High-toughness pet foamed sheet and method for manufacturing the same

Abstract

This invention discloses a high-strength and tough PET foam sheet and its preparation method, belonging to the field of foam material technology. It comprises the following raw materials in parts by weight: 100 parts food-grade PET resin, 3-7 parts melt reinforcing agent, 3-5 parts crystallization toughening agent, 1-3 parts in-situ fiber-forming reinforcing agent, 1-5 parts compatibility dispersant, and 8-10 parts cyclopentane. The preparation method includes: S1, mixing dried food-grade PET resin with melt reinforcing agent, crystallization toughening agent, in-situ fiber-forming reinforcing agent, and compatibility dispersant to obtain a premix; S2, melting and plasticizing the premix, injecting liquid cyclopentane for blending, and then extruding to a normal pressure environment to obtain a foam sheet blank; S3, cooling and shaping the foam sheet blank, drawing, trimming, and winding to obtain a high-strength and tough PET foam sheet. The foam sheet obtained by this invention has fine and uniform pores, possessing high flexural strength, high modulus, and high impact toughness, with comprehensive performance far exceeding that of traditional PET foam materials.

Description

Technical Field

[0001] This invention belongs to the field of foamed materials technology, specifically relating to a high-strength and tough PET foamed sheet and its preparation method. Background Technology

[0002] Foamed PET materials, due to their lightweight, heat-insulating, cushioning, and recyclable properties, show great potential as a replacement for expanded polystyrene (EPS) in food packaging. However, PET's inherent low melt strength and slow crystallization rate are the main obstacles to achieving high-quality foaming. Low melt strength causes the cell walls to easily break and merge during the foaming process, making it difficult to form uniform and fine cells; the slow crystallization rate prevents the cell structure from stabilizing quickly after molding, resulting in product shrinkage, poor dimensional stability, and insufficient toughness.

[0003] Existing technologies typically employ the addition of multifunctional epoxy resin chain extenders to improve melt strength and the addition of nucleating agents such as inorganic salts and sorbitol derivatives to promote crystallization. However, this approach has significant limitations: First, improving melt strength often comes at the cost of sacrificing melt flowability, increasing processing difficulty; second, while increasing the crystallization rate helps with shaping, rapid crystallization is usually accompanied by a decrease in spherulite size and an increase in material brittleness, offering limited improvement to the toughness of foamed products, and may even worsen it; third, when used in food packaging, the food contact safety of various additives must be guaranteed, further limiting the types of additives that can be selected.

[0004] Cyclopentane, as an environmentally friendly physical blowing agent, exhibits particularly poor compatibility with non-polar PET when used in PET foaming. Although adding compatibilizers can improve this, a key technical challenge remains to be overcome in this field: how to simultaneously address multiple issues such as melt strength, crystallization rate, interfacial compatibility, and final product toughness through a comprehensive formulation design, without compromising food safety or introducing processing difficulties. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects of the prior art and provide a high-strength and tough PET foam sheet and its preparation method. By introducing a crystallizing toughening agent and cooperating with an in-situ fiber-forming reinforcing agent, the foaming processability of PET is synergistically improved while ensuring that all raw material components meet food contact safety standards, and the final foam sheet is endowed with an excellent balance of strength and toughness.

[0006] The objective of this invention can be achieved through the following technical solutions: A high-strength and tough PET foam sheet, comprising the following raw materials by weight: 100 parts food-grade PET resin, 3-7 parts melt reinforcing agent, 3-5 parts crystallizing toughening agent, 1-3 parts in-situ fiber-forming reinforcing agent, 1-5 parts compatibility dispersant and 8-10 parts cyclopentane; The crystallizing toughening agent is prepared by the following method: Thermoplastic polyester elastomer (TPEE) is vacuum dried at 80-100℃ for 4-6 hours, and sorbitol nucleating agent is dried at 100-120℃ for 2-4 hours to completely remove moisture and prevent degradation during processing. Then, the dried TPEE is added to a Hacker internal mixer and heated to 200-220℃ until completely melted. The dried sorbitol nucleating agent is then slowly added at 200-400 rpm. After the addition is complete, the temperature is maintained and the mixture is continued to be mixed for 15-30 minutes to ensure that the TPEE melt is fully wetted and coated with the sorbitol nucleating agent particles. After the blend is discharged, it is quickly placed in liquid nitrogen for quenching to make it brittle. Then, it is pulverized in a cryogenic pulverizer and passed through a 400-mesh sieve to obtain a powdered crystalline toughening agent.

[0007] Furthermore, the mass ratio of TPEE to sorbitol nucleating agent is 1-2:1; the TPEE is a polyester elastomer manufactured by DuPont, model Hytrel 3078FG or Hytrel 4068FG, which has good compatibility with PET and meets relevant food contact safety requirements; the sorbitol nucleating agent is di(3,4-dimethyldibenzyl)sorbitol (DMDBS); the crystallizing toughening agent obtained by the above method is a sea-island structure composite particle, in which TPEE is a continuous sea phase and DMDBS is a dispersed island phase. In the subsequent PET foaming process, the composite particle is heated and melted. The TPEE phase acts as a carrier to promote the final dispersion and release of DMDBS in the PET melt, allowing it to fully exert its heterogeneous nucleation effect and greatly accelerate PET crystallization; at the same time, TPEE itself is dispersed in the matrix as an elastomer phase, playing a toughening effect.

[0008] Furthermore, the intrinsic viscosity of the food-grade PET resin is 0.75-0.95 dL / g, preferably YS-C01 from Hainan Yisheng and CZ-318 from Jiangsu Sanfangxiang. This intrinsic viscosity range can take into account both melt processability and the mechanical properties of the final product.

[0009] Furthermore, the melt reinforcing agent is an epoxy-functionalized styrene-acrylate copolymer, specifically a chain extender from BASF, such as Joncryl® ADR-4468 or Joncryl® ADR-4400. At processing temperature, its epoxy functional groups can react with the carboxyl groups at the ends of the PET molecular chains to achieve chain extension and slight branching, thereby significantly improving melt elasticity and strength and providing the necessary melt skeleton support for foaming.

[0010] Furthermore, the in-situ fiber-forming reinforcing agent is polyamide 6 (PA6), preferably Sinopec Baling Petrochemical BL2280; PA6 and PET are partially compatible systems, and in the high shear and tensile flow field of a twin-screw extruder, its dispersed phase is easily stretched in-situ into micron-sized fibers. These microfibers can not only serve as a physical reinforcing skeleton to improve the modulus and strength of the material, but also produce a multi-scale synergistic toughening effect with the TPEE elastomer in the crystalline toughening agent.

[0011] Furthermore, the compatibility dispersant is maleic anhydride-grafted polyethylene (PE-g-MAH), preferably Dow AMPLIFY™ TY 1053H, with a grafting rate of 0.8-1.2%. The main function of this compatibility dispersant is to improve the interfacial compatibility between the non-polar cyclopentane blowing agent and the polar PET melt, and to promote the uniform dispersion and dissolution of cyclopentane in the melt at a smaller size, forming a stable homogeneous / micro-dispersed system. This is the basis for obtaining a uniform and fine cell structure.

[0012] A method for preparing high-strength and tough PET foam sheet includes the following steps: S1. Dry the food-grade PET resin at 140-160℃ until the moisture content is less than 50ppm. Then, mix the dried food-grade PET resin with melt reinforcing agent, crystallizing toughening agent, in-situ fiber forming reinforcing agent and compatibilizing dispersant in a high-speed mixer for 5-15 minutes to ensure that each component is initially and evenly dispersed to obtain a premix. S2. The premixed material is added to a twin-screw extruder with seven independent temperature control zones for melting and plasticizing. Liquid cyclopentane is injected in the fourth temperature zone, and the die head pressure is controlled at 10-18 MPa to ensure that the cyclopentane is fully dissolved and finely dispersed in the melt. Then, it is extruded to an atmospheric pressure environment through a slit-type flat extrusion die to obtain a foamed sheet preform. S3. The foamed sheet blank is fed into a three-stage slow cooling and shaping roller group. The roller temperature decreases gradually from the inlet to the outlet: the first roller is 110-140℃, the second roller is 70-100℃, and the third roller is 30-60℃. The gradient slow cooling process is conducive to further crystallization and release of internal stress, preventing product warping. After traction, edge trimming and winding, high-strength and tough PET foamed sheet is obtained.

[0013] Furthermore, the length-to-diameter ratio of the twin-screw extruder is 44-48:1; the temperature settings for each zone are: Zone 1 235-250℃, Zone 2 260-270℃, Zone 3 265-275℃, Zone 4 255-265℃, Zone 5 245-260℃, Zone 6 235-250℃, and Zone 7 230-245℃; Zone 1 is the solid conveying zone, Zones 2 and 3 are the melt plasticizing zone, Zone 4 is the foaming agent injection and mixing zone, Zones 5 and 6 are the homogenization, cooling, and pressurization zone, and Zone 7 is the constant temperature conveying zone.

[0014] Furthermore, the die head temperature is 190-205℃. When the melt leaves the die lip and the pressure drops sharply, cyclopentane vaporizes and foams. At the same time, DMDBS in the crystallizing toughening agent effectively induces the rapid crystallization of PET in the cell wall, instantly solidifying the cell structure.

[0015] Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following significant advantages: This invention involves mixing DMDBS and TPEE in a specific ratio, followed by freeze-pulverization to obtain a crystallizing toughening agent. During processing, the crystallizing toughening agent effectively releases and uniformly distributes DMDBS, ensuring extremely high heterogeneous nucleation efficiency. At the same time, the TPEE phase is also well dispersed, playing an elastic toughening role. This integrated design and synergistic mechanism fundamentally achieves precise control over the crystallization behavior and toughness contribution of PET. The crystallizing toughening agent (micro-nano scale) of this invention is combined with in-situ fiber-forming PA6 (micron scale) to form a multi-scale reinforcing and toughening network in the PET matrix; PA6 microfibers serve as the macroscopic reinforcing skeleton, mainly bearing the load; TPEE elastomer particles serve as microscopic toughening points, blunting crack tips and inducing plastic deformation; DMDBS ensures rapid crystallization of the matrix to provide rigidity; the synergistic effect of the three enables the foamed material to exhibit an excellent balance of strength and toughness even at low density; The preparation method of this invention is highly compatible with existing PET extrusion foaming production lines, with a clear process window. In particular, the matching of the die temperature and the PET crystallization temperature is easy to implement and control. The resulting foamed sheet has fine and uniform pores, and possesses high flexural strength, high modulus and high impact toughness. Its comprehensive performance far exceeds that of traditional PET foam materials. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1 This embodiment provides a crystallizing toughening agent, which is prepared by the following method: 100 parts by weight of TPEE (DuPont Hytrel 3078FG) were vacuum dried at 80°C for 4 hours, and 100 parts by weight of DMDBS were dried at 100°C for 4 hours. The dried TPEE was then added to a Hacker internal mixer and heated to 200°C until completely melted. The dried DMDBS was then slowly added at 200 rpm. After the addition was complete, the temperature was maintained and the mixture was continued to be mixed for 15 minutes. After discharge, the mixture was quickly placed in liquid nitrogen for quenching to make it brittle. It was then pulverized in a cryogenic pulverizer and passed through a 400-mesh sieve to obtain a powdered crystalline toughening agent.

[0018] Example 2 This embodiment provides a crystallizing toughening agent, which is prepared by the following method: 150 parts by weight of TPEE (DuPont Hytrel 4068FG) were vacuum dried at 90°C for 6 hours, and 100 parts by weight of DMDBS were dried at 110°C for 3 hours. The dried TPEE was then added to a Hacker internal mixer and heated to 210°C until completely melted. The dried DMDBS was then slowly added at 300 rpm. After the addition was complete, the temperature was maintained and the mixture was continued to be mixed for 25 minutes. After discharge, the mixture was quickly placed in liquid nitrogen for quenching to make it brittle. It was then pulverized in a cryogenic pulverizer and passed through a 400-mesh sieve to obtain a powdered crystalline toughening agent.

[0019] Example 3 This embodiment provides a crystallizing toughening agent, which is prepared by the following method: 200 parts by weight of TPEE (DuPont Hytrel 4068FG) were vacuum dried at 100°C for 5 hours, and 100 parts by weight of DMDBS were dried at 120°C for 2 hours. The dried TPEE was then added to a Hacker internal mixer and heated at 220°C until completely melted. The dried DMDBS was then slowly added at 400 rpm. After the addition was complete, the temperature was maintained and the mixture was continued to be mixed for 30 minutes. After discharge, the mixture was quickly placed in liquid nitrogen for quenching to make it brittle. It was then pulverized in a cryogenic pulverizer and passed through a 400-mesh sieve to obtain a powdered crystalline toughening agent.

[0020] Example 4 This embodiment provides a high-strength and tough PET foam sheet, which comprises the following raw materials by weight: 100 parts of food-grade PET resin (intrinsic viscosity 0.86 dL / g, Hainan Yisheng YS-C01), 3 parts of melt reinforcing agent (BASF Joncryl® ADR-4468), 3 parts of crystallizing toughening agent prepared in Example 1, 1 part of in-situ fiber-forming reinforcing agent (PA6 BL2280), 1 part of compatibility dispersant (Dow AMPLIFY™ TY 1053H), and 8 parts of cyclopentane; This high-strength and tough PET foam sheet is prepared by the following steps: S1. Dry the food-grade PET resin at 140℃ to a moisture content of 30ppm, and then mix the dried food-grade PET resin with melt reinforcing agent, crystallizing toughening agent, in-situ fiber-forming reinforcing agent and compatibilizing dispersant in a high-speed mixer for 5 minutes to obtain a premix. S2. The premixed material is added to a twin-screw extruder with a length-to-diameter ratio of 46:1 and seven independent temperature control zones for melt plasticization. The temperature of each zone is set as follows: Zone 1 235℃, Zone 2 260℃, Zone 3 265℃, Zone 4 255℃, Zone 5 245℃, Zone 6 235℃, Zone 7 230℃. Liquid cyclopentane is injected in the fourth temperature zone, and the die head pressure is controlled at 10MPa. Then, it is extruded to an atmospheric pressure environment through a slit-type flat extrusion die at a temperature of 190℃ to obtain a foamed sheet preform. S3. The foamed sheet blank is fed into a three-stage slow cooling and shaping roller group. The roller temperature decreases gradually from the inlet to the outlet: 110°C for the first roller, 70°C for the second roller, and 30°C for the third roller. After traction, edge trimming, and winding, a high-strength and tough PET foamed sheet with a thickness of 5mm is obtained.

[0021] Example 5 This embodiment provides a high-strength and tough PET foam sheet, which comprises the following raw materials by weight: 100 parts of food-grade PET resin (intrinsic viscosity 0.83 dL / g, Jiangsu Sanfangxiang CZ-318), 5 parts of melt reinforcing agent (BASF Joncryl® ADR-4468), 4 parts of crystallizing toughening agent prepared in Example 2, 2 parts of in-situ fiber-forming reinforcing agent (PA6 BL2280), 3 parts of compatibility dispersant (Dow AMPLIFY™ TY 1053H), and 9 parts of cyclopentane; This high-strength and tough PET foam sheet is prepared by the following steps: S1. Dry the food-grade PET resin at 150°C until the water content is 30ppm. Then, mix the dried food-grade PET resin with melt reinforcing agent, crystallizing toughening agent, in-situ fiber-forming reinforcing agent and compatibilizing dispersant in a high-speed mixer for 10 minutes to obtain a premix. S2. The premixed material is added to a twin-screw extruder with a length-to-diameter ratio of 46:1 and seven independent temperature control zones for melt plasticization. The temperature of each zone is set as follows: Zone 1 245℃, Zone 2 265℃, Zone 3 270℃, Zone 4 260℃, Zone 5 255℃, Zone 6 242℃, Zone 7 238℃. Liquid cyclopentane is injected in the fourth temperature zone, and the die head pressure is controlled at 14MPa. Then, it is extruded to an atmospheric pressure environment through a slit-type flat extrusion die at a temperature of 200℃ to obtain a foamed sheet preform. S3. The foamed sheet blank is fed into a three-stage slow cooling and shaping roller group. The roller temperature decreases gradually from the inlet to the outlet: 130°C for the first roller, 85°C for the second roller, and 45°C for the third roller. After traction, edge trimming, and winding, a high-strength and tough PET foamed sheet with a thickness of 5mm is obtained.

[0022] Example 6 This embodiment provides a high-strength and tough PET foam sheet, which comprises the following raw materials by weight: 100 parts of food-grade PET resin (intrinsic viscosity 0.83 dL / g, Jiangsu Sanfangxiang CZ-318), 7 parts of melt reinforcing agent (BASF Joncryl® ADR-4400), 5 parts of crystallizing toughening agent prepared in Example 3, 3 parts of in-situ fiber-forming reinforcing agent (PA6 BL2280), 5 parts of compatibility dispersant (Dow AMPLIFY™ TY 1053H) and 10 parts of cyclopentane; This high-strength and tough PET foam sheet is prepared by the following steps: S1. Dry the food-grade PET resin at 160℃ to a moisture content of 25ppm, and then mix the dried food-grade PET resin with melt reinforcing agent, crystallizing toughening agent, in-situ fiber-forming reinforcing agent and compatibilizing dispersant in a high-speed mixer for 15min to obtain a premix. S2. The premixed material is added to a twin-screw extruder with a length-to-diameter ratio of 46:1 and seven independent temperature control zones for melt plasticization. The temperature of each zone is set as follows: Zone 1 250℃, Zone 2 270℃, Zone 3 275℃, Zone 4 265℃, Zone 5 260℃, Zone 6 250℃, Zone 7 245℃. Liquid cyclopentane is injected in the fourth temperature zone, and the die head pressure is controlled at 18MPa. Then, it is extruded through a slit-type flat extrusion die at a temperature of 205℃ to a normal pressure environment to obtain a foamed sheet preform. S3. The foamed sheet blank is fed into a three-stage slow cooling and shaping roller group. The roller temperature decreases gradually from the inlet to the outlet: 140°C for the first roller, 100°C for the second roller, and 60°C for the third roller. After traction, edge trimming, and winding, high-strength and tough PET foamed sheet is obtained.

[0023] Comparative Example 1 The difference between this comparative example and Example 5 is that an equal amount of DMDBS was used to replace the crystallizing toughening agent prepared in Example 2, while the other raw materials and steps were the same.

[0024] Comparative Example 2 The difference between this comparative example and Example 5 is that an equal amount of TPEE (DuPont Hytrel 4068FG) was used to replace the crystallizing toughening agent prepared in Example 2, while the other raw materials and steps were the same.

[0025] Comparative Example 3 The difference between this comparative example and Example 5 is that an equal amount of food-grade microcrystalline cellulose short fibers are used to replace the in-situ fiber-forming reinforcing agent, while the other raw materials and steps are the same.

[0026] Performance tests were conducted on Examples 4-6 and Comparative Examples 1-3: Apparent density: Tested according to GB / T 6343 "Determination of apparent density of foamed plastics and rubber"; Average cell diameter and cell size CV (coefficient of variation): The cross-section of the foamed sheet was observed using a scanning electron microscope (SEM). The diameter of at least 100 cells was randomly measured using image analysis software. The average cell diameter was calculated, and the cell size CV was calculated as a percentage of the standard deviation of the average cell diameter to evaluate the cell uniformity.

[0027] Bending strength and bending modulus: Three-point bending test was conducted according to GB / T 9341 "Determination of bending properties of plastics".

[0028] Notched impact strength: Tested according to GB / T 1843 "Determination of impact strength of plastic cantilever beam", the specimen is a notched specimen.

[0029] Compressive strength: Tested according to GB / T 8813 "Determination of compressive properties of rigid foamed plastics".

[0030] Total migration: Based on GB 31604.1 "National Food Safety Standard General Rules for Migration Test of Food Contact Materials and Articles" and related methods, simulate food contact conditions and determine the total migration of non-volatile substances to assess their food contact safety.

[0031] The results are shown in Table 1: Table 1 As shown in Table 1, the PET foamed sheets prepared in Examples 4-6 of this invention exhibited a fine and uniform cell structure at low density and demonstrated excellent comprehensive mechanical properties, with Example 5 showing the best performance. Compared with Example 5, Comparative Example 1, due to uneven dispersion and easy aggregation of the nucleating agent, resulted in large and uneven cells, leading to a significant decrease in all mechanical properties, especially an impact toughness loss exceeding 50%. This demonstrates the crucial role of TPEE as a dispersion carrier in the crystallizing toughening agent. Comparative Example 2, lacking efficient heterogeneous nucleation sites, had a slow crystallization rate and poor cell stability and size uniformity. Although it had a certain toughening effect, the improvement in material rigidity was limited. Comparative Example 3, because the reinforcing phase could not form microfibers in situ during processing and had weak interfacial bonding with the matrix, had a much weaker reinforcing and toughening effect than PA6 with in-situ fiber formation. The total migration of all samples met food safety standards. In summary, this invention, through the multi-scale synergistic design of crystallizing toughening agents and in-situ fiber-forming reinforcing agents, simultaneously and effectively solves the synergistic problems of pore structure control, rigidity improvement and toughness enhancement in PET foaming while ensuring food safety, and achieves significant optimization of comprehensive performance.

[0032] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0033] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-strength and tough PET foam sheet, characterized in that, Including the following parts by weight of raw materials: 100 parts food-grade PET resin, 3-7 parts melt reinforcing agent, 3-5 parts crystallizing toughening agent, 1-3 parts in-situ fiber-forming reinforcing agent, 1-5 parts compatibilizing dispersant, and 8-10 parts cyclopentane; The crystallizing toughening agent is prepared by the following method: TPEE and sorbitol nucleating agent were dried separately. Then, the dried TPEE was heated to 200-220℃ until completely melted. The dried sorbitol nucleating agent was added at a speed of 200-400 rpm. After the addition was completed, the temperature was maintained and the mixture was continued to be mixed for 15-30 minutes. After discharge, the mixture was quenched in liquid nitrogen and then pulverized in a low-temperature pulverizer. After passing through a 400-mesh sieve, the crystallizing toughening agent was obtained.

2. The high-strength and tough PET foam sheet according to claim 1, characterized in that, The mass ratio of TPEE to sorbitol nucleating agent is 1-2:1; the TPEE is Hytrel 3078FG or Hytrel 4068FG; the sorbitol nucleating agent is di(3,4-dimethyldibenzyl)sorbitol.

3. The high-strength and tough PET foam sheet according to claim 1, characterized in that, The intrinsic viscosity of the food-grade PET resin is 0.75-0.95 dL / g.

4. The high-strength and tough PET foam sheet according to claim 1, characterized in that, The melt enhancer is either Joncryl® ADR-4468 or Joncryl® ADR-4400.

5. The high-strength and tough PET foam sheet according to claim 1, characterized in that, The in-situ fiber-forming reinforcing agent is polyamide 6 with model number BL2280.

6. The high-strength and tough PET foam sheet according to claim 1, characterized in that, The compatibility dispersant is maleic anhydride-grafted polyethylene with model number AMPLIFY™ TY 1053H.

7. The method for preparing a high-strength and tough PET foam sheet according to claim 1, characterized in that, Includes the following steps: S1. Dry the food-grade PET resin to a moisture content of less than 50 ppm, and then mix the dried food-grade PET resin with melt reinforcing agent, crystallization toughening agent, in-situ fiber forming reinforcing agent and compatibilizer to obtain a premix. S2. The premixed material is added to a twin-screw extruder with seven independent temperature control zones for melting and plasticizing. Liquid cyclopentane is injected in the fourth temperature zone, and the die head pressure is controlled at 10-18 MPa. Then, it is extruded to an atmospheric pressure environment through a slit-type flat extrusion die to obtain a foamed sheet preform. S3. The foamed sheet blank is fed into a three-stage slow cooling and shaping roller group for cooling and shaping. Then, after traction, edge trimming and winding, high-strength and tough PET foamed sheet is obtained.

8. The method for preparing a high-strength and tough PET foam sheet according to claim 7, characterized in that, The twin-screw extruder has an aspect ratio of 44-48:1; the temperature settings for each zone are: Zone 1 235-250℃, Zone 2 260-270℃, Zone 3 265-275℃, Zone 4 255-265℃, Zone 5 245-260℃, Zone 6 235-250℃, and Zone 7 230-245℃.

9. The method for preparing a high-strength and tough PET foam sheet according to claim 7, characterized in that, The temperature of the die head is 190-205℃.

10. A method for preparing a high-strength and tough PET foam sheet according to claim 7, characterized in that, The temperature of the three-stage slow cooling and shaping roller group decreases gradually from the inlet to the outlet: 110-140℃ for the first roller, 70-100℃ for the second roller, and 30-60℃ for the third roller.

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