Composite fiber with dynamic and static sensing function based on thermal shrinkage process and rapid preparation method

Abstract

A composite fiber with dynamic and static sensing capabilities based on heat-shrinkable technology and its rapid preparation method are disclosed. This relates to the field of composite fiber technology with a core-shell structure. The fiber has a core-shell structure, consisting of, from the inside out, a fiber core layer, a piezoresistive layer, a second conductive layer, a piezoelectric layer, a first conductive layer, and an insulating protective layer; or, from the inside out, a metal core layer, a piezoelectric layer, a first conductive layer, a piezoresistive layer, and an insulating protective layer. This composite coaxial multilayer functional structure integrates dynamic (piezoelectric effect) and static (piezoresistive effect) sensing functions into a single fiber, overcoming the sensing limitations of traditional single-material or single-physical-effect fibers. It achieves simultaneous detection of broadband (dynamic and static) force and motion signals. The preparation process requires no complex equipment, only heat-shrinkable molding and spraying processes, significantly shortening the manufacturing time of a single fiber, greatly reducing costs, and achieving high interlayer bonding strength, avoiding the interface delamination risk of traditional melt co-extrusion processes.

Description

Technical Field

[0001] This invention relates to the field of composite fiber technology with core-shell structure, specifically to a composite fiber based on heat shrinking process with dynamic and static sensing functions and a rapid preparation method. Background Technology

[0002] With the rapid development of smart wearable devices, flexible electronics, medical monitoring, and the Internet of Things (IoT), the demand for high-performance smart sensing materials is becoming increasingly urgent. Smart fibers, as flexible sensing units that can be directly integrated into textiles, have become a research hotspot in the field of smart materials due to their lightweight, weavability, and strong environmental adaptability. Traditional smart sensing fibers mainly imbue their resistive, capacitive, or piezoelectric response properties by embedding sensing materials (such as metal wires, carbon-based materials, or conductive polymers) into a fiber substrate. However, existing technologies generally suffer from problems such as limited material systems, complex fabrication processes, and insufficient dynamic response performance, severely restricting their large-scale application.

[0003] In terms of materials, traditional sensing fibers often use metals (such as copper, silver, or shape memory alloys) as the core conductive layer or sensing layer. Although metal materials possess good conductivity and mechanical strength, their inherent defects are significant: metal core fibers have high density and poor flexibility, making them prone to plastic deformation or even breakage under repeated bending or stretching conditions, leading to a decline in sensing performance; at the same time, metal materials have poor chemical stability and are easily oxidized and degraded in humid or corrosive environments. In addition, the rigidity of metal fibers makes them poorly compatible with the mechanical properties of human skin or flexible substrates, limiting their application in wearable devices. In recent years, researchers have attempted to use non-metallic materials (such as carbon fibers and conductive polymers) to replace metals, but single material systems often struggle to simultaneously meet the requirements of high sensitivity, wide sensing range, and long-term stability.

[0004] At the manufacturing process level, existing smart fiber manufacturing technologies largely rely on complex processing equipment and multi-step molding processes. For example, the most common method for manufacturing metal-core sensing fibers is the fused die pressing method. Other methods include manufacturing metal-core piezoelectric fibers through dip coating, hydrothermal extrusion, and coaxial electrospinning to create piezoelectric bending sensors for airflow velocity sensing. Electrowetting-assisted dry spinning is also used to produce metal-core piezoelectric fibers. These methods are not only energy-intensive and have long production cycles, but are also prone to performance fluctuations due to poor interlayer bonding. For instance, the multilayer piezoelectric fiber preparation method proposed in patent CN109554814A requires precise coating and high-temperature sintering to achieve functional layer stacking, resulting in low process tolerance and high equipment costs. Furthermore, traditional processes impose stringent requirements on the thermal stability and rheological properties of materials, limiting the application expansion of novel functional materials. How to achieve rapid and low-cost preparation of high-performance composite fibers has become a critical technological bottleneck that the industry urgently needs to overcome.

[0005] In terms of sensing performance, existing smart fibers generally have limitations in both dynamic and static sensing capabilities. Sensing fibers constructed from single piezoresistive or piezoelectric materials often only respond to dynamic force signals (such as vibration and impact), while lacking sufficient sensitivity to static forces (such as continuous pressure and deformation), or exhibiting signal drift issues. For example, piezoresistive fibers based on carbon nanotubes are prone to resistance baseline drift under static pressure due to creep effects; while piezoelectric fibers (such as PVDF), although sensitive to dynamic strain, cannot capture static force information. Furthermore, the sensing signals of traditional fibers are easily affected by environmental temperature and humidity interference, and their long-term stability is insufficient to meet the requirements of high-precision scenarios such as medical monitoring or industrial inspection. Therefore, developing composite fiber structures that combine dynamic and static sensing, wideband response, and resistance to environmental interference is key to improving the practicality of smart fibers.

[0006] To address the aforementioned issues, some studies have attempted to optimize sensing performance through material composites and structural design. For example, patent CN112301500A proposes coating a metal wire surface with a piezoresistive / piezoelectric dual-layer structure to broaden the sensing range. However, the rigidity of the metal core leads to a decrease in fiber flexibility, and the interlayer interface is prone to peeling and failure after repeated deformation. Another study (Advanced Materials, 2021) uses a hollow fiber embedded with liquid metal to improve flexibility, but the complex encapsulation process and the risk of liquid metal leakage have hindered its industrialization. Therefore, existing technologies have not effectively solved the problem of synergistic optimization of materials, structure, and processes, and a new solution that can balance high performance, low cost, and ease of manufacturing is urgently needed.

[0007] In summary, the further development of smart sensing fibers faces three core challenges: First, how to overcome the mechanical performance limitations of metal core materials and achieve a balance between high strength, lightweight, and flexibility through innovation in non-metallic materials; second, how to simplify the preparation process of composite fibers and develop efficient molding technologies that do not require complex equipment; and third, how to achieve accurate sensing of dynamic and static forces and improve signal stability through multi-physical effect coupling (such as piezoresistive-piezoelectric synergy). Breakthroughs in these technological bottlenecks will directly promote the large-scale application of smart fibers in wearable health monitoring, robotic tactile sensing, and smart textiles. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a composite fiber with dynamic and static sensing functions based on heat shrinking technology and a rapid preparation method thereof.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A composite fiber based on heat-shrink technology with dynamic and static sensing functions has a core-shell structure, consisting of a metal core layer, a piezoelectric layer, a first conductive layer, a piezoresistive layer, and an insulating protective layer from the inside out. The piezoelectric layer is a piezoelectric heat-shrinkable tube heat-shrinkable coated on the outer surface of the metal core layer. The first conductive layer is a conductive paint / adhesive sprayed onto the surface of the piezoelectric heat-shrinkable tube. The piezoresistive layer is a piezoresistive heat-shrinkable tube heat-shrinkable coated on the outside of the first conductive layer. The insulating protective layer is an insulating heat-shrinkable tube heat-shrinkable coated on the outside of the conductive paint / adhesive.

[0010] A composite fiber with dynamic and static sensing function based on heat shrinking technology has a core-shell structure, consisting of a fiber core layer, a piezoresistive layer, a second conductive layer, a piezoelectric layer, a first conductive layer, and an insulating protective layer from the inside out. The piezoresistive layer is a piezoresistive heat shrink tube heat-shrinkable and coated on the outside of the fiber core layer. The second conductive layer is a conductive paint / adhesive sprayed onto the surface of the piezoresistive heat shrink tube. The piezoelectric layer is a piezoelectric heat shrink tube heat-shrinkable and coated on the outer surface of the second conductive layer. The first conductive layer is a conductive paint / adhesive sprayed onto the surface of the piezoelectric heat shrink tube. The insulating protective layer is an insulating heat shrink tube heat-shrinkable and coated on the outside of the conductive paint / adhesive.

[0011] The piezoelectric heat shrink tubing is any one of PVDF tubing, odd-numbered nylon tubing, or aromatic polyurea tubing.

[0012] The insulating heat shrink tubing is any one of EPDM heat shrink tubing, cross-linked PEEK heat shrink tubing, polytetrafluoroethylene (PTFE) heat shrink tubing, or silicone rubber heat shrink tubing.

[0013] The piezoresistive heat shrink tubing is any one of polyaniline conductive polymer tubing, polypyrrole conductive polymer tubing, cross-linked PA66 tubing, or metal-based composite tubing.

[0014] The metal core layer is a solid core or a hollow core composed of metal.

[0015] The fiber core layer is a solid core or a hollow core composed of non-metallic materials.

[0016] A rapid preparation method for the composite fiber with dynamic and static sensing function based on the heat shrinking process, comprising the following steps: Step 1: Install a piezoelectric heat shrink tubing over the metal core layer. Select a piezoelectric heat shrink tubing that is compatible with the metal core layer based on the shrinkage ratio of the piezoelectric heat shrink tubing. Step 2: Place the piezoelectric heat shrink tubing on the outside of the metal core layer, and by setting the temperature of the hot air gun to 150℃-175℃, at a distance of 5-10 cm from the piezoelectric heat shrink tubing, at a sweeping speed of 10-15 cm / s, heat shrink the piezoelectric heat shrink tubing onto the outer surface of the metal core layer, and the two are seamlessly and tightly bonded together to obtain piezoelectric fibers. Step 3: Place the piezoelectric fiber prepared in Step 2 into a heating furnace for heating. Set the heating furnace temperature rise rate to 1℃-5℃ per minute to ensure that the piezoelectric heat shrink tube achieves uniform heat shrinkage behavior across the entire cross-section. Step 4: After the piezoelectric heat shrink tubing from Step 3 has cooled to room temperature naturally, a conductive film is uniformly coated on its surface as the first conductive layer. Step 5: Based on the shrinkage ratio of the piezoresistive heat shrink tubing, select a piezoresistive heat shrink tubing that is compatible with the heat-shrinked piezoelectric heat shrink tubing. Step 6: Place the piezoresistive heat shrink tubing on the outside of the first conductive layer, and by setting the temperature of the hot air gun to 80℃-150℃, at a sweeping speed of 10-15 cm / s within a range of 5-10 cm from the piezoresistive heat shrink tubing, heat shrink the piezoresistive heat shrink tubing onto the outer surface of the heat shrink tubing, and ensure that the two are seamlessly and tightly bonded, thus obtaining the piezoelectric-piezoresistive heat shrink tubing. Step 7: Place the piezoelectric-piezoresistive heat shrink tubing prepared in Step 6 into a heating furnace for heating. Set the temperature rise rate of the heating furnace to ensure that the piezoresistive heat shrink tubing achieves uniform heat shrinkage behavior across the entire cross-section. Step 8: After the piezoresistive heat shrink tubing from Step 7 has cooled to room temperature naturally, an insulating heat shrink tubing is installed over the piezoresistive heat shrink tubing. Considering the shrinkage ratio of the insulating heat shrink tubing, an insulating heat shrink tubing that is compatible with the heat-shrinked piezoresistive heat shrink tubing is selected. Step 9: Place the insulating heat shrink tubing over the outside of the piezoresistive heat shrink tubing, and by setting the temperature of the hot air gun to 135℃-150℃, at a sweeping speed of 10-15 cm / second within a range of 5-10 cm from the insulating heat shrink tubing, heat shrink the insulating heat shrink tubing onto the outer surface of the piezoresistive layer, and ensure that the two are seamlessly and tightly bonded together, to obtain a metal core piezoelectric-piezoresistive composite fiber. Step 10: Place the metal core piezoelectric-piezoresistive composite fiber prepared in Step 9 into a heating furnace for heating. Set the temperature rise rate of the heating furnace to 1°C-3°C per minute to ensure that the metal core piezoelectric-piezoresistive composite fiber achieves uniform thermal shrinkage behavior across the entire cross-section. Step 11: After the metal core piezoelectric-piezoresistive composite fiber from Step 10 has cooled naturally to room temperature, it can be removed, and the manufacturing process is complete.

[0017] A rapid preparation method for the composite fiber with dynamic and static sensing function based on the heat shrinking process, characterized by comprising the following steps: Step 1: Install a pressure resistance heat shrink tubing over the fiber core layer. Select a pressure resistance heat shrink tubing that is compatible with the fiber core layer based on the shrinkage ratio of the heat shrink tubing. Step 2: Place the piezoresistive heat shrink tubing on the outside of the fiber core layer, and by setting the temperature of the hot air gun to 80℃-150℃, at a sweeping speed of 10-15 cm / second within a range of 5-10 cm from the piezoresistive heat shrink tubing, heat shrink the piezoresistive heat shrink tubing onto the outer surface of the fiber core layer, and ensure that the two are seamlessly and tightly bonded. Step 3: Place the piezoresistive heat shrink tubing made in Step 2 into a heating furnace for a secondary heating process. Set the temperature rise rate of the heating furnace to ensure that the piezoresistive heat shrink tubing achieves uniform heat shrinkage behavior across the entire cross-section. Step 4: After the piezoresistive heat shrink tubing from Step 3 has cooled to room temperature naturally, a conductive film is uniformly coated on the surface of the piezoresistive heat shrink tubing as a second conductive layer. Step 5: After completing Step 4, install a piezoelectric heat shrink tubing over the piezoresistive heat shrink tubing. Select a piezoelectric heat shrink tubing that is compatible with the piezoresistive heat shrink tubing based on the shrinkage ratio of the piezoelectric heat shrink tubing. Step 6: Place the piezoelectric heat shrink tubing on the outside of the second conductive layer, and by setting the temperature of the hot air gun to 150℃-175℃, at a sweeping speed of 10-15 cm / second within a range of 5-10 cm from the piezoelectric heat shrink tubing, heat shrink the piezoelectric heat shrink tubing to the outer surface of the second conductive layer, and the two are seamlessly and tightly bonded together, to obtain the piezoresistive-piezoelectric heat shrink tubing. Step 7: Place the piezoresistive-piezoelectric heat shrink tubing prepared in Step 6 into a heating furnace for heating. Set the temperature rise rate of the heating furnace to 1°C-5°C per minute to ensure that the piezoresistive-piezoelectric heat shrink tubing achieves uniform heat shrinkage behavior across the entire cross-section. Step 8: After the piezoresistive-piezoelectric heat shrink tubing from Step 7 has cooled naturally to room temperature, a conductive film is uniformly coated on its surface as the first conductive layer. Step 9: After completing Step 8, install an insulating heat shrink tubing over the piezoresistive-piezoelectric heat shrink tubing. Select an insulating heat shrink tubing that is compatible with the piezoresistive-piezoelectric heat shrink tubing according to the shrinkage ratio of the insulating heat shrink tubing. Step 10: Place the insulating heat shrink tubing over the outside of the piezoresistive-piezoelectric heat shrink tubing, and by setting the temperature of the hot air gun to 135℃-150℃, at a sweeping speed of 10-15 cm / s within a range of 5-10 cm from the insulating heat shrink tubing, heat shrink the insulating heat shrink tubing to the outer surface of the first conductive layer, and ensure that the two are seamlessly and tightly bonded together, to obtain a non-metallic core piezoresistive-piezoelectric composite fiber. Step 11: Place the non-metallic core piezoresistive-piezoelectric composite fiber prepared in Step 10 into a heating furnace for heating. Set the temperature rise rate of the heating furnace to 1℃-3℃ per minute to ensure that the non-metallic core piezoresistive-piezoelectric composite fiber achieves uniform thermal shrinkage behavior across the entire cross-section. Step 12: After the non-metallic core piezoresistive-piezoelectric composite fiber from Step 11 has cooled naturally to room temperature, it is removed, and the manufacturing process is complete.

[0018] The beneficial effects of this invention are: The composite coaxial multilayer functional structure integrates dynamic (piezoelectric effect) and static (piezoresistive effect) sensing functions into a single fiber, breaking through the sensing limitations of traditional single-material or single-physical-effect fibers, and realizing the synchronous detection of broadband (dynamic and static) force and motion signals.

[0019] Signal stability has been optimized. The synergistic design of the conductive layer and the piezoresistive / piezoelectric layer enhances the efficiency of electrical signal transmission and reduces environmental interference. At the same time, the insulating protective layer improves the durability and resistance to environmental erosion of the fiber.

[0020] This interlayer bonding technology eliminates the need for complex equipment. It uses heat-shrinkable functional tubing (piezoresistive, piezoelectric, and insulating tubing) directly fitted onto the core substrate. A heat-shrink process achieves a tight bond between the functional layers, avoiding complex processes such as traditional multi-layer melt co-extrusion, chemical deposition, or vacuum coating, significantly reducing equipment dependence and manufacturing costs. Conductive pathways are rapidly constructed through a spray coating process, simplifying process steps, improving production efficiency, and making it suitable for mass production.

[0021] The piezoresistive-piezoelectric dual-mode sensing mechanism uses a piezoresistive layer (such as conductive polymer tubes made of polyaniline, polypyrrole, etc., cross-linked PA66 tubes, and metal-based composite tubes) to sense static pressure and deformation through resistance changes, while a piezoelectric layer (such as PVDF tubes, odd-numbered nylon tubes, or aromatic polyurea tubes) captures dynamic vibrations and instantaneous impacts through charge output. The dual-mode synergy significantly broadens the sensing range and sensitivity.

[0022] Replacing traditional metals (such as copper and silver) with high-performance non-metallic materials such as Kevlar, PEEK, and PA66 as the fiber core layer significantly improves the fiber's tensile strength, flexibility, abrasion resistance, and fatigue resistance, while reducing fiber weight. This solves problems such as high fiber density, easy oxidation and breakage, and poor compatibility with flexible substrates associated with metal core fibers. Solid or hollow core layer designs are supported; hollow structures can further reduce weight or integrate other functional materials (such as fluid sensing media), expanding application scenarios. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the specific manufacturing process of Embodiment 1 of the present invention.

[0024] Figure 2 This is a schematic diagram of the structure of a metal-core piezoelectric-piezoresistive composite fiber.

[0025] Figure 3 These are the test results of the voltage sensed by the metal core piezoelectric-piezoresistive composite fiber of the present invention under different pressures.

[0026] Figure 4 The results are the voltage sensing test results of the metal core piezoelectric-piezoresistive composite fiber of this invention under different vibrations.

[0027] Figure 5 This is a flowchart illustrating the specific manufacturing process of Embodiment 2 of the present invention.

[0028] Figure 6 These are schematic diagrams of the structure of a non-metallic core piezoelectric-piezoresistive composite fiber, where a is a schematic diagram of the solid cross-section of the non-metallic core coaxial composite piezoelectric-piezoresistive fiber, b is a schematic diagram of the hollow cross-section of the non-metallic core coaxial composite piezoelectric-piezoresistive fiber, c is a schematic diagram of the cross-section of the non-metallic core layer and the piezoelectric layer combined into a non-metallic core coaxial composite piezoelectric-piezoresistive fiber, d is a schematic diagram of the cross-section of the non-metallic core coaxial composite piezoelectric fiber, and e is a schematic diagram of the cross-section of the non-metallic core coaxial composite piezoelectric fiber.

[0029] Figure 7 This is a comparative curve of the measured stress and strain of the sensing composite fiber made of the metallic copper core and the non-metallic Kevlar core of the present invention.

[0030] Figure 8 This is a force-resistance relationship test curve of the non-metallic piezoelectric-piezoresistive composite fiber PA66 coated with conductive silver paint according to the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1 like Figure 2As shown, this invention discloses a metal-core piezoelectric-piezoresistive composite fiber, which has a core-shell structure, consisting of a metal core layer 7, a piezoelectric layer 4, a first conductive layer 5, a piezoresistive layer 2, and an insulating protective layer 6, arranged sequentially from the inside out. The piezoelectric layer 4 is a piezoelectric heat-shrinkable tube heat-shrinkable coated on the outer surface of the metal core layer 7. The first conductive layer 5 is a conductive paint / adhesive sprayed onto the surface of the piezoelectric heat-shrinkable tube. The piezoresistive layer 2 is a piezoresistive heat-shrinkable tube heat-shrinkable coated on the outside of the first conductive layer 5. The insulating protective layer is an insulating heat-shrinkable tube heat-shrinkable coated on the outside of the conductive paint / adhesive. The piezoelectric layer 4 is any one of PVDF tube, odd-numbered nylon tube, or aromatic polyurea that is heat-shrinkably coated on the outer surface of the conductive layer; the first conductive layer is any one of conductive silver paint, epoxy conductive adhesive, polyurethane conductive adhesive, or anisotropic conductive adhesive; the insulating protective layer is an insulating heat-shrinkable tube that is heat-shrinkably coated on the outside of the conductive layer, such as EPDM heat-shrinkable tube, cross-linked PEEK heat-shrinkable tube, polytetrafluoroethylene PTFE heat-shrinkable tube, or silicone rubber heat-shrinkable tube; and the piezoresistive layer is any one of piezoresistive materials such as conductive polymer tubes like polyaniline or polypyrrole, cross-linked PA66 tube, or metal-based composite tube that is heat-shrinkably coated on the outer surface of the fiber core layer.

[0033] The metal core layer is a solid core or a hollow core composed of metal.

[0034] like Figure 1 As shown, this invention also discloses a rapid preparation method for the above-mentioned composite fiber with dynamic and static sensing functions based on heat shrinking process, which includes the following steps: Step 1: Install PVDF heat shrink tubing over the copper core. Given that the shrinkage ratio of PVDF heat shrink tubing ranges from 2:1 to 3:1, select a PVDF heat shrink tubing that is compatible with the copper core. Step 2: Place the PVDF tube on the outside of the metal core layer, and by setting the hot air gun temperature to 150℃-175℃, at a sweeping speed of 10-15 cm / s within a range of 5-10 cm from the piezoelectric tube, heat shrink the piezoelectric tube onto the outer surface of the metal core, and ensure that the two are seamlessly and tightly bonded. Step 3: Place the piezoelectric fiber prepared in Step 2 into a heating furnace for heating. Set the heating furnace temperature rise rate to 1℃-5℃ per minute to ensure that the piezoelectric heat shrink tube achieves uniform heat shrinkage behavior across the entire cross-section. Step 4: After the piezoelectric heat shrink tubing from Step 3 has cooled to room temperature naturally, coat its surface with a layer of conductive silver paint evenly. Step 5: Given that the shrinkage ratio range of cross-linked PA66 heat shrink tubing is 2:1-4:1, select a piezoresistive heat shrink tubing that is compatible with the heat-shrinked piezoelectric heat shrink tubing. Step 6: Place the cross-linked PA66 tube on the outside of the piezoelectric layer, and by setting the hot air gun temperature to 80℃-150℃, at a sweeping speed of 10-15 cm / s within a range of 5-10 cm from the piezoresistive heat shrink tube, heat shrink the piezoresistive heat shrink tube onto the outer surface of the piezoelectric heat shrink tube, and ensure that the two are seamlessly and tightly bonded. Step 7: Place the piezoelectric-piezoresistive heat shrink tubing prepared in Step 6 into a heating furnace for heating. Set the temperature rise rate of the heating furnace to 5℃-20℃ per minute for small heating furnaces and 1℃-5℃ per minute for large industrial heating furnaces to ensure that the cross-linked PA66 heat shrink tubing achieves uniform heat shrinkage behavior across the entire cross-section. Step 8: After the piezoresistive heat shrink tubing from Step 7 has cooled naturally to room temperature, an insulating heat shrink tubing is then fitted over the piezoresistive heat shrink tubing. Given that the shrinkage ratio of the insulating heat shrink tubing is in the range of 2:1, an insulating heat shrink tubing suitable for the compressed piezoresistive heat shrink tubing is selected. Step 9: Place the insulating heat shrink tubing over the outside of the piezoresistive heat shrink tubing, and by setting the temperature of the hot air gun to 135℃-150℃, at a distance of 5-10 cm from the insulating heat shrink tubing, use a sweeping speed of 10-15 cm / second to heat shrink the insulating heat shrink tubing onto the outer surface of the piezoresistive layer, ensuring a seamless and tight fit between the two. Step 10: Place the metal core piezoelectric-piezoresistive composite fiber prepared in Step 9 into a heating furnace for heating. Set the temperature rise rate of the heating furnace to 1°C-3°C per minute to ensure that the metal core piezoelectric-piezoresistive composite fiber achieves uniform thermal shrinkage behavior across the entire cross-section. Step 11: After the piezoelectric-piezoresistive composite fiber from Step 10 has cooled naturally to room temperature, it can be removed, and the manufacturing process is complete.

[0035] The above manufacturing process can also be simplified to produce metal core piezoelectric composite fibers or metal core piezoresistive composite fibers according to actual needs.

[0036] See Figure 3 The test results of the voltage sensing of the metal copper core PVDF piezoelectric composite fiber prepared by this method under different pressures (tested 10 times at the same location under the same pressure) were used to test the piezoelectric memory function and pressure sensing performance of the PVDF piezoelectric heat shrink tubing after heat shrinking. The results show that the metal core thermoplastic piezoelectric fiber manufactured by heat shrinking has good piezoelectric performance, and the pressure and piezoelectric sensing are linearly related within a certain range.

[0037] See Figure 4 The test results of voltage sensing of different vibrations by the PVDF piezoelectric composite fiber with copper core prepared by this method indicate that the thermoplastic piezoelectric fiber with metal core manufactured by heat shrinking method has a stable vibration sensing capability.

[0038] Example 2 like Figure 6As shown, this invention discloses a non-metallic core piezoelectric composite fiber with a core-shell structure, comprising, from the inside out, a fiber core layer 1 (non-metallic core layer), a piezoresistive layer 2, a conductive layer 3, a piezoelectric layer 4, a first conductive layer 5, and an insulating protective layer 6. The fiber core layer is a solid or hollow core composed of non-metals (such as Kevlar, PEEK, PA66, or carbon nanotubes). The piezoresistive layer is a piezoresistive material, such as polyaniline, polypyrrole, or other conductive polymer tubes, or cross-linked PA66 tubes, heat-shrinkably coated onto the outer surface of the fiber core layer. The metal-based composite tube, wherein the conductive layer and the first conductive layer are conductive paint or adhesive (conductive silver paint, epoxy conductive adhesive, polyurethane conductive adhesive, anisotropic conductive adhesive, etc.) sprayed on the surface of the piezoresistive layer, the piezoelectric layer is PVDF tube, odd-numbered nylon tube, or aromatic polyurea tube, etc., which are heat-shrinkable and coated on the outer surface of the conductive layer, and the insulating protective layer is insulating heat-shrinkable tubing such as EPDM heat-shrinkable tubing, cross-linked PEEK heat-shrinkable tubing, polytetrafluoroethylene PTFE heat-shrinkable tubing, silicone rubber heat-shrinkable tubing, etc., which are heat-shrinkable and coated on the outside of the conductive layer.

[0039] Replacing traditional metals (such as copper and silver) with high-performance non-metallic materials such as Kevlar, PEEK, and PA66 as the fiber core layer significantly improves the fiber's tensile strength, flexibility, abrasion resistance, and fatigue resistance, while reducing fiber weight. This solves problems such as high fiber density, easy oxidation and breakage, and poor compatibility with flexible substrates associated with metal core fibers. Solid or hollow core layer designs are supported; hollow structures can further reduce weight or integrate other functional materials (such as fluid sensing media), expanding application scenarios.

[0040] like Figure 5 As shown, the present invention also provides a rapid preparation method for the above-mentioned composite fiber with dynamic and static sensing function based on heat shrinking process, which includes the following steps: Step 1: Install a pressure resistance heat shrink tubing over the fiber core layer. Select a pressure resistance heat shrink tubing that is compatible with the fiber core layer according to the shrinkage ratio of the pressure resistance heat shrink tubing. Use cross-linked PA66 heat shrink tubing as the pressure resistance heat shrink tubing, with a shrinkage ratio range of 2:1-4:1. Step 2: Place the piezoresistive heat shrink tubing on the outside of the fiber core layer, and by setting the temperature of the hot air gun to 80℃-150℃, at a sweeping speed of 10-15 cm / second within a range of 5-10 cm from the piezoresistive heat shrink tubing, heat shrink the piezoresistive heat shrink tubing onto the outer surface of the fiber core layer, and ensure that the two are seamlessly and tightly bonded. Step 3: Place the piezoresistive heat shrink tubing made in Step 2 into a heating furnace for a secondary heating process. Set the temperature rise rate of the heating furnace to 5℃-20℃ per minute for small heating furnaces and 1℃-5℃ per minute for large industrial heating furnaces to ensure that the piezoresistive heat shrink tubing achieves uniform heat shrinkage behavior across the entire cross-section. Step 4: After the piezoresistive heat shrink tubing from Step 3 has cooled to room temperature naturally, a conductive film is uniformly coated on the surface of the piezoresistive heat shrink tubing as a second conductive layer. Step 5: After completing Step 4, install a piezoelectric heat shrink tubing over the piezoresistive heat shrink tubing. Select a piezoelectric heat shrink tubing that is compatible with the piezoresistive heat shrink tubing based on its shrinkage ratio. Use PVDF tubing as the piezoelectric heat shrink tubing. Given that the shrinkage ratio of PVDF tubing is in the range of 2:1-3:1, select a PVDF tubing that is compatible with the piezoresistive heat shrink tubing. Step 6: Place the piezoelectric heat shrink tubing on the outside of the second conductive layer, and by setting the hot air gun temperature to 150℃-175℃, at a distance of 5-10 cm from the piezoelectric heat shrink tubing, at a sweeping speed of 10-15 cm / s, heat shrink the piezoelectric heat shrink tubing onto the outer surface of the piezoresistive layer, and ensure that the two are seamlessly and tightly bonded together, thus obtaining the piezoresistive-piezoelectric heat shrink tubing. Step 7: Place the piezoresistive-piezoelectric heat shrink tubing prepared in Step 6 into a heating furnace for heating. Set the temperature rise rate of the heating furnace to 1°C-5°C per minute to ensure that the piezoresistive-piezoelectric heat shrink tubing achieves uniform heat shrinkage behavior across the entire cross-section. Step 8: After the piezoresistive-piezoelectric heat shrink tubing from Step 7 has cooled naturally to room temperature, a conductive film is uniformly coated on its surface as the first conductive layer. Step 9: After completing Step 8, install an insulating heat shrink tubing over the piezoresistive-piezoelectric heat shrink tubing. Select an insulating heat shrink tubing that is compatible with the piezoresistive-piezoelectric heat shrink tubing according to the shrinkage ratio of the insulating heat shrink tubing. Step 10: Place the insulating heat shrink tubing over the outside of the piezoresistive-piezoelectric heat shrink tubing, and by setting the temperature of the hot air gun to 135℃-150℃, at a sweeping speed of 10-15 cm / s within a range of 5-10 cm from the insulating heat shrink tubing, heat shrink the insulating heat shrink tubing to the outer surface of the first conductive layer, and ensure that the two are seamlessly and tightly bonded together, thus obtaining the piezoresistive-piezoelectric composite fiber. Step 11: Place the piezoresistive-piezoelectric composite fiber prepared in Step 10 into a heating furnace for heating. Set the heating furnace temperature rise rate to 1℃-3℃ per minute to ensure that the piezoresistive-piezoelectric composite fiber achieves uniform thermal shrinkage behavior across the entire cross-section. Step 12: After the piezoresistive-piezoelectric composite fiber from Step 11 has cooled naturally to room temperature, it can be removed, and the manufacturing process is complete.

[0041] Figure 7This is a comparative curve of the stress-strain measured values ​​of the sensing composite fiber made with a metallic copper core and a non-metallic Kevlar core according to the present invention. The experimental results show that replacing the metallic copper core with Kevlar fiber in the composite fiber can significantly improve the tensile strength (in this experiment, the tensile strength of the Kevlar core composite fiber is 6 times that of the metallic copper core composite fiber), flexibility, and fatigue resistance. At the same time, the specific strength of Kevlar fiber is 5 times that of steel wire, and its density is only 1 / 6 that of copper, which greatly reduces the weight of the composite fiber. The non-metallic core sensing composite fiber of the present invention solves the problems of high density, easy oxidation and breakage, and poor compatibility with flexible substrates of metallic core sensing fibers.

[0042] Figure 8 This is a force-resistance relationship test curve of the non-metallic piezoelectric-piezoresistive composite fiber PA66 coated with conductive silver paint according to the present invention. It shows that the piezoresistive fiber manufactured by the heat shrinking process of the present invention has good piezoresistive performance, and the pressure and piezoresistive perception are linearly related within a certain range.

[0043] It supports flexible selection of non-metallic core layers to adapt to different application requirements (such as high elasticity, ultralight, or high strength scenarios). At the same time, the heat shrinking process has low requirements for material thermal stability and can be compatible with more functional materials. It enhances the interfacial bonding. The heat shrinking process achieves interlayer bonding through physical shrinkage rather than chemical bonding, avoiding the risk of interfacial delamination in traditional processes and improving the structural reliability of fibers under repeated deformation.

[0044] In summary, the composite fiber of this invention, through the deep integration of material innovation (non-metallic core layer), structural innovation (coaxial multifunctional layer), and process innovation (thermal shrinkage rapid prototyping), solves the bottlenecks of traditional smart fibers in terms of mechanical properties, sensing dimensions, manufacturing costs, and environmental adaptability, providing a high-performance, low-cost sensing fiber solution for fields such as smart wearables, robotic tactile sensing, and health monitoring.

[0045] The embodiments should not be regarded as limitations on the present invention, but any improvements made based on the spirit of the present invention should be within the protection scope of the present invention.

Claims

1. A composite fiber with dynamic and static sensing functions based on heat shrinking technology, characterized in that: It has a core-shell structure, consisting of a fiber core layer (1), a piezoresistive layer (2), a second conductive layer (3), a piezoelectric layer (4), a first conductive layer (5), and an insulating protective layer (6) from the inside out. The piezoresistive layer (2) is a piezoresistive heat-shrinkable tube heat-shrinkable coated on the outside of the fiber core layer (1). The second conductive layer (3) is a conductive paint / adhesive sprayed onto the surface of the piezoresistive heat-shrinkable tube. The piezoelectric layer (4) is a piezoelectric heat-shrinkable tube heat-shrinkable coated on the outside of the second conductive layer (3). The first conductive layer (5) is a conductive paint / adhesive sprayed onto the surface of the piezoelectric heat-shrinkable tube. The insulating protective layer (6) is an insulating heat-shrinkable tube heat-shrinkable coated on the outside of the conductive paint / adhesive. The piezoelectric heat shrink tubing is any one of PVDF tubing, odd-numbered nylon tubing, or aromatic polyurea tubing, and the piezoresistive heat shrink tubing is any one of polyaniline conductive polymer tubing, polypyrrole conductive polymer tubing, cross-linked PA66 tubing, or metal-based composite tubing.

2. The composite fiber with dynamic and static sensing function based on heat shrinking process according to claim 1, characterized in that: The insulating heat shrink tubing is any one of EPDM heat shrink tubing, cross-linked PEEK heat shrink tubing, polytetrafluoroethylene (PTFE) heat shrink tubing, or silicone rubber heat shrink tubing.

3. The composite fiber with dynamic and static sensing function based on heat shrinking process according to claim 1, characterized in that: The fiber core layer (1) is a solid core or hollow core composed of non-metallic materials.

4. A rapid preparation method for the composite fiber with dynamic and static sensing function based on the heat-shrinking process as described in claim 1, characterized in that: It includes the following steps: Step 1: The fiber core layer (1) is covered with a pressure resistance heat shrink tube. According to the shrinkage ratio of the pressure resistance heat shrink tube, a pressure resistance heat shrink tube that is compatible with the fiber core layer (1) is selected. Step 2: Place the pressure resistance heat shrink tube on the outside of the fiber core layer (1), and by setting the temperature of the hot air gun to 80℃-150℃, at a distance of 5-10 cm from the pressure resistance heat shrink tube, at a sweeping speed of 10-15 cm / second, heat shrink the pressure resistance heat shrink tube onto the outer surface of the fiber core layer (1), and the two are seamlessly and tightly bonded. Step 3: Place the piezoresistive heat shrink tubing made in Step 2 into a heating furnace for a secondary heating process. Set the temperature rise rate of the heating furnace to ensure that the piezoresistive heat shrink tubing achieves uniform heat shrinkage behavior across the entire cross-section. Step 4: After the piezoresistive heat shrink tubing from Step 3 has cooled to room temperature naturally, a conductive film is uniformly coated on the surface of the piezoresistive heat shrink tubing as the second conductive layer (3). Step 5: After completing Step 4, install a piezoelectric heat shrink tubing over the piezoresistive heat shrink tubing. Select a piezoelectric heat shrink tubing that is compatible with the piezoresistive heat shrink tubing based on the shrinkage ratio of the piezoelectric heat shrink tubing. Step 6: Place the piezoelectric heat shrink tube on the outside of the second conductive layer (3), and by setting the temperature of the hot air gun to 150℃-175℃, at a distance of 5-10 cm from the piezoelectric heat shrink tube, at a sweeping speed of 10-15 cm / s, heat shrink the piezoelectric heat shrink tube on the outer surface of the second conductive layer (3), and the two are seamlessly and tightly bonded together to obtain the piezoresistive-piezoelectric heat shrink tube. Step 7: Place the piezoresistive-piezoelectric heat shrink tubing prepared in Step 6 into a heating furnace for heating. Set the temperature rise rate of the heating furnace to 1°C-5°C per minute to ensure that the piezoresistive-piezoelectric heat shrink tubing achieves uniform heat shrinkage behavior across the entire cross-section. Step 8: After the piezoresistive-piezoelectric heat shrink tube from step 7 has cooled naturally to room temperature, a conductive film is uniformly coated on its surface as the first conductive layer (5). Step 9: After completing Step 8, install an insulating heat shrink tubing over the piezoresistive-piezoelectric heat shrink tubing. Select an insulating heat shrink tubing that is compatible with the piezoresistive-piezoelectric heat shrink tubing according to the shrinkage ratio of the insulating heat shrink tubing. Step 10: Place the insulating heat shrink tubing on the outside of the piezoresistive-piezoelectric heat shrink tubing, and by setting the temperature of the hot air gun to 135℃-150℃, at a distance of 5-10 cm from the insulating heat shrink tubing, at a sweeping speed of 10-15 cm / s, heat shrink the insulating heat shrink tubing on the outer surface of the first conductive layer (5), and the two are seamlessly and tightly bonded together to obtain a non-metallic core piezoresistive-piezoelectric composite fiber. Step 11: Place the non-metallic core piezoresistive-piezoelectric composite fiber prepared in Step 10 into a heating furnace for heating. Set the temperature rise rate of the heating furnace to 1℃-3℃ per minute to ensure that the non-metallic core piezoresistive-piezoelectric composite fiber achieves uniform thermal shrinkage behavior across the entire cross-section. Step 12: After the non-metallic core piezoresistive-piezoelectric composite fiber from Step 11 has cooled naturally to room temperature, it is removed, and the manufacturing process is complete.

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