Preparation method of supercritical blank mold foaming product

Abstract

The invention provides a preparation method of a supercritical blank mold foaming product, and belongs to the technical field of high polymer material processing. By using the special mold, the raw materials can be subjected to one-time foaming molding; foaming and rapid cooling are carried out in the mold, the shrinkage rate is controlled through directional cooling of the cold runner, and the accuracy of the size of a product, the high yield of the product and high-rate foaming of the product are ensured. Meanwhile, the technical scheme provided by the invention can solve the problems that in the prior art, the process period is long, the production efficiency is low, the equipment investment cost is high, the product size stability is poor, the melt internal stress is difficult to release, and the product yield is influenced.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing technology, and in particular to a method for preparing supercritical preform foamed products. Background Technology

[0002] Foamed polymer products are widely used in automobiles, communications, footwear, and sporting goods, offering excellent properties such as lightweight, shock absorption, and resilience. Traditional chemical foaming processes are limited by technology, making it difficult to achieve high-ratio foaming of thermoplastic elastomers, engineering plastics, and specialty polymers. Furthermore, chemically foamed products suffer from numerous drawbacks, such as unpleasant odors and poor permanent compression set. Supercritical fluid foaming technology can significantly broaden the range of foamable materials. By controlling the cell structure, environmentally friendly, high-performance, ultra-low-density, lightweight foamed products can be manufactured.

[0003] Supercritical fluid foaming technology uses supercritical carbon dioxide or nitrogen as a physical foaming agent. By controlling process parameters such as the foaming agent ratio and foaming temperature, the foaming ratio and cell size can be precisely controlled, resulting in foamed products with excellent mechanical properties, a wide range of applicable materials, and environmental friendliness. Currently, the main methods for preparing high-performance foamed materials using supercritical fluid foaming technology include continuous extrusion foaming, injection molding foaming, and intermittent autoclave foaming. Continuous extrusion foaming has high efficiency but produces products with limited shape options. Injection molding foaming can produce products of various shapes, but with lower product ratios. Intermittent autoclave foaming can produce high-ratio products of various shapes, but its production efficiency is low. It generally requires three steps: injection molding, autoclave foaming, and compression molding. Furthermore, the use of autoclaves, supercritical gases, and preform and finished product molds in the production process leads to high production costs.

[0004] Currently, Chinese patent (CN109385058A) discloses a method for preparing polymer moldless three-dimensional foamed products using supercritical fluid. The specific steps are as follows: polymer raw materials are pressurized to form a foamed pre-molded part; the pre-molded part is preheated in a preheating system; after reaching the preheated temperature, the pre-molded part is sent into a three-dimensional foaming tank; the sealing lid of the three-dimensional foaming tank is closed; the air inlet valve is opened; supercritical fluid is introduced; the temperature and pressure are adjusted to the target; the supercritical fluid swells and diffuses into the polymer for 30-120 minutes; the pressure release device is opened to release pressure and foam, thus obtaining polymer microporous foamed products with controllable shape, dimensional accuracy, fine pores, and product density. However, the method provided in this patent relies on an autoclave. In actual production, to achieve precise and stable product dimensions, the temperature control requirements for the equipment are extremely high, resulting in significant equipment investment. For products with special shapes, because the edges and corners are rounded when using this process to foam the material, it is difficult to achieve precise foaming dimensions, making it impossible to foam complex-shaped products, especially those with recesses.

[0005] Chinese patent (CN109955424A) discloses a process for molding and foaming polymers using supercritical rapid swelling. Supercritical fluid and polymer melt are rapidly and uniformly mixed within the injection molding machine barrel by mechanical stirring with a screw. This homogeneous solution, injected into the mold cavity, allows for temperature control and further diffusion of the supercritical fluid, enabling regulation of melt strength and increased gas solubility before foaming. This two-step, staged method of melt blending and solid-state swelling foaming ensures rapid diffusion and swelling of the supercritical fluid within the polymer matrix. While retaining the advantages of compression-molded foamed products, it overcomes the bottleneck of excessively long swelling times due to gas diffusion in existing compression-molded foaming processes. However, this process still requires further optimization of the mold structure and injection molding machine barrel.

[0006] Chinese Patent (CN119458741A) discloses a shoe sole forming device, belonging to the field of shoe sole processing technology. It includes a base, inside which are arranged injection molding components, mold components, ejector components, and heat dissipation components. The heat dissipation components include a sliding groove with an air inlet groove on its side wall and an exhaust groove at the top of its inner side wall. By sending air from the receiving cylinder into the movable groove, the air pressure at the bottom of the sliding top plate is increased, causing the sliding top plate to move upward. The air inlet ejector and ejector ejector move upward, ejecting the formed shoe sole. Air from the movable groove enters the sliding groove through the air inlet groove and is then discharged through the exhaust groove, blowing away the heat accumulated at the bottom of the shoe sole and improving heat dissipation. This solves the problem that existing molds cannot dissipate heat from the formed shoe sole. This patent mainly focuses on solving the problems of low heat dissipation efficiency after the sole is formed and the difficulty of demolding due to residual heat in the mold. The process it adopts is only injection molding, mold opening and closing, ejection and airflow heat dissipation. Moreover, it does not clearly integrate foaming and shaping steps, and it is likely still dependent on traditional foaming process.

[0007] Chinese Patent (CN111286070A) discloses a supercritical fluid injection molding foamed polylactic acid (PLA) foam material and its preparation method. This invention utilizes bio-filler cellulose nanofibers to modify and prepare a lightweight, high-strength PLA foam material. Cellulose nanofibers are used as nucleating agents to improve the crystallinity and melt properties of the PLA material. The prepared cellulose nanofiber-modified PLA composite material is uniformly mixed with a supercritical fluid foaming agent in a microporous injection molding machine. Combined with an open-mold foaming device, microporous injection molding is performed to obtain a fully bio-based PLA foam material. This patent mainly addresses the poor foaming performance of PLA by enhancing the melt strength and crystallinity of PLA through cellulose nanofibers. However, the process is relatively complex, requiring two melt-blending extrusion processes to prepare cellulose nanofibers and reinforced PLA composite materials, followed by foaming using a microporous injection molding machine, and the foaming ratio is relatively low.

[0008] Chinese patent (CN111283947A) discloses a supercritical fluid gas injection system and method for micro-foamed injection molding. The system includes a gas source, a main circuit unit, a branch circuit unit, a gas injector, a main circuit quick-stop valve, branch circuit quick-stop valves, and a gas injection control device. The gas source, main circuit unit, main circuit quick-stop valve, and gas injector are connected in series. The branch circuit quick-stop valves are connected in series with the branch circuit unit between the outlet of the main circuit quick-stop valve and the inlet of the gas injector. The gas injection control device controls the opening and closing of the main circuit quick-stop valve and the branch circuit quick-stop valve, such that when the main circuit quick-stop valve is open, the branch circuit quick-stop valve is closed; and when the main circuit quick-stop valve is closed, the branch circuit quick-stop valve is open. This patent focuses on supercritical fluid gas injection systems in micro-foamed injection molding, primarily addressing the gas surge problem during injection. It optimizes only the localized problem of unstable gas flow caused by gas surge, which affects the uniformity of the single-phase melt.

[0009] Therefore, there is an urgent need for a new supercritical foaming process that can integrate injection molding, foaming and hot pressing into a continuous process. Through equipment structure innovation and process parameter optimization, it can achieve efficient and low-cost production of foamed products, while ensuring dimensional accuracy and high foaming ratio, thus overcoming the shortcomings of existing technologies. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing supercritical preform foamed products. The technical solution provided by this invention can solve the problems in the prior art, such as long process cycle, low production efficiency, high equipment investment cost, poor product dimensional stability, and difficulty in releasing stress in the melt, which affects product yield.

[0011] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing supercritical preform foamed products, comprising the following steps: After the polymer particles are dried and melted, they are injected into the mold core, the mold is closed, a vacuum is drawn, supercritical fluid is injected, the mixture is dissolved to equilibrium, the pressure is released, and the temperature is lowered to obtain the supercritical preform foamed product.

[0012] Preferably, the polymer particles include one or more of polyethylene, polylactic acid, polypropylene, polystyrene, polymethyl methacrylate, polycarbonate, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, polyamide, polyimide, polyphenylene sulfide, polyethersulfone, polyetheretherketone, rubber, silicone rubber, ethylene propylene diene monomer (EPDM) rubber, ethylene-vinyl acetate copolymer, thermoplastic polyurethane elastomer, thermoplastic polyester elastomer, and thermoplastic polyamide elastomer.

[0013] Preferably, the drying temperature is 10~150℃ and the drying time is 0.3~10h; the melting treatment temperature is 100~400℃ and the melting treatment time is 2~60min.

[0014] More preferably, the drying temperature is 100°C and the drying time is 5 hours; the melting treatment temperature is 220°C and the melting treatment time is 5 minutes.

[0015] Preferably, the amount of polymer particles injected into the mold is 2-95% of the mold core volume or calculated according to Formula I: Injection amount = density after foaming × volume of the mold, Formula I; the mold is preheated to 1-70°C below the melting point of the polymer particles before injection; the injection time is 2-30s; the supercritical fluid includes CO2 and / or N2; the volume ratio of CO2 to N2 is 1-5:2-7.

[0016] More preferably, the amount of polymer particles injected into the mold is 8% of the mold core volume or calculated according to Formula I: Injection amount = density after foaming × volume of mold, Formula I; the mold is preheated to 50°C below the melting point of the polymer particles before injection; the injection time is 5s; the supercritical fluid includes CO2 and / or N2; the volume ratio of CO2 to N2 is 1:2.

[0017] Preferably, the method for achieving dissolution equilibrium is as follows: treatment for 2 to 60 minutes at a pressure of 1 to 50 MPa and a temperature 1 to 65°C lower than the melting point of the polymer particles; the depressurization rate is 1 to 1000 MPa / s; the cooling rate is 10 to 50°C / s; and the cooling method is to introduce a coolant at -5 to -10°C.

[0018] More preferably, the method for achieving dissolution equilibrium is as follows: treatment for 5 minutes at 32 MPa and a temperature 65°C below the melting point of the polymer particles; the depressurization rate is 100 MPa / s; the cooling rate is 40°C / s; and the cooling method is to introduce a coolant at -5°C.

[0019] Preferably, the mold includes a mold core and a mold shell; The mold shell is provided with a locking device, a sealing ring (8), a heating and cooling outlet (9), a three-way high-temperature solenoid valve (10), an exhaust port (11), an air inlet (13), and an exhaust groove (14); the locking device includes a padlock (7) and a buckle (12); The mold core is provided with a positioning groove (15); The mold core is made of breathable steel, and the surface of the breathable steel is coated with Teflon. The mold core is located inside the mold shell and is fitted into the mold by the positioning groove (15).

[0020] The present invention also provides supercritical preform foamed products prepared by the aforementioned preparation method.

[0021] The beneficial effects of this invention compared to the prior art are as follows: The present invention uses, for example Figure 1 The specialized mold shown allows raw materials to be foamed and molded in one step, eliminating the need for small blank molds and requiring only one mold, thus saving mold costs. By using in-mold foaming, the gas consumption during the preparation of foamed products is far lower than that of an autoclave, reducing overall costs by more than 70%. At the same time, the invention controls the shrinkage rate through directional cooling in a cold runner after foaming, ensuring that the dimensional tolerance of the product is controlled within ±0.5mm and the density deviation is ≤3%, eliminating the need for secondary molding correction and resulting in extremely high yield.

[0022] The technical solution provided by this invention does not require autoclaves or molding machines, only a casting machine and a special mold, which can significantly reduce equipment investment costs. Furthermore, this invention can calculate the quantitative injection product mass (M=ρ*V) based on the customer's required product density and mold volume, ensuring the accuracy of product dimensions. This invention effectively eliminates internal stress through quantitative injection casting, making it less prone to internal defects during high-ratio foaming of the material; after the molten material is poured into the mandrel, the introduction of supercritical fluid reduces the time for fluid penetration into the molten material to the dissolution equilibrium time of the traditional preform.

[0023] The preparation method provided by this invention can significantly shorten the production cycle and improve production efficiency. By integrating injection molding, gas infiltration, and foaming and shaping into the same equipment and dedicated mold, the step-by-step processes of traditional methods are avoided, reducing the production cycle by more than 60%, from the traditional 120 minutes to less than 45 minutes. Furthermore, the technical solution provided by this invention can solve the problems of long process cycles, low production efficiency, high equipment investment costs, poor product dimensional stability, and difficulty in releasing melt stress, which affects product yield in existing technologies.

[0024] Compared to Chinese patents (CN109385058A) and (CN109955424A), this invention can integrate injection molding, gas permeation and foaming shaping into one mold, and the mold provided by this invention can be applied to products of various shapes to achieve precise foaming.

[0025] Compared to the Chinese patent (CN119458741A), this invention integrates the three key steps of injection molding, foaming, and shaping into a single device, completely eliminating the reliance on a high-pressure autoclave. Its mold adopts a layered design, possesses precise quantitative injection calculation capabilities, and can finely control process parameters. In solving practical production problems, this invention overcomes many long-standing problems of traditional processes, such as long cycle times, high equipment costs, poor dimensional stability, and difficulty in releasing internal stress. It utilizes a fully integrated process that combines casting, supercritical fluid infiltration, rapid pressure relief foaming, and rapid shaping via cold runners.

[0026] Compared to the Chinese patent (CN111286070A), this invention cleverly integrates casting, gas infiltration, and foaming shaping into the same mold. It also innovatively adopts a detachable, breathable steel core mold and a high-pressure outer mold structure, and precisely controls the shrinkage rate through rapid cooling via cold runners.

[0027] Compared to Chinese patent (CN111283947A), this invention effectively solves the problems of low efficiency, high equipment cost, and poor dimensional accuracy of traditional processes. Moreover, this invention focuses on the continuous production process and supporting equipment of supercritical foamed products, and successfully realizes an innovative model that integrates casting, foaming, cooling and shaping into one. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 An enlarged view of the supercritical preform foaming equipment and foaming mold; Figure 2 Modeling diagram of a supercritical preform foaming mold; Figure 3 This is a diagram showing the combined state of a supercritical preform foaming mold. Figure 4 A modeling diagram of a supercritical preform foaming mold in its combined state; Figure 5 This is a side section view of a supercritical preform foaming mold in its assembled state; Figure 6 This is a cross-sectional view of a supercritical preform foaming mold in its combined state; Figure 7 This is a cross-sectional view of the bottom of the mold shell of a supercritical preform foaming mold; Figure 8This is a cross-sectional view of the bottom of the outer shell of the supercritical preform foaming mold in its assembled state; Figure 9 A magnified micrograph of the supercritical preform foamed product prepared in Example 1; Figure 10 This is a photograph of the supercritical preform foamed product obtained in Example 1; Figure 11 This is a photograph of the supercritical preform foamed product obtained in Example 2; Figure 12 This is a magnified micrograph of the supercritical preform foamed product obtained in Example 4; Figure 13 This is a photograph of the supercritical preform foam product prepared in Example 4; Figure 14 This is a magnified micrograph of the supercritical preform foamed product obtained in Example 5; Figure 15 This is a photograph of the supercritical preform foamed product obtained in Example 5; Figure 16 This is a magnified microscopic image of the supercritical preform foamed product prepared in Comparative Example 1. Figure 17 The image shows a physical picture of the supercritical preform foam product prepared in Comparative Example 1. Figure 18 This is a magnified microscopic image of the supercritical preform foamed product prepared in Comparative Example 2. Figure 19 The image shows a physical picture of the supercritical preform foam product prepared in Comparative Example 2. In the diagram, 1-supercritical fluid injection device, 2-melting and casting device, 3-material handling device, 4-rotary production line, 5-special mold, 6-mold core, 7-padlock, 8-sealing ring, 9-heating and cooling outlet, 10-three-way high-temperature solenoid valve, 11-vent hole, 12-lock, 13-air inlet, 14-vent groove, 15-positioning groove, 16-material cylinder. Detailed Implementation

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0031] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0032] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0033] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0034] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0035] This invention provides a method for preparing supercritical preform foamed products, comprising the following steps: After the polymer particles are dried and melted, they are injected into the mold core, the mold is closed, a vacuum is drawn, supercritical fluid is injected, the mixture is dissolved to equilibrium, the pressure is released, and the temperature is lowered to obtain the supercritical preform foamed product.

[0036] In this invention, the polymer particles preferably include one or more of polyethylene, polylactic acid, polypropylene, polystyrene, polymethyl methacrylate, polycarbonate, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, polyamide, polyimide, polyphenylene sulfide, polyethersulfone, polyetheretherketone, rubber, silicone rubber, ethylene propylene diene monomer (EPDM) rubber, ethylene-vinyl acetate copolymer, thermoplastic polyurethane elastomer, thermoplastic polyester elastomer, and thermoplastic polyamide elastomer, and more preferably include polylactic acid, polystyrene, polycarbonate, and polyethylene terephthalate. One or more of glycol esters, polyimide, polyethersulfone, rubber, EPDM rubber, and thermoplastic polyurethane elastomers, more preferably including one or more of polystyrene, polyethylene terephthalate, polyethersulfone, and EPDM rubber; the drying temperature is preferably 10~150℃, more preferably 50~100℃, and even more preferably 80℃; the drying time is preferably 0.3~10h, more preferably 3~7h, and even more preferably 5h; the melt treatment temperature is preferably 100~400℃, more preferably... The preferred temperature is 150~350℃, more preferably 180~300℃, and even more preferably 250℃; the preferred melting time is 2~60 min, more preferably 5~50 min, even more preferably 10~40 min, and even more preferably 30 min; the preferred amount of polymer particles injected into the mold is 2~95% of the mold core volume, more preferably 10~80%, even more preferably 30~60%, and even more preferably 50%; the preferred amount of polymer particles injected into the mold is... The injection volume is calculated according to Formula I: Injection amount = density after foaming × volume of mold, Formula I; Preheating the mold before injection is preferably 1~70℃ below the melting point of the polymer particles, more preferably 5~60℃, even more preferably 10~50℃, and still more preferably 40℃; the injection time is preferably 2~30s, more preferably 10s; the supercritical fluid preferably includes CO2 and / or N2; the volume ratio of CO2 to N2 is preferably 1~5:2~7, more preferably 3~4:3~6, and even more preferably 3.5:5; The preferred method for achieving dissolution equilibrium is: treatment at 1~50 MPa and a temperature 1~65°C below the melting point of the polymer particles for 2~60 min, more preferably at 5~40 MPa and a temperature 5~50°C below the melting point of the polymer particles for 10~50 min, even more preferably at 10~30 MPa and a temperature 10~40°C below the melting point of the polymer particles for 20~40 min, and even more preferably at 20 MPa and a temperature 30°C below the melting point of the polymer particles for 30 min; the preferred rate of pressure relief is 1~1000 MPa / s, more preferably 100~800 MPa / s, even more preferably 300~600 MPa / s, and even more preferably 500 MPa / s; the preferred rate of cooling is 10~50°C / s. The temperature is preferably 20~40℃ / s, and even more preferably 30℃ / s; the cooling method is preferably to introduce a coolant at -5~-10℃, more preferably -6~-8℃, and even more preferably -7℃; the coolant enters the outer shell interlayer through the heating and cooling outlet, and conducts heat evenly through the micropores of the ventilated steel mold core to achieve directional cooling; the mold includes a mold core and a mold shell; the mold shell is provided with a locking device, a sealing ring (8), a heating and cooling outlet (9), a three-way high-temperature solenoid valve (10), an exhaust port (11), an air inlet (13), and an exhaust groove (14); the mold core is provided with a positioning groove (15); the locking device includes a padlock (7) and a buckle (12); the mold core is made of ventilated steel, and the surface of the ventilated steel is coated with Teflon; the mold core is located inside the mold shell and is fitted into the mold through the positioning groove (15).

[0037] The present invention also provides supercritical preform foamed products prepared by the aforementioned preparation method.

[0038] Example 1

[0039] A method for preparing a supercritical preform foamed product, comprising the following steps: In a barrel 16 at 100°C, thermoplastic polyester elastomer (TPEE) is dried for 5 hours. Then, it is heated and melted at 220°C for 5 minutes using a melt casting device 2. Within 5 seconds, it is injected into the mold core 6 of a mold that is preheated (through a heating and cooling outlet 9) to a temperature 50°C below the melting point of the polymer particles. The injection volume is 8% of the mold core volume. The mold is closed, and supercritical fluid CO2 is injected through a one-way air inlet 13 on the side of the mold. The mold is treated at 32 MPa and 155°C for 5 minutes. The pressure is then released to standard atmospheric pressure at a rate of 100 MPa / s through the venting groove 14 and the one-way valve venting hole 11 on the side of the mold, triggering the TPEE melt to foam and fill the cavity. Cooling liquid at -5°C is introduced through the heating and cooling outlet 9 located at the bottom of the mold shell, and the product is cooled at a rate of 40°C / s for 25 seconds. The mold is then opened to obtain the molded TPEE shoe sole foam product.

[0040] Example 2

[0041] A method for preparing a supercritical preform foamed product, comprising the following steps: In a barrel 16 at 80°C, thermoplastic polyurethane elastomer (TPU) is dried for 4 hours. Then, it is heated and melted at 190°C for 3 minutes using a melt casting device 2. Within 10 seconds, it is injected into a mold core 6 that is preheated (through a heating and cooling outlet 9) to a temperature 30°C below the melting point of the polymer particles. The injection volume is 10% of the mold core volume. The mold is closed, and supercritical fluid N2 is injected through a one-way air inlet 13 on the side of the mold. The mold is treated at 28 MPa and 140°C for 2 minutes. The pressure is then released to standard atmospheric pressure at a rate of 50 MPa / s through the venting groove 14 and the one-way valve venting hole 11 on the side of the mold, triggering the TPU melt to foam and fill the cavity. Cooling liquid at -10°C is introduced through the heating and cooling outlet 9 located at the bottom of the mold shell, and the product is cooled at a rate of 35°C / s for 20 seconds. The mold is then opened to obtain the molded TPU sports protective gear foam product.

[0042] Example 3

[0043] A method for preparing a supercritical preform foamed product, comprising the following steps: In a barrel 16 at 70°C, the thermoplastic polyamide elastic TPAE body is dried for 4.5 hours. Then, it is heated and melted at 200°C for 4 minutes using a melt casting device 2. Within 5 seconds, it is injected into the mold core 6 of a mold that is preheated (through a heating and cooling outlet 9) to a temperature 10°C below the melting point of the polymer particles. The injection volume is 5% of the mold core volume. The mold is closed, and supercritical fluids CO2 and N2 with a volume ratio of 1:2 are injected through a one-way air inlet 13 on the side of the mold. The mixture is treated at 30 MPa and 160°C for 8 minutes. The pressure is then released to standard atmospheric pressure at a rate of 200 MPa / s through the venting groove 14 and the one-way valve venting hole 11 on the side of the mold. This triggers the foaming of the thermoplastic polyamide TPAE melt and its filling of the cavity. Cooling liquid at -10°C is introduced through the heating and cooling outlet 9 located at the bottom of the mold shell. The product is cooled at a rate of 45°C / s for 25 seconds. The mold is then opened to obtain the molded TPAE shoe sole foam product.

[0044] Example 4

[0045] A method for preparing a supercritical preform foamed product, comprising the following steps: In a barrel 16 at 80°C, a 30% EVA / 70% TPEE (30% ethylene-vinyl acetate / 70% thermoplastic polyester elastomer) modified elastomer material is dried for 3 hours, and then heated and melted at 155°C for 3 minutes using a melt casting device 2. The mold volume is 2300 cm³. 3 The expected density of the foamed product is 0.078 g / cm³. 3 According to Formula I: Injection amount = density after foaming × volume of mold, the injection amount of raw material is calculated to be 179.4g. It is injected into the mold core 6 of the mold that is preheated (preheated through heating and cooling outlet 9) to 118°C within 23s. The mold is closed, and supercritical fluids CO2 and N2 with a volume ratio of 5:5 are injected through the one-way air inlet 13 on the side of the mold. The mixture is treated for 5min at 40MPa and a temperature 50°C lower than the melting point of the polymer particles. The pressure is released to standard atmospheric pressure at a rate of 200MPa / s through the venting groove 14 and the one-way valve venting hole 11 on the side of the mold. Cooling liquid at -10°C is introduced through the heating and cooling outlet 9 located at the bottom of the mold shell, and the temperature is reduced at a rate of 40°C / s for 25s. The mold is then opened to obtain the supercritical preform foamed product.

[0046] Example 5

[0047] A method for preparing a supercritical preform foamed product, comprising the following steps: The polyethylene was dried in a barrel 16 at 80°C for 3 hours, and then heated and melted at 190°C for 8 minutes using a melting and casting device 2. The mold volume was 2000 cm³. 3The expected density of the foamed product is 0.03 g / cm³. 3 According to Formula I: Injection amount = density after foaming × volume of mold, the injection amount of raw material is calculated to be 60g. It is injected into the mold core 6 of the mold that is preheated (by heating and cooling outlet 9) to a temperature 10°C lower than the melting point of polymer particles within 10s. The mold is closed, and supercritical fluid N2 is injected through the one-way air inlet 13 on the side of the mold. It is treated for 6 minutes at 35MPa and a temperature 10°C lower than the melting point of polymer particles. The pressure is released to standard atmospheric pressure at a rate of 10MPa / s through the exhaust groove 14 and the one-way valve exhaust hole 11 on the side of the mold. Cooling liquid at -5°C is introduced through the heating and cooling outlet 9 located at the bottom of the mold shell, and the temperature is reduced at a rate of 10°C / s for 20s. The mold is then opened to obtain the supercritical preform foamed product.

[0048] Example 6

[0049] A supercritical preform foaming device includes a supercritical fluid injection device 1, a melting and casting device 2, a material handling device 3, a rotary production line 4, a foaming mold 5, and a material cylinder 16; the supercritical preform foaming device is as follows: Figure 1 As shown; The supercritical fluid injection device 1 is used to inject supercritical fluid into the foaming mold 5; the melt casting device 2 is used to heat and melt the polymer particles and transfer them into the foaming mold 5; the material handling device 3 is used to open the lid of the foaming mold 5 to handle the material; the foaming mold 5 is located on a rotatable rotary production line 4; the material cylinder 16 is used to dry the polymer particles. In the preparation of supercritical preform foamed products, polymer particles are placed in a material cylinder 16 for drying, then heated and melted by a melting and casting device 2, and then transferred to a foaming mold 5. Supercritical fluid is injected through a supercritical fluid injection device 1. After the reaction is completed, the lid of the foaming mold 5 is opened using a material handling device 3, and the supercritical preform foamed product is taken out. The foaming mold 5 is rotated to the bottom of the melting and casting device 2 by a rotatable rotary production line 4, and heated and melted polymer particles are injected again. This process is repeated.

[0050] Example 7

[0051] A supercritical preform foaming mold, the mold comprising a mold core and a mold shell; The mold shell is equipped with a padlock 7, a sealing ring 8, a heating and cooling outlet 9, a three-way high-temperature solenoid valve 10, an exhaust hole 11, a buckle 12, an air inlet 13, and an exhaust groove 14. The mold core is provided with a positioning groove 15; The mold core is made of breathable steel, and the surface of the breathable steel is coated with Teflon. The mold core is located inside the mold shell and is assembled into the mold by the positioning groove 15; There are two heating and cooling outlets 9; there are four exhaust holes 11, which are one-way valve exhaust holes; the three-way high-temperature solenoid valve 10 is used to control the mold temperature.

[0052] The supercritical preform foaming mold, such as Figures 2 to 8 As shown.

[0053] Comparative Example 1 A 30% EVA / 70% TPEE (30% ethylene-vinyl acetate / 70% thermoplastic polyester elastomer) modified elastomer material was dried at 80℃ for 4 hours. The material was then injected into a mold using an injection molding machine to obtain a solid preform. The solid preform was placed in an autoclave, and supercritical N2 and CO2 at 30 MPa were introduced and maintained for 2.5 hours. After dissolution equilibrium, the pressure was released to allow foaming, obtaining a foamed preform. The obtained foamed preform was then sanded to remove the outer layer and placed in a thermoforming machine, maintained at 150℃ for 5 minutes to obtain the finished product.

[0054] Comparative Example 2 Supercritical preform foamed products were prepared according to the method in Example 4, except that the cooling liquid was not introduced and the products were allowed to cool naturally.

[0055] Experimental Example 1 The foamed products prepared in Examples 1-5 and Comparative Examples 1-2 were observed and measured for cell diameter (scanning electron microscopy), morphology, resilience (rebound tester), and material loss rate. The results are shown in Table 1 and... Figures 9 to 19 As shown.

[0056] Table 1 Performance Measurement and Observation Results Group <![CDATA[Density after foaming / g / cm 3 > Cell diameter / µm Rebound performance / % Single / Double Process Time / min Single and dual gas usage (g) Single / Double Material Loss Rate / % Appearance Example 1 0.08 30 75 10.5 30 0 Dimensional tolerances are controlled within ±0.12mm, the cell structure is fine and uniform, and the product has no collapse or bubbling. Example 2 0.1 150 72 5.5 20 0 Dimensional tolerances are controlled within ±0.10mm, the cell structure is fine and uniform, and the product has no collapse or bubbling. Example 3 0.05 80 80 12.5 25 0 Dimensional tolerances are controlled within ±0.08mm, the cell structure is fine and uniform, and the product has no collapse or bubbling. Example 4 0.078 100 76 8.8 45 0 The exterior shows no signs of collapse, and the internal pores are uniform and fine. Example 5 0.03 100 45 14.5 35 0 The pore structure is fine and uniform, and the product has no collapse or bubbling. Comparative Example 1 0.08 200 75 155 5000 10 There is internal collapse and rough pores. Comparative Example 2 0.125 500 60 40 25 2 The material surface shrinks, resulting in poor shaping and large internal pores. From Table 1 and Figures 9 to 19 It can be seen that the supercritical preform foamed product prepared by the present invention has uniform and fine internal pores, and the product has no collapse or bubbling. Compared with the conventional preparation method in Comparative Example 1, it has better resilience performance.

[0057] As can be seen from the above embodiments, the present invention provides a method for preparing supercritical preform foamed products. By designing an injection molding equipment with a casting method and a specially made mold, the present invention achieves injection molding, foaming, and shaping in one machine, greatly improving production efficiency while saving equipment and energy costs, thus reducing overall costs. The present invention ensures product dimensional accuracy, high product yield, and high-ratio foaming by foaming and rapidly cooling within the mold, and controlling shrinkage rate through directional cooling in the cold runner.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a supercritical preform foamed product, characterized in that, Includes the following steps: After the polymer particles are dried and melted, they are injected into the mold core, the mold is closed, a vacuum is drawn, supercritical fluid is injected, the mixture is dissolved to equilibrium, the pressure is released, and the temperature is lowered to obtain the supercritical preform foamed product.

2. The preparation method according to claim 1, characterized in that, The polymer particles include one or more of the following: polyethylene, polylactic acid, polypropylene, polystyrene, polymethyl methacrylate, polycarbonate, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, polyamide, polyimide, polyphenylene sulfide, polyethersulfone, polyetheretherketone, rubber, silicone rubber, ethylene propylene diene monomer (EPDM) rubber, ethylene-vinyl acetate copolymer, thermoplastic polyurethane elastomer, thermoplastic polyester elastomer, and thermoplastic polyamide elastomer.

3. The preparation method according to claim 1, characterized in that, The drying temperature is 10~150℃, and the drying time is 0.3~10h; the melting treatment temperature is 100~400℃, and the melting treatment time is 2~60min.

4. The preparation method according to claim 3, characterized in that, The drying temperature is 100℃ and the drying time is 5 hours; the melting treatment temperature is 220℃ and the melting treatment time is 5 minutes.

5. The preparation method according to claim 1, characterized in that, The amount of polymer particles injected into the mold is 2-95% of the mold core volume or calculated according to Formula I: Injection amount = density after foaming × volume of the mold, Formula I; the mold is preheated to 1-70°C below the melting point of the polymer particles before injection; the injection time is 2-30s; the supercritical fluid includes CO2 and / or N2; the volume ratio of CO2 to N2 is 1-5:2-7.

6. The preparation method according to claim 5, characterized in that, The amount of polymer particles injected into the mold is 8% of the mold core volume or calculated according to Formula I: Injection amount = density after foaming × volume of the mold, Formula I; the mold is preheated to 50°C below the melting point of the polymer particles before injection; the injection time is 5s; the supercritical fluid includes CO2 and / or N2; the volume ratio of CO2 to N2 is 1:

2.

7. The preparation method according to claim 1, characterized in that, The method for achieving dissolution equilibrium is as follows: treatment for 2 to 60 minutes at a pressure of 1 to 50 MPa and a temperature 1 to 65°C lower than the melting point of the polymer particles; the depressurization rate is 1 to 1000 MPa / s; the cooling rate is 10 to 50°C / s; and the cooling method is to introduce a coolant at -5 to -10°C.

8. The preparation method according to claim 7, characterized in that, The method for achieving dissolution equilibrium is as follows: treatment for 5 minutes at 32 MPa and a temperature 65°C below the melting point of the polymer particles; the depressurization rate is 100 MPa / s; the cooling rate is 40°C / s; and the cooling method is to introduce a coolant at -5°C.

9. The preparation method according to claim 1, characterized in that, The mold includes a mold core and a mold shell; The mold shell is provided with a locking device, a sealing ring (8), a heating and cooling outlet (9), a three-way high-temperature solenoid valve (10), an exhaust port (11), an air inlet (13), and an exhaust groove (14); the locking device includes a padlock (7) and a buckle (12); The mold core is provided with a positioning groove (15); The mold core is made of breathable steel, and the surface of the breathable steel is coated with Teflon. The mold core is located inside the mold shell and is fitted into the mold by the positioning groove (15).

10. The supercritical preform foamed product prepared by the preparation method according to any one of claims 1 to 9.

Images