A particle fusion supercritical compression foaming production process and device

Abstract

The present invention relates to a particle fusion supercritical compression foaming production process and device, and belongs to the field of supercritical foaming technology. In the foaming method provided by the present invention, by increasing the gas-solid interface of the material, short-distance diffusion is carried out in units of polymer particles, the swelling time is shortened, and at the same time, the advantage of the compression foaming process in producing large-sized foam materials is ensured by utilizing one-piece molding in a confined space. In addition, the present invention also adopts the design of inner and outer molds, wherein the inner mold can be replaced in size and shape, which improves the utilization rate of the equipment itself and the product diversification to a certain extent. That is, the new method of this patent adopts particle fusion technology to effectively overcome the shortcomings of supercritical compression foaming and utilizes the design of one-piece molding and double molds to fully retain its advantages, which is very important for the industrial development of this technology.

Description

Technical Field

[0001] The invention relates to a particle fusion supercritical mold compression foaming production process and a device, belonging to the technical field of supercritical foaming. Background Art

[0002] The green preparation method of compression foaming uses a physical foaming agent mainly composed of supercritical carbon dioxide (CO2), which can achieve a micron or even nanometer-scale pore size and a wide range (5 to 50 times) of material foaming ratio, which is suitable for large-scale and large-scale production of semi-crystalline and amorphous polymer materials. The above advantages have made this technology widely concerned by the industry in recent years. However, compared with the existing compression chemical foaming, supercritical compression foaming requires physical foaming agents such as CO2 to diffuse from the outside to the inside of the polymer material to form a homogeneous solution. Therefore, for large-sized foaming materials, the physical foaming agent has a long diffusion distance inside the material, resulting in a very long swelling time, which seriously affects the production efficiency and hinders its industrialization process. Summary of the invention

[0003] The technical concept of the present invention is: increase the gas-solid interface of the material, diffuse in short distances with polymer particles as units, shorten the swelling time, and improve production efficiency (break the whole into parts); in addition, the limited mold cavity makes the particles squeeze each other to achieve the effect of eliminating the interface and forming an integrated molding, which ensures the advantages of the molded foaming process in producing large-size foam materials (combining the parts into a whole). In addition, the present invention also adopts the design of inner and outer molds, in which the size and shape of the inner mold can be changed, which improves the utilization rate of the equipment itself and the product diversification to a certain extent. That is, the new method of this patent adopts particle fusion technology to effectively overcome the shortcomings of slow diffusion of physical foaming agents in solid polymer materials during supercritical molded foaming, and fully retains its advantages of finer pore morphology and better material properties by using the design of integrated molding and double molds; the large gas-solid interface of the particle morphology is used to accelerate the penetration efficiency of supercritical fluid in the polymer matrix (reduce swelling time), and at the same time, the molding and foaming technologies are synchronously coupled to achieve the synergistic effect of efficient integrated molding and foaming, which plays an important role in promoting the industrialization development of supercritical solid foaming technology.

[0004] A particle fusion supercritical compression foaming production process comprises the following steps:

[0005] Step 1: Put the polymer material into the pretreatment kettle for drying, and then use the vacuum feeder to push the material into the high-temperature mold cavity to fill the mold cavity;

[0006] Step 2: Fill the air chamber connected to the mold cavity with high-pressure supercritical gas, and fill the supercritical gas into the gaps between the polymer raw materials, so that the supercritical fluid penetrates into the polymer material for a certain period of time at a certain temperature and pressure;

[0007] Step 3: Raise the temperature of the supercritical fluid to the melting point of the polymer material, so that the surface of the polymer material in contact with the supercritical fluid melts in a relatively short time, and the molecular chains inside the polymer material have a certain degree of mobility; then apply static pressure on the dispersed polymer material through a pressing component, so that the dispersed polymer materials are squeezed against each other to eliminate the gaps between the materials, and finally form a complete polymer blank with a certain size and shape;

[0008] In the fourth step, the polymer material in the mold cavity is pressed and formed, and then swells for a certain period of time to reach system equilibrium, and then the pressure is quickly released in the closed mold state or directly released in the open mold to induce bubble nucleation and subsequent rapid growth of bubbles, and then a microporous polymer foam material is obtained.

[0009] In one embodiment, in the diffusion process of the supercritical fluid in step 1 before the polymer material is formed, a large number of interfaces between the materials help to shorten the physical diffusion distance and improve the swelling efficiency of the supercritical fluid in the polymer matrix.

[0010] In one embodiment, the polymer material in a dispersed state swollen with a supercritical fluid in step 1 is not directly foamed, but is pressed and molded in a high-pressure mold and then foamed. The foamed material obtained is a molded part rather than dispersed foam beads, foam rods or foam sheets.

[0011] In one embodiment, the particle size of the granular polymer raw material in step 1 is 0.05-1.5 mm.

[0012] In one embodiment, the temperature of the mold in step 1 is close to the melting point of the crystalline polymer or the flow softening region temperature of the amorphous polymer, for example, 1 to 10° C. lower than the melting point of the crystalline polymer.

[0013] In one embodiment, after the supercritical fluid is added in step 2, the pressure in the mold is 5-25 MPa, and the pressure in the lower air chamber is slightly higher than that in the upper air chamber by about 0.05 MPa, and is maintained for 5-30 minutes.

[0014] In one embodiment, the static pressure in step 3 is 20-100 MPa, and the holding time is 5-30 min.

[0015] A particle fusion supercritical compression foaming production device, comprising:

[0016] A feeding device for feeding a granular polymer raw material into the mold;

[0017] The mold includes an outer mold and a detachable inner mold, and the inner mold is located inside the outer mold. The outer mold is composed of an outer mold upper mold and an outer mold lower mold pressed and sealed together, and the inner mold is composed of an inner mold upper mold and an inner mold lower mold pressed and sealed together; the interior of the inner mold is a mold cavity; the outer mold upper mold and the outer mold lower mold are between the sealing surface;

[0018] An upper air chamber is formed between the upper die of the outer die and the upper die of the inner die, and a lower air chamber is formed between the lower die of the outer die and the lower die of the inner die;

[0019] The inner mold is provided with ventilation holes on one side facing the upper air chamber and the lower air chamber, so that the upper air chamber and the lower air chamber are connected with the mold cavity;

[0020] A pressing plate is provided above the inner mold, and air holes are provided on the pressing plate; the pressing plate is installed on the upper mold of the inner mold, close to the upper air chamber end, and can move up and down in the mold cavity in a controlled manner;

[0021] The upper gas chamber and the lower gas chamber are communicated with the gas container through the gas inlet.

[0022] In one embodiment, a mold air outlet 12 is further provided on the outer mold upper mold and / or the outer mold lower mold. The mold air outlet 12 is connected to an exhaust port 15. The exhaust port 15 is used to exhaust the gas in the mold.

[0023] In one embodiment, a valve for controlling the opening and closing of the exhaust port is provided on the exhaust port.

[0024] In one embodiment, the gas inlet is connected to the gas container via a booster pump and / or a control valve; the booster pump 17 is used to increase the pressure of the output gas in the gas container.

[0025] In one embodiment, the feeding device is also connected to the pretreatment device, and the pretreatment device 1 is provided with a feeding and discharging system, a stirring system, a heating and cooling configuration and / or a temperature control system.

[0026] In one embodiment, the mold cavity is provided with a grid or vent holes, the aperture of which is smaller than the size of the polymer material. The inner mold is replaceable, and is divided into an upper mold and an lower mold, which are mechanically fixed in the outer mold cavity or on the outer mold. The mold cavity can change size and shape with the replacement of the inner mold.

[0027] In one embodiment, the pressing plate is a plate-like structure with vent holes. The pressing plate is fixed to the end of the inner mold cavity close to the upper air chamber, and its up and down movement is adjusted by a displacement control device. (The specific control device and power device can be placed inside the fixed block of the inner mold and the outer mold, that is, the part filled with the grid.

[0028] In one embodiment, the feeding device is a vacuum feeder.

[0029] The above-mentioned particle fusion supercritical compression foaming production device is used to produce molded foaming materials.

[0030] In one embodiment, the application refers to improving the swelling efficiency of the foaming material, improving the uniformity of the pore structure inside the profile, and combining molding with foaming, so that the polymer foaming material can have a more controllable foaming ratio, higher pore density, better compression strength, and more consistent morphology uniformity.

[0031] Beneficial Effects

[0032] 1. Supercritical fluid can quickly diffuse into the interior of the polymer material matrix through a large number of gas-solid interfaces between dispersed polymer materials, greatly shortening the diffusion time of supercritical fluid, improving production efficiency and reducing production cycle;

[0033] 2. The swelling, molding and foaming of polymer materials are all completed in the same process, achieving the purpose of simple process flow and low production cost;

[0034] 3. While improving the gas diffusion efficiency, it also retains the advantages of molded foaming, such as a wide range of applicable materials, controllable foaming ratio, and uniform and dense pores;

[0035] 4. The dual mold design of fixed mold and replaceable inner mold and multi-layer molding are suitable for industrial production and can be used to produce foam sheets, plates, special-shaped materials, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a production device diagram provided by the present invention.

[0037] Figure 2 This is an enlarged view of the mold structure.

[0038] Figure 3 Overall side profile of Example 1.

[0039] Figure 4 This is a SEM image taken by liquid nitrogen quenching in Example 1.

[0040] Figure 5 This is the overall side profile diagram of Example 2.

[0041] Figure 6 This is a SEM image taken by liquid nitrogen quenching in Example 2.

[0042] Figure 7 This is the overall side profile of Control Example 1.

[0043] Figure 8 This is a side outer SEM image of Control Example 1 taken using liquid nitrogen quenching.

[0044] Fig. 9 This is a SEM image of the inner side of the control example 1 taken using liquid nitrogen quenching.

[0045] Fig.10 This is the overall side profile of Control Example 2.

[0046] Fig.11 This is the SEM image of Control Example 2 taken using liquid nitrogen quenching.

[0047] Among them, 1. pretreatment device; 2. first valve; 3. feeding device; 4. second valve; 5. outer mold upper mold; 6. outer mold lower mold; 7. sealing surface; 8. inner mold upper mold; 9. inner mold lower mold; 10. mold cavity; 11. upper air chamber; 12. mold air outlet; 13. pressure plate; 14. gas inlet; 15. exhaust port; 16. tee; 17. booster pump; 18. control valve; 19. gas container; 20. lower air chamber; 21. vent; 22. vent. DETAILED DESCRIPTION

[0048] In the technical solution adopted by the present invention, the production efficiency of supercritical compression foaming is improved by accelerating the diffusion of physical foaming agent in the material. At the same time, the advantage of compression foaming process in producing large-sized foam materials is ensured by integrated molding in confined space. In addition, the present invention also adopts the design of inner and outer molds, in which the inner mold can be changed in size and shape, which improves the utilization rate of the equipment itself and product diversification to a certain extent.

[0049] The diffusion speed of physical foaming agents in materials is mainly affected by two factors: (1) the diffusion rate of physical foaming agents in the polymer matrix; (2) the number of interfaces between the material and the physical foaming agent before foaming and the diffusion distance required to achieve uniform swelling. The use of supercritical fluid technology can significantly increase the diffusion rate of physical foaming agents, but the specific surface area of ​​large-sized materials is very small and the diffusion distance is too long.

[0050] The method adopted by the present invention is to introduce a large number of gas-solid contact interfaces and shorten the diffusion distance of the physical foaming agent, which can accelerate the diffusion of the physical foaming agent in the material. The introduction of the interface is equivalent to dividing the original whole into many small units. Under the guiding ideology of "breaking the whole into parts", the innovative introduction of the "particle fusion" technology allows the physical foaming agent to diffuse a short distance for each particle of the polymer material at the same time and make all particles reach swelling saturation. The "particle fusion" technology ensures that the relative spatial position of each polymer particle in the material does not change, and the restricted extrusion behavior in the mold cavity causes the particles to squeeze each other, thereby eliminating the interface between the particles and completing the one-piece molding.

[0051] More specifically, the steps of the supercritical foaming processing method of the present invention are as follows:

[0052] The foaming polymer used in the present invention can be any general plastic, engineering plastic or special engineering plastic that can produce foaming materials, and can be amorphous or semi-crystalline thermoplastic polymers such as polystyrene, polyethylene, polypropylene, polylactic acid, polyurethane, polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polyimide, polyphenylene sulfide, polyetherimide, and their copolymers or blends. The resin raw material usually also includes processing aids, such as masterbatch, inorganic filler, flame retardant, nucleating agent, etc., which are premixed with the resin raw material and then added to the injection molding machine.

[0053] First, the polymer particles are put into the pretreatment kettle for drying. The polymer material can be in the shape of particles, rods, sheets, etc., as long as the direction of the airflow from the air chamber into the mold cavity is perpendicular to the stacking gap between the polymers. Then the material is driven into the high-temperature mold cavity (the high-temperature mold cavity temperature refers to the temperature close to the melting point of the crystalline polymer or the flow softening area temperature of the amorphous polymer. In some cases, the close here can be understood as a certain numerical range below the above temperature, such as below 1-10°C) through the vacuum feeder, filling the mold cavity (adjustable volume), and accurately feeding by controlling the feeding time or the material level meter. High-pressure supercritical gas is injected into the air chamber through the gas container. After the supercritical fluid is added, the pressure in the mold is 5~25 MPa, and the air pressure in the lower air chamber is slightly higher than that in the upper air chamber by about 0.05 MPa, and maintained for 5~30 min. The supercritical fluid quickly diffuses to the gaps between the particles to the gaps of the polymer pellets, and quickly penetrates into the polymer pellets under the action of high temperature and high pressure.

[0054] The filling of supercritical fluid also accelerates heat transfer. After the temperature of the supercritical fluid is increased, the surface of the polymer particles begins to melt in a short time, making the molecular chain have a certain activity. Then the pressing plate is pressed down to apply a static pressure of 20~100 MPa to the material in the mold cavity. The pressing plate is provided with openings, and the size of the openings is smaller than the particle size of the polymer particles, so that the materials are further compacted, the gaps between the particles are reduced, and finally a complete polymer profile with a certain size is formed. Then, after stabilizing for 5~30 minutes (depending on the temperature, pressure and material, the swelling time can be 1~120 minutes), the pressure is quickly released or the mold is opened for foaming in the closed mold state to induce the nucleation of the bubbles and the rapid growth of the bubbles, and finally a polymer foam material with a microporous structure is obtained.

[0055] Based on the above method, the device provided by the present invention is as follows Figure 1 As shown, including:

[0056] A feeding device 3, used to feed the granular polymer raw material into the mold;

[0057] The mold includes an outer mold and a detachable inner mold, and the inner mold is located inside the outer mold. The outer mold is composed of an outer mold upper mold 5 and an outer mold lower mold 6 pressed and sealed against each other, and the inner mold is composed of an inner mold upper mold 8 and an inner mold lower mold 9 pressed against each other; the interior of the inner mold is a mold cavity 10; between the outer mold upper mold 5 and the outer mold lower mold 6 is a sealing surface 7;

[0058] An upper air chamber 11 is formed between the outer mold upper mold 5 and the inner mold upper mold 8, and a lower air chamber 20 is formed between the outer mold lower mold 6 and the inner mold lower mold 9;

[0059] The inner mold is provided with ventilation holes 21 and 22 on one side facing the upper air chamber 11 and the lower air chamber 20, respectively, so that the upper air chamber 11 and the lower air chamber 20 are communicated with the mold cavity 10;

[0060] A pressing plate 13 is provided above the inner mold, and air holes are provided on the pressing plate 13; the pressing plate 13 is installed on the upper mold of the inner mold, close to the end of the upper air chamber 11, and can be controlled to move up and down in the mold cavity 10, and the movement here can be automatically controlled by a common power control device;

[0061] The upper gas chamber 11 and the lower gas chamber 20 are connected to the gas container 19 through the gas inlet 14 .

[0062] In one embodiment, the outer mold upper mold 5 and / or the outer mold lower mold 6 are further provided with an exhaust port 15 for exhausting the gas in the mold.

[0063] In one embodiment, the exhaust port 15 is provided with a valve for controlling the opening and closing of the exhaust port 15 .

[0064] In one embodiment, the gas inlet 14 is connected to the gas container 19 via a booster pump 17 and / or a control valve 18 ; the booster pump 17 is used to increase the pressure of the output gas in the gas container 19 .

[0065] In one embodiment, the feeding device 3 is also connected to the pretreatment device 1, and the pretreatment device 1 is provided with a feeding and discharging system, a stirring system, a heating and cooling configuration and / or a temperature control system.

[0066] In one embodiment, the mold cavity 10 is provided with a grid or vent holes, the aperture of which is smaller than the size of the polymer material. The vent holes or grids can be used to confine the polymer raw material particles in the inner mold cavity to prevent contact or blockage of the gas inlet and outlet. The inner mold is replaceable and is divided into an upper and lower mold, which are mechanically fixed in the outer mold cavity or on the outer mold. The mold cavity can change size and shape as the inner mold is replaced.

[0067] In one embodiment, the pressing plate 13 is a plate-like structure with vents. The pressing plate here is fixed to the end of the inner mold cavity close to the upper air chamber, and its up and down movement is adjusted by a displacement control device. (The specific control device and power device can be placed inside the fixed block of the inner mold and the outer mold, that is, the part filled with the grid.

[0068] In one embodiment, the feeding device 3 is a vacuum feeder.

[0069] Example 1

[0070] Taking the production of polypropylene foam material as an example, first, the polypropylene raw material with an average particle size of 4 mm is added to the mold through the feeding device 3, the temperature in the mold is preheated to 150°C, and then supercritical liquid carbon dioxide is supplied into the mold from the gas container 19, and the internal pressure of the mold 10 reaches 13 MPa, which is maintained for 10 min, and then the temperature is raised to 153°C, and the pressing plate 13 is moved downward to maintain a static pressure of 30 MPa on the polymer for 5 min, and the pressure is quickly released.

[0071] Example 2

[0072] Taking the production of polylactic acid foam material as an example, first, the PLA raw material with an average particle size of 5 mm is added to the mold through the feeding device 3, the temperature in the mold is preheated to 145°C, and then supercritical liquid carbon dioxide is supplied into the mold from the gas container 19, and the internal pressure of the mold 10 reaches 13 MPa, which is maintained for 10 min, and then the temperature is raised to 150°C, and the pressing plate 13 is moved downward to maintain a static pressure of 30 MPa on the polymer for 5 min, and the pressure is quickly released.

[0073] Comparative Example 1

[0074] The difference from Example 1 is that the polymer raw material of the plate is used, and because the sample has been formed into a plate before foaming, it is not necessary to reshape the pellets in the mold cavity by extrusion during the foaming process. The other process parameters are the same.

[0075] Taking the production of polypropylene foam material as an example, first, a 10 mm thick polypropylene sheet is added to the mold through the feeding device 3, the temperature in the mold is preheated to 150°C, and then supercritical liquid carbon dioxide is supplied into the mold from the gas container 19, and the internal pressure of the mold 10 reaches 13 MPa, maintained for 10 minutes, heated to 153°C, maintained for 5 minutes, and quickly released the pressure.

[0076] Comparative Example 2

[0077] The difference from Example 1 is that after the polymer in a pellet state is added into the mold and heated, a pressing plate is not used for downward extrusion molding, and other process parameters are the same.

[0078] Taking the production of polypropylene foam material as an example, first, the polypropylene raw material with an average particle size of 4 mm is added to the mold through the feeding device 3, the temperature in the mold is preheated to 150°C, and then supercritical liquid carbon dioxide is supplied into the mold from the gas container 19, and the internal pressure of the mold 10 reaches 13 MPa and is maintained for 10 minutes. After the temperature is raised to 153°C, it is maintained for 5 minutes and the pressure is quickly released.

[0079]

[0080] The SEM characterization results of the above foaming materials are as follows Figure 3-Figure 11 As shown, it can be seen from the figure that the foamed material prepared by the present invention has a smaller average pore diameter and a higher pore density, and has excellent mechanical properties. By comparing Example 1 and Control Example 1, it can be seen that since Control Example 1 uses a directly formed plate as the processing raw material form, the supercritical gas penetration effect in a short time is extremely poor, the foaming ratio of the inner and outer parts is significantly different, and is much smaller than the foaming ratio of Example 1, and the pore structure is also uneven. By using granular raw materials for foaming, the density and compression strength of the pores are significantly improved, and the material obtained by the integrated foaming molding process of the present invention is consistent in morphology inside and outside as a whole. It can be seen from Example 1 and Control Example 2 that if the pressure molding method of the pressing plate is not adopted, the obtained pore density is much lower than that of Example 1, and the compression strength is low, and the adhesion between the foamed particles of the material is poor.

[0081] From the above, it can be seen that the above-mentioned particle fusion supercritical compression foaming production device, when used in the production of molded foamed materials, can improve the swelling efficiency of the foamed materials, improve the uniformity of the pore structure inside the profile, and combine molding with foaming, so that the polymer foamed materials can have a more controllable foaming ratio, higher pore density, better compression strength, and more consistent morphology uniformity.

Claims

1. A particle fusion supercritical compression foaming production process, characterized in that: The steps include: In the first step, the polymer material is put into a pretreatment kettle for drying, and then the material is driven into a high-temperature mold cavity to fill the mold cavity; Step 2: Fill the mold cavity with high-pressure supercritical gas, and allow the supercritical gas to fill the gaps between the polymer raw materials, so that the supercritical fluid penetrates into the polymer material; Step 3, raising the temperature of the supercritical fluid to melt the surface of the polymer material in contact with the supercritical fluid, and then applying static pressure on the dispersed polymer material through a pressing component to form a complete polymer blank; Step 4: After the polymer material in the mold cavity is pressed and formed, it swells to reach system equilibrium, and then the pressure is quickly released in a closed mold state or directly released in an open mold to obtain a microporous polymer foam material; The polymer material is in the form of particles; the particle size of the particles is 0.02-5 mm; In step 1, the temperature of the high temperature mold cavity is 1-10°C lower than the melting point of the crystalline polymer or the flow softening zone temperature of the amorphous polymer; In the second step, after the supercritical fluid is added, the pressure in the mold is kept at 5-25 MPa, and the air pressure in the lower air chamber is 0.05 MPa higher than that in the upper air chamber, and maintained for 5-30 min.

2. The particle fusion supercritical compression foaming production process according to claim 1, characterized in that: In step 3, the static pressure is 20-100 MPa, maintained for 5-30 min; the swelling time is 1-120 min.

3. A particle fusion supercritical molded foaming production device used in the particle fusion supercritical molded foaming production process according to claim 1, characterized in that: include: A feeding device (3) for feeding a granular polymer raw material into the mold; The mold includes an outer mold and a detachable inner mold, and the inner mold is located inside the outer mold. The outer mold is composed of an outer mold upper mold (5) and an outer mold lower mold (6) pressed together and sealed, and the inner mold is composed of an inner mold upper mold (8) and an inner mold lower mold (9) pressed together; the interior of the inner mold is a mold cavity (10); and a sealing surface (7) is between the outer mold upper mold (5) and the outer mold lower mold (6); An upper air chamber (11) is formed between the outer mold upper mold (5) and the inner mold upper mold (8), and a lower air chamber (20) is formed between the outer mold lower mold (6) and the inner mold lower mold (9); A plurality of vent holes (21, 22) are respectively provided on a surface of the inner mold facing the upper air chamber (11) and the lower air chamber (20), so that the upper air chamber (11) and the lower air chamber (20) are in communication with the mold cavity (10); A pressing plate (13) is provided above the inner mold, and an air hole is provided on the pressing plate (13); the pressing plate (13) is installed on the upper mold of the inner mold, close to the end of the upper air chamber (11), and moves up and down in the mold cavity (10) in a controlled manner; The upper gas chamber (11) and the lower gas chamber (20) are connected to the gas container (19) via the gas inlet (14); The gas inlet (14) and the gas container (19) are connected via a booster pump (17) and / or a control valve (18); the booster pump (17) is used to increase the pressure of the output gas in the gas container (19); grids or vents are distributed on the mold cavity (10), and the aperture of the grids or vents is smaller than the size of the polymer material; the feeding device (3) is a vacuum feeder.

4. The particle fusion supercritical compression foaming production device according to claim 3, characterized in that: The outer mold upper mold (5) and / or the outer mold lower mold (6) are also provided with a mold air outlet (12), and the mold air outlet (12) is connected to the exhaust port (15), and the exhaust port (15) is used to exhaust the gas in the mold.

5. The particle fusion supercritical compression foaming production device according to claim 3, characterized in that: The exhaust port (15) is provided with a valve for controlling the opening and closing of the exhaust port (15).

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