Multifunctional composite structure printing consumable as well as preparation method and application thereof

Abstract

The invention provides a multifunctional composite structure printing consumable as well as a preparation method and application thereof, and belongs to the technical field of 3D printing materials. By arranging the outer layer easy to print, the main functions of supporting or lubricating the core layer, reducing friction between consumables and a nozzle and assisting extrusion of core layer materials in the extrusion and wire feeding process are achieved, the high-viscosity or high-load core layer materials can be smoothly extruded out by an extrusion head, then the consumable extrusion stability is improved, and equipment damage such as nozzle abrasion is reduced; meanwhile, better surface smoothness or other auxiliary characteristics are provided in the printing process, and it is ensured that the surface quality of a printed piece is stable; and the difficult-to-extrude core layer coated by the easy-to-print outer layer takes a functionalized difficult-to-print material as a raw material, so that the printed piece can be endowed with flame retardance, electric conduction, wave absorption, chemical corrosion resistance or other functions, and the multifunctional 3D printed piece is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of 3D printing materials, and particularly relates to a multifunctional composite structure printing consumable and a preparation method and application thereof. BACKGROUND

[0002] Fused Deposition Modeling (FDM, also known as Fused Filament Fabrication, FFF) is one of the most widely used additive manufacturing technologies at present. FDM uses thermoplastic filaments as printing consumables, and forms a three-dimensional object by melting and extruding the filaments through a heated nozzle and layer-by-layer accumulation on a moving platform. Due to its simple operation and relatively low equipment cost, it has been widely used in education, medical treatment, industrial prototype development, home consumption, and even aerospace and other fields.

[0003] However, the current mainstream FDM consumables are usually single materials, such as PLA (polylactic acid), ABS (acrylonitrile-butadiene-styrene copolymer), PETG (polyethylene terephthalate-1,4-cyclohexane dimethyl ester), and nylon (PA series). Most of the above materials only have one or two relatively outstanding properties, such as PLA which is easy to print but lacks toughness and heat resistance, ABS which has good toughness but relatively complex layer bonding and printing odor management, PETG which has good comprehensive performance but is difficult to use in high-temperature environments, and TPU which has high layer adhesion but low mechanical strength. When multiple requirements such as high rigidity, high toughness, wear resistance, fatigue resistance, flame retardance, or precise control of mechanical properties are needed, it is difficult to meet all requirements with a single material. At the same time, FDM also has the problem of difficulty in extruding functional materials with high filler content. In order to achieve special functions such as electromagnetic shielding, flame retardance, corrosion resistance, thermal conductivity, or electrical conductivity, it is often necessary to blend a high proportion of inorganic fillers such as carbon nanotubes, metal powders, or ceramic particles into the matrix, but too high a doping amount will result in a significant reduction in the melt index, poor extrusion flowability, and problems such as nozzle blockage or unstable flow. Moreover, the printing threshold of high-performance polymers is high. High-performance engineering plastics such as PEEK (polyether ether ketone), PPS (polyphenylene sulfide), and polyetherimide (PEI) often require expensive industrial-grade 3D printers and harsh printing environments (high-temperature sealed chamber, high-torque extrusion head, high-temperature and wear-resistant nozzle, etc.) due to their high melting point, high viscosity, and narrow thermal stability range, resulting in high use cost and difficulty in popularization. Conventional FDM cannot meet the technical requirements. In addition, when facing higher or more complex performance requirements, it is often necessary to replace the printing material multiple times or use a multi-extrusion head device. The multi-head or mixing extrusion hardware is expensive and complex to operate, and requires strict material switching for manual or mechanical switching. Ordinary FDM machines generally only have a single extrusion head, making it difficult to combine multiple properties or functions in the same forming process. This not only increases the cost and difficulty of printing hardware, but also limits the comprehensive improvement of the printed parts in terms of mechanics, heat, electricity, and magnetism.

[0004] To overcome the limitations of single material, a small number of multi-layer or multi-core co-extruded wire products have been introduced, combining two or more materials in the same filament, but these materials are mostly limited to simple bi-component or surface coating layers, and the compatibility and functionality can only be improved to a limited extent. In particular, for high-doped inorganic / metallic fillers or high-performance polymers, there are still great challenges in stable extrusion and performance compatibility.

[0005] Therefore, it is a technical problem to be solved in the art to provide a 3D printing consumable that can realize multi-functional stacking of materials and solve the extrusion problem of difficult-to-extrude materials. SUMMARY

[0006] The purpose of the present application is to provide a multi-functional composite structure printing consumable and its preparation method and application. The multi-functional composite structure printing consumable provided by the present application has smooth wire feeding during printing, no obvious plug or instability, high external finish, and the printed part can be endowed with flame retardant, conductive, wave-absorbing, chemical corrosion-resistant or other functions, realizing multi-functional stacking of materials.

[0007] To achieve the above-mentioned purposes of the application, the present application provides the following technical solutions: The present application provides a multi-functional composite structure printing consumable, comprising a difficult-to-extrude core layer and an easy-to-print outer layer covering the difficult-to-extrude core layer; the melt index of the easy-to-print outer layer is higher than that of the difficult-to-extrude core layer; the number of the difficult-to-extrude core layer is greater than or equal to 1. The cross-sectional diameter of the easy-to-print outer layer in the cross-section of the multi-functional composite structure printing consumable accounts for 1-99%, and the cross-sectional diameter of the difficult-to-extrude core layer accounts for 1-99%.

[0008] Preferably, the raw material for preparing the difficult-to-extrude core layer comprises one or more of high-performance polymers, polymer composites and powder reinforced materials.

[0009] Preferably, the raw material for preparing the easy-to-print outer layer comprises any one of PLA, ABS, PETG, PA, TPU, PC, PPS, PEEK, PEI and their modified products or blends.

[0010] Preferably, the melt index of the easy-to-print outer layer is 5-50 g / 10 min.

[0011] Preferably, when the number of the difficult-to-extrude core layer is 1, the structure of the difficult-to-extrude core layer and the easy-to-print outer layer is a double-layer coaxial structure; when the number of the difficult-to-extrude core layer is greater than or equal to 2, the structure of the difficult-to-extrude core layer and the easy-to-print outer layer is a multi-core coaxial structure.

[0012] Preferably, the multifunctional composite structure printing consumables further comprise a functional layer; the functional layer is a bonding layer and / or a transition layer; the functional layer is located between the difficult-to-extrude core layer and the easy-to-print outer layer.

[0013] Preferably, when the multifunctional composite structure printing consumables comprise a functional layer and the number of difficult-to-extrude core layers is 1, the structure of the difficult-to-extrude core layer, the functional layer and the easy-to-print outer layer is a multi-layer coaxial structure; when the multifunctional composite structure printing consumables comprise a functional layer and the number of difficult-to-extrude core layers is ≥2, the structure of the difficult-to-extrude core layer, the functional layer and the easy-to-print outer layer is a multi-core multi-layer hybrid structure.

[0014] The application provides a preparation method of the multifunctional composite structure printing consumables, comprising the following steps: placing raw materials of the easy-to-print outer layer in a first channel of an extruder, placing raw materials of the difficult-to-extrude core layer in other channels of the extruder, and then performing multi-channel die co-extrusion molding to obtain the multifunctional composite structure printing consumables.

[0015] Preferably, after the multi-channel die co-extrusion molding, the product of the multi-channel die co-extrusion molding is further put into a sizing tank or a sizing device, and then sequentially cooled and solidified under the action of a traction roller.

[0016] The application provides an application of the multifunctional composite structure printing consumables or the multifunctional composite structure printing consumables prepared by the preparation method in the fields of aerospace, national defense and military industry, medical treatment and automobile manufacturing.

[0017] This invention provides a multifunctional composite structure printing consumable, comprising a difficult-to-extract core layer and an easily printable outer layer covering the difficult-to-extract core layer; the melt flow index of the easily printable outer layer is higher than that of the difficult-to-extract core layer; the number of difficult-to-extract core layers is ≥1; the cross-sectional diameter of the easily printable outer layer accounts for 1~99% of the cross-sectional diameter of the multifunctional composite structure printing consumable, and the cross-sectional diameter of the difficult-to-extract core layer accounts for 1~99%. The main function of the easily printable outer layer in this invention is to support or lubricate the core layer during extrusion and filament feeding, reduce friction between the consumable and the nozzle, assist in the extrusion of the core layer material, and allow high-viscosity or high-load core layer material to be smoothly extruded by the extruder head, thereby improving the extrusion stability of the consumable and reducing equipment damage such as nozzle wear. Simultaneously, it provides better surface finish or other auxiliary properties during printing and ensures stable surface quality of the printed parts. The difficult-to-extract core layer covered by the easily printable outer layer uses functionalized difficult-to-extract materials as raw materials, which can endow the printed parts with flame retardancy, conductivity, wave absorption, chemical corrosion resistance, or other functions, thus obtaining multifunctional 3D printed parts. This invention improves the printability of difficult-to-print materials and overcomes the limitations of traditional single-material consumables in integrating multiple functions such as mechanical reinforcement, printability, electrical and thermal conductivity, intelligent sensing, electromagnetic shielding, and flame retardancy. The results of the embodiments show that the multifunctional composite printing consumable provided by this invention ensures smooth filament feeding during printing, with no obvious clogging or instability, and a high surface finish. The overall performance of the printed parts can be controlled by adjusting the amount of the difficult-to-extract core layer and the easy-to-print outer layer. Attached Figure Description

[0018] Figure 1 A schematic diagram of the multifunctional composite structure printing consumable and its performance testing provided by the present invention; Figure 2 Schematic diagrams of the double-layer coaxial structure and the multi-core coaxial structure provided by the present invention; Figure 3 A schematic diagram of the multi-core, multi-layer hybrid structure provided by the present invention; Figure 4 Comparison charts of the mechanical properties of the printed parts provided for application examples 2-4 and comparative application examples 1-2; Figure 5 A comparison chart of the limiting oxygen index performance of the printed parts provided in Application Example 5 and Comparative Application Examples 3-5. Detailed Implementation

[0019] This invention provides a multifunctional composite structure printing consumable, comprising a difficult-to-extrude core layer and an easy-to-print outer layer covering the difficult-to-extrude core layer; the melt flow index of the easy-to-print outer layer is higher than that of the difficult-to-extrude core layer; the number of the difficult-to-extrude core layers is ≥1. In the cross-section of the multifunctional composite structure printing consumable, the cross-sectional diameter of the easily printable outer layer accounts for 1~99%, and the cross-sectional diameter of the difficult-to-extrude core layer accounts for 1~99%.

[0020] The multifunctional composite structure printing consumable provided by this invention and its performance test schematic diagram are shown below. Figure 1 As shown. Figure 1 As shown, the upper left part is a schematic structure of a fused deposition modeling (FDM) 3D printer, demonstrating the compatibility of the consumable material of this invention with conventional FDM equipment; the upper right part is an enlarged schematic diagram of the cross-section of the consumable material of this invention, showing a multi-layered coaxial structure composed of an easily printable outer layer, a functional layer, and a difficult-to-extrude core layer; the lower left part is a graph showing the relationship between mechanical properties and the volume fraction of nylon (PA), with embedded photographs of typical cross-sections to characterize the effect of the multi-layer design on improving the flexural modulus; the lower middle part is a schematic diagram of bending loading, comparing the deformation of high-stiffness and low-stiffness splines under the same load; the lower right part is a schematic diagram of flame retardant performance testing, showing the different combustion behaviors of the material under open flame, illustrating that the composite consumable material of this invention has superior flame retardant properties. Figure 1 It can be seen that the preparation of multifunctional composite structure printing consumables using the method of the present invention can improve the mechanical properties and thermal insulation and flame retardant properties of the material.

[0021] The multifunctional composite printing consumable provided by this invention includes a difficult-to-extrude core layer. In this invention, the raw materials for preparing the difficult-to-extrude core layer preferably include one or more of high-performance polymers, polymer composites, and powder-reinforced materials; the high-performance polymer preferably includes any one of PLA, ABS, PETG, PA, TPU, PC, PPS, PEEK, PEI, and their modifiers or blends; the modifier is preferably improved using a compatibilizer, flame retardant, or toughening agent. This invention does not impose any special limitations on the specific types and amounts of the compatibilizer, flame retardant, and toughening agent; they can be selected based on the technical knowledge of those skilled in the art and performance requirements. In this invention, the polymer composite material is preferably a polymer composite material with a high inorganic filler or metal powder doping ratio; the polymer in the polymer composite material preferably includes any one or more of PLA, ABS, PETG, PA, TPU, PC, PPS, PEEK, and PEI; the inorganic filler in the polymer composite material preferably includes one or more of carbon black powder, carbon nanotube powder, ceramic powder, glass fiber, and carbon fiber; the metal powder in the polymer composite material includes one or more of steel powder, copper powder, and aluminum powder; the powder reinforcing material preferably includes one or more of inorganic fillers and metal powders. This invention does not specifically limit the types of inorganic fillers and metal powders in the powder reinforcing material; inorganic fillers and metal powders well-known to those skilled in the art can be used according to the required performance of the 3D printing consumables. By using the above-mentioned raw materials as raw materials for preparing difficult-to-extrude core layers, this invention can endow printed parts with flame retardancy, conductivity, microwave absorption, chemical corrosion resistance, or other functions, thereby obtaining multifunctional 3D printed parts.

[0022] The multifunctional composite printing consumable provided by this invention includes an easily printable outer layer covering the difficult-to-extrude core layer. In this invention, the raw materials for preparing the easily printable outer layer preferably include easily extrudable materials, more preferably any one of PLA, ABS, PETG, PA, TPU, PC, PPS, PEEK, PEI, and their modified or blended products; the modifier in the modified product is preferably a compatibilizer, flame retardant, or toughening agent. This invention does not impose any special limitations on the specific types and amounts of the compatibilizer, flame retardant, and toughening agent; they can be selected based on the technical knowledge of those skilled in the art and performance requirements. As one embodiment of this invention, the compatibilizer can be maleic anhydride-grafted polyolefin; the toughening agent can be maleic anhydride-grafted ethylene propylene rubber; the flame retardant can be a halogen-free flame retardant; the halogen-free flame retardant can be melamine polyphosphate; and the mass of the modifier is 2-10% of the total mass of the modified product. In this invention, the main function of the printable outer layer is to support or lubricate the core layer during extrusion and filament feeding, reduce friction between the consumable and the nozzle, assist in the extrusion of the core layer material, and allow high-viscosity or high-load core layer material to be smoothly extruded by the extruder head, thereby improving the extrusion stability of the consumable and reducing equipment damage such as nozzle wear. At the same time, it provides better surface finish or other auxiliary properties during the printing process and ensures stable surface quality of the printed parts.

[0023] In this invention, the melt index of the easily printable outer layer is higher than that of the difficult-to-extrude core layer; the melt index of the easily printable outer layer is preferably 5~50 g / 10 min. By controlling the melt index of both, this invention facilitates the protection of the difficult-to-extrude core layer by the easily printable outer layer.

[0024] In this invention, the cross-sectional diameter ratio of the easily printable outer layer in the cross-section of the multifunctional composite structure printing consumable is preferably 1-99%; the cross-sectional diameter ratio of the difficult-to-extrude core layer is preferably 1-99%. As one embodiment of this invention, the cross-sectional diameter ratio of the easily printable outer layer in the cross-section of the multifunctional composite structure printing consumable can be 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%; the cross-sectional diameter ratio of the difficult-to-extrude core layer can be 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%. By controlling the cross-sectional diameter ratio of the easily printable outer layer and the difficult-to-extrude core layer, this invention can control the amount of both, thereby regulating the amount of the difficult-to-extrude core layer added, and consequently, regulating the various properties of the 3D printed part.

[0025] In this invention, the melt flow index of the easily printable outer layer is higher than that of the difficult-to-extrude core layer. This invention does not impose a specific limit on the melt flow index of the easily printable outer layer; it is determined based on the technical knowledge of those skilled in the art, as long as it ensures good flowability during fused extrusion 3D printing. By using an easily printable outer layer with a high melt flow index to coat a difficult-to-extrude core layer with a low melt flow index, this invention ensures good flowability of the 3D printing filament during fused extrusion 3D printing, avoiding problems such as nozzle clogging or unstable flow rate.

[0026] In this invention, the number of the difficult-to-extrude core layers is ≥1. As one embodiment of this invention, the number of difficult-to-extrude core layers can be 1 to 10, or even 2, 3, 4, 5, 6, 7, 8, or 9. By controlling the number of difficult-to-extrude core layers, this invention allows for the selection of the properties of the difficult-to-extrude core layers based on the required material properties, thus preparing difficult-to-extrude core layers with different numbers and properties. This allows for the simultaneous imparting of flame retardancy, conductivity, microwave absorption, chemical corrosion resistance, or other functions to the printed parts.

[0027] The multifunctional composite printing consumable provided by this invention preferably further includes a functional layer; the functional layer is preferably an adhesive layer and / or a transition layer; the functional layer is preferably located between the difficult-to-extrude core layer and the easy-to-print outer layer; the number of functional layers is preferably 1 to 5. As one embodiment of this invention, the number of functional layers can be 2, 3, or 4. By introducing functional layers, this invention can improve the interfacial bonding force, thereby enhancing the bonding stability between the difficult-to-extrude core layer and the easy-to-print outer layer.

[0028] This invention does not impose a specific limitation on the thickness of the functional layer; it can be determined based on the technical knowledge of those skilled in the art. As one embodiment of this invention, the cross-sectional diameter ratio of the functional layer in the cross-sectional area of ​​the multifunctional composite printing consumable can be 1-99%, and can also be 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%. By controlling the cross-sectional diameter ratio of the functional layer, this invention can further improve the bonding stability between the difficult-to-extrude core layer and the easily printable outer layer.

[0029] This invention does not specifically limit the raw materials used to prepare the functional layer; any substance with good adhesive properties can be used. As one embodiment of this invention, the raw material for preparing the functional layer can be any one of TPE (thermoplastic elastomer), TPU (thermoplastic polyurethane), and PC (polycarbonate); the PC is preferably flame-retardant modified PC; the flame retardant is preferably a brominated or halogen-free flame retardant. This invention does not specifically limit the type of flame retardant; commercially available brominated or halogen-free flame retardants well known to those skilled in the art can be used. By using a substance with good adhesive properties as the raw material for the functional layer, this invention can further improve the bonding stability between the difficult-to-extrude core layer and the easily printable outer layer.

[0030] In this invention, when the number of the difficult-to-extrude core layer is one, the structure of the difficult-to-extrude core layer and the easy-to-print outer layer is preferably a double-layer coaxial structure. In this invention, the easy-to-print outer layer covers the outer surface of the difficult-to-extrude core layer in the double-layer coaxial structure, and the difficult-to-extrude core layer and the easy-to-print outer layer are coaxially distributed.

[0031] In this invention, when the number of the difficult-to-extrude core layers is ≥2, the structure of the difficult-to-extrude core layers and the easily printable outer layer is preferably a multi-core coaxial structure; the multiple difficult-to-extrude core layers are preferably concentrically or eccentrically distributed in cross-section; the composition of the multiple difficult-to-extrude core layers is preferably the same or different. In this invention, the multiple difficult-to-extrude core layers in the multi-core coaxial structure are concentrically or eccentrically distributed; the materials of the multiple difficult-to-extrude core layers are the same or different.

[0032] Schematic diagrams of the double-layer coaxial structure and multi-core coaxial structure provided by this invention are shown below. Figure 2 As shown. Figure 2 middle, Figure 2 The structure is a double-layer coaxial structure, with the core layer, which is difficult to extrude, located in the center, and the outer layer, which is easy to print, covering its outer surface; Figure 2 The structure below is a multi-core coaxial structure, with multiple difficult-to-extrude core layers distributed concentrically or eccentrically in cross-section, and completely covered by an easy-to-print outer layer.

[0033] In this invention, when the multifunctional composite printing consumable includes a functional layer and has one difficult-to-extrude core layer, the structure of the difficult-to-extrude core layer, the functional layer, and the easy-to-print outer layer is preferably a multi-layer coaxial structure. In this invention, the functional layer covers the outer surface of the difficult-to-extrude core layer, the easy-to-print outer layer covers the outer surface of the functional layer, and the difficult-to-extrude core layer, the functional layer, and the easy-to-print outer layer are coaxially distributed.

[0034] In this invention, when the multifunctional composite printing consumable includes a functional layer and the number of difficult-to-extrude core layers is ≥2, the structure of the difficult-to-extrude core layer, the functional layer, and the easily printable outer layer is preferably a multi-core, multi-layer hybrid structure. In this invention, the multi-core, multi-layer hybrid structure is preferably: each difficult-to-extrude core layer surface is first coated with a functional layer, and then an easily printable outer layer is coated around all the functional layers to form a multi-core, multi-layer hybrid structure. In this invention, the surface of each difficult-to-extrude core layer is preferably coated with a functional layer, or the surfaces of all difficult-to-extrude core layers are jointly coated with a functional layer; the difficult-to-extrude core layer, the functional layer, and the easily printable outer layer are preferably coaxially distributed.

[0035] A schematic diagram of the multi-core, multi-layer hybrid structure provided by this invention is shown below. Figure 3 As shown. Figure 3 As shown, each difficult-to-extrude core layer surface is individually or jointly covered with a functional layer, and then the entire structure is covered by an easy-to-print outer layer, forming a multi-core, multi-layer coaxial composite structure.

[0036] This invention does not impose any special limitations on the size of the multifunctional composite structure printing consumable; it can be determined according to the technical requirements of subsequent fused extrusion 3D printing. As one embodiment of this invention, the diameter of the multifunctional composite structure printing consumable can be 1.75 mm or 2.85 mm.

[0037] This invention features an easily printable outer layer, whose main function is to support or lubricate the core layer during extrusion and filament feeding, reducing friction between the filament and the nozzle, and assisting in the extrusion of the core material. This allows high-viscosity or high-load core material to be smoothly extruded from the extruder head, thereby improving the extrusion stability of the filament and reducing equipment damage such as nozzle wear. Simultaneously, it provides better surface finish or other auxiliary properties during printing and ensures stable surface quality of the printed parts. The difficult-to-extrude core layer, covered by the easily printable outer layer, uses functionalized difficult-to-print materials as raw materials, which can endow the printed parts with flame retardancy, conductivity, microwave absorption, chemical corrosion resistance, or other functions, resulting in multifunctional 3D printed parts. This invention, through its multi-layered, multi-core printing filament structure design, improves the printability of difficult-to-print materials and overcomes the limitations of traditional single-material filaments in integrating multiple functions such as mechanical reinforcement, printability, electrical and thermal conductivity, intelligent sensing, electromagnetic shielding, and flame retardancy.

[0038] The multifunctional composite printing consumable provided by this invention can be used on most single-extrusion head or dual-extrusion head FDM printers without the need for multiple nozzles or high-torque feeding systems, and without significant modifications to hardware equipment. This significantly lowers the barrier to entry and cost of multifunctional printing, and has excellent compatibility.

[0039] This invention, through multi-layer or multi-core design, allows a single wire to possess multiple properties such as high rigidity, high toughness, high temperature resistance, wear resistance, and flame retardancy, reducing the complexity of using multiple single consumables and replacing nozzles, and providing a more targeted material solution for complex part structures.

[0040] The present invention also provides a method for preparing the multifunctional composite structure printing consumable described in the above technical solution, comprising: placing the raw material for the easily printable outer layer in the first channel of an extruder, placing the raw material for the difficult-to-extrude core layer in other channels of an extruder, and then performing multi-channel die head co-extrusion molding to obtain the multifunctional composite structure printing consumable.

[0041] The present invention does not impose any special limitations on the specific model and source of the extruder. Any commercially available extruder known to those skilled in the art can be used, as long as it can meet the requirements for raw material placement and melt extrusion.

[0042] In this invention, the raw materials for the easily printable outer layer and the difficult-to-extrude core layer are preferably the same as those described above, and will not be repeated here.

[0043] In this invention, the raw material for the difficult-to-extrude core layer is preferably added in the form of masterbatch; the preferred method for preparing the masterbatch is to sequentially mix and extrude / granulate the raw material for the difficult-to-extrude core layer to obtain the masterbatch. In this invention, the raw material for the difficult-to-extrude core layer is preferably dried before mixing. This invention does not have specific limitations on the specific drying operation, as long as it removes attached volatile impurities. This invention does not have specific limitations on the specific type of raw material for the difficult-to-extrude core layer, and it can be conventionally selected based on the performance requirements of the 3D printed part. This invention does not have specific limitations on the specific parameters of the mixing and extrusion / granulation, and the parameters can be determined based on the technical knowledge of those skilled in the art. This invention does not have specific limitations on the particle size of the masterbatch, and it can be determined based on the technical knowledge of those skilled in the art.

[0044] In this invention, the mixing and extrusion granulation are preferably carried out in a twin-screw extruder or a kneading device. This invention does not impose any particular limitation on the specific model or source of the twin-screw extruder or kneading device; any commercially available twin-screw extruder or kneading device well-known to those skilled in the art can be used.

[0045] In this invention, the raw materials for the easily printable outer layer and the difficult-to-extrude core layer are preferably dried before being fed into the extruder. This invention does not have specific limitations on the specific drying process; it is sufficient to remove any attached volatile impurities.

[0046] In this invention, when the number of the difficult-to-extract core layers is 1, the raw material of the difficult-to-extract core layer is preferably placed in the second channel of the extruder; when the number of the difficult-to-extract core layers is ≥2, the raw material of the difficult-to-extract core layers is preferably placed sequentially in the second channel, third channel, fourth channel and subsequent channels of the extruder.

[0047] In this invention, when the multifunctional composite printing consumable includes a functional layer, the raw material of the functional layer is preferably placed in the second channel of the extruder, while the raw material of the core layer, which is difficult to extrude, is moved backward in sequence.

[0048] This invention does not impose specific limitations on the detailed process parameters for the multi-channel die co-extrusion molding. The parameters can be set according to the technical knowledge of those skilled in the art, ensuring that a multi-functional composite printing consumable with the required dimensions and structure is obtained. By employing multi-channel die co-extrusion molding, this invention allows the molten polymer and powder material in each channel to converge at the end of the die along a predetermined path. Then, based on the flow channel geometry within the die, a structure is achieved where a difficult-to-extrude core layer and an easily printable outer layer are configured. As one embodiment of this invention, the temperature for multi-channel die co-extrusion molding can be: 200~207℃ for the first zone, 207~208℃ for the second zone, 209~210℃ for the third zone, 211~213℃ for the fourth zone, 214~218℃ for the fifth zone, and a nozzle temperature of 218~223℃; or it can be: 205℃ for the first zone, 208℃ for the second zone, 210℃ for the third zone, 212℃ for the fourth zone, 215℃ for the fifth zone, and a nozzle temperature of 220℃.

[0049] In the multi-channel die co-extrusion molding process, this invention preferably further includes feeding the co-extruded product into a sizing tank or sizing device, and sequentially cooling and curing it under the action of traction rollers to obtain a multifunctional composite structure printing consumable. This invention does not have a specific limitation on the source of the sizing tank or sizing device; any sizing tank or sizing device well-known to those skilled in the art can be used. This invention also does not have a specific limitation on the specific cooling and curing operations; any operation that yields a multifunctional composite structure printing consumable of the required size is acceptable.

[0050] After obtaining the multifunctional composite structure printing consumable, the present invention preferably further includes winding the multifunctional composite structure printing consumable into a disc or cutting it into segments. The present invention does not have specific limitations on the specific operation of winding into a disc or cutting into segments; it can be determined based on the technical common sense of those skilled in the art. The present invention facilitates subsequent transportation and use by winding into a disc or cutting into segments.

[0051] This invention utilizes a co-extrusion method to effectively combine easily printable materials with high-performance or highly doped materials that are difficult to melt-extrude within the same filament. This ensures printability while allowing some of the difficult-to-print high-performance polymers, highly filler-doped materials, or functional powder reinforcements to be placed in the core layer. During printing, these are melt-coated and stably formed by the easily extruded outer polymer layer, significantly improving the applicability and overall performance of fused extrusion 3D printing. This multi-layered composite structure not only meets the requirements for multifunctionality (such as flame retardancy, conductivity, and chemical resistance) but also utilizes the outer material to support and protect the core layer during filament feeding and extrusion, reducing the risk of clogging, surface defects, and delamination. This ensures stable printing of high-performance materials on conventional or slightly modified FDM equipment, greatly enhancing the overall mechanical, thermal, and functional properties of printed parts. It also provides a new avenue for the application of highly doped functional fillers or difficult-to-extrude polymers in FDM processes.

[0052] This invention also provides applications of the multifunctional composite structure printing consumables described in the above technical solutions or the multifunctional composite structure printing consumables prepared by the preparation methods described in the above technical solutions in the fields of aerospace, defense, medical and automotive manufacturing.

[0053] In this invention, the preferred method of application is to perform melt extrusion 3D printing on a multifunctional composite structure printing consumable according to the shape of the desired device to obtain a 3D printed part.

[0054] This invention leverages the differences in materials selected for the difficult-to-extrude core layer and the easy-to-print outer layer to allow the manufactured part to exhibit multiple superimposed characteristics, such as "high-strength outer layer + tough core layer," "flame-retardant core layer + decorative outer layer," and "locally conductive core material + insulating shell." Furthermore, through printing path design, eccentric core material can be distributed to specific areas of the part, further achieving functional gradients or differentiated functional distributions.

[0055] The solution provided by this invention, through material composites and functional superposition, greatly expands the application of FDM in fields with higher requirements for mechanics, thermals and special functions, such as industry, electronics, electrical appliances, automobiles and aerospace, and has great promotional value and market prospects.

[0056] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0057] Example 1 A multifunctional composite printing consumable is composed of a difficult-to-extrude core layer and an easy-to-print outer layer; the melt flow index of the easy-to-print outer layer is higher than that of the difficult-to-extrude core layer; the number of the difficult-to-extrude core layer is one; the structure of the difficult-to-extrude core layer and the easy-to-print outer layer is a double-layer coaxial structure. The raw materials for preparing the difficult-to-extrude core layer are nylon 12 particles and stainless steel powder, wherein the mass of stainless steel powder is 65% of the total mass of nylon 12 particles and stainless steel powder; The raw materials for preparing the printable outer layer are PLA particles and a compatibilizer; the compatibilizer is maleic anhydride-grafted polyolefin; the mass of the compatibilizer is 2% of the total mass of the printable outer layer raw materials; In the cross-section of the multifunctional composite structure printing consumable, the cross-sectional diameter of the easily printable outer layer accounts for 30%, and the cross-sectional diameter of the difficult-to-extrude core layer accounts for 70%. The preparation method of the multifunctional composite structure printing consumable is as follows: (1) Heat the nylon 12 particles to 80°C and dry them for 4 hours. Dry the stainless steel powder. Then, mix the nylon 12 and stainless steel powder in a twin-screw extruder and extrude and granulate them to obtain masterbatch. (2) After drying and mixing, PLA particles and compatibilizer are placed in the first channel of the extruder. The masterbatch obtained in step (1) is placed in the second channel of the extruder after drying. In the multi-channel co-extrusion die, the thickness of the difficult-to-extrude core layer is controlled to be 70% of the cross-sectional diameter, and the thickness of the easy-to-print outer layer is controlled to be 30% of the cross-sectional diameter. Then, the multi-channel die is co-extruded and formed. After that, the sizing, cooling, curing and winding into a disc are carried out in the sizing water tank to obtain a multi-functional composite structure printing consumable with a diameter of 1.75 mm. The temperature control of the multi-channel die co-extrusion is as follows: 205℃ in the first zone, 208℃ in the second zone, 210℃ in the third zone, 212℃ in the fourth zone, 215℃ in the fifth zone and the nozzle temperature is 220℃.

[0058] Application Example 1 The performance of the multifunctional composite structure printing consumable prepared in Example 1 was tested by using a conventional FDM machine (hardened steel nozzle) for printing at a nozzle temperature of 230°C to obtain the printed part.

[0059] Analysis shows that in the multifunctional composite printing consumable provided in Example 1, the outer layer is made of PLA material, which can ensure smooth filament feeding and thus ensure no obvious clogging or instability. It has a high surface finish, while the high metal content in the core layer gives the printed parts a high density and metallic texture, which can achieve electromagnetic shielding or near-metallic surface treatment to a certain extent.

[0060] Example 2 A multifunctional composite printing consumable is composed of a difficult-to-extrude core layer and an easy-to-print outer layer; the melt flow index of the easy-to-print outer layer is higher than that of the difficult-to-extrude core layer; the number of the difficult-to-extrude core layer is one; the structure of the difficult-to-extrude core layer and the easy-to-print outer layer is a double-layer coaxial structure. The raw material for preparing the difficult-to-extrude core layer is PA6 particles (characteristics: high strength, poor interlayer adhesion, easy to curl edges); the raw material for preparing the easy-to-print outer layer is TPU 95A particles and a compatibilizer. In the cross-section of the multifunctional composite structure printing consumable, the cross-sectional diameter of the easily printable outer layer accounts for 65%, while the cross-sectional diameter of the difficult-to-extrude core layer accounts for 35%. The preparation method of the multifunctional composite structure printing consumable is as follows: TPU 95A granules and compatibilizer were dried and mixed, then placed in the first channel of an extruder. PA6 granules were heated to 80°C and dried for 4 hours, then placed in the second channel of the extruder. In a multi-channel co-extrusion die, the thickness of the difficult-to-extrude core layer was controlled to be 35% of the cross-sectional diameter, and the thickness of the easily printable outer layer was controlled to be 65% of the cross-sectional diameter. Then, multi-channel co-extrusion molding was performed. Afterwards, the material was sized, cooled, cured, and wound into a disc in a sizing tank to obtain a multi-functional composite structure printing consumable with a diameter of 1.75 mm. The temperature control of the multi-channel co-extrusion molding was as follows: Zone 1 205°C, Zone 2 208°C, Zone 3 210°C, Zone 4 212°C, Zone 5 215°C, and the nozzle temperature was 220°C.

[0061] Example 3 In the cross-section of the multifunctional composite structure printing consumable, the cross-sectional diameter of the easily printable outer layer accounts for 57%, and the cross-sectional diameter of the difficult-to-extrude core layer accounts for 43%; other conditions are the same as in Example 2.

[0062] Example 4 The cross-sectional diameter of the easily printable outer layer of the multifunctional composite structure printing consumable accounts for 35%, and the cross-sectional diameter of the difficult-to-extrude core layer accounts for 65%; other conditions are the same as in Example 2.

[0063] Comparative Example 1 A 3D printing consumable, the preparation method is as follows: TPU 95A granules and compatibilizer are dried and mixed, then placed in the first channel of an extruder for extrusion molding. After extrusion molding, the granules are cooled, cured, and wound into a disc to obtain a 3D printing filament with a diameter of 1.75 mm. The extrusion molding temperature is controlled as follows: 205℃ in the first zone, 208℃ in the second zone, 210℃ in the third zone, 212℃ in the fourth zone, 215℃ in the fifth zone, and the nozzle temperature is 220℃.

[0064] Comparative Example 2 A 3D printing consumable, the preparation method is as follows: PA6 granules were heated to 80°C and dried for 4 hours. They were then placed in the first channel of an extruder and extruded. After that, they were cooled, cured, and wound into a disc to obtain 3D printing consumables with a diameter of 1.75 mm. The extrusion temperature was controlled as follows: 205°C in the first zone, 208°C in the second zone, 210°C in the third zone, 212°C in the fourth zone, 215°C in the fifth zone, and the nozzle temperature was 220°C.

[0065] Application Examples 2-4 and Comparative Application Examples 1-2 The performance of the multifunctional composite structure printing consumables prepared in Examples 2-4 and the 3D printing consumables prepared in Comparative Examples 1-2 were tested. The method was as follows: printing was performed using a conventional FDM machine (hardened steel nozzle) with a nozzle temperature of 240°C to obtain printed parts, namely Application Examples 2-4 and Comparative Application Examples 1-2.

[0066] The mechanical properties of the printed parts obtained by applying Examples 2-4 and comparing them with those obtained by applying Examples 1-2 are as follows: Figure 4 As shown, Figure 4 In the graph, the vertical axis represents the flexural modulus, and the horizontal axis represents the volume fraction of nylon (PA). Figure 4 As observed during the printing process, when the nylon content is 0%, using TPU alone as the consumable eliminates the risk of edge warping, but results in the lowest mechanical properties of the printed part. When the nylon content is 100%, using PA alone as the consumable yields the highest mechanical properties, but the risk of edge warping during printing is high. However, when both nylon and TPU materials are present to form a multi-layered composite structure, the risk of edge warping can be reduced while simultaneously improving the mechanical properties of the materials, achieving a balance between molding stability and high mechanical performance. This demonstrates that in the multi-functional composite printing consumables provided in Examples 2-4, the outer layer of TPU material ensures interlayer adhesion and reduces the risk of edge warping, while the nylon in the core layer imparts high mechanical strength to the printed part. By changing the ratio of the inner and outer layer materials, a wide range of adjustments to the mechanical properties of the printed part can be achieved.

[0067] Example 5 A multifunctional composite printing consumable is composed of a difficult-to-extrude core layer, a functional layer, and an easy-to-print outer layer; the melt flow index of the easy-to-print outer layer is higher than that of the difficult-to-extrude core layer; the number of the difficult-to-extrude core layer is one; the structure of the difficult-to-extrude core layer, the functional layer, and the easy-to-print outer layer is a multi-layer coaxial structure. The raw materials for preparing the difficult-to-extrude core layer are nylon 12 particles and a toughening agent, wherein the toughening agent is maleic anhydride-grafted ethylene propylene rubber, and its mass is 10% of the total mass of the difficult-to-extrude core layer raw materials; The raw materials for preparing the functional layer are PC and a halogen-free flame retardant, wherein the halogen-free flame retardant is melamine polyphosphate, and its amount is 20% of the total mass of the functional layer raw materials; The raw material for preparing the easily printable outer layer is PETG; In the cross-section of the multifunctional composite structure printing consumable, the cross-sectional diameter of the easily printable outer layer accounts for 30%, the cross-sectional diameter of the functional layer accounts for 5%, and the cross-sectional diameter of the difficult-to-extrude core layer accounts for 65%. The preparation method of the multifunctional composite structure printing consumable is as follows: (1) Heat nylon 12 particles to 80°C and dry for 4 hours. After drying the toughening agent, mix it with nylon 12 in a twin-screw extruder and then extrude and granulate it to obtain a difficult-to-extrude core layer masterbatch. (2) After drying PC and halogen-free flame retardant respectively, they are mixed and extruded in a twin-screw extruder to obtain functional layer masterbatch; (3) Place PETG in the first channel of the extruder, place the functional layer masterbatch obtained in step (2) in the second channel, and place the difficult-to-extrude core layer masterbatch obtained in step (1) in the third channel. In the multi-channel co-extrusion die, control the thickness of the difficult-to-extrude core layer to be 65%, the thickness of the functional layer to be 5%, and the thickness of the easily printable outer layer to be 30%. After co-extrusion by the multi-channel die, the material is then sized, cooled, cured, and wound into a disc through a sizing water tank to obtain a multi-functional composite structure printing consumable with a diameter of 1.75 mm. The extrusion temperature range is controlled sequentially as follows: Zone 1 205℃, Zone 2 208℃, Zone 3 210℃, Zone 4 212℃, Zone 5 215℃, and the nozzle temperature is 220℃.

[0068] Application Example 5 Using the 3D printing consumables provided in Example 5 as raw materials, a conventional FDM machine (hardened steel nozzle) was used to print at a nozzle temperature of 240°C to obtain printed parts.

[0069] The results show that the outer PETG layer ensures stable filament feeding and good surface quality; the middle flame-retardant PC provides significant flame retardancy and high-temperature stability; and the inner nylon 12 core, with the help of toughening agents, significantly improves toughness and fatigue resistance. The limiting oxygen index (LOI) of the printed parts is increased to 29.0%, and the flame retardant performance is significantly better than that of the comparative material. It also possesses excellent toughness and molding adaptability, and can be used stably in the range of 240~260℃, meeting higher safety levels and application requirements.

[0070] Comparative Example 3 A 3D printing consumable, the preparation method is as follows: Pure PETG was heated to 80℃ and dried for 4 hours. It was then placed in the first channel of an extruder and extruded through a single channel. After cooling, curing, and winding into a disc, a 3D printing consumable with a diameter of 1.75mm was obtained. The extrusion temperature range was: Zone 1 205℃, Zone 2 208℃, Zone 3 210℃, Zone 4 212℃, Zone 5 215℃, and the nozzle temperature was 220℃.

[0071] Comparative Application Example 3 Using the 3D printing consumables provided in Comparative Example 3 as raw materials, a conventional FDM machine (hardened steel nozzle) was used to print at a nozzle temperature of 240°C, resulting in a printed part.

[0072] Results: The printing process was smooth and the surface quality was good, but the limiting oxygen index (LOI) was only 20.0%, which is flammable and cannot meet the requirements of applications with strict flame retardancy, such as aviation, electrical and automotive.

[0073] Comparative Example 4 A 3D printing consumable, the preparation method is as follows: Pure PC was heated to 80℃ and dried for 4 hours. It was then placed in the first channel of the extruder and extruded through a single channel. After cooling, curing, and winding into a disc, a 3D printing consumable with a diameter of 1.75mm was obtained. The extrusion temperature range was: Zone 1 205℃, Zone 2 208℃, Zone 3 210℃, Zone 4 212℃, Zone 5 215℃, and the nozzle temperature was 220℃.

[0074] Comparative Application Example 4 Using the 3D printing filaments provided in Comparative Example 4 as raw materials, a conventional FDM machine (hardened steel nozzle) was used to print at a nozzle temperature of 240°C, resulting in a printed part.

[0075] Results: The limiting oxygen index (LOI) was 25.0%, indicating a certain degree of self-extinguishing properties. However, the feeding resistance during printing was high, the interlayer bonding was poor, and the risk of warping and cracking was high, resulting in insufficient molding stability and adaptability.

[0076] Comparative Example 5 A 3D printing consumable, the preparation method is as follows: (1) After drying PC and melamine polyphosphate (10% by mass) separately, they are mixed and extruded into granules in a twin-screw extruder to obtain flame-retardant PC masterbatch; (2) The masterbatch is placed in the first channel of the extruder, and extruded through a single channel. It is then cooled, solidified, and wound into a disc to obtain a 3D printing consumable with a diameter of 1.75 mm. The extrusion molding temperature range is: 205℃ in the first zone, 208℃ in the second zone, 210℃ in the third zone, 212℃ in the fourth zone, and 215℃ in the fifth zone. The nozzle temperature is 220℃.

[0077] Comparative Application Example 5 Using the 3D printing filaments provided in Comparative Example 5 as raw materials, a conventional FDM machine (hardened steel nozzle) was used to print at a nozzle temperature of 240°C, resulting in a printed part.

[0078] Results: Flame retardant performance was improved, with an LOI of 28.0%, which was significantly better than pure PC; however, the overall melt flow index was still low, the feeding and extrusion processes were unstable, the printed surface was rough, the notched impact toughness was poor, and interlayer cracking was prone to occur during long-term printing, which was still insufficient to meet the requirements of high-safety scenarios for molding stability and comprehensive performance.

[0079] Figure 5 A comparison chart showing the Limiting Oxygen Index (LOI) performance of the printed parts provided in Application Example 5 and Comparative Application Examples 3-5. Figure 5 Based on the above, it can be seen that: compared to the application example 3 (pure PETG) sample, the LOI is approximately 20.0%, which is easy to print but lacks sufficient flame retardancy; compared to the application example 4 (pure PC) sample, the LOI is approximately 25.0%, which has moderate flame retardancy but is difficult to print; compared to the application example 5 (flame-retardant PC) sample, the LOI is approximately 28.0%, which shows improved flame retardancy but insufficient printability and toughness; and the application example 5 (PETG outer layer / flame-retardant PC functional layer / nylon core layer) sample has an LOI of approximately 29.0%. Therefore, it is evident that this invention, through multi-layer synergistic design, not only significantly outperforms the comparative materials in flame retardancy but also demonstrates superior printability and high toughness compared to the comparative materials.

[0080] Example 6 A multifunctional composite printing consumable is composed of a difficult-to-extrude core layer and an easy-to-print outer layer; the melt index of the easy-to-print outer layer is higher than that of the difficult-to-extrude core layer; the number of the difficult-to-extrude core layers is two (i.e., difficult-to-extrude core layer A and difficult-to-extrude core layer B); the structure of the difficult-to-extrude core layer and the easy-to-print outer layer is a multi-core coaxial structure. The raw materials for preparing the difficult-to-extrude core layer A are conductive carbon black and ABS, with the mass of conductive carbon black being 65% of the total mass of ABS and conductive carbon black; the raw material for preparing the difficult-to-extrude core layer B is flame-retardant modified ABS; the flame retardant in the flame-retardant modified ABS is a halogen-free flame retardant, and the amount of flame retardant is 20% of the total mass of the flame-retardant modified ABS. The raw material for preparing the easily printable outer layer is ABS; In the cross-section of the multifunctional composite structure printing consumable, the cross-sectional diameter of the easily printable outer layer accounts for 30%, the cross-sectional diameter of the difficult-to-extrude core layer accounts for 70%, and the diameter ratio of the difficult-to-extrude core layer A to the difficult-to-extrude core layer B is 1:1. The preparation method of the multifunctional composite structure printing consumable is as follows: (1) After drying the conductive carbon black and ABS respectively, they were mixed and extruded in a twin-screw extruder to obtain the difficult-to-extrude core layer A masterbatch; (2) After drying the halogen-free flame retardant and ABS respectively, they were mixed and extruded in a twin-screw extruder to obtain the difficult-to-extrude core layer B masterbatch. (3) After drying the ABS, place it in the first channel of the extruder. After drying the difficult-to-extrude core layer A masterbatch obtained in step (1), place it in the second channel of the extruder. After drying the difficult-to-extrude core layer B masterbatch obtained in step (2), place it in the second channel of the extruder. In the multi-channel co-extrusion die, control the thickness of the difficult-to-extrude core layer to be 70% of the cross-sectional diameter, the diameter ratio of the difficult-to-extrude core layer A to the difficult-to-extrude core layer B to be 1:1, and the thickness of the easily printable outer layer to be 30% of the cross-sectional diameter. Then, perform multi-channel co-extrusion molding. Afterward, perform sizing, cooling, curing and winding into a disc in the sizing water tank to obtain a multi-functional composite structure printing consumable with a diameter of 1.75mm. The temperature control of the multi-channel co-extrusion molding is as follows: 205℃ in the first zone, 208℃ in the second zone, 210℃ in the third zone, 212℃ in the fourth zone, 215℃ in the fifth zone and the nozzle temperature is 220℃.

[0081] Application Example 6 The performance of the multifunctional composite structure printing consumable prepared in Example 6 was tested by using a conventional FDM machine (hardened steel nozzle) for printing at a nozzle temperature of 230°C to obtain the printed part.

[0082] Analysis shows that in the multifunctional composite structure printing consumable provided in Example 6, the outer layer is made of PLA material. Through printing path design, conductive core material can be used in local areas of the part (such as circuit paths, sensors, or anti-static areas), while other parts benefit from the safety of flame-retardant ABS. The uniform outer ABS layer ensures the smoothness of the printing process and the consistency of appearance, without the need for multiple printhead switching.

[0083] The advantages of this invention are: Significantly improved printability: By setting a PETG outer layer with a higher melt index, the risk of feeding friction and nozzle clogging is effectively reduced, enabling smooth extrusion of high-viscosity or high-load core materials and compatibility with conventional FDM equipment; Multifunctional synergistic enhancement: Adopting a design of "flame-retardant PC functional layer + nylon tough core layer", it takes into account flame retardancy (LOI≈29%), heat resistance and mechanical toughness, achieving comprehensive performance that cannot be achieved by single-layer materials; Excellent structural stability: The multi-layer coaxial structure improves the interlayer bonding force and avoids the warping, delamination and surface defects that are common when extruding single high-performance materials; Wide range of applications: It can be promoted in fields with high requirements for flame retardancy and mechanical properties, such as aerospace, automotive, electrical and medical, reducing the threshold and cost of using high-performance consumables; Highly customizable: By adjusting the ratio of inner and outer layers and the types of materials, functional gradients can be flexibly designed to achieve a controllable distribution of mechanical, thermal and functional properties, meeting the needs of complex structural components.

[0084] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A multifunctional composite printing consumable, comprising a difficult-to-extrude core layer and an easy-to-print outer layer covering the difficult-to-extrude core layer; wherein the melt flow index of the easy-to-print outer layer is higher than that of the difficult-to-extrude core layer; and wherein the number of the difficult-to-extrude core layers is ≥1. In the cross-section of the multifunctional composite structure printing consumable, the cross-sectional diameter of the easily printable outer layer accounts for 1~99%, and the cross-sectional diameter of the difficult-to-extrude core layer accounts for 1~99%.

2. The multifunctional composite structure printing consumable according to claim 1, characterized in that, The raw materials for preparing the difficult-to-extrude core layer include one or more of high-performance polymers, polymer composites, and powder-reinforced materials.

3. The multifunctional composite structure printing consumable according to claim 1, characterized in that, The raw materials for preparing the printable outer layer include any one of PLA, ABS, PETG, PA, TPU, PC, PPS, PEEK, PEI, and their modified or blended products.

4. The multifunctional composite structure printing consumable according to claim 1, characterized in that, The melt flow index of the printable outer layer is 5~50g / 10min.

5. The multifunctional composite structure printing consumable according to claim 1, characterized in that, When the number of the difficult-to-extrude core layer is 1, the structure of the difficult-to-extrude core layer and the easy-to-print outer layer is a double-layer coaxial structure; when the number of the difficult-to-extrude core layer is ≥2, the structure of the difficult-to-extrude core layer and the easy-to-print outer layer is a multi-core coaxial structure.

6. The multifunctional composite structure printing consumable according to claim 1, characterized in that, The multifunctional composite printing consumable also includes a functional layer; the functional layer is an adhesive layer and / or a transition layer; the functional layer is located between the difficult-to-extrude core layer and the easy-to-print outer layer.

7. The multifunctional composite structure printing consumable according to claim 6, characterized in that, When the multifunctional composite printing consumable includes a functional layer and the number of difficult-to-extrude core layers is 1, the structure of the difficult-to-extrude core layer, the functional layer, and the easy-to-print outer layer is a multi-layer coaxial structure; when the multifunctional composite printing consumable includes a functional layer and the number of difficult-to-extrude core layers is ≥2, the structure of the difficult-to-extrude core layer, the functional layer, and the easy-to-print outer layer is a multi-core multi-layer hybrid structure.

8. A method for preparing the multifunctional composite structure printing consumable according to any one of claims 1 to 7, characterized in that, include: The material for the easily printable outer layer is placed in the first channel of the extruder, while the material for the difficult-to-extrude core layer is placed in other channels of the extruder. Then, multi-channel die head co-extrusion molding is performed to obtain a multifunctional composite structure printing consumable.

9. The preparation method according to claim 8, characterized in that, After the multi-channel die co-extrusion molding is completed, the product co-extruded by the multi-channel die is also put into a sizing tank or sizing device, and then cooled and cured in sequence under the action of traction rollers.

10. The application of the multifunctional composite structure printing consumable as described in any one of claims 1 to 7 or the multifunctional composite structure printing consumable prepared by the preparation method described in any one of claims 8 to 9 in the fields of aerospace, defense, medical and automotive manufacturing.

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