CN110983764B

CN110983764B - A kind of conductive aramid fiber with composite metal coating structure

Info

Publication number: CN110983764B
Application number: CN201911326096.XA
Authority: CN
Inventors: 邵勤思; 张蕾蕾; 李晓琳; 傅倩茹; 李敏娜; 王莎莎; 容忠言; 张久俊; 白瑞成
Original assignee: SHANGHAI UNIVERSITY
Current assignee: SHANGHAI UNIVERSITY
Priority date: 2019-12-20
Filing date: 2019-12-20
Publication date: 2022-04-05
Anticipated expiration: 2039-12-20
Also published as: CN110983764A

Abstract

The invention belongs to the technical field of electromagnetic shielding materials and conductive materials, and discloses a conductive aromatic polyamide fiber with a composite metal coating structure, wherein a chemical nickel plating or nickel alloy layer is deposited on the base of the aromatic polyamide synthetic fiber; Electroless nickel or nickel alloy layer is deposited on the substrate with electroplated copper metal layer; electroplated nickel metal layer is deposited on the substrate with electroplated copper metal layer; on the substrate electroplated with nickel metal layer, electroplated silver metal is selectively deposited or not deposited layer; preparation methods include washing and degreasing, pretreatment, activation, reduction, electroless plating, and electroplating. The chemical plating of the present invention can endow the fibers with continuous electrical conductivity, and subsequent electroplating can effectively avoid the shortcomings of chemical plating and improve production efficiency. The conductive aromatic polyamide fiber prepared by the method has both conductive, lightweight, high-strength and flame-retardant properties, and has broad application prospects in the field of electromagnetic shielding.

Description

Conductive aromatic polyamide fiber with composite metal coating structure

Technical Field

The invention belongs to the technical field of electromagnetic shielding materials and conductive materials, and particularly relates to a conductive aromatic polyamide fiber with a composite metal coating structure.

Background

Currently, the closest prior art: the electromagnetic environment of modern instruments and equipment is increasingly complex, and research and development of efficient wide-frequency electromagnetic shielding materials have great practical significance to national defense construction and social life. Aromatic polyamide fiber, abbreviated as aramid fiber, has at least 85% of amido bonds in the molecular structure directly connected with 2 aromatic rings, is mainly divided into poly-p-phenylene terephthalamide (PPTA, aramid 1414) and poly-m-phenylene isophthalamide (PMIA, aramid 1313), and also comprises aramid fiber 14, poly-copolymerized aramid fiber, heterocyclic aramid fiber and other various types. The conductive aramid fiber has the advantages of conductivity, light weight, high strength, flame retardance, flexibility, good durability, high compatibility, processability and the like, can reduce the weight by 50-90% compared with copper fiber and stainless steel fiber, and is a light electromagnetic shielding material and a conductive material which are preferred by special departments such as aerospace, electronic communication and the like.

The patent CN102421277A and CN104831527A have used a vacuum coating method to prepare conductive aramid fiber material, but the method mainly aims at the flat samples such as paper, fabric, and film, and the samples in fiber state have uneven sputtering phenomenon, and the equipment is expensive.

At present, the research on the conductive aramid fiber is mainly focused on the chemical plating field, such as patent CN104179004A of the university of the great industry, patent CN107326657A of sengilo, patent CN105133301A of the university of shanghai, patent CN107164951A of the science and technology of seville metal material, patent CN105839402A of the university of wuhan and han theory, and other research papers, such as: "Surface dispersed metal-attached fiber prepared by two-inserted poly (subpamine) function, ACS application. Mater. Interface, 2013,5, 2062-. The key points of the researches are mainly focused on the research and development of chemical plating pretreatment and a plating solution formula, wherein the strength of the fiber is often damaged and the catalytic effect is not ideal by a classic 'etching-sensitizing-activating' pretreatment method, while a newly developed pretreatment method has the disadvantages of complex process, higher cost and unclear prospect of large-scale industrial application and basically stays in a laboratory stage. Chemical plating can endow aramid fiber with the conductive characteristic, but basically only can plate single-layer metal, and has certain limitation in the field of electromagnetic shielding; the existence of a reducing agent in the plating solution influences the long-term stability of the plating solution; for silver with the best conductivity, the standard electrode potential is positive, and the silver has an autocatalytic deposition effect, so that the chemical plating solution is very easy to decompose and turbid, poor plating and waste are easily caused, and the electromagnetic shielding efficiency of the silver is further influenced. At present, the technology of chemical nickel plating is relatively stable and mature, the cost is lower, the reaction is controllable, the plating solution can be kept in a clear state all the time in the plating process, but the electromagnetic shielding efficiency of the plating layer is general.

In summary, the problems of the prior art are as follows: in the prior art, the vacuum coating technology is mainly used for two-dimensional plane samples, is not suitable for fibrous samples and is expensive in equipment.

In the prior art, the high strength of aramid fiber is often damaged by common etching treatment, and noble metal catalytic points and anchor points obtained by a most classical etching-sensitizing-activating pretreatment method of chemical plating are often insufficient to support a subsequent plating layer; the industrial application of in-situ deposition of a polymeric tie layer between fibers and plating is not obvious in view of cost considerations.

In the prior art, the plating solution of the chemical plating technology is unstable, poor plating and waste are easily caused, and a high-quality and large-thickness plating layer is difficult to obtain, so that the electromagnetic shielding efficiency is influenced; meanwhile, the plating solution can not be recycled for a long time, and the production cost is increased.

In the prior art, the chemical nickel plating technology is the most widely applied chemical plating technology, the plating solution can be kept in a clear state all the time, the reaction and the cost are controllable, but the electric conductivity and the electromagnetic shielding efficiency of the obtained plating layer are general.

In the prior art, the influence of the structural design of the coating on the shielding effectiveness is not considered, and the conductivity, the magnetic conductivity, the corrosion resistance, the durability, the economy and the light weight of the coating are not considered, so that the fiber cannot be endowed with good metal texture, and more effective electromagnetic shielding cannot be performed, so that the advantages of the metalized aramid fiber cannot be exerted.

There is a certain difficulty in solving the above problems. The aramid fiber has high crystallinity, particularly para-aramid fiber, the crystallinity is over 80 percent, the surface is smooth and compact, the reaction energy is low, compared with fibers such as terylene and cotton, a metal coating is difficult to deposit on the surface of the aramid fiber, and a process method needs to be carefully considered; meanwhile, the strength of the aramid fiber cannot be reduced too much by all treatment modes. In view of the sensitive use of conductive aramid, there are fewer related references, adding to the corresponding difficulties. However, the strategic value and significance of the metallized conductive aramid fiber are determined in the application field, and the prior art needs to be improved so as to improve the broadband electromagnetic shielding efficiency and obtain the ideal performance.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a conductive aromatic polyamide fiber with a composite metal coating structure. The invention selects the mode of multilayer combination of the high-permeability plating layer and the high-conductivity plating layer, and has the advantages of conductivity, magnetism conductivity, corrosion resistance, durability, economy and light weight of the plating layer, the total plating thickness can reach more than 1 micron, the fiber has good metal texture, and the intrinsic characteristics of light weight, high strength, heat resistance, flexibility, strong processability and the like of the fiber. The conductive aromatic polyamide fiber provided by the invention has flexible designability, can perform more effective electromagnetic shielding, and has wide application prospect in the fields of aviation, aerospace, deep sea, satellite, communication, electronics, medical treatment and the like.

The invention is realized by the following steps, and the conductive aromatic polyamide fiber with the composite metal coating structure comprises:

(1) an aromatic polyamide synthetic fiber substrate;

(2) depositing a layer of chemical nickel plating or nickel alloy layer on the substrate (1);

(3) depositing a layer of electroplated copper metal layer on the substrate in the step (2);

(4) depositing a nickel electroplating metal layer on the substrate in the step (3);

(5) and (4) optionally depositing a silver electroplating metal layer on the substrate.

Further, the chemical structural formula of the aromatic polyamide fiber is shown in the specification

Wherein Ar is₁Is composed of

Ar₂、Ar₃Is composed of

One of them, Ar₂And Ar₃May be the same chemical structure segment.

Further, the fibers are present in the form of fibers, yarns, and fabrics.

Further, the nickel alloy component is a nickel-phosphorus, nickel-boron, or nickel-phosphorus-boron alloy plating layer.

Another object of the present invention is to provide a method for preparing an electrically conductive aromatic polyamide fiber having a composite metal plating structure, comprising the steps of:

(a) washing and removing oil, and removing dirt, oil agent and impurities on the surface of the fiber;

(b) pretreating, swelling the fiber, improving the wettability and the surface area of the fiber surface, and improving the bonding fastness of the fiber matrix and a subsequent plating layer;

(c) activating, namely soaking the fiber by using a noble metal salt solution to form a thin noble metal ion active layer on the surface of the fiber;

(d) reducing, namely soaking the fibers by using a reducing solution to form a noble metal simple substance particle layer on the surfaces of the fibers, wherein the noble metal simple substance particle layer can be used as an anchoring point between the fibers and a subsequent plating layer and also has a catalytic function;

(e) chemical plating, namely depositing a layer of metal nickel or nickel alloy on the surface of the fiber;

(f) electroplating copper, namely depositing a metal copper layer on the surface of the fiber treated in the step (e);

(g) electroplating nickel, and depositing a metal nickel layer on the surface of the fiber treated in the step (f);

(h) optionally, depositing a metallic silver layer on the surface of the fiber treated in (g).

Wherein Ar is₁Is composed of

Ar₂、Ar₃Is composed of

One of them, Ar₂And Ar₃May be the same chemical structure segment.

The fibers are present in the form of fibers, yarns or fabrics.

The washing and oil removing process in the step (a) comprises the following steps: putting the aromatic polyamide fiber into 0.01-20 wt% of sodium hydroxide (NaOH) or potassium hydroxide (KOH) solution, ultrasonically cleaning for 5-60 min, taking out, and rinsing with deionized water.

The pretreatment process of the step (b) is as follows: and (3) putting the deoiled fiber into a pretreatment solution, dipping for 5-60 min at 25-150 ℃, taking out, and rinsing with deionized water.

Further, the pretreatment solution is sulfuric acid (H)₂SO₄) Solution, calcium chloride (CaCl)₂) In dimethyl sulfoxide (DMSO), CaCl₂N-methylpyrrolidone (NMP) solution of (5), CaCl₂Dimethylacetamide (DMAc) solution, or CaCl₂Of Dimethylformamide (DMF), in particular calcium chloride (CaCl)₂) In Dimethylsulfoxide (DMSO). The concentration of the sulfuric acid solution is 10-98 wt%, and the concentration of the calcium chloride solution is 3-5 wt%. These solvents are those used in the polymerization or spinning of aromatic polyamide fibers,the fiber has the function of swelling the fiber, can improve the wettability and the surface area of the fiber, increases the adsorbability of the fiber to ions, and does not damage the chemical structure and the strength of the fiber; the calcium chloride has the function of dissolving aid; the heating may further promote swelling of the fibers

The activation process of the step (c) is as follows: and (3) putting the pretreated fiber into a noble metal salt solution with the concentration of 0.1-100 g/L, soaking at 25-120 ℃ for 5-90 min, taking out, and slowly rinsing with deionized water.

The noble metal salt is silver nitrate (AgNO)₃) Or palladium chloride (PdCl)₂) Especially silver nitrate, since Ag⁺The ions can be adsorbed with Cl on the surface of the fiber after swelling treatment^-An AgCl layer (insoluble in water) is formed, which is reduced to an Ag interfacial layer with catalysis and riveting after reduction treatment.

The solvent is NMP, DMSO, DMAc, DMF or water, and particularly DMSO can further swell the fiber to allow noble metal ions to better permeate into the fiber. Appropriate heating further promotes swelling of the fibers and diffusion of metal ions.

After activation treatment, an AgCl interface layer or a Pd layer is absorbed on the surface of the swelled fiber²⁺The ionic layer has a thickness of about 100 to 1000 nm.

The reduction process in the step (d) is as follows: and (3) putting the activated fiber into a reducing solution for reduction treatment, wherein the concentration of the reducing solution is 1-10 g/L, soaking for 5-30 min at 25-35 ℃, taking out, and rinsing with deionized water.

Further, the reducing agent comprises stannous chloride, sodium borohydride, dimethylamino borane or hydrazine hydrate, especially sodium borohydride.

The solvent is NMP, DMSO, DMAc, DMF or water, especially water.

The aqueous solution of sodium borohydride in the step can achieve good reduction effect at very dilute concentration and normal temperature (1 g/L).

After reduction treatment, the noble metal ion layer on the surface of the fiber is reduced into a noble metal single layer, the thickness of the layer is about 100-1000 nm, the noble metal single layer is formed by noble metal nano particles, deposition of subsequent chemical plating metal can be catalyzed, the riveting effect is achieved, and the bonding fastness of the subsequent plating layer and the fiber substrate is improved.

The chemical plating process in the step (e) comprises the following steps: preparing a chemical nickel plating solution by using nickel salt, a complexing agent, a reducing agent, a buffering agent, a stabilizing agent and the like, and depositing a nickel-based metal plating layer on the surface of the fiber at the temperature of 30-90 ℃, wherein the content of nickel is 85-100 wt%, and the thickness of the plating layer is 100-500 nm. As the underlying nickel-based metal layer, the plating layer needs to ensure certain thickness (>100nm) and continuity so as to withstand the impact of subsequent current and ensure the effective performance of subsequent electroplating. The defects (cracks, poor plating and the like) of the chemical plating layer have inheritance, and the quality of the chemical plating layer has great influence on the quality of the whole composite plating layer, so the plating speed and the internal stress of the plating layer need to be controlled to ensure the quality of the plating layer.

The reducing agent used in this step is generally sodium hypophosphite, dimethylamino borane, hydrazine hydrate.

Further, by adjusting the pH value of the solution and the concentration of each component, phosphorus and boron elements in the reducing agent can be co-deposited with nickel, so that nickel-phosphorus, nickel-boron or nickel-phosphorus-boron alloy is obtained.

The chemical nickel plating is the most stable one of all chemical plating, is low in price, has high plating quality, and can endow the fiber with initial conductivity.

The process of electroplating copper in the step (f) comprises the following steps: preparing an electroplating copper solution by using copper salt, a complexing agent, a stabilizing agent, a buffering agent and the like, depositing for 15-120 min at 25-60 ℃ under a certain current or voltage, and depositing a metal copper coating with the thickness of 250-1000 nm, preferably 500-800 nm, on the surface of the fiber treated by the step (e). The electroplated copper layer is used as the second layer of the composite coating, has the conductivity and electromagnetic shielding effectiveness which are second only to that of silver, and has the price and the relative atomic mass which are lower than those of silver, so that the cost performance is high. The copper plating layer is the main body of the composite plating layer, which ensures that the composite plating layer has good conductivity and electromagnetic shielding effectiveness, so that the composite plating layer has certain thickness (larger than the nickel plating layer and the silver plating layer);

the process of electroplating nickel in the step (g) is as follows: preparing an electroplating nickel solution by using nickel salt, a complexing agent, a stabilizing agent, a buffering agent, a brightening agent and the like, depositing for 15-60 min at 40-70 ℃ under a certain current or voltage, and depositing a metal nickel coating with the thickness of 200-500 nm, preferably 200-300 nm on the surface of the fiber treated by the step (f). The nickel electroplated layer can solve the problems of poor corrosion resistance and durability of the copper electroplated layer, prevent copper atoms from diffusing outwards, and simultaneously has better magnetic conductivity and electrical conductivity.

The optional silver electroplating process of step (f) is as follows: silver salt, complexing agent, stabilizer, buffering agent, brightener and the like are used to prepare an electrosilvering solution, the solution is deposited for 15-60 min at 25-45 ℃ under a certain current or voltage, and a metal silver coating with the thickness of 200-500 nm, especially 200-300 nm, is deposited on the surface of the fiber treated by the step (g). The silver layer can further improve the conductivity, electromagnetic shielding efficiency and corrosion resistance of the fiber, and improve the welding performance of the fiber, thereby meeting the requirements of more severe application environments.

Another object of the present invention is to provide an aerospace electromagnetic shielding material and conductor prepared using the conductive aramid fiber having a composite metal plating structure.

Another object of the present invention is to provide a marine and satellite electromagnetic shielding material and a conductor prepared using the conductive aramid fiber having a composite metal plating structure.

The invention also aims to provide an electromagnetic shielding material and a conductor prepared by using the conductive aromatic polyamide fiber with the composite metal coating structure in the communication and medical fields.

In summary, the advantages and positive effects of the invention are: according to the invention, the surface of the aromatic polyamide fiber is plated with the multiple metal conductive layers, so that the aromatic polyamide fiber has good conductivity and metal texture, and has the performances of light weight, high strength, flame retardance, heat resistance, strong processability and the like. The material can be widely applied to special fields of aviation, aerospace, navigation, satellites, communication, medical treatment and the like, and can be used as an electromagnetic shielding material, a conductor and the like.

The chemical plating can endow the fiber with continuous conductivity, the subsequent electroplating can effectively avoid the defects of the chemical plating, improve the utilization rate and the production efficiency of the plating solution, reduce the cost, obtain the required weight gain/thickening rate according to the design and endow the fiber with better metal texture. The electroplating is carried out on the surface of a good conductor, so the method firstly uses an electroless plating method to plate a nickel-based metal on the surface of the aramid fiber, and then designs and electroplates a multi-layer metal electroplated layer structure on the aramid fiber.

In the composition of the composite plating layer, the nickel-based chemical plating layer is mainly used for endowing the fiber with primary conductivity, so that the subsequent electroplating process becomes feasible; compared with other chemical plating layers, the nickel-based metal plating solution is stable, the quality of the plating layer is high, and the bonding firmness with the aramid fiber substrate is the best. The electroplated copper layer is used as a second layer and a main body structure of the composite coating, has the conductivity and electromagnetic shielding efficiency second only to silver, and has higher cost performance and relative atomic mass lower than that of silver; the next third nickel electroplated layer solves the problem of poor corrosion resistance and durability of the copper electroplated layer, can prevent copper atoms from diffusing outwards, and has better magnetic permeability and electrical conductivity; the outermost silver plating layer (which can be selectively plated) can further improve the conductivity, electromagnetic shielding performance and corrosion resistance of the fiber, and simultaneously endow the fiber with good welding performance.

The structural design of the composite coating refers to the design concept of a macroscopic layered electromagnetic shielding structure, integrates the characteristics of various single-layer shielding materials, combines the intrinsic performance and the structural effect of the materials together to play a role, selects a mode of multilayer combination of a high-permeability material and a high-permeability material, considers the durability, the economy and the light weight of the coating, can carry out more effective shielding, and meets more complex and severe use requirements.

The electroless nickel and nickel alloys of the present invention impart primary conductivity to the fibers and provide for electroplating, as opposed to the prior art of simple electroless plating.

Compared with products such as conductive terylene, conductive cotton and the like, the conductive aramid product has very high value and wide application in special fields due to incomparable advantages, but the plating difficulty of the aramid fiber is different from that of common fiber in the same day due to the characteristics of high crystallinity and high inertia of the aramid fiber. The invention provides a new idea for solving the problem of preparation of the conductive aramid fiber.

Drawings

Fig. 1 is a flow chart of a method for preparing an electrically conductive aromatic polyamide fiber with a composite metal plating structure according to an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a conductive aramid fiber composite metal plating layer according to an embodiment of the present invention.

FIG. 3 is a scanning electron microscope photograph of an all para-aramid fiber provided in an embodiment of the present invention.

FIG. 4 is a (a) SEM and cross-sectional (b) TEM image of an aramid fiber after swelling-activation-reduction as described in example 1, provided in accordance with an embodiment of the present invention.

FIG. 5 is a scanning electron microscope photograph of para-aramid fiber after electroless nickel plating according to the method described in example 1, in accordance with an embodiment of the present invention.

FIG. 6 is a scanning electron microscope photograph of para-aramid fiber provided in accordance with an embodiment of the present invention after electro-coppering as described in example 1.

FIG. 7 is a scanning electron microscope photomicrograph of para-aramid fiber after being electroplated with nickel as described in example 1, in accordance with an embodiment of the present invention.

FIG. 8 is a scanning electron microscope photograph of para-aramid fiber after electro-silvering as described in example 1, in accordance with an embodiment of the present invention.

Fig. 9 is a photograph of electromagnetic shielding effectiveness data of the conductive aramid fabric according to the present invention prepared in the methods of examples 1 and 2, which includes six sets of data plated with: Ni-P-B, Ni, Ni-P-B/Cu/Ni, Ni/Cu/Ni, Ni-P-B/Cu/Ni/Ag, Ni/Cu/Ni/Ag. Of these, the former two are obtained by electroless plating, and the latter four are obtained by combining electroless plating (first layer) and electroplating (second to fourth layers).

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The prior art does not select a mode of combining a high-permeability coating and a high-permeability coating in a multilayer manner, does not give consideration to the conductivity, the permeability, the corrosion resistance, the economy and the light weight of the coatings, cannot endow the fiber with good metal texture, and cannot carry out more effective electromagnetic shielding. In the prior art, the vacuum deposition method has high cost and is not suitable for fiber samples. In the prior art, the chemical plating solution is easy to decompose and turbid, poor plating and waste are easy to cause, and a high-quality plating layer is difficult to obtain.

In view of the problems of the prior art, the present invention provides a conductive aromatic polyamide fiber with a composite metal plating structure, and the present invention is described in detail below with reference to the accompanying drawings.

The conductive aromatic polyamide fiber with the composite metal coating structure provided by the embodiment of the invention is short for aramid fiber, and the structural formula is as follows:

wherein Ar is₁Is composed of

Ar₂、Ar₃Is composed of

One of them, Ar₂And Ar₃May be the same chemical structure segment.

The method comprises the steps of firstly, cleaning and deoiling aromatic polyamide fiber to remove oil agent and dirt on the surface of the fiber; then, pretreating the fiber to increase the wettability and the surface area of the fiber surface so as to improve the bonding fastness between a subsequent plating layer and a base material; the activation is to adsorb a layer of noble metal ions on the surface of the pretreated fiber; forming a noble metal anchor point and a catalytic point which are firmly combined with the substrate on the surface of the fiber after reduction treatment; then chemically plating nickel on the surface of the fiber; and then sequentially carrying out an electro-coppering process, an electro-nickelling process and an electro-silvering process (optional), and finally obtaining the conductive aromatic polyamide fiber with the composite metal coating structure.

The plated aramid fibers of the present invention may be present in the form of fibers, yarns, fabrics, and the like.

As shown in fig. 1, a method for preparing an electrically conductive aromatic polyamide fiber with a composite metal plating structure provided in an embodiment of the present invention specifically includes:

s101, washing and removing oil. Putting the aromatic polyamide fiber into 0.01-20 wt% of sodium hydroxide (NaOH) or potassium hydroxide (KOH) solution, ultrasonically cleaning for 5-60 min, taking out, and rinsing with deionized water to remove dirt, oil and impurities on the surface of the fiber.

And S102, preprocessing. And (3) putting the washed fiber into a pretreatment solution, dipping for 5-60 min at 25-150 ℃, taking out, and rinsing with deionized water. The pretreatment solution is sulfuric acid (H)₂SO₄) Solution, calcium chloride (CaCl)₂) In dimethyl sulfoxide (DMSO), CaCl₂N-methylpyrrolidone (NMP) solution of (5), CaCl₂Dimethylacetamide (DMAc) solution, or CaCl₂Of Dimethylformamide (DMF), in particular calcium chloride (CaCl)₂) In Dimethylsulfoxide (DMSO). The concentration of the sulfuric acid solution is 10-98 wt%, and the concentration of the calcium chloride solution is 3-5 wt%. The step is used for increasing the wettability and the surface area of the fiber surface and improving the bonding firmness of the fiber and a subsequent metal coating.

And S103, activating. And (3) putting the pretreated fiber into a silver nitrate or palladium chloride solution with the concentration of 0.1-100 g/L, particularly a silver nitrate solution, soaking for 5-90 min at 25-120 ℃, taking out, and slowly rinsing with deionized water. The solvent of the activating solution may be NMP, DMSO, DMAc, DMF or water, especially DMSO. The activation treatment can form a thin active layer of noble metal ions on the surface of the fiber.

And S104, reducing. And (3) putting the activated fiber into a stannous chloride, sodium borohydride, dimethylamine borane or hydrazine hydrate solution with the concentration of 1-10 g/L, soaking for 5-30 min at 25-35 ℃, taking out, and rinsing with deionized water. The solvent of the reducing solution may be NMP, DMSO, DMAc, DMF or water, especially water. After reduction, noble metal target points which are firmly combined with the substrate are formed on the surface of the fiber, and the target points can be used as anchoring points and catalytic points of a subsequent chemical plating layer.

And S105, chemically plating nickel. Nickel salt, complexing agent, reducing agent, buffering agent, stabilizer, etc. are compounded into chemical nickel plating solution, and one layer of nickel-base metal is deposited homogeneously on the surface of fiber. The chemical nickel plating generally uses sodium hypophosphite, dimethylamino borane, hydrazine hydrate and the like as reducing agents, and the codeposition of phosphorus, boron and nickel in the reducing agents can be controlled by adjusting the pH value of the plating solution and the concentration of each component, so that pure nickel or alloy plating layers of nickel-phosphorus, nickel-boron, nickel-phosphorus-boron and the like can be respectively obtained. The nickel and nickel alloy coatings differ in structure and performance, and the composition can be designed according to specific application scenarios.

S106, electroplating copper, preparing an electroplating copper solution by using copper salt, a complexing agent, a stabilizing agent, a buffering agent and the like, immersing the fiber with the surface coated with nickel or nickel alloy into the electroplating copper solution, and depositing a layer of metallic copper on the chemical coating of the nickel or nickel alloy under a certain current or voltage. The copper plating layer can enable the fiber to have good conductivity and good electromagnetic shielding efficiency (second to silver), and meanwhile, the fiber is light in weight and high in cost performance.

S107, electroplating nickel, preparing nickel salt, a complexing agent, a stabilizing agent, a buffering agent, a brightening agent and the like into an electroplating nickel solution, immersing the fibers with copper plated on the surface into the electroplating nickel solution, and depositing a layer of metal nickel on the copper electroplated layer under a certain current or voltage. When the fiber is in service in air, the nickel coating is more stable than the copper coating, the attenuation of the conductivity is relatively slow, the fiber has better corrosion resistance and durability, and the good magnetic conductivity also has a certain magnetic shielding effect.

And S108, optionally, after the seventh step of nickel electroplating, preparing silver electroplating solution by using silver salt, complexing agent, stabilizer, buffering agent, brightener and the like, and depositing a layer of metal silver on the fiber nickel electroplating layer under a certain current or voltage, wherein the nickel electroplating layer also plays a role in separation, so that copper atoms are prevented from directly diffusing to the silver layer. The silver plating layer can further improve the conductivity, durability and electromagnetic shielding effectiveness of the fiber and improve the weldability of the fiber.

The structure of the conductive aromatic polyamide fiber prepared by the process is shown in figure 2, wherein the optimal thickness of the electroless nickel plating layer or the nickel alloy layer is 100-500 nm, the optimal thickness of the electroplated copper layer is 500-800 nm, the optimal thickness of the electroplated nickel layer is 200-300 nm, and the optimal thickness of the electroplated silver layer is 200-300 nm.

The invention is further described with reference to specific embodiments and the accompanying drawings.

Example 1:

the preparation method of the conductive aromatic polyamide fiber with the composite metal coating structure provided by the embodiment of the invention comprises the following steps:

the first step is as follows: deoiling, namely putting the poly-p-phenylene terephthamide (PPTA) fiber into 0.01 wt% of sodium hydroxide solution, ultrasonically cleaning for 30min at normal temperature, taking out, and rinsing with deionized water.

The second step is that: pretreating by immersing the fibres in CaCl₂DMSO solution (CaCl)₂Content of 5 wt%), soaked at 60 deg.C for 30min, and rinsed with deionized water.

The third step: activating, putting the pretreated fiber into AgNO₃DMSO solution (AgNO)₃The concentration of (1) is 10g/L), the temperature is 80 ℃, and the solution is taken out and rinsed slowly after 60 min.

The fourth step: and (3) reducing, namely putting the activated fiber into 1g/L sodium borohydride aqueous solution, carrying out reduction treatment at normal temperature, taking out after 10min, and rinsing the fiber by using deionized water.

The fifth step: chemical nickel plating, the reduced fiber is put into a chemical nickel plating solution, and the formula of the chemical nickel plating solution is as follows: 10-20 g/L of nickel sulfate, 25-35 g/L of sodium citrate, 5-10 g/L of sodium hypophosphite, 0.1-0.5 g/L of dimethylamino borane and 10mg/L of sodium dodecyl sulfate. Adjusting the pH value to 9.5-10.5 by using ammonia water, plating for 30min at 50 ℃, and rinsing by using deionized water.

And a sixth step: and (2) copper electroplating, namely placing the fibers subjected to chemical nickel plating into copper electroplating solution, wherein the formula of the copper electroplating solution is as follows: 5-10 g/L of basic copper carbonate, 80-100 g/L of hydroxyethylidene diphosphonic acid, 40-50 g/L of potassium carbonate and 0.1-0.3 g/L of selenium dioxide. Adjusting the pH value to 9.0-10.0 by using potassium hydroxide. And taking the fiber as a cathode and the electrolytic copper foil as an anode, plating for 60min at the temperature of 30-40 ℃, and rinsing with deionized water.

The seventh step: and (2) electroplating nickel, namely putting the fibers after copper electroplating into a nickel electroplating solution, wherein the formula of the nickel electroplating solution is as follows: 100-150 g/L of nickel sulfate, 10-20 g/L of nickel chloride, 100-150 g/L of sodium citrate, 30-50 g/L of boric acid, 0.5-0.8 g/L of saccharin, 0.05-0.08 g/L of sodium dodecyl sulfate and pH value of 6.0-7.0. And taking the fiber as a cathode and the electrolytic nickel foil as an anode, plating for 30min at 40-50 ℃, and rinsing with deionized water.

Eighth step: and (3) silver electroplating, namely putting the fibers subjected to nickel electroplating into a silver electroplating solution, wherein the formula of the silver electroplating solution is as follows: 30-40 g/L of silver nitrate, 100-120 g/L of 5, 5-dimethyl hydantoin, 50-70 g/L of potassium carbonate, 40-50 g/L of sodium pyrophosphate, 0.5-1 g/L of L-histidine and 10mL/L of a stabilizer, and the pH value is adjusted to 10.0-11.0 by using potassium hydroxide. The stabilizer is a solution prepared from 4-8 g/L of 1, 4-butynediol, 2-4 g/L of triethanolamine and 2-4 g/L of vanillin. And taking the fiber as a cathode and the electrolytic silver foil as an anode, plating for 30min at 25-30 ℃, and rinsing with deionized water.

The scanning electron microscope picture of the PPTA fiber used in this example is shown in FIG. 3, and the fiber is rigid and has a very dense surface.

After the swelling-activating-reducing treatment is performed according to the process of the embodiment 1, the topography of the surface and the cross section of the fiber is shown in fig. 4, and it can be seen that after the pretreatment process, an Ag nanoparticle catalyst layer with a thickness of about 1 μm is formed on the surface of the fiber, the enrichment of Ag nanoparticles can catalyze the subsequent electroless nickel plating reaction, which is beneficial to the formation of a continuous nickel plating layer, and meanwhile, the Ag nanoparticle layer also plays a role in riveting, so that the bonding fastness of the electroless nickel plating layer and the fiber substrate is increased.

FIG. 5 is a scanning electron microscope topography of the fiber surface after electroless nickel plating according to the process of example 1. In addition, the composition of the nickel can be determined by combining energy spectrum (EDS) and X-ray photoelectron spectroscopy (XPS) analysis.

FIG. 6 is a scanning electron microscope topographical view of the fiber surface after copper electroplating according to the process of example 1.

FIG. 7 is a scanning electron microscope topography of the fiber surface after nickel electroplating according to the process of example 1.

FIG. 8 is a scanning electron microscope topographical view of the fiber surface after silver electroplating according to the process of example 1.

As can be seen from fig. 5 to 8, a flat, dense, continuous metal coating is formed on the surface of the fiber after each step of coating.

Example 2:

the preparation method of the conductive aromatic polyamide fiber with the composite metal coating structure provided by the embodiment of the invention comprises the following fifth step of chemical plating:

the fifth step: chemical nickel plating, the reduced fiber is put into a chemical nickel plating solution, and the formula of the chemical nickel plating solution is as follows: 10-20 g/L of nickel sulfate, 25-35 g/L of sodium citrate, 10-15 g/L of sodium hypophosphite, 2.5-5.0 g/L of dimethylamino borane and 10mg/L of sodium dodecyl sulfate. Adjusting the pH value to 8.0-9.0 by using ammonia water, plating for 30min at 50 ℃, and rinsing by using deionized water.

Except for this step, the other process steps were identical to example 1.

The analysis of energy spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) can determine that the plating component obtained by the fifth electroless nickel plating process of example 2 is a nickel-phosphorus-boron alloy, and is a high-phosphorus alloy, and the phosphorus content is greater than 10 wt%.

The flat electrical resistance of the PPTA plain weave fabrics after each of the electroless, electrolytic copper and electrolytic nickel and silver plating steps were tested using the processes of example 1 and example 2, respectively, and the data is shown in table 1. As can be seen from Table 1, with the gradual development of the plating process, the plane resistance of the PPTA fabric is rapidly reduced, and the conductivity of the sample after electroplating is greatly improved. The chemical nickel-phosphorus-boron alloy layer has poorer conductivity than the chemical nickel plating layer; but the difference of the electrical conductivity of the two samples becomes smaller through the subsequent copper electroplating and nickel electroplating processes; after the final silver electroplating process, the conductivity of the electroless nickel-phosphorus-boron alloy layer substrate is slightly higher than that of the electroless nickel substrate. In the early-stage experiment, after the PPTA fabric is subjected to chemical silvering, the optimal plane resistance value is 20-30 m omega/□; after silver plating according to examples 1 and 2, the sheet resistance was about 5.5 m.OMEGA./□, and the conductivity was greatly improved.

The nickel-phosphorus-boron alloy plating layer and the nickel plating layer have different electrical conductivity, magnetism and acid and alkali corrosion resistance, after electroplating is carried out on the nickel-phosphorus-boron alloy plating layer and the nickel plating layer, the electrical conductivity of the obtained composite plating layer is slightly different, and the required plating layer structure and the corresponding process conditions can be selected according to different application scenes.

TABLE 1 plane resistance of the samples of example 1 and example 2

The PPTA plain weave fabrics were plated by the processes of example 1 and example 2, respectively, and the electromagnetic shielding effectiveness of the fabrics in the frequency range of 30 kHz-1.5 GHz after each step of electroless plating, electro-coppering, electro-nickel plating and electro-silver plating was tested, and the related data are shown in FIG. 9. It can be seen from the figure that compared with a pure chemical nickel plating process, the electromagnetic shielding performance of the electroplated sample is greatly improved, especially after the final silver electroplating process, the electromagnetic shielding performance is stabilized at about 90db, and the method can be applied to application scenes with more strict requirements on the electromagnetic shielding performance. In the early experiment, after the PPTA fabric is subjected to chemical silver plating, the optimal shielding value in the frequency range of 30 kHz-1.5 GHz is 70-75 db, which is basically equal to the electromagnetic shielding performance of the Ni/Cu/Ni sample in the embodiment 1, and is far inferior to the electromagnetic shielding performance of the samples after the silver plating in the embodiments 1 and 2. The chemical silver plating solution can not be recycled, and the electroplating solution can be recycled, so that the economy is higher.

The nickel-phosphorus-boron alloy plating layer and the nickel plating layer have different electrical conductivity, magnetism and acid and alkali corrosion resistance, after electroplating is carried out on the nickel-phosphorus-boron alloy plating layer and the nickel plating layer, the electromagnetic shielding performance of the obtained composite plating layer is slightly different, and the required plating layer structure and the corresponding process conditions can be selected according to different application scenes.

The advantages and value of the process of the invention can be demonstrated by the above comparison.

Example 3:

the first step is as follows: deoiling, namely putting the poly-p-phenylene terephthamide (PPTA) fiber into 0.1 wt% of sodium hydroxide solution, ultrasonically cleaning for 10min at normal temperature, taking out, and rinsing with deionized water.

The second step is that: pretreating by immersing the fibres in CaCl₂DMF solution (CaCl) of₂Content of 5 wt%), soaked at 100 deg.C for 20min, and rinsed with deionized water.

The third step: activating, putting the pretreated fiber into AgNO₃NMP solution (AgNO)₃30g/L) at 85 deg.C for 30min, and slowly rinsing.

The fourth step: and (3) reducing, namely putting the activated fiber into a 2g/L sodium borohydride aqueous solution, carrying out reduction treatment at normal temperature, taking out after 10min, and rinsing the fiber by using deionized water.

The fifth step: chemical nickel plating, the reduced fiber is put into a chemical nickel plating solution, and the formula of the chemical nickel plating solution is as follows: 10-20 g/L of nickel sulfate, 20-35 g/L of sodium citrate, 5-10 g/L of ammonium chloride, 10-15 g/L of sodium hypophosphite, 2.5-5.0 g/L of dimethylamino borane and 20mg/L of sodium dodecyl sulfate. Adjusting the pH value to 8.0-9.0 by using KOH, plating for 45min at 45 ℃, and rinsing by using deionized water.

And a sixth step: and (2) copper electroplating, namely placing the fibers subjected to chemical nickel plating into copper electroplating solution, wherein the formula of the copper electroplating solution is as follows: 5-10 g/L of basic copper carbonate, 80-100 g/L of hydroxyethylidene diphosphonic acid, 40-50 g/L of potassium carbonate and 0.1-0.3 g/L of selenium dioxide. Adjusting the pH value to 9.0-10.0 by using potassium hydroxide. And taking the fiber as a cathode and the electrolytic copper foil as an anode, plating for 90min at the temperature of 30-40 ℃, and rinsing with deionized water.

The seventh step: and (2) electroplating nickel, namely putting the fibers after copper electroplating into a nickel electroplating solution, wherein the formula of the nickel electroplating solution is as follows: 300-350 g/L of nickel sulfate, 12-15 g/L of sodium chloride, 30-40 g/L of boric acid, 0.2-0.4 g/L of coumarin, 0.5-0.8 g/L of saccharin, 0.8-1.0g/L of 1, 4-butynediol, 0.05-0.08 g/L of sodium dodecyl sulfate and pH value of 3-4. And taking the fiber as a cathode and electrolytic nickel foil as an anode, plating for 45min at 50-60 ℃, and rinsing with deionized water.

Optionally, the eighth step: and (3) silver electroplating, namely putting the fibers subjected to nickel electroplating into a silver electroplating solution, wherein the formula of the silver electroplating solution is as follows: 30-40 g/L of silver nitrate, 100-120 g/L of 5, 5-dimethyl hydantoin, 50-70 g/L of potassium carbonate, 40-50 g/L of sodium pyrophosphate, 0.5-1 g/L of L-histidine and 10mL/L of a stabilizer, and the pH value is adjusted to 10.0-11.0 by using potassium hydroxide. The stabilizer is a solution prepared from 4-8 g/L of 1, 4-butynediol, 2-4 g/L of triethanolamine and 2-4 g/L of vanillin. And taking the fiber as a cathode and the electrolytic silver foil as an anode, plating for 45min at 25-30 ℃, and rinsing with deionized water.

Example 4:

the first step is as follows: deoiling, namely putting the poly-p-phenylene terephthamide (PPTA) fiber into 0.02 wt% of sodium hydroxide solution, ultrasonically cleaning for 20min at normal temperature, taking out, and rinsing with deionized water.

The second step is that: pretreating, namely soaking the fiber into a sulfuric acid solution containing 50 wt%, soaking for 15min at 60 ℃, taking out, and rinsing with deionized water.

The third step: activating, putting the pretreated fiber into 0.1g/L PdCl₂The solution (containing 3.5mL/L hydrochloric acid) is activated at 30 deg.C for 25min, and slowly rinsed.

The fourth step: reducing, putting the activated fiber into 20g/L SnCl₂The solution (the solution additionally contains 15mL/L hydrochloric acid) is subjected to reduction treatment at normal temperature, and is taken out after 10min and rinsed by deionized water.

The fifth step: chemical nickel plating, the reduced fiber is put into a chemical nickel plating solution, and the formula of the chemical nickel plating solution is as follows: 10-20 g/L of nickel sulfate, 20-35 g/L of sodium citrate, 3-8 g/L of sodium hypophosphite, 1-5 g/L of dimethylamino borane and 15mg/L of sodium dodecyl sulfate. Adjusting the pH value to 9.0-10.0 by using ammonia water, plating for 30min at 55 ℃, and rinsing by using deionized water.

And a sixth step: and (2) copper electroplating, namely placing the fibers subjected to chemical nickel plating into copper electroplating solution, wherein the formula of the copper electroplating solution is as follows: 35-45 g/L of copper sulfate, 250-300 g/L of citric acid, 1-5 g/L of triethanolamine, 15-20 g/L of sodium bicarbonate and 0.01-0.05 g/L of selenium dioxide, and adjusting the pH value to 9.0-10.0 by using potassium hydroxide. And (3) plating the fiber as a cathode and the electrolytic copper foil as an anode for 100min at the temperature of 30-40 ℃, and rinsing with deionized water.

The seventh step: and (2) electroplating nickel, namely putting the fibers after copper electroplating into a nickel electroplating solution, wherein the formula of the nickel electroplating solution is as follows: 300-350 g/L of nickel sulfate, 12-15 g/L of sodium chloride, 30-40 g/L of boric acid, 0.2-0.4 g/L of coumarin, 0.5-0.8 g/L of saccharin, 0.8-1.0g/L of 1, 4-butynediol, 0.05-0.08 g/L of sodium dodecyl sulfate and pH value of 3-4. And taking the fiber as a cathode and electrolytic nickel foil as an anode, plating for 30min at 50-60 ℃, and rinsing with deionized water.

Eighth step: and (3) silver electroplating, namely putting the fibers subjected to nickel electroplating into a silver electroplating solution, wherein the formula of the silver electroplating solution is as follows: 30-40 g/L silver nitrate, 100-120 g/L5, 5-dimethyl hydantoin, 50-70 g/L potassium carbonate, 40-50 g/L sodium pyrophosphate, 0.5-1 g/L tryptophan, 0.1g/L polyethylene glycol (molecular weight 1000), 10mL/L stabilizer, and the pH value is adjusted to 10.0-11.0 by using potassium hydroxide. The stabilizer is a solution prepared from 4-8 g/L1, 4-butynediol and 2-4 g/L triethanolamine. And (3) taking the fiber as a cathode and the electrolytic silver foil as an anode, plating for 60min at 25-30 ℃, and rinsing with deionized water.

Example 5:

the first step is as follows: deoiling, namely putting the poly-p-phenylene terephthamide (PPTA) fiber into 0.05 wt% of sodium hydroxide solution, ultrasonically cleaning for 15min at normal temperature, taking out, and rinsing with deionized water.

The second step is that: pretreating by immersing the fibres in CaCl₂NMP solution (CaCl)₂Content of 3 wt%), soaked at 60 deg.C for 45min, and rinsed with deionized water.

The third step: activating, putting the pretreated fiber into AgNO₃DMAc solution (AgNO)₃50g/L) at a temperature of 75 ℃ for 10min, and then taking out and slowly rinsing.

The fourth step: and (3) reducing, namely putting the activated fiber into a 2g/L sodium borohydride aqueous solution, carrying out reduction treatment at normal temperature, taking out the fiber after 5min, and rinsing the fiber with deionized water.

The fifth step: chemical nickel plating, the reduced fiber is put into a chemical nickel plating solution, and the formula of the chemical nickel plating solution is as follows: 10-20 g/L of nickel acetate, 15-25 g/L of sodium citrate, 1-5 g/L of ammonium chloride, 5-10 g/L of sodium hypophosphite, 0.1-0.5 g/L of dimethylamino borane and 10mg/L of sodium dodecyl sulfate. Adjusting the pH value to 9.5-10.5 by using KOH, plating for 30min at 55 ℃, and rinsing by using deionized water.

And a sixth step: and (2) copper electroplating, namely placing the fibers subjected to chemical nickel plating into copper electroplating solution, wherein the formula of the copper electroplating solution is as follows: 15-25 g/L of basic copper carbonate, 100-150 g/L of triethanolamine, 20-30 g/L of ammonium citrate, 5-10 g/L of potassium nitrate and 0.1-0.3 g/L of selenium dioxide. Adjusting the pH value to 9.0-10.0 by using potassium hydroxide. And taking the fiber as a cathode and the electrolytic copper foil as an anode, plating for 45min at 30-40 ℃, and rinsing with deionized water.

The seventh step: and (2) electroplating nickel, namely putting the fibers after copper electroplating into a nickel electroplating solution, wherein the formula of the nickel electroplating solution is as follows: 280-320 g/L of nickel sulfate, 50-100 g/L of nickel chloride, 40-60 g/L of boric acid, 0.5-0.8 g/L of saccharin, 0.8-1.0g/L of 1, 4-butynediol, 0.05-0.08 g/L of sodium dodecyl sulfonate and pH value of 3-4. And (3) taking the fiber as a cathode and the electrolytic nickel foil as an anode, plating for 30min at 55-60 ℃, and rinsing with deionized water.

Eighth step: and (3) silver electroplating, namely putting the fibers subjected to nickel electroplating into a silver electroplating solution, wherein the formula of the silver electroplating solution is as follows: 30-40 g/L of silver nitrate, 200-250 g/L of sodium thiosulfate, 40-60 g/L of potassium carbonate, 40-60 g/L of potassium metabisulfite, 0.3-0.6 g/L of thiosemicarbazide, 0.5-1 g/L of tryptophan and 0.1-0.5 g/L of triethanolamine, and the pH value is adjusted to 9.0-10.0 by using potassium hydroxide. And taking the fiber as a cathode and the electrolytic silver foil as an anode, plating for 30min at 25-30 ℃, and rinsing with deionized water.

Example 6:

the first step is as follows: deoiling, namely putting the poly-p-phenylene terephthamide (PPTA) fiber into 0.01 wt% potassium hydroxide solution, ultrasonically cleaning for 40min at normal temperature, taking out, and rinsing with deionized water.

The second step is that: pretreating by immersing the fibres in CaCl₂DMAc solution (CaCl) of₂Content of 5 wt%), soaked at 90 deg.C for 25min, and then rinsed with deionized water.

The third step: activating, putting the pretreated fiber into AgNO₃DMF solution (AgNO)₃60g/L) at 100 deg.C for 5min, and slowly rinsing.

The fifth step: chemical nickel plating, the reduced fiber is put into a chemical nickel plating solution, and the formula of the chemical nickel plating solution is as follows: 20-25 g/L of nickel sulfate, 5-10 g/L of sodium citrate, 40-45 g/L of sodium pyrophosphate, 1-1.5 g/L of dimethylamino borane and 10mg/L of sodium dodecyl sulfate. Adjusting the pH value to 10.0-10.5 by using ammonia water, plating for 30min at 30 ℃, and rinsing by using deionized water.

The seventh step: and (2) electroplating nickel, namely putting the fibers after copper electroplating into a nickel electroplating solution, wherein the formula of the nickel electroplating solution is as follows: 100-150 g/L of nickel sulfate, 10-20 g/L of nickel chloride, 100-150 g/L of sodium citrate, 30-50 g/L of boric acid, 0.5-0.8 g/L of saccharin, 0.05-0.08 g/L of sodium dodecyl sulfate and pH value of 6.0-7.0. And taking the fiber as a cathode and the electrolytic nickel foil as an anode, plating for 30min at 40-50 ℃, and rinsing with deionized water. .

Eighth step: and (3) silver electroplating, namely putting the fibers subjected to nickel electroplating into a silver electroplating solution, wherein the formula of the silver electroplating solution is as follows: putting the fibers after nickel electroplating into an electroplating silver solution, wherein the formula of the electroplating silver is as follows: 30-40 g/L of silver nitrate, 200-250 g/L of sodium thiosulfate, 40-60 g/L of potassium carbonate, 40-60 g/L of potassium metabisulfite, 0.3-0.6 g/L of thiosemicarbazide, 0.5-1 g/L of L-histidine and 0.1-0.5 g/L of triethanolamine, and the pH value is adjusted to 9.0-10.0 by using potassium hydroxide. And taking the fiber as a cathode and the electrolytic silver foil as an anode, plating for 30min at 25-30 ℃, and rinsing with deionized water.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principles of the present invention are intended to be included within the scope of the present invention.

Claims

1. The preparation method of the conductive aromatic polyamide fiber with the composite metal coating structure is characterized by comprising the following steps of:

firstly, washing and removing oil to remove dirt, oil agent and impurities on the surface of the fiber;

secondly, pretreating and swelling the fibers; the method specifically comprises the following steps: pre-treating, namely putting the cleaned fiber into a pre-treating solution, dipping for 5-60 min at 25-150 ℃, taking out, rinsing with deionized water, wherein the pre-treating solution is sulfuric acid (H)₂SO₄) Solution, calcium chloride (CaCl)₂) In dimethyl sulfoxide (DMSO), CaCl₂N-methylpyrrolidone (NMP) solution of (5), CaCl₂Dimethylacetamide (DMAc) solution, or CaCl₂The concentration of the dimethyl formamide (DMF) solution is 10-98 wt%, and the concentration of the calcium chloride solution is 3-5 wt%;

step three, activation, namely soaking the fiber by using a noble metal salt solution to form a thin catalytic active layer on the surface of the fiber;

fourthly, reducing, namely soaking the fibers by using a reducing solution to form a precious metal particle layer on the surfaces of the fibers to be used as an anchoring point between the fibers and a subsequent plating layer;

fifthly, chemical plating is carried out, and a layer of metal nickel or nickel alloy is deposited on the surface of the fiber; the thickness of the plating layer is 100-500 nm;

sixthly, electroplating copper, and depositing a metal copper layer on the surface of the fiber treated in the fifth step; the thickness of the metal copper plating layer is 250-1000 nm;

step seven, electroplating nickel, and depositing a metal nickel layer on the surface of the fiber treated in the step six;

and step eight, selectively depositing a layer of metal silver on the surface of the fiber treated by the step seven.

2. The method for preparing the conductive aromatic polyamide fiber with the composite metal plating structure according to claim 1, wherein the first step specifically comprises: washing and removing oil, namely putting the aromatic polyamide fiber into 0.01-20 wt% of sodium hydroxide or potassium hydroxide solution, ultrasonically cleaning for 5-60 min, taking out, and rinsing with deionized water to remove dirt, oil and impurities on the surface of the fiber;

the third step specifically comprises: activating, namely putting the pretreated fiber into a silver nitrate or palladium chloride solution with the concentration of 0.1-20 g/L, soaking at 25-120 ℃ for 5-60 min, taking out, and slowly rinsing with deionized water; the solvent of the activating solution is NMP, DMSO, DMAc, DMF or water;

the fourth step specifically includes: reducing, namely putting the activated fiber into a stannous chloride, sodium borohydride, dimethylamine borane or hydrazine hydrate solution with the concentration of 1-10 g/L, soaking for 5-30 min at 25-35 ℃, taking out, and rinsing with deionized water; the solvent of the reducing solution is NMP, DMSO, DMAc, DMF or water; after reduction, a noble metal target point firmly combined with the substrate is formed on the surface of the fiber, and the target point is used as an anchoring point and a catalytic point of a subsequent chemical plating layer.

3. The method for preparing conductive aromatic polyamide fiber with composite metal coating structure as claimed in claim 1, wherein the fifth step of electroless plating comprises: preparing a chemical nickel plating solution by using nickel salt, a complexing agent, a reducing agent, a buffering agent and a stabilizing agent, and depositing a layer of metal nickel or nickel alloy on the surface of the fiber;

the reducing agent is sodium hypophosphite, dimethylamino borane and hydrazine hydrate;

by adjusting the pH value of the solution and the concentration of each component, the phosphorus and boron elements in the reducing agent and the nickel are co-deposited to obtain the nickel-phosphorus, nickel-boron or nickel-phosphorus-boron alloy.

4. The method for preparing an electrically conductive aromatic polyamide fiber having a composite metal plating structure of claim 1, wherein the sixth step of copper electroplating comprises: preparing an electrolytic copper plating solution by using a copper salt, a complexing agent, a stabilizing agent and a buffering agent, and depositing a metal copper plating layer on the fiber surface treated in the fifth step under a certain current or voltage;

the process of the seventh step of nickel electroplating comprises the following steps: preparing an electroplating nickel solution by using nickel salt, a complexing agent, a stabilizing agent, a buffering agent and a brightening agent, and depositing a metal nickel coating on the surface of the fiber treated in the sixth step under a certain current or voltage;

the eighth step of the optional silver electroplating process comprises the following steps: silver salt, complexing agent, stabilizer, buffering agent and brightening agent are used to prepare silver electroplating solution, and under a certain current or voltage, a layer of metallic silver coating is deposited on the surface of the fiber treated by the seventh step.

5. An electrically conductive aromatic polyamide fiber having a composite metal plating structure prepared by the method for preparing an electrically conductive aromatic polyamide fiber having a composite metal plating structure of claim 1, wherein an electroless nickel or nickel alloy layer is deposited on a substrate of the aromatic polyamide synthetic fiber; depositing an electroplated copper metal layer on the substrate of the electroless nickel or nickel alloy plating layer;

depositing a nickel electroplating metal layer on the substrate of the copper electroplating metal layer;

and selectively depositing or not depositing an electroplated silver metal layer on the substrate of the electroplated nickel metal layer.

6. The conductive aromatic polyamide fiber having a composite metal plating structure of claim 5, wherein the aromatic polyamide fiber has a chemical formula of: (I)

Or (a)

）

Wherein Ar is₁、Ar₂、Ar₃Is composed of

、

、

、

And

one of them.

7. The electrically conductive aramid fiber having a composite metal plating structure of claim 5, wherein the aramid fiber is present in the form of a fiber, yarn, fabric;

the chemical nickel-plating alloy layer comprises nickel and phosphorus, nickel and boron, or nickel, phosphorus and boron alloy plating layers.

8. An aerospace electromagnetic shielding material and conductor prepared by using the conductive aromatic polyamide fiber with a composite metal plating layer structure of claim 5.

9. A marine, satellite electromagnetic shielding material and conductor prepared by using the conductive aromatic polyamide fiber with a composite metal plating layer structure of claim 5.

10. An electromagnetic shielding material and a conductor in the communication and medical fields, which are prepared by using the conductive aromatic polyamide fiber with the composite metal coating structure of claim 5.