A method for producing a foamed product based on 3D printing and supercritical foaming

Abstract

The present application relates to a kind of based on 3D printing and supercritical foaming preparation foamed product method, belong to foaming technical field.The present application provides a kind of based on 3D printing and supercritical foaming preparation foamed product method, the method includes modification step, 3D printing step, irradiation crosslinking step and foaming step.Preparation foamed product using the method of the present application, can be combined with the internal structure that 3D printing can do and the cell structure that supercritical foaming technology can do Preparation high-performance foamed product, can realize the integrated molding of complex structure foamed product, and, intelligent degree is high, can not use injection mold, improve yield and save cost.Foamed product prepared using the method of the present application has energy feedback, can realize structure freedom and precision customization, and the characteristics such as uniform foot feeling, and no chemical residue, and the performance is superior.At the same time, foaming ratio controllable of foamed product prepared using the method of the present application.

Description

Technical Field

[0001] This invention relates to a method for preparing foamed products based on 3D printing and supercritical foaming, belonging to the field of foaming technology. Background Technology

[0002] Foam materials are lightweight materials that have formed a porous structure within their structure through physical or chemical methods. Due to their lightweight, high resilience, and shock absorption properties, foam materials are widely used in the manufacture of sports equipment such as shoe midsoles. However, manufacturing complex structures for sports equipment like shoe midsoles remains a challenge, and how to precisely control the microscopic pore morphology and macroscopic foam structure is a problem that urgently needs to be solved.

[0003] 3D printing (3DP), also known as additive manufacturing technology (AM), is a technique for manufacturing solid parts by adding materials layer by layer based on 3D CAD data. 3D printing can precisely manufacture sports equipment such as shoe midsoles with complex structures. However, excessive weight and high printing costs are challenges, and the performance of sports equipment such as shoe midsoles made purely using 3D printing technology is far inferior to that of foam materials. Therefore, it is necessary to combine 3D printing with foam materials to achieve a complementary advantage.

[0004] However, existing 3D printing foam materials mostly use traditional chemical foaming, which does not involve supercritical foaming. This means they cannot combine the superior performance of supercritical foaming with the superior performance of 3D printing. Furthermore, they suffer from drawbacks such as chemical residues, numerous processing steps affecting yield, large dimensional control errors, and difficulty in manufacturing complex shapes. Additionally, existing 3D printing foam materials often use TPU, which has high density and poor foot feel. These shortcomings severely limit the application of supercritical foaming technology and 3D printing technology in the fabrication of sports equipment such as shoe midsoles. Summary of the Invention

[0005] To address the aforementioned shortcomings, this invention provides a method for preparing foamed products based on 3D printing and supercritical foaming, the method comprising the following steps: Modification step: The thermoplastic polyester elastomer and the foaming modifier are mixed and then molded to obtain the modified thermoplastic polyester elastomer; the foaming modifier contains nucleating agents, dispersants, antioxidants and ultraviolet absorbers. 3D printing steps: 3D printing is performed using a modified thermoplastic polyester elastomer to obtain a 3D printed part; the stacking structure of the 3D printed part is Rectilinear, Concentric, Honeycomb, Gyroid, Cubic and / or Octagram. Irradiation crosslinking step: The 3D printed part is subjected to irradiation crosslinking to obtain the irradiated crosslinked 3D printed part; the irradiation crosslinking dose is 3Mev~7Mev; Foaming step: Supercritical foaming is performed on the irradiated cross-linked 3D printed parts to obtain foamed products.

[0006] In one embodiment of the present invention, the mass ratio of nucleating agent, dispersant, antioxidant and ultraviolet absorber in the foaming modifier is 0.1~0.3:0.2~0.5:0.1~0.2:0.5~1; the mass ratio of the thermoplastic polyester elastomer and the foaming modifier is 98~99:1~2.

[0007] In one embodiment of the present invention, the nucleating agent comprises TMC300 nucleating agent and / or TMC200 nucleating agent; the dispersant comprises No. 10 white oil and / or No. 15 white oil; and the antioxidant comprises antioxidant 1076 and / or antioxidant 1010.

[0008] In one embodiment of the present invention, the molding includes injection molding and / or extrusion molding.

[0009] In one embodiment of the present invention, the 3D printing step includes: first preparing 3D printing filament using a modified thermoplastic polyester elastomer, and then using the 3D printing filament for 3D printing to obtain a 3D printed part.

[0010] In one embodiment of the present invention, in the irradiation crosslinking step, the dose of the irradiation crosslinking is 5 MeV to 7 MeV.

[0011] In one embodiment of the present invention, the supercritical foaming includes the following steps: Saturation step: The irradiated cross-linked 3D printed part is placed in a foaming container at the primary foaming temperature T1, and a physical foaming agent is introduced into the foaming container until the pressure inside the foaming container reaches the primary foaming pressure P1; the irradiated cross-linked 3D printed part is continuously placed in the foaming container at the primary foaming pressure P1 and the primary foaming temperature T1, so that the physical foaming agent reaches a dissolution balance in the irradiated cross-linked 3D printed part; the time for the physical foaming agent to reach a dissolution balance in the irradiated cross-linked 3D printed part is the primary placement time t1; One-stage foaming step: After the saturation step, the pressure inside the foaming container is released to 0MPa at a depressurization rate R, so that the irradiated cross-linked 3D printed part undergoes one-stage foaming, resulting in a one-stage foamed 3D printed part. Heating Step: After the first foaming step is completed, the temperature inside the foaming container is raised to the second foaming temperature T2, and a physical foaming agent is introduced into the foaming container until the pressure inside the foaming container reaches the second foaming pressure P2; the 3D printed part that has undergone the first foaming is continuously placed in the foaming container at the pressure of the second foaming pressure P2 and the temperature of the second foaming temperature T2, causing the air in the pores of the 3D printed part that has undergone the first foaming to expand; the time for the gas in the pores of the 3D printed part that has undergone the first foaming to expand is the second placement time t2. Secondary foaming step: After the heating step is completed, the pressure in the foaming container is released to 0MPa at a depressurization rate R, so that the 3D printed part that was foamed once will undergo secondary foaming to obtain a foamed product.

[0012] In one embodiment of the present invention, the secondary foaming temperature T2 = the primary foaming temperature T1 + (30~40)℃; the secondary foaming pressure P2 = the primary foaming pressure P1 + (5~10)MPa.

[0013] In one embodiment of the present invention, the primary foaming temperature T1 is 110℃~130℃; the secondary foaming temperature T2 is 150℃~170℃; the primary foaming pressure P1 is 15MPa~25MPa; the secondary foaming pressure P2 is 20MPa~35MPa; the primary placement time t1 is 120min~130min; the secondary placement time t2 is 20min~25min; and the depressurization rate R is 5MPa / s~8MPa / s.

[0014] In one embodiment of the present invention, the physical foaming agent comprises supercritical carbon dioxide fluid and / or supercritical nitrogen fluid.

[0015] In one embodiment of the present invention, the physical foaming agent is composed of supercritical carbon dioxide fluid and supercritical nitrogen fluid; the pressure ratio of the supercritical carbon dioxide fluid and the supercritical nitrogen fluid in the physical foaming agent is 5~7:8~30.

[0016] In one embodiment of the present invention, the foaming density ratio of the foamed product is 12 to 16 times.

[0017] In one embodiment of the present invention, the foamed product includes a foamed shoe material midsole, a foamed insole, or a foamed irregularly shaped structural component.

[0018] In one embodiment of the present invention, the foamed product is a foamed shoe material midsole; when the foamed product is a foamed shoe material midsole, in the 3D printing step, the heel area of ​​the shoe material midsole-shaped 3D printed part adopts a Gyroid (spiral curved surface) stacking structure, and the forefoot area of ​​the shoe material midsole-shaped 3D printed part adopts a Cubic (cubic) stacking structure.

[0019] The present invention also provides a foamed product, which is prepared by the above method.

[0020] In one embodiment of the present invention, the foaming density ratio of the foamed product is 12 to 16 times.

[0021] In one embodiment of the present invention, the foamed product includes a foamed shoe material midsole, a foamed insole, or a foamed irregularly shaped structural component.

[0022] This invention also provides the application of the above method in the preparation of foamed products.

[0023] In one embodiment of the present invention, the foaming density ratio of the foamed product is 12 to 16 times.

[0024] In one embodiment of the present invention, the foamed product includes a foamed shoe material midsole, a foamed insole, or a foamed irregularly shaped structural component.

[0025] The technical solution of this invention has the following advantages: This invention provides a method for preparing foamed products based on 3D printing and supercritical foaming. The method includes a modification step, a 3D printing step, an irradiation crosslinking step, and a foaming step. Using this method, high-performance foamed products can be prepared by combining the internal structures achievable through 3D printing with the cell structures achievable through supercritical foaming technology. It enables the one-piece molding of complex foamed products and features a high degree of automation, eliminating the need for injection molds, thus improving yield and saving costs. The foamed products prepared using this method exhibit strong energy feedback, allowing for structural freedom and precise customization, uniform foot feel, and no chemical residue, resulting in superior performance. Furthermore, the foaming ratio of the 3D-printed parts can be controlled by adjusting the foaming temperature and irradiation crosslinking dosage, with the foaming ratio controllable within the range of 1 to 18 times. Therefore, this method has significant application prospects in the preparation of foamed products such as shoe midsoles.

[0026] Furthermore, the modification step includes: mixing the thermoplastic polyester elastomer and a foaming modifier, followed by molding to obtain the modified thermoplastic polyester elastomer; the foaming modifier comprises a nucleating agent, a dispersant, an antioxidant, and an ultraviolet absorber. This modification step increases the crystallinity of the thermoplastic polyester elastomer, reduces the difficulty of printing and processing the thermoplastic polyester elastomer, and enhances the mechanical properties of the printed structure, which is beneficial for subsequent 3D printing.

[0027] Furthermore, the foaming step includes: supercritical foaming of the irradiated cross-linked 3D printed part to obtain a foamed product; the supercritical foaming includes: first, saturating the irradiated cross-linked 3D printed part in a physical foaming agent for primary foaming, and then expanding the primary foamed 3D printed part in a physical foaming agent for secondary foaming. The secondary foaming process in the foaming step can obtain a foamed product with a lower open-cell ratio, thereby improving the mechanical properties of the foamed product, such as resilience and tear resistance, and also ensuring that the appearance of the foamed product remains relatively intact. Attached Figure Description

[0028] Figure 1 Photograph of the shoe material midsole prepared in Example 1.

[0029] Figure 2 : A diagram of the foam structure of the shoe material midsole obtained in Example 1.

[0030] Figure 3 : Stacked structure of shoe material midsole obtained in Example 1. Detailed Implementation

[0031] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0032] For any experimental steps or conditions not specified in the following examples, the procedures or conditions described in the literature in this field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0033] The twin-screw extruder used in the following embodiments is a CJWS-35 extruder with an L / D ratio of 52 from Changzhou Jinwei Intelligent Chemical Equipment Co., Ltd., with a maximum extrusion temperature of 210℃ in the highest section (sections 6-8); the wire drawing machine used in the following embodiments is a single-coil wire drawing machine from Suzhou Enbede Machinery Co., Ltd., with four temperature sections ranging from low to high: 200℃, 210℃, 210℃, and 200℃; the 3D printer used in the following embodiments is a Tuozhu H2DC printer; and the irradiation crosslinking equipment used in the following embodiments is an irradiation accelerator from CGN Irradiation Technology Co., Ltd.

[0034] Example 1: A shoe midsole and its preparation method This embodiment provides a shoe material midsole, and the preparation method of the shoe material midsole includes the following steps: Modification steps: TPEE 4058 (purchased from Celanese), TMC300 nucleating agent, white oil (purchased from Suzhou Hesen Special Oils Co., Ltd., No. 10 food-grade white oil), antioxidant 1076 (purchased from BASF) and anti-UV masterbatch (purchased from Celanese) were mixed in a mass ratio of 98.6:0.2:0.5:0.2:0.5 and then extruded into granules using a twin-screw extruder to obtain modified thermoplastic polyester elastomer; 3D printing steps: First, 3D printing filament is prepared using modified thermoplastic polyester elastomer. Then, 3D printing is performed using the 3D printing filament to obtain a 3D printed part in the shape of a shoe midsole (midsole length is 280mm). During 3D printing, the heel area of ​​the shoe midsole 3D printed part adopts a Gyroid (spiral curved surface) stacked structure, and the forefoot area adopts a Cubic (cubic) stacked structure (the heel area adopts a Gyroid structure, which can efficiently convert impact kinetic energy into elastic potential energy and feedback, ensuring a smooth landing; the forefoot area adopts a Cubic structure, which can provide more direct rigid support when pushing off the ground, in order to achieve efficient "propulsion rebound" and reduce energy loss). Irradiation crosslinking step: Apply 5 MeV irradiation crosslinking to the 3D printed part using an irradiation crosslinking device to obtain an irradiation crosslinked 3D printed part; Saturation step: The irradiated cross-linked 3D printed part is placed in a supercritical foaming vessel (internal dimensions of 1m×2m) at a temperature of 120℃ (primary foaming temperature T1), and supercritical carbon dioxide and supercritical nitrogen are introduced into the supercritical foaming vessel at a pressure ratio of 7:17 until the pressure inside the supercritical foaming vessel reaches 24MPa (primary foaming pressure P1); the irradiated cross-linked 3D printed part is placed in the supercritical foaming vessel at a pressure of 24MPa and a temperature of 120℃ for 120 minutes to allow the supercritical carbon dioxide and supercritical nitrogen to reach dissolution equilibrium in the irradiated cross-linked 3D printed part; One-stage foaming step: After the saturation step, the pressure in the supercritical foaming vessel is released to 0 MPa at a rate of 7 MPa / s (pressure relief rate R), causing the irradiated cross-linked 3D printed part to undergo one-stage foaming, resulting in a one-stage foamed 3D printed part. Heating Step: After the first foaming step is completed, the temperature inside the foaming container is raised to 160℃ (secondary foaming temperature T2), and supercritical carbon dioxide and supercritical nitrogen with a pressure ratio of 7:23 are introduced into the supercritical foaming kettle until the pressure inside the supercritical foaming kettle reaches 30MPa (secondary foaming pressure P2); the 3D printed part after the first foaming is placed in the supercritical foaming kettle at a pressure of 30MPa and a temperature of 160℃ for 20 minutes, so that the air in the pores of the 3D printed part after the first foaming expands; Secondary foaming step: After the heating step, the pressure inside the supercritical foaming reactor is released to 0 MPa at a rate of 7 MPa / s (pressure relief rate R), causing the 3D printed part to undergo secondary foaming after the primary foaming, resulting in a foamed product. This shoe material midsole is named Shoe Material Midsole 1.

[0035] Comparative Example 1: A shoe material midsole and its preparation method This comparative example provides a shoe material midsole. The preparation method of the shoe material midsole is as follows: based on Example 1, the mass ratio of TPEE 4058, TMC300 nucleating agent, white oil, antioxidant 1076, and anti-UV masterbatch in the foaming modifier is replaced with 98.6:0.2:0.5:0:0. This shoe material midsole is named Shoe Material Midsole 2.

[0036] Comparative Example 2: A shoe material midsole and its preparation method This comparative example provides a shoe material midsole. The preparation method of the shoe material midsole is as follows: based on Example 1, the mass ratio of TPEE 4058, TMC300 nucleating agent, white oil, antioxidant 1076, and UV-resistant masterbatch in the foaming modifier is replaced to 98.6:0.2:0.5:0:0.5. This shoe material midsole is named Shoe Material Midsole 3. During the actual 3D printing process, it was found that the preform was difficult to cool and solidify before foaming, and the final foamed product lacked shape.

[0037] Comparative Example 3: A shoe material midsole and its preparation method This comparative example provides a shoe material midsole. The preparation method of the shoe material midsole is as follows: based on Example 1, the 3D printed structure of the shoe material midsole 3D printed part is replaced with the entire shoe using a Gyroid (spiral curved surface). This shoe material midsole is named shoe material midsole 4. The printed structure of this shoe material midsole is lightweight and material-saving, with an internal structure that meanders like waves, resulting in light weight and strong pressure resistance.

[0038] Comparative Example 4: A shoe material midsole and its preparation method This comparative example provides a shoe material midsole. The preparation method of the shoe material midsole is as follows: based on Example 1, the 3D printed structure of the shoe material midsole-shaped 3D printed part is replaced with the entire shoe made of Cubic (cubic). This shoe material midsole is named shoe material midsole 5. The printed structure of this shoe material midsole is high-strength, very strong in all directions, and the stress direction is relatively uniform.

[0039] Comparative Example 5: A shoe material midsole and its preparation method This comparative example provides a shoe material midsole, which is prepared by replacing the foaming pressure in the first foaming step of Example 1 with 28 MPa instead of 24 MPa. This shoe material midsole is named Shoe Material Midsole 6.

[0040] Comparative Example 6: A shoe material midsole and its preparation method This comparative example provides a shoe material midsole, which is prepared by removing the radiation crosslinking step from Example 1. This shoe material midsole is named Shoe Material Midsole 7. During the actual foaming process, Shoe Material Midsole 7 exhibited 100% foam bulging due to excessively low melt strength, making subsequent testing impossible.

[0041] Comparative Example 7: A shoe material midsole and its preparation method This comparative example provides a shoe material midsole, the preparation method of which is as follows: based on Example 1, only one foaming process is performed after the saturation step, without subsequent heating and secondary foaming processes. The specific operation is as follows: Saturation step: The irradiated cross-linked 3D printed part is placed in a supercritical foaming vessel (internal dimensions 1m×2m) at a temperature of 160℃ (foaming temperature), and supercritical carbon dioxide and supercritical nitrogen are introduced into the supercritical foaming vessel at a pressure ratio of 7:17 until the pressure inside the supercritical foaming vessel reaches 24MPa (foaming pressure); the irradiated cross-linked 3D printed part is placed in the supercritical foaming vessel at a pressure of 24MPa and a temperature of 160℃ for 120 minutes to allow the supercritical carbon dioxide and supercritical nitrogen to reach dissolution equilibrium in the irradiated cross-linked 3D printed part; Foaming Step: After the saturation step, the pressure inside the supercritical foaming reactor is released to 0 MPa at a rate of 7 MPa / s (pressure relief rate R), causing the irradiated cross-linked 3D printed part to foam, resulting in a foamed product. This shoe material midsole is named "Shoe Material Midsole 8".

[0042] Comparative Example 8: A shoe material midsole and its preparation method This comparative example provides a shoe material midsole. The preparation method of the shoe material midsole is as follows: based on Comparative Example 7, the supercritical carbon dioxide and supercritical nitrogen used in the saturation step with a pressure ratio of 7:17 are replaced with supercritical carbon dioxide and supercritical nitrogen with a pressure ratio of 3:15, reducing the pressure inside the supercritical foaming reactor from 24 MPa to 20 MPa. This shoe material midsole is named Shoe Material Midsole 9. During the actual foaming process, Shoe Material Midsole 9 suffers from low pressure, resulting in low bubble nucleation density and a foaming ratio that does not meet requirements.

[0043] Experiment Example 1: Performance Verification of Foamed Products This experimental example provides performance testing for midsoles made of different shoe materials. The experimental procedure is as follows: The density of the shoe material midsole 1 to shoe material midsole 8 obtained in Example 1 and Comparative Examples 2 to 7 was tested using the drainage method specified in GB / T 4472-2011, and the foaming ratio was calculated based on the density (the calculation formula is: ratio = density before foaming / density after foaming). The results are shown in Table 1.

[0044] The hardness of the shoe material midsole 1 to shoe material midsole 8 obtained in Example 1 and Comparative Examples 2 to 7 was tested using the method specified in GB / T10807-2006, and the results are shown in Table 1.

[0045] The pendulum rebound performance of the shoe material midsole 1 to shoe material midsole 8 obtained in Example 1 and Comparative Examples 2 to 7 was tested using the method specified in HG / T4993-2016. The results are shown in Table 1.

[0046] The delamination tear performance of the shoe material midsoles 1 to 8 obtained in Example 1 and Comparative Examples 2 to 7 was tested using the method specified in GB / T3903.29, and the results are shown in Table 1.

[0047] The external structure of the shoe material midsole 1 obtained in Example 1 was observed and photographed, and the results are as follows: Figure 1 As shown. The cell structure of the shoe material midsole 1 obtained in Example 1 was observed using a scanning electron microscope, and the results are as follows. Figure 2 As shown. The internal structure (heel area) of the shoe material midsole 1 obtained in Example 1 was observed after cutting it open, and the results are as follows. Figure 3 As shown.

[0048] Depend on Figures 1-3As shown in Table 1, the shoe material midsole 1 obtained in Example 1 is far superior in performance to the shoe material midsole 2 to shoe material midsole 9 obtained in Comparative Examples 2 to 8. Among them, Comparative Example 1 did not add antioxidants and anti-UV additives, and the resulting shoe blank was yellowish in color and not resistant to light aging. Comparative Example 2 also had similar problems. Compared with Example 1, Comparative Example 5 had too high a primary pressure and too large a primary foaming ratio, resulting in no shaping effect and poor final foaming results. Comparative Example 6 had insufficient melt strength to support the final expansion ratio, making it difficult to maintain the overall shape. Comparative Example 7 did not use a secondary foaming process, resulting in an overly intense foaming process, excessive average kinetic energy of cell nucleation, uncontrolled cell long stroke, inability to maintain the shoe blank shape, failure to maintain the printed structure, and a counterproductive effect on the performance of maintaining the cell structure.

[0049] Table 1 Performance of different shoe midsoles

[0050] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing foamed products based on 3D printing and supercritical foaming, characterized in that, The method includes the following steps: Modification step: The thermoplastic polyester elastomer and the foaming modifier are mixed and then molded to obtain the modified thermoplastic polyester elastomer; the foaming modifier contains nucleating agents, dispersants, antioxidants and ultraviolet absorbers. 3D printing steps: 3D printing is performed using a modified thermoplastic polyester elastomer to obtain a 3D printed part; the stacking structure of the 3D printed part is Rectilinear, Concentric, Honeycomb, Gyroid, Cubic and / or Octagram. Irradiation crosslinking step: The 3D printed part is subjected to irradiation crosslinking to obtain the irradiated crosslinked 3D printed part; the irradiation crosslinking dose is 3Mev~7Mev; Foaming step: Supercritical foaming is performed on the irradiated cross-linked 3D printed parts to obtain foamed products.

2. The method as described in claim 1, characterized in that, In the foaming modifier, the mass ratio of nucleating agent, dispersant, antioxidant and ultraviolet absorber is 0.1~0.3:0.2~0.5:0.1~0.2:0.5~1; the mixing mass ratio of thermoplastic polyester elastomer and foaming modifier is 98~99:1~2.

3. The method as described in claim 1 or 2, characterized in that, The nucleating agent comprises TMC300 nucleating agent and / or TMC200 nucleating agent; the dispersant comprises No. 10 white oil and / or No. 15 white oil; the antioxidant comprises antioxidant 1076 and / or antioxidant 1010.

4. The method as described in claim 1, characterized in that, The 3D printing steps include: first, preparing 3D printing filament using a modified thermoplastic polyester elastomer, and then using the 3D printing filament for 3D printing to obtain a 3D printed part.

5. The method as described in claim 1, characterized in that, The supercritical foaming process includes the following steps: Saturation step: The irradiated cross-linked 3D printed part is placed in a foaming container at the primary foaming temperature T1, and a physical foaming agent is introduced into the foaming container until the pressure inside the foaming container reaches the primary foaming pressure P1; the irradiated cross-linked 3D printed part is continuously placed in the foaming container at the primary foaming pressure P1 and the primary foaming temperature T1, so that the physical foaming agent reaches a dissolution balance in the irradiated cross-linked 3D printed part; the time for the physical foaming agent to reach a dissolution balance in the irradiated cross-linked 3D printed part is the primary placement time t1; One-stage foaming step: After the saturation step, the pressure inside the foaming container is released to 0MPa at a depressurization rate R, so that the irradiated cross-linked 3D printed part undergoes one-stage foaming, resulting in a one-stage foamed 3D printed part. Heating Step: After the first foaming step is completed, the temperature inside the foaming container is raised to the second foaming temperature T2, and a physical foaming agent is introduced into the foaming container until the pressure inside the foaming container reaches the second foaming pressure P2; the 3D printed part that has undergone the first foaming is continuously placed in the foaming container at the pressure of the second foaming pressure P2 and the temperature of the second foaming temperature T2, causing the gas in the pores of the 3D printed part that has undergone the first foaming to expand; the time for the air in the pores of the 3D printed part that has undergone the first foaming to expand is the second placement time t2. Secondary foaming step: After the heating step is completed, the pressure in the foaming container is released to 0MPa at a depressurization rate R, so that the 3D printed part that was foamed once will undergo secondary foaming to obtain a foamed product.

6. The method as described in claim 5, characterized in that, The secondary foaming temperature T2 = the primary foaming temperature T1 + (30~40)℃; the secondary foaming pressure P2 = the primary foaming pressure P1 + (5~10)MPa.

7. The method as described in claim 6, characterized in that, The primary foaming temperature T1 is 110℃~130℃; the secondary foaming temperature T2 is 150℃~170℃; the primary foaming pressure P1 is 15MPa~25MPa; the secondary foaming pressure P2 is 20MPa~35MPa; the primary placement time t1 is 120min~130min; the secondary placement time t2 is 20min~25min; and the depressurization rate R is 5MPa / s~8MPa / s.

8. The method as described in claim 6 or 7, characterized in that, The physical foaming agent includes supercritical carbon dioxide fluid and / or supercritical nitrogen fluid.

9. A foamed product, characterized in that, The foamed product is prepared by the method according to any one of claims 1 to 8.

10. The application of the method according to any one of claims 1 to 8 in the preparation of foamed products.

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