A supercritical fluid-assisted injection molding apparatus and method of supercritical fluid-assisted injection molding

Abstract

The application discloses a supercritical fluid assisted injection molding equipment and an assisted injection molding method thereof, and relates to the technical field of plastic material forming, which comprises a piezoelectric ceramic ring and a ceramic sheet with nanoscale micropores. A periodic pressure fluctuation is formed at the outlet of the micropores by a standing wave field excited by high-frequency vibration of the piezoelectric ceramic ring, and the supercritical fluid is continuously broken into nanobubble nuclei. At the same time, the pressure fluctuation offsets the change in the aperture of the nanoscale micropores caused by thermal deformation, thereby avoiding fluid turbulence and bubble size discretization caused by the change in the aperture. Previously, a negative charge enrichment area formed by a dielectric functional coating in a low-frequency pre-polarization stage wraps the nanobubbles with negative charges through electrophoresis at the moment when the nanobubbles leave the micropores. The surface zeta potential effectively neutralizes the surface energy surge caused by the high-curvature interface, inhibits the instantaneous coalescence tendency of the nanobubbles caused by energy imbalance, and maintains the stable monodisperse state of the nanobubble group from the initial formation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of forming technology of plastic materials, in particular to a supercritical fluid assisted injection molding device and a supercritical fluid assisted injection molding method. BACKGROUND

[0002] In the injection molding process, carbon dioxide in a supercritical state is dispersed into micron-sized bubbles by an injector and injected into a high-temperature melt for sufficient and uniform mixing / diffusion, which is beneficial to improving the mechanical properties and surface quality of the product after injection molding.

[0003] However, the micron-sized bubbles have a large size, which makes the contact interface between the gas and the melt not as good as that of nanometer-sized bubbles, and the gas cannot penetrate into the fine gaps of the free volume of the melt material, resulting in limited effective reaction area per unit volume and limited improvement in the mechanical properties and surface quality of the product after injection molding.

[0004] Although nanometer-sized bubbles have obvious advantages, it is difficult to generate stable nanometer-sized bubbles through the nanometer-sized pores of the injector, because the nanometer-sized pores are greatly affected by thermal deformation, making it difficult to generate stable nanometer-sized bubbles, which makes it difficult to mix with the melt sufficiently and uniformly, and it is difficult to maintain a high level of effective reaction area per unit volume.

[0005] In addition, the high curvature of the directly generated nanometer-sized bubbles increases the surface energy, which is thermodynamically unstable. In order to reduce the surface energy, the nanometer-sized bubbles have a tendency to spontaneously merge and recombine into micron-sized bubbles.

[0006] The instability of the supercritical state carbon dioxide nanometer-sized bubbles during the generation process and the thermodynamic instability after the generation seriously hinder the wide application in the injection molding process. SUMMARY

[0007] One of the purposes of the present application is to solve the problem of the instability of the supercritical state carbon dioxide nanometer-sized bubbles during the generation process and the thermodynamic instability after the generation in the prior art, which seriously hinders the wide application in the injection molding process.

[0008] The second purpose of the present application is to provide a supercritical fluid assisted injection molding method.

[0009] To achieve the above-mentioned one of the purposes, the present application adopts the following technical scheme: a supercritical fluid assisted injection molding device, comprising a barrel and a screw arranged in the barrel, the screw is driven to rotate by a motor, the device further comprises an injector embedded in the barrel, a constraint shaft arranged at the bottom of the cavity of the injector is provided with a main channel penetrating upward and downward, a plurality of ceramic sheets arranged along the main channel in the axial direction are provided with nanometer-sized micropores, and the surface of the micropores is coated with a dielectric functional coating.

[0010] A coaxial sleeve is embedded in a piezoelectric ceramic ring outside the constraint shaft, and the piezoelectric ceramic ring corresponds to the ceramic sheet and is configured as:

[0011] Low-frequency vibration is generated to cause the dielectric functional coating to be polarized, and negative ions in the environment are attracted to form a negative charge enrichment area.

[0012] High-frequency vibration is generated to excite a standing wave field, and the fluid flowing through the micro-hole is broken into nanobubble nuclei through the periodic pressure fluctuations formed at the outlet of the micro-hole, and the nanobubble nuclei are shaped in the low-pressure area of the pressure fluctuations. At the same time, the pressure fluctuations caused by high-frequency vibration offset the change in the aperture of the micro-hole caused by thermal deformation.

[0013] During the bubble shaping stage, the negative charge enrichment area causes the nanobubble to be wrapped by negative charges at the moment of leaving the micro-hole through electrophoresis, and the surface dynamic potential effectively neutralizes the surface energy surge caused by the high-curvature interface of the nanobubble, thereby inhibiting the tendency of instantaneous coalescence of the bubble due to energy imbalance.

[0014] The beneficial effects of the present application are:

[0015] The present application uses the periodic high-pressure shear zone and low-pressure expansion zone of the pressure fluctuations formed at the outlet of the micro-hole by the standing wave field excited by the high-frequency vibration of the piezoelectric ceramic ring to continuously break the supercritical fluid into nanobubble nuclei, and at the same time, the pressure fluctuations offset the change in the aperture of the nanoscale micro-hole caused by thermal deformation, thereby avoiding the turbulent flow of the fluid and the dispersion of the bubble size caused by the change in the aperture. The negative charge enrichment area formed by the dielectric functional coating in the low-frequency pre-polarization stage effectively neutralizes the surface energy surge caused by the high-curvature interface through electrophoresis, thereby inhibiting the tendency of instantaneous coalescence of the bubble due to energy imbalance. The nanobubble group maintains a stable monodisperse state from the initial formation, solves the instability of the supercritical state carbon dioxide nanobubble in the generation process and the thermodynamic instability after generation in the prior art, and seriously hinders the widespread application in the injection molding process. Finally, the nanobubble is continuously and uniformly distributed in the melt.

[0016] Further, in the embodiment of the present application, the dielectric functional coating is a zirconium oxide dielectric layer, which forms a charge enrichment area with a dynamic potential of -30mV to -50mV under the low-frequency vibration of 10-15kHz of the piezoelectric ceramic ring.

[0017] Further, in the embodiment of the present application, the oscillation frequency of the high-frequency vibration of the piezoelectric ceramic ring is 50-80kHz.

[0018] Further, in the embodiment of the present application, the positive electrode conductive wire connected with the external power source is connected to the positive electrode conductive layer on the outer surface of the piezoelectric ceramic ring, and the composite conductive layer arranged on the inner surface of the constraint shaft is connected to the negative electrode conductive wire of the external power source to form a closed loop.

[0019] Further, in the embodiment of the present application, the composite conductive layer is composed of a zirconium oxide-based dielectric layer and a graphene conductive layer covering the surface of the dielectric layer, and the graphene conductive layer is conductive to the negative electrode conductive wire through a copper rod.

[0020] Further, in the embodiment of the present application, the supercritical fluid assisted injection molding device further comprises a carbon dioxide storage tank, a booster pump and a preheater connected in sequence, and the preheater is in communication with the injector.

[0021] To achieve the above-mentioned purpose two, the present application adopts the following technical scheme: a supercritical fluid assisted injection molding method, comprising the following steps:

[0022] An alternating current is applied to the piezoelectric ceramic ring corresponding to the ceramic sheet to generate low-frequency vibration, so that the dielectric functional coating on the surface of the ceramic sheet micropore is polarized to form a negative charge enrichment area by attracting negative ions in the environment.

[0023] The carbon dioxide fluid in a supercritical state is injected into the main channel, at this time the piezoelectric ceramic ring is switched to high-frequency vibration to excite a standing wave field, so that the periodic pressure fluctuation formed at the outlet of the ceramic sheet micropore in the main channel breaks the fluid flowing through the micropore into nanobubble nuclei and makes the nanobubble nuclei complete bubble shaping in the low-pressure area of the pressure fluctuation.

[0024] At the same time, the pressure fluctuation caused by high-frequency vibration offsets the change in the pore size of the micropore caused by thermal deformation.

[0025] In the bubble shaping stage, the nanobubble nuclei are immediately wrapped by negative charges through electrophoresis at the moment of leaving the micropore, the surface zeta potential effectively neutralizes the surface energy surge caused by the high-curvature interface of the nanobubble nuclei, and the tendency of instantaneous coalescence of the nanobubble nuclei due to energy imbalance is inhibited, so that the nanobubble nuclei maintain a stable monodisperse state from the initial formation.

[0026] Finally, the nanobubble nuclei in a stable monodisperse state are mixed / diffused with the melt to assist the plasticizing and molding of the melt.

[0027] Further, in the embodiment of the present application, after plasticizing and molding, the piezoelectric ceramic ring is switched to ultrahigh-frequency vibration to use the local shock wave generated by the collapse of cavitation bubbles to flush the inner wall of the micropore and peel off possible residues.

[0028] Further, in the embodiment of the present application, the oscillation frequency of the ultrahigh-frequency vibration is above 150 kHz.

[0029] Further, in the embodiment of the present application, after the piezoelectric ceramic ring is switched to ultrahigh frequency vibration, reverse pulse voltage is applied to the positive and negative conductive wires, and the cleaning agent is introduced into the micropore channel through the electroosmotic flow effect to clean. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a schematic diagram of the supercritical fluid assisted injection molding equipment in the embodiment of the present application.

[0031] Figure 2 It is a structural schematic diagram of the injector in the embodiment of the present application.

[0032] 1, barrel, 2, screw, 3, mold, 4, storage tank, 5, booster pump, 6, preheater;

[0033] 10, injector, 11, constraint shaft, 12, main channel, 13, ceramic sheet, 14, piezoelectric ceramic ring. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme of the present application clear, complete and the advantages more clear and obvious, the following will be further described in detail in combination with the drawings. It should be understood that the specific embodiments described here are part of the embodiments of the present application, not all the embodiments, only to explain the embodiments of the present application, and not for limiting the embodiments of the present application, all other embodiments obtained by the ordinary skilled in the art without creative labor are within the scope of protection of the present application.

[0035] In the description of the present application, it should be noted that the terms "center", "middle", "upper", "lower", "left", "right", "inner", "outer", "top", "bottom", "side", "vertical", "horizontal" and the like indicate the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore it cannot be understood as a limitation on the present application. In addition, the terms "one", "first", "second", "third", "fourth", "fifth", "sixth" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0036] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "linking" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0037] For the purpose of simplicity and illustration, the principles of the embodiments are primarily described by reference to examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments. It will be apparent, however, to one skilled in the art that the embodiments can be practiced without the specific details and that numerous implementation choices can be made. In some instances, well-known supercritical fluid assisted injection molding methods and structures have not been described in detail in order to avoid unnecessarily obscuring the embodiments. Embodiment 1

[0038] It should be noted that the drawings of the specification should be understood as part of the content of the specification, and the structure shape, connection relationship, fitting relationship, and position relationship that can be unambiguously obtained from the drawings should be understood as part of the content of the specification.

[0039] A supercritical fluid assisted injection molding device, as shown in Figure 1 , Figure 2 includes a barrel 1 and a screw 2 arranged in the barrel 1, the screw 2 is driven to rotate by a motor, and the device further includes an injector 10 embedded in the barrel 1, a constraint shaft 11 arranged at the bottom of the cavity of the injector 10 is provided with a main channel 12 penetrating up and down, and a plurality of ceramic sheets 13 arranged axially along the main channel 12 each have nanoscale micropores, and the surface of the micropores is coated with a dielectric functional coating.

[0040] A piezoelectric ceramic ring 14 coaxially sleeved outside the constraint shaft 11 corresponds to the ceramic sheet 13, and the piezoelectric ceramic ring 14 is configured to:

[0041] Generate low-frequency vibration to cause the dielectric functional coating to polarize and attract negative ions in the environment to form a negative charge enrichment area.

[0042] Generate high-frequency vibration to excite a standing wave field, break the fluid flowing through the micropores into nanobubble nuclei through periodic pressure fluctuations formed at the outlet of the micropores, and complete bubble shaping in the low-pressure area of the pressure fluctuations. At the same time, the pressure fluctuations caused by high-frequency vibration offset the change in pore size caused by thermal deformation of the micropores.

[0043] In the bubble shaping stage, the negative charge enrichment zone makes the nanobubbles wrapped by negative charges at the moment of leaving the micro-holes through electrophoresis. The surface zeta potential effectively neutralizes the surface energy surge caused by the high-curvature interface of nanobubbles, inhibiting the tendency of instantaneous coalescence due to energy imbalance.

[0044] The specific implementation process is as follows:

[0045] Before injection molding, low-frequency alternating current (10-15 kHz) is applied to the piezoelectric ceramic ring 14 to induce radial micro-vibration of the piezoelectric ceramic ring 14. This vibration is transmitted to the micro-holes through the constraint shaft 11, causing the polarization of the dielectric functional coating coated on the surface of the micro-holes, attracting negative ions in the environment to form a stable negative charge enrichment zone.

[0046] When the screw 2 starts to rotate to push the plastic melt, the supercritical fluid, i.e. supercritical carbon dioxide, is pressed into the main channel 12 of the constraint shaft 11, and when it flows through the micro-holes of the ceramic sheet 13, the piezoelectric ceramic ring 14 is switched to high-frequency oscillation mode (50-80 kHz), and the radial standing wave field generated by its vibration forms periodic high-pressure shear zone and low-pressure expansion zone pressure fluctuations at the micro-hole outlet: in the high-pressure shear zone, the supercritical carbon dioxide is severely sheared into nanoscale bubble nuclei; in the low-pressure expansion zone, the bubble nuclei rapidly expand and shape due to the sudden drop in pressure. At the same time, the surface negative charge of the dielectric functional coating migrates to the interface of the newly formed bubbles (the bubble surface zeta potential is stable at -30 mV to -50 mV) through electrophoresis, establishing a Coulomb repulsion barrier to inhibit coalescence.

[0047] The standing wave field and the Coulomb repulsion can work together. The standing wave field forms a specific distribution pattern in space through its pressure distribution, avoiding random collision and coalescence of nanobubbles. At the same time, the Coulomb repulsion provides additional repulsive force when nanobubbles approach, further enhancing the effect of inhibiting coalescence. The combined action of the two can better maintain stability, so that the nanobubbles remain in a relatively stable dispersed state for a certain period of time.

[0048] The metastable state of nanobubbles enables the bubble group to maintain a long-term stable distribution in the melt, avoiding the rapid coalescence of micron-sized bubbles that leads to a sudden change in local concentration. This stability not only ensures uniformity of dissolution, but also allows the contact interface between the nanobubbles and the melt to be continuously updated by the generation of new nanobubbles, enabling the carbon dioxide molecules to circulate and refresh the contact sites with the melt, thereby improving the dissolution efficiency.

[0049] The present application has the advantages that, in the bubble generation stage, the piezoceramic ring 14 vibrates at high frequency, the excited standing wave field forms periodic high-pressure shear zone and low-pressure expansion zone pressure fluctuations at the micro-pore outlet, which continuously breaks the supercritical fluid into nanobubble nuclei, at the same time, the pressure fluctuations offset the pore size change caused by thermal deformation of the nanoscale micro-pores, avoiding the fluid turbulence and bubble size discretization caused by the change of pore size. Previously, the negative charge enrichment area formed by the dielectric functional coating in the low-frequency pre-polarization stage, through electrophoresis, the nanobubbles are wrapped by negative charges at the moment of leaving the micro-pore, the surface zeta potential effectively neutralizes the surface energy surge caused by the high-curvature interface, and the instantaneous coalescence tendency of the bubbles caused by energy imbalance is suppressed. The nanobubble group maintains a stable monodisperse state from the initial formation, solves the instability of supercritical state carbon dioxide nanobubbles in the generation process and the thermodynamic instability after generation in the prior art, and seriously hinders the wide application in the injection molding process. Finally, the nanobubbles are uniformly and continuously distributed in the melt.

[0050] During injection molding, the pressure change in the mold 3 cavity will change the state of the gas dissolved in the melt. The nanoscale bubbles are stably dispersed in the melt, and can form a more uniform and fine micro-porous structure when the pressure changes. Taking the preparation of micro-porous plastics as an example, the micro-pores formed by nanoscale bubbles are smaller in size and more uniform in distribution, which can effectively improve the comprehensive performance of the product, such as improving the strength of the product and improving the surface flatness of the product, etc., as follows:

[0051] The microporous plastics prepared by micron-sized bubbles have micropores with sizes generally between 10-100 pm. In some common microporous injection experiments, the literature "Research on the Process of Bubble Structure Formation and Evolution of Products in Microporous Foaming Injection Molding Technology and Its Products" indicates that using micron-sized bubbles for nucleation foaming, the average size of the micropores of the final product is about 20 pm. The microporous plastics prepared by nanometer-sized bubbles can be prepared by conducting comparative experiments: using nanometer-sized bubbles and micron-sized bubbles to prepare microporous plastics, respectively, and using microcharacterization methods such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to observe and count the size distribution of micropores. In a series of experiments, microporous plastic products prepared by nanometer-sized bubbles were measured for a large number of micropore sizes under SEM images, and statistical analysis showed that the average size of the micropores of the products prepared by micron-sized bubbles was about 20 pm, and the average size of the micropores of the products prepared by nanometer-sized bubbles was about 480 nm. Referring to the relevant research literature such as "Size control of nanobubbles generated from Shirasu-porous-glass (SPG) membranes", it is mentioned that nanometer-sized bubbles with an average diameter of 360-720 nm (0.36 pm-0.72 pm) can be prepared under certain conditions. The micropores formed by nanometer-sized bubbles are significantly smaller than the micropores formed by micron-sized bubbles, so the fine and dense micropores formed by nanometer-sized bubbles make the product surface more smooth.

[0052] Taking tensile strength as an example, larger and unevenly distributed micropores are prone to become stress concentration points, reducing the load-bearing capacity of the material. Therefore, compared with the micropores formed by micron-sized bubbles, the fine and dense micropores formed by nanometer-sized bubbles of the application can improve the strength of the product and improve the impact resistance of the material.

[0053] Specifically, the dielectric functional coating is a zirconia dielectric layer, which forms a charge-rich region with a zeta potential of -30 mV to -50 mV under the low-frequency vibration of 10-15 kHz of the piezoelectric ceramic ring 14.

[0054] Specifically, the oscillation frequency of the high-frequency vibration of the piezoelectric ceramic ring 14 is 50-80 kHz.

[0055] Specifically, the positive electrode conductive wire connected to the external power source is connected to the positive electrode conductive layer on the outer surface of the piezoelectric ceramic ring 14, and the composite conductive layer arranged on the inner surface of the constraint shaft 11 is connected to the negative electrode conductive wire of the external power source to form a closed loop.

[0056] More specifically, the composite conductive layer is composed of a zirconia-based dielectric layer and a graphene conductive layer covering the surface thereof, and the graphene conductive layer is connected to the negative electrode conductive wire through a copper rod.

[0057] Specifically, as Figure 1As shown, the supercritical fluid assisted injection molding apparatus further comprises a carbon dioxide storage tank 4, a booster pump 5 and a pre-heater 6 connected in sequence, the pre-heater 6 being in communication with the injector 10.

[0058] The implementation process is as follows:

[0059] The flow path of supercritical carbon dioxide in the injection molding process starts from the storage tank 4 storing liquid carbon dioxide. The liquid carbon dioxide is pressurized to a supercritical state (≥7.4 MPa / 31°C) by the booster pump 5, which has both the diffusion of gas and the solubility of liquid, becoming an ideal processing medium. Then, the carbon dioxide enters the pre-heating link and is preheated to 40-60°C by the pre-heater 6, which is precisely temperature-controlled to achieve a stable supercritical phase state, ensuring the uniformity of subsequent mixing with the melt.

[0060] The supercritical carbon dioxide after pre-treatment is injected into the barrel 1 through the injector 10 and fully contacts with the molten plastic raw material, i.e. the melt. Due to the penetration of supercritical carbon dioxide to the polymer chain, it can effectively reduce the melt viscosity and promote the uniform dispersion of the internal microstructure of the material.

[0061] The mixed melt enters the cavity of the mold 3 under the high pressure drive of the screw 2, at this time the pressure in the mold 3 rapidly decreases, and the supercritical carbon dioxide dissolved in the melt instantaneously gasifies and expands due to the sudden pressure drop, and this phase change process forms a uniformly distributed micro-porous structure in the material. The size and distribution of these micro-pores directly affect the mechanical properties and surface quality of the molded product.

[0062] It should be noted that the injector is not continuously dispersing supercritical carbon dioxide into nanoscale bubbles and injecting into the high-temperature melt for sufficient uniform mixing / diffusion. Because during the injection molding process, after the melt is filled in the cavity of the mold 3 driven by the screw 2, the melt in the cavity of the mold 3 is in the process of cooling and molding, and the melt in the barrel 1 is under the pressure of the screw 2 to maintain the pressure of the melt in the cavity of the mold 3, and no longer be transported.

[0063] In the above holding pressure stage, the melt, i.e. the polymer material, can be partially decomposed at high temperature to produce some small molecule gases, which can be ionized or chemically reacted to generate negative ions under certain conditions. And, additives used in the injection molding process, such as some additives with polarity or easy ionization, can also produce negative ions through chemical reactions when interacting with the melt or the surrounding environment. In addition, the high-temperature melt before melting usually contains a certain amount of water vapor, which is easy to release after melting, so that water vapor exists in the environment of the injector. At this time, the dielectric functional coating on the surface of the ceramic 13 micropores is polarized when the piezoelectric ceramic ring 14 vibrates under the action of low-frequency alternating current, and the electric field generated by the polarized dielectric functional coating can ionize or adsorb electrons from some particles in the surrounding gas or water vapor, thereby forming negative ions and forming a stable negative charge enrichment area. Example 2

[0064] A supercritical fluid assisted injection molding method using the device of Example 1, comprising the following steps:

[0065] An alternating current is applied to the piezoelectric ceramic ring 14 corresponding to the ceramic sheet 13 to make it vibrate at a low frequency, so that the dielectric functional coating on the surface of the micropores of the ceramic sheet 13 is polarized, and the negative ions in the environment are attracted to form a negative charge enrichment area.

[0066] The carbon dioxide fluid in a supercritical state is injected into the main channel 12, and at this time the piezoelectric ceramic ring 14 is switched to high-frequency vibration to excite a standing wave field, so that the periodic pressure fluctuation formed at the micropore outlet of the ceramic sheet 13 in the main channel 12 breaks the fluid flowing through the micropore into nanobubble nuclei and makes it complete bubble shaping in the low pressure area of the pressure fluctuation.

[0067] At the same time, the pressure fluctuation caused by high-frequency vibration offsets the change in pore size caused by thermal deformation of the micropore.

[0068] In the bubble shaping stage, the negative charge enrichment area makes the nanobubble wrapped by negative charge at the moment of leaving the micropore through electrophoresis, and the surface zeta potential effectively neutralizes the surface energy surge caused by the high-curvature interface of the nanobubble, inhibiting the tendency of instantaneous coalescence of the nanobubble due to energy imbalance, so that the nanobubble maintains a stable monodisperse state from the initial formation.

[0069] Finally, the nanobubbles in a stable monodisperse state are mixed / diffused with the melt to assist its plasticizing and molding. The problem of instability in the generation process of supercritical carbon dioxide nanobubbles and the thermodynamic instability after generation in the prior art seriously hinders the widespread application in the injection molding process.

[0070] Specifically, after plasticizing and molding, the piezoelectric ceramic ring 14 is switched to ultrasonic vibration, and the local shock wave generated by the collapse of the cavitation bubble is used to flush the inner wall of the micropore to strip the possible residues attached.

[0071] More specifically, the oscillation frequency of the ultrasonic vibration is above 150 kHz.

[0072] More specifically, after the piezoelectric ceramic ring 14 is switched to ultrasonic vibration, a reverse pulse voltage is applied to the positive and negative conductive wires to guide the cleaning agent into the micropore channel through the electroosmotic effect for cleaning.

[0073] Specifically, the oscillation frequency of the piezoelectric ceramic ring 14 is raised to above 150 kHz, and the local shock wave (peak pressure ≥ 15 MPa) generated by the collapse of the cavitation bubble is used to flush the inner wall of the micropore to strip the possible residues attached; at the same time, a reverse pulse voltage (-500 V / 10 ms) is applied to the positive and negative conductive wires to guide the cleaning agent into the micropore channel through the electroosmotic effect for cleaning.

[0074] More specifically, after a reverse pulse voltage is applied to the positive and negative conductive wires on the outer surface of the constraint shaft 11, the main channel 12 thereof will be charged to form an alternating electric field, which will attract ions with opposite charges in the cleaning agent solution to form a double-layer structure at the interface where the main channel 12 contacts the cleaning agent solution. Under the action of the electric field, the ions in the double-layer structure will move directionally, and this movement of the ions will drive the surrounding solvent molecules to move together, thereby generating electroosmotic flow. Under the action of the electroosmotic flow, the cleaning agent-containing solution will flow along the main channel 12, thereby achieving the purpose of guiding the cleaning agent into the micropore channel. In this way, the nanoscale micropores are less likely to be clogged.

[0075] Specifically, if the melt material is a hygroscopic material such as PA66 (nylon 66), and the melt contains a small amount of moisture, carbon dioxide will form a carbonic acid environment with the moisture, thereby triggering the hydrolysis of the amide bond, leading to a decrease in molecular weight and a decay of mechanical properties.

[0076] To this end, the following scheme is proposed:

[0077] Before plasticizing the PA66 base material, the inorganic composite core-shell structure particles are premixed with the PA66 base material at a mass ratio of 0.3%-0.8%, and the mixture is then fed into the barrel 1.

[0078] After that, when supercritical carbon dioxide is injected into the melt through the injector 10, the melt temperature is maintained in the range of 240-250°C, and the pressure is stabilized at 12-15 MPa, ensuring that the carbon dioxide is completely dissolved in the PA66 matrix.

[0079] The inorganic composite core-shell structure particle adopts hydroxyapatite / zinc oxide core-shell structure particle, the surface dynamic potential of which can reversibly change in the pH=3-6 range to attract and neutralize the H+ ions generated by hydrolysis, thereby slowing down the speed of amide bond hydrolysis, because the reduction of H+ ion concentration will inhibit the progress of the hydrolysis reaction.

[0080] Although the above describes the illustrative specific embodiments of the present application in order to enable a person skilled in the art to understand the present application, the present application is not limited to the scope of the specific embodiments, and all the inventions using the concept of the present application are within the protection scope of the present application as long as various changes are within the spirit and scope of the present application defined and determined by the appended claims.

Claims

1. A supercritical fluid assisted injection molding apparatus comprising a barrel and a screw disposed within the barrel, the screw being driven in rotational motion by a motor, characterized in that, The device also comprises an injector embedded in the barrel, a constraint shaft provided at the bottom of the injector cavity, a main channel penetrating through the constraint shaft, a plurality of ceramic sheets provided along the main channel, each ceramic sheet having nano-scale micropores, and a dielectric functional coating on the surface of the micropores. A coaxial sleeve is embedded in the piezoelectric ceramic ring outside the constraint shaft and corresponds to the ceramic sheet, and the piezoelectric ceramic ring is configured to: Generate low-frequency vibration to cause the dielectric functional coating to polarize and attract negative ions in the environment to form a negative charge enrichment area; Generate high-frequency vibration to excite a standing wave field, and break the fluid flowing through the micropores into nano-bubble nuclei through the periodic pressure fluctuations formed at the outlet of the micropores, and complete the bubble shaping in the low-pressure area of the pressure fluctuations; at the same time, the high-frequency vibration causes the pressure fluctuations to offset the change in the aperture of the micropores caused by thermal deformation; During the bubble shaping stage, the negative charge enrichment area causes the nano-bubbles to be wrapped by negative charges at the moment of leaving the micropores through electrophoresis, effectively neutralizing the surface potential of the nano-bubbles and inhibiting the instantaneous coalescence tendency of the bubbles caused by energy imbalance.

2. The supercritical fluid assisted injection molding apparatus of claim 1, wherein, The dielectric functional coating is a zirconium oxide dielectric layer, which forms a charge enrichment area with a zeta potential of -30 mV to -50 mV under the low-frequency vibration of 10-15 kHz of the piezoelectric ceramic ring.

3. The supercritical fluid assisted injection molding apparatus of claim 1, wherein, The oscillation frequency of the high-frequency vibration of the piezoelectric ceramic ring is 50-80 kHz.

4. The supercritical fluid assisted injection molding apparatus of claim 1, wherein, The positive electrode conductive wire connected to the external power source is connected to the positive electrode conductive layer on the outer surface of the piezoelectric ceramic ring, and the composite conductive layer provided on the inner surface of the constraint shaft serves as a negative electrode circuit and is connected to the negative electrode conductive wire of the external power source to form a closed circuit.

5. The supercritical fluid assisted injection molding apparatus of claim 4, wherein, The composite conductive layer is composed of a zirconium oxide-based dielectric layer and a graphene conductive layer covering the surface of the zirconium oxide-based dielectric layer, and the graphene conductive layer is connected to the negative electrode conductive wire through a copper rod.

6. The supercritical fluid assisted injection molding apparatus of claim 1, wherein, The supercritical fluid assisted injection molding device also comprises a carbon dioxide storage tank, a booster pump and a preheater connected in sequence, and the preheater is in communication with the injector.

7. A supercritical fluid assisted injection molding process characterized by, The method is based on the supercritical fluid assisted injection molding device of claim 1, comprising the following steps: An alternating current is applied to the piezoelectric ceramic ring corresponding to the ceramic sheet to generate low-frequency vibration, polarize the dielectric functional coating on the surface of the micropores of the ceramic sheet, and attract negative ions in the environment to form a negative charge enrichment area; The carbon dioxide fluid in a supercritical state is injected into the main channel, at this time the piezoelectric ceramic ring is switched to high-frequency vibration to excite a standing wave field, and the periodic pressure fluctuations formed at the outlet of the micropores of the ceramic sheet in the main channel break the fluid flowing through the micropores into nano-bubble nuclei, and complete the bubble shaping in the low-pressure area of the pressure fluctuations; At the same time, the high-frequency vibration causes the pressure fluctuations to offset the change in the aperture of the micropores caused by thermal deformation; During the bubble shaping stage, the negative charge enrichment area causes the nano-bubbles to be wrapped by negative charges at the moment of leaving the micropores through electrophoresis, effectively neutralizing the surface potential of the nano-bubbles and inhibiting the instantaneous coalescence tendency of the bubbles caused by energy imbalance, and maintaining a stable monodisperse state of the nano-bubbles from the initial formation. Finally, the nano-bubbles with stable monodisperse state are mixed / diffused with the melt to assist plasticizing forming.

8. The supercritical fluid assisted injection molding method of claim 7, wherein, After plasticizing forming, the piezoelectric ceramic ring is switched to ultra-high frequency vibration, and the local shock wave generated by the collapse of cavitation bubbles is used to flush the inner wall of the micro-hole to strip the possible attached residues.

9. The supercritical fluid assisted injection molding method of claim 8, wherein, The oscillation frequency of the ultra-high frequency vibration is above 150 kHz.

10. The supercritical fluid assisted injection molding process of claim 8, wherein, After the piezoelectric ceramic ring is switched to ultra-high frequency vibration, a reverse pulse voltage is applied to the positive and negative conductive wires, and the cleaning agent is introduced into the micro-hole channel through the electroosmotic flow effect for cleaning.

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