Conductive fiber, conductive elastic piece and manufacturing method

Abstract

The invention discloses a conductive fiber, a conductive elastic piece and a manufacturing method, and belongs to the technical field of composite conductive structures. The conductive fiber comprises a fiber body and a conductive layer, and the conductive layer covers the fiber body; the fiber body comprises at least one section of bending unit, and the bending units are arranged at intervals or continuously. The conductive fiber serves as a main conductive channel, and compared with a traditional conductive adhesive depending on micron conductive particles, the number of interface electron jumping times can be reduced by 50% or above; the fiber body comprises at least one section of bending unit, the bending unit can be gradually straightened in the stretching process of the elastic matrix, and the situation that the conductive fiber is quickly straightened in the stretching process, elastic deformation is restrained or interface shear damage is caused is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite conductive structure, and particularly relates to a conductive fiber, a conductive elastic element and a manufacturing method. BACKGROUND

[0002] As the core material of emerging fields such as flexible electronics, wearable devices and intelligent sensors, the conductive elastic element realizes the dual characteristics of electrical conductivity and mechanical elasticity through the composite design of the elastic matrix and the conductive filler. In the current technical system, the elastic matrix needs to be optimized in flexibility and interface compatibility through graft modification, copolymerization control or plasticizer addition, and the conductive network construction depends on the load of the conductive filler above the percolation threshold. However, the introduction of high-concentration conductive filler will destroy the cross-linking structure of the polymer molecular chain, resulting in the reduction of the cross-linking density of the elastic matrix, the abnormal rise of the elastic modulus and the significant deterioration of the elongation at break, which makes the material show the tendency of brittleness or hardening. This mutual exclusion effect of electrical conductivity and elasticity seriously restricts the reliability of the conductive elastic element in the dynamic deformation scene, and becomes the key technical bottleneck restricting the industrial application of the conductive elastic element. SUMMARY

[0003] The present application provides a conductive fiber, a conductive elastic element and a manufacturing method to solve the problem that the electrical conductivity and elasticity are difficult to be considered in the conductive elastic element.

[0004] In a first aspect, the present application provides a conductive fiber, which comprises a fiber body and a conductive layer, and the conductive layer is arranged on the fiber body; the fiber body comprises at least one bending unit, and the bending units are arranged at intervals or continuously.

[0005] In some embodiments, the bending unit comprises at least one of a corrugated unit, a zigzag unit and an arc unit, the bending period length L of the bending unit is 0.1-0.2 mm, and the amplitude height H of the bending unit is 0.04-0.12 mm.

[0006] In some embodiments, the length of the fiber body is 0.3-0.5 mm, the diameter of the fiber body is 0.005-0.01 mm, the length-diameter ratio of the fiber body is 30-100, and the bending units are continuously distributed on the whole length of the fiber body.

[0007] In some embodiments, the fiber body comprises at least one of a polyimide fiber, a poly-p-phenylene terephthalamide fiber, a poly-p-phenylene benzobisoxazole fiber and a carbon fiber.

[0008] In some embodiments, the conductive layer comprises at least one of a silver layer, a copper layer, a nickel layer and a palladium layer, and the thickness of the conductive layer is 1-3 μm.

[0009] In a second aspect, the present application provides an electrically conductive elastic member, which comprises the electrically conductive fiber, the elastic matrix and the bridging conductor provided in the first aspect of the present application. The electrically conductive fiber and the bridging conductor are dispersed in the elastic matrix, and the electrically conductive fiber and the bridging conductor are in contact and connected together to form a continuous conductive network in the elastic matrix.

[0010] In some embodiments, the bridging conductor comprises micro-nano conductive particles or fibers; the micro-nano conductive particles or fibers comprise metalized multi-walled carbon nanotubes, and the metalized multi-walled carbon nanotubes comprise multi-walled carbon nanotubes and a metal layer. The multi-walled carbon nanotubes have a length of 10-30 μm and an outer diameter of 5-15 nm. The metal layer has a thickness of 0.5-2 μm, and the metal layer comprises a silver layer.

[0011] In some embodiments, the electrically conductive fiber accounts for 10-20 wt% of the mass of the electrically conductive elastic member; the bridging conductor accounts for 5-10 wt% of the mass of the electrically conductive elastic member; and the mass ratio of the electrically conductive fiber to the bridging conductor is (1-4):1.

[0012] In some embodiments, the elastic matrix comprises any one of thermosetting elastic material or thermoplastic elastic material.

[0013] In a third aspect, the present application provides a manufacturing method of an electrically conductive fiber, which comprises: treating a fiber bundle to obtain a fiber body with bending units; covering an electrically conductive layer on the surface of the fiber body to obtain the electrically conductive fiber.

[0014] In some embodiments, the step of treating the fiber bundle comprises: threading the fiber bundle into a gear jig; applying an initial pressure to the threaded fiber bundle; heating the fiber bundle to above the resin glass transition temperature; driving the gear jig to form an indentation on the fiber bundle, while continuously pulling the fiber bundle through the gear jig to obtain the fiber body with bending units.

[0015] In a fourth aspect, the present application provides a manufacturing method of an electrically conductive elastic member, which comprises: preparing the electrically conductive fiber provided in the first aspect or the second aspect or the third aspect of the present application; preparing a bridging conductor; The conductive fiber and the bridging conductive body are dispersed in an elastic matrix to process the conductive elastic member.

[0016] In the present application, the conductive fiber serves as a main conductive channel, which can reduce the number of interface electron hopping by more than 50% compared with the traditional conductive adhesive relying on micron conductive particles; the fiber body includes at least one bending unit, which can be gradually straightened during the stretching of the elastic matrix, thereby avoiding the rapid straightening of the conductive fiber during stretching, restricting the elastic deformation or causing interface shear damage. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0018] Figure 1 Structure diagram of the fiber body in some embodiments of the present application; Figure 2 Structure diagram of the fiber body in some other embodiments of the present application; Figure 3 Structure diagram of the fiber body in some other embodiments of the present application. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0020] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0021] "A and / or B" includes the following three combinations: only A, only B, and a combination of A and B.

[0022] In this application, the word "exemplary" is used to mean "serving as an example, instance, or illustration." Any implementation described as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations. The following description is presented to enable any person skilled in the art to make and use the application. Details are set forth in the following description for purpose of explanation. It should be appreciated that one of ordinary skill in the art will readily recognize that the application can be practiced without the use of these specific details. In other instances, well-known structures and processes have not been described in detail in order to avoid obscuring the description of the application. Thus, the present application is not intended to be limited by the embodiments shown, but is to be accorded with the widest scope consistent with the principles and features disclosed.

[0023] The performance of the conductive elastomer depends on the flexibility of the elastomer matrix, the interface compatibility, and the effective construction of the conductive network. Generally, the flexibility and compatibility of the matrix can be optimized by graft modification, copolymerization regulation, or the addition of plasticizers, while the conductive performance needs to be achieved by adding conductive fillers above the percolation threshold. However, high filler loading, while improving the conductivity, also brings a series of significant problems: Firstly, the introduction of high-concentration conductive fillers will destroy the cross-linking structure between polymer molecular chains, leading to a decrease in matrix cross-linking density, an abnormal increase in elastic modulus, and a significant decrease in elongation at break, thus making the material brittle or hardening, damaging its essential high-elasticity characteristics.

[0024] Secondly, too high a content of fillers will lead to their agglomeration in the elastomer matrix, destroying the uniform continuous conductive network formed and dividing it into isolated "conductive islands". Although the conductivity of the conductive elastomer depends on the electron tunneling effect, after the destruction of the conductive network, the distance that the electrons are forced to cross between the islands is much larger than the inter-particle distance within the network. Since the tunneling probability decays exponentially with distance, these wide inter-island gaps will introduce a huge tunneling resistance, becoming a bottleneck for the conductive path, thus greatly reducing the overall conductivity efficiency.

[0025] In addition, the long-term stability of the conductive elastomer made of such a high-filler system is often poor. Under repeated dynamic loads such as stretching and bending, the internal conductive fillers are prone to displacement or debonding, leading to a decrease in the continuity of the conductive network and a further increase in the interface, which is manifested as a significant increase in resistance and deterioration of electrical performance stability.

[0026] In a first aspect, the embodiment provides a conductive fiber, the conductive fiber comprising a fiber body and a conductive layer, the conductive layer being arranged on the fiber body; the fiber body comprising at least one bending unit, the bending units being arranged in a spaced manner or in a continuous manner.

[0027] The conductive fiber serves as a main conductive channel, and compared with a traditional conductive adhesive relying on micron conductive particles, the conductive fiber can reduce the number of interface electron hopping by more than 50%. The fiber body includes at least one bending unit, and the bending unit can be gradually straightened during the stretching of the elastic matrix; if a straight fiber is used, it is easy to be quickly straightened during stretching, which restricts the elastic deformation or causes interface shear damage, affecting the overall elasticity.

[0028] In some embodiments, the bending units are continuously distributed over the entire length of the fiber body, so that the conductive fiber as a whole forms a buffer space suitable for the stretching deformation of the elastic matrix, ensuring the overall elastic effect.

[0029] In some embodiments, the bending period length L of the bending unit is 0.1-0.2 mm, and the amplitude height H of the bending unit is 0.04-0.12 mm. The bending period length L refers to the axial length corresponding to a complete bending unit; the amplitude height H refers to the radial distance between the wave crest and the wave trough of the bending unit.

[0030] The bending unit in this size range can balance flexibility and elastic recovery force, effectively deform with the elastic matrix, and is not prone to irreversible plastic deformation, ensuring the durability of the conductive elastic part in repeated stretching-retraction cycles. During stretching, the conductive fiber can effectively maintain the continuity of the conductive path through the gradual unfolding of its small bending units, thereby making the resistance change rate smaller and more stable.

[0031] Specifically, the bending period length L is any one of 0.10 mm, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, 0.16 mm, 0.17 mm, 0.18 mm, 0.19 mm, 0.20 mm, or a range value between any two of them.

[0032] Specifically, the amplitude height H is any one of 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, 0.10 mm, 0.11 mm, 0.12 mm, or a range value between any two of them.

[0033] In some embodiments, the bending unit includes at least one of a corrugated unit, a fold line unit, and an arc line unit, so that the fiber body has a stretching and contracting space. Specifically, the types of bending units on the same conductive fiber can be the same or different. That is, the same conductive fiber can include two or three of a corrugated unit, a fold line unit, and an arc line unit, or only one of a corrugated unit, a fold line unit, and an arc line unit.

[0034] Specifically, the bending period length L and the amplitude height H of the bending units on the same conductive fiber can be consistent or different from each other. To simplify the process and facilitate production and processing, bending units of the same type and with the same size parameters can be used.

[0035] As shown in Figure 1 , the bending unit includes a wave unit, and the wave unit is continuously distributed over the entire length of the fiber body.

[0036] As shown in Figure 2 , the bending unit includes a fold line unit, and the fold line unit is continuously distributed over the entire length of the fiber body.

[0037] As shown in Figure 3 , the bending unit includes an arc line unit, and the arc line unit is continuously distributed over the entire length of the fiber body.

[0038] In some embodiments, the length of the fiber body is 0.3-0.5 mm, the diameter is 0.005-0.01 mm, and the length-diameter ratio is 30-100. The millimeter-level length of 0.3-0.5 mm of the fiber body makes it easy to disperse uniformly in the elastic matrix, avoids the problem of easy entanglement and clumping of long fibers, and ensures the smooth progress of the mixing and molding process. The extremely thin diameter endows the single fiber body with extremely high flexibility, enabling it to fully adapt to the deformation of the elastic matrix and bend and orient in a complex three-dimensional network without piercing or damaging the matrix structure. The high length-diameter ratio ensures that the single fiber can effectively lap in the matrix to form a broad three-dimensional conductive network. The length of the fiber body refers to the total unfolded length of the fiber body when it is straightened.

[0039] Specifically, the length of the fiber body is any one of 0.30 mm, 0.31 mm, 0.32 mm, 0.33 mm, 0.34 mm, 0.35 mm, 0.36 mm, 0.37 mm, 0.38 mm, 0.39 mm, 0.40 mm, 0.41 mm, 0.42 mm, 0.43 mm, 0.44 mm, 0.45 mm, 0.46 mm, 0.47 mm, 0.48 mm, 0.49 mm, 0.50 mm or a range value between any two of them.

[0040] Specifically, the diameter of the fiber body is any one of 0.005 mm, 0.006 mm, 0.007 mm, 0.008 mm, 0.009 mm, 0.010 mm or a range value between any two of them.

[0041] Specifically, the length-diameter ratio of the fiber body is any one of 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 or a range value between any two of them.

[0042] In some embodiments, the fiber body comprises at least one of polyimide fiber (PI fiber), poly-p-phenylene terephthalamide fiber (Kevlar fiber), poly-p-phenylene-benzobisoxazole fiber (PBO fiber), carbon fiber. Polyimide fiber, poly-p-phenylene terephthalamide fiber, poly-p-phenylene-benzobisoxazole fiber, carbon fiber are all high-performance fibers, which have high tensile strength and modulus, so that the prepared conductive fiber is not easy to break during processing and service, can withstand the stress generated by the repeated deformation of the elastic matrix, and ensures the durability and reliability of the conductive network under long-term dynamic use; and these fibers have high glass transition temperature, which can withstand the high temperature environment in the preparation process of the conductive layer, and maintain the integrity of the fiber structure and mechanical properties.

[0043] In some embodiments, the conductive layer comprises at least one of silver layer, copper layer, nickel layer, palladium layer; the thickness of the conductive layer is 1-3 μm. Due to the conductivity of the conductive layer, the contact resistance is extremely low, thereby forming a very stable and reliable three-dimensional conductive network. The thickness of the conductive layer is set to 1-3 μm, which can ensure the continuity and reliability of the plating layer, can provide stable high conductivity, and will not excessively sacrifice the flexibility of the fiber or significantly increase the cost, which meets the requirements of the conductive elastic member for dynamic stability and durability.

[0044] Specifically, the thickness of the conductive layer is any one of 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm or a range value between any two of them.

[0045] In a second aspect, the present embodiment provides a conductive elastic member, comprising the conductive fiber provided by the first aspect of the present application, an elastic matrix and a bridging conductive body; the conductive fiber and the bridging conductive body are dispersed in the elastic matrix, and the conductive fiber and the bridging conductive body are in contact and connected, and together form a continuous conductive network in the elastic matrix.

[0046] The continuous conductive network formed by the conductive fiber and the bridging conductive body can significantly reduce the critical addition amount of the conductive filler, effectively inhibit the elastic degradation of the matrix caused by excessive filler, so that the conductive elastic member has higher elastic modulus and lower percolation threshold while maintaining excellent conductivity; the conductive fiber comprises a bending unit, so that the conductive elastic member exhibits more stable resistance performance in the tensile cycle test; the conductivity attenuation is less after the aging test, the fiber and the elastic matrix interface have low peeling degree, and excellent durability and structural reliability are shown.

[0047] In some embodiments, the bridging conductors comprise micro-nano conductive particles or micro-nano conductive fibers; illustratively, the bridging conductors comprise metalized multi-walled carbon nanotubes, which comprise multi-walled carbon nanotubes (MWCNTs) and a metal layer; the multi-walled carbon nanotubes have a length of 10-30 μm and an outer diameter of 5-15 nm; the metal layer has a thickness of 0.5-2 μm, and the metal layer comprises a silver layer.

[0048] The multi-walled carbon nanotubes have a very high length-diameter ratio and a nanoscale diameter, can effectively infiltrate and fill the tiny gaps between the conductive fiber network, form a large number of conductive paths at a very low addition amount, and greatly reduce the percolation threshold of the system. The metal layer on the surface of the multi-walled carbon nanotubes and the conductive layer of the conductive fiber form a metal-metal contact, which can reduce the contact resistance and improve the electron transport efficiency. The metalized multi-walled carbon nanotubes have both the flexibility of carbon nanotubes and the ductility of metal, can better deform with the elastic matrix, are not easy to separate from the matrix in dynamic work, and ensure durability. The thickness of the silver layer is 0.5-2 μm, which can cover all defects and gaps on the surface of the MWCNTs, ensure the formation of a continuous and dense layer structure, realize complete metal conduction, and at the same time control the cost while retaining the flexibility of the MWCNTs.

[0049] Specifically, the length of the multi-walled carbon nanotubes is any one of 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm or a range value between any two of them.

[0050] Specifically, the outer diameter of the multi-walled carbon nanotubes is any one of 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm or a range value between any two of them.

[0051] Specifically, the thickness of the metal layer is any one of 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm or a range value between any two of them.

[0052] In some embodiments, the mass fraction of the conductive fibers in the conductive elastic member is 10-20 wt%; the mass fraction of the bridging conductors in the conductive elastic member is 5-10 wt%; and the mass ratio of the conductive fibers to the bridging conductors is (1-4):1.

[0053] The mass fraction of the conductive fiber in the conductive elastic member is 10 wt% to 20 wt%, and this amount ensures that the wave-shaped metalized fiber can serve as the main conductive network to form a continuous long-range conductive path in the elastic matrix.

[0054] The mass fraction of the bridging conductive body in the conductive elastic member is 5 wt% to 10 wt%, and this amount is intended to efficiently "bridge" the small gaps between adjacent main conductive fibers, repair network defects, and significantly reduce the contact resistance, so that the conductive network quickly reaches and exceeds the percolation threshold under a low total filler amount, achieving extremely high electrical conductivity.

[0055] The total filler amount of the conductive fiber and the bridging conductive body is not more than 30 wt%, which maximizes the high elasticity, low modulus, and good tensile properties of the elastic matrix itself while obtaining excellent electrical conductivity, solving the traditional contradiction between electrical conductivity and elasticity.

[0056] The mass ratio of the conductive fiber to the bridging conductive body is (1 to 4): 1, which ensures that there is a sufficient number of bridging conductive bodies to effectively connect the main conductive fibers and form a stable "trunk-bridge" type conductive network structure. The conductive network under this ratio can adapt to stress through the deformation of the conductive fiber and the nanoscale action of the bridging body, rather than direct fracture, thereby exhibiting more stable resistance performance and lower electrical conductivity decay after aging test.

[0057] Specifically, the mass fraction of the conductive fiber in the conductive elastic member is any one of 10.0 wt%, 10.5 wt%, 11.0 wt%, 11.5 wt%, 12.0 wt%, 12.5 wt%, 13.0 wt%, 13.5 wt%, 14.0 wt%, 14.5 wt%, 15.0 wt%, 15.5 wt%, 16.0 wt%, 16.5 wt%, 17.0 wt%, 17.5 wt%, 18.0 wt%, 18.5 wt%, 19.0 wt%, 19.5 wt%, 20.0 wt%, or a range value between any two of them.

[0058] Specifically, the mass fraction of the bridging conductive body in the conductive elastic member is any one of 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt%, 10.0 wt%, or a range value between any two of them.

[0059] Specifically, the mass ratio of the conductive fiber to the bridging conductive body is any one of 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or a range value between any two of them.

[0060] In some embodiments, the elastic material comprises a thermoset elastic material. Illustratively, the thermoset elastic material comprises at least one of silicone rubber, polyurethane rubber, epoxy-based elastomer, acrylate rubber.

[0061] In some embodiments, the elastic material comprises a thermoplastic elastic material. Illustratively, the thermoplastic elastic material comprises at least one of styrenic (such as SBS, SEBS), thermoplastic polyurethane (TPU), thermoplastic polyolefin (TPO, TPV), polyamide (TPAE).

[0062] In a third aspect, the embodiments provide a method for manufacturing a conductive fiber, comprising: treating the fiber bundle to obtain a fiber body with bending units; covering a conductive layer on the surface of the fiber body to obtain the conductive fiber.

[0063] In some embodiments, the step of treating the fiber body comprises: threading the fiber bundle into a gear jig; applying an initial pressure to the threaded fiber bundle; heating the fiber bundle to above the resin glass transition temperature; driving the gear jig to form an indentation on the fiber bundle while continuously pulling the fiber bundle through the gear jig to cut the fiber body with bending units.

[0064] Specifically, the initial pressure applied to the fiber body is 0.5-3 N. More specifically, the initial pressure applied to the fiber body is any one of 0.5 N, 0.6 N, 0.7 N, 0.8 N, 0.9 N, 1.0 N, 1.1 N, 1.2 N, 1.3 N, 1.4 N, 1.5 N, 1.6 N, 1.7 N, 1.8 N, 1.9 N, 2.0 N, 2.1 N, 2.2 N, 2.3 N, 2.4 N, 2.5 N, 2.6 N, 2.7 N, 2.8 N, 2.9 N, 3.0 N or a range value between any two of them.

[0065] Specifically, the fiber bundle is heated to above the resin glass transition temperature by blowing hot air on the fiber bundle.

[0066] In some embodiments, the step of covering a conductive layer on the surface of the fiber body comprises forming a conductive layer on the surface of the fiber body by a metallization process, the metallization process comprising a dry process and a wet process.

[0067] Specifically, the dry process includes a magnetron sputtering method, i.e., forming a metal plating layer on the surface of the fiber body by magnetron sputtering treatment, the metal plating layer including one or more of silver, copper, nickel, or palladium.

[0068] It should be noted that for PBO, Kevlar and other high-inert and smooth-surface fibers, in order to ensure the adhesion between the conductive layer and the fiber body, a transition layer can be added between the two. For example, in the dry process (magnetron sputtering method) of PBO or Kevlar fiber, a layer of chromium is first deposited as a transition layer. Specifically, the wet process includes sequentially performing swelling treatment, hydrolysis treatment, metal ion adsorption and reduction treatment, and electroplating or chemical plating treatment on the fiber body; wherein the metal ions include one or more of Ag + , Cu 2+ , Ni 2+ , Pd 2+ .

[0069] In a fourth aspect, the present embodiment provides a manufacturing method of the conductive elastic member, the manufacturing method comprising: preparing the conductive fiber provided in the first aspect and / or the second aspect and / or the third aspect of the present application; preparing the bridging conductive body provided in the second aspect of the present application; dispersing the conductive fiber and the bridging conductive body in the elastic matrix provided in the second aspect of the present application, and processing to obtain the conductive elastic member.

[0070] In some embodiments, the step of preparing the bridging conductive body provided in the second aspect of the present application comprises: oxidizing the multi-walled carbon nanotubes (MWCNTs) to introduce carboxyl groups on the surface of the multi-walled carbon nanotubes, to obtain carboxylated multi-walled carbon nanotubes; metalizing the carboxylated multi-walled carbon nanotubes to form a metal layer, the metal layer being disposed on the carboxylated multi-walled carbon nanotubes, to obtain metalized multi-walled carbon nanotubes.

[0071] Illustratively, the step of oxidizing the multi-walled carbon nanotubes (MWCNTs) comprises: soaking the multi-walled carbon nanotubes in a mixed solution of sulfuric acid and nitric acid at a volume ratio of 3:1, and reacting at 65 ℃ for 4h.

[0072] Illustratively, the step of metalizing the carboxylated multi-walled carbon nanotubes comprises: first soaking the carboxylated multi-walled carbon nanotubes in a solution containing 0.01-0.8 mol / L Ag + , Cu 2+ , Ni 2+ , or Pd 2+The metal ions are adsorbed by immersing the metal salt solution, and then the adsorbed metal ions are reduced by using sodium borohydride solution, stannous chloride solution, ascorbic acid solution, hydrazine hydrate or photocatalytic reduction method, followed by chemical silver plating or chemical copper plating.

[0073] In some examples, the step of metallizing the carboxylated multi-walled carbon nanotubes includes immersing the carboxylated multi-walled carbon nanotubes in a silver citrate ethanol solution with a concentration of 0.1-0.5 mol / L for 6-8 hours, and then calcining and reducing the immersed carboxylated multi-walled carbon nanotubes at 500-600°C to coat the surface of the carboxylated multi-walled carbon nanotubes with elemental silver. In this process, 0.1-2 wt% of PVP and ascorbic acid can be added to the silver citrate ethanol solution, and the molar ratio of silver to ascorbic acid is controlled to be 1:(1-2), so as to promote decomposition and reduction, enhance the adhesion of the silver layer, and thicken the silver layer.

[0074] In some embodiments, the elastic matrix comprises a thermosetting elastic material. For example, a two-component thermosetting elastomer is used, and the conductive fibers and the bridging conductors are dispersed in the elastic matrix provided in the second aspect. The step of processing the conductive elastic member includes: adding the prepared conductive fibers and bridging conductors to component A at a proportion, wherein the amount of conductive fibers added is 10 wt% to 20 wt%, the amount of bridging conductors added is 5 wt% to 10 wt%, and the total content of conductive fillers is 15 wt% to 30 wt%; and stirring at a uniform speed until the mixture is uniform. Then, the mixed component A and component B are poured into a container and stirred until uniform. The obtained mixed compound is subjected to vacuum degassing treatment, and then injected into a mold or coated on the surface of a substrate within the operation period. The obtained mixture is cured at room temperature or accelerated curing by heating according to the process requirements. Finally, the conductive elastic member is obtained after demolding. In the above process, "component A" refers to the base polymer part of the two-component thermosetting elastomer, and "component B" refers to the curing agent or crosslinking agent part of the two-component thermosetting elastomer.

[0075] In some embodiments, the elastic matrix comprises a thermoplastic elastomer. For example, a thermoplastic polyurethane elastomer (TPU) or a thermoplastic polyolefin elastomer (SEBS) is used, and the conductive fibers and the bridging conductors are dispersed in the elastic matrix provided in the second aspect. The step of processing the conductive elastic member includes: preparing thermoplastic polyurethane (TPU) or thermoplastic polyolefin elastomer (SEBS) particles as matrix raw materials; and melt blending the obtained conductive fibers and bridging conductors with the matrix raw materials at a proportion, wherein the amount of conductive fibers added is 10 wt% to 20 wt% of the total mass of the composite material, the amount of bridging conductors added is 5 wt% to 10 wt%, and the total content of conductive fillers is 15 wt% to 30 wt%. After stirring and mixing uniformly under heating conditions, the composite particles are prepared by extrusion granulation. Finally, the conductive elastic member is obtained by low-temperature injection molding process.

[0076] The application will be described below with reference to specific embodiments.

[0077] Example 1 (1) Preparation of the fiber body: the PI fiber was inserted into the gear jig, an initial pressure of 1.5 N was applied to the inserted PI fiber, hot air was blown to heat the PI fiber to above the resin glass transition temperature, the gear jig was driven to form an indentation on the fiber body, and the pressure was removed after the fiber temperature dropped below Tg, thereby obtaining a PI fiber with corrugated units.

[0078] (2) The conductive layer was coated on the surface of the fiber body: first, the fiber body was placed in acetone and swelled at room temperature for 20 min, then filtered, and washed and filtered with pure water three times; then the swelled PI fiber was placed in a 0.5 M sodium hydroxide solution and hydrolyzed at room temperature for 5 min, then filtered, and washed and filtered with pure water three times; then the hydrolyzed PI fiber was placed in a 0.1 M silver nitrate solution and reacted for 1 h, then filtered, and washed and filtered with pure water three times; then the reacted PI fiber was placed in a 0.1 M sodium borohydride solution and reacted for 1 h, then filtered, and washed and filtered with pure water three times; then the reduced PI fiber was placed in a copper plating solution for chemical copper plating, then filtered, and washed and filtered with pure water three times, thereby obtaining a conductive fiber with a copper layer thickness of 2.5 μm.

[0079] (3) The corrugated metalized fiber was cut, the bending period length L of the corrugated unit was 0.15 mm, the amplitude height H was 0.08 mm, the length of the fiber body was 0.4 mm, the diameter was 0.008 mm, and the length-diameter ratio was 50:1.

[0080] (4) Oxidation step of the multi-walled carbon nanotube: the multi-walled carbon nanotube was immersed in a mixed solution of sulfuric acid and nitric acid with a volume ratio of 3:1, and reacted at 65 °C for 4 h.

[0081] (5) Metalization step of the multi-walled carbon nanotube: the carboxylated multi-walled carbon nanotube was immersed in an ethanol solution containing 0.5 M silver citrate, then heat treated at 500 °C for 30 min, thereby obtaining a metalized multi-walled carbon nanotube, and the silver layer thickness of the metalized multi-walled carbon nanotube was 1.5 μm; (6) Preparation of conductive elastic member: the corrugated metalized PI fiber is added into an ethanol aqueous solution containing 5 wt% silane coupling agent KH560 and reacted at 70 °C for 1 h, and then filtered and baked at 70 °C for 1 h to obtain the KH560 modified corrugated metalized PI fiber; 18 wt% of the KH560 modified fiber is added into the A component of 30% high hysteresis type addition type silicone rubber and uniformly mixed by high intensity stirring to obtain a fiber master batch; 8 wt% of silver plated carbon nanotubes is added into the A component of 30% high hysteresis type addition type silicone rubber and uniformly mixed by high intensity stirring to obtain a carbon nanotube master batch; the two master batches and the remaining 40% A component are uniformly mixed by high intensity stirring, and then the mixture is uniformly mixed with the B component by high intensity stirring; the uniformly mixed rubber is vacuumed to remove bubbles, and finally cured at room temperature to obtain the conductive elastic member.

[0082] Example 2 The difference between Example 2 and Example 1 is that: In step (1), the fiber bundle used is Kevlar fiber; In step (2), a conductive layer is coated on the surface of the fiber body by magnetron sputtering method; before magnetron sputtering, the Kevlar fiber is subjected to oxygen plasma etching treatment to enhance the bonding force between the fiber and the metal layer; then, a chromium target with a purity of not less than 99.95% is used to perform magnetron sputtering under the conditions of a base vacuum better than 5×10 -4 Pa, argon as working gas, substrate temperature 80 °C, DC 40 W sputtering power, finally forming a chromium layer with a thickness of 10 nm on the surface of the fiber as a transition layer; then, a copper target with a purity of not less than 99.99% is used to perform magnetron sputtering under the conditions of a base vacuum better than 5×10 -4 Pa, argon as working gas, substrate temperature 80 °C, DC 200 W sputtering power, finally forming a copper layer with a thickness of 1.5 μm on the chromium layer; In step (6), the mass fraction of the conductive fiber is 12 wt%; the mass fraction of the bridging conductive body is 8 wt%.

[0083] Example 3 The difference between Example 3 and Example 1 is that: In step (1), the fiber bundle used is PBO fiber; In step (6), the mass fraction of the conductive fiber is 18 wt%; the mass fraction of the bridging conductive body is 9 wt%.

[0084] Example 4 The difference between Example 4 and Example 1 is that: In step (1), the fiber bundle used is carbon fiber; In step (6), the mass fraction of the conductive fiber is 16 wt%; the mass fraction of the bridging conductive body is 9 wt%.

[0085] Example 5 Example 5 differs from Example 1 in that: In step (6), the corrugated metalized PI fiber is added to an ethanol aqueous solution containing 5 wt% silane coupling agent KH550 and reacted at 70 °C for 1 h, and then filtered and baked at 70 °C for 1 h to obtain KH550 modified conductive fiber; 13 wt% KH550 modified conductive fiber is added to 30% thermoplastic polyurethane elastomer (TPU) fine particles, and then mixed, extruded and granulated by a twin-screw extruder to obtain a fiber master batch; 9 wt% silver-plated carbon nanotubes are added to 30% thermoplastic polyurethane elastomer (TPU) fine particles, and then granulated by a twin-screw extruder with side feeding to obtain a carbon nanotube master batch; the fiber master batch, the carbon nanotube master batch and the remaining 40% thermoplastic polyurethane elastomer (TPU) fine particles are uniformly mixed, and an injection molding machine is used to injection mold under medium-low temperature conditions to obtain a conductive elastic part.

[0086] Example 6 Example 6 differs from Example 1 in that: In step (3), the length of the prepared fiber body is 0.3 mm, and the aspect ratio is 37.5:1; the rest is the same as Example 1.

[0087] Example 7 Example 7 differs from Example 1 in that: In step (3), the length of the prepared fiber body is 0.5 mm, and the aspect ratio is 62.5:1; the rest is the same as Example 1.

[0088] Example 8 Example 8 differs from Example 1 in that: In step (2), the thickness of the prepared copper layer is 1 μm; the rest is the same as Example 1.

[0089] Example 9 Example 9 differs from Example 1 in that: In step (2), the thickness of the prepared copper layer is 3 μm; the rest is the same as Example 1.

[0090] Example 10 Example 10 differs from Example 1 in that: In step (5), the thickness of the silver layer of the metalized multi-walled carbon nanotube is 0.5 μm; the rest is the same as Example 1.

[0091] Example 11 Example 11 differs from Example 1 in that: In step (5), the silver layer of the metalized multi-walled carbon nanotube has a thickness of 2 μm; the rest is the same as in Example 1.

[0092] Comparative Example 1 The difference between Comparative Example 1 and Example 5 is that: In step (1), the PI fiber is not subjected to hot tooth pressing treatment, i.e., the obtained fiber body does not have bending units; the rest is the same as in Example 5.

[0093] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that: In step (2), the prepared copper layer has a thickness of 0.5 μm; the rest is the same as in Example 1.

[0094] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that: In step (5), the silver layer of the metalized multi-walled carbon nanotube has a thickness of 0.1 μm; the rest is the same as in Example 1.

[0095] Some of the formulations and parameters of the above examples and comparative examples are shown in Table 1.

[0096] Table 1 Some of the formulations and parameters of the examples and comparative examples

[0097] The conductive elastic members prepared in the above examples and comparative examples are subjected to volume resistivity test, Shore hardness test, tensile cycle test, aging test, tensile strength test and peeling strength test, and the test results are shown in Table 2.

[0098] Surface resistance test: The protected electrode is connected to the high end of the low resistance tester, the protection electrode is connected to the guard end, and the unprotected electrode is connected to the low end. Set the instrument to measure resistance mode and set the appropriate test current (1-100 mA). The electrode clamp is pressed evenly on the surface of the sample, and the test is started. Read the resistance value after 60 s of power on. If the surface resistance of the sample is 0.1 Ω or less, it is determined to be qualified.

[0099] Shore hardness test: Place the sample on the workbench and press the durometer vertically so that the pressure foot is in full contact with the sample surface. Apply the maximum pressure smoothly within 1 s, and read the instantaneous value within 1-1.5 s after the pressure foot contacts the sample. Test only once at the same position to avoid cumulative error of indentation. Test 3 points at different positions on the sample surface and take the average value. If the hardness of the sample is controlled within Shore A 50-100 / Shore D 30-70, it is determined to be qualified.

[0100] Tensile cycle test: Prepare dumbbell-shaped samples according to ISO 37 standard and measure the initial resistance R0 of the sample at zero strain. Set the tensile rate and strain amplitude, cyclically stretch 1000 times, pause every 100 times to record the resistance R n . According to the formula: R / R0 = (R n - R0) / R0 x 100%, calculate the resistance change rate. If the resistance growth rate < 10%, it is determined to be qualified.

[0101] Aging test: 1. Silicone rubber matrix: measure the initial resistivity of the sample σ0. Perform high temperature aging and hygrothermal aging tests on the sample: (1) high temperature aging: place in a 125 °C oven for 168 h; (2) hygrothermal aging: place in an 85 °C / 85% RH environment for 168 h. After the test is completed, take it out and restore it in a standard environment (23 °C / 50% RH) for 12 h to stabilize its state, and measure the resistivity of the aged sample σ. According to the formula: σ = (σ0- σ) / σ0 x 100%, calculate the conductivity decrease rate, where σ represents the conductivity decrease rate. If the conductivity decrease rate < 10%, it is determined to be qualified.

[0102] 2. TPU / SEBS matrix: measure the initial resistivity of the sample σ0. Perform high temperature aging and hygrothermal aging tests on the sample: (1) high temperature aging: place in a 85 °C oven for 168 h; (2) hygrothermal aging: place in an 70 °C / 85% RH environment for 168 h. After the test is completed, take it out and restore it in a standard environment (23 °C / 50% RH) for 12 h to stabilize its state, and measure the resistivity of the aged sample σ. According to the formula: σ = (σ0- σ) / σ0 x 100%, calculate the conductivity decrease rate, where σ represents the conductivity decrease rate. If the conductivity decrease rate < 10%, it is determined to be qualified.

[0103] Peeling strength test: Set the peeling angle and peeling rate, record the peeling force curve. According to the formula: peeling strength = average peeling force (N) / sample width (mm), calculate the peeling strength. Observe whether the peeling interface belongs to cohesive failure in the adhesive layer or to fiber-matrix interface failure. If the interface strength ≥ 1.5 N / mm, it is determined to be qualified.

[0104] Table 2 Test results of samples prepared by examples and comparative examples

[0105] Comparing Example 1, 8, 9 with Comparative Example 2, when the thickness of the conductive layer reaches 2.5 microns, the surface resistance is as low as 0.03 ohms, and the tensile cycle resistance change rate is only 3%-4%, showing excellent conductive durability. When the thickness is 1 micron, the resistance rises to 0.3 ohms, and the performance is close to the qualified critical value. When the thickness is only 0.5 microns, the resistance is as high as 1.4 ohms, and the tensile cycle change rate is as high as 60%, which completely fails to form an effective conductive path.

[0106] Comparing Example 1, 10, 11 with Comparative Example 3, the 1.5-micron-thick silver layer stabilizes the surface resistance at 0.01-0.03 ohms, and the tensile change rate is controlled at 2%-4%. When the thickness is reduced to 0.5 microns, the resistance performance decreases significantly. When the thickness is only 0.1 microns, the resistance reaches 0.3 ohms, and the tensile change rate rises to 28%, indicating that an excessively thin silver layer is difficult to form an effective conductive bridge.

[0107] Comparing Example 5 with Comparative Example 1, the sample with the corrugated structure has a surface resistance of 0.1 ohms and a tensile change rate of 9%, and all tests are qualified. The comparative sample without the corrugated structure has a resistance of 1.2 ohms and a tensile change rate of 72%, and the performance deteriorates significantly, indicating that the corrugated unit can effectively maintain the conductive stability.

[0108] In the above examples, the description of each example focuses on different aspects, and the parts not described in detail in a certain example can be referred to the relevant description of other examples.

[0109] The conductive fiber, the conductive elastic member, and the manufacturing method provided by the embodiments of the present application are described in detail above, and specific examples are applied in this paper to describe the principles and implementation manners of the present application. The above example description is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation manner and application range will be changed, and the above description should not be understood as a limitation of the present application.

Claims

1. A conductive fiber, characterized in that, The conductive fiber includes a fiber body and a conductive layer, the conductive layer being coated on the fiber body; the fiber body includes at least one bending unit, the bending units being spaced apart or continuously arranged.

2. The conductive fiber according to claim 1, characterized in that, The bending unit includes at least one of a corrugated unit, a broken line unit, and an arc unit. The bending period length L of the bending unit is 0.1~0.2mm, and the amplitude height H of the bending unit is 0.04~0.12mm.

3. The conductive fiber according to claim 1, characterized in that, The fiber body has a length of 0.3~0.5mm, a diameter of 0.005~0.01mm, and an aspect ratio of 30~100; the bending units are continuously distributed along the entire length of the fiber body.

4. The conductive fiber according to claim 1, characterized in that, The fiber body comprises at least one of polyimide fiber, poly(p-phenylene terephthalamide) fiber, poly(p-phenylene benzodioxazole) fiber, and carbon fiber; and / or The conductive layer includes at least one of a silver layer, a copper layer, a nickel layer, and a palladium layer; the thickness of the conductive layer is 1~3μm.

5. A conductive elastic element, characterized in that, The conductive elastic element includes the conductive fiber, elastic matrix, and bridging conductor as described in any one of claims 1 to 4; The conductive fibers and the bridging conductors are dispersed in the elastic matrix, and the conductive fibers and the bridging conductors are in contact with each other, forming a continuous conductive network in the elastic matrix.

6. The conductive elastic element according to claim 5, characterized in that, The bridging conductor includes micro- and nano-scale conductive particles or fibers; the micro- and nano-scale conductive particles or fibers include metallized multi-walled carbon nanotubes, and the metallized multi-walled carbon nanotubes include multi-walled carbon nanotubes and a metal layer. The multi-walled carbon nanotubes have a length of 10~30μm and an outer diameter of 5~15nm. The thickness of the metal layer is 0.5~2μm, and the metal layer includes a silver layer.

7. The conductive elastic element according to claim 5, characterized in that, The conductive fiber accounts for 10-20 wt% of the mass fraction of the conductive elastic element; the bridging conductor accounts for 5-10 wt% of the mass fraction of the conductive elastic element; and the mass ratio of the conductive fiber to the bridging conductor is (1-4):

1.

8. The conductive elastic element according to claim 5, characterized in that, The elastic matrix includes either thermosetting elastic materials or thermoplastic elastic materials.

9. A method for manufacturing conductive fibers, characterized in that, The manufacturing method includes: The fiber bundles are processed to obtain a fiber body with bending units; A conductive layer is coated on the surface of the fiber body to obtain the conductive fiber.

10. The method for manufacturing conductive fibers according to claim 9, characterized in that, The steps for processing the fiber bundles include: The fiber bundle is threaded into the gear fixture; An initial pressure is applied to the inserted fiber bundle; The fiber bundle is heated to above the glass transition temperature of the resin. The gear jig is driven to form an indentation on the fiber bundle, while simultaneously pulling the fiber bundle continuously through the gear jig to obtain the fiber body of the bending unit.

11. A method for manufacturing a conductive elastic element, characterized in that, The manufacturing method includes: Prepare the conductive fiber as described in any one of claims 1 to 10; Preparation of bridging conductors; The conductive fibers and the bridging conductors are dispersed in an elastic matrix to obtain the conductive elastic element.

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