred evenly to obtain a dropping solution, and set aside;

[0010] Purified water, 10 vol% ammonia water, fatty alcohol polyoxyethylene ether and sodium dodecylbenzene sulfonate were added to a three-necked flask and stirred. The temperature of the three-necked flask was raised to 50-60° C. The dropping liquid was slowly added dropwise to the three-necked flask. After the addition was complete, the mixture was kept warm for 3-4 hours and post-treated to obtain polysiloxane microspheres.

[0011] A2. Add polysiloxane microspheres, ferric chloride, titanium tetrachloride and purified water to a three-necked flask and ultrasonically disperse for 60-80 min. Maintaining the ultrasonic dispersion state, add ammonia water dropwise to the three-necked flask to adjust the pH of the system to 10-12. Ultrasonic dispersion is performed at room temperature for 2-3 h, and post-processing is performed to obtain composite silane microspheres.

[0012] A3. Add composite silane microspheres, anhydrous ethanol and KH-550 into a three-necked flask, ultrasonically disperse for 30-50 minutes, add 10 vol% ammonia water into the three-necked flask, stir at room temperature for 2-3 hours, and post-treat to obtain modified composite microspheres.

[0013] Furthermore, in step A1, the amount ratio of trimethoxysilyl methyl mercaptan, trimethoxysilane, tetramethoxysilane and anhydrous ethanol is 2g:3g:2g:10g; the amount ratio of purified water, 10vol% ammonia water, fatty alcohol polyoxyethylene ether and sodium dodecylbenzenesulfonate to the dropping liquid is 100g:8g:3g:2g:40g, and the post-processing operation includes: after the reaction is completed, the temperature of the three-necked flask is lowered to room temperature, filtered, the filter cake is washed three times with a saturated sodium carbonate solution, and then washed with purified water until neutral, the filter cake is transferred to a drying oven at a temperature of 70-80°C, and vacuum dried to constant weight to obtain polysiloxane microspheres; the polysiloxane microspheres, trimethoxysilane and tetramethoxysilane in step A2 are added. The amount ratio of ferric chloride, titanium tetrachloride and purified water is 8g:2g:1g:100mL, and the post-processing operation includes: after the reaction is completed, filtering with suction, washing the filter cake with purified water until neutral, transferring the filter cake to a drying oven at a temperature of 65-75°C, and vacuum drying to constant weight to obtain composite silane microspheres; in step A3, the amount ratio of composite silane microspheres, anhydrous ethanol, KH-550 and 10vol% ammonia water is 3g:15mL:2g:5mL, and the post-processing operation includes: after the reaction is completed, filtering with suction, washing the filter cake with purified water until neutral, transferring the filter cake to a drying oven at a temperature of 65-75°C, and vacuum drying to constant weight to obtain modified composite microspheres.

[0014] Furthermore, the preparation method of modified polypropylene is as follows: polypropylene and N,N-dimethylformamide are added to a three-necked flask, sealed and stirred for 20-22 hours, the temperature of the three-necked flask is increased to 60-70°C, the mixed solution is added to the three-necked flask, stirred for 30-50 minutes, the reaction system is transferred to a torque rheometer, the torque rheometer speed is set to 50-60r / min, the temperature is set to 100-110°C, the reaction is carried out for 3-5 hours, and the modified polypropylene is obtained by post-processing.

[0015] Furthermore, the mixed solution is obtained by adding maleic anhydride, dicumyl peroxide and N,N-dimethylformamide in a ratio of 3g:1g:4g to a beaker and stirring to dissolve; the polypropylene, N,N-dimethylformamide and the mixed solution are used in a ratio of 2g:15g:1g, and the post-processing operation includes: after the reaction is completed, the temperature of the torque rheometer is lowered to room temperature, the reaction system in the torque rheometer is transferred to a beaker, toluene is added to the beaker in a weight ratio of 1:10, the temperature of the beaker is increased to 55-65°C, and the system is stirred until it is dissolved, methanol is slowly added to the beaker, stirred for 10-20 minutes, the temperature of the beaker is lowered to room temperature, and filtered, the filter cake is washed three times with methanol and then dried, and the filter cake is transferred to a drying oven at a temperature of 60-70°C and dried to constant weight to obtain modified polypropylene.

[0016] Furthermore, the preparation method of modified graphene is as follows: graphene oxide, 2-hydroxyethylamine, and deionized water are added to a three-necked flask, ultrasonically dispersed for 30-40 minutes, the three-necked flask is fixed on an iron stand with a mechanical stirrer, stirred, 0.1 mol / L hydrochloric acid is added to the three-necked flask, the pH of the system is adjusted to 8-9, the reaction is carried out at room temperature for 20-22 hours, and the modified graphene is obtained by post-treatment.

[0017] Furthermore, the usage ratio of graphene oxide, 2-hydroxyethylamine, and deionized water is 3g:2g:50mL, and the post-treatment operation includes: after the reaction is completed, filtering, washing the filter cake with deionized water and anhydrous ethanol three times respectively, and then drying, transferring the filter cake to a drying oven at a temperature of 60-80°C, and vacuum drying to constant weight to obtain modified graphene.

[0018] Furthermore, the additive is composed of a lubricant, a dispersant, an antioxidant and an antioxidant in a dosage ratio of 2g:1g:1g:1g, wherein the lubricant is one or more of butyl stearate, oleamide, and ethylene bisstearamide; the dispersant is one or more of zinc stearate, calcium stearate, magnesium stearate, and cadmium stearate; the antioxidant is one or more of antioxidant DPPD, antioxidant PPD, and antioxidant H; and the antioxidant is one or more of butylated hydroxyanisole, dibutylhydroxytoluene, and tert-butylhydroquinone.

[0019] The invention discloses a method for preparing an ultra-high barrier multi-layer co-extruded film for food packaging. The raw materials constituting the upper surface layer, the core layer and the lower surface layer are respectively added into three twin-screw extruders. After melt extrusion, the raw materials are fed into a multi-layer co-extrusion film blowing machine for extrusion and film blowing. The film is passed through a casting cooling device, a thickness measuring and control device, a corona treatment device, a cooling treatment device and a vacuum box. The obtained multi-layer film is then processed by a roller-type shaping device, a traction and trimming device and a winding device to obtain a multi-layer co-extruded film with a thickness of 20-25 μm. The thickness of the upper surface layer is 5-7 μm, the thickness of the core layer is 5-7 μm, and the thickness of the lower surface layer is 10-12 μm.

[0020] Furthermore, the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials for the upper surface layer are 260°C, 265°C, 270°C, 270°C, 270°C, and 265°C respectively; the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials for the core layer are 250°C, 255°C, 260°C, 260°C, 260°C, and 265°C respectively; the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials for the lower surface layer are 240°C, 245°C, 250°C, 250°C, 250°C, and 245°C respectively.

[0021] The present invention has the following beneficial effects:

[0022] 1. The multi-layer co-extruded film of the present invention is prepared by melt-extrusion of the raw materials constituting the upper surface layer, the core layer and the lower surface layer, and co-extrusion molding in a multi-layer co-extrusion film blowing machine. By optimizing the composition of the lower surface layer, modified composite microspheres containing ferroferric oxide and titanium dioxide are added to the raw materials constituting the lower surface layer. Both ferroferric oxide and titanium dioxide have antibacterial properties, which can inhibit the growth of microorganisms and help reduce bacterial and mold contamination on the surface of food. In addition, ferroferric oxide and titanium dioxide can also act as oxidants to reduce the oxygen content in the food sealing system, slow down the oxidation reaction in the food, and maintain their taste and freshness. In addition, by controlling the composition ratio of ferroferric oxide and titanium dioxide in the co-extruded film, the co-extruded film can maintain transparency while achieving a good preservation effect. By optimizing the composition of the core layer and the upper surface layer, the core layer and the upper surface layer are matched with each other to form a barrier system with synergistic cooperation, thereby improving the gas barrier performance.

[0023] 2. When preparing the multi-layer co-extruded film of the present invention, trimethoxysilyl methyl mercaptan, trimethoxysilane and tetramethoxysilane are reacted in an alkaline emulsification system to generate polysilane microspheres with a porous structure. The mercapto group on the polysiloxane is a functional group containing a sulfur atom, which usually has strong sulfur affinity and metal affinity, and can react chemically with the surface of metals, metal oxides, etc., thereby improving the adsorption performance of the silane microspheres on materials such as ferroferric oxide and titanium dioxide, so that the iron ions and titanium ions in the reaction system grow on the composite silane microspheres in the form of surface growth in an ammonia environment, and the composite silane microspheres are modified by KH-550 to prepare a KH-550 modified multi-layer co-extruded film. Modified composite microspheres are modified to improve the dispersibility of the modified composite microspheres in the mixed system. Silane microspheres modified with ferroferric oxide and titanium dioxide can introduce tiny pore structures into the film or cause changes in the microstructure of the material to form pore structures in the film. These pores can increase the diffusion rate of gas molecules and improve the air permeability of the film. Maleic anhydride modified polypropylene can increase the hydrophilicity of the film. Hydrophilic films usually have higher air permeability than hydrophobic films because they allow gas molecules to pass through more easily, so that during the food preservation process of the multi-layer co-extruded film, oxygen in the food preservation environment can penetrate into the lower surface layer, reducing the oxygen in the food preservation environment and improving the preservation effect.

[0024] 3. When preparing the multi-layer co-extruded film of the present invention, graphene oxide is modified by 2-hydroxyethylamine to prepare modified graphene modified with 2-hydroxyethylamine. Ethylene-vinyl alcohol copolymer, nylon 6, modified polypropylene, and modified graphene all have similar polarities and are easier to mix together to form a uniform dispersion system. In addition, ethylene-vinyl alcohol copolymer, nylon 6, modified graphene, and modified polypropylene all have good gas barrier properties and water vapor barrier properties. The combination of modified graphene and modified polypropylene can further improve the gas barrier performance and water vapor barrier performance of the film layer; when preparing a multi-layer co-extruded film, modified polypropylene is used as a compatibilizer between the core layer and the lower surface layer to improve the compatibility between the core layer and the lower surface layer, and ethylene-vinyl alcohol copolymer is used as a compatibilizer between the core layer and the upper surface layer to improve the compatibility between the core layer and the upper surface layer, and the extrusion temperature of the upper surface layer, the core layer and the lower surface layer is optimized, so that the upper surface layer, the core layer and the lower surface layer form a stable co-extruded film, thereby improving the mechanical properties of the multi-layer co-extruded film. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only 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.

[0026] Figure 1 This is a schematic diagram of the partially cutaway structure of the multi-layer co-extruded film provided by the present invention.

[0027] In the figure: 100, upper surface layer; 200, core layer; 300, lower surface layer. DETAILED DESCRIPTION

[0028] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. 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 creative efforts are within the scope of protection of the present invention.

[0029] Example 1

[0030] See also Figure 1 The method for preparing the ultra-high barrier multi-layer co-extruded film for food packaging provided in this embodiment comprises the following steps:

[0031] S1. Preparation of modified composite microspheres

[0032] Weigh: 10 g of trimethoxysilyl methyl mercaptan, 15 g of trimethoxysilane, 10 g of tetramethoxysilane and 50 mL of anhydrous ethanol into a three-necked flask, stir evenly to obtain a dropwise solution, and set aside;

[0033] Weigh: 500g of purified water, 40g of 10vol% ammonia water, 15g of fatty alcohol polyoxyethylene ether and 10g of sodium dodecylbenzenesulfonate are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 50°C. 200g of the dropwise addition liquid is slowly added dropwise to the three-necked flask. After the addition is complete, the reaction is kept warm for 3h. The temperature of the three-necked flask is lowered to room temperature, filtered, and the filter cake is washed three times with a saturated sodium carbonate aqueous solution and then washed with purified water until neutral. The filter cake is transferred to a drying oven at a temperature of 70°C and vacuum dried to constant weight to obtain polysiloxane microspheres;

[0034] Weigh 20 g of polysiloxane microspheres, 5 g of ferric chloride, 2.5 g of titanium tetrachloride, and 250 mL of purified water into a three-necked flask and ultrasonically disperse for 60 min. Maintaining the ultrasonic dispersion state, add ammonia water dropwise to the three-necked flask to adjust the system pH to 10. Ultrasonic dispersion is carried out at room temperature for 2 h, and the filter cake is washed with purified water until neutral. The filter cake is transferred to a drying oven at a temperature of 65°C and vacuum dried to constant weight to obtain composite silane microspheres.

[0035] Weigh: 21 g of composite silane microspheres, 105 mL of anhydrous ethanol and 14 g of KH-550 were added to a three-necked flask and ultrasonically dispersed for 30 min. 35 mL of 10 vol% ammonia water was added to the three-necked flask and stirred at room temperature for 2 h. After post-treatment, the filter cake was filtered and washed with purified water until neutral. The filter cake was transferred to a drying oven at a temperature of 65°C and vacuum dried to constant weight to obtain modified composite microspheres.

[0036] S2. Preparation of modified polypropylene

[0037] Add maleic anhydride, dicumyl peroxide, and N,N-dimethylformamide in a ratio of 3 g:1 g:4 g into a beaker, stir and dissolve to obtain a mixed solution, which is set aside;

[0038] Weigh: 40 g of polypropylene and 300 g of N,N-dimethylformamide are added to a three-necked flask, sealed and stirred for 20 hours, the temperature of the three-necked flask is raised to 60°C, 20 g of the mixed solution is added to the three-necked flask, stirred for 30 minutes, and the reaction system is transferred to a torque rheometer. The torque rheometer speed is set to 50 r / min and the temperature is 100°C. The reaction is carried out for 3 hours. The temperature of the torque rheometer is lowered to room temperature. The reaction system in the torque rheometer is transferred to a beaker, and toluene is added to the beaker at a weight ratio of 1:10. The temperature of the beaker is raised to 55°C and stirred until the system is dissolved. Methanol is slowly added to the beaker and stirred for 10 minutes. The temperature of the beaker is lowered to room temperature. Filter, wash the filter cake three times with methanol and then dry it. Transfer it to a drying oven at a temperature of 60°C and dry it to constant weight to obtain modified polypropylene.

[0039] S3. Preparation of modified graphene

[0040] Weigh: 15 g of graphene oxide, 10 g of 2-hydroxyethylamine, and 250 mL of deionized water into a three-necked flask, ultrasonically disperse for 30 min, fix the three-necked flask on an iron stand with mechanical stirring, stir, add 0.1 mol / L hydrochloric acid to the three-necked flask, adjust the pH of the system to 8, react at room temperature for 20 h, filter, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and then dry it. Transfer the filter cake to a drying oven at a temperature of 60°C and vacuum dry it to constant weight to obtain modified graphene.

[0041] S4. Preparation of raw materials for the upper surface layer, core layer, and lower surface layer

[0042] Weigh and mix 500 g of ethylene-vinyl alcohol copolymer, 180 g of nylon 6, 50 g of modified graphene, 4 g of butyl stearate, 2 g of zinc stearate, 2 g of antioxidant DPPD, and 2 g of butylated hydroxyanisole to obtain the raw materials for the upper surface layer 100;

[0043] Weigh and mix 500 g of ethylene-vinyl alcohol copolymer, 170 g of modified polypropylene, 80 g of modified graphene, 4 g of butyl stearate, 2 g of zinc stearate, 2 g of antioxidant DPPD, and 2 g of butylated hydroxyanisole to obtain the raw materials for the core layer 200;

[0044] The lower surface layer 300 is prepared by weighing: 500 g of polyvinylidene fluoride, 200 g of modified polypropylene, 80 g of modified composite microspheres, 4 g of butyl stearate, 2 g of zinc stearate, 2 g of antioxidant DPPD and 2 g of butylated hydroxyanisole, and mixing them evenly to obtain the constituent raw materials of the lower surface layer 300.

[0045] S5. Preparation of multi-layer co-extruded film

[0046] The raw materials constituting the upper surface layer 100, the core layer 200 and the lower surface layer 300 are added to three twin-screw extruders respectively. The temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials of the upper surface layer 100 are 260°C, 265°C, 270°C, 270°C, 270°C and 265°C respectively; the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials of the core layer 200 are 250°C, 255°C, 260°C, 260°C, 260°C and 265°C respectively; the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials of the lower surface layer 300 are 250°C, 255°C, 260°C, 260°C, 265°C respectively. The temperatures of the sections are 240°C, 245°C, 250°C, 250°C, 250°C, and 245°C, respectively. The raw materials constituting the upper surface layer 100, the core layer 200, and the lower surface layer 300 are melt-extruded and then enter into a multi-layer co-extrusion film blowing machine for extrusion and film blowing. The film is passed through a casting cooling device, a thickness measuring and control device, a corona treatment device, a cooling treatment device, and a vacuum box. The obtained multi-layer film is then processed by a roller-type shaping device, a traction and trimming device, and a winding device to obtain a multi-layer co-extruded film with a thickness of 20-25 μm, wherein the thickness of the upper surface layer 100 is 5-7 μm, the thickness of the core layer 200 is 5-7 μm, and the thickness of the lower surface layer 300 is 10-12 μm.

[0047] Example 2

[0048] See also Figure 1 The method for preparing the ultra-high barrier multi-layer co-extruded film for food packaging provided in this embodiment comprises the following steps:

[0049] S1. Preparation of modified composite microspheres

[0050] Weigh: 10 g of trimethoxysilyl methyl mercaptan, 15 g of trimethoxysilane, 10 g of tetramethoxysilane and 50 mL of anhydrous ethanol into a three-necked flask, stir evenly to obtain a dropwise solution, and set aside;

[0051] Weigh: 500g of purified water, 40g of 10vol% ammonia water, 15g of fatty alcohol polyoxyethylene ether and 10g of sodium dodecylbenzenesulfonate are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 55°C. 200g of the dropwise addition liquid is slowly added dropwise to the three-necked flask. After the addition is complete, the reaction is kept warm for 3.5h. The temperature of the three-necked flask is lowered to room temperature, filtered, and the filter cake is washed three times with a saturated sodium carbonate aqueous solution and then washed with purified water until neutral. The filter cake is transferred to a drying oven at a temperature of 75°C and vacuum dried to constant weight to obtain polysiloxane microspheres;

[0052] Weigh: 20 g of polysiloxane microspheres, 5 g of ferric chloride, 2.5 g of titanium tetrachloride, and 250 mL of purified water into a three-necked flask, and ultrasonically disperse for 70 min. Maintaining the ultrasonic dispersion state, add ammonia water dropwise to the three-necked flask to adjust the system pH to 11, and ultrasonically disperse at room temperature for 2.5 h. Filter, wash the filter cake with purified water until neutral, transfer the filter cake to a drying oven at 70°C, and vacuum dry to constant weight to obtain composite silane microspheres;

[0053] Weigh: 21 g of composite silane microspheres, 105 mL of anhydrous ethanol and 14 g of KH-550 were added to a three-necked flask and ultrasonically dispersed for 40 min. 35 mL of 10 vol% ammonia water was added to the three-necked flask and stirred at room temperature for 2.5 h. After post-treatment, the filter cake was filtered and washed with purified water until neutral. The filter cake was transferred to a drying oven at 70°C and vacuum dried to constant weight to obtain modified composite microspheres.

[0054] S2. Preparation of modified polypropylene

[0055] Add maleic anhydride, dicumyl peroxide, and N,N-dimethylformamide in a ratio of 3 g:1 g:4 g into a beaker, stir and dissolve to obtain a mixed solution, which is set aside;

[0056] Weigh: 40 g of polypropylene and 300 g of N,N-dimethylformamide are added to a three-necked flask, sealed and stirred for 21 hours, the temperature of the three-necked flask is raised to 65°C, 20 g of the mixed solution is added to the three-necked flask, and stirred for 40 minutes. The reaction system is transferred to a torque rheometer, and the torque rheometer speed is set to 55 r / min and the temperature is 105°C. The reaction is carried out for 4 hours. The temperature of the torque rheometer is lowered to room temperature, and the reaction system in the torque rheometer is transferred to a beaker. Toluene is added to the beaker at a weight ratio of 1:10, the temperature of the beaker is raised to 60°C, and stirred until the system is dissolved. Methanol is slowly added to the beaker, stirred for 15 minutes, the temperature of the beaker is lowered to room temperature, and filtered. The filter cake is washed three times with methanol and then dried. It is transferred to a drying oven at a temperature of 65°C and dried to constant weight to obtain modified polypropylene.

[0057] S3. Preparation of modified graphene

[0058] Weigh: 15 g of graphene oxide, 10 g of 2-hydroxyethylamine, and 250 mL of deionized water into a three-necked flask, ultrasonically disperse for 35 min, fix the three-necked flask on an iron stand with a mechanical stirrer, stir, add 0.1 mol / L hydrochloric acid to the three-necked flask, adjust the pH of the system to 8.5, react at room temperature for 21 h, filter, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and then drain, transfer the filter cake to a drying oven at a temperature of 70 ° C, and vacuum dry to constant weight to obtain modified graphene.

[0059] S4. Preparation of raw materials for the upper surface layer, core layer, and lower surface layer

[0060] Weigh and mix 500 g of ethylene-vinyl alcohol copolymer, 180 g of nylon 6, 50 g of modified graphene, 4 g of oleamide, 2 g of calcium stearate, 2 g of antioxidant PPD, and 2 g of butylated hydroxytoluene to obtain the raw materials for the upper surface layer 100;

[0061] Weigh and mix 500 g of ethylene-vinyl alcohol copolymer, 170 g of modified polypropylene, 80 g of modified graphene, 4 g of oleamide, 2 g of calcium stearate, 2 g of antioxidant PPD, and 2 g of butylated hydroxytoluene to obtain the raw materials for the core layer 200;

[0062] The lower surface layer 300 is prepared by weighing: 500 g of polyvinylidene fluoride, 200 g of modified polypropylene, 80 g of modified composite microspheres, 4 g of oleamide, 2 g of calcium stearate, 2 g of antioxidant PPD and 2 g of butylated hydroxytoluene, and mixing them evenly to obtain the constituent raw materials of the lower surface layer 300 .

[0063] S5. Preparation of multi-layer co-extruded film

[0064] The raw materials constituting the upper surface layer 100, the core layer 200 and the lower surface layer 300 are added to three twin-screw extruders respectively. The temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials of the upper surface layer 100 are 260°C, 265°C, 270°C, 270°C, 270°C and 265°C respectively; the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials of the core layer 200 are 250°C, 255°C, 260°C, 260°C, 260°C and 265°C respectively; the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials of the lower surface layer 300 are 250°C, 255°C, 260°C, 260°C, 265°C respectively. The temperatures of the sections are 240°C, 245°C, 250°C, 250°C, 250°C, and 245°C, respectively. The raw materials constituting the upper surface layer 100, the core layer 200, and the lower surface layer 300 are melt-extruded and then enter into a multi-layer co-extrusion film blowing machine for extrusion and film blowing. The film is passed through a casting cooling device, a thickness measuring and control device, a corona treatment device, a cooling treatment device, and a vacuum box. The obtained multi-layer film is then processed by a roller-type shaping device, a traction and trimming device, and a winding device to obtain a multi-layer co-extruded film with a thickness of 20-25 μm, wherein the thickness of the upper surface layer 100 is 5-7 μm, the thickness of the core layer 200 is 5-7 μm, and the thickness of the lower surface layer 300 is 10-12 μm.

[0065] Example 3

[0066] See also Figure 1 The method for preparing the ultra-high barrier multi-layer co-extruded film for food packaging provided in this embodiment comprises the following steps:

[0067] S1. Preparation of modified composite microspheres

[0068] Weigh: 10 g of trimethoxysilyl methyl mercaptan, 15 g of trimethoxysilane, 10 g of tetramethoxysilane and 50 mL of anhydrous ethanol into a three-necked flask, stir evenly to obtain a dropwise solution, and set aside;

[0069] Weigh: 500g of purified water, 40g of 10vol% ammonia water, 15g of fatty alcohol polyoxyethylene ether and 10g of sodium dodecylbenzenesulfonate are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 60°C. 200g of the dropwise addition liquid is slowly added dropwise to the three-necked flask. After the addition is complete, the reaction is kept warm for 4h. The temperature of the three-necked flask is lowered to room temperature, filtered, and the filter cake is washed three times with a saturated sodium carbonate aqueous solution and then washed with purified water until neutral. The filter cake is transferred to a drying oven at a temperature of 80°C and vacuum dried to constant weight to obtain polysiloxane microspheres;

[0070] Weigh 20 g of polysiloxane microspheres, 5 g of ferric chloride, 2.5 g of titanium tetrachloride, and 250 mL of purified water into a three-necked flask and ultrasonically disperse for 80 min. Maintaining the ultrasonic dispersion state, add ammonia water dropwise to the three-necked flask to adjust the system pH to 12. Ultrasonic dispersion is carried out at room temperature for 3 h, and the filter cake is washed with purified water until neutral. The filter cake is transferred to a drying oven at a temperature of 75°C and vacuum dried to constant weight to obtain composite silane microspheres.

[0071] Weigh: 21 g of composite silane microspheres, 105 mL of anhydrous ethanol and 14 g of KH-550 were added to a three-necked flask and ultrasonically dispersed for 50 min. 35 mL of 10 vol% ammonia water was added to the three-necked flask and stirred at room temperature for 3 h. After post-treatment, the filter cake was filtered and washed with purified water until neutral. The filter cake was transferred to a drying oven at a temperature of 75°C and vacuum dried to constant weight to obtain modified composite microspheres.

[0072] S2. Preparation of modified polypropylene

[0073] Add maleic anhydride, dicumyl peroxide, and N,N-dimethylformamide in a ratio of 3 g:1 g:4 g into a beaker, stir and dissolve to obtain a mixed solution, which is set aside;

[0074] Weigh: 40 g of polypropylene and 300 g of N,N-dimethylformamide are added to a three-necked flask, sealed and stirred for 22 hours, the temperature of the three-necked flask is raised to 70°C, 20 g of the mixed solution is added to the three-necked flask, and stirred for 50 minutes. The reaction system is transferred to a torque rheometer, and the torque rheometer speed is set to 60 r / min and the temperature is 110°C. The reaction is carried out for 5 hours. The temperature of the torque rheometer is lowered to room temperature, and the reaction system in the torque rheometer is transferred to a beaker. Toluene is added to the beaker at a weight ratio of 1:10, the temperature of the beaker is raised to 65°C, and stirred until the system is dissolved. Methanol is slowly added to the beaker, stirred for 20 minutes, the temperature of the beaker is lowered to room temperature, and filtered. The filter cake is washed three times with methanol and then dried. It is transferred to a drying oven at a temperature of 70°C and dried to constant weight to obtain modified polypropylene.

[0075] S3. Preparation of modified graphene

[0076] Weigh: 15 g of graphene oxide, 10 g of 2-hydroxyethylamine, and 250 mL of deionized water into a three-necked flask, ultrasonically disperse for 40 min, fix the three-necked flask on an iron stand with a mechanical stirrer, stir, add 0.1 mol / L hydrochloric acid to the three-necked flask, adjust the pH of the system to 9, react at room temperature for 22 h, filter, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and then drain, transfer the filter cake to a drying oven at a temperature of 80 ° C, and vacuum dry to constant weight to obtain modified graphene.

[0077] S4. Preparation of raw materials for the upper surface layer, core layer, and lower surface layer

[0078] Weigh and mix 500 g of ethylene-vinyl alcohol copolymer, 180 g of nylon 6, 50 g of modified graphene, 4 g of ethylene bisstearamide, 2 g of magnesium stearate, 2 g of antioxidant H, and 2 g of tert-butylhydroquinone to obtain the raw materials for the upper surface layer 100;

[0079] Weigh and mix 500 g of ethylene-vinyl alcohol copolymer, 170 g of modified polypropylene, 80 g of modified graphene, 4 g of ethylene bisstearamide, 2 g of magnesium stearate, 2 g of antioxidant H, and 2 g of tert-butylhydroquinone to obtain the raw materials for the core layer 200;

[0080] The lower surface layer 300 is prepared by weighing: 500 g of polyvinylidene fluoride, 200 g of modified polypropylene, 80 g of modified composite microspheres, 4 g of ethylene bisstearamide, 2 g of magnesium stearate, 2 g of antioxidant H and 2 g of tert-butylhydroquinone, and mixing them evenly to obtain the constituent raw materials of the lower surface layer 300.

[0081] S5. Preparation of multi-layer co-extruded film

[0082] The raw materials constituting the upper surface layer 100, the core layer 200 and the lower surface layer 300 are added to three twin-screw extruders respectively. The temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials of the upper surface layer 100 are 260°C, 265°C, 270°C, 270°C, 270°C and 265°C respectively; the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials of the core layer 200 are 250°C, 255°C, 260°C, 260°C, 260°C and 265°C respectively; the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials of the lower surface layer 300 are 250°C, 255°C, 260°C, 260°C, 265°C respectively. The temperatures of the sections are 240°C, 245°C, 250°C, 250°C, 250°C, and 245°C, respectively. The raw materials constituting the upper surface layer 100, the core layer 200, and the lower surface layer 300 are melt-extruded and then enter into a multi-layer co-extrusion film blowing machine for extrusion and film blowing. The film is passed through a casting cooling device, a thickness measuring and control device, a corona treatment device, a cooling treatment device, and a vacuum box. The obtained multi-layer film is then processed by a roller-type shaping device, a traction and trimming device, and a winding device to obtain a multi-layer co-extruded film with a thickness of 20-25 μm, wherein the thickness of the upper surface layer 100 is 5-7 μm, the thickness of the core layer 200 is 5-7 μm, and the thickness of the lower surface layer 300 is 10-12 μm.

[0083] Comparative Example 1

[0084] The difference between this comparative example and Example 1 is that the modified composite microspheres in step S4 are replaced by an equal amount of polysiloxane microspheres in step S1.

[0085] Comparative Example 2

[0086] The difference between this comparative example and Example 1 is that step S2 is omitted, and an equal amount of polypropylene replaces the modified polypropylene in step S4.

[0087] Comparative Example 3

[0088] The difference between this comparative example and Example 1 is that step S3 is eliminated and the modified graphene in step S4 is replaced by an equal amount of graphene.

[0089] Performance testing:

[0090] The barrier properties, mechanical properties, and freshness preservation properties of the multilayer co-extruded films prepared in Examples 1-3 and Comparative Examples 1-3 were tested. The gas barrier and mechanical properties were measured by measuring the tensile strength, nominal strain at break, moisture permeability, and oxygen permeability of the samples in accordance with the standard GB / T 10457-2021, "General Rules for Quality of Plastic Self-Adhesive Cling Film for Food Use." The freshness preservation performance test involved sealing fresh spinach and beef with the samples and placing them in an environment at a temperature of 10±2°C and a humidity of 50-75% for 24 hours. The samples were then subjected to sensory evaluation and graded according to the standards NY / T-1985-2011 and GB / T 17238-2008. The specific test results are shown in the table below:

[0091]

[0092]

[0093] Data Analysis:

[0094] Comparative analysis of the data in the above table shows that the multi-layer co-extruded film prepared by the present invention has a transverse tensile strength of 21.9 MPa, a longitudinal tensile strength of 27.7 MPa, a transverse nominal strain at break of 470%, and a longitudinal nominal strain at break of 576%. The preservation level of spinach and beef has reached level 1, and the moisture permeability has been reduced to 0.05 g·(m 2 24h) -1 , oxygen permeability is reduced to 0.52cm 3 ·(cm 2 ·24h·0.1MPa) -1 All test data are better than those of the comparative example, indicating that the multi-layer co-extruded film prepared by the present invention has good mechanical properties and good oxygen barrier properties, and can play a stable preservation role for spinach and beef.

[0095] The above contents are merely examples and explanations of the structure of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

[0096] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0097] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. An ultra-high barrier multi-layer co-extruded film for food packaging, comprising an upper surface layer (100), a core layer (200) and a lower surface layer (300) arranged in sequence from top to bottom, characterized in that: The upper surface layer (100) is composed of ethylene-vinyl alcohol copolymer, nylon 6, modified graphene and additives in a ratio of 50g:18g:5g:1g; the core layer (200) is composed of ethylene-vinyl alcohol copolymer, modified polypropylene, modified graphene and additives in a ratio of 50g:17g:5g:1g; and the lower surface layer (300) is composed of polyvinylidene fluoride, modified polypropylene, modified composite microspheres and additives in a ratio of 50g:20g:8g:1g; The modified composite microspheres are prepared by the following steps: A1, trimethoxysilyl methyl mercaptan, trimethoxysilane, tetramethoxysilane and anhydrous ethanol are added to a three-necked flask, stirred to obtain a dropping solution, and the mixture is standby, wherein the amount ratio of trimethoxysilyl methyl mercaptan, trimethoxysilane, tetramethoxysilane and anhydrous ethanol is 2g:3g:2g:10g; Purified water, 10 vol% ammonia water, fatty alcohol polyoxyethylene ether and sodium dodecylbenzenesulfonate are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 50-60° C., and a dropping liquid is slowly added dropwise to the three-necked flask. After the addition is complete, the mixture is kept warm for 3-4 hours and post-treated to obtain polysiloxane microspheres, wherein the amount ratio of purified water, 10 vol% ammonia water, fatty alcohol polyoxyethylene ether and sodium dodecylbenzenesulfonate to the dropping liquid is 100 g:8 g:3 g:2 g:40 g; A2, polysiloxane microspheres, ferric chloride, titanium tetrachloride and purified water were added to a three-necked flask, ultrasonically dispersed for 60-80 min, and the ultrasonic dispersion state was maintained. Ammonia water was added dropwise to the three-necked flask to adjust the pH of the system to 10-12, and ultrasonically dispersed at room temperature for 2-3 h. After post-treatment, composite silane microspheres were obtained, wherein the amount ratio of polysiloxane microspheres, ferric chloride, titanium tetrachloride and purified water was 8 g:2 g:1 g:100 mL; A3, the composite silane microspheres, anhydrous ethanol and KH-550 were added to a three-necked flask, ultrasonically dispersed for 30-50 min, 10 vol% ammonia water was added to the three-necked flask, stirred at room temperature for 2-3 h, and post-treated to obtain modified composite microspheres, wherein the amount ratio of the composite silane microspheres, anhydrous ethanol, KH-550 and 10 vol% ammonia water was 3 g:15 mL:2 g:5 mL; The preparation method of modified polypropylene comprises the following steps: adding polypropylene and N,N-dimethylformamide into a three-necked flask, sealing and stirring for 20-22 hours, raising the temperature of the three-necked flask to 60-70° C., adding a mixed solution into the three-necked flask, stirring for 30-50 minutes, transferring the reaction system into a torque rheometer, setting the torque rheometer speed to 50-60 r / min and the temperature to 100-110° C., reacting for 3-5 hours, and post-treating to obtain modified polypropylene, wherein the mixed solution is prepared by adding maleic anhydride, dicumyl peroxide, and N,N-dimethylformamide in a ratio of 3g:1g:4g into a beaker, stirring and dissolving, wherein the polypropylene, N,N-dimethylformamide, and the mixed solution are in a ratio of 2g:15g:1g; The preparation method of modified graphene is as follows: graphene oxide, 2-hydroxyethylamine, and deionized water are added to a three-necked flask, ultrasonically dispersed for 30-40 minutes, the three-necked flask is fixed on an iron stand with a mechanical stirrer, stirred, 0.1 mol / L hydrochloric acid is added to the three-necked flask, the pH of the system is adjusted to 8-9, the reaction is carried out at room temperature for 20-22 hours, and the modified graphene is obtained by post-treatment, wherein the amount ratio of graphene oxide, 2-hydroxyethylamine, and deionized water is 3g:2g:50mL.

2. The ultra-high barrier multi-layer co-extruded film for food packaging according to claim 1, characterized in that: In step A1, the post-processing operation includes: after the reaction is completed, the temperature of the three-necked flask is lowered to room temperature, suction filtration is performed, the filter cake is washed three times with a saturated sodium carbonate aqueous solution, and then washed with purified water until neutral, the filter cake is transferred to a drying oven at a temperature of 70-80°C, and vacuum dried to constant weight to obtain polysiloxane microspheres; in step A2, the post-processing operation includes: after the reaction is completed, suction filtration, the filter cake is washed with purified water until neutral, the filter cake is transferred to a drying oven at a temperature of 65-75°C, and vacuum dried to constant weight to obtain composite silane microspheres; in step A3, the post-processing operation includes: after the reaction is completed, suction filtration, the filter cake is washed with purified water until neutral, the filter cake is transferred to a drying oven at a temperature of 65-75°C, and vacuum dried to constant weight to obtain modified composite microspheres.

3. The ultra-high barrier multi-layer co-extruded film for food packaging according to claim 1, characterized in that: In the preparation method of modified polypropylene, the post-processing operation includes: after the reaction is completed, the temperature of the torque rheometer is lowered to room temperature, the reaction system in the torque rheometer is transferred to a beaker, toluene is added to the beaker at a weight ratio of 1:10, the temperature of the beaker is increased to 55-65°C, and stirring is performed until the system is dissolved, methanol is slowly added to the beaker, stirred for 10-20 minutes, the temperature of the beaker is lowered to room temperature, and filtered, the filter cake is washed three times with methanol and then dried, and it is transferred to a drying oven at a temperature of 60-70°C and dried to constant weight to obtain modified polypropylene.

4. The ultra-high barrier multi-layer co-extruded film for food packaging according to claim 1, characterized in that: In the preparation method of modified graphene, the post-processing operation includes: after the reaction is completed, filtering, washing the filter cake with deionized water and anhydrous ethanol three times respectively, and then drying it, transferring the filter cake to a drying oven at a temperature of 60-80°C, and vacuum drying to constant weight to obtain modified graphene.

5. The ultra-high barrier multi-layer co-extruded film for food packaging according to claim 1, characterized in that: The additives are composed of a lubricant, a dispersant, an antioxidant and an antioxidant in a dosage ratio of 2g:1g:1g:1g, wherein the lubricant is one or more of butyl stearate, oleamide and ethylene bisstearamide; the dispersant is one or more of zinc stearate, calcium stearate, magnesium stearate and cadmium stearate; the antioxidant is one or more of antioxidant DPPD, antioxidant PPD and antioxidant H; and the antioxidant is one or more of butylated hydroxyanisole, dibutylhydroxytoluene and tert-butylhydroquinone.

6. The method for preparing the ultra-high barrier multi-layer co-extruded film for food packaging according to any one of claims 1 to 5, characterized in that: The raw materials constituting the upper surface layer (100), the core layer (200) and the lower surface layer (300) are respectively added into three twin-screw extruders, melt-extruded and then fed into a multi-layer co-extrusion film blowing machine for extrusion and film blowing. The multi-layer film is passed through a casting cooling device, a thickness measuring and control device, a corona treatment device, a cooling treatment device and a vacuum box, and then passed through a roller shaping device, a traction trimming device and a winding device to obtain a multi-layer co-extruded film with a thickness of 20-25 μm, wherein the thickness of the upper surface layer (100) is 5-7 μm, the thickness of the core layer (200) is 5-7 μm, and the thickness of the lower surface layer (300) is 10-12 μm.

7. The method for preparing an ultra-high barrier multi-layer co-extruded film for food packaging according to claim 6, characterized in that: The temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials for the upper surface layer (100) are 260°C, 265°C, 270°C, 270°C, 270°C, and 265°C, respectively; the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials for the core layer (200) are 250°C, 255°C, 260°C, 260°C, 260°C, and 265°C, respectively; the temperatures of the six temperature sections from the feed end to the discharge end of the twin-screw extruder containing the raw materials for the lower surface layer (300) are 240°C, 245°C, 250°C, 250°C, 250°C, and 245°C, respectively.

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