Preparation method and application of high-temperature-resistant and microwave-resistant PET material

Abstract

The application discloses a preparation method and application of a PET composite material for high-temperature-resistant and microwave-resistant food contact compatible with an electromagnetic oven. The preparation method comprises the following steps: firstly, low-temperature plasma activation and nano ceramic heat insulation coating of a PET film, chromium-free passivation and micro-roughening treatment of a food-grade aluminum foil, and water-resistant and oil-resistant coating of a food-grade base paper to complete the functional modification of the three types of substrates; secondly, the modified PET substrate, the passivated aluminum foil and the low-hygroscopic functional paper are sequentially laminated through twice dry compounding; and finally, a three-stage gradient heating program is adopted to complete the crosslinking and curing of the adhesive layer. The composite material prepared by the application can be compatible with both the electromagnetic oven and the microwave heating scene, has no delamination and deformation under long-time heating of the electromagnetic oven, has good high-temperature stability of interlayer bonding force, has no abnormal smell and abnormal smell under microwave heating, and meets the national standard for food contact safety indexes, and can be processed into various disposable food contact containers, and is suitable for multiple scene applications such as pre-prepared dishes, take-out and instant food.

Description

Technical Field

[0001] This invention relates to the technical field of PET material preparation methods, specifically to a method for preparing and applying a high-temperature and microwave-resistant PET material. Background Technology

[0002] With the rapid development of the pre-cooked food industry, food delivery, and convenient heating foods, the market demand for food contact packaging containers that can be directly heated continues to increase. Currently, most common disposable food packaging is made of pure paper, ordinary plastic, or a single aluminum-plastic composite structure, which has obvious limitations in terms of scenario compatibility: ordinary paper and PET plastic containers can only be used in microwave ovens and cannot be used for induction heating on induction cookers; although metal containers can be used on induction cookers, they cannot be used in microwave ovens, and their high cost and weight make them unsuitable for disposable catering scenarios.

[0003] Existing paper-aluminum-plastic composite packaging containing aluminum foil can utilize the electromagnetic induction effect of aluminum foil for induction cooker heating, but it still has several shortcomings: First, the long-term operating temperature of ordinary PET film is usually below 120℃. When heated by an induction cooker, the aluminum foil induction heating temperature is high, which can easily lead to melting and deformation of the PET layer, failure and delamination of the interlayer adhesive layer, and cannot meet the requirements of long-term induction cooker heating; Second, conventional aluminum foil composite films are prone to problems such as tip arcing and localized overheating in microwave ovens, making them incompatible with microwave heating scenarios and limiting their application range; Third, traditional aluminum foil surface passivation mostly uses... The use of chromium-containing treatment processes poses a risk of heavy metal migration, making it difficult to meet the safety requirements for food contact materials; fourth, the water resistance, oil resistance, and moisture resistance of ordinary paper-based composite structures are limited. After contact with oily or soupy foods or in high-temperature and high-humidity environments, the paper is prone to moisture absorption deformation and a decrease in interlayer peel strength; fifth, most existing composite films use constant-temperature curing processes, resulting in uneven cross-linking reaction rates of the adhesives. This can lead to problems such as excessively rapid surface cross-linking and insufficient internal curing, which not only affects the high-temperature stability of interlayer bonding but also increases the risk of free small molecules migrating to the food side.

[0004] Therefore, developing a PET composite packaging material that is compatible with both induction cookers and microwave ovens, has stable high-temperature resistance, and is safe for food contact is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing and applying high-temperature and microwave-resistant PET materials, thus solving the problems mentioned in the background section.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a high-temperature and microwave-resistant PET material, comprising the following steps: (1) Functional modification of substrate: S1. Take a PET film, perform low-temperature plasma activation treatment on one side of its surface, coat the activated surface with a nano-ceramic heat insulation coating and heat cure it to obtain a modified PET substrate with a surface ceramic functional layer. S2. Take food-grade aluminum foil and perform chromium-free passivation treatment on both sides to form a continuous and dense passivation protective layer, thus obtaining a passivated aluminum foil substrate. S3. Take food-grade base paper, apply water-resistant and oil-resistant coating to one side of its surface and cure it to obtain low moisture absorption functional paper substrate. (2) First dry lamination: Food-grade solvent-free polyurethane adhesive is coated on the first surface of the passivated aluminum foil substrate, and the coated surface is aligned and pressed with the non-ceramic coating surface of the modified PET substrate to obtain a PET-aluminum foil primary composite film. (3) Second dry lamination: Food-grade solvent-free polyurethane adhesive is coated on the second surface of the passivated aluminum foil in the PET-aluminum foil primary composite film. The coated surface is then aligned and pressed with the uncoated surface of the low moisture absorption functional paper substrate to obtain a composite semi-finished product consisting of a ceramic functional layer, a PET layer, an adhesive layer, a passivated aluminum foil layer, an adhesive layer, a base paper layer, and a water-resistant and oil-resistant layer stacked sequentially. (4) Gradient curing: The composite semi-finished product is placed in a constant temperature and humidity curing environment, and the adhesive layer is cross-linked and cured by a segmented gradient heating program to obtain the induction cooker compatible high temperature and microwave resistant PET composite material.

[0007] Preferably, in step (1) S1, the PET film is a high-temperature resistant copolymer PET film with a thickness of 12~25μm; the discharge power of the low-temperature plasma activation treatment is 300~500W, the processing linear velocity is 10~20m / min, and the processing atmosphere is an argon-oxygen mixture with a volume ratio of 3:1; the nano-ceramic heat insulation coating is a nano-silica-alumina composite ceramic coating with a dry film thickness of 2~5μm, a thermal curing temperature of 120~150℃, and a curing time of 30~60s.

[0008] Preferably, in step (1) S2, the food-grade aluminum foil is 8011-O state soft food-grade aluminum foil with a thickness of 9~15μm and a pinhole count per unit area of ​​≤50 / m. 2 The chromium-free passivation treatment uses a titanium-zirconium food-grade passivation solution with a pH value of 3.5~4.5, a treatment temperature of 40~60℃, a treatment time of 5~15s, and a passivation protective layer thickness of 0.05~0.2μm. After passivation treatment, the surface wetting tension of both sides of the aluminum foil is ≥38mN / m. Before the first dry lamination, the passivated aluminum foil undergoes a micro-roughening treatment on the adhesive coating areas on both sides. The micro-roughening is performed using a food-grade weak acid etching process. The etching solution is a 1%~3% (w / w) citric acid aqueous solution. The treatment temperature is 25~35℃ and the treatment time is 3~8s. After the treatment, the surface roughness Ra of the aluminum foil coating area is 0.2~0.5μm.

[0009] Preferably, in step (1) S3, the food-grade base paper is pure wood pulp food-grade white cardboard with a basis weight of 180~250g / m³. 2 Lateral flexural strength ≥30 times, Cobb water absorption ≤15g / m² 2 The water-resistant and oil-repellent coating uses a water-based fluorocarbon food-grade oil-repellent agent, with a dry film coating weight of 0.5~1.5 g / m². 2 After coating and curing, the base paper has an oil resistance Kit value ≥10 and a moisture absorption rate ≤2% after being placed in an environment of 23℃ and 65% relative humidity for 24 hours.

[0010] Preferably, in step (2), the food-grade solvent-free polyurethane adhesive is a two-component aliphatic solvent-free polyurethane adhesive that conforms to GB4806.10-2016 standard for adhesives for food contact; the dry basis application rate of the adhesive is 2.5~3.5 g / m³. 2 The surface temperature of the composite roller is 70~90℃, the composite line pressure is 0.3~0.5MPa, and the operating line speed of the composite machine is 120~180m / min.

[0011] Preferably, in step (3), the food-grade solvent-free polyurethane adhesive used for the second dry lamination is the same as that used for the first lamination, and the dry-based adhesive application rate is 3.0~4.0 g / m². 2 The surface temperature of the composite roller is 60~80℃, the composite line pressure is 0.2~0.4MPa, and the operating line speed of the composite machine is 100~150m / min; the areal density deviation of the obtained composite semi-finished product is controlled within ±3%.

[0012] Preferably, the segmented gradient heating and curing process in step (4) is a three-stage constant temperature and humidity curing process: the first stage is to keep the temperature at 35~40℃ and relative humidity at 40%~60% for 12~18h; the second stage is to raise the temperature to 45~50℃ and keep the temperature at 24~36h; the third stage is to raise the temperature to 55~60℃ and keep the temperature at 12~18h, with a total curing time of 48~72h; the circulating wind speed in the curing room is controlled at 0.2~0.5m / s; After gradient curing, the composite material is placed in a standard environment of 23~25℃ and 50%±5% relative humidity for 24 hours for aging equilibrium treatment.

[0013] The obtained PET composite material meets the following performance requirements: after continuous heating on a 2200W rated power induction cooker for 15 minutes, the film layer shows no delamination, wrinkling, or melting deformation; the maximum temperature of the PET surface on the food contact side is ≤180℃; and the in-plane heating uniformity deviation is ≤±10%. The interlayer peel strength at room temperature is ≥2.5N / 15mm, and after being boiled at 121℃ for 30 minutes, the interlayer peel strength is ≥2.0N / 15mm. After heating in an 800W rated power microwave oven for 5 minutes, there is no arcing, no local overheating deformation, and no odor release.

[0014] The composite material after aging equilibrium treatment meets the following food contact safety requirements: the residual amount of free isocyanate in the adhesive layer is ≤0.01mg / dm³. 2 The total migration amount after immersion in 4% acetic acid medium at 60°C for 10 days is ≤0.5 mg / dm³. 2 The heavy metal migration levels meet the requirements of the national food safety standard GB4806.9-2016.

[0015] This invention also proposes the application of the induction cooker compatible high temperature and microwave resistant PET composite material prepared according to the above method in the preparation of disposable food contact containers. The composite material is die-cut and pressed into a container that can be heated in an induction cooker or microwave oven. The container is any one of paper bowl, paper lunch box, paper cup, or food tray.

[0016] This invention provides a method for preparing and applying a high-temperature and microwave-resistant PET material, which has the following beneficial effects: 1. After plasma activation, the PET film is coated with a nano-ceramic heat-insulating coating, which not only enhances the coating adhesion but also blocks the heat conduction of the aluminum foil, reducing the surface temperature of the PET on the food side and alleviating melting deformation during induction cooker heating; the aluminum foil adopts chromium-free titanium zirconium passivation instead of the traditional chromium-containing process, forming a dense protective layer and improving wetting tension to meet food contact safety requirements. Combined with the micro-roughening of the coating area to increase the bonding area, it improves the interlayer peel strength and temperature resistance stability; the base paper is coated with water-resistant and oil-resistant coating to reduce moisture absorption and the risk of oil penetration, and improve dimensional stability in oily and soupy environments.

[0017] 2. Two-stage composite matching of corresponding process parameters ensures substrate bonding effect and controls surface density deviation; three-stage gradient heating and curing allows the adhesive to gradually cross-link and cure, avoiding the problem of uneven curing in constant temperature curing. The cross-linking of the adhesive layer is more complete and uniform, which can improve the interlayer peel strength after room temperature and high temperature cooking, while reducing free isocyanate residue, reducing the risk of small molecule migration, and meeting food contact safety requirements.

[0018] 3. The aluminum foil layer can respond to the alternating magnetic field of the induction cooker to induce heating. Combined with the buffering and temperature equalization effect of the ceramic heat insulation layer, it ensures that there is no delamination, wrinkling, or melting deformation under long-term heating of the induction cooker, and the heating uniformity is stable. The thin passivated aluminum foil with dielectric layers on both sides can avoid tip arcing and local overheating during microwave heating, and there is no odor release. It is suitable for microwave scenarios and expands the application range. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation method of the present invention; Figure 2 This is a schematic diagram of a layered structure of a composite material. Figure 3 This is a comparison chart of interlayer peel strength; Figure 4 Comparison of the highest temperatures reached when PET surfaces are heated by an induction cooker; Figure 5 This is a schematic diagram of the PET composite material prepared in Example 1; Figure 6 This is a schematic diagram of the PET composite material structure prepared in Example 2; Figure 7 This is a schematic diagram of the PET composite material prepared in Example 3. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0021] like Figure 1 As shown, the preparation method of the high temperature and microwave resistant PET material of the present invention includes four major processes in sequence: substrate functionalization modification, first dry lamination, second dry lamination, three-stage gradient curing and aging balance treatment. Among them, the substrate functionalization modification is carried out independently on three types of substrates: PET film, aluminum foil and base paper.

[0022] like Figure 2 As shown, the composite material obtained by the present invention has a seven-layer laminated structure, which consists of a ceramic functional layer, a PET substrate layer, a first adhesive layer, a passivated aluminum foil layer, a second adhesive layer, a base paper layer, and a water-resistant and oil-resistant layer from top to bottom. The upper ceramic functional layer is the food contact side.

[0023] All raw and auxiliary materials used in the following examples are food-grade commercially available products: the high-temperature resistant copolymer PET film meets the standards for plastic materials for food contact; the 8011-O state soft aluminum foil meets the relevant requirements for aluminum foil for food contact; the titanium-zirconium passivation solution is a food-grade chromium-free passivating agent; the water-based fluorocarbon oil repellent meets the specifications for additives in paper for food contact; and the two-component aliphatic solvent-free polyurethane adhesive meets the GB4806.10-2016 standard.

[0024] Example 1: The preparation steps of the induction cooker-compatible high-temperature and microwave-resistant PET composite material in this embodiment are as follows: (1) Functional modification of substrate: S1. Take a high-temperature resistant copolymer PET film with a thickness of 16μm and perform low-temperature plasma activation treatment on one side of its surface: discharge power 400W, treatment line speed 15m / min, treatment atmosphere is argon-oxygen mixed gas with a volume ratio of 3:1; after activation, coat the activated surface with a nano-silica-alumina composite ceramic heat insulation coating, control the dry film thickness to 3μm, and heat cure at 135℃ for 45s to obtain a modified PET substrate with a surface ceramic functional layer.

[0025] S2. Take a 12μm thick 8011-O state soft food-grade aluminum foil with a pinhole count ≤50 per unit area. 2 Chromium-free passivation treatment was performed on both sides of the aluminum foil: a titanium-zirconium food-grade passivation solution was used, the pH value of the passivation solution was adjusted to 4.0, the treatment temperature was 50℃, and the treatment time was 10s, forming a continuous passivation protective layer with a thickness of about 0.1μm. After passivation, the wetting tension of both sides of the aluminum foil was ≥38mN / m.

[0026] After passivation, the adhesive coating area on both sides of the aluminum foil is subjected to micro-roughening treatment: a 2% citric acid aqueous solution is used as the etching solution, the treatment temperature is 30℃, the treatment time is 5s, and after etching, it is washed with pure water and dried with hot air to obtain the passivated aluminum foil substrate; the surface roughness Ra of the coating area after treatment is about 0.35μm.

[0027] S3, Take a quantity of 220g / m 2 Food-grade white cardboard made from pure wood pulp, with a transverse folding endurance of ≥30 times and a Cobb water absorption value of ≤15g / m³. 2 A water-based fluorocarbon food-grade oil repellent was applied to one side of the surface, with the dry film coating amount controlled at 1.0 g / m². 2 After being cured by hot air, a low-moisture-absorbing functional paper substrate is obtained; the oil resistance Kit value of the cured base paper is ≥10, and the moisture absorption rate is ≤2% after being placed in an environment of 23℃ and 65% relative humidity for 24 hours.

[0028] (2) First dry lamination: A two-component aliphatic solvent-free polyurethane adhesive is coated on the first surface of the passivated aluminum foil substrate, with the dry adhesive application amount controlled at 3.0 g / m². 2 The adhesive-coated surface is aligned and bonded with the non-ceramic coating surface of the modified PET substrate, and then pressed by a composite roller. The surface temperature of the composite roller is 80℃, the composite line pressure is 0.4MPa, and the running line speed of the composite machine is 150m / min to obtain a PET-aluminum foil primary composite film.

[0029] (3) Second dry lamination: The same solvent-free polyurethane adhesive is coated on the second surface of the passivated aluminum foil in the PET-aluminum foil primary composite film. The dry adhesive application amount is controlled at 3.5 g / m. 2 The coated surface is aligned and pressed with the uncoated surface of the low-moisture-absorbing functional paper substrate. The surface temperature of the composite roller is 70℃, the composite line pressure is 0.3MPa, and the running line speed of the composite machine is 120m / min. The areal density deviation of the resulting composite semi-finished product is controlled within ±3%, and finally a structure is formed by stacking the ceramic functional layer, PET layer, adhesive layer, passivated aluminum foil layer, adhesive layer, base paper layer, and water-resistant and oil-resistant layer in sequence.

[0030] (4) Gradient curing: The composite semi-finished product is sent into a constant temperature and humidity curing chamber and a three-stage gradient curing process is adopted: the first stage is to keep the temperature at 38℃ and 50% relative humidity for 15 hours, the second stage is to raise the temperature to 48℃ and keep the temperature for 30 hours, and the third stage is to raise the temperature to 58℃ and keep the temperature for 15 hours, with a total curing time of 60 hours; the circulating wind speed in the curing chamber is controlled at 0.3 m / s.

[0031] After curing, the composite material is placed in a standard environment of 23~25℃ and 50%±5% relative humidity for 24 hours for aging equilibrium treatment, and the finished PET composite material is obtained.

[0032] like Figure 5 As shown, the PET composite material prepared in this embodiment consists of the following layers from top to bottom: a 3 μm thick nano-SiO2-Al2O3 ceramic functional layer, a 16 μm thick high-temperature resistant copolymer PET layer, a solvent-free polyurethane adhesive layer, a 12 μm thick 8011 passivated aluminum foil layer, a solvent-free polyurethane adhesive layer, and a basis weight of 220 g / m³. 2 The food-grade white cardboard base layer has a dry film weight of 1.0 g / m³. 2 A water-based fluorocarbon water-resistant and oil-repellent layer; this composite material can be processed into rolls and die-cut and pressed into paper bowl-shaped containers. Example 2: The preparation method in this embodiment is basically the same as that in Example 1, except that the process parameters are as follows: S1 has a PET film thickness of 12μm, a plasma discharge power of 300W, a processing line speed of 20m / min, a ceramic coating dry film thickness of 2μm, a thermal curing temperature of 120℃, and a curing time of 60s. In S2, the aluminum foil thickness is 9μm, the passivation solution pH value is 3.5, the processing temperature is 40℃, the processing time is 15s, and the passivation protective layer thickness is 0.05μm; the micro-roughening etching solution has a citric acid mass fraction of 1%, the processing temperature is 25℃, the processing time is 8s, and the Ra after processing is about 0.2μm. S3 medium base paper basis weight 180g / m³ 2 Oil repellent dry film coating amount: 0.5 g / m²2 ; The initial dry-based adhesive application rate is 2.5 g / m². 2 The temperature of the composite roller is 70℃, the linear pressure is 0.3MPa, and the linear speed is 180m / min. The second dry-based adhesive application rate is 3.0 g / m². 2 The temperature of the composite roller is 60℃, the linear pressure is 0.2MPa, and the linear speed is 150m / min. Gradient curing: The first stage is curing at 35℃ and 40% relative humidity for 12 hours, the second stage is curing at 45℃ for 36 hours, and the third stage is curing at 55℃ for 12 hours, with a total duration of 60 hours and a circulation wind speed of 0.2 m / s.

[0033] like Figure 6 As shown, the PET composite material prepared in this embodiment consists of the following layers from top to bottom: a nano-SiO2-Al2O3 ceramic functional layer with a dry film thickness of 2 μm, a high-temperature resistant copolymer PET layer with a thickness of 12 μm, a solvent-free polyurethane adhesive layer, an 8011 passivated aluminum foil layer with a thickness of 9 μm, a passivation layer thickness of 0.05 μm, and a surface roughness Ra of approximately 0.2 μm, a solvent-free polyurethane adhesive layer, and a basis weight of 180 g / m³. 2 The food-grade white cardboard base layer has a dry film weight of 0.5 g / m³. 2 A water-based fluorocarbon water-resistant and oil-resistant layer; the composite material can be processed into rolls and die-cut and pressed into paper bowl-shaped containers.

[0034] Example 3: The preparation method in this embodiment is basically the same as that in Example 1, except that the process parameters are as follows: In S1, the PET film thickness is 25μm, the plasma discharge power is 500W, the processing line speed is 10m / min, the dry film thickness of the ceramic coating is 5μm, the heat curing temperature is 150℃, and the curing time is 30s. In S2, the aluminum foil thickness is 15μm, the passivation solution pH value is 4.5, the processing temperature is 60℃, the processing time is 5s, and the passivation protective layer thickness is 0.2μm; the micro-roughening etching solution has a citric acid mass fraction of 3%, the processing temperature is 35℃, the processing time is 3s, and the Ra after processing is about 0.5μm. S3 medium base paper basis weight 250g / m 2 Oil repellent dry film coating amount: 1.5 g / m² 2 ; The initial dry-based adhesive application rate was 3.5 g / m². 2 The temperature of the composite roller is 90℃, the linear pressure is 0.5MPa, and the linear speed is 120m / min. The second dry-based adhesive application rate is 4.0 g / m². 2 The temperature of the composite roller is 80℃, the linear pressure is 0.4MPa, and the linear speed is 100m / min. Gradient curing: The first stage is curing at 40℃ and 60% relative humidity for 18 hours, the second stage is curing at 50℃ for 24 hours, and the third stage is curing at 60℃ for 18 hours, with a total duration of 60 hours and a circulation wind speed of 0.5 m / s.

[0035] like Figure 7 As shown, the PET composite material prepared in this embodiment consists of, from top to bottom: a nano-SiO2-Al2O3 ceramic functional layer with a dry film thickness of 2.5 μm, a high-temperature resistant copolymer PET layer with a thickness of 14 μm, and a dry base adhesive application amount of 2.8 g / m³. 2 The first solvent-free polyurethane adhesive layer, a 10μm thick double-sided passivated 8011 aluminum foil layer, and a dry-based adhesive application rate of 3.2g / m² 2 The second solvent-free polyurethane adhesive layer, with a basis weight of 200 g / m³ 2 The food-grade white cardboard base layer has a dry film weight of 0.8 g / m³. 2 A water-based fluorocarbon water-resistant and oil-resistant layer; the composite material can be processed into rolls and die-cut and pressed into paper bowl-shaped containers.

[0036] Comparative Example 1: This comparative example omits the nano-ceramic heat-insulating coating on the surface of the PET film. The rest of the preparation process and parameters are completely consistent with those of Example 1: High-temperature resistant copolymer PET film of the same specification is taken and subjected to low-temperature plasma activation treatment with the same parameters. The nano-ceramic coating is not coated. The activated surface is directly bonded to the adhesive. The subsequent dry lamination, gradient curing and other processes are the same as those of Example 1.

[0037] Comparative Example 2: This comparative example uses conventional constant temperature curing instead of three-stage gradient temperature curing. The rest of the preparation process and parameters are completely consistent with Example 1: The composite semi-finished product is placed in a curing chamber at 50°C and 50% relative humidity for 60 hours of constant temperature curing. The circulating wind speed in the curing chamber is the same as in Example 1. After curing, the standard environmental aging balance treatment is also carried out.

[0038] Comparative Example 3: This comparative example omits the chromium-free passivation and micro-roughening treatment of the aluminum foil. The remaining preparation processes and parameters are completely consistent with those of Example 1: 8011-O state food-grade aluminum foil of the same specification is taken, and without passivation and weak acid etching treatment, double-sided dry lamination is directly performed. The subsequent processes are the same as those of Example 1.

[0039] Performance testing: The composite materials prepared in the above three sets of examples and three sets of comparative examples were subjected to performance testing. The test methods and results are as follows: 1. Induction cooker heating performance: The sample was made into a flat-bottomed container with a diameter of 15cm, 500mL of room temperature water was added, and it was placed on a 2200W rated power induction cooker and heated continuously for 15min. The appearance was observed and the surface temperature of the PET was measured.

[0040] 2. Peel strength: The peel strength at room temperature was tested according to GB / T8808-1988 "Peel Test Method for Flexible Composite Plastic Materials"; the peel strength was tested again after the sample was boiled at 121℃ for 30 minutes.

[0041] 3. Microwave compatibility performance: After filling the sample with water, place it in an 800W microwave oven and heat for 5 minutes. Observe whether there is sparking, deformation, or odor release.

[0042] 4. Food contact safety performance: Free isocyanate residue, total migration in 4% acetic acid medium and heavy metal migration were tested according to GB31604 series standards.

[0043] The test results are as follows: like Figure 3 As shown, the peel strength at room temperature and the peel strength after cooking of the samples in each embodiment are significantly better than those of the comparative examples, with the interlayer bonding strength of Example 3 being the highest. The peel strength of Comparative Examples 2 and 3 decreased significantly after high-temperature cooking and could not meet the requirements.

[0044] like Figure 4 As shown, in Comparative Example 1, the highest surface temperature of the PET reached 197°C after heating with an induction cooker because no nano-ceramic heat insulation coating was applied, exceeding the limit requirement; the highest surface temperature of the PET samples in each embodiment was controlled within 180°C, meeting the requirements for high-temperature resistance.

[0045] ; Test results show that the PET composite material prepared using the method of this invention meets all design requirements and is suitable for both induction cookers and microwave heating applications. The interlayer bonding is stable, and food contact safety is compliant. This composite material can be die-cut and press-molded into various disposable food contact containers such as paper bowls, paper lunch boxes, paper cups, and food trays, suitable for industrial applications in multiple fields. Specific application scenarios include: In the pre-cooked food industry, it can be used as a packaging container for pre-cooked food products, allowing consumers to reheat them directly in a microwave oven or induction cooker without having to change the container, thus simplifying the consumption process. In the food delivery and fast food sector, it is suitable for packaging hot soup and hot oil fast food. Relying on the excellent water-resistant, oil-proof, and high-temperature resistant properties of the material, it can effectively avoid problems such as oil leakage, water leakage, and heat deformation of the container. At the same time, it supports reheating and reheating after the user arrives at home. In the field of instant food, it is used as a packaging container for instant noodles, self-heating rice, instant porridge and other ready-to-eat foods, and is compatible with mainstream household heating equipment, making it more widely applicable. In the supermarket fresh food and cooked food sector, it can be used as a cooked food packaging tray and a fresh food heating packaging box, suitable for on-site heating of cooked food in supermarkets and secondary heating by customers at home; For convenient home dining scenarios, it can be used as disposable heatable tableware and snack trays. It is safe and non-toxic, and produces no odor when heated, combining practicality and safety.

[0046] This material is compatible with existing flexible packaging mass production equipment, making production convenient and cost-controllable, and possessing good feasibility for industrial production and market promotion.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-temperature and microwave-resistant PET material, characterized in that, Includes the following steps: (1) Functional modification of substrate: S1. Take a PET film, perform low-temperature plasma activation treatment on one side of its surface, coat the activated surface with a nano-ceramic heat insulation coating and heat cure it to obtain a modified PET substrate with a surface ceramic functional layer. S2. Take food-grade aluminum foil and perform chromium-free passivation treatment on both sides to form a continuous and dense passivation protective layer, thus obtaining a passivated aluminum foil substrate. S3. Take food-grade base paper, apply water-resistant and oil-resistant coating to one side of its surface and cure it to obtain low moisture absorption functional paper substrate. (2) First dry lamination: Food-grade solvent-free polyurethane adhesive is coated on the first surface of the passivated aluminum foil substrate, and the coated surface is aligned and pressed with the non-ceramic coating surface of the modified PET substrate to obtain a PET-aluminum foil primary composite film. (3) Second dry lamination: Food-grade solvent-free polyurethane adhesive is coated on the second surface of the passivated aluminum foil in the PET-aluminum foil primary composite film. The coated surface is then aligned and pressed with the uncoated surface of the low moisture absorption functional paper substrate to obtain a composite semi-finished product consisting of a ceramic functional layer, a PET layer, an adhesive layer, a passivated aluminum foil layer, an adhesive layer, a base paper layer, and a water-resistant and oil-resistant layer stacked sequentially. (4) Gradient curing: The composite semi-finished product is placed in a constant temperature and humidity curing environment, and the adhesive layer is cross-linked and cured by a segmented gradient heating program to obtain the induction cooker compatible high temperature and microwave resistant PET composite material.

2. The method for preparing high-temperature and microwave-resistant PET material according to claim 1, characterized in that, In step (1) S1, the PET film is a high-temperature resistant copolymer PET film with a thickness of 12~25μm; the discharge power of the low-temperature plasma activation treatment is 300~500W, the treatment line speed is 10~20m / min, and the treatment atmosphere is an argon-oxygen mixture with a volume ratio of 3:1; the nano-ceramic heat insulation coating is a nano-silica-alumina composite ceramic coating with a dry film thickness of 2~5μm, a heat curing temperature of 120~150℃, and a curing time of 30~60s.

3. The method for preparing high-temperature and microwave-resistant PET material according to claim 1, characterized in that, In step (1) S2, the food-grade aluminum foil is 8011-O state soft food-grade aluminum foil with a thickness of 9~15μm and a pinhole count of ≤50 per unit area. 2 The chromium-free passivation treatment uses a titanium-zirconium food-grade passivation solution with a pH value of 3.5~4.5, a treatment temperature of 40~60℃, a treatment time of 5~15s, and a passivation protective layer thickness of 0.05~0.2μm. After passivation treatment, the surface wetting tension of both sides of the aluminum foil is ≥38mN / m. Before the first dry lamination, the passivated aluminum foil undergoes a micro-roughening treatment on the adhesive coating areas on both sides. The micro-roughening is performed using a food-grade weak acid etching process. The etching solution is a 1%~3% (w / w) citric acid aqueous solution. The treatment temperature is 25~35℃ and the treatment time is 3~8s. After the treatment, the surface roughness Ra of the aluminum foil coating area is 0.2~0.5μm.

4. The method for preparing high-temperature and microwave-resistant PET material according to claim 1, characterized in that, In step (1) S3, the food-grade base paper is pure wood pulp food-grade white cardboard with a basis weight of 180~250g / m³. 2 Lateral flexural strength ≥30 times, Cobb water absorption ≤15g / m² 2 The water-resistant and oil-repellent coating uses a water-based fluorocarbon food-grade oil-repellent agent, with a dry film coating weight of 0.5~1.5 g / m². 2 After coating and curing, the base paper has an oil resistance Kit value ≥10 and a moisture absorption rate ≤2% after being placed in an environment of 23℃ and 65% relative humidity for 24 hours.

5. The method for preparing high-temperature and microwave-resistant PET material according to claim 1, characterized in that, In step (2), the food-grade solvent-free polyurethane adhesive is a two-component aliphatic solvent-free polyurethane adhesive that conforms to GB4806.10-2016 standard for adhesives for food contact; the dry basis application rate of the adhesive is 2.5~3.5 g / m³. 2 The surface temperature of the composite roller is 70~90℃, the composite line pressure is 0.3~0.5MPa, and the operating line speed of the composite machine is 120~180m / min.

6. The method for preparing the high-temperature and microwave-resistant PET material according to claim 5, characterized in that, In step (3), the food-grade solvent-free polyurethane adhesive used for the second dry lamination is the same as that used for the first lamination, with a dry application rate of 3.0~4.0 g / m³. 2 The surface temperature of the composite roller is 60~80℃, the composite line pressure is 0.2~0.4MPa, and the running line speed of the composite machine is 100~150m / min; the areal density deviation of the obtained composite semi-finished product is controlled within ±3%.

7. The method for preparing high-temperature and microwave-resistant PET material according to claim 1, characterized in that, The segmented gradient heating and curing process described in step (4) is a three-stage constant temperature and humidity curing process: the first stage is to keep the temperature at 35~40℃ and relative humidity at 40%~60% for 12~18h; the second stage is to raise the temperature to 45~50℃ and keep the temperature at 24~36h; the third stage is to raise the temperature to 55~60℃ and keep the temperature at 12~18h, with a total curing time of 48~72h; the circulating wind speed in the curing room is controlled at 0.2~0.5m / s; After gradient curing, the composite material is placed in a standard environment of 23~25℃ and 50%±5% relative humidity for 24 hours for aging equilibrium treatment.

8. The application of the induction cooker-compatible high-temperature and microwave-resistant PET composite material prepared according to any one of claims 1-7 in the preparation of disposable food contact containers, characterized in that, The composite material is die-cut and pressed to form a container that can be heated in an induction cooker or microwave oven. The container can be any one of a paper bowl, paper lunch box, paper cup, or food tray.

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