Method and system for the production of a physically foamed film based on the coordinated injection of multiple gases

Abstract

This disclosure relates to the fields of polymer material processing and plastic foaming molding technology, and particularly to a method and system for preparing physically foamed films based on multi-gas synergistic injection. The method includes: melting and plasticizing a surface functional material through a first extruder and a third extruder; melting and plasticizing an intermediate foaming material through a second extruder; injecting carbon dioxide and butane or ethanol in a specific ratio into the second extruder via a plunger pump under pressure and in a unidirectional manner, mixing it with the molten intermediate foaming material to form a preliminary foamed melt; the preliminary foamed melt being metered by a melt pump and then entering a static mixer for split compaction and cell homogenization control; and conveying the three streams of melt from the first, second, and third extruders to a multi-layer in-mold distribution mold, where in-mold composite shaping is performed in the molten state to form a three-layer composite structure, achieving dual assurance of safety performance and foaming quality.

Description

Technical Field

[0001] This disclosure relates to the fields of polymer material processing and plastic foaming technology, and in particular to a method and system for preparing physical foamed films based on multi-gas synergistic injection. Background Technology

[0002] Currently, the mainstream manufacturing processes for plastic films mainly include three categories: non-foamed solid structure preparation, traditional gas foaming preparation, and multi-layer structure post-coating preparation. Among these, the non-foamed solid structure preparation process uses a solid substrate, requiring a large amount of raw materials during production. This not only increases raw material loss but also results in a high surface density, making it difficult to meet the demands of lightweight production and applications. Traditional gas foaming, a commonly used technology for plastic film preparation, suffers from poor foaming stability. Furthermore, the film is directly fed into the molding die after foaming, lacking effective intermediate control, leading to uneven cell size distribution, difficulty in controlling pore diameter precision, poor product quality consistency, and a tendency to produce defects such as localized over-foaming and structural porosity. In addition, this process often uses a single gas foaming system; pure carbon dioxide foaming suffers from poor foaming uniformity and high product surface roughness, while pure butane foaming poses flammable and explosive safety hazards, neither of which can meet the comprehensive requirements of industrial production. The preparation of multilayer plastic films often relies on post-coating processes, which require an additional coating step. This not only increases the complexity of the process and raises the production costs and overall production costs, but also leads to insufficient interlayer bonding strength, affecting the structural stability of the product.

[0003] Current plastic film manufacturing technologies still face numerous technical bottlenecks that urgently need to be overcome. Non-foamed structure manufacturing processes consume large amounts of raw materials, which not only increases raw material costs but also makes it difficult to achieve lightweight products, failing to align with the current industry trend towards lightweight and energy-saving manufacturing. In gas foaming processes, the precise control of cell size and distribution accuracy is difficult, resulting in insufficient product quality stability and an inability to guarantee consistency in large-scale mass production. When multi-layer structures are manufactured using post-coating processes, the interlayer bonding is weak, making them prone to delamination and other failures during subsequent processing and use, severely impacting product lifespan and performance. In summary, all existing manufacturing processes have significant shortcomings, including excessive raw material consumption, prominent process defects, or high overall costs, resulting in persistently high overall production costs and failing to achieve a balance between economy, practicality, and structural stability. Summary of the Invention

[0004] This disclosure provides a method and system for preparing physically foamed thin films based on multi-gas synergistic injection, to at least solve one of the problems existing in the above-mentioned related technologies. The technical solution is as follows: In a first aspect, embodiments of this disclosure provide a method for preparing a physically foamed thin film based on multi-gas synergistic injection, comprising the following steps: The surface functional material is melt-plasticized using the first extruder and the third extruder, respectively. The intermediate layer foaming material is melted and plasticized in the second extruder. Carbon dioxide and butane or ethanol are injected into the second extruder in a unidirectional manner under pressure by a plunger pump according to the ratio, and mixed with the molten intermediate layer foaming material to complete the initial foaming solution. The pre-foamed melt is metered by a melt pump and then enters a static mixer for split compaction and cell homogenization control. The melt from the first, second, and third extruders is transported to a multi-layer in-mold distribution die, where it is composite-shaped in the molten state to form a three-layer composite structure.

[0005] Optionally, after forming the three-layer composite structure, the following steps are also included: The three-layer composite structure is subjected to three-roll calendering and cooling to obtain a multi-layer composite foamed film.

[0006] Optionally, the carbon dioxide is the main gas, with an injection ratio of ≤65%; the butane or the ethanol is the auxiliary gas, with the butane injection ratio ≥25% and the ethanol injection ratio ≥15%.

[0007] Optionally, the gas injection pressure is 10–20 MPa, the gas injection temperature is 180–260℃, and the gas injection frequency is controlled by a frequency converter of 20–50 Hz.

[0008] Optionally, carbon dioxide and butane or ethanol are pressurized separately by a plunger pump and injected unidirectionally into the second extruder through a confluence plate and a confluence valve. The foaming ratio is controlled by the operating frequency of the plunger pump.

[0009] Optionally, the static mixer is a baffle type with 12–32 units arranged in an alternating pattern, and a length-to-diameter ratio L / D of 1:6.5–10.

[0010] Optionally, the multi-layer in-mold distribution mold has three layers, including a first layer, a second layer, and a third layer with independent temperature control. The temperature of the first layer is controlled at 220-260℃, the temperature of the second layer is controlled at 120-160℃, and the temperature of the third layer is controlled at 210-260℃.

[0011] Optionally, the surface functional material and the intermediate foam layer material are selected from one or more of PP, PE, PET, PC, HiPS, and GPPS.

[0012] Optionally, the surface functional material in the first extruder is PC material, the surface functional material in the third extruder is PP material, and the intermediate foaming material in the second extruder is PE, GPPS, or PET material.

[0013] Secondly, embodiments of this disclosure also provide a physical foaming film preparation system based on multi-gas synergistic injection, comprising: The first and third extruders are used for melting and plasticizing surface functional materials; The second extruder is used to melt and plasticize the intermediate layer foam material; A plunger pump is used to inject carbon dioxide and butane or ethanol into the second extruder in a unidirectional manner after pressurization in a certain ratio to mix with the molten intermediate layer foaming material to complete the initial foaming melt. A static mixer is used to split, compact, and homogenize the pre-foamed solution. A melt pump is connected to a static mixer and a second extruder, wherein the pre-foamed melt from the second extruder is metered and pumped into the static mixer; The multi-layer in-mold distribution mold combines the surface functional materials melted by the first and third extruders with the melt after being split, compacted and homogenized by the static mixer, and then performs in-mold composite shaping in the molten state to form a three-layer composite structure.

[0014] The advantages or beneficial effects of the above technical solutions include at least the following: First, in terms of cost control, the present invention can achieve an adjustable foaming ratio of 3.5 to 30 times. The foamed structure effectively reduces the amount of solid substrate used, and the raw material cost can be reduced by about 50%. This solves the problem of high raw material input and high cost of existing non-foamed structures, and balances economy and practicality.

[0015] Secondly, in terms of improving safety performance and foaming quality, a multi-gas synergistic injection system of carbon dioxide and butane or ethanol is adopted. Carbon dioxide can effectively suppress the flammability and explosion risk of butane, fundamentally solving the safety hazards of single butane foaming. At the same time, butane or ethanol can improve foaming uniformity and improve the surface smoothness of the product, making up for the defects of uneven foaming and high surface roughness in single carbon dioxide foaming, thus achieving dual protection of safety performance and foaming quality. Third, in terms of bubble cell precision control, by using melt pump metering and baffle plate type static mixer for flow splitting and compaction, and bubble cell homogenization control, the bubble cell diameter can be stably controlled within 0.2mm–0.5mm, which meets the requirements of optical grade applications. This effectively solves the technical problems of uneven bubble cell size, uncontrollable pore diameter, and poor product consistency in traditional gas foaming processes, and improves product quality stability and adaptability to large-scale production. Fourth, in terms of the bonding performance of multi-layer structures, the use of multi-layer in-mold distribution molds to achieve one-time composite shaping of the surface and intermediate layer melts in a molten state eliminates the need for additional coating processes. This not only simplifies the process and improves production efficiency, but also significantly enhances the interlayer interface bonding strength, completely solving the problems of weak interlayer bonding and easy delamination in traditional post-coating processes, thereby improving the product's structural stability and service life. Fifth, in terms of material compatibility, the multi-layer mold is equipped with an independent temperature control unit, which can accurately control the temperature of the three-layer structure. It is compatible with materials with different melting points such as PC, PP, PE, PET, HIPS, and GPPS. The surface and intermediate layer materials can be flexibly selected according to actual needs, adapting to a variety of application scenarios and improving the versatility and flexibility of the technology.

[0016] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of this disclosure will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0017] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this disclosure and should not be construed as limiting the scope of this disclosure.

[0018] Figure 1 This is a flowchart of a physical foaming film preparation method based on multi-gas synergistic injection in an embodiment of this disclosure; Figure 2 A flowchart illustrating the specific implementation of step S10 in this embodiment of the present disclosure; Figure 3 This is a flowchart illustrating the specific implementation of step S20 in the embodiments of this disclosure; Figure 4 This is a flowchart of a physical foaming film preparation method based on multi-gas synergistic injection according to another embodiment of this disclosure; Figure 5 This is a schematic diagram of the structure of the multilayer composite foamed film in the embodiments of this disclosure; Figure 6 This is a schematic diagram of a physical foaming film preparation system based on multi-gas synergistic injection in an embodiment of this disclosure. Detailed Implementation

[0019] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of this disclosure. Therefore, the drawings and description are to be considered exemplary in nature and not restrictive.

[0020] In a first aspect, embodiments of this disclosure provide a method for preparing physically foamed thin films based on multi-gas synergistic injection, such as... Figure 1 As shown, it includes the following steps: S10, the surface functional material is melted and plasticized using a first extruder and a third extruder, respectively; in one embodiment, such as Figure 2 As shown, the specific implementation steps include the following: S101. Use a robotic arm to grab and open the packaging bag of the surface functional material and feed it into the mixer; The surface functional materials include one or more of the following materials: PP, PE, PET, PC, HiPS, GPPS, etc.

[0021] S102. Mix the surface functional material and functional additives or masterbatch in a mixer; S103. The mixed raw materials are fed into the barrel of the first extruder or the third extruder by a feeder. The feeding into the barrel of the first extruder or the third extruder in steps S101-S103 is done in parallel. That is, the robot, the mixer and the feeder have two sets of barrels to be used to feed the materials to the first extruder or the third extruder respectively.

[0022] S104, The screw in the first or third extruder heats, melts, and plasticizes the raw material to form a surface functional material melt; S105. The surface functional material solution is filtered by a screen changer to intercept impurities.

[0023] S20. The intermediate layer foaming material is melted and plasticized using a second extruder. Carbon dioxide and butane or ethanol are mixed in a specific ratio and injected unidirectionally into the second extruder under pressure via a plunger pump, mixing with the molten intermediate layer foaming material to complete the initial foaming solution. In one embodiment, such as... Figure 3 As shown, the preparation process of the preliminary foamed solution (achieved in conjunction with a second extruder) is as follows: S201, also involves a robotic arm gripping and opening the packaging bag of the intermediate layer foam material and feeding it into a mixer; wherein, the intermediate layer foam material is one or more of the following materials: PP, PE, PET, PC, HiPS and GPPS, etc. S202. Mix the intermediate layer foaming material and functional additives or masterbatch in a mixer; S203. The mixed raw materials are fed into the barrel of the second extruder by a suction feeder. S204, the screw in the third extruder heats, melts, and plasticizes the raw material, and mixes it evenly; S205. The main gas carbon dioxide and the auxiliary gas butane or ethanol are pressurized separately using a plunger pump. The pump's operating frequency controls the initial bubble ratio, typically using a frequency converter. The gas injection pressure can be 10–20 MPa (as those skilled in the art will know, the specific value depends on the product being applied). The gas injection temperature should match the melt temperature (e.g., 180–260°C). The gas injection frequency can be selected from 20–50 Hz, controlled by a frequency converter (as those skilled in the art will know, the specific value depends on the product and the plunger rod stroke of the plunger pump). S206. The pressurized main gas carbon dioxide and auxiliary gas butane or ethanol are conveyed through a confluence plate to a confluence valve (specifically a one-way valve) to inject the mixed gas into the second extruder. Under the stirring of the screw in the second extruder, the mixture is mixed with the molten intermediate layer foaming material to complete the initial foaming melt. Carbon dioxide is chosen as the main gas because it is non-flammable, which improves the safety of the system and can suppress the combustion risk of ethanol or butane. The mixed use of carbon dioxide and ethanol or butane can provide better extrusion foaming capability. In an optional embodiment, the carbon dioxide is the main gas, with an injection ratio ≤65%; the butane or ethanol is the auxiliary gas, with the butane injection ratio ≥25% and the ethanol injection ratio ≥15%.

[0024] A multi-gas synergistic injection system using carbon dioxide and butane or ethanol is adopted. Carbon dioxide can effectively suppress the flammability and explosion risk of butane, fundamentally solving the safety hazards of single butane foaming. At the same time, butane or ethanol can improve foaming uniformity and enhance product surface smoothness, making up for the defects of uneven foaming and high surface roughness in single carbon dioxide foaming, thus achieving dual protection of safety performance and foaming quality.

[0025] In one embodiment, the initial foamed melt in step S206 also needs to be cooled under controlled temperature in the rear section of the barrel of the second extruder to control the gas release rate and avoid premature expansion or secondary foaming.

[0026] S30. The preliminary foamed melt is metered by a melt pump and then enters a static mixer for split compaction and cell homogenization control. In this step, the melt pump can measure the extrusion amount of the initial foamed melt; the static mixer is used for compaction and pore control, while further cooling of the initial foamed melt and adjusting the size of the bubble pores; wherein, the static mixer can be selected as a baffle type, the number of units can be 12-32, the internal structure can be staggered, and the length-to-diameter ratio (L / D ratio) can be selected as 1:6.5-10. Those skilled in the art can select a specific ratio according to the diameter of the main screw, so that 3) the flow can be split, superimposed and compressed without moving parts, thereby realizing the redispersion and homogenization of bubbles.

[0027] In a preferred embodiment, the pressurization pressure of the plunger pump in S205 is further adjusted. Simultaneously, the length-to-diameter ratio of the static mixer is designed based on the main screw diameter, and the speed is adjusted according to the pressurization pressure of different products to control the residence time of the initial foamed melt in the static mixer. Furthermore, the feed metering is performed by adjusting the speed of the melt pump according to the required bubble pore size of different products and the pressurization pressure of the plunger pump. Through these comprehensive adjustments, the bubble pore size can be achieved to 0.2mm–0.5mm, enabling optical-grade structural control and adjustment of the material's mechanical properties.

[0028] S40. The three streams of melt from the first extruder, the second extruder, and the third extruder are transported to the multi-layer in-mold distribution mold, and in-mold composite shaping is performed in the molten state to form a three-layer composite structure.

[0029] In this process, the multi-layer in-mold distribution mold distributes three streams of melt within the mold and directly bonds each layer in a molten state to form a three-layer composite structure. This step avoids the traditional coating process and achieves high bonding strength between layers.

[0030] In one alternative embodiment, after forming the three-layer composite structure, as Figure 4 As shown, it also includes the following steps: S50. The three-layer composite structure is calendered and cooled to obtain a multi-layer composite foamed film.

[0031] This step includes traction and winding / cutting steps after three-roll calendering and cooling. The three-roll calendering is achieved by a three-roll calender, which can adjust the calendering thickness; cooling is achieved by cooling and shaping by a cooling rack; and traction is achieved by a traction machine.

[0032] In one optional embodiment, the gas injection pressure is 10–20 MPa, the gas injection temperature is 180–260°C, and the gas injection frequency is controlled by a frequency converter of 20–50 Hz.

[0033] In one alternative embodiment, carbon dioxide and butane or ethanol are pressurized separately by a plunger pump and injected unidirectionally into a second extruder through a confluence plate and a confluence valve. The foaming ratio is controlled by the operating frequency of the plunger pump.

[0034] In one optional embodiment, the static mixer is a baffle type with 12–32 units arranged in an alternating pattern, and a length-to-diameter ratio (L / D) of 1:6.5–10.

[0035] In one optional embodiment, the multi-layer in-mold distribution mold has three layers, including a first layer, a second layer, and a third layer with independent temperature control. The temperature of the first layer is controlled at 220-260°C, the temperature of the second layer is controlled at 120-160°C, and the temperature of the third layer is controlled at 210-260°C. This setting ensures the quality and functionality of the material in each layer.

[0036] In one optional embodiment, the surface functional material and the intermediate foam layer material are selected from one or more of PP, PE, PET, PC, HiPS, and GPPS. Figure 5 As shown, a multilayer composite foamed film can be prepared by the method in the above embodiments. Its structure includes: two surface layers (functional layers) and at least one foamed layer, wherein the foamed layer has a closed-cell structure and a relatively uniform pore size distribution.

[0037] In one optional embodiment, the surface functional material in the first extruder is PC material, the surface functional material in the third extruder is PP material, and the intermediate layer foaming material in the second extruder is PE, GPPS, or PET material.

[0038] Secondly, embodiments of this disclosure also provide a physical foaming film preparation system based on multi-gas synergistic injection, such as... Figure 6 As shown, it includes: The first extruder 100 and the third extruder 300 are used for melt plasticizing surface functional materials; The second extruder 200 is used to melt and plasticize the intermediate layer foam material; The plunger pump 8 is used to inject carbon dioxide and butane or ethanol into the second extruder 200 in a unidirectional manner after pressurization according to the ratio, so as to mix with the molten intermediate layer foaming material to complete the initial foaming melt. Static mixer 12 performs splitting, compaction, and cell homogenization control on the preliminary foamed solution; Melt pump 13 is connected to static mixer 12 and second extruder 200, wherein the pre-foamed melt in the second extruder 200 is metered and pumped into the static mixer 12; The multi-layer in-mold distribution mold 15 combines the surface functional material melted by the first extruder 100 and the third extruder 300 with the melt after being split, compacted and homogenized by the static mixer 12, and the melt after being homogenized and regulated by the foam cells, and performs in-mold composite shaping in the molten state to form a three-layer composite structure.

[0039] Both the first extruder 100 and the third extruder 300 have screws for heating and stirring, and barrels for containing the screws and raw materials.

[0040] In one embodiment, such as Figure 6 As shown, it also includes a robotic arm 1 for implementing steps S101 and S201 in the above embodiments.

[0041] In one embodiment, such as Figure 6 As shown, it also includes a mixer 2 for implementing steps S102 and S202 in the above embodiments.

[0042] In one embodiment, such as Figure 6 As shown, it also includes a suction machine 3 for implementing steps S103 and S203 in the above embodiments.

[0043] In one embodiment, such as Figure 6 As shown, it also includes the barrels 4 of the first extruder 100, the second extruder 200 and the third extruder 300, which are used to contain the mixed raw materials conveyed by the feeder 3.

[0044] In one embodiment, such as Figure 6 As shown, it also includes containers (5, 6 and 7 in the figure) for containing carbon dioxide, butane and ethanol, and the three containers are respectively connected to three plunger pumps 8.

[0045] In one embodiment, such as Figure 6 As shown, it also includes a confluence valve 9 connected to the three plunger pumps 8. The confluence valve is a one-way valve, which mixes the three gases and pumps them into the second extruder 200.

[0046] In one embodiment, such as Figure 6 As shown, screen changers 11 are also installed on the pipelines of the first extruder 100, the second extruder 200 and the third extruder 300 to filter impurities. The screen changers 11 on the pipelines of the first extruder 100 and the third extruder 300 are installed after melting, while the screen changers 11 on the pipeline of the second extruder 200 are installed before melting.

[0047] In one embodiment, such as Figure 6 As shown, it also includes a distributor 14, which is used to separately input the three layers of melt into the multi-layer mold and distribute it into the mold 15 to achieve composite shaping.

[0048] In one embodiment, such as Figure 6 As shown, it also includes a three-roll calender 16 for calendering the three-layer composite structure to obtain a customized thickness.

[0049] In one embodiment, such as Figure 6 As shown, it also includes a cooling rack 17 for cooling physically foamed films disposed after the three-roll calender 16, a traction machine 18 for pulling film products, a cutting machine 19 for cutting film products, and a winding machine 20 for final winding.

[0050] Those skilled in the art can undoubtedly determine that, without contradiction, each component in the physical foaming film preparation system based on multi-gas synergistic injection in this embodiment can be used to implement the steps of the above-mentioned physical foaming film preparation method based on multi-gas synergistic injection, and the functions and effects they achieve are all equivalent and will not exceed the possible combinations of embodiments in this application.

[0051] In the description of this embodiment, the terms "an embodiment," "some embodiments," "preferred embodiments," "specific examples," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this disclosure. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0052] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0053] The above are merely specific embodiments of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in this disclosure, and these should all be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for preparing physically foamed thin films based on multi-gas synergistic injection, characterized in that, Includes the following steps: The surface functional material is melt-plasticized using the first extruder and the third extruder, respectively. The intermediate layer foaming material is melted and plasticized in the second extruder. Carbon dioxide and butane or ethanol are injected into the second extruder in a unidirectional manner under pressure by a plunger pump according to the ratio, and mixed with the molten intermediate layer foaming material to complete the initial foaming solution. The pre-foamed melt is metered by a melt pump and then enters a static mixer for split compaction and cell homogenization control. The melt from the first, second, and third extruders is transported to a multi-layer in-mold distribution die, where it is composite-shaped in the molten state to form a three-layer composite structure.

2. The method as described in claim 1, characterized in that, After forming the three-layer composite structure, the following steps are also included: The three-layer composite structure is subjected to three-roll calendering and cooling to obtain a multi-layer composite foamed film.

3. The method as described in claim 1 or 2, characterized in that, The carbon dioxide is the main gas, with an injection ratio of ≤65%; the butane or the ethanol is the auxiliary gas, with the butane injection ratio ≥25% and the ethanol injection ratio ≥15%.

4. The method as described in claim 1 or 2, characterized in that, The gas injection pressure is 10–20 MPa, the gas injection temperature is 180–260℃, and the gas injection frequency is controlled by a frequency converter of 20–50 Hz.

5. The method as described in claim 1 or 2, characterized in that, Carbon dioxide and butane or ethanol are pressurized separately by a plunger pump and injected unidirectionally into the second extruder through a confluence plate and confluence valve. The foaming ratio is controlled by the frequency of the plunger pump.

6. The method as described in claim 1 or 2, characterized in that, The static mixer is a baffle type with 12–32 units arranged in an alternating pattern inside, and a length-to-diameter ratio (L / D) of 1:6.5–10.

7. The method as described in claim 1 or 2, characterized in that, The multi-layer in-mold distribution mold consists of three layers, including a first layer, a second layer, and a third layer with independent temperature control. The temperature of the first layer is controlled at 220-260℃, the temperature of the second layer is controlled at 120-160℃, and the temperature of the third layer is controlled at 210-260℃.

8. The method as described in claim 1, characterized in that, The surface functional material and the intermediate foam layer material are selected from one or more of PP, PE, PET, PC, HiPS, and GPPS.

9. The method as described in claim 8, characterized in that, The surface functional material in the first extruder is PC material, the surface functional material in the third extruder is PP material, and the intermediate layer foaming material in the second extruder is PE, GPPS, or PET material.

10. A physical foaming film preparation system based on multi-gas synergistic injection, characterized in that, include: The first and third extruders are used for melting and plasticizing surface functional materials; The second extruder is used to melt and plasticize the intermediate layer foam material; A plunger pump is used to inject carbon dioxide and butane or ethanol into the second extruder in a unidirectional manner after pressurization in a certain ratio to mix with the molten intermediate layer foaming material to complete the initial foaming melt. A static mixer is used to split, compact, and homogenize the pre-foamed solution. A melt pump is connected to a static mixer and a second extruder, wherein the pre-foamed melt from the second extruder is metered and pumped into the static mixer; The multi-layer in-mold distribution mold combines the surface functional materials melted by the first and third extruders with the melt after being split, compacted and homogenized by the static mixer, and then performs in-mold composite shaping in the molten state to form a three-layer composite structure.

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