US20170204519A1

US20170204519A1 - Method for plating nonwoven fabric by using continuous electroless and electrolytic plating processes

Info

Publication number: US20170204519A1
Application number: US15/326,583
Authority: US
Inventors: Gyu Beom Kwag; Seung Won Kang; Nam Kwi Lee; Min Hwan Chang; Jong Gil Lee; Soo Hyung HUR; Min Young Park; Byung Rok KANG; Ji Hun Kang
Original assignee: BULLSONE MATERIAL Co Ltd; Clean & Science Co Ltd
Current assignee: BULLSONE MATERIAL Co Ltd; Clean & Science Co Ltd
Priority date: 2014-07-17
Filing date: 2015-06-30
Publication date: 2017-07-20
Also published as: JP6797790B2; JP2017526816A; DE112015003301T5; JP2020007639A; DE112015003301B4; WO2016010287A1; KR101604858B1; KR20160010700A

Abstract

The present invention relates to: a method for plating nonwoven fabric with metals (copper and nickel, or nickel and nickel) by electroless and electrolytic continuous processes; and a nonwoven fabric plated by the method. The present invention can prepare a metal-plated nonwoven fabric by electrolytic plating a space of metal ions, which are formed by performing electroless plating with copper or nickel, with nickel in a short amount of time, thereby filling up the space, and thus has excellent conductivity while being thin. A desired conductivity can be obtained by changing the composition of a plating solution or controlling the plating velocity, and a line capable of performing plating with copper and nickel, nickel and nickel, nickel alone, or copper alone, in combination, can be manufactured. In addition, a highly conductive nonwoven fabric having no difference in plating thickness of nonwoven fabric performed by only electroless plating can be produced.

Description

FIELD

This application claims priority to and the benefit of Korean Patent
Application No. 10-2014-0090300 filed in the Korean Intellectual Property Office on 17 Jul. 2014, the entire contents of which are incorporated herein by reference.
The present invention relates to a method for plating a nonwoven fabric using continuous electroless and electrolytic plating processes and a nonwoven fabric plated by the method and, more specifically, to a preparation of a metal-plated nonwoven fabric to improve conductivity by enhancing the binding strength between metals, with which a nonwoven fabric is surface-treated, and fibers which constitute the nonwoven fabric.

BACKGROUND

Today, a carbon fiber-reinforced composite material that starts to develop rapidly together with the development of aerospace industries is one of the advanced materials that are used in various fields, such as electrical and electronic materials, civil engineering and building materials, automobiles, ships, military equipment, and sporting goods as well as aerospace industries.
However, the carbon fiber-reinforced composite material is recently used in a very limited role, due to its low conductivity, for automotive electronics and communication device housing that need to implement mechanical properties and electromagnetic wave shielding performance at the same time.
Therefore, in order to overcome the disadvantage, a polymer composite material having electromagnetic shielding efficiency has been developed by adding carbon fiber, carbon black, CNT, TiO₂, nickel-coated graphite, and the latest announced graphene, as a filler for implementing an electromagnetic wave shielding function, to the polymer composite material. However, such a developed polymer composite material has many problems in the commercialization thereof due to the problems in dispersion and deteriorations in mechanical properties. Moreover, there are many trials and errors due to price disadvantages and mechanical properties.
Meanwhile, an electroless or electrolytic surface treatment process of the conventional art, of which respective steps are separated for conducting treatment and then re-treatment, has problems in that the processing time is not shortened, the price competitiveness is decreased, and the production facilities are also not simplified.
A CVD process or a sputtering manner has been used before in order to increase the binding strength between carbon fibers and a metal, but does not have price competitiveness due to high production costs, causing many problems.
Moreover, an electroless carbon fiber plating method is somewhat limited in increasing conductivity in carbon fibers by containing a phosphor component due to chemical ionic binding, and an electrolytic plating method may increase conductivity, but does not achieve uniform plating on each filament of the carbon fiber, and thus each filament is not suitable as an important composite material. A plated carbon fiber produced by electrolytic plating has a lot of lint and causes a lot of filament disconnection, and thus is limited in the use thereof as a composite material that needs to maintain the plating states of products.
With respect to the hybrid type of the continuous process developed in the present invention, when all filaments of carbon fibers are first plated through electroless plating, followed by complete removal of a chemical reagent and then electrolytic plating, all carbon fibers are uniformly plated, and a plating layer, which is dense between metals, is formed in spite of a short electroplating time such that the plating layer has a small thickness and rapidly improved conductivity, and thus is very suitable for the use of a composite material.
In cases of the conventional production, respectively different production processes are conducted, and thus, the production processes had a high cost, production facilities were very expensive, and the control of conductivity through the adjustment of the plating thickness of a product was very difficult.
However, the hybrid type of the continuous process developed in the present invention has a low cost and allows easy control by continuously performing electroless and electrolytic plating using a single production facility, so that competitive products can be produced and quality inspection is easy.
Throughout the entire specification, many papers and patent documents are referenced and their citations are represented. The disclosure of the cited papers and patent documents are entirely incorporated by reference into the present specification, and the level of the technical field within which the present invention falls and the details of the present invention are explained more clearly.

DETAILED DESCRIPTION

Technical Problem

The present inventors searched and endeavored to develop a method for preparing a metal-plated fiber nonwoven fabric with excellent economical feasibility and conductivity, and as a result, the present inventors verified that the adoption of the continuous electroless and electrolytic surface treatment processes has advantages in shortening of the process time, having price competitiveness, and simplifying production facilities when compared with only an electroless or electrolytic surface treatment process of the conventional art, and induces not only dense plating between metal structures, leading excellent conductivity, but also low production costs, when compared with products of the conventional art.
Accordingly, an aspect of the present invention is to provide a method for plating a non-woven fabric with metals (cooper and nickel) through continuous electroless and electrolytic processes.
Another aspect of the present invention is to provide a non-woven fabric plated with metals (cooper and nickel).
Other purposes and advantages of the present invention will become more obvious with the following detailed description of the invention, claims, and drawings.

Technical Solution

In accordance with an aspect of the present invention, there is provided a method for plating a non-woven fabric with metals through continuous electroless and electrolytic processes, the method comprising:
(a) allowing a non-woven fabric to pass through an electroless plating liquid to plate the non-woven fabric with copper for 6-10 minutes, the electroless plating liquid containing, on the basis of the volume of pure water, 2.5-5.5 g/l Cu ions, 20-55 g/l EDTA, 2.5-4.5 g/l formalin, 2-6 g/l triethanolamine (TEA), 8-12 ml/l 25% NaOH, and 0.008-0.15 g/l 2,2′-bipiridine and having a pH of 12-13 and a temperature of 36-45° C.; and
(b) allowing the copper-plated non-woven fabric in step (a) to pass through an electrolytic plating liquid to plate the copper-plated non-woven fabric with nickel for 1-3 minutes, the electrolytic plating liquid containing 280-320 g/l Ni(NH₂SO₃)₂, 15-25 g/l NiCl₂, and 35-45 g/l H₃BO₃and having a pH of 4.0-4.2 and a temperature of 50-60° C.
In accordance with another aspect of the present invention, there is provided a method for plating a non-woven fabric with metals through continuous electroless and electrolytic processes, the method comprising:
(a) allowing a non-woven fabric to pass through an electroless plating liquid to plate the non-woven fabric with nickel for 6-10 minutes, the electroless plating liquid containing, on the basis of the volume of pure water, 5-7 g/l Ni ions, 20-30 g/l NaH₂PO₂, 20-30 g/l Na₃C₆H₅O₇, and 0.0005-0.001 g/l potassium thiosulfate and having a pH of 8.5-9.5 and a temperature of 30-35° C.; and (b) allowing the nickel-plated non-woven fabric in step (a) to pass through an electrolytic plating liquid to plate the nickel-plated non-woven fabric with nickel for 1-3 minutes, the electrolytic plating liquid containing 280-320 g/l Ni(NH₂SO₃)₂, 15-25 g/l NiCl₂, and 35-45 g/l H₃BO₃and having a pH of 4.0-4.2 and a temperature of 50-55° C.
The present inventors searched and endeavored to develop a method for preparing a metal-plated fiber nonwoven fabric with excellent economical feasibility and conductivity, and as a result, the present inventors verified that the adoption of the continuous electroless and electrolytic surface treatment processes has advantages in shortening of the process time, having price competitiveness, and simplifying production facilities when compared with only an electroless or electrolytic surface treatment process of the conventional art, and induces not only dense plating between metal structures, leading excellent conductivity, but also low production costs, when compared with products of the conventional art.
The method of the present invention is characterized in that a fiber nonwoven fabric is first electroless-plated (with copper or nickel) through surface treatment by a non-oxidation method and is then electro-plated (with nickel), thereby minimizing the production process and allowing continuous processes like anodizing, thus preparing a high-functional nonwoven fabric with relatively superior conductivity.
The method of the present invention is implemented in a manner in which electroless copper plating or electroless nickel plating is first performed, followed by electrolytic plating.
The method of the present invention may be applied to the nonwoven fabric by various known preparing methods, and for example, may be applied to a dry-laid nonwoven fabric, a wet-laid nonwoven fabric, a spunbond nonwoven fabric, or the like. According to an embodiment of the present invention, the method of the present invention may be applied to a carbon fiber nonwoven fabric or a PET nonwoven fabric, as a wet-laid nonwoven fabric. The preparing methods of the above-described dry-laid nonwoven fabric, wet-laid nonwoven fabric, or a spunbond nonwoven fabric are widely known in the art, and Korean Patent Publication No. 10-2012-0121079, Korean Patent Registration No. 101049623, Korean Patent Registration No. 101133851, and Korean Patent Registration No. 101156844 are incorporated herein by reference.
The plating method of the present invention may be applied to various kinds of nonwoven fabrics, for example, a nonwoven fabric manufactured of a carbon fiber, a polyester fiber, a glass fiber, an aramid fiber, a ceramic fiber, a metal fiber, a polyimide fiber, a polybenzoxazole fiber, a natural fiber, or a mixed fiber thereof.
The polyester fiber includes polyethylene terephthalate (PET), polyglycolide (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and Vectran, but is not limited thereto.
According to an embodiment of the present invention, the method of the present invention may be applied to a carbon fiber nonwoven fabric or a PET nonwoven fabric.
Meanwhile, the nonwoven fabric, to which the method of the present invention is applied, may be manufactured by mixing the foregoing fiber (referred to as “first fiber”) with a second fiber as a reinforcing fiber. The reinforcing fiber is a material for increasing the strength of the nonwoven fabric, and is a low-melting fiber or a low-melting filament, and for example, an L/M polyester fiber (LMP) may be used. The low-melting polyester fiber has a melting point lower than 255° C., which is the melting point of general polyester, and is used for the purpose of thermal fusion.
According to the present invention, the low-melting fiber as the second fiber is an L/M polyethylene terephthalate (low-melting PET). The melting point of L/M polyethylene terephthalate is relatively low, and thus, the L/M polyethylene terephthalate, when heated and compressed at 100° C., is melted and mixed with the first fiber, thereby increasing the strength of the entire nonwoven fabric.
The method for plating a nonwoven fabric with metals through continuous electroless and electrolytic processes of the present invention is ultimately for manufacturing a metal-plated nonwoven fabric, and may be used with the same meaning as a method for manufacturing a metal-plated nonwoven fabric through continuous electroless and electrolytic processes.
Hereinafter, the method of the present invention for manufacturing a metal-plated nonwoven fabric through continuous electroless and electrolytic processes will be described by the steps as below:
(a) Electroless Plating Process
First, a nonwoven fabric is electroless-plated with a metal.
In one embodiment, in cases where the carbon fiber nonwoven fabric is plated with copper, an electroless plating liquid contains pure water, a copper metal salt, a complexing agent, a reducing agent, a stabilizer, and a pH adjusting agent.
The copper metal salt contained in the electroless plating liquid supplies copper ions to impart conductivity to carbon fibers. Meanwhile, formalin as a reducing agent, EDTA as a complexing agent, triethanolamine (TEA) and 2,2′-bipiridine as stabilizers, and 25% NaOH as a pH adjusting agent were used.
As can be confirmed in examples, with the increase in the concentrations of formalin as a reducing agent and NaOH as a pH adjusting agent, which are contained in the electroless plating liquid, the plating rate was increased, but the lifetime of the plating liquid was shortened, and thus, considering this matter, the contents of the reducing agent and the pH adjusting agent were adopted.
Meanwhile, as can be clearly confirmed from examples, as a result of testing the plating rate and the liquid stability by adjusting the content of the reducing agent when the contents of the copper ions and the complexing agent increase at the same ratio, the plating rate and the thickness of the plating layer can be controlled by adjusting the concentrations of copper ions and formalin as a reducing agent, and through the control of the thickness of the plating layer, the specific gravity, strength, elastic modulus, and strain can be controlled. However, as the plating layer is thicker, the specific gravity is increased, and the strength, elastic modulus, and strain deteriorate, and thus the present invention has solved the above problems by performing electrolytic plating together with the adjustment of the concentrations of the copper ions and formalin as a reducing agent, thereby improving conductivity through a thin thickness. This is why the present invention adopts continuous electroless and electrolytic processes.
According to an embodiment of the present invention, the electroless plating step in step (a) is characterized by allowing the nonwoven fabric to pass through an electroless plating liquid to plate the nonwoven fabric with copper for 6-10 minutes, the electroless plating liquid containing, on the basis of the volume of pure water, 4.5-5.5 g/l Cu ions, 45-55 g/l EDTA, 3.5-4.5 g/l formalin, 4-6 g/l triethanolamine (TEA), 8-12 ml/l 25% NaOH, and 0.01-0.15 g/l 2,2′-bipiridine and having a pH of 12-13 and a temperature of 40-45° C.
In another embodiment, in cases where the nonwoven fabric is plated with nickel, the electroless plating liquid contains pure water, a nickel metal salt, a pH buffer, a reducing agent, and a stabilizer.
The nickel metal salt contained in the electroless plating liquid supplies nickel ions to impart conductivity to the nonwoven fabric, and NaH₂PO₂as a reducing agent, potassium thiosulfate as a stabilizer, and Na₃C₆H₅O₇as a pH buffer may be used.
After the electroless plating, three stages of washing are conducted, and the third washing in the three stages of washing is conducted by adding 1-2% H₂SO₄. This is for keeping the pH of an electrolytic plating bath and activating surfaces of the electroless-plated carbon fibers.
(b) Electrolytic Plating Process
After step (a), the copper or nickel electroless-plated nonwoven fabric is continuously plated with nickel through an electrolytic plating process.
Here, one of the characteristics of the present invention is that the electrical conductivity of the fiber or nonwoven fabric is improved by conducting an electroless plating process and then conducting a nickel electrolytic plating process.
An electrolytic plating liquid for conducting the electrolytic plating process employs Ni(NH₂SO₃)₂and NiCl₂, as nickel metal salts, and H₃BO₃, as a pH buffer.
As can be clearly confirmed from examples, the carbon fibers obtained by continuous electroless and electrolytic processes reduced the electric resistance value by about 32- to 37-fold compared with non-plated carbon fibers, and reduced by 2-fold compared with comparative examples, thereby improving electrical conductivity. Therefore, it can be seen that even a nonwoven fabric manufactured of carbon fibers had improved electrical conductivity.
It is considered that the electrical conductivity was improved in a manner in which, after electroless plating, copper or nickel pores were filled by Ni electrolytic plating in a fast time.
According to an embodiment of the present invention, the electrolytic plating process in step (c) is conducted by applying a constant voltage (CV) of 5-15 V.
In cases of continuous electroless copper plating and electrolytic nickel plating processes, the electrolytic plating process is conducted by applying a constant voltage (CV) of 5-10 V, and more preferably 6-8 V.
In cases of continuous electroless nickel plating and electrolytic nickel plating processes, the electrolytic plating process is performed by applying a constant voltage (CV) of 10-15 V.
The advantage of the electroless and electrolytic plating processes is that an alloy layer is formed that: exhibits excellent electrical conductivity; is effective in adhesive strength and ductility; and has excellent electrical conductivity even with a thin thickness due to an electrolytic metal material adhering to spaces of the metal, which are generated in the electroless plating. In addition, the electroless and electrolytic plating processes have an advantage in that a fiber or nonwoven fabric can be uniformly plated.
Electroless (copper or nickel) plating is first conducted and then electrolytic plating is continuously conducted while a voltage is applied to a bath in which a nonwoven fabric is placed, so that electrolyte ions are combined with pores generated from electroless plating, thereby producing a product with a small plating thickness and improved conductivity.
According to the present invention, the non-woven fabric in step (a) may be pre-treated, before step (a), by a method including the following steps:
(i) degreasing and softening the non-woven fabric by allowing the non-woven fabric to pass through an aqueous solution containing a surfactant, an organic solvent, and a non-ionic surfactant;
(ii) performing an etching process for neutralizing, cleaning, and conditioning actions by allowing the non-woven fabric as the product in step (a) to pass through an aqueous solution containing sodium bisulfite (NaHSO₃), sulfuric acid (H₂SO₄), ammonium persulfate ((NH₄)₂S₂O₈), and pure water;
(iii) performing a sensitizing process by allowing the non-woven fabric as the product in step (ii) to an aqueous solution of PdCl₂; and
(iv) performing an activating process by allowing the non-woven fabric as the product in step (iii) to pass through an aqueous solution of sulfuric acid (H₂SO₄).
(i) Degreasing and Softening Carbon Fiber
As for the pretreatment of the nonwoven fabric in the method of the present invention, the non-woven fabric is first degreased and softened by allowing non-woven fabric to pass through an aqueous solution containing a surfactant, an organic solvent, and a non-ionic surfactant.
The aqueous solution containing a surfactant, an organic solvent, and a non-ionic surfactant functions as a degreasing action of removing epoxy or urethane that has been sized on the carbon fibers, and at the same time, functions as an action of softening surfaces of the fibers through swelling.
According to the present invention, the aqueous solution in step (i) contains 15-35 wt % of a solution, as a surfactant, in which pure water and NaOH are mixed at a weight ratio of 40-49:1-10, 50-80 wt % of diethyl propanediol and 5-15 wt % of dipropylene glycol methyl ether as organic solvents, and 400-600 ppm of a non-ionic surfactant, and more preferably, contains 20-30 wt % of a solution, as a surfactant, in which pure water and NaOH are mixed at a weight ratio of 45-48:2-5, 58-72 wt % of diethyl propanediol and 8-12 wt % of dipropylene glycol methyl ether as organic solvents, and 400-600 ppm of a non-ionic surfactant.
The non-ionic surfactant includes various non-ionic surfactants known in the art, but the non-ionic surfactant is preferably ethoxylated linear alcohol, ethoxylated linear alkyl-phenol, or ethoxylated linear thiol, and more preferably, ethoxylated linear alcohol.
According to still another preferable embodiment of the present invention, step (i) was carried out at a temperature of 40-60° C. for 1-5 minutes, and more preferably at a temperature of 45-55° C. for 1-3 minutes.
(ii) Etching Process
Then, an etching process is performed to neutralize strong alkali components, assist a washing action for a next process, a sensitizing process, and conduct a conditioning action.
An aqueous solution for the etching process contains sodium bisulfate (NaHSO₃), sulfuric acid (H₂SO₄), ammonium persulfate ((NH₄)₂S₂O₈), and pure water.
According to the present invention, the aqueous solution in step (ii) contains 0.1-10 wt % of sodium bisulfate (NaHSO₃), 0.1-3 wt % of sulfuric acid (H₂SO₄), 5-25 wt % of ammonium persulfate ((NH₄)₂S₂O₈), and 62-94.8 wt % of pure water, and more preferably, contains 0.8-2 wt % of sodium bisulfite (NaHSO₃), 0.3-1 wt % of sulfuric acid (H₂SO₄), 10-20 wt % of ammonium persulfate ((NH₄)₂S₂O₈), and 77-88.9 wt % of pure water.
According to an embodiment of the present invention, step (ii) is performed at a temperature of 20-25° C. for 1-5 minutes, and more preferably at a temperature of 20-25° C. for 1-3 minutes.
(iii) Sensitizing Process
Then, a sensitizing process is performed by allowing the nonwoven fabric as the product in step (ii) to pass through an aqueous solution of PdCl₂.
The sensitizing process is for allowing metal ions to be adsorbed on surfaces of the surface-modified fibers or nonwoven fabric.
The concentration of the aqueous solution of PdCl₂is more preferably 10-30%, and still more preferably 15-25%.
According to an embodiment of the present invention, step (iii) is performed at a temperature of 20-40° C. for 1-5 minutes, and more preferably at a temperature of 25-35° C. for 1-3 minutes.
(iv) Activating Process
Then, an activating process is performed by allowing the nonwoven fabric as the product in step (iii) to pass through an aqueous solution of sulfuric acid (H₂SO₄).
Herein, it has been described that the activating process is performed after the sensitizing process, but the performing of the activating process together with the sensitizing process is included within the scope of the present invention.
The activating process is performed in order to remove colloidized Sn, for the prevention of Pd oxidation.
More preferably, the concentration of the aqueous solution of sulfuric acid (H₂SO₄) is 5-15%.
According to still another preferable embodiment of the present invention, step (iv) is performed at a temperature of 40-60° C. for 1-5 minutes, and more preferably at a temperature of 45-55° C. for 1-3 minutes.
The nonwoven fabric may be pre-treated by the above-described method, and the pre-treated nonwoven fabric may be plated with metals, copper and nickel, or nickel and nickel, by continuous electroless and electrolytic processes. Meanwhile, it has been described that the pre-treatment process is performed after the nonwoven fabric is manufactured, but the pre-treatment of the fibers per se may be applied before the nonwoven fabric is manufactured.
According to still another aspect of the present invention, the present invention provides a metal (copper and nickel)-plated nonwoven fabric manufactured by the method of the present invention.
According to another aspect of the present invention, the present invention provides a metal (nickel and nickel)-plated nonwoven fabric manufactured by the method of the present invention.
Since the nonwoven fabric plated with copper and nickel or nickel and nickel of the present invention is manufactured by the foregoing method for manufacturing metal-plated carbon fibers using continuous electroless and electrolytic processes of the present invention, the overlapping descriptions therebetween are omitted to avoid excessive complexity of the specification due to repetitive descriptions thereof.

Advantageous Effects

Features and advantages of the present invention are summarized as follows:
(a) The plating method used in the present invention allows continuous processes and achieves stable treatment, and at the same time, allows fibers or nonwoven fabric to have high electrical conductivity by introducing a copper-nickel alloy or nickel-nickel metal onto surfaces of carbon fibers.
(b) Furthermore, when a composite material is prepared using such fibers or nonwoven fabric, there is no separation between the carbon fibers and the copper-nickel plating or nickel-nickel plating at the time of product molding, and thus the same conductivity is maintained upon the completion of the composite material. Therefore, unlike conventional products, the present composite can reduce the process and costs for adding a conductive fiber for the purpose of increasing electrical conductivity, and has no problems in mechanical property, which is one of the important features of the composite material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an apparatus for surface treatment of a nonwoven fabric according to the present invention (side view). FIG. 1 is a schematic view illustrating that the apparatus works through installed rollers in an arrow direction. A carbon fiber nonwoven fabric or a PET nonwoven fabric is allowed to pass through a pre-treatment bath for determining the adhesive strength of the plating and the pre-treatment for the plating, followed by primary plating in an electroless plating bath. Here, copper or nickel may be selected for electroless plating. After the primary electroless plating, the nonwoven fabric, which has been subjected to electroless plating, is finally subjected to nickel plating. The electrolytic plating is carried out by connecting an electroless plate to a positive (+) electrode and connecting a roller to a negative (−) electrode, and finally, a conductive nonwoven fabric having a double structure of copper-nickel or nickel-nickel is manufactured as a product.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail with reference to examples. These examples are only for illustrating the present invention more specifically, and it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples.

EXAMPLES

Throughout the present specification, the term “%” used to express the concentration of a specific material, unless otherwise particularly stated, refers to (wt/wt)% for solid/solid, (wt/vol)% for solid/liquid, and (vol/vol)% for liquid/liquid.

Example 1

Manufacturing of Carbon Fiber Nonwoven Fabric and PET Nonwoven Fabric

Carbon Fiber Nonwoven Fabric
A carbon fiber nonwoven fabric was prepared in a form of a wet-laid nonwoven fabric.
First, carbon fibers (12K, purchased from Toray, Hyosung, or Taekwang (TK)) were cut into about 6 mm in length, and the cut carbon fiber chops were dispersed in water. The dispersed carbon fiber chops are allowed to float on the water, and were allowed to form a layer with a predetermined thickness in the water through left and right vibration. Then, the carbon fiber layer was taken up, dried, and then compressed using a roller, thereby manufacturing a nonwoven fabric.
Meanwhile, in order to increase the strength of the nonwoven fabric, L/M PET (low-melting PET chop 6 mm) was dispersed together with 6 mm-length carbon fiber chops in water, followed by compressing using a heating roller at 100° C., thereby manufacturing a nonwoven fabric. L/M PET can be melted at about 100° C., and thus, a nonwoven fabric manufactured by mixing a small amount of L/M PET with carbon fibers and heating and compressing the mixture has a stronger intensity compared with a nonwoven fabric manufactured of 100% carbon fibers.
PET Nonwoven Fabric
The PET nonwoven fabric was manufactured in a wet-laid form. The
PET nonwoven fabric was manufactured by the method same as the foregoing method for manufacturing a carbon fiber nonwoven fabric except that 6 mm-length chops of PET (purchased from TEIJIN, Japan) instead of a carbon fiber were used. As described above, in order to increase the intensity of the PET nonwoven fabric, a predetermined amount of L/M PET may be added to manufacture a nonwoven fabric.
Pre-Treatment of Carbon Fiber Nonwoven Fabric and PET Nonwoven Fabric
1) Degreasing and Softening Processes
First, a process was performed that removes epoxy or urethane sized on the carbon fibers and softens surfaces of the fibers through swelling at the same time by using an organic solvent.
The degreasing and softening process was performed by allowing the carbon fiber nonwoven fabric or the PET nonwoven fabric in example 1 to pass through a pretreatment bath containing: as a surfactant, 25 wt % of a solution in which pure water and NaOH were mixed at a weight ratio of 47:3; as organic solvents, 65 wt % of diethyl propanediol and 10 wt % of dipropylene glycol methyl ether; and, as a non-ionic surfactant (low foam), 500 ppm ethoxylated linear alcohol. The degreasing and softening process was performed at a temperature of 50° C. for 2 minutes.
2) Etching Process
An etching process was performed to neutralize a strong alkali component of NaOH using sulfuric acid (H₂SO₄), reduce the load of a sensitizing process as a next process, and perform a washing action and a conditioning action using ammonium peroxysulfate ((NH₄)₂S₂O₈), thereby enhancing the adsorption of palladium.
Specifically, an etching process was performed by allowing the nonwoven fabric, which had gone through the degreasing and softening process, to pass through a pretreatment bath containing 1 wt % of sodium bisulfate (NaHSO₃), 0.5 wt % of sulfuric acid (H₂SO₄), 5 wt % of ammonium persulfate ((NH₄)₂S₂O₈), and 83.5 wt % of pure water, to perform neutralizing, washing, and conditioning actions. The etching process was performed at a temperature of 20-25° C. for 2 minutes.
3) Sensitizing Process (Catalyst Imparting Process)
A sensitizing process was performed by treating the nonwoven fabric, which had gone through the etching process, with 20% PdCl₂at a temperature of 30° C. for 2 minutes. The sensitizing process is performed in order to allow metal ions to be adsorbed on surfaces of the surface-modified carbon fibers or PET.
4) Activating Process
For an activating process, which is performed together with the sensitizing process, the nonwoven fabric was treated with 10% sulfuric acid (H₂SO₄) at a temperature of 50° C. for 2 minutes in order to remove colloidized Sn for the prevention of Pd oxidation.
The nonwoven fabric was pre-treated by the above processes. The carbon fiber nonwoven fabric and the PET nonwoven fabric were pretreated by the same processes.

Examples 2 and 3

Copper and Nickel-Plated Carbon Fibers Obtained by Continuous Electroless and Electrolytic Plating Processes

The carbon fibers (12K, purchased from Toray) pretreated in example 1 and the carbon fibers (12K, purchased from Taekwang (TK)) pretreated in example 1 were subjected to an electroless copper plating process under the composition and conditions shown in table 1 below and then continuously subjected to an electrolytic nickel plating process under the composition and conditions shown in table 2 below, using a plating apparatus shown in the accompanying FIG. 1, thereby preparing copper and nickel-plated carbon fibers, which were then used for examples 2 and 3, respectively. Hereinafter, the contents of ingredients of the plating liquids are on the basis of 1 L of pure water.

TABLE 1

Electroless Cu plating liquid

—	Ingredient	Content (conditions)

Metal salt	Cu ion	3	g/l
Complexing agent	EDTA	30	g/l
Reducing agent	Formalin	3.0	g/l
Stabilizer	TEA (Triethnaol amine)	3	g/l
	2,2′-bipiridine	0.01	g/l
pH Adjusting agent	NaOH (25%)	12	ml/l

Temperature

38°

C.

pH

12.5

Treatment time	6	min

TABLE 2

Electrolytic Ni plating liquid

—	Ingredient	Content (conditions)

Electrolytic	Nickel metal salt	Ni(NH₂SO₃)₂	300	g/l
plating solution		NiCl₂	20	g/l
	pH Buffer	H₃BO₃	40	g/l

Temperature

55°

C.

pH

4.2

Treatment time	1	min

Example 4

The carbon fibers pretreated in example 1 were subjected to an electroless copper plating process under the composition and conditions shown in table 3 below and then continuously subjected to an electrolytic nickel plating process under the composition and conditions shown in table 4 below, using the plating apparatus in the accompanying FIG. 1, thereby preparing copper and nickel-plated carbon fibers.

TABLE 3

Electroless Cu plating liquid

—	Ingredient	Content (conditions)

Metal salt	Cu ion	2.5-3.5	g/l
Complexing agent	EDTA	25-35	g/l
Reducing agent	Formalin	2.5-3.5	g/l
Stabilizer	TEA (Triethnaol amine)	2-3	g/l
	2,2′-bipiridine	0.008-0.01	g/l
pH Adjusting agent	NaOH (25%)	8-12	ml/l

Temperature

36-40°

C.

pH

12-13

Treatment time	6-10	min

TABLE 4

Electrolytic Ni plating liquid

—	Ingredient	Content (conditions)

Electrolytic	Nickel metal salt	Ni(NH₂SO₃)₂	280-320	g/l
plating solution		NiCl₂	15-25	g/l
	pH Buffer	H₃BO₃	35-45	g/l

Temperature

50-55°

C.

pH

4.0-4.2

Treatment time	1-3	min

For the electrolytic plating, a constant voltage (CV) of 5-10 V was applied to an electrolytic nickel bath. A Ni metal plate or Ni balls were used for a metal plate used as a positive electrode.

Example 5

The carbon fibers pretreated in example 1 were subjected to an electroless copper plating process under the composition and conditions shown in table 5 below and then continuously subjected to an electrolytic nickel plating process under the composition and conditions shown in table 6 below, using the plating apparatus in the accompanying FIG. 1, thereby preparing copper and nickel-plated carbon fibers.

TABLE 5

Electroless Cu plating liquid

—	Ingredient	Content (conditions)

Metal salt	Cu ion	4.5-5.5	g/l
Complexing agent	EDTA	45-55	g/l
Reducing agent	Formalin	3.5-4.5	g/l
Stabilizer	TEA(Triethnaol amine)	4-6	g/l
	2,2′-bipiridine	0.01-0.15	g/l
pH Adjusting agent	NaOH(25%)	8-12	ml/l
Temperature		40-45°	C.

pH

12-13

Treatment time		6-10	min

TABLE 6

Electrolytic Ni plating liquid

—	Ingredient	Content (conditions)

Temperature

50-55°

C.

pH

4.0-4.2

Treatment time	1-3	min

Example 6

Nickel and Nickel-Plated Carbon Fibers Obtained by Continuous Electroless and Electrolytic Plating Processes

The carbon fibers pretreated in example 1 were subjected to an electroless nickel plating process under the composition and conditions shown in table 7 below and then continuously subjected to an electrolytic nickel plating process under the composition and conditions shown in table 8 below, using the plating apparatus in the accompanying FIG. 1, thereby preparing nickel and nickel-plated carbon fibers.

TABLE 7

Electroless Ni plating liquid

—	Ingredient	Content (conditions)

Metal salt	Niion	5-7	g/l
Reducing agent	NaH₂PO₂	20-30	g/l
pH Buffer	Na₃C₆H₅O₇	20-30	g/l
Stabilizer	potassium thiosulfate	0.0005 g-0.001	g/l

Temperature

30-35°

C.

pH

8.5-9.5

Treatment time	6-10	min

TABLE 8

Electrolytic Ni plating liquid

—	Ingredient	Content (conditions)

Temperature

50-55°

C.

pH

4.0-4.2

Treatment time	1-3	min

For the electrolytic plating, a constant voltage (CV) of 10-15 V was applied to an electrolytic nickel bath. A Ni metal plate or Ni balls were used for a metal plate used as a positive electrode.

Test Example 1

Measurement on Change in Current Density and Linear Resistance Value of Plated Carbon Fiber

The optimization conditions for electroless and electrolytic plating were set by adjusting the concentration of NaOH, which adjusts pH, and the concentration of HCHO, which helps the reduction reaction of Cu, in the composition and conditions for preparing copper and nickel-plated carbon fibers in example 4.
While the amount of 25% NaOH was changed to 8, 9, 10, 11, and 12 ml/l and the amount of HCHO was changed to 2.5, 2.7, 2.9, 3.1, and 3.3 g/l, respectively, the change in the current density (A) flowing through the carbon fibers was measured, and the linear resistance (Ω/30 cm) of the finally obtained products (copper and nickel-plated carbon fibers) was evaluated, and the results were summarized in table 9 below. A constant voltage (CV) of 7 V was applied to an electrolytic nickel bath, and the other conditions that were uniformly maintained were summarized in tables 10 and 11 below.

TABLE 9

		Current		Plating
		density	Resistance	liquid
HCHO	NaOH	(A)	(Ω/30 cm)	run time

2.5	8	100	0.8	10 turns
	9	110	0.6
	10	120	0.4
	11	130	0.3
	12	140	0.2
2.7	8	110	0.7	8 turns
	9	120	0.6
	10	130	0.5
	11	140	0.3
	12	150	0.2
2.9	8	120	0.6	6 turns
	9	130	0.5
	10	140	0.4
	11	150	0.3
	12	160	0.2
3.1	8	130	0.6	4 turns
	9	140	0.5
	10	150	0.4
	11	160	0.3
	12	170	0.2
3.3	8	140	0.5	2 turns
	9	150	0.4
	10	160	0.3
	11	170	0.2
	12	180	0.1

In table 9 above, 1 turn represents 1 make-up amount of electroless copper plating.

TABLE 10

Electroless Cu plating liquid

—	Ingredient	Content (conditions)

Metal salt	Cu ion	3	g/l
Complexing agent	EDTA	30	g/l
Reducing agent	Formalin(HCHO)	2.5-3.3	g/l
Stabilizer	TEA (Triethnaol amine)	3	g/l
	2,2′-bipiridine	0.10	g/l
pH Adjusting agent	NaOH (25%)	8-12	ml/l

Temperature

37°

C.

pH

12.5

Treatment time	6	min

TABLE 11

Electrolytic plating liquid

—	Ingredient	Content (conditions)

Temperature

55°

C.

pH

4.2

Treatment time	1	min
Constant voltage (Cv)	7	V

As can be confirmed from table 9 above, as the amounts of the reducing agent and NaOH were increased, the plating rate was increased, but the lifetime of the plating liquid was shortened. Therefore, it may be preferable to maintain the amount of the reducing agent at the minimum (2.5-3.0 g/l) and increase the amount of NaOH to the maximum.

Test Example 2

Tests on Plating Rate and Liquid Stability

As for tests on the plating rate and the liquid stability through the adjustment of the concentrations of copper ions and a complexing agent (EDTA), the optimization conditions for copper plating were tested by adjusting the amount of the reducing agent (table 12) when the copper ions and the complexing agent were increased at the same ratio, and the other components and conditions that were uniformly maintained were summarized in tables 13 and 14 below.

TABLE 12

Metal	Reducing	Complexing		Plating
salt	agent	agent		thickness
(Cu)	(HCHO)	(EDTA)	NaOH	(μm)

2.5	2.5	25	12	0.2-0.3
3.5	3.0	35	12	0.3-0.5
4.5	3.5	45	12	0.4-0.6
5.5	4	55	12	0.5-0.8

TABLE 13

Electroless Cu plating liquid

—	Ingredient	Content (conditions)

Metal salt	Cu ion	2.5-5.5	g/l
Complexing agent	EDTA	25-55	g/l
Reducing agent	Formalin	2.5-4	g/l
Stabilizer	TEA (Triethnaol amine)	3	g/l
	2,2′-bipiridine	0.01	g/l
pH Adjusting agent	NaOH (25%)	12	ml/l

Temperature

37°

C.

pH

12.5

Treatment time	6	min

TABLE 14

Electrolytic plating liquid

—	Ingredient	Content (conditions)

Temperature

55°

C.

pH

4.2

Treatment time	1	min
C.V	7	V

As can be seen from table 12 above, it was verified that, as the concentrations of copper and HCHO were higher, high-rate plating was allowable, and the thickness of the plating layer was increased (plating thickness: 0.7 μm or more). For a plating thickness of 0.3 μm preferable for the carbon fibers, the best products were obtained when the concentration of copper ions was 2.5-3.0 g/l and the concentration of HCHO was 2.5-3.0 g/l.
As the plating thickness of the carbon fiber increases, the specific gravity increases and the strength, elastic modulus, and strain deteriorate, and thus preferably, carbon fibers with excellent electrical conductivity are prepared by conducting Ni electrolytic plating on Cu pores in a shorter time after the electroless plating, rather than compulsorily increasing the plating thickness in the electroless plating.

Test Example 3

Comparison of Physical Properties and Electrical Conductivity

Table 15 shows the comparison of physical properties, electrical conductivity, and the like between the copper and nickel-plated carbon fibers in examples 2 and 3 and nickel-plated carbon fibers on the market prepared by an electroless plating process, as comparative example 1.

TABLE 15

	Comparative
—	example 1	Example 2	Example 3	Note

Strand strenth	280	380	338	—
(kgf/mm²)(Range)		(367~405)	(325~353)
Elastic modulus (tons/mm²)	22.0	20.0	22.5	—
Strain (%)	1.2	1.9	1.5	—
Specific gravity (g/cm³)	2.70	2.7277	2.7894	—
Diameter (μm)	7.5	7.828	7.705	—
Tex (Fiber thickness)	1420	1575	1561	—
Electrical resistance (Ω/m)	—	0.8	0.7	—
Electrical resistance (Ωcm)	7.5 × 10⁻⁵	4.62 × 10⁻⁵	4.05 × 10⁻⁵	—
Electrical resistance	—	32-Fold	37-Fold	General CF:
compared with general CF		reduction	redution	1.50 × 100⁻³
				Ωcm base
Coating thickness (nm)	250	240	350	—
		(210~271)	(305~392)

As can be seen from table 15 above, the copper and nickel-plated carbon fibers in examples 2 and 3 had excellent physical properties and exhibited excellent electrical conductivity values due to the low electrical conductivity values, compared with comparative example 1 prepared by the electroless plating process.

Example 7

Copper and Nickel-Plated Carbon Fiber Nonwoven Fabric and PET Nonwoven Fabric Obtained by Continuous Electroless and Electrolytic Plating Processes

The carbon fiber nonwoven fabric and the PET nonwoven fabric in example 1 were subjected to an electroless copper plating process in the compositions and conditions shown in table 16 below and then continuously subjected to an electrolytic nickel plating process in the compositions and conditions shown in table 17 below, using the plating apparatus in the accompanying FIG. 1, thereby manufacturing copper and nickel-plated carbon fiber nonwoven fabric and PET nonwoven fabric.

TABLE 16

Electroless Cu plating liquid

—	Ingredient	Content (conditions)

Metal salt	Cu ion	4.5-5.5	g/l
Complexing agent	EDTA	45-55	g/l
Reducing agent	Formalin	3.5-4.5	g/l
Stabilizer	TEA (Triethnaol amine)	4-6	g/l
	2,2′-bipiridine	0.01-0.15	g/l
pH Adjusting agent	NaOH (25%)	8-12	ml/l

Temperature

40-45°

C.

pH

12-13

Treatment time	6-10	min

TABLE 17

Electrolytic Ni plating liquid

—	Ingredient	Content (conditions)

Electrolytic	Nickel Metal salt	Ni(NH₂SO₃)₂	280-320	g/l
plating solution		NiCl₂	15-25	g/l
	pH Buffer	H₃BO₃	35-45	g/l
Temperature			50-55°	C.

pH

4.0-4.2

Treatment time			1-3	min

Example 8

Nickel-Plated Carbon Fiber Nonwoven Fabric and PET Nonwoven Fabric Obtained by Continuous Electroless and Electrolytic Plating Processes

The nonwoven fabric pretreated in example 1 was subjected to an electroless copper plating process in the compositions and conditions shown in table 18 below and then continuously subjected to an electrolytic nickel plating process in the compositions and conditions shown in table 19 below, using the plating apparatus in the accompanying FIG. 1, thereby manufacturing a nickel-plated nonwoven fabric.

TABLE 18

Electroless Ni plating liquid

—	Ingredient	Content (conditions)

Temperature

30-35°

C.

pH

8.5-9.5

Treatment time	6-10	min

TABLE 19

Electrolytic Ni plating liquid

—	Ingredient	Content (conditions)

Temperature

50-55°

C.

pH

4.0-4.2

Treatment time	1-3	min

Test Example 4

Electrical Characteristics of Nonwoven Fabric

The plated nonwoven fabrics in examples 7 and 8 above were analyzed for electrical characteristics as shown in Table 20 and 21 below, respectively.

	TABLE 20

	Basis	Electrical characteristics after Copper/
	weight	Nickel double plating

		before		Surface	Volume	Electrical
		plating	Resistance	resisance	resistance	conductivity
Item	Composition	(g/m²)	(Ω)	(Ω/square)	(Ω*cm)	(S/cm)

1	C/F 100%	15	2*10⁻¹	9.97*10⁻²	3.69*10⁻²	2.7*10¹
2	C/F 80% +	20	3.88*10⁻¹	1.76*10⁰	3.69*10⁻²	2.7*10¹
	L/M PET
	20%
3	PET 80% +	5	1.79*10²	8.12*10²	1.62*10⁰	6.15*10⁻¹
	L/M PET
	20%
4	PET 60% +	10	6.91*10⁻¹	3.13*10⁰	1.25*10⁻²	7.97*10¹
	L/M PET
	40%

	TABLE 21

	Basis	Electrical characteristics after Nickel/
	weight	Nickel double plating

		before		Surface	Volume	Electrical
		plating	Resistance	resistance	resistance	conductivity
Item	Composition	(g/m²)	(Ω)	(Ω/square)	(Ω*cm)	(S/cm)

1	C/F: 70%	15	6.62*10⁻¹	3.00*10⁰	5.70*10⁻²	1.75*10¹
	1.1 d L/M
	PET: 30%

C/F: Carbon fiber
L/M PET: Low-melting PET
PET: Polyethylene terephthalate

Although the present invention has been described in detail with reference to the specific features, it will be apparent to those skilled in the art that this description is only for a preferred embodiment and does not limit the scope of the present invention. Thus, the substantial scope of the present invention will be defined by the appended claims and equivalents thereof.

Claims

1. A method for plating a non-woven fabric with metals through continuous electroless and electrolytic processes, the method comprising:

(a) allowing a non-woven fabric to pass through an electroless plating liquid to plate the non-woven fabric with copper for 6-10 minutes, the electroless plating liquid containing, on the basis of the volume of pure water, 2.5-5.5 g/l Cu ions, 20-55 g/l EDTA, 2.5-4.5 g/l formalin, 2-6 g/l triethanolamine (TEA), 8-12 ml/l 25% NaOH, and 0.008-0.15 g/l 2,2′-bipiridine and having a pH of 12-13 and a temperature of 36-45° C.; and

(b) allowing the copper-plated non-woven fabric in step (a) to pass through an electrolytic plating liquid to plate the copper-plated non-woven fabric with nickel for 1-3 minutes, the electrolytic plating liquid containing 280-320 g/l Ni(NH₂SO₃)₂, 15-25 g/l NiCl₂, and 35-45 g/l H₃BO₃and having a pH of 4.0-4.2 and a temperature of 50-60° C.

2. (canceled)

3. The method of claim 1, wherein the non-woven fabric is manufactured from a carbon fiber, a polyester fiber, a glass fiber, an aramid fiber, a ceramic fiber, a metal fiber, a polyimide fiber, a polybenzoxazole fiber, a natural fiber, or a mixed fiber thereof.

4. The method of claim 3, wherein the polyester fiber is polyethylene terephthalate (PET), polyglycolide (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), or Vectran.

5. The method of claim 1, wherein in step (a), the non-woven fabric is allowed to pass through an electroless plating liquid to plate the non-woven fabric with copper for 6-10 minutes, the electroless plating liquid containing, on the basis of the volume of pure water, 4.5-5.5 g/l Cu ions, 45-55 g/l EDTA, 3.5-4.5 g/l formalin, 4-6 g/l triethanolamine (TEA), 8-12 ml/l 25% NaOH, and 0.01-0.15 g/l 2,2′-bipiridine and having a pH of 12-13 and a temperature of 40-45 ° C.

6. The method of claim 1, wherein step (b) is performed by applying a constant voltage (CV) of 5-15 V.

7. The method of claim 1, wherein the non-woven fabric in step (a) is pre-treated, before step (a), by a method comprising the following steps:

(i) degreasing and softening the non-woven fabric by allowing the non-woven fabric to pass through an aqueous solution containing a surfactant, an organic solvent, and a non-ionic surfactant;

(ii) performing an etching process for neutralizing, cleaning, and conditioning actions by allowing the non-woven fabric as the product in step (a) to pass through an aqueous solution containing sodium bisulfite (NaHSO₃), sulfuric acid (H₂SO₄), ammonium persulfate ((NH₄)₂S₂O₈), and pure water;

(iii) performing a sensitizing process by allowing the non-woven fabric as the product in step (ii) to an aqueous solution of PdCl₂; and

(iv) performing an activating process by allowing the non-woven fabric as the product in step (iii) to pass through an aqueous solution of sulfuric acid (H₂SO₄).

8. The method of claim 7, wherein the aqueous solution in step (i) contains: as a surfactant, 15-35 wt % of a solution in which pure water and NaOH are mixed at a weight ratio of 40-49:1-10; as organic solvents, 50-80 wt % of diethyl propanediol and 5-15 wt % of dipropylene glycol methyl ether; and 400-600 ppm of a non-ionic surfactant.

9. The method of claim 7, wherein the aqueous solution in step (ii) contains 0.1-10 wt % of sodium bisulfite (NaHSO₃), 0.1-3 wt % of sulfuric acid (H₂SO₄), 5-25 wt % of ammonium persulfate ((NH₄)₂S₂O₈), and 62-94.8 wt % of pure water.

10. The method of claim 7, wherein step (i) is performed at a temperature of 40-60° C. for 1-5 min, step (ii) is performed at a temperature of 20-25° C. for 1-5 min, step (iii) is performed at a temperature of 20-40° C. for 1-5 min, and step (iv) is performed at a temperature of 40-60° C. for 1-5 min.

11. A method for plating a non-woven fabric with metals through continuous electroless and electrolytic processes, the method comprising:

(a) allowing a non-woven fabric to pass through an electroless plating liquid to plate the non-woven fabric with nickel for 6-10 minutes, the electroless plating liquid containing, on the basis of the volume of pure water, 5-7 g/l Ni ions, 20-30 g/l NaH₂PO₂, 20-30 g/l Na₃C₆H₅O₇, and 0.0005-0.001 g/l potassium thiosulfate and having a pH of 8.5-9.5 and a temperature of 30-35° C.; and

(b) allowing the nickel-plated non-woven fabric in step (a) to pass through an electrolytic plating liquid to plate the nickel-plated non-woven fabric with nickel for 1-3 minutes, the electrolytic plating liquid containing 280-320 g/l Ni(NH₂SO₃)₂, 15-25 g/l NiCl₂, and 35-45 g/l H₃BO₃and having a pH of 4.0-4.2 and a temperature of 50-55° C.

12. The method of claim 11, wherein the non-woven fabric is manufactured from a carbon fiber, a polyester fiber, a glass fiber, an aramid fiber, a ceramic fiber, a metal fiber, a polyimide fiber, a polybenzoxazole fiber, a natural fiber, or a mixed fiber thereof.

13. The method of claim 12, wherein the polyester fiber is polyethylene terephthalate (PET), polyglycolide (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), or Vectran.

14. The method of claim 11, wherein step (b) is performed by applying a constant voltage (CV) of 5-15 V.

15. The method of claim 11, wherein the non-woven fabric in step (a) is pre-treated, before step (a), by a method comprising the following steps:

16. The method of claim 15, wherein the aqueous solution in step (i) contains: as a surfactant, 15-35 wt % of a solution in which pure water and NaOH are mixed at a weight ratio of 40-49:1-10; as organic solvents, 50-80 wt % of diethyl propanediol and 5-15 wt % of dipropylene glycol methyl ether; and 400-600 ppm of a non-ionic surfactant.

17. The method of claim 15, wherein the aqueous solution in step (ii) contains 0.1-10 wt % of sodium bisulfite (NaHSO₃), 0.1-3 wt % of sulfuric acid (H₂SO₄), 5-25 wt % of ammonium persulfate ((NH₄)₂S₂O₈), and 62-94.8 wt % of pure water.

18. The method of claim 15, wherein step (i) is performed at a temperature of 40-60° C. for 1-5 min, step (ii) is performed at a temperature of 20-25° C. for 1-5 min, step (iii) is performed at a temperature of 20-40° C. for 1-5 min, and step (iv) is performed ata temperature of 40-60° C. for 1-5 min.