PET modified atmosphere food packaging material and preparation method thereof

Abstract

The invention relates to the technical field of modified atmosphere packaging materials, in particular to a PET (Polyethylene Terephthalate) modified atmosphere food packaging material and a preparation method thereof, which are used for solving the problems that a traditional material lacks enough gas permeability regulation and control capability and is difficult to realize modified atmosphere environment control. The PET modified atmosphere food packaging material is formed by co-extruding the outer layer, the bonding layer, the blocking layer, the bonding layer and the inner layer in sequence, the PET modified atmosphere food packaging material has good blocking performance through the blocking layer, the modified atmosphere environment in a package can be accurately maintained for a long time, and the preservation period of food is effectively prolonged; the outer layer prepared from the modified PET has high stiffness, tensile resistance, puncture resistance, good flexibility and impact resistance, and is not easy to deform and damage during transportation and stacking; and the metallocene polyethylene is used as the inner layer, so that the formed film has high strength, good toughness and puncture resistance, and can effectively protect contents.

Description

Technical Field

[0001] This invention relates to the field of modified atmosphere packaging materials technology, specifically to PET modified atmosphere food packaging materials and their preparation methods. Background Technology

[0002] In the food packaging industry, modified atmosphere packaging is a commonly used preservation technology. By adjusting the gas composition inside the packaging, such as reducing the proportion of oxygen and increasing the proportion of carbon dioxide, the oxidation process in food can be effectively inhibited and the shelf life of food can be extended. Modified atmosphere packaging materials usually need to have good gas barrier properties to maintain a stable specific gas environment inside the packaging, while also having a certain mechanical strength and good transparency so that users can directly observe the state of the food inside the packaging.

[0003] Currently, commonly used modified atmosphere packaging materials mainly include plastic films such as polyethylene and polypropylene, and aluminum foil. Although these traditional materials can maintain the freshness of food to a certain extent, they often face problems such as high cost and insufficient mechanical properties in the production process of multi-layer composite materials. In addition, although these materials can provide good sealing performance, their gas barrier performance is insufficient, which fails to effectively maintain the stability of the gas concentration inside the packaging, resulting in the food quality and safety not being optimally guaranteed.

[0004] Therefore, the PET modified atmosphere food packaging material and its preparation method of the present invention are of great significance for improving the quality stability of food during storage and transportation, and for meeting consumers' needs for food safety and health. Summary of the Invention

[0005] In order to overcome the above-mentioned technical problems, the purpose of this invention is to provide PET modified atmosphere food packaging material and its preparation method, which solves the problems of insufficient mechanical properties and insufficient gas barrier properties of traditional materials.

[0006] The objective of this invention can be achieved through the following technical solutions: In the first aspect, this application provides a PET modified atmosphere food packaging material, which is co-extruded sequentially from an outer layer, a first adhesive layer, a barrier layer, a second adhesive layer, and an inner layer. The outer layer is made of modified PET; the barrier layer is made of high-barrier resin; the first / second adhesive layer is made of maleic anhydride-grafted polyolefin elastomer; the inner layer is made of metallocene polyethylene; the thickness ratio of the outer layer, first adhesive layer, barrier layer, second adhesive layer, and inner layer is 8-10:1-2:1-2:1-2:6-8; the maleic anhydride-grafted polyolefin elastomer is Bondyram 7109; and the metallocene polyethylene is HPR3518CB.

[0007] In a preferred embodiment of the present invention, the modified PET is prepared by the following steps: Step a1: Add zinc oxide powder, catalyst and ethylene glycol to a three-necked flask equipped with a stirrer and thermometer, mix and stir for 30 min, transfer to a melt polymerization reactor, add terephthalic acid, purge with nitrogen for protection, and esterify to 250℃ at a heating rate of 1-2℃ / min for 2-3 h under conditions of 40-90 r / min and 50℃, followed by vacuum polycondensation for 1 h. After the reaction is completed, cool in a water bath and then send to a pelletizer to pelletize to obtain masterbatch. Step a2: Add the masterbatch and epoxy chain extender to the mixer. The screw speed is 70-80 r / min. Set the temperature zones as follows: melt the feed at zone 1 (200-210℃); mix and react at zone 2 (230-240℃); plasticize at zone 3 (250-260℃), granulate and dry. Add the chain extender and antioxidant, and mechanically stir for 3-5 min. Transfer to a twin-screw extruder. Set the extruder temperature to 220-280℃ and the screw speed to 60 r / min. After extrusion, cool and shape the product in a cooling water tank, then pelletize it in a pelletizer. Place it in a vacuum drying oven at 120℃ and dry for 6-12 h to obtain the intermediate product. Step a3: Vacuum dry the intermediate product at 120℃ for 6 hours, vacuum dry the polyester elastomer at 100℃ for 6 hours, put the intermediate product and polyester elastomer into a mixer and mix for 3-5 minutes, then add them into a twin-screw extruder with a screw speed of 50-70 r / min. Set the temperature zones as follows: melt the material in zone 1 at 210-220℃; mix and react in zone 2 at 233-245℃; plasticize and extrude in zone 3 at 265-275℃. After cooling in a cooling water tank and drying with a blower, pelletize the pellets and dry them in a forced-air drying oven at 80-100℃ for 4-6 hours to obtain modified PET.

[0008] In a preferred embodiment of the present invention, the ratio of zinc oxide powder, catalyst, ethylene glycol and terephthalic acid in step a1 is 2-3g: 0.3-0.5g: 120-150mL: 330-350g; the particle size of the zinc oxide powder is 100-150nm; and the catalyst is antimony glycolate.

[0009] In a preferred embodiment of the present invention, the ratio of the masterbatch, epoxy chain extender, chain extender and antioxidant in step a2 is 350-400g: 2-4g: 1-3g: 0.3-0.5g; the epoxy chain extender is ADR-4368C; the chain extender is pyromellitic dianhydride; and the antioxidant is 1010.

[0010] In a preferred embodiment of the present invention, the ratio of the intermediate product to the polyester elastomer in step a3 is 370-380g: 23-28g; the polyester elastomer is TPEE G3548.

[0011] In a preferred embodiment of the present invention, the high-barrier resin is prepared by the following steps: Dimethyl methylphosphonate and dipentaerythritol were added to a three-necked flask equipped with a stirrer and thermometer, mixed and stirred for 30 min, heated to 180 °C, protected with nitrogen, and refluxed for 4-5 h to obtain a phosphorus-containing polyol; polybutylene adipate was placed in a forced-air drying oven and dried at 70 °C for 6-8 h, then the phosphorus-containing polyol, sorbitol, 1,4-cyclohexanediethanol and hydroxyl-terminated polydimethylsiloxane were added, mixed and stirred at 25 °C for 10-15 min, and then added to the dimethyl methylphosphonate. In the screw extruder, the screw speed is 100-120 r / min. The temperature zones of the extruder are set as follows: feeding and melting at 135℃ in zone 1; mixing at 150℃ in zone 2; reaction at 165℃ in zone 3; and reaction completion at 170-175℃ in zone 4. The crosslinking agent is injected into zone 3 through the side liquid injection port in the extruder. The extruded material is cooled by a cold water tank, dried by a blower, pelletized by a pelletizer, and dried at 60℃ for 4 hours to obtain a high-barrier resin.

[0012] In a preferred embodiment of the present invention, the ratio of dimethyl methylphosphonate, dipentaerythritol, polybutylene adipate terephthalate, sorbitol, 1,4-cyclohexanediethanol, hydroxyl-terminated polydimethylsiloxane, and crosslinking agent is 12-15 mL: 23-28 g: 400 g: 3-4 g: 2-3 g: 8-10 g: 4-5 g; the polybutylene adipate terephthalate is of type TH801T; the hydroxyl-terminated polydimethylsiloxane is produced by Wuhan Yuancheng Chemical Co., Ltd., and is of type YC-022; the crosslinking agent is of type YD-100.

[0013] Secondly, this application provides a method for preparing PET modified atmosphere food packaging material, including the following steps: Step 1: Weigh out 42-48 parts of modified PET, 7-9 parts of high barrier resin, 15-20 parts of maleic anhydride-grafted polyolefin elastomer, 30-36 parts of metallocene polyethylene, 0.1-0.3 parts of antioxidant 1010 and 0.05-0.15 parts of erucamide according to the following weight proportions. Step 2: The modified PET, high-barrier resin, maleic anhydride-grafted polyolefin elastomer, and metallocene polyethylene are dried at 80℃ for 4-6 hours and set aside. The antioxidant and erucamide are mixed and stirred for 30 minutes and then divided into two equal parts. The two parts are mixed and stirred with the modified PET and metallocene polyethylene for 30 minutes respectively. The mixture is then prepared by five extruders with co-extrusion dies. The speed and temperature of the five extruders are adjusted, and the extrusion is carried out in the order of outer layer, first adhesive layer, barrier layer, second adhesive layer, and inner layer to achieve a layer thickness ratio of 8-10:1-2:1-2:1-2:6-8. After extrusion, the mixture is blown and cooled to obtain PET modified atmosphere food packaging material.

[0014] In a preferred embodiment of the present invention, the rotation speed and temperature of the five extruders in step two are as follows: the outer layer extruder has a rotation speed of 40-50 r / min and a temperature of 240-260°C; the first adhesive layer extruder has a rotation speed of 5-10 r / min and a temperature of 195-210°C; the barrier layer extruder has a rotation speed of 5-10 r / min and a temperature of 165-180°C; the second adhesive layer extruder has a rotation speed of 5-10 r / min and a temperature of 195-210°C; and the inner layer extruder has a rotation speed of 30-40 r / min and a temperature of 175-190°C. The blow-up ratio of the blown film is 2-2.8.

[0015] The beneficial effects of this invention are: The present invention relates to a PET modified atmosphere food packaging material and its preparation method. Modified PET, high-barrier resin, maleic anhydride-grafted polyolefin elastomer, and metallocene polyethylene are dried separately and set aside. Antioxidant and erucamide are mixed and stirred, then evenly divided and separately mixed with modified PET and metallocene polyethylene. The mixture is prepared using five extruders and co-extrusion dies. The speed and temperature of the five extruders are adjusted to control the layer thickness ratio. Co-extrusion is performed in the order of outer layer, first adhesive layer, barrier layer, second adhesive layer, and inner layer. After extrusion, the mixture is blown and cooled to obtain the PET modified atmosphere food packaging material. This PET modified atmosphere food packaging material, through its high-barrier resin layer, possesses excellent barrier properties, accurately maintaining the modified atmosphere environment inside the packaging for a long time, effectively extending the shelf life of the food. The modified PET layer of this material gives it high stiffness, tensile strength, puncture resistance, and good flexibility and impact resistance, making it less prone to deformation and damage during transportation and stacking. The metallocene polyethylene, as the inner layer, forms a film with high strength, good toughness, and puncture resistance, effectively protecting the contents.

[0016] In the preparation of modified atmosphere packaging materials for PET, modified PET was first prepared. Terephthalic acid and ethylene glycol underwent esterification under a catalyst to generate oligomers. Under high temperature and vacuum conditions, further transesterification reactions occurred between oligomer molecules, removing ethylene glycol and causing molecular chain growth to form high-molecular-weight PET. Nano-zinc oxide was in situ embedded within the matrix during this process, yielding masterbatch. The dispersed nano-zinc oxide can release zinc ions, catalyze the generation of active oxygen, and scatter / absorb ultraviolet light, endowing the packaging material with antibacterial and UV-shielding functions. Nanoparticles, acting as physical cross-linking points, can restrict the movement of PET molecular chains, enhancing mechanical and thermal properties and improving matrix strength and thermal stability. The epoxy groups of the epoxy chain extender undergo ring-opening addition reactions with the carboxyl groups of the masterbatch to form ether bonds, effectively "sealing" and connecting the molecular chains. The anhydride groups of the chain extender and the masterbatch... The hydroxyl groups undergo esterification to form new ester bonds, increasing the molecular weight and melt strength of PET, yielding an intermediate product. The synergistic effect of the two chain extenders introduces a long-chain branched structure, increasing molecular chain entanglement and making the melt exhibit high viscoelasticity under stress, effectively preventing sagging and bubble breakage. The chain extenders consume the terminal carboxyl groups that catalyze thermal degradation, reducing the acidity of the system and thus inhibiting the degradation of PET in subsequent high-temperature processing, maintaining performance stability, and improving the melt strength and elasticity of the material. Under high temperature and shear force, the intermediate product is compounded with polyester elastomer to obtain modified PET. The polyester elastomer is a block copolymer composed of hard and soft segments. When the material is impacted, it can effectively induce crazing and shear banding through its own deformation, absorbing and dispersing impact energy, thereby preventing crack propagation and significantly improving the elongation at break and impact strength of the material.

[0017] In the process of preparing PET modified atmosphere food packaging materials, a high-barrier resin was first prepared. Under heating, the methyl ester group in dimethyl methylphosphonate undergoes an ester exchange reaction with the hydroxyl group in dipentaerythritol, removing methanol and forming a new ester bond. Dipentaerythritol has six hydroxyl groups, while dimethyl methylphosphonate has two methyl ester groups. By controlling the ratio, a phosphorus-containing polyol is generated, whose molecular ends are rich in hydroxyl groups. Phosphorus is firmly incorporated into the polymer backbone through chemical bonds, becoming an intrinsic component of the material. When heated or burned, it promotes char formation, isolates oxygen and heat, and exerts a highly efficient, long-lasting, and migration-free flame-retardant effect. The aziridine ring of the crosslinking agent undergoes a ring-opening addition reaction with the hydroxyl-containing component to form... Stable amine-ether bonds are formed, and this reaction is completed in the molten polybutylene adipate-terephthalate matrix, bridging the linear polybutylene adipate-terephthalate molecular chains with various polyols to obtain a high-barrier resin. The cross-linked network greatly restricts the degree of freedom and free volume of polymer chain segments. The diffusion of small gas molecules in the material must bypass this dense molecular network, making the path extremely tortuous and difficult, thereby reducing oxygen and water vapor permeability. Sorbitol and 1,4-cyclohexanediethanol provide high functionality and rigid cyclic structures, improving the strength, modulus and heat resistance of the material. Attached Figure Description

[0018] The invention will now be further described with reference to the accompanying drawings.

[0019] Figure 1 This is a schematic diagram showing the gas permeability (oxygen permeability) test results of the PET modified atmosphere food packaging materials in Examples 1-3 and Comparative Examples 1-3 of this invention.

[0020] Figure 2 This is a schematic diagram showing the water vapor transmission rate test results of PET modified atmosphere food packaging materials in Examples 1-3 and Comparative Examples 1-3 of this invention.

[0021] Figure 3 This is a schematic diagram showing the tensile strength (longitudinal) test results of the PET modified atmosphere food packaging materials in Examples 1-3 and Comparative Examples 1-3 of this invention. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: This embodiment describes a method for preparing PET modified atmosphere food packaging material, including the following steps: Step S1: Add 2g of zinc oxide powder with a particle size of 100nm, 0.3g of antimony glycol and 120mL of ethylene glycol to a three-necked flask equipped with a stirrer and thermometer. Mix and stir for 30min. Transfer to a melt polymerization reactor, add 330g of terephthalic acid, purge with nitrogen for protection, and esterify at 250℃ for 2h at a heating rate of 1℃ / min under conditions of 40r / min and 50℃. Vacuum polycondensation for 1h. After the reaction is completed, cool in a water bath and send to a pelletizer to pelletize to obtain masterbatch. Step S2: Add 350g of masterbatch and 2g of epoxy chain extender ADR-4368C to a mixer. Set the screw speed to 70r / min and set the temperature zones as follows: melt feeding at zone 1 (200℃); mix and react at zone 2 (230℃); plasticize at zone 3 (250℃), granulate and dry. Add 1g of pyromellitic dianhydride and 0.3g of antioxidant 1010, stir mechanically for 3min, transfer to a twin-screw extruder, set the extruder temperature to 220℃ and the screw speed to 60r / min. After extrusion, cool and shape the product in a cooling water tank, add it to a pelletizer for pelletizing, and dry it in a vacuum drying oven at 120℃ for 6h to obtain the intermediate product. Step S3: Vacuum dry 370g of intermediate product at 120℃ for 6h, vacuum dry 23g of polyester elastomer TPEE G3548 at 100℃ for 6h, put the intermediate product and polyester elastomer into a mixer and mix for 3min, then add to a twin-screw extruder with a screw speed of 50r / min. Set the temperature zones as follows: melt feeding at zone 1 temperature of 210℃; mix and react at zone 2 temperature of 233℃; plasticize and extrude at zone 3 temperature of 265℃. After cooling in a cooling water tank and drying with a blower, pelletize by a pelletizer and dry in an 80℃ drying oven for 4h to obtain modified PET. Step S4: Add 12 mL of dimethyl methylphosphonate and 23 g of dipentaerythritol to a three-necked flask equipped with a stirrer and thermometer, mix and stir for 30 min, heat to 180 °C, purge with nitrogen for protection, and reflux for 4 h to obtain a phosphorus-containing polyol; place 400 g of polybutylene adipate terephthalate TH801T in a forced-air drying oven and dry at 70 °C for 6 h, then add the phosphorus-containing polyol, 3 g of sorbitol, and 2 g of... 1,4-cyclohexanediethanol and 8g of hydroxyl-terminated polydimethylsiloxane YC-022 were mixed and stirred at 25°C for 10min, and then added to a twin-screw extruder. The screw speed was 100r / min. The temperature zones of the extruder were set as follows: feeding and melting at 135°C in zone 1; mixing at 150°C in zone 2; reaction at 165°C in zone 3; and reaction completion at 170°C in zone 4. 4g of crosslinking agent YD-100 was injected into zone 3 through the side liquid injection port of the extruder. The extruded material was cooled in a cold water tank, dried by a blower, pelletized by a pelletizer, and dried at 60°C for 4h to obtain a high-barrier resin. Step S5: Weigh out 42 parts modified PET, 7 parts high barrier resin, 15 parts maleic anhydride-grafted polyolefin elastomer Bondyram 7109, 30 parts metallocene polyethylene HPR3518CB, 0.1 parts antioxidant 1010 and 0.05 parts erucamide by weight. Step S6: Modified PET, high-barrier resin, maleic anhydride-grafted polyolefin elastomer, and metallocene polyethylene are dried at 80℃ for 4 hours and set aside. Antioxidant and erucamide are mixed and stirred for 30 minutes, then divided into two equal portions. Each portion is mixed with modified PET and metallocene polyethylene for 30 minutes. The mixture is then prepared using five extruders with co-extrusion dies. The speed and temperature of the five extruders are adjusted: the outer layer extruder speed is 40 r / min, and the temperature is 240℃. The first adhesive layer extruder speed... The extruders for the outer layer, first adhesive layer, barrier layer, second adhesive layer, and inner layer were co-extruded at a speed of 5 r / min and a temperature of 195℃, respectively. The extruders for the second adhesive layer and the inner layer were also co-extruded at a speed of 5 r / min and a temperature of 165℃, respectively. The layer thickness ratio was 8:1:1:1:6. After extrusion, the material was blown into a film and cooled. The blow-up ratio was 2, resulting in PET modified atmosphere food packaging material.

[0024] Example 2: This embodiment describes a method for preparing PET modified atmosphere food packaging material, including the following steps: Step S1: Add 2.5g of zinc oxide powder with a particle size of 125nm, 0.4g of antimony glycol and 135mL of ethylene glycol to a three-necked flask equipped with a stirrer and thermometer. Mix and stir for 30min. Transfer to a melt polymerization reactor, add 340g of terephthalic acid, purge with nitrogen for protection, and esterify at 250℃ for 2.5h at a heating rate of 1.5℃ / min under conditions of 65r / min and 50℃. Vacuum polycondensation for 1h. After the reaction is completed, cool in a water bath and send to a pelletizer to pelletize to obtain masterbatch. Step S2: Add 375g of masterbatch and 3g of epoxy chain extender ADR-4368C to a mixer. Set the screw speed to 75r / min and set the temperature zones as follows: melt feeding at zone 1 temperature of 205℃; mix and react at zone 2 temperature of 235℃; plasticize at zone 3 temperature of 255℃, granulate and dry. Add 2g of pyromellitic dianhydride and 0.4g of antioxidant 1010, stir mechanically for 4min, transfer to a twin-screw extruder, set the extruder temperature to 250℃ and the screw speed to 60r / min. After extrusion, cool and shape in a cooling water tank, add to a pelletizer for pelletizing, and dry in a vacuum drying oven at 120℃ for 9h to obtain the intermediate product. Step S3: Vacuum dry 375g of intermediate product at 120℃ for 6h, vacuum dry 25g of polyester elastomer TPEE G3548 at 100℃ for 6h, put the intermediate product and polyester elastomer into a mixer and mix for 4min, then add to a twin-screw extruder with a screw speed of 60r / min. Set the temperature zones as follows: melt feeding at zone 1 temperature of 215℃; mix and react at zone 2 temperature of 240℃; plasticize and extrude at zone 3 temperature of 270℃. After cooling in a cooling water tank and drying with a blower, pelletize by a pelletizer and dry in a 90℃ forced-air drying oven for 5h to obtain modified PET. Step S4: Add 14 mL of dimethyl methylphosphonate and 25 g of dipentaerythritol to a three-necked flask equipped with a stirrer and thermometer, mix and stir for 30 min, heat to 180 °C, purge with nitrogen for protection, and reflux for 4.5 h to obtain a phosphorus-containing polyol; place 400 g of polybutylene adipate terephthalate TH801T in a forced-air drying oven and dry at 70 °C for 7 h, then add the phosphorus-containing polyol, 3.5 g of sorbitol, and 2.5 g of... 1,4-cyclohexanediethanol and 9g of hydroxyl-terminated polydimethylsiloxane YC-022 were mixed and stirred at 25℃ for 13min, and then added to a twin-screw extruder with a screw speed of 110r / min. The temperature zones of the extruder were set as follows: Zone 1 at 135℃ for feeding and melting; Zone 2 at 150℃ for mixing; Zone 3 at 165℃ for reaction; and Zone 4 at 173℃ for reaction completion. 4.5g of crosslinking agent YD-100 was injected into Zone 3 through the side liquid injection port of the extruder. The extruded material was cooled in a cold water tank, dried by a blower, pelletized by a pelletizer, and dried at 60℃ for 4h to obtain a high-barrier resin. Step S5: Weigh out 45 parts modified PET, 8 parts high barrier resin, 18 parts maleic anhydride-grafted polyolefin elastomer Bondyram 7109, 33 parts metallocene polyethylene HPR3518CB, 0.2 parts antioxidant 1010 and 0.1 parts erucamide by weight. Step S6: The modified PET, high-barrier resin, maleic anhydride-grafted polyolefin elastomer, and metallocene polyethylene were dried at 80℃ for 5 hours and set aside. The antioxidant and erucamide were mixed and stirred for 30 minutes, then divided into two equal portions. Each portion was mixed with the modified PET and metallocene polyethylene for 30 minutes. The mixture was then processed using five extruders (A, B, C, D, E) with co-extrusion dies. The speed and temperature of the five extruders were adjusted: the outer layer extruder was set to 45 r / min and the temperature to 250℃; the first adhesive layer extruder... The extruders were operated at 8 r / min and 200℃. The barrier layer extruder operated at 8 r / min and 170℃. The second adhesive layer extruder operated at 8 r / min and 200℃. The inner layer extruder operated at 35 r / min and 185℃. The outer layer, first adhesive layer, barrier layer, second adhesive layer, and inner layer were co-extruded in that order to achieve a layer thickness ratio of 9:1.5:1.5:1.5:7. After extrusion, the material was blown into a film and cooled. The blow-up ratio was 2.4, resulting in PET modified atmosphere food packaging material.

[0025] Example 3: This embodiment describes a method for preparing PET modified atmosphere food packaging material, including the following steps: Step S1: Add 3g of zinc oxide powder with a particle size of 150nm, 0.5g of antimony glycol and 150mL of ethylene glycol to a three-necked flask equipped with a stirrer and thermometer. Mix and stir for 30min. Transfer to a melt polymerization reactor, add 350g of terephthalic acid, purge with nitrogen for protection, and esterify at 250℃ for 3h at a heating rate of 2℃ / min under conditions of 90r / min and 50℃. Vacuum polycondensation for 1h. After the reaction is completed, cool in a water bath and send to a pelletizer to pelletize to obtain masterbatch. Step S2: Add 400g of masterbatch and 4g of epoxy chain extender ADR-4368C to a mixer. Set the screw speed to 80r / min and set the temperature zones as follows: melt feeding at zone 1 (210℃); mix and react at zone 2 (240℃); plasticize at zone 3 (260℃), granulate and dry. Add 3g of pyromellitic dianhydride and 0.5g of antioxidant 1010, stir mechanically for 5min, transfer to a twin-screw extruder, set the extruder temperature to 280℃ and the screw speed to 60r / min. After extrusion, cool and shape the product in a cooling water bath, add it to a pelletizer for pelletizing, and dry it in a vacuum drying oven at 120℃ for 12h to obtain the intermediate product. Step S3: Vacuum dry 380g of intermediate product at 120℃ for 6h, vacuum dry 28g of polyester elastomer TPEE G3548 at 100℃ for 6h, put the intermediate product and polyester elastomer into a mixer and mix for 5min, then add to a twin-screw extruder with a screw speed of 70r / min. Set the temperature zones as follows: melt feeding at zone 1 temperature of 220℃; mix and react at zone 2 temperature of 245℃; plasticize and extrude at zone 3 temperature of 275℃. After cooling in a cooling water tank and drying with a blower, pelletize by a pelletizer and dry in a 100℃ forced-air drying oven for 6h to obtain modified PET. Step S4: Add 15 mL of dimethyl methylphosphonate and 28 g of dipentaerythritol to a three-necked flask equipped with a stirrer and thermometer, mix and stir for 30 min, heat to 180 °C, purge with nitrogen for protection, and reflux for 5 h to obtain a phosphorus-containing polyol; place 400 g of polybutylene adipate terephthalate TH801T in a forced-air drying oven and dry at 70 °C for 8 h, then add the phosphorus-containing polyol, 4 g of sorbitol, and 3 g of... 1,4-cyclohexanediethanol and 10g of hydroxyl-terminated polydimethylsiloxane YC-022 were mixed and stirred at 25℃ for 15min, and then added to a twin-screw extruder. The screw speed was 120r / min. The temperature zones of the extruder were set as follows: feeding and melting at 135℃ in zone 1; mixing at 150℃ in zone 2; reaction at 165℃ in zone 3; and reaction completion at 175℃ in zone 4. 5g of crosslinking agent YD-100 was injected into zone 3 through the side liquid injection port of the extruder. The extruded material was cooled in a cold water tank, dried by a blower, pelletized by a pelletizer, and dried at 60℃ for 4h to obtain a high-barrier resin. Step S5: Weigh out 48 parts of modified PET, 9 parts of high barrier resin, 20 parts of maleic anhydride-grafted polyolefin elastomer Bondyram 7109, 36 parts of metallocene polyethylene HPR3518CB, 0.3 parts of antioxidant 1010 and 0.15 parts of erucamide by weight. Step S6: Modified PET, high-barrier resin, maleic anhydride-grafted polyolefin elastomer, and metallocene polyethylene are dried at 80℃ for 6 hours and set aside. Antioxidant and erucamide are mixed and stirred for 30 minutes, then divided into two equal portions. Each portion is mixed with modified PET and metallocene polyethylene for 30 minutes. The mixture is then extruded using five extruders (A, B, C, D, E) and co-extrusion dies. The speed and temperature of the five extruders are adjusted. The outer extruder's speed is 50 r / min, and the temperature is 260℃. The first adhesive layer is extruded. The extruder operates at a speed of 10 r / min and a temperature of 210℃. The barrier layer extruder operates at a speed of 10 r / min and a temperature of 180℃. The second adhesive layer extruder operates at a speed of 10 r / min and a temperature of 210℃. The inner layer extruder operates at a speed of 40 r / min and a temperature of 190℃. The outer layer, first adhesive layer, barrier layer, second adhesive layer, and inner layer are co-extruded in that order to achieve a layer thickness ratio of 10:2:2:2:8. After extrusion, the material is blown into a film and cooled, with a blow-up ratio of 2.8, to obtain PET modified atmosphere food packaging material.

[0026] Comparative Example 1: This comparative example demonstrates a method for preparing PET modified atmosphere food packaging material, including the following steps: Step S1: Add 2.5g of zinc oxide powder with a particle size of 125nm, 0.4g of antimony glycol and 135mL of ethylene glycol to a three-necked flask equipped with a stirrer and thermometer. Mix and stir for 30min. Transfer to a melt polymerization reactor, add 340g of terephthalic acid, purge with nitrogen for protection, and esterify at 250℃ for 2.5h at a heating rate of 1.5℃ / min under conditions of 65r / min and 50℃. Vacuum polycondensation for 1h. After the reaction is completed, cool in a water bath and send to a pelletizer to pelletize to obtain masterbatch. Step S2: Add 375g of masterbatch and 3g of epoxy chain extender ADR-4368C to a mixer. Set the screw speed to 75r / min and set the temperature zones as follows: melt feeding at zone 1 temperature of 205℃; mix and react at zone 2 temperature of 235℃; plasticize at zone 3 temperature of 255℃, granulate and dry. Add 2g of pyromellitic dianhydride and 0.4g of antioxidant 1010, stir mechanically for 4min, transfer to a twin-screw extruder, set the extruder temperature to 250℃ and the screw speed to 60r / min. After extrusion, cool and shape in a cooling water tank, add to a pelletizer for pelletizing, and dry in a vacuum drying oven at 120℃ for 9h to obtain modified PET. Step S3: Weigh out 45 parts of modified PET, 9 parts of maleic anhydride-grafted polyolefin elastomer Bondyram 7109, 33 parts of metallocene polyethylene HPR3518CB, 0.2 parts of antioxidant 1010 and 0.1 parts of erucamide by weight. Step S4: The modified PET, maleic anhydride-grafted polyolefin elastomer, and metallocene polyethylene were dried at 80°C for 5 hours and set aside. The antioxidant and erucamide were mixed and stirred for 30 minutes and then divided into two equal parts. The two parts were mixed and stirred with the modified PET and metallocene polyethylene for 30 minutes respectively. The mixture was then prepared using three extruders and co-extrusion dies. The speed and temperature of the three extruders were adjusted as follows: the speed of the outer layer extruder was 45 r / min and the temperature was 250°C; the speed of the adhesive layer extruder was 8 r / min and the temperature was 200°C; and the speed of the inner layer extruder was 35 r / min and the temperature was 185°C. The outer layer, adhesive layer, and inner layer were co-extruded in that order to achieve a layer thickness ratio of 9:1.5:7. After extrusion, the mixture was blown into film and cooled. The blow-up ratio was 2.4, and the PET modified atmosphere food packaging material was obtained.

[0027] Comparative Example 2: This comparative example demonstrates a method for preparing PET modified atmosphere food packaging material, including the following steps: Step S1: Add 2.5g of zinc oxide powder with a particle size of 125nm, 0.4g of antimony glycol and 135mL of ethylene glycol to a three-necked flask equipped with a stirrer and thermometer. Mix and stir for 30min. Transfer to a melt polymerization reactor, add 340g of terephthalic acid, purge with nitrogen for protection, and esterify at 250℃ for 2.5h at a heating rate of 1.5℃ / min under conditions of 65r / min and 50℃. Vacuum polycondensation for 1h. After the reaction is completed, cool in a water bath and send to a pelletizer to pelletize to obtain masterbatch. Step S2: Add 375g of masterbatch and 3g of epoxy chain extender ADR-4368C to a mixer. Set the screw speed to 75r / min and set the temperature zones as follows: melt feeding at zone 1 temperature of 205℃; mix and react at zone 2 temperature of 235℃; plasticize at zone 3 temperature of 255℃, granulate and dry. Add 2g of pyromellitic dianhydride and 0.4g of antioxidant 1010, stir mechanically for 4min, transfer to a twin-screw extruder, set the extruder temperature to 250℃ and the screw speed to 60r / min. After extrusion, cool and shape in a cooling water tank, add to a pelletizer for pelletizing, and dry in a vacuum drying oven at 120℃ for 9h to obtain the intermediate product. Step S3: Vacuum dry 375g of intermediate product at 120℃ for 6h, vacuum dry 25g of polyester elastomer TPEE G3548 at 100℃ for 6h, put the intermediate product and polyester elastomer into a mixer and mix for 4min, then add to a twin-screw extruder with a screw speed of 60r / min. Set the temperature zones as follows: melt feeding at zone 1 temperature of 215℃; mix and react at zone 2 temperature of 240℃; plasticize and extrude at zone 3 temperature of 270℃. After cooling in a cooling water tank and drying with a blower, pelletize by a pelletizer and dry in a 90℃ forced-air drying oven for 5h to obtain modified PET. Step S4: Weigh out 45 parts of modified PET, 9 parts of maleic anhydride-grafted polyolefin elastomer Bondyram 7109, 33 parts of metallocene polyethylene HPR3518CB, 0.2 parts of antioxidant 1010 and 0.1 parts of erucamide by weight. Step S5: The modified PET, maleic anhydride-grafted polyolefin elastomer, and metallocene polyethylene were dried at 80℃ for 5 hours and set aside. The antioxidant and erucamide were mixed and stirred for 30 minutes and then divided into two equal parts. The two parts were mixed and stirred with the modified PET and metallocene polyethylene for 30 minutes respectively. The mixture was then prepared by three extruders with co-extrusion dies. The speed and temperature of the three extruders were adjusted as follows: the speed of the outer layer extruder was 45 r / min and the temperature was 250℃; the speed of the adhesive layer extruder was 8 r / min and the temperature was 200℃; and the speed of the inner layer extruder was 35 r / min and the temperature was 185℃. The outer layer, adhesive layer, and inner layer were co-extruded in that order to achieve a layer thickness ratio of 9:1.5:7. After extrusion, the mixture was blown into film and cooled. The blow-up ratio was 2.4 to obtain PET modified atmosphere food packaging material.

[0028] Comparative Example 3: This comparative example demonstrates a method for preparing PET modified atmosphere food packaging material, including the following steps: Step S1: Add 2.5g of zinc oxide powder with a particle size of 125nm, 0.4g of antimony glycol and 135mL of ethylene glycol to a three-necked flask equipped with a stirrer and thermometer. Mix and stir for 30min. Transfer to a melt polymerization reactor, add 340g of terephthalic acid, purge with nitrogen for protection, and esterify at 250℃ for 2.5h at a heating rate of 1.5℃ / min under conditions of 65r / min and 50℃. Vacuum polycondensation for 1h. After the reaction is completed, cool in a water bath and send to a pelletizer to pelletize to obtain masterbatch. Step S2: Add 375g of masterbatch and 3g of epoxy chain extender ADR-4368C to a mixer. Set the screw speed to 75r / min and set the temperature zones as follows: melt feeding at zone 1 temperature of 205℃; mix and react at zone 2 temperature of 235℃; plasticize at zone 3 temperature of 255℃, granulate and dry. Add 2g of pyromellitic dianhydride and 0.4g of antioxidant 1010, stir mechanically for 4min, transfer to a twin-screw extruder, set the extruder temperature to 250℃ and the screw speed to 60r / min. After extrusion, cool and shape in a cooling water tank, add to a pelletizer for pelletizing, and dry in a vacuum drying oven at 120℃ for 9h to obtain modified PET. Step S3: Add 14 mL of dimethyl methylphosphonate and 25 g of dipentaerythritol to a three-necked flask equipped with a stirrer and thermometer, mix and stir for 30 min, heat to 180 °C, purge with nitrogen for protection, and reflux for 4.5 h to obtain a phosphorus-containing polyol; place 400 g of polybutylene adipate terephthalate TH801T in a forced-air drying oven and dry at 70 °C for 7 h, then add the phosphorus-containing polyol, 3.5 g of sorbitol, and 2.5 g of... 1,4-cyclohexanediethanol and 9g of hydroxyl-terminated polydimethylsiloxane YC-022 were mixed and stirred at 25℃ for 13min, and then added to a twin-screw extruder with a screw speed of 110r / min. The temperature zones of the extruder were set as follows: Zone 1 at 135℃ for feeding and melting; Zone 2 at 150℃ for mixing; Zone 3 at 165℃ for reaction; and Zone 4 at 173℃ for reaction completion. 4.5g of crosslinking agent YD-100 was injected into Zone 3 through the side liquid injection port of the extruder. The extruded material was cooled in a cold water tank, dried by a blower, pelletized by a pelletizer, and dried at 60℃ for 4h to obtain a high-barrier resin. Step S4: Weigh out 45 parts modified PET, 8 parts high barrier resin, 18 parts maleic anhydride-grafted polyolefin elastomer Bondyram 7109, 33 parts metallocene polyethylene HPR3518CB, 0.2 parts antioxidant 1010 and 0.1 parts erucamide by weight. Step S5: The modified PET, high-barrier resin, maleic anhydride-grafted polyolefin elastomer, and metallocene polyethylene were dried at 80°C for 5 hours and set aside. The antioxidant and erucamide were mixed and stirred for 30 minutes, then divided into two equal portions. Each portion was mixed with the modified PET and metallocene polyethylene for 30 minutes. The mixture was then processed using five extruders with co-extrusion dies. The speed and temperature of the five extruders were adjusted: the outer layer extruder was set to 45 r / min and 250°C, and the first adhesive layer extruder was set to 8 r / min. The extruders for the outer layer, first adhesive layer, barrier layer, second adhesive layer, and inner layer were co-extruded at a speed of 8 r / min and a temperature of 200℃, 8 r / min and 200℃ respectively, and 35 r / min and 185℃ respectively, achieving a layer thickness ratio of 9:1.5:1.5:1.5:7. After extrusion, the material was blown and cooled, with a blow-up ratio of 2.4, to obtain PET modified atmosphere food packaging material.

[0029] The PET modified atmosphere packaging materials prepared in Examples 1-3 and Comparative Examples 1-3 were tested for gas permeability (oxygen permeability) according to standard GB / T 1038-2000 "Test Method for Gas Permeability of Plastic Films and Sheets - Differential Pressure Method", for water vapor permeability according to standard GB / T 1037-2021 "Determination of Water Vapor Permeability of Plastic Films and Sheets - Cup Weight Gain and Weight Loss Method", and for tensile strength (longitudinal) according to standard GB / T 1040.3-2006 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets". The test results are as follows: Figure 1-3 As shown: Comparing Examples 1-3 with Comparative Examples 1-3: In Example 1, the raw material dosage and preparation conditions were the lowest. The chain extension reaction was insufficient due to the low temperature, resulting in lower barrier properties and strength compared to Example 2. Toughness was also lower due to the low polyester elastomer content. In Example 3, the raw material dosage and preparation conditions were the highest. Excessive polymerization stirring speed and chain extension temperature introduced more thermal degradation, affecting molecular weight. An excessively thick barrier layer increased brittleness. An excessively high blow-up ratio may affect thickness uniformity. Its barrier properties were better than Example 1 but not as good as Example 2, while its toughness was superior due to the high polyester elastomer content. In Example 2, the raw material dosage and preparation conditions were moderate, resulting in a sufficient chain extension reaction and a moderate barrier layer thickness. The stable blown film process gives it optimal barrier properties, and the moderate polyester elastomer content results in high tensile strength. Comparing Example 2 with Comparative Example 1, it can be seen that Comparative Example 1 lacks polyester elastomer toughening and a high-barrier resin layer, resulting in high brittleness and weak barrier performance. Comparing Example 2 with Comparative Example 2, it can be seen that Comparative Example 2 lacks a high-barrier resin layer, has polyester elastomer toughening, and has good tensile strength, but lacks the barrier performance of the high-barrier resin layer. Comparing Example 2 with Comparative Example 3, it can be seen that Comparative Example 3 lacks polyester elastomer toughening, has lower tensile strength, and the high-barrier resin layer provides good barrier performance.

[0030] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above 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 one or more embodiments or examples.

[0031] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in this application, they should all fall within the protection scope of the present invention.

Claims

1. A PET modified atmosphere food packaging material, characterized in that, It is co-extruded sequentially from an outer layer, a first adhesive layer, a barrier layer, a second adhesive layer, and an inner layer. The outer layer is made of modified PET, the barrier layer is made of high-barrier resin, the first / second adhesive layers are made of maleic anhydride-grafted polyolefin elastomer, and the inner layer is made of metallocene polyethylene. The modified PET is prepared by the following steps: Step a1: Mix and stir zinc oxide powder, catalyst and ethylene glycol, transfer to melt polymerization kettle, add terephthalic acid, purge with nitrogen, heat up for esterification, vacuum polycondensation, cool in water bath after reaction, and send to pelletizer to pelletize to obtain masterbatch; Step a2: Add the masterbatch and epoxy chain extender to the mixer, and set the temperature zones of "low temperature mixing - medium temperature reaction": Zone 1 feeding and melting; Zone 2 mixing and reaction; Zone 3 plasticizing, granulation, drying, adding chain extender and antioxidant and mechanical stirring, transferring to a twin-screw extruder for extrusion, cooling and shaping in a cooling water tank, adding to a pelletizer for pelletizing, drying, and obtaining the intermediate product; Step a3: Dry the intermediate product and the polyester elastomer. Put the intermediate product and the polyester elastomer into a mixer and mix them. Add them to a twin-screw extruder for melt extrusion. After cooling in a cooling water tank and drying with a blower, pelletize them with a pelletizer and dry them to obtain modified PET.

2. The PET modified atmosphere food packaging material according to claim 1, characterized in that, The thickness ratio of the outer layer, the first adhesive layer, the barrier layer, the second adhesive layer, and the inner layer is 8-10:1-2:1-2:1-2:6-8; the maleic anhydride-grafted polyolefin elastomer is of type Bondyram 7109; and the metallocene polyethylene is of type HPR3518CB.

3. The PET modified atmosphere packaging material according to claim 1, characterized in that, In step a1, the ratio of zinc oxide powder, catalyst, ethylene glycol, and terephthalic acid is 2-3g: 0.3-0.5g: 120-150mL: 330-350g; the particle size of the zinc oxide powder is 100-150nm; and the catalyst is antimony glycolate.

4. The PET modified atmosphere packaging material according to claim 1, characterized in that, In step a2, the ratio of the masterbatch, epoxy chain extender, chain extender, and antioxidant is 350-400g: 2-4g: 1-3g: 0.3-0.5g; the epoxy chain extender is ADR-4368C; the chain extender is pyromellitic dianhydride; and the antioxidant is 1010.

5. The PET modified atmosphere food packaging material according to claim 1, characterized in that, The ratio of the intermediate product to the polyester elastomer in step a3 is 370-380g: 23-28g; the polyester elastomer is TPEE G3548.

6. The PET modified atmosphere food packaging material according to claim 1, characterized in that, The high-barrier resin is prepared by the following steps: Dimethyl methylphosphonate and dipentaerythritol were mixed and stirred, heated, and refluxed under nitrogen protection to obtain a phosphorus-containing polyol. Polybutylene adipate-terephthalate was dried, and phosphorus-containing polyol, sorbitol, 1,4-cyclohexanediethanol and hydroxyl-terminated polydimethylsiloxane were added, mixed and stirred, and then added to a twin-screw extruder for melt extrusion. The crosslinking agent was injected through the side liquid injection port in the extruder. The extruded material was cooled in a cold water tank, dried by a blower, pelletized by a pelletizer, and dried to obtain a high-barrier resin.

7. The PET modified atmosphere packaging material according to claim 6, characterized in that, The ratio of dimethyl methylphosphonate, dipentaerythritol, polybutylene adipate terephthalate, sorbitol, 1,4-cyclohexanediethanol, hydroxyl-terminated polydimethylsiloxane, and crosslinking agent is 12-15 mL: 23-28 g: 400 g: 3-4 g: 2-3 g: 8-10 g: 4-5 g; the polybutylene adipate terephthalate is of type TH801T; the hydroxyl-terminated polydimethylsiloxane is of type YC-022; and the crosslinking agent is of type YD-100.

8. A method for preparing a PET modified atmosphere food packaging material as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Weigh out 42-48 parts of modified PET, 7-9 parts of high barrier resin, 15-20 parts of maleic anhydride-grafted polyolefin elastomer, 30-36 parts of metallocene polyethylene, 0.1-0.3 parts of antioxidant 1010 and 0.05-0.15 parts of erucamide according to the following weight proportions. Step 2: Dry the modified PET, high-barrier resin, maleic anhydride-grafted polyolefin elastomer, and metallocene polyethylene separately and set aside. Mix the antioxidant and erucamide and then divide them equally. Mix them separately with the modified PET and metallocene polyethylene. Produce the mixture using five extruders and co-extrusion dies. Adjust the speed and temperature of the five extruders and co-extrude the mixture in the following order: outer layer, first adhesive layer, barrier layer, second adhesive layer, and inner layer. The layer thickness ratio is 8-10:1-2:1-2:1-2:6-8. After extrusion, blow film and cool to obtain PET modified atmosphere food packaging material.

9. The method for preparing PET modified atmosphere food packaging material according to claim 8, characterized in that, In step two, the five extruders are installed in the following order: outer layer, first adhesive layer, barrier layer, second adhesive layer, and inner layer. Their rotation speeds and temperatures are as follows: outer layer extruder: 40-50 r / min, temperature 240-260℃; first adhesive layer extruder: 5-10 r / min, temperature 195-210℃; barrier layer extruder: 5-10 r / min, temperature 165-180℃; second adhesive layer extruder: 5-10 r / min, temperature 195-210℃; inner layer extruder: 30-40 r / min, temperature 175-190℃. The blow-up ratio of the blown film is 2-2.8.

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