Bamboo-plastic composite material wire for 3D printing and preparation method and production line thereof

Abstract

This invention discloses a bamboo-plastic composite filament for 3D printing, its preparation method, and a production line. The filament has a skin-core structure, with both the skin and core layers composed of bamboo-plastic composite materials. The skin layer uses a formulation with high long-branched polybutylene succinate (PBS) content and low bamboo powder / modified calcium carbonate content, while the core layer uses a high-filler formulation, forming "homogeneous yet heterogeneous" functional zones. This invention also provides an extrusion production line including an online cooling water fluctuation detection system and a wire diameter error AI tester. This invention solves the problems of high surface friction, feeding difficulties, and poor surface quality of homogeneous filaments with high bamboo powder content through the skin-core structure, and utilizes the high melt strength and topological structure of long-branched PBS to enhance interlayer adhesion. Actual measurements show that the filament has a surface friction coefficient as low as 0.21, no clogging after 4 hours of continuous printing, uniform wire diameter (1.72 mm, 0% roundness), tensile strength of 47.3 MPa, and no interlayer separation after a 2-meter drop.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing material manufacturing technology, specifically relating to a bamboo-plastic composite filament for FDM (Fused Deposition Modeling) 3D printing, a method for preparing the filament, and a dedicated production line for implementing the method. Background Technology

[0002] Currently, fused deposition modeling (FDM) is one of the most widely used 3D printing technologies. Polybutylene succinate (PBS), an aliphatic polyester with good biodegradability and biocompatibility, is considered a highly promising green 3D printing material. However, commercially available ordinary linear PBS suffers from problems such as difficulty in controlling filament fabrication precision, insufficient mechanical properties of printed products, and weak interlayer bonding when applied to FDM technology.

[0003] Our team previously applied for "A Green and Environmentally Friendly High-Performance Bamboo-Plastic Composite Material and Its Preparation Method and Application" (Application No. 202511060395.9). This material achieves excellent mechanical properties through the synergistic effect of long-chain branched PBS, KH-570 modified calcium carbonate, and bamboo powder. However, when applying this material to FDM 3D printing filaments, new technical problems were discovered: 1. High filament surface friction and feeding difficulties: Although bamboo-plastic composites with high bamboo powder content (10-20 parts) have excellent mechanical properties, they also have high surface roughness and a high coefficient of friction. In FDM printers, when the feed gear contacts the filament surface, the excessively high coefficient of friction will lead to increased feeding resistance. This can cause uneven printing layer thickness, or even clogging and material breakage, seriously affecting printing continuity and product quality.

[0004] 2. Poor surface quality during homogeneous wire extrusion: When extruding wire using bamboo-plastic composite materials with a homogeneous structure, the uneven distribution of fillers (bamboo powder, calcium carbonate) in the melt can easily cause a "sharkskin" phenomenon or microscopic unevenness on the wire surface, further exacerbating feeding difficulties and affecting the accuracy of wire diameter measurement and printing appearance.

[0005] 3. Reduced flexibility of high-filler filaments: Bamboo powder and calcium carbonate, as rigid fillers, can improve strength, but they reduce the flexibility of the filaments, making them prone to breakage at bends during printing.

[0006] Therefore, developing a PBS-based 3D printing filament that can maintain high mechanical properties while solving problems such as high surface friction, feeding difficulties, and poor surface quality is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a bamboo-plastic composite wire that can overcome the problems of high surface friction and feeding difficulties of bamboo-plastic composite wire with high bamboo powder content; improve the problem of poor surface quality during extrusion of homogeneous bamboo-plastic composite wire; and improve its mechanical properties and interlayer adhesion while maintaining the flexibility of the wire.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: Unlike conventional skin-core structures that use different materials (such as PLA skin / TPU core), the skin and core of this invention are both made of bamboo-plastic composite material, but the formulations of the skin and core differ, forming a "homogeneous but heterogeneous" functional partition: Skin layer: A formulation with high long-chain branched PBS content and low bamboo powder / calcium carbonate content (95-100 parts long-chain branched PBS, 0-10 parts bamboo powder + modified calcium carbonate). The main function of the skin layer is to provide a smooth surface, reduce the coefficient of friction, improve printing feed performance, and ensure the melt flowability of the filament surface.

[0009] Core layer: A conventional or high bamboo powder / calcium carbonate content formulation is used (80-90 parts long-chain branched PBS, 20-40 parts bamboo powder + modified calcium carbonate). The main function of the core layer is to provide the overall mechanical properties (strength, stiffness, toughness) and high melt strength of the filament, ensuring the structural performance of the printed product.

[0010] Compared with the prior art, the present invention has the following beneficial effects: The cortex and core layers use the same matrix (both are long-branched PBS), so there are no interfacial compatibility issues between dissimilar materials, and the interlayer bonding is strong. The low-filler formulation of the skin layer makes its surface smooth, its coefficient of friction low, and its feeding smooth; The high filler formulation in the core layer ensures mechanical properties, while the high content of long-chain branched PBS in the core layer maintains high melt strength and suppresses sagging due to its own weight during wire extrusion.

[0011] Preferably, the skin layer and the core layer have a concentric circle structure, that is, the core layer is located at the geometric center of the wire cross-section, and the skin layer thickness is uniformly distributed along the circumference. The concentric circle structure can ensure symmetrical melt flow during extrusion, uniform cooling and shrinkage, and minimal wire diameter fluctuation. At the same time, it ensures that the core layer is located on the neutral axis when the wire is bent, providing uniform bending support.

[0012] The bamboo-plastic composite material used in this invention includes long-chain branched polybutylene succinate (PBS), modified calcium carbonate, bamboo powder, and fluorine-containing additives. Wherein: Long-chain branched PBS is obtained by reactive extrusion of linear PBS, composite initiator and multifunctional monomer; modified calcium carbonate is obtained by loading silane coupling agent KH-570 onto the surface of heavy calcium carbonate, with the amount of KH-570 being 1.5 to 3 wt% of the heavy calcium carbonate; the fluorinated auxiliary agent is perfluorohexanoic acid.

[0013] Preferred formulation for the cortex (parts by weight): 95-100 parts long-branched PBS, 0-5 parts modified calcium carbonate, 0-5 parts bamboo powder, and 0.3-0.8 parts perfluorohexanoic acid.

[0014] Optimal core layer formulation (parts by weight): 80-90 parts long-branched PBS, 10-20 parts modified calcium carbonate, 10-20 parts bamboo powder, and 0.5-1.5 parts perfluorohexanoic acid.

[0015] The thickness of the sheath accounts for 10%-40% of the total diameter of the wire.

[0016] Includes the following steps: S1: Prepare bamboo-plastic composite material according to the aforementioned scheme.

[0017] S2: A 3D wire extrusion production line, including an online cooling water fluctuation detection system and a wire diameter error AI tester, is used to co-extrude the skin and core granules through a co-extrusion die to obtain 3D printed filament. In step S2, the melt extrusion process parameters are as follows: extrusion screw processing temperature in zones I-VI is 130-180 ℃; cooling water temperature is 7-15 ℃; and winding frequency is 5-20 Hz.

[0018] The 3D filament extrusion production line is characterized in that it comprises: A first extruder is used for melting and extruding the skin layer material; a second extruder is used for melting and extruding the core layer material; a skin-core co-extrusion die is connected to the first and second extruders; a cooling water tank is located after the co-extrusion die; a traction device is located after the cooling water tank; a winding machine is located after the traction device; an online cooling water fluctuation detection system is connected to the cooling water tank and includes: an inlet assembly (containing an adjustable inlet diameter and an adjustable filter diameter), an outlet height controller, and a temperature detector; the system controls the inlet diameter and filter diameter based on the monitored water flow fluctuation information to stabilize the water flow; a wire diameter error AI tester is located after the cooling water tank and includes: an online wire diameter monitoring unit and an AI control unit; the AI ​​control unit is electrically connected to the online wire diameter monitoring unit, the traction device, and the first and second extruders, and is used to receive wire diameter error data and adjust the traction speed and extrusion speed in conjunction with a built-in algorithm to form a closed-loop control.

[0019] The AI ​​control unit of the wire diameter error AI tester incorporates a PID control algorithm or a neural network model trained based on historical data. Feedback from the liquid level sensor adjusts the outlet height to control the liquid level and flow rate distribution within the cooling water tank. Compared to existing ordinary PBS wires and homogeneous bamboo-plastic composite wires, this invention has the following significant advantages: 1. Significantly reduced surface friction coefficient and smooth feeding: Due to the low-filler formula in the sheath, the filament surface is smooth, resulting in a significantly reduced friction coefficient. The measured surface friction coefficient is 0.21 (0.38 for homogeneous bamboo-plastic filament), and continuous printing for 4 hours was completed without clogging, while homogeneous filament experienced clogging 3 times under the same conditions. This fundamentally solves the problem of feeding difficulties with filaments containing high bamboo powder content.

[0020] 2. High wire diameter accuracy: The high content of long-chain branched PBS in the core layer provides high melt strength, suppressing sagging and necking caused by its own weight during extrusion; combined with the concentric circle structure and AI wire diameter closed-loop control, the measured wire diameter is uniform (1.72 mm, out-of-roundness is 0), which is far superior to homogeneous wire (fluctuation ±0.10 mm).

[0021] 3. Excellent mechanical properties and strong interlayer adhesion: The high filler formulation of the core layer ensures tensile strength (47.3 MPa) and impact strength (17 kJ / m²); utilizing the unique topological structure of long-branched PBS, the interlayer bonding mechanism of FDM printing is fundamentally improved. During 3D printing, molten filament is extruded from the nozzle and deposited on the surface of the upper layer. In the long-branched topological structure of the material of this invention, the branches extend outward in the molten state. When the newly deposited filament comes into contact with the cooled filament below, the long-branched molecular chains in the upper filament can physically entangle with the molecular chains and branches on the surface of the lower filament with a higher probability. This "mechanical interlocking" effect induced by the topological structure greatly increases the density of entanglement points per unit interface area, thus macroscopically manifesting as a significant improvement in interlayer adhesion. The topological structure of long-branched PBS increases the probability of interlayer physical entanglement during printing; no interlayer separation was observed in the 2-meter drop test, while interlayer cracking occurred in homogeneous filaments.

[0022] 4. Strong bonding between skin and core: The skin and core layers have the same matrix (both are long-branched PBS), forming a continuous transition during melt co-extrusion, and there are no interfacial weaknesses between dissimilar materials. Detailed Implementation

[0023] To make the above features and advantages of the present invention more apparent and understandable, specific embodiments are described below in detail. Example

[0024] Preparation of bamboo-plastic composite granules (1) Cortex formulation (parts by weight): 100 parts long-branched PBS, 2 parts modified calcium carbonate, 2 parts bamboo powder (250 mesh, moisture content 0.1%), 0.5 parts perfluorohexanoic acid.

[0025] (2) Core layer formulation (parts by weight): 100 parts long-branched PBS, 15 parts modified calcium carbonate, 15 parts bamboo powder (250 mesh, moisture content 0.1%), 1.0 part perfluorohexanoic acid.

[0026] Synthesis of long-branched PBS: It was obtained by reaction extrusion of linear PBS, 0.4 parts of a composite initiator (BPO:DHBP=7:3), and 4 parts of 1,6-hexanediol diacrylate.

[0027] Modified calcium carbonate: KH-570 is used at a rate of 2.5 wt% of heavy calcium carbonate.

[0028] Preparation steps: S11: In a high-speed mixer, KH-570 is sprayed onto the surface of heavy calcium carbonate and mixed at 1200 rpm for 10 minutes to obtain modified calcium carbonate.

[0029] S12: According to the formulations for the cortex and core layers respectively, long-branched PBS, modified calcium carbonate, bamboo powder and perfluorohexanoic acid are mixed in a high-speed mixer at 1500 rpm for 15 minutes.

[0030] S13: The mixture is fed into a twin-screw extruder for granulation to obtain skin granules and core granules. Extrusion temperatures: Zone 1 130 ℃, Zone 2 145 ℃, Zone 3 155 ℃, Zone 4 165 ℃, Zone 5 175 ℃, and die head 175 ℃.

[0031] The production line for preparing 3D printing filaments is configured as follows: The 3D filament extrusion production line designed independently by this invention includes a first extruder (skin layer), a second extruder (core layer), a skin-core co-extrusion die (concentric circle structure, core layer center deviation ≤0.05mm), a cooling water tank, a traction device, a winding machine, and integrates an online cooling water fluctuation detection system and a wire diameter error AI tester.

[0032] Process parameters: Skin extrusion temperature: 150 ℃ (Zone I), 155 ℃ (Zone II), 160 ℃ (Zone III), 160 ℃ (Zone IV); Core extrusion temperature: 165 ℃ (Zone I), 170 ℃ (Zone II), 175 ℃ (Zone III), 180 ℃ (Zone IV); Co-extrusion die temperature: 170 ℃; Skin thickness percentage: 25%.

[0033] Cooling water tank: water temperature controlled at 10±1 ℃; cooling water fluctuation online detection system is activated, and the inlet diameter and filter aperture are automatically adjusted when the water flow fluctuation rate exceeds 5%; wire diameter control: target wire diameter 1.75 mm, AI control unit (PID + feedforward) links to adjust traction speed and extrusion speed; winding frequency: 12 Hz.

[0034] Performance testing. The above-mentioned filaments were printed with standard test strips on an FDM printer (printing temperature 180 ℃, bed temperature 60 ℃, speed 50 mm / s), and the tests were conducted by Guangdong Torch Testing Co., Ltd. (Report No.: WTM2601221). Surface friction coefficient and printhead clogging rate were also tested.

[0035] Test methods: Surface friction coefficient: Refer to GB / T 10006-2021, the static friction coefficient between the wire and the feeding gear (simulating the contact surface of the feeding gear). Printing blockage rate: Record the number of times the wire blocks or feeds fail during 4 consecutive printing sessions (printing a standard 20 mm cube model).

[0036] The test results are shown in Table 1. Example

[0037] It is basically the same as Example 1, except that: Cortex formulation: 98 parts long-branched PBS, 1 part modified calcium carbonate, 1 part bamboo powder, 0.4 parts perfluorohexanoic acid; cortex thickness accounts for 20%.

[0038] Core layer formulation: 85 parts long-branched PBS, 18 parts modified calcium carbonate, 18 parts bamboo powder, and 1.2 parts perfluorohexanoic acid.

[0039] The process parameters were the same as in Example 1. The test results are shown in Table 1.

[0040] Using the same formulation as the core layer in Example 1 (i.e., homogeneous structure, without a sheath), the filaments were prepared using a conventional 3D filament production line (without an online cooling water fluctuation detection system and AI wire diameter control), and test strips were printed on the same FDM printer with the same parameters. The test results are shown in Table 1.

[0041] Commercially available linear PBS (melt index 22 g / 10 min) granules were used to prepare filaments using a conventional 3D filament production line, and test strips were printed on the same FDM printer. The test results are shown in Table 1.

[0042] The same formulation and process as in Example 1 were used, but the concentricity of the core-sheath co-extrusion die was adjusted so that the core center deviated from the wire center by approximately 0.15 mm (eccentricity of approximately 8.6%). The test results are shown in Table 1.

[0043] Performance Comparison Summary The performance test data of Examples 1-2 and Comparative Examples 1-3 are summarized in Table 1.

[0044] Inspection items unit Testing standards Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Wire diameter uniformity (direct) mm Refer to GB / T3177-2009 1.72 / 1.72 / 1.72 (Average 1.72) 1.73 / 1.73 / 1.72 (Average 1.73) 1.70~1.80 (fluctuation ±0.10) 1.65~1.85 (fluctuation ±0.15) 1.72~1.78 (fluctuation ±0.03) Out-of-roundness (difference between maximum and minimum diameters) mm Refer to GB / T3091-2025 0 / 0 / 0 0.01 / 0 / 0.01 0.04~0.06 0.08~0.12 0.04 static surface friction coefficient — GB / T10006-2021 0.21 0.23 0.38 0.25 0.22 Printing nozzle blockage rate (times / 4 hours) Second-rate Continuous printing for 4 hours 0 0 3 1 1 Drop test — 2 meters high The exterior is intact, with no interlayer separation. The exterior is intact, with no interlayer separation. Fine interlayer cracks appeared in some areas. Interlaminar cracking and partial fracture occurred. The exterior is intact, with no interlayer separation. Tensile strength MPa ISO 527-2:2025 47.3 44.8 28.6 22.4 46.1 Impact strength of cantilever beam (without notch) <![CDATA[kJ / m 2 ]]> ASTM D 256-24 17 15.5 9.5 6.8 16.2 Printing duration (until the first nozzle blockage) h _ ＞8 ＞8 0.5 2.5 4 The data in Table 1 clearly shows that: Surface friction and feeding performance: The surface friction coefficients of Examples 1 and 2 (0.21-0.23) were significantly lower than those of Comparative Example 1 (0.38) and close to those of ordinary PBS (0.25). Furthermore, both examples maintained continuous printing for 8 hours without clogging, while Comparative Example 1 experienced clogging after only 0.5 hours. This demonstrates that the low-filler design of the skin layer in this invention effectively solves the feeding difficulties of filaments with high bamboo powder content.

[0045] Wire diameter accuracy: The wire diameter of Example 1 is uniform and the out-of-roundness is 0 (concentric circle structure), which is better than that of Comparative Example 3 (eccentric circle, out-of-roundness 0.04), demonstrating the contribution of the concentric circle structure to the wire diameter accuracy.

[0046] Interlayer bonding strength: Both Example 1 and Comparative Example 3 (eccentric circle) passed the 2-meter drop test, indicating that the skin-core structure itself does not impair interlayer bonding strength. However, Comparative Example 1 (homogeneous) showed interlayer cracks, indicating that the homogeneous high-filler structure has interlayer bonding weaknesses.

[0047] Mechanical properties: The tensile strength and impact strength of Example 1 are significantly better than those of Comparative Example 1 and Comparative Example 2, proving that the reinforcing effect of the high filler formulation in the core layer is fully utilized.

[0048] Effect of eccentric circles: The wire diameter fluctuation and out-of-roundness of Comparative Example 3 are higher than those of Example 1, and the printing blockage rate (1 time / 4 h) is higher than that of Example 1 (0 times), proving that the concentric circle structure is superior to the eccentric circle structure.

[0049] Mechanism verification of long-branched interlayer adhesion Printed samples from Example 1 and Comparative Example 2 were broken in liquid nitrogen, and their interlayer interfaces were observed using a scanning electron microscope (SEM).

[0050] Comparative Example 2 (Linear PBS): The interlayer interface is clearly visible, showing a smooth fracture surface, indicating weak bonding between the two layers.

[0051] Example 1 (long-branched PBS skin-core structure): The interlayer interfaces are indistinct, and numerous filamentous plastic deformation marks appear on the cross-section. Furthermore, fibrous protrusions of the other layer material, pulled out from the surface of one layer, can be observed. This directly demonstrates that the long-branched molecular chains have formed strong physical entanglements between the layers. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Those skilled in the art can make various modifications and variations to the present invention without departing from its conceptual framework. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A bamboo-plastic composite filament for 3D printing, characterized in that, The wire has a sheath-core structure, and both the sheath and the core are made of bamboo-plastic composite material; the bamboo-plastic composite material includes long-chain branched polybutylene succinate, modified calcium carbonate, bamboo powder and fluorine-containing additives; In the bamboo-plastic composite material of the outer layer, the mass content of long-chain branched PBS is higher than that of the core layer, and the mass content of bamboo powder and modified calcium carbonate is lower than that of the core layer. In the bamboo-plastic composite material of the core layer, the mass content of bamboo powder and modified calcium carbonate is higher than that of the skin layer.

2. The bamboo-plastic composite filament for 3D printing according to claim 1, characterized in that, The sheath and core are concentric circles, with the core located at the geometric center of the wire cross-section. The thickness of the sheath is uniformly distributed circumferentially. The wire's out-of-roundness is ≤0.02 mm, and the core's eccentricity is ≤5%.

3. The bamboo-plastic composite filament for 3D printing according to claim 1, characterized in that, The long-branched PBS is obtained by reactive extrusion of linear PBS, a composite initiator, and a multifunctional monomer; the modified calcium carbonate is obtained by loading a silane coupling agent KH-570 onto the surface of heavy calcium carbonate, wherein the mass of the silane coupling agent KH-570 is 1.5 to 3 wt% of the heavy calcium carbonate; the fluorinated auxiliary agent is perfluorohexanoic acid.

4. The bamboo-plastic composite filament for 3D printing according to claim 1, characterized in that, The thickness of the sheath layer accounts for 10%-40% of the total diameter of the wire; in the bamboo-plastic composite material of the sheath layer and the core layer, the total weight parts of long-chain branched PBS, modified calcium carbonate, bamboo powder, and fluorine-containing additives are 100 parts, wherein: Cortex: 95-100 parts long-branched PBS, 0-5 parts modified calcium carbonate, 0-5 parts bamboo powder, 0.3-0.8 parts fluorine-containing additives; Core layer: 80-90 parts long-branched PBS, 10-20 parts modified calcium carbonate, 10-20 parts bamboo powder, and 0.5-1.5 parts fluorine-containing additives.

5. A method for preparing bamboo-plastic composite filament for 3D printing as described in any one of claims 1-4, characterized in that, Includes the following steps: S1: Prepare the outer layer bamboo-plastic composite material granules and the core layer bamboo-plastic composite material granules separately: S11: In a high-speed mixer, silane coupling agent KH-570 is loaded onto the surface of heavy calcium carbonate to obtain modified calcium carbonate. S12: According to the skin layer formula and the core layer formula, long branched PBS, modified calcium carbonate, bamboo powder and fluorine-containing additives are mixed and granulated by a twin-screw extruder to obtain skin layer granules and core layer granules. S2: Using a 3D filament extrusion production line, the skin granules and core granules are co-extruded through a co-extrusion die to obtain 3D printed filaments; The 3D wire extrusion production line includes an online cooling water fluctuation detection system and a wire diameter error AI tester. During the extrusion process: The cooling water fluctuation online detection system monitors the cooling water flow fluctuation, temperature and liquid level in real time, and automatically adjusts the inlet diameter, filter aperture and outlet height according to the feedback information to control the cooling conditions. The wire diameter error AI tester monitors the wire diameter in real time and sends the wire diameter error data to the AI ​​control unit. The AI ​​control unit calculates and outputs control signals according to a preset algorithm, and adjusts the traction speed and extrusion speed in a coordinated manner to keep the wire diameter stable within the target range.

6. The preparation method according to claim 5, characterized in that, In step S2, the process parameters for skin-core co-extrusion are: skin extrusion temperature 140-160 ℃, core extrusion temperature 160-180 ℃, cooling water temperature 7-15 ℃, and winding frequency 5-20 Hz.

7. A method for preparing the wire according to any one of claims 1-4, characterized in that, Include: A first extruder is used for melting and extruding the skin layer material; a second extruder is used for melting and extruding the core layer material; a skin-core co-extrusion die is connected to the first and second extruders; a cooling water tank is disposed after the co-extrusion die; and a traction device is disposed after the cooling water tank. A winding machine is installed after the traction device; A cooling water fluctuation online detection system, connected to the cooling water tank, includes: an inlet assembly (containing an adjustable-diameter inlet and an adjustable-aperture filter), an outlet height controller, and a temperature detector; the system controls the inlet diameter and filter aperture based on the monitored water flow fluctuation information to stabilize the water flow; a wire diameter error AI tester, located after the cooling water tank, includes: an online wire diameter monitoring unit and an AI control unit; the AI ​​control unit is electrically connected to the online wire diameter monitoring unit, the traction device, and the first and second extruders, and is used to receive wire diameter error data and adjust the traction speed and extrusion speed in conjunction with a built-in algorithm to form a closed-loop control.

8. The 3D filament extrusion production line according to claim 7, characterized in that, The AI ​​control unit of the wire diameter error AI tester has a built-in PID control algorithm or a neural network model trained based on historical data.

9. The 3D filament extrusion production line according to claim 7, characterized in that, The cooling water fluctuation online detection system also includes a liquid level sensor. The outlet height regulator adjusts the outlet height according to the feedback information from the liquid level sensor to control the liquid level and flow rate distribution in the cooling water tank.