High-barrier three-layer PET / PETG co-extrusion cast film and preparation method thereof

Abstract

The invention provides a high-barrier three-layer PET / PETG co-extrusion cast film and a preparation method, the cast film comprises an outer layer, a middle layer and an inner layer, and the three layers are respectively selected from one or more modified materials of PET, PETG, PCTG, APTG, PEN and PEIT. After being independently supplied, each layer of material is synchronously extruded through a three-layer co-extrusion die head, and is fused and compounded at an outlet of the die head to form the cast film with a three-layer structure, and an adhesive does not need to be used. In the preparation process, the materials are subjected to the steps of pretreatment, co-extrusion, tape casting and surface treatment, and integrated forming of the membrane material is achieved. The cast film prepared by the invention has excellent high-temperature water resistance, high-temperature oil resistance and gas barrier property in a high-temperature environment, has good mechanical strength and processing adaptability, and is suitable for the fields of food packaging, medicine packaging, health care product packaging, cosmetic packaging, high-end industrial product packaging and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of PET packaging films, and particularly to a high-barrier three-layer PET / PETG co-extruded cast film and a preparation method thereof. Background Art

[0002] With the rapid popularization of takeaway services and disposable food packaging supplies, the market's requirements for the performance of packaging materials are constantly increasing. Especially under high-temperature conditions, such as in scenarios like oven heating and microwave reheating, packaging containers not only need to maintain good mechanical strength but also possess excellent waterproof and oil-proof properties to prevent the penetration of grease and moisture, ensuring food safety and the consumer experience. Therefore, developing packaging film materials with high-temperature tolerance, anti-permeation performance, and excellent barrier properties has become an important direction for current technological development.

[0003] Currently, the commonly used single-layer polyethylene terephthalate (PET) film has certain mechanical properties and transparency, but its waterproof, oil-proof, and gas barrier properties are still insufficient under high-temperature environments, and leakage is likely to occur. In addition, to improve the barrier and mechanical properties of the PET film, the traditional technology generally uses the biaxial stretching process (BOPET) to orient the film material to improve its denseness and strength. However, biaxial stretching not only requires a dedicated production line with high costs and high energy consumption but also makes the production process complex and the finished product rate low, restricting the rapid and low-cost popularization and application of packaging film materials.

[0004] For example, Chinese Patent CN117227292A discloses a high-barrier biaxially stretched polyethylene film and its preparation method and application, providing a PET composite film with high-temperature resistance and good barrier properties. By laminating a special functional layer on the PET film, the overall heat resistance and barrier properties are improved. However, this solution still relies on multi-step lamination and stretching processes, with a complex preparation process, high energy consumption, and limited stability of the lamination interface, presenting a risk of delamination and peeling. Another Chinese Patent CN117261397A discloses a shrinkage force controllable composite heat shrinkable film, production process, and shrinkage force control method, providing a three-layer composite heat shrinkable film. Using PETG material combined with PS or K resin to regulate the shrinkage force of the film, although there are improvements in heat shrinkage performance control, it is still based on biaxial stretching and mainly targets the heat shrink packaging field, unable to meet the comprehensive requirements of food packaging for waterproof, oil-proof, and high-barrier properties at high temperatures.

[0005] Therefore, aiming at the problems of poor high-temperature protection, insufficient barrier properties, complex production processes, and high energy consumption of PET film materials in the prior art, it is urgent to develop a packaging film that can be formed without biaxial stretching and has both high-temperature waterproof and oil-proof properties and high-barrier properties, as well as its preparation method, so as to simplify the production process, reduce energy consumption, and improve the overall performance and application adaptability of the packaging film. Summary of the Invention

[0006] In view of the technical problems of the existing PET films mentioned above, such as insufficient waterproof and oil-proof performance under high-temperature conditions, limited barrier performance, complex production processes, and dependence on biaxial stretching, a high-barrier three-layer PET / PETG coextruded cast film and its preparation method are provided. The present invention mainly uses modified polyester materials to form a three-layer structure system of outer layer - middle layer - inner layer through independent formulation design and thickness control, and through coextrusion die head synchronous extrusion and casting cooling and shaping, an integrated cast film with excellent high-temperature waterproof and oil-proof performance, high barrier property, and excellent mechanical properties can be obtained without the traditional biaxial stretching process, thereby simplifying the production process, reducing the manufacturing cost, and improving the comprehensive performance and application range of the film material.

[0007] The technical means adopted in the present invention are as follows: A high-barrier three-layer PET / PETG coextruded cast film, comprising: An outer layer, a middle layer, and an inner layer, and the three layers respectively select one or more modified materials from PET, PETG, PCTG, APTG, PEN, and PEIT; Among them, PET can be modified polyethylene terephthalate, PETG is modified polyethylene terephthalate-1,4-cyclohexanedimethanol ester (CHDM content < 50%), PCTG is modified polyethylene terephthalate-1,4-cyclohexanedimethanol ester (CHDM content > 50%), APTG is modified amorphous polyethylene terephthalate, PEN is modified polyethylene naphthalate, and PEIT is modified polyethylene terephthalate isoisophthalate; The outer layer, the middle layer, and the inner layer are respectively synchronously extruded through a three-channel coextrusion die head, and the melt flow channels are combined and compounded in the die head to form a three-layer structure cast film without using adhesives.

[0008] Furthermore, the materials of the outer layer, the middle layer, and the inner layer can be the same or different, satisfying any of the following structural forms: the outer layer and the inner layer are of the same material, and the middle layer is of a material different from the outer layer; the middle layer and the inner layer are of the same material, and the outer layer is of a material different from the middle layer.

[0009] For example: modified PETG / modified PET / modified PETG, modified PET / modified PETG / modified PET, modified PETG / modified PET / modified PET, modified PET / modified PETG / modified PETG.

[0010] Furthermore, the thicknesses of the outer layer and the inner layer are respectively 2 - 50 μm, accounting for 1 - 50% of the total thickness, and the thickness of the middle layer is 5 - 150 μm, accounting for 10 - 90% of the total thickness.

[0011] Further, the outer layer, the middle layer, and the inner layer respectively comprise the following components in parts by weight: 90 - 100 parts of polyester material, which is a modified material selected from one or more of PET, PETG, PCTG, APTG, PEN, and PEIT; 0.01 - 1 part of plasticizer, which is selected from tributyl acetylcitrate or the like.

[0012] 0.01 - 0.5 part of lubricant, which is selected from ethylene bisstearamide or the like.

[0013] 0.01 - 5 parts of talcum powder, which is talcum powder with a mesh size of 1000 - 8000.

[0014] 0.01 - 0.5 part of dispersant, which is selected from fatty acid esters or composite dispersants.

[0015] 0.01 - 1 part of chain extender, which is selected from epoxy - type or anhydride - type chain extenders.

[0016] 0.01 - 1 part of hydrolysis inhibitor, which is selected from carbodiimide - type or polycarbodiimide - type.

[0017] 0.01 - 1 part of antioxidant, which is selected from phosphite - type or ultraviolet absorber - type.

[0018] Further, the formulations of the outer layer, the middle layer, and the inner layer can be the same or different.

[0019] The present invention also discloses a preparation method of the above - mentioned high - barrier three - layer PET / PETG co - extrusion cast film, comprising the following steps: Raw material pretreatment: drying and dehumidifying the polyester materials selected for the outer layer, the middle layer, and the inner layer respectively. For example, the drying temperature of PET resin is 160 - 180°C, the drying temperature of PETG resin is 130 - 150°C, and the drying time is 4 - 6 hours; Mix the polyester material of each layer with the other components of this layer in a high - speed mixer and then extrude through a screw. The melt - compounding temperature is 250 - 290°C; Three - layer co - extrusion: adopt a co - extrusion die head with three channels, extrude the outer layer, the middle layer, and the inner layer synchronously, and complete the melt - flow channel confluence and compounding in the die head. The extrusion temperature is 270 - 290°C; Cast forming: quickly cool and shape the extruded melt on a cooling roll at 20 - 30°C; Surface treatment: perform corona treatment or plasma treatment on the surface of the formed film to obtain the finished product.

[0020] Further, the co - extrusion die head adopts a fishtail - type flow channel structure design to achieve uniform distribution of each layer of melt and stable combination of interfaces.

[0021] Furthermore, the fish-tail type runner structure includes three independent channels. The melt of each layer enters the die through its respective runner. Each layer of the runner has a tapered structure, which gradually reduces the cross-sectional area of the melt of each layer during the flow process. The tapered runners converge at the die outlet to form a laminated melt flow, and the laminated melt after convergence is extruded synchronously at the die outlet to form a continuous and uniform three-layer coextruded cast film.

[0022] Furthermore, the high-barrier three-layer PET / PETG coextruded cast film is resistant to boiling water at 100 °C, hot oil at 210 °C, and the oxygen and water vapor transmission rates are < 10 cm3 / (m2·24h).

[0023] Furthermore, the elastic modulus of the high-barrier three-layer PET / PETG coextruded cast film is 1800 - 2400 MPa, the tensile strength is 50 - 70 MPa, and the elongation at break is 100 - 500%.

[0024] The present invention has the following advantages: 1. Through the three-layer structure design and material formula optimization of the present invention, the cast film obtained can still maintain excellent waterproof and oil-proof properties under high-temperature environments (such as boiling water at 100 °C and hot oil at 210 °C). At the same time, the modified PET in the middle layer endows the film with good gas barrier and water vapor barrier properties, significantly improving the freshness preservation effect of the packaging.

[0025] 2. The present invention adopts a unique material modification system and coextrusion casting forming process, and excellent mechanical properties and barrier properties can be obtained without the traditional biaxial stretching process, simplifying the production process, reducing equipment investment and energy consumption, and improving production efficiency and cost-effectiveness.

[0026] 3. The film obtained by the present invention has a high elastic modulus (1800 - 2400 MPa), high tensile strength (50 - 70 MPa) and good elongation at break (100 - 500%), taking into account both rigidity and flexibility. The performance of the film can also be customized according to different application requirements by adjusting the thickness ratio and specific formula of each layer to meet the mechanical property requirements in various packaging scenarios.

[0027] 4. The present invention forms a three-layer structure through in-mold coextrusion compounding, without the use of adhesives, simplifying the composite processing process of the film. At the same time, the optimized formula reduces the material usage, improves environmental friendliness, and meets the requirements of sustainable development.

[0028] In summary, through the optimization of the three-layer structure design, formulation system, and forming process, the present invention innovatively realizes a three-layer PET / PETG co-extruded cast film with high-temperature waterproof and oil-proof properties and high barrier performance that can be formed without biaxial stretching. This film not only exhibits excellent anti-permeation and barrier properties in high-temperature environments but also has excellent mechanical properties, processing adaptability, and environmental characteristics.

[0029] The present invention not only simplifies the production process and reduces the manufacturing cost but also improves the customizability and application scope of the film properties. It is particularly suitable for application scenarios that require excellent barrier properties and high-temperature resistance, such as food packaging, pharmaceutical packaging, and high-end industrial product packaging, and has broad market prospects and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 It is a SEM cross-sectional view of the high-barrier PETG / PET / PETG three-layer co-extruded cast film prepared by the preparation method of the present invention.

[0032] Figure 2 It is a mechanical property diagram of the co-extruded cast film with a high-barrier PETG / PET / PETG three-layer structure provided by the present invention, where the thickness of the co-extruded film is 50 μm.

[0033] Figure 3 It is a mechanical property diagram of the co-extruded cast film with a high-barrier PETG / PET / PET three-layer structure provided by the present invention, where the thickness of the co-extruded film is 50 μm. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0035] Example 1 As Figure 1 shown, the high-barrier PETG / PET / PETG three-layer co-extruded cast film provided by the present invention includes: Outer layer PETG: 95 parts by weight of PETG resin, 0.3 parts by weight of acetyl tributyl citrate as plasticizer, 0.1 parts by weight of ethylene bisstearamide as lubricant, 2.5 parts by weight of talc powder with a particle size of 1000 - 8000 mesh, 0.1 parts by weight of fatty acid ester as dispersant; 0.2 parts by weight of epoxy chain extender; 0.1 parts by weight of carbodiimide as anti-hydrolysis agent; 0.1 parts by weight of phosphite as antioxidant.

[0036] Middle layer PET: 92 parts by weight of PET resin, 0.3 parts by weight of plasticizer, 0.1 parts by weight of lubricant, 5 parts by weight of talc powder, 0.1 parts by weight of dispersant; 0.2 parts by weight of chain extender; 0.1 parts by weight of anti-hydrolysis agent.

[0037] Inner layer PETG: 95 parts by weight of PETG resin, 0.3 parts by weight of plasticizer, 0.1 parts by weight of lubricant, 2.5 parts by weight of talc powder, 0.1 parts by weight of dispersant; 0.2 parts by weight of chain extender; 0.1 parts by weight of anti-hydrolysis agent; 0.1 parts by weight of antioxidant.

[0038] Film thickness parameter: 30 μm.

[0039] Coextrusion die head parameters: The die head temperature distribution is 270 - 290 °C, and a fishtail-type runner structure is adopted to achieve uniform distribution of each layer of melt and stable combination of interfaces. Specifically, the fishtail-type runner structure includes three independent channels. Each layer of melt enters the die head through its respective channel. Each layer of runner has a tapered structure, so that the cross-sectional area of each layer of melt gradually decreases during the flow process. The tapered runners converge at the die head outlet to form a laminated melt flow. The laminated melt after convergence is simultaneously extruded at the die head outlet to form a continuous and uniform three-layer coextruded cast film. That is, the fishtail-type runner structure design controls the melt flow rate and direction by gradually reducing the cross-sectional area of the runner, so that different melt layers achieve pressure balance and velocity matching in the convergence area, reduce interface disturbance, ensure uniform thickness of each layer, and improve the overall quality of the cast film.

[0040] Preparation process parameters: Extrusion temperature 280 °C, casting speed 60 m / min, cooling roll temperature 25 °C.

[0041] As Figure 1 shown, it can be seen that the film extruded by the preparation method of the present invention presents a three-layer structure, and the film surfaces between the three layers are uniformly fused, presenting an excellent composite structure.

[0042] Performance test results: The elastic modulus can reach 1900 MPa, the tensile strength can reach 55 MPa, the maximum tensile force can reach 65 N, and the elongation at break can reach 300%.

[0043] Performance test method: The film is vacuum adsorbed on the pulp molded lunch box in a heated state, and 100 °C hot water and 210 °C hot oil are respectively poured into it. After 30 minutes of refinement, there is no leakage at the bottom of the lunch box.

[0044] Example 2 On the basis of Example 1, a high-barrier PETG / PET / PETG three-layer co-extruded cast film is provided, including: Outer layer PETG: 99 parts by weight of PETG resin, 0.1 part by weight of plasticizer, 0.1 part by weight of lubricant, 0.5 part by weight of talcum powder, 0.1 part by weight of dispersant; 0.2 part by weight of chain extender; 0.1 part by weight of anti-hydrolytic agent; 0.1 part by weight of antioxidant.

[0045] Middle layer PET: 99 parts by weight of PET resin, 0.1 part by weight of plasticizer, 0.1 part by weight of lubricant, 0.5 part by weight of talcum powder, 0.1 part by weight of dispersant; 0.2 part by weight of chain extender; 0.1 part by weight of anti-hydrolytic agent; 0.1 part by weight of antioxidant.

[0046] Inner layer PETG: 99 parts by weight of PETG resin, 0.1 part by weight of plasticizer, 0.1 part by weight of lubricant, 0.5 part by weight of talcum powder, 0.1 part by weight of dispersant; 0.2 part by weight of chain extender; 0.1 part by weight of anti-hydrolytic agent; 0.1 part by weight of antioxidant.

[0047] Film thickness parameter: 50 μm.

[0048] Co-extrusion die head parameter: The die head temperature distribution is 280 - 290 °C, and a fish-tail type runner structure design is adopted.

[0049] Preparation process parameter: Extrusion temperature 280 °C, casting speed 60 m / min, cooling roll temperature 25 °C.

[0050] As Figure 2 shown, the mechanical property diagram of the PETG / PET / PETG three-layer co-extruded cast film prepared by the present invention is given. In the figure, the vertical coordinate: force value; the horizontal coordinate: displacement. Test conditions: Electronic tensile testing machine TSL-1002, Jinan Sike Testing Technology Co., Ltd. Test environment, temperature 23 ± 2 °C, humidity 50 ± 5%, and the sample is placed for at least 24 hours after production.

[0051] The colored curve areas in the figure are the test results of 4 repetitions of the same material.

[0052] Performance test results: The elastic modulus can reach 1800 - 2000 MPa, the tensile strength can reach 50 MPa, the maximum tensile force can reach 45 N, and the elongation at break can reach 380%.

[0053] Performance test method: The film is adsorbed on the pulp molded lunch box by vacuum under heating conditions. 100°C hot water and 210°C hot oil are respectively poured into it. After being refined for 30 minutes, there is no leakage at the bottom of the lunch box.

[0054] Example 3 On the basis of Example 1, a high-barrier PETG / PET / PET three-layer coextruded cast film is provided, including: Outer layer PETG: 80 parts by weight of PETG resin, 17.5 parts by weight of PET resin, 0.1 part by weight of plasticizer, 0.1 part by weight of lubricant, 2 parts by weight of talcum powder, 0.1 part by weight of dispersant; 0.1 part by weight of anti-hydrolysis agent.

[0055] Middle layer PET: 99.5 parts by weight of PET resin, 0.1 part by weight of plasticizer, 0.1 part by weight of lubricant, 0.1 part by weight of dispersant, 0.1 part by weight of anti-hydrolysis agent, 0.1 part by weight.

[0056] Inner layer PET: 99.5 parts by weight of PET resin, 0.1 part by weight of plasticizer, 0.1 part by weight of lubricant, 0.1 part by weight of dispersant, 0.1 part by weight of anti-hydrolysis agent.

[0057] Film thickness parameter: 40 μm.

[0058] Coextrusion die head parameters: Die head temperature distribution is 280 - 285°C, and a fish-tail type runner structure design is adopted.

[0059] Preparation process parameters: Extrusion temperature is 280°C, casting speed is 60 m / min, and the temperature of the cooling roll is 25°C.

[0060] As Figure 3 shown, the mechanical property diagram of the PETG / PET / PET three-layer coextruded cast film is given. Test conditions: Electronic tensile testing machine TSL-1002, Jinan Sike Testing Technology Co., Ltd. Test environment, temperature 23 ± 2°C, humidity 50 ± 5%, and the samples are placed for at least 24 hours after production.

[0061] Performance test results: The elastic modulus can reach 1950 MPa, the tensile strength can reach 50 MPa, the maximum tensile force can reach 60 N, and the elongation at break can reach 450%.

[0062] Performance test method: The film is adsorbed on the pulp molded lunch box by vacuum under heating conditions. 100°C hot water and 210°C hot oil are respectively poured into it. After being refined for 30 minutes, there is no leakage at the bottom of the lunch box.

[0063] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high barrier three-layer PET / PETG co-extruded cast film, characterized in that: Comprising: An outer layer, a middle layer, and an inner layer, and the three layers are respectively made of one or more modified materials selected from PET, PETG, PCTG, APTG, PEN, and PEIT; The outer layer, the middle layer, and the inner layer are respectively co-extruded synchronously through a co-extrusion die head with three channels, and the melt flow channels are merged and compounded within the die head to form a three-layer cast film without using adhesives.

2. The high barrier three-layer PET / PETG co-extruded cast film according to claim 1, characterized in that: The modified materials of the outer layer, the middle layer, and the inner layer can be the same or different, and satisfy any of the following structural forms: the outer layer and the inner layer are made of the same material, and the middle layer is made of a material different from the outer layer; the middle layer and the inner layer are made of the same material, and the outer layer is made of a material different from the middle layer.

3. The high-barrier three-layer PET / PETG coextruded cast film according to claim 2, characterized in that, The thicknesses of the outer layer and the inner layer are respectively 2-50 μm, accounting for 1-50% of the total thickness, and the thickness of the middle layer is 5-150 μm, accounting for 10-90% of the total thickness.

4. The high-barrier three-layer PET / PETG coextruded cast film according to claim 3, wherein The outer layer, the middle layer, and the inner layer respectively comprise the following components in parts by weight: 90-100 parts of polyester material, and one or more modified materials selected from PET, PETG, PCTG, APTG, PEN, and PEIT; 0.01-1 part of plasticizer, 0.01-0.5 part of lubricant, 0.01-5 parts of talcum powder, 0.01-0.5 part of dispersant, 0.01-1 part of chain extender, 0.01-1 part of hydrolysis inhibitor, 0.01-1 part of antioxidant.

5. The high-barrier three-layer PET / PETG coextruded cast film according to claim 4, wherein, The formulations of the outer layer, the middle layer, and the inner layer can be the same or different.

6. A preparation method of a high-barrier three-layer PET / PETG co-extruded cast film as described in any one of claims 1 to 5, characterized in that, Including the following steps: Raw material pretreatment, drying and dehumidifying the polyester materials selected for the outer layer, the middle layer, and the inner layer respectively, and the drying time is 4-6 hours; Mixing the polyester material of each layer with the other components of this layer in a high-speed mixer and then extruding through a screw, and the melt compounding temperature is 250-290 °C; Three-layer co-extrusion, using a co-extrusion die head with three channels, the outer layer, the middle layer, and the inner layer are co-extruded synchronously and the melt flow channels are merged and compounded within the die head, and the extrusion temperature is 270-290 °C; Cast forming, quickly cooling and shaping the extruded melt on a cooling roll at 20-30 °C; Surface treatment, corona treatment or plasma treatment on the surface of the formed film to obtain the finished product.

7. The preparation method according to claim 6, characterized in that, The co-extrusion die head adopts a fish-tail type runner structure design to achieve uniform distribution of each layer of melt and stable combination of interfaces.

8. The preparation method according to claim 7, wherein The fish-tail type runner structure includes three independent channels, and the melts of each layer enter the die head through their respective channels. Each layer of runner has a tapered structure, so that the cross-sectional area of each layer of melt gradually decreases during the flow process. The tapered runners converge at the die head outlet to form a laminated melt flow, and the laminated melt after convergence is co-extruded synchronously at the die head outlet to form a continuous and uniform three-layer co-extruded cast film.

9. The preparation method according to claim 8, characterized in that, The high-barrier three-layer PET / PETG co-extruded cast film can withstand boiling water at 100 °C, high-temperature hot oil at 210 °C, and the oxygen and water vapor transmission rates < 10 cm3 / (m2·24h).

10. The preparation method according to claim 6, characterized in that, The high-barrier three-layer PET / PETG co-extruded cast film has an elastic modulus of 1800-2400 MPa, a tensile strength of 50-70 MPa, and an elongation at break of 100-500%.

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