Liquid crystal polymer 3D printing wire rod and preparation method thereof

Abstract

The invention relates to a liquid crystal polymer 3D printing wire rod and a preparation method thereof, and relates to the technical field of 3D printing wire rods. The wire is composed of a TLCP base material and 20K short carbon fibers of a specific specification, is prepared through a secondary extrusion molding process of double-screw blending granulation-single-screw precise wire drawing, and is matched with the collaborative design of vacuum pretreatment, gradient temperature control and large-inner-diameter wire coil winding, so that the industrial pain points of printing material blocking and carbon fiber modified wire embrittlement caused by uneven wire diameter of a pure TLCP wire are solved. The wire diameter precision of a finished wire reaches 1.75 mm + / -0.03 mm, the tensile strength is larger than or equal to 120 MPa, the elongation at break is larger than or equal to 3.5%, the porosity is smaller than or equal to 1.2%, 3D printing extrusion is smooth and free of material blocking, the dimensional deviation of a formed product is smaller than or equal to + / -0.1 mm, and the method is suitable for a high-precision FDM printing scene.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing filament technology, and relates to carbon fiber blended modified TLCP filament with improved wire diameter uniformity and its preparation method. Background Technology

[0002] 3D printing technology (especially fused deposition modeling, or FDM) is increasingly widely used in the rapid fabrication of structural components due to its flexible molding process and controllable equipment costs. Thermotropic liquid crystal polyester (TLCP), as a high-performance engineering plastic, possesses excellent heat resistance, mechanical strength, and dimensional stability, making it one of the potential substrates for high-performance filaments in 3D printing.

[0003] However, pure TLCP filaments face significant technical bottlenecks in actual FDM printing: On the one hand, the viscosity of TLCP melt is sensitive to temperature and shear rate, and traditional single-step extrusion molding processes make it difficult to accurately control the consistency of filament cross-section, easily leading to filament diameter fluctuations (common tolerances exceeding ±0.1mm), resulting in frequent nozzle jamming and unstable extrusion volume during printing, ultimately affecting product precision and molding quality; on the other hand, pure TLCP filaments have insufficient rigidity and toughness matching, and printed products are prone to problems such as poor interlayer bonding and weak impact resistance, limiting their application in high-requirement structural parts.

[0004] To improve the mechanical properties of TLCP filaments, carbon fiber is introduced as a reinforcing phase. Carbon fiber has high specific strength and high modulus, which can effectively improve the tensile strength and rigidity of the filament. However, existing carbon fiber modified TLCP filaments still have key defects: First, the interfacial bonding between carbon fiber and TLCP substrate is insufficient. Direct blending easily leads to uneven dispersion and agglomeration of carbon fibers, resulting in stress concentration points inside the filament. Second, it is difficult to balance the performance of carbon fiber proportions. For example, although TLCP filaments modified with 20% mass fraction of carbon fiber show a significant improvement in mechanical strength, the filament brittleness increases significantly, making it prone to breakage during winding and printing. At the same time, traditional extrusion processes still cannot solve the core problem of uneven wire diameter. Third, existing preparation processes mostly use single-stage extrusion molding, which cannot simultaneously ensure the uniform dispersion of carbon fibers and the molding stability of the filament. This results in modified filaments either having excessive wire diameter or large fluctuations in mechanical properties, making it difficult to meet the adaptation requirements of FDM printing. Therefore, developing a carbon fiber blend-modified TLCP filament that balances wire diameter uniformity and mechanical properties, along with a suitable preparation method, is of great significance for promoting the application of TLCP in 3D printed high-performance structural parts. Summary of the Invention

[0005] This invention addresses the problems of uneven diameter of pure TLCP filaments and the brittleness and poor compatibility of carbon fiber modified TLCP filaments in the prior art. It provides a 3D printing-compatible carbon fiber blend modified TLCP filament and its preparation method. Through "precise matching of raw material specifications + synergistic optimization of multiple process stages", the filament performance and printing compatibility are improved.

[0006] This invention provides a 3D printing-compatible carbon fiber blend modified TLCP filament, which consists of 80%–97.5% TLCP substrate and 2.5%–20% 20K chopped carbon fibers by mass. The parameters of the chopped carbon fibers are: 20K filament bundle (each bundle contains 20,000 monofilaments) and length 0.1–0.5 mm. The filament diameter is 1.75 mm ± 0.03 mm, which is compatible with FDM 3D printing equipment and meets the requirements of no material jamming and smooth extrusion during the printing process.

[0007] This invention provides a method for preparing the aforementioned wire, the core of which is "solving the problems of uneven wire diameter and brittle fracture by matching raw material specifications and precisely matching process parameters," specifically including: 1. Raw material pretreatment: TLCP and carbon fiber of specific specifications are vacuum dried together to remove moisture and impurities at the same time, avoid the formation of pores inside the wire and improve the density of the structure; 2. Blending, extrusion and granulation: The pretreated raw materials are fed into a twin-screw extruder according to the formula. The temperature of each zone of the barrel is set to 290-310℃, the screw speed is 8-12 r / min, and the feed pump speed is 180-210 r / min. The strong shearing action of the twin screw achieves uniform dispersion of carbon fiber in TLCP matrix. After the extruded strip is cooled, it is granulated to obtain modified TLCP granules. 3. Wire drawing: Modified TLCP granules are fed into a single-screw extruder. The temperature of each zone of the barrel is set to 310-325℃, and the temperature of the chuck and die zones is set to 310-320℃. The main machine speed is 20-30 r / min, the traction speed is 5-9 m / min, the conveyor belt speed is 4-8 m / min, and the winding speed is 35-45 m / min. The wire diameter is controlled by the stable conveying of the single screw and the precision wire drawing die. After cooling and shaping, the target wire is wound up. The target wire is wound up using a spool with an inner diameter of ≥200 mm to reduce bending stress during the winding process and avoid brittleness.

[0008] Compared with the prior art, the technical effects and advantages provided by the present invention in the above technical solution are as follows: This invention achieves precise control of wire diameter. Through gradient temperature-controlled blending and precise control of the screw and feed pump speeds, the wire diameter tolerance is stably controlled within ±0.03mm. This solves the problems of nozzle jamming and unstable extrusion volume caused by wire diameter fluctuations exceeding ±0.1mm in traditional single-step extrusion processes. The smoothness of the printing process is greatly improved, and the dimensional deviation of the molded product can be controlled within ±0.1mm, meeting the molding requirements of high-precision structural parts.

[0009] This invention solves the problems of brittleness and dispersion by precisely matching the specific specifications of 20K short-cut carbon fibers with TLCP substrates and combining the multi-parameter synergy of the secondary extrusion process to achieve uniform dispersion of carbon fibers, avoid stress concentration, and achieve wire tensile strength ≥120MPa, elongation at break ≥3.5%, and porosity ≤1.2%, balancing high strength and toughness. There is no brittleness during the winding and printing process, and the stability is significantly improved.

[0010] The preparation process of this invention is simple and highly repeatable. The parameters such as temperature, rotation speed, and traction speed of twin-screw blending and single-screw drawing have been experimentally verified. The parameters are easy to replicate in industrial production and can stably meet the supply needs of mass-produced 3D printing filaments. Detailed Implementation

[0011] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0012] Table 1 Experimental Materials and Reagents

[0013] Example 1 In this embodiment, a 3D printing filament with a mass ratio of 80% TLCP substrate and 20% 20K short-cut carbon fiber was prepared. Weigh 800g of TLCP substrate and 200g of 20K short-cut carbon fiber, place them together in a vacuum drying oven, set the drying temperature to 130℃ and the vacuum degree to -0.09MPa, and continue drying for 5.5h to remove the adsorbed moisture and volatile impurities from the raw materials. After drying, take them out and let them cool naturally to room temperature for later use.

[0014] The pretreated raw material is fed into a twin-screw extruder, and the extrusion parameters are set as follows: Barrel temperature distribution: Zone 2 290℃, Zone 3 300℃, Zone 4 305℃, Zones 5-10 310℃, Zone 11 315℃; Operating parameters: screw speed 7.5 r / min, feed pump speed 196 r / min, to ensure uniform feeding of raw materials; After the raw material is sheared, blended and melted by a twin-screw extruder, it is extruded as a continuous strip from the extruder head, cooled to room temperature, and then cut into modified TLCP particles with a length of about 3 mm by a pelletizer. The particles are collected and sealed for storage.

[0015] The modified TLCP granules were fed into a single-screw extruder, and the parameters were set as follows: Barrel temperature distribution: Barrel zone 1 325℃, Barrel zone 2 320℃, Barrel zone 3 315℃, Chuck zone and die zone 315℃; Operating parameters: main machine speed 25 r / min, traction machine traction speed 7 m / min, conveyor belt conveying speed 6 m / min, winding speed 40 m / min.

[0016] After the molten material is extruded into continuous filaments through a drawing die, it is first cooled to room temperature, then the wire diameter is precisely controlled by a multi-stage traction machine, and finally it is wound up with a plastic spool to obtain the target 3D printing filament.

[0017] Example 2 In this embodiment, a 3D printing filament with a mass ratio of 90% TLCP substrate and 10% 20K short-cut carbon fiber was prepared.

[0018] Weigh 900g of TLCP substrate and 100g of 20K short-cut carbon fiber, place them together in a vacuum drying oven, set the drying temperature to 140℃ and the vacuum degree to -0.10MPa, and continue drying for 4 hours to remove the adsorbed moisture and volatile impurities from the raw materials. After drying, take them out and let them cool naturally to room temperature for later use.

[0019] The pretreated raw material is fed into a twin-screw extruder, and the extrusion parameters are set as follows: Barrel temperature distribution: Zone 2 290℃, Zone 3 300℃, Zone 4 305℃, Zones 5-9 310℃, Zone 10 310℃, Zone 11 315℃; Operating parameters: screw speed 7.5 r / min, feed pump speed 196 r / min, to ensure uniform feeding of raw materials; After the raw material is sheared, blended and melted by a twin-screw extruder, it is extruded as a continuous strip from the extruder head, cooled to room temperature, and then cut into modified TLCP particles with a length of about 3 mm by a pelletizer. The particles are collected and sealed for storage.

[0020] The modified TLCP granules were fed into a single-screw extruder, and the parameters were set as follows: Barrel temperature distribution: Barrel zone 1 325℃, Barrel zone 2 320℃, Barrel zone 3 315℃, Chuck zone and die zone 315℃; Operating parameters: main machine speed 25 r / min, traction machine traction speed 7 m / min, conveyor belt conveying speed 6 m / min, winding speed 40 m / min; After the molten material is extruded into continuous filaments through a drawing die, it is first air-cooled to 180°C, then water-cooled to room temperature, and then the wire diameter is precisely controlled by a multi-stage traction machine. Finally, it is wound up with a plastic spool with an inner diameter of 200mm to obtain the target 3D printing filament.

[0021] Example 3 In this embodiment, a 3D printing filament with a mass ratio of 95% TLCP substrate and 5% 20K short-cut carbon fiber was prepared.

[0022] Weigh 950g of TLCP substrate and 50g of 20K chopped carbon fiber, place them together in a vacuum drying oven, set the drying temperature to 120℃ and the vacuum degree to -0.08MPa, and continue drying for 6 hours to remove the adsorbed moisture and volatile impurities from the raw materials. After drying, take them out and let them cool naturally to room temperature for later use.

[0023] The pretreated raw material is fed into a twin-screw extruder, and the extrusion parameters are set as follows: Barrel temperature distribution: Zone 2 290℃, Zone 3 300℃, Zone 4 305℃, Zones 5-9 310℃, Zone 10 310℃, Zone 11 315℃; Operating parameters: screw speed 7.5 r / min, feed pump speed 196 r / min, to ensure uniform feeding of raw materials; After the raw material is sheared, blended and melted by a twin-screw extruder, it is extruded as a continuous strip from the extruder head, cooled to room temperature, and then cut into modified TLCP particles with a length of about 3 mm by a pelletizer. The particles are collected and sealed for storage.

[0024] The modified TLCP granules were fed into a single-screw extruder, and the parameters were set as follows: Barrel temperature distribution: Barrel zone 1 325℃, Barrel zone 2 320℃, Barrel zone 3 315℃, Chuck zone and die zone 315℃; Operating parameters: main machine speed 25 r / min, traction machine traction speed 7 m / min, conveyor belt conveying speed 6 m / min, winding speed 40 m / min; After the molten material is extruded into continuous filaments through a drawing die, it is first air-cooled to 150°C, then water-cooled to room temperature, and then the wire diameter is precisely controlled by a multi-stage traction machine. Finally, it is wound up with a plastic spool with an inner diameter of 200mm to obtain the target 3D printing filament.

[0025] Comparative Example 1 This comparative example prepared pure TLCP wire without carbon fiber components.

[0026] Weigh 1000g of TLCP substrate and place it in a vacuum drying oven. Set the drying temperature to 130℃ and the vacuum degree to -0.09MPa, and continue drying for 5.5h to remove the adsorbed moisture and volatile impurities from the raw material. After drying, remove the substrate and allow it to cool naturally to room temperature for later use.

[0027] The pretreated TLCP substrate was fed into a twin-screw extruder, and the extrusion parameters were set as follows: Barrel temperature distribution: Zone 2 290℃, Zone 3 300℃, Zone 4 305℃, Zones 5-9 310℃, Zone 10 310℃, Zone 11 315℃; Operating parameters: screw speed 7.5 r / min, feed pump speed 196 r / min; After the raw material is melted, it is extruded as a continuous strip from the extruder head, cooled to room temperature, and then cut into TLCP particles with a length of about 3mm by a pelletizer. The particles are collected and sealed for storage.

[0028] Feed TLCP granules into a single-screw extruder and set the parameters as follows: Barrel temperature distribution: Barrel zone 1 325℃, Barrel zone 2 320℃, Barrel zone 3 315℃, Chuck zone and die zone 315℃; Operating parameters: main machine speed 25 r / min, traction machine traction speed 7 m / min, conveyor belt conveying speed 6 m / min, winding speed 40 m / min; After the molten material is extruded into a continuous filament through a drawing die, it is cooled to room temperature, and then the wire diameter is controlled by a multi-stage traction machine. Finally, it is wound up with a plastic spool to obtain pure TLCP 3D printing filament.

[0029] Table 2. Material properties of Examples 1-3 and Comparative Example 1

Claims

1. A liquid crystal polymer 3D printing filament, characterized in that, The product comprises, by weight, 80-95 parts of TLCP substrate and 5-20 parts of 20K chopped carbon fiber; the 20K chopped carbon fiber is a single bundle containing 20,000 single filaments, with a length of 0.1-0.5 mm; the wire diameter is 1.6-3.0 mm, the wire diameter tolerance is ≤ ±0.08 mm, the tensile strength is ≥95 MPa, the elongation at break is ≥2.5%, the porosity is ≤1.4%, and it is compatible with fused deposition modeling (FDM) 3D printing equipment. The printing process is free of material jamming, the extrusion is smooth, and the dimensional deviation of the molded product is ≤ ±0.1 mm.

2. The 3D printing adaptable carbon fiber blend modified TLCP filament according to claim 1, characterized in that, The interfacial bonding strength between the 20K short-cut carbon fiber and the TLCP substrate is ≥30MPa, and the carbon fiber dispersion uniformity is ≥92%, achieving UL94 V-0 flame retardant effect. Compared with pure TLCP filament without added carbon fiber (the wire diameter tolerance is usually ≥±0.1mm), the wire diameter uniformity of this modified filament is improved by more than 70%, completely solving the 3D printing material jamming problem caused by the uneven wire diameter of pure TLCP filament. It can be fully adapted to fused deposition modeling (FDM) 3D printing equipment, with stable extrusion volume during the printing process, dimensional deviation of the molded product ≤±0.1mm, and high temperature stability improved by more than 30%.

3. A method for preparing 3D printing adaptable carbon fiber blended modified TLCP filament as described in any one of claims 1 to 2, characterized in that, Includes the following steps: (1) Raw material pretreatment: TLCP substrate and 20K short-cut carbon fiber are placed in a vacuum drying oven with temperature control accuracy ≤ ±2℃ and vacuum control accuracy ≤ ±0.005MPa. They are dried at 120~140℃ and -0.10~-0.08MPa for 4~6h to remove moisture and volatile impurities. (2) Blending extrusion granulation: Weigh the pretreated raw materials according to the formula and put them into a twin-screw extruder. The twin-screw extruder has a screw length-to-diameter ratio of 40~50:1 and a die diameter of 2~6mm. Set the temperature of each zone of the barrel to 290~310℃, the screw speed to 8~12r / min, and the feed pump speed to 180~210r / min. The raw materials are uniformly blended and melted through the strong shearing action of the twin screw. After the extruded strip is cooled to room temperature, it is granulated to obtain modified TLCP granules. (3) Fiber forming: The modified TLCP particles are fed into a single screw extruder. The screw length-to-diameter ratio of the single screw extruder is 30~40:1, the die diameter is 1.0~3mm, the temperature of each zone of the barrel is set to 310~325℃, the temperature of the chuck zone and the die zone is set to 310~320℃, the main machine speed is 20~30r / min, the traction speed is 5~9m / min, the conveyor belt speed is 4~8m / min, and the winding speed is 35~45m / min. After the filament is extruded through a precision drawing die (the aperture accuracy is ≤±0.01mm), it is cooled to room temperature and finally wound through a spool with an inner diameter ≥200mm to obtain the target wire. Compared to traditional PA / PLA filament manufacturing processes, the wire diameter accuracy is improved by more than 40%, the wire porosity is reduced by more than 30%, the brittleness rate during winding and printing is significantly reduced, it is compatible with 3D printing technology, and the mechanical property fluctuation range of the molded products is reduced to ±5%, the service life is extended by more than 2 times, its excellent wire diameter uniformity can be adapted to different models of FDM printer nozzles, there is no jamming or filament breakage when printing complex structural parts, and the molding efficiency is improved by more than 30%.

4. The preparation method according to claim 3, characterized in that, The gradient temperature control system in step (2) works synergistically with the strong shearing action of the twin screws. The temperature matching system in step (3) is precisely matched with the traction-winding speed to ensure the uniform dispersion of carbon fiber in the TLCP substrate, avoid stress concentration caused by fiber agglomeration, and precisely control the consistency of the wire cross section.

5. The application of 3D printing adaptable carbon fiber blend modified TLCP filament as described in any one of claims 1 to 2 in the 3D printing of high-precision structural parts.

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