Thermoplastic polymer 3D printing wire rod containing liquid and semi-solid functional core layers and coaxial co-extrusion preparation process of thermoplastic polymer 3D printing wire rod

Abstract

The invention discloses a thermoplastic polymer 3D printing wire containing liquid and semi-solid functional core layers and a coaxial co-extrusion preparation process thereof, the thermoplastic polymer 3D printing wire is of a coaxial core-shell structure, and the thermoplastic polymer 3D printing wire comprises an outer thermoplastic polymer thin-walled tube and an inner liquid and semi-solid functional core layer from outside to inside. The coaxial core-shell structure composed of the outer thermoplastic polymer thin-walled tube and the inner liquid and semi-solid functional core layer is adopted, and the limitation that a traditional FDM consumable can only achieve the single function of structure forming is broken through; a printed piece can be endowed with various special functions such as ultra-soft touch feeling, self-repairing, electric conduction, high water absorption and responsiveness, the use requirements of scenes such as soft robots, medical consumables, electronic devices and self-repairing structural parts are effectively met, meanwhile, the finished wire can be directly matched with an existing FDM printer, equipment does not need to be transformed, and the production cost is reduced. The application threshold of the functional 3D printing technology is greatly reduced, and the application boundary of the FDM technology is widened.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, specifically to a thermoplastic polymer 3D printing filament containing liquid and semi-solid functional core layers and its coaxial co-extrusion preparation process. Background Technology

[0002] Fused Deposition Modeling (FDM) technology has become one of the most widely used additive manufacturing technologies, also known as 3D printing, due to its advantages such as low equipment cost, ease of operation, and flexible molding. Its core relies on thermoplastic polymer consumables to achieve structural molding. Current FDM consumables are mainly single-component thermoplastic solid materials, such as PLA, ABS, TPU, and PETG, and are widely used in industrial model making, everyday product processing, and simple structural component molding. To meet complex functional requirements such as flexible touch, self-healing, conductivity, and chemical reactivity, various technological attempts have emerged in the industry. These include using dedicated direct-write printing equipment (DIW) to directly print liquid or soft materials such as silicone and epoxy resin; developing soft solid consumables such as TPU; using traditional coaxial coating processes to prepare composite filaments; and achieving multi-material composites through multi-material independent extrusion or twin-screw one-step methods.

[0003] However, existing technologies have many insurmountable drawbacks: dedicated direct-write printing equipment is expensive, costing 5 to 10 times more than ordinary FDM printers, and cannot print complex suspended structures, relying on support materials and having extremely poor versatility; existing soft solid consumables such as TPU can only reach a minimum hardness of 85A, far from achieving the ultra-soft touch similar to human skin (0A to 20A), and do not possess the self-healing and responsive functions unique to liquid or gel materials; traditional coaxial coating processes are only suitable for solid core and solid shell structures, and cannot adapt to the composite requirements of outer plastic and inner liquid or gel, easily leading to problems such as leakage, bamboo effect, pipe blockage, poor coaxiality, uneven wall thickness, and collapse after cooling; multi-material independent extrusion equipment has a complex structure and is difficult to control, and the twin-screw one-step method has poor coating performance for high-viscosity liquids or gels, easily generating bubbles and interface delamination, and cannot achieve continuous and stable production. In addition, existing technologies also face core technical bottlenecks: lack of effective thermal isolation design, the high temperature of the outer melt can easily cause the core fluid to solidify, vaporize or degenerate prematurely; pressure matching imbalance, if the core injection pressure is too high, it can easily burst the outer layer, and if it is too low, it will produce voids; wall thickness is difficult to control, if the wall is too thick, it will lose its functional characteristics, and if the wall is too thin, it will be easily crushed and leaked by the extrusion gears during printing.

[0004] Therefore, there is an urgent need to develop a dedicated thermoplastic polymer 3D printing filament containing liquid and semi-solid functional core layers and its corresponding preparation process to solve the technical shortcomings of existing technologies, such as insufficient functional expansion, poor equipment adaptability, unstable production process, and many product quality defects. This would enable integrated printing of rigid support with flexible or functional filling to meet the complex application needs of multiple fields. Summary of the Invention

[0005] The purpose of this invention is to provide a thermoplastic polymer 3D printing filament containing liquid and semi-solid functional core layers and its coaxial co-extrusion preparation process, so as to solve the problems existing in the prior art mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a thermoplastic polymer 3D printing filament containing a liquid and semi-solid functional core layer and its coaxial co-extrusion preparation process, which is a coaxial core-shell structure, including an outer thermoplastic polymer thin-walled tube and an inner liquid and semi-solid functional core layer disposed from the outside to the inside;

[0007] The outer thermoplastic polymer thin-walled tube is made of one or more blends of PLA, ABS, PETG, nylon, TPU, and EVA. The wall thickness of the outer thermoplastic polymer thin-walled tube is 0.3-0.5 mm, the ratio of the wall thickness to the wire radius is 0.15-0.3, and the outer diameter of the wire is 1.75 mm or 2.85 mm.

[0008] The inner liquid and semi-solid functional core layer is selected from one or a mixture of cured resins, gel elastomers, and functional soft rubbers. The viscosity of the inner liquid and semi-solid functional core layer at the injection temperature is 500-50000 cps, and the volume ratio of the core layer to the outer layer is 1:1.5-1:3.

[0009] Preferably, the outer thermoplastic polymer thin-walled tube has a surface roughness Ra≤0.8μm, a roundness error≤0.03mm, an axial tensile strength≥15MPa, and a radial compressive strength≥5MPa.

[0010] Preferably, the inner liquid and semi-solid functional core layer is one or a mixture of two-component epoxy resin, polyurethane prepolymer, silicone liquid rubber, TPR resin slurry, hydrogel, superabsorbent resin slurry, PVA-borax gel, magnetorheological fluid, and shear thickening fluid.

[0011] When the viscosity of the inner liquid and semi-solid functional core layer is too low, 2-5% fumed silica or thixotropic agent is added to improve thixotropy.

[0012] Preferably, the sealing performance of the wire meets the following requirements:

[0013] No leakage was observed for 30 minutes at 25℃ and 1MPa pressure.

[0014] At temperatures of 180-260℃, the core layer does not solidify prematurely or leak when the outer layer melts.

[0015] A coaxial co-extrusion process for preparing any of the wires described in the present invention includes the following steps: raw material pretreatment, outer layer melt plasticizing, core layer precise conveying, coaxial co-extrusion molding, multi-stage synergistic cooling and shaping, traction winding and post-processing.

[0016] The coaxial co-extrusion process employs a coaxial co-extrusion die with a cold core and hot skin insulation design, a dual-path pressure-balanced feeding system, and a multi-stage cooling and shaping unit to achieve continuous and complete encapsulation of the inner liquid and semi-solid functional core layer by the outer thermoplastic polymer thin-walled tube.

[0017] Preferably, in the raw material pretreatment step, the moisture content of the outer layer raw material after drying is ≤0.05%, and the core layer raw material is subjected to vacuum degassing treatment with a vacuum degree ≤-0.09MPa and a degassing time of 30-60min.

[0018] Preferably, the outer layer melting and plasticizing step uses a single-screw extruder with an aspect ratio of 24-40 and a compression ratio of 2.5-3.5, with three-stage temperature control, and the outer layer melt extrusion pressure is 5-30 MPa with a fluctuation range of ±0.1 MPa; in the core layer precise delivery step, the core layer injection pressure is 0.1-0.5 MPa higher than the outer layer melt pressure, the feeding speed is 0.1-5 ml / min, and the flow rate accuracy is ±0.01 ml / min.

[0019] Preferably, the coaxial co-extrusion die includes an outer annular flow channel, a central injection needle tube, a self-centering guide cone, and a heat insulation structure;

[0020] The heat insulation structure is a combination of Teflon coating and air insulation layer or a combination of Teflon coating and circulating cooling medium layer, ensuring that the temperature of the outer wall of the injection needle is 50-150°C lower than the temperature of the outer melt.

[0021] The inner diameter of the central injection needle is 0.5-1.0 mm, and the needle tip extends to the mold head outlet, with a distance of ≤5 mm from the outlet end face;

[0022] The self-centering guide cone has a cone angle of 6°-15°.

[0023] Preferably, in the multi-stage synergistic cooling and shaping step, the wind speed of the first-stage annular air cooling is 1-5 m / s and the temperature is 20-30℃, the water temperature of the second-stage vertical water-cooling is 15-35℃ and the cooling time is 3-5 s, and the wind speed of the third-stage air cooling for water removal is 3-8 m / s.

[0024] The multi-stage synergistic cooling and shaping process ensures that the outer thermoplastic polymer thin-walled tube is completely cured, and the roundness error of the cured outer thermoplastic polymer thin-walled tube is ≤0.03mm.

[0025] Preferably, in the traction and winding step, the traction speed is 0.5-5 m / min, the ratio of traction speed to outer layer extrusion speed is 1.0-1.5, the winding tension is 0.5-2.0 N, and the wire spacing is 1.2 times the wire diameter;

[0026] The post-processing steps include hot melt adhesive sealing at both ends of the wire, with a sealing length of 5-10mm, cutting to 100-500m / roll, and sealing with nitrogen-filled gas. The storage environment is 20-25℃ and humidity ≤60%.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1) This application adopts a coaxial core-shell structure composed of an outer thermoplastic polymer thin-walled tube and an inner liquid and semi-solid functional core layer, which breaks the limitation of traditional FDM consumables that can only achieve the single function of structural forming. By selecting different types of core layer materials, the printed parts can be endowed with a variety of special functions such as ultra-soft touch, self-healing, conductivity, high water absorption, and responsiveness, which effectively meets the usage needs of soft robots, medical consumables, electronic devices, self-healing structural parts and other scenarios. At the same time, the finished filament can be directly adapted to existing FDM printers without any modification to the equipment, which greatly reduces the application threshold of functional 3D printing technology and broadens the application boundaries of FDM technology.

[0029] 2) The preparation process of this application, through the heat insulation design of cold core and hot skin, ensures that the temperature of the outer wall of the injection needle is 50 to 150 degrees Celsius lower than the temperature of the outer melt, avoiding the problem of premature solidification, vaporization, or denaturation of the core material caused by the high temperature of the outer melt. The core layer activity retention rate is over 95%. Through dual-path pressure balance control, the core layer injection pressure is 0.1 to 0.5 MPa higher than the outer melt pressure, effectively solving the problems of leakage and voids. The coating qualification rate is over 98%. It adopts a first-stage annular air cooling and a second-stage vertical drop cooling system. The multi-stage synergistic cooling and shaping design, featuring water-cooled three-stage air-cooled dewatering and combined with micro-negative pressure sizing technology, completely solves the problem of wire flattening after cooling. This ensures that the roundness error of the outer thermoplastic polymer thin-walled tube does not exceed 0.03 mm, and the coaxiality deviation of the wire does not exceed 0.02 mm. By optimizing the wall thickness parameters from 0.3 to 0.5 mm and the core layer viscosity range from 500 to 50000 cps, the problem of the outer layer or core layer being crushed during printing is avoided, effectively improving the product yield.

[0030] 3) The outer thermoplastic polymer thin-walled tube of this application is compatible with a variety of mainstream thermoplastic polymers such as PLA, ABS, PETG, nylon, TPU, and EVA. The inner liquid and semi-solid functional core layers can be made of more than ten kinds of functional materials such as two-component epoxy resin, polyurethane prepolymer, silicone liquid rubber, TPR resin slurry, hydrogel, superabsorbent resin slurry, PVA-borax gel, magnetorheological fluid, and shear thickening fluid. When the viscosity of the core layer material is too low, the viscosity can be adjusted by adding 2 to 5% fumed silica or thixotropic agent to meet the personalized needs of different application scenarios. The flexible combination of the outer and core layer materials enables this application to adapt to the usage requirements of multiple fields and multiple working conditions, and has strong practicality and promotional value.

[0031] 4) The manufacturing process of this application can achieve continuous mass production with a production speed of 0.5 to 5 meters per minute. The daily production capacity of a single production line is more than 1,000 rolls, with each roll being 300 meters long. This is more than 5 times more efficient than the traditional intermittent process. The process is equipped with an online detection and control unit, which uses a laser biaxial diameter gauge, a coaxiality detector, a pressure sensor, and a PLC controller to adjust parameters in real time. This ensures that the outer diameter fluctuation of the wire does not exceed ±0.02 mm and the coaxiality deviation does not exceed 0.02 mm. The product quality is stable and uniform between batches. In addition, the axial tensile strength of the finished wire is above 15 MPa and the radial compressive strength is above 5 MPa. It can maintain a leak-free state for 30 minutes at 25 degrees Celsius and 1 MPa pressure. When the outer layer melts at an FDM printing temperature of 180 to 260 degrees Celsius, the core layer does not solidify prematurely or leak. The structural stability and reliability are extremely high. Attached Figure Description

[0032] Figure 1 This is a schematic cross-sectional view of the coaxial co-extrusion die head of this application;

[0033] Figure 2 This is a process flow diagram for this application. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] In the description of the invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] In the description of the invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] In the description of the invention, it should be noted that the execution order of the steps is not limited by the sequence number. The possible changes in the order of some steps, the synchronous execution of steps, and the split execution of steps are all within the scope of protection of this application.

[0038] Please see Figure 1-2 The present invention provides a technical solution: a thermoplastic polymer 3D printing filament containing liquid and semi-solid functional core layers and its coaxial co-extrusion preparation process, which is a coaxial core-shell structure, including an outer thermoplastic polymer thin-walled tube and an inner liquid and semi-solid functional core layer arranged from the outside to the inside;

[0039] The outer thermoplastic polymer thin-walled tube is made of one or more blends of PLA, ABS, PETG, nylon, TPU, and EVA. The wall thickness of the outer thermoplastic polymer thin-walled tube is 0.3-0.5 mm, the ratio of the wall thickness of the outer thermoplastic polymer thin-walled tube to the wire radius is 0.15-0.3, and the outer diameter of the outer thermoplastic polymer thin-walled tube wire is 1.75 mm or 2.85 mm.

[0040] The inner liquid and semi-solid functional core layers are selected from one or a mixture of cured resins, gel elastomers, and functional soft rubbers. The viscosity of the inner liquid and semi-solid functional core layers at the injection temperature is 500-50000 cps, and the volume ratio of the core layer to the outer layer is 1:1.5-1:3.

[0041] Specifically, the filament of this application has a coaxial core-shell structure with an outer thermoplastic polymer thin-walled tube and an inner liquid and semi-solid functional core layer arranged from the outside in. First, this structure breaks through the functional limitations of traditional FDM consumables made of a single thermoplastic solid material, achieving an integrated design of "rigid support and flexible / functional filling". The outer thermoplastic polymer thin-walled tube provides reliable structural support, ensuring that the filament can be adapted to the existing filament feeding mechanism of FDM printers without equipment modification. The inner liquid and semi-solid functional core layer endows the printed parts with a flexible touch, self-healing, conductivity, high water absorption and other extended functions, meeting the complex needs of multiple fields such as soft robots, medical consumables, and electronic devices. Second, the outer layer material is compatible with a variety of mainstream thermoplastic polymers such as PLA, ABS, and PETG, while the inner core material covers a variety of types such as curable resins, gel elastomers and functional soft rubbers, greatly expanding the flexibility of material combinations. It can be flexibly matched according to different application scenarios, making it highly practical. Furthermore, the wall thickness is set at 0.3-0.5mm, and the ratio of wall thickness to wire radius is controlled at 0.15-0.3. This avoids the loss of core layer functional characteristics due to excessive wall thickness, and also prevents the problem of leakage caused by the extrusion gears during printing due to excessive wall thickness. The core layer viscosity is controlled at 500-50000cps, and with a core layer to outer layer volume ratio of 1:1.5-1:3, the functional performance of the core layer and the structural stability of the wire are balanced, effectively avoiding traditional defects such as the "bamboo effect" and ensuring that the wire maintains its structural integrity during storage, transportation and printing.

[0042] The outer thermoplastic polymer thin-walled tube has a surface roughness Ra ≤ 0.8 μm, a roundness error ≤ 0.03 mm, an axial tensile strength ≥ 15 MPa, and a radial compressive strength ≥ 5 MPa. Specifically, strict control of surface roughness and roundness error ensures smooth contact between the filament and the FDM printer's filament feeding mechanism, reducing frictional resistance during filament feeding and avoiding problems such as filament feeding jamming and unevenness caused by surface roughness or poor roundness, thus ensuring the continuity and stability of the printing process. The design with an axial tensile strength ≥ 15 MPa effectively resists the traction force of the filament feeding mechanism and the stress during printing, preventing filament breakage during filament feeding or printing and reducing the printing failure rate; the radial compressive strength ≥ 5 MPa ensures that the filament can withstand the pressure of the extrusion gears during filament feeding without collapsing or deforming, thereby preventing leakage of the core layer due to pressure damage to the outer layer. Therefore, this application effectively solves the problems of poor printing stability and easy leakage of core layer caused by poor surface quality and insufficient structural strength of traditional composite wires, significantly improves the forming quality and consistency of printed parts, and provides a reliable guarantee for the printing of complex structural parts in the future.

[0043] The inner liquid and semi-solid functional core layer is one or a mixture of two-component epoxy resin, polyurethane prepolymer, silicone liquid rubber, TPR resin slurry, hydrogel, superabsorbent resin slurry, PVA-borax gel, magnetorheological fluid, and shear thickening fluid.

[0044] When the viscosity of the inner liquid and semi-solid functional core layers is too low, add 2-5% fumed silica or thixotropic agent to improve thixotropy.

[0045] Specifically, firstly, the core materials, including two-component epoxy resin, polyurethane prepolymer, silicone liquid rubber, and hydrogel, cover various types such as cured, gel-type, and functional soft rubber, meeting the functional requirements of different application scenarios. For example, silicone liquid rubber provides an ultra-soft touch, hydrogel has high water absorption, and magnetorheological fluid enables responsive functions, breaking through the limitation of traditional FDM consumables that can only achieve structural molding, and endowing printed parts with rich special functions. Secondly, addressing the traditional shortcomings of excessively low core layer viscosity, such as leakage and "bamboo effect," the proposed viscosity adjustment scheme can precisely control the thixotropy of the core layer, stabilizing the core layer viscosity within a reasonable range of 500-50000 cps. This ensures that the core layer can be uniformly filled into the outer thin-walled tube during preparation, without voids or interface delamination, while maintaining a stable state during printing, preventing printing defects caused by improper viscosity. In addition, the combination of multiple core material options and viscosity adjustment technology enables the wire to adapt to more complex working conditions, further expanding the application boundaries of the wire and solving the technical bottlenecks of traditional core materials having single functions and difficult viscosity control.

[0046] The sealing performance of the wire meets the following requirements:

[0047] No leakage was observed for 30 minutes at 25℃ and 1MPa pressure.

[0048] At temperatures of 180-260℃, the core layer does not solidify prematurely or leak when the outer layer melts.

[0049] Specifically, this application addresses the main drawbacks of traditional coaxial composite filaments, namely poor sealing performance and easy core layer failure at high temperatures. During storage and transportation, strict room-temperature sealing performance ensures no leakage of the core layer, preventing filament scrap due to leakage, reducing losses during storage and transportation, and extending the shelf life of the filament. The leak-free characteristic also ensures a clean filament appearance, preventing core layer contamination from affecting filament feeding smoothness. During printing, within the FDM printing temperature range of 180-260℃, the requirement for the core layer not to prematurely solidify or leak ensures that the core layer retains its original functional characteristics after the outer layer melts during printing, smoothly filling the printed structure. This avoids tube blockage problems caused by premature core layer solidification and prevents printed part defects and equipment contamination caused by core layer leakage. This sealing performance allows the filament to maintain structural integrity and functional stability throughout its entire lifecycle (storage, transportation, printing), significantly improving product reliability and user experience, and solving the technical problems of poor sealing and easy high-temperature failure in traditional "outer plastic, inner liquid / gel" structure filaments.

[0050] According to another aspect of this application, a coaxial co-extrusion process for preparing the above-mentioned wire is also provided, including raw material pretreatment, outer layer melt plasticizing, core layer precise conveying, coaxial co-extrusion molding, multi-stage synergistic cooling and shaping, traction winding and post-processing steps.

[0051] The coaxial co-extrusion process employs a coaxial co-extrusion die with a cold core and hot skin insulation design, a dual-path pressure-balanced feeding system, and a multi-stage cooling and shaping unit to achieve continuous and complete encapsulation of the inner liquid and semi-solid functional core layers by the outer thermoplastic polymer thin-walled tube.

[0052] Specifically, firstly, the complete process steps form a closed-loop production flow, ensuring effective control at every stage from raw materials to finished products. Secondly, the coaxial co-extrusion die with cold core and hot skin insulation design solves the problem of premature solidification, vaporization, or denaturation of the core layer caused by the lack of thermal insulation in traditional processes, ensuring the activity and functional integrity of the core layer material. The dual-path pressure-balanced feeding system, through precise pressure control, avoids the problem of excessive core layer injection pressure causing the outer layer to burst or insufficient pressure causing gaps, achieving continuous and complete coverage of the core layer by the outer layer. The multi-stage cooling and shaping unit effectively solves the defects of flattening and poor roundness of the wire after cooling. The combination of these core equipment and process steps enables the process to be adapted to a variety of outer layer polymers and core layer functional materials, achieving continuous production with a production speed of 0.5-5 meters per minute and a daily capacity of over 1,000 rolls per line. This is more than 5 times more efficient than the traditional intermittent process, while ensuring that the coaxiality deviation of the finished wire is ≤0.02mm and the wire diameter fluctuation is ≤±0.02mm. This significantly improves product quality and production efficiency, and solves the problems of instability, poor adaptability, and low efficiency of traditional preparation processes.

[0053] In the raw material pretreatment step, the moisture content of the outer layer raw material after drying is ≤0.05%, and the core layer raw material undergoes vacuum degassing treatment with a vacuum degree ≤-0.09MPa and a degassing time of 30-60 minutes. Specifically, for the outer layer raw material, the requirement of a moisture content ≤0.05% avoids the generation of bubbles during the melting and plasticizing process, ensuring that the outer layer thermoplastic polymer can be fully melted to form a uniform and dense thin-walled tube. This prevents problems such as insufficient outer layer strength and uneven wall thickness caused by bubbles, ensuring the structural stability and sealing performance of the outer layer. For the core layer raw material, vacuum degassing treatment can completely remove bubbles from the core layer material, preventing bubbles from causing uneven core layer filling and interface peeling during coaxial co-extrusion, or core layer leakage and printing failure due to bubble rupture during printing. The combination of a degassing time of 30-60 minutes and a vacuum degree of ≤-0.09MPa ensures the degassing effect while avoiding core layer material deformation caused by excessive degassing. The optimization of the raw material pretreatment steps reduces product defects from the source, improves the stability of subsequent steps such as melt plasticizing and coaxial co-extrusion, thereby increasing the overall yield and solving problems such as bubbles, interface peeling, and sealing failure caused by insufficient raw material pretreatment in traditional processes.

[0054] The outer layer melting and plasticizing step utilizes a single-screw extruder with an L / D ratio of 24-40 and a compression ratio of 2.5-3.5, featuring three-stage temperature control. The outer layer melt extrusion pressure is 5-30 MPa, with a fluctuation range of ±0.1 MPa. In the core layer precision delivery step, the core layer injection pressure is 0.1-0.5 MPa higher than the outer layer melt pressure, with a feeding rate of 0.1-5 ml / min and a flow rate accuracy of ±0.01 ml / min. Specifically, the single-screw extruder design with an L / D ratio of 24-40 and a compression ratio of 2.5-3.5, combined with the three-stage temperature control mode, ensures that the outer layer thermoplastic polymer raw material can be fully melted and uniformly plasticized, avoiding problems such as uneven outer layer wall thickness and loose structure caused by insufficient melting. The outer layer melt extrusion pressure is controlled at 5-30 MPa with a fluctuation range of ±0.1 MPa, ensuring the flow stability of the outer layer molten billet within the flow channel, providing a good foundation for the subsequent uniform coating of the core layer. The setting of a core layer injection pressure 0.1-0.5 MPa higher than the outer layer melt pressure achieves dual-path pressure balance. This ensures that the core layer fully fills the internal cavity of the outer thin-walled tube, preventing voids, while also preventing the outer layer from bursting due to excessive pressure. Precise control of the feeding rate (0.1-5 ml / min) and flow rate accuracy (±0.01 ml / min) ensures a stable core-to-outer layer volume ratio of 1:1.5-1:3, avoiding functional instability or structural imbalance caused by uneven core layer feeding. This synergistic control of parameters ensures a precise match between the outer melt and core filling, guaranteeing wire coaxiality and structural consistency. It solves problems such as leakage, voids, and uncontrolled volume ratios caused by pressure imbalance and insufficient feeding accuracy in traditional processes, thus improving product quality stability.

[0055] The coaxial co-extrusion die head includes an outer annular flow channel, a central injection needle tube, a self-centering guide cone, and a heat insulation structure;

[0056] The heat insulation structure is a combination of Teflon coating and air insulation layer or a combination of Teflon coating and circulating cooling medium layer, ensuring that the temperature of the outer wall of the injection needle is 50-150℃ lower than the temperature of the outer melt.

[0057] The inner diameter of the central injection needle is 0.5-1.0 mm, and the needle tip extends to the mold head outlet, with a distance of ≤5 mm from the outlet end face;

[0058] The self-centering guide cone has a cone angle of 6°-15°.

[0059] Specifically, the outer ring flow channel design ensures uniform pressure of the outer melt layer, preventing melt stagnation and providing a flow channel foundation for uniform outer layer coating. The design of the central injection needle tube with an inner diameter of 0.5-1.0mm and the needle tip extending to the die head outlet ensures that the core layer material can be accurately injected into the center of the outer melt billet, preventing core layer offset. The self-centering guide cone with a cone angle of 6°-15° guides the outer melt layer to uniformly wrap around the central injection needle tube, directly ensuring the coaxiality of the wire, making the coaxiality deviation ≤0.02mm, solving the coaxiality problem caused by insufficient guidance in traditional dies. The heat insulation structure adopts a combination of Teflon coating and air heat insulation layer or circulating cooling medium layer to ensure that the temperature of the outer wall of the injection needle tube is 50-150℃ lower than the temperature of the outer melt layer, effectively preventing the high temperature of the outer melt layer from being transferred to the core layer, causing core layer solidification, vaporization, or denaturation, ensuring the activity and functional integrity of the core layer material, and solving the core bottleneck of traditional dies lacking effective heat insulation design. The optimization of parameters and the synergy of the structure of each component of the die head ensured the precise and uniform coating of the outer layer onto the core layer, avoiding surface defects such as burrs and uneven wall thickness, and laying a key foundation for the subsequent cooling, traction and printing performance of the wire.

[0060] In the multi-stage synergistic cooling process, the wind speed of the first-stage annular air cooling is 1-5 m / s and the temperature is 20-30℃; the water temperature of the second-stage vertical water-falling cooling is 15-35℃ and the cooling time is 3-5 s; and the wind speed of the third-stage air cooling dewatering is 3-8 m / s.

[0061] The outer thermoplastic polymer thin-walled tube is completely cured through a multi-stage synergistic cooling and shaping process, and the roundness error of the cured outer thermoplastic polymer thin-walled tube is ≤0.03mm.

[0062] Specifically, the first-stage annular air cooling system has a wind speed of 1-5 m / s and a temperature of 20-30℃, which can quickly form a solidified shell on the outer surface of the wire when it is first extruded, with a thickness of ≥0.1mm. This effectively prevents the outer layer from bulging due to core pressure and provides structural support for subsequent cooling and shaping. The second-stage vertical water cooling system has a water temperature of 15-35℃ and a cooling time of 3-5 seconds. Combined with micro-negative pressure sizing technology, it ensures that the outer thermoplastic polymer is fully crystallized or vitrified and hardened, with a crystallinity of ≥60%. This locks in the core shape and ensures that the outer layer roundness error is ≤0.03mm, solving the problems of insufficient cooling and flattening caused by traditional single-stage cooling. The third-stage air cooling system has a dewatering wind speed of 3-8 m / s, which can completely remove moisture from the surface of the wire, avoid increased wire feeding resistance caused by secondary moisture absorption, and ensure smooth wire feeding during printing. The multi-stage synergistic cooling and shaping design enables step-by-step processing from initial curing to complete curing and then to surface drying. This ensures the structural strength and roundness accuracy of the outer layer, while also guaranteeing the cleanliness and dryness of the filament surface. It solves the structural defects and filament feeding problems caused by improper cooling speed and incomplete drying in traditional cooling processes, thereby improving the filament's printability and structural stability.

[0063] In the traction and winding step, the traction speed is 0.5-5m / min, the ratio of traction speed to outer layer extrusion speed is 1.0-1.5, the winding tension is 0.5-2.0N, and the wire spacing is 1.2 times the wire diameter;

[0064] The post-processing steps include hot melt adhesive sealing at both ends of the wire, with a sealing length of 5-10mm, cutting at 100-500m / roll, and sealing with nitrogen filling. The storage environment is 20-25℃ and humidity ≤60%.

[0065] Specifically, the traction speed is set at 0.5-5 meters per minute, with a ratio of 1.0-1.5 to the outer extrusion speed. This moderately stretches the outer tube wall, further improving the roundness of the wire while ensuring wire diameter fluctuation ≤ ±0.02mm. The winding tension is controlled at 0.5-2.0N to prevent wire deformation due to excessive tension or loose winding due to insufficient tension. Combined with a wire spacing of 1.2 times the wire diameter, this ensures neat winding, facilitating subsequent storage and use. In the post-processing steps, the hot melt adhesive seals both ends of the wire for 5-10mm, effectively preventing core layer leakage. Cutting specifications of 100-500m / roll adapt to different user needs. Nitrogen-filled sealed packaging and a storage environment of 20-25℃ and ≤60% humidity prevent moisture absorption or core layer deterioration, extending the wire's shelf life. Precise control of traction and winding parameters ensures the uniformity of wire dimensions, while optimization of post-processing steps ensures the stability of wire during storage and transportation. This solves problems such as wire diameter deviation caused by mismatched traction speeds, deformation caused by improper winding, and leakage caused by insufficient sealing in post-processing, which are common in traditional processes. This comprehensively improves the practicality of the product and the user experience.

[0066] Example 1: 3D printing filament and preparation of a combination of PLA outer layer and silicone liquid rubber core layer

[0067] The 3D printing filament prepared in this embodiment, which contains a PLA outer layer and a silicone liquid rubber core layer, has an outer diameter of 1.75 mm and adopts a coaxial core-shell structure. It consists of a thin-walled tube made of PLA thermoplastic polymer and a liquid functional core layer made of silicone liquid rubber, arranged from the outside to the inside.

[0068] 1. Raw material pretreatment

[0069] PLA particles with a particle size of 0.5-1.0 mm were selected as the raw material for the outer layer thermoplastic polymer thin-walled tube. They were placed in a hopper drying device and dried at 60°C for 3 hours. After drying, the moisture content of the raw material was controlled at 0.03%. Silicone liquid rubber with a viscosity of 5000 cps at 25°C was selected as the raw material for the inner layer liquid functional core layer. It was added to the core layer raw material storage tank, and the vacuum degassing device was turned on. Degassing was performed at a pressure of -0.09 MPa for 30 minutes. In this embodiment, the viscosity of the core material met the requirements, and no thixotropic agent was added.

[0070] 2. Device parameter settings

[0071] The outer extrusion unit uses a single-screw extruder with a length-to-diameter ratio of 24-40 and a compression ratio of 2.5-3.5. The three-stage temperature control parameters are set as follows: feed stage 120℃, compression stage 180℃, and melt stage 210℃. The screw speed is 30 r / min, and the pressure in the pressure stabilizing tank at the extruder outlet is controlled at 10 MPa. The metering pump in the core layer feeding unit has a feeding rate set at 0.3 ml / min, a core layer injection pressure controlled at 10.3 MPa, and a precision delivery tube insulation temperature of 25℃. The inner diameter of the central injection needle in the coaxial co-extrusion die is 0 mm. The wire diameter is 0.8mm, and the heat insulation structure uses a combination of Teflon coating and 3mm air insulation layer. The inner diameter of the sizing die hole is consistent with the wire specification, which is 1.75mm. In the multi-stage cooling and shaping unit, the first-stage annular air cooler has a wind speed of 3m / s and a temperature of 25℃, the second-stage cooling water tank has a water temperature of 20℃ and a length of 4m, and the third-stage air cooler dewatering has a wind speed of 5m / s. The traction and winding unit has a traction speed of 1.5m / min, a traction speed to extrusion speed ratio of 1.2, a winding tension of 1.0N, and an automatic wire guide spacing of 2.1mm.

[0072] 3. Preparation process

[0073] The outer single-screw extruder is started, and the temperature is raised according to the set three-stage temperature control parameters. After reaching the target temperature, it is held for 30 minutes to ensure that the PLA raw material is completely melted and plasticized. Then, the extruder screw is started, and the molten PLA melt is stabilized by the pressure stabilizing tank and enters the outer annular flow channel of the coaxial co-extrusion die. Under the guidance of the self-centering guide cone, a uniform tubular molten billet is formed. Simultaneously, the core layer feeding unit is started. After degassing, the silicone liquid rubber is precisely injected into the central cavity of the tubular molten billet through the precision delivery pipe and the central injection needle. The composite structure of "outer plastic and inner liquid" is formed through the sizing die hole at the die head outlet and then enters the first-stage annular air cooling device for preliminary cooling, the second-stage vertical water drop cooling tank for complete solidification, and the third-stage air-cooled dehydration device to remove surface moisture. Finally, it is wound by a constant tension winding machine. After winding, the two ends of the wire are sealed with hot melt adhesive, cut at 300m / roll, and sealed with nitrogen filling.

[0074] 4. Finished product performance testing

[0075] Testing revealed that the finished filament exhibits a complete coaxial core-shell structure. The outer PLA thin-walled tube has a wall thickness of 0.4 mm, with the wall thickness-to-filament radius ratio falling within the set range of 0.15-0.3. The filament's outer diameter is 1.75 ± 0.01 mm, coaxiality deviation is 0.015 mm, and roundness error is 0.02 mm. The sealing performance meets the set requirements, maintaining a leak-free state for 30 minutes at 25℃ and 1 MPa pressure. Axial tensile strength is ≥15 MPa, and radial compressive strength is ≥5 MPa, effectively resisting traction and extrusion pressure during printing. This filament is directly compatible with existing FDM printers, ensuring smooth filament feeding, a smooth printed surface, no core leakage, and an ultra-soft 10A feel, fully meeting the printing application requirements for flexible structural components.

[0076] Example 2: 3D printing filament composed of a PETG outer layer and a two-component epoxy resin core layer and its preparation

[0077] The 3D printing filament prepared in this embodiment, which contains a PETG outer layer and a two-component epoxy resin core layer, has an outer diameter of 2.85 mm and adopts a coaxial core-shell structure. It consists of a thermoplastic polymer thin-walled tube made of PETG and a liquid functional core layer made of two-component epoxy resin, arranged from the outside to the inside.

[0078] 1. Raw material pretreatment

[0079] PETG granules with a particle size of 1.0-2.0 mm were selected as the raw material for the outer layer thermoplastic polymer thin-walled tube. They were placed in a hopper drying device and dried at 70℃ for 2 hours. After drying, the moisture content of the raw material was 0.04%. Two-component epoxy resin was selected as the raw material for the inner liquid functional core layer. It was premixed with agent A and agent B in a 1:1 ratio. The mixing temperature was controlled at 20-30℃, the stirring speed was 500-800 r / min, and the mixing time was 5-10 min to ensure that the raw material did not undergo a curing reaction. The viscosity at 25℃ after mixing was 10000 cps. Then, the mixed two-component epoxy resin was added to the core layer raw material storage tank and degassed at -0.09 MPa pressure for 40 min. To avoid premature curing, the injection operation was completed within 30 min after mixing.

[0080] 2. Device parameter settings

[0081] The outer extrusion unit features a single-screw extruder with a length-to-diameter ratio of 24-40 and a compression ratio of 2.5-3.5. The three-stage temperature control parameters are set as follows: feed stage 140℃, compression stage 200℃, and melt stage 220℃. The screw speed is 40 r / min, and the pressure in the pressure stabilizing tank is controlled at 15 MPa. The core layer feeding unit has a metering pump feeding rate of 0.8 ml / min, a core layer injection pressure of 15.5 MPa, and a precision delivery pipe insulation temperature of 30℃. The inner diameter of the central injection needle in the coaxial co-extrusion die is 1.0 mm. The heat insulation structure is a combination of Teflon coating and 4mm air insulation layer, and the inner diameter of the sizing die is 2.85mm. In the multi-stage cooling and shaping unit, the first-stage annular air cooler has a wind speed of 4m / s and a temperature of 25℃, the second-stage cooling water tank has a water temperature of 25℃ and a length of 5m, and the third-stage air cooler dewatering has a wind speed of 6m / s. The traction and winding unit has a traction speed of 2.0m / min, a traction speed to extrusion speed ratio of 1.3, a winding tension of 1.5N, and an automatic wire guide spacing of 3.4mm.

[0082] 3. Preparation process

[0083] The PETG granules are prepared according to a complete process: raw material pretreatment, outer layer melt plasticization, core layer precise conveying, coaxial co-extrusion molding, multi-stage synergistic cooling and shaping, traction winding and post-treatment. After being processed by a hopper drying device, the PETG granules enter a single-screw extruder to complete melt plasticization and form a uniform tubular molten blank. The two-component epoxy resin is degassed and precisely metered before being injected into the central cavity of the tubular molten blank. After being formed by a die, the composite wire passes through a three-stage cooling and shaping device to complete curing and surface drying. Finally, it is wound up by a traction winding unit. After winding, it is sealed with hot melt adhesive, cut, and sealed with nitrogen gas.

[0084] 4. Finished product performance testing

[0085] The finished filament has a complete structure. The outer PETG thin-walled tube has a wall thickness of 0.5mm, and the ratio of wall thickness to filament radius meets the design requirements. The outer diameter of the filament is 2.85±0.02mm, the coaxiality deviation is 0.018mm, and the roundness error is 0.025mm. The sealing performance meets the standards, maintaining no leakage for 30 minutes at 25℃ and 1MPa pressure. The axial tensile strength is ≥15MPa, the radial compressive strength is ≥5MPa, and the structural stability is good. After printing, the printed part is heated to 80℃ to cure the core layer. The tensile strength of the cured printed part is ≥30MPa, which has the characteristics of being hard on the outside and tough on the inside. There is no core layer leakage, making it suitable for component printing scenarios with combined requirements for structural strength and toughness.

[0086] Example 3: 3D Printing Filament Combining TPU Outer Layer and Hydrogel Core Layer and its Preparation

[0087] The 3D printing filament prepared in this embodiment, which contains a TPU outer layer and a hydrogel core layer, has an outer diameter of 1.75 mm and adopts a coaxial core-shell structure. It consists of a thermoplastic polymer thin-walled tube made of TPU and a semi-solid functional core layer made of hydrogel, arranged from the outside to the inside.

[0088] 1. Raw material pretreatment

[0089] TPU particles with a Shore hardness of 95A and a particle size of 0.8-1.5mm were selected as the raw material for the outer layer thermoplastic polymer thin-walled tube. They were placed in a hopper drying device and dried at 70℃ for 2 hours. After drying, the moisture content of the raw material was 0.03%. Hydrogel with a viscosity of 20000cps at 25℃ was selected as the raw material for the inner semi-solid functional core layer. After being added to the core layer raw material storage tank, it was degassed at -0.09MPa pressure for 60 minutes. In order to improve the thixotropy of the core material and avoid the "bamboo effect", 3% fumed silica was added to the hydrogel.

[0090] 2. Device parameter settings

[0091] The single-screw extruder of the outer extrusion unit has a length-to-diameter ratio of 24-40 and a compression ratio of 2.5-3.5. The three-stage temperature control parameters are set as follows: feed stage 140℃, compression stage 180℃, and melt stage 200℃. The screw speed is 25 r / min, and the pressure in the pressure stabilizing tank is controlled at 8 MPa. The metering pump of the core layer feeding unit has a feed rate of 0.2 ml / min, a core layer injection pressure of 8.2 MPa, and a precision delivery pipe insulation temperature of 20℃. The inner diameter of the central injection needle in the coaxial co-extrusion die is 0.7 mm. The heat insulation structure is a combination of Teflon coating and 2mm air insulation layer, and the inner diameter of the sizing die is 1.75mm. In the multi-stage cooling and shaping unit, the first-stage annular air cooler has a wind speed of 2m / s and a temperature of 20℃, the second-stage cooling water tank has a water temperature of 15℃ and a length of 3m, and the third-stage air cooler dewatering unit has a wind speed of 4m / s. The traction and winding unit has a traction speed of 1.2m / min, a traction speed to extrusion speed ratio of 1.1, a winding tension of 0.8N, and an automatic wire guide spacing of 2.1mm.

[0092] 3. Preparation process

[0093] Following a complete manufacturing process, TPU granules are dried and melt-plasticized to form uniform tubular ingots; hydrogels are degassed and treated with thixotropic agents, then injected into the center of the tubular ingots through a precision conveying system; composite wires are formed by a die head and then undergo a first-stage annular air-cooling for initial curing, a second-stage vertical water-cooling for complete curing, and a third-stage air-cooling for dehydration and drying. Finally, the wires are wound up by a traction winding unit and then sealed, cut, and packaged as required.

[0094] 4. Finished product performance testing

[0095] The finished filament has a complete structure, with an outer TPU thin-walled tube having a wall thickness of 0.35mm. The ratio of wall thickness to filament radius conforms to the set range of 0.15-0.3. The outer diameter of the filament is 1.75±0.01mm, the coaxiality deviation is 0.012mm, and the roundness error is 0.02mm. It has good sealing performance, maintaining no leakage for 30 minutes at 25℃ and 1MPa pressure. The axial tensile strength is ≥15MPa, and the radial compressive strength is ≥5MPa. The printed parts have high water absorption and excellent flexibility, with no leakage in the core hydrogel layer. The tensile elongation at break is ≥200%, making it suitable for printing scenarios such as medical consumables where water absorption and flexibility are strictly required.

[0096] Comparative Example 1

[0097] To verify the superiority of the process of this invention, the 3D printing filament containing a PLA outer layer and a silicone liquid rubber core layer prepared in Example 1 was used as the test object. The specifications of the test filament are an outer diameter of 1.75 mm. The coaxial co-extrusion preparation process of this invention was comprehensively compared with the traditional coaxial coating process (no heat insulation design, no pressure balance control, single-stage cooling). The test results are shown in the table below:

[0098] Comparison Projects The process of this invention Traditional coaxial coating process coaxiality deviation ≤0.02mm ≥0.05mm Wire diameter fluctuation ±0.02mm ±0.05mm Leakage rate ＜1% ≥15% Pipe blockage frequency 0 times / 100h ≥5 times / 100h Finished Product Rate ≥97% ≤80% Production speed 0.5-5 m / min ≤0.3m / min

[0099] Comparative analysis: Traditional coaxial coating process lacks effective thermal isolation design, allowing the high temperature of the outer melt to be directly transferred to the core layer. This causes the core layer's silicone liquid rubber to solidify prematurely, leading to frequent pipe blockages, with a blockage frequency exceeding 5 times per 100 hours. Furthermore, the lack of a pressure balance control mechanism means the core layer injection pressure cannot be precisely matched with the outer melt pressure, resulting in a leakage rate exceeding 15% and a yield rate below 80%. The single-stage cooling method cannot ensure sufficient wire curing, resulting in a coaxiality deviation ≥0.05mm and a wire diameter fluctuation of ±0.05mm, leading to extremely poor product dimensional accuracy and limited production speed to ≤0.3m / min. This invention, through its "cold core, hot skin" insulation design, ensures that the outer wall temperature of the injection needle is 50-150°C lower than the outer melt temperature, effectively preventing premature curing or deformation of the core layer and achieving a plugging frequency of 0 times / 100h. Dual-path pressure balance control ensures that the core layer injection pressure is 0.1-0.5 MPa higher than the outer melt pressure, strictly controlling the leakage rate to within 1%. Multi-stage coordinated cooling and shaping, combined with online detection and control units, precisely control the wire curing process, ensuring coaxiality deviation ≤0.02mm and wire diameter fluctuation ±0.02mm, increasing the yield to over 97% and significantly improving production speed to 0.5-5 m / min. This comprehensively solves the core technical defects of traditional processes, achieving a qualitative improvement in both product quality and production efficiency.

[0100] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A thermoplastic polymer 3D printing filament containing liquid and semi-solid functional core layers, characterized in that, It has a coaxial core-shell structure, consisting of an outer thermoplastic polymer thin-walled tube and an inner liquid and semi-solid functional core layer arranged from the outside to the inside; The outer thermoplastic polymer thin-walled tube is made of one or more blends of PLA, ABS, PETG, nylon, TPU, and EVA. The wall thickness of the outer thermoplastic polymer thin-walled tube is 0.3-0.5 mm, the ratio of the wall thickness to the wire radius is 0.15-0.3, and the outer diameter of the wire is 1.75 mm or 2.85 mm. The inner liquid and semi-solid functional core layer is selected from one or a mixture of cured resins, gel elastomers, and functional soft rubbers. The viscosity of the inner liquid and semi-solid functional core layer at the injection temperature is 500-50000 cps, and the volume ratio of the core layer to the outer layer is 1:1.5-1:

3.

2. The thermoplastic polymer 3D printing filament containing liquid and semi-solid functional core layers according to claim 1, characterized in that, The outer thermoplastic polymer thin-walled tube has a surface roughness Ra≤0.8μm, a roundness error≤0.03mm, an axial tensile strength≥15MPa, and a radial compressive strength≥5MPa.

3. The thermoplastic polymer 3D printing filament containing liquid and semi-solid functional core layers according to claim 1, characterized in that, The inner liquid and semi-solid functional core layer is one or a mixture of two-component epoxy resin, polyurethane prepolymer, silicone liquid rubber, TPR resin slurry, hydrogel, superabsorbent resin slurry, PVA-borax gel, magnetorheological fluid, and shear thickening fluid. When the viscosity of the inner liquid and semi-solid functional core layer is too low, 2-5% fumed silica or thixotropic agent is added to improve thixotropy.

4. The thermoplastic polymer 3D printing filament containing liquid and semi-solid functional core layers according to claim 1, characterized in that, The sealing performance of the wire meets the following requirements: No leakage was observed for 30 minutes at 25℃ and 1MPa pressure. At temperatures of 180-260℃, the core layer does not solidify prematurely or leak when the outer layer melts.

5. A coaxial co-extrusion process for preparing the wire according to any one of claims 1 to 4, characterized in that, This includes raw material pretreatment, outer layer melting and plasticizing, core layer precise delivery, coaxial co-extrusion molding, multi-stage synergistic cooling and shaping, traction winding and post-processing steps; The coaxial co-extrusion process employs a coaxial co-extrusion die with a cold core and hot skin insulation design, a dual-path pressure-balanced feeding system, and a multi-stage cooling and shaping unit to achieve continuous and complete encapsulation of the inner liquid and semi-solid functional core layer by the outer thermoplastic polymer thin-walled tube.

6. The coaxial co-extrusion preparation process according to claim 5, characterized in that, In the raw material pretreatment step, the moisture content of the outer layer raw material after drying is ≤0.05%, and the core layer raw material is subjected to vacuum degassing treatment with a vacuum degree ≤-0.09MPa and a degassing time of 30-60min.

7. The coaxial co-extrusion preparation process according to claim 5, characterized in that, The outer layer melting and plasticizing step uses a single-screw extruder with an aspect ratio of 24-40 and a compression ratio of 2.5-3.5, with three-stage temperature control. The outer layer melt extrusion pressure is 5-30 MPa, with a fluctuation range of ±0.1 MPa. In the core layer precision conveying step, the core layer injection pressure is 0.1-0.5 MPa higher than the outer layer melt pressure, the feeding speed is 0.1-5 ml / min, and the flow rate accuracy is ±0.01 ml / min.

8. The coaxial co-extrusion preparation process according to claim 5, characterized in that, The coaxial co-extrusion die head includes an outer annular flow channel, a central injection needle tube, a self-centering guide cone, and a heat insulation structure; The heat insulation structure is a combination of Teflon coating and air insulation layer or a combination of Teflon coating and circulating cooling medium layer. The inner diameter of the central injection needle is 0.5-1.0 mm, and the needle tip extends to the mold head outlet, with a distance of ≤5 mm from the outlet end face; The self-centering guide cone has a cone angle of 6°-15°.

9. The coaxial co-extrusion preparation process according to claim 5, characterized in that, In the multi-stage synergistic cooling and shaping process, the wind speed of the first-stage annular air cooling is 1-5 m / s and the temperature is 20-30℃; the water temperature of the second-stage vertical water-falling cooling is 15-35℃ and the cooling time is 3-5 s; and the wind speed of the third-stage air cooling dewatering is 3-8 m / s. The multi-stage synergistic cooling and shaping process ensures that the outer thermoplastic polymer thin-walled tube is completely cured, and the roundness error of the cured outer thermoplastic polymer thin-walled tube is ≤0.03mm.

10. The coaxial co-extrusion preparation process according to claim 5, characterized in that, In the traction and winding step, the traction speed is 0.5-5 m / min, the ratio of traction speed to outer layer extrusion speed is 1.0-1.5, the winding tension is 0.5-2.0 N, and the wire spacing is 1.2 times the wire diameter. The post-processing steps include hot melt adhesive sealing at both ends of the wire, with a sealing length of 5-10mm, cutting at 100-500m / roll, and sealing with nitrogen filling. The storage environment is 20-25℃ and humidity ≤60%.

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