Nonwoven fabric or nonwoven composite material for shielding and absorbing electromagnetic wave

Abstract

The present invention relates to a nonwoven fabric or nonwoven composite material comprising the nonwoven fabric for shielding and absorbing electromagnetic waves, manufactured by using a carbon fiber plated with metal (copper and nickel) produced in an electroless or electrolysis continuous process. The nonwoven fabric of the present invention is thinner and stronger than the conventional art, and has an advantage of being capable of controlling conductivity by controlling only the content of the carbon fiber plated with metal, without need for further addition of conductive powder.

Claims

1. A method for manufacturing a nonwoven fabric for shielding and absorbing electromagnetic waves comprising: (a) copper plating the carbon fiber to pass through an electroless plating solution, wherein the electroless plating solution comprises 2.5-3.5 g/L Cu ions, 25-35 g/L EDTA, 2.5-3.5 g/L formalin, 2-3 g/L triethanolamine (TEA), 8-12 mL/L 25% NaOH, and 0.008-0.01 g/L 2,2-bipiridine on the basis of the volume of pure water, wherein the electroless plating solution has pH of 12-13 and a temperature of 36-45 C.; (b) nickel plating the copper-plated carbon fiber to pass through an electrolytic plating solution, wherein the electrolytic plating solution containing 280-320 g/L Ni(NH.sub.2SO.sub.3).sub.2, 15-25 g/L NiCl.sub.2 and 35-45 g/L H.sub.3BO.sub.3, wherein the electrolytic plating solution has pH of 4.0-4.2 and a temperature of 50-60 C.; (c) cutting copper and nickel-plated carbon fibers into chopped carbon fibers with a length of 3-500 mm; (d) mixing and dispersing the chopped copper and nickel-plated carbon fibers, which correspond to a resultant product in step (c), with water at a weight ratio of 1:100-600; (e) adding 3-30%(w/v) of the resultant product in step (d) to water, followed by dispersing; and (f) filtering the resultant product in step (e) and removing water.

2. The method of claim 1, wherein the mixing in step (d) is performed by further adding, as a nonwoven fabric strength reinforcing agent, natural pulp or a low-melting thermoplastic resin.

3. The method of claim 2, wherein the nonwoven fabric strength reinforcing agent is added in 1-50 wt % on the basis of the total weight of the chopped copper and nickel-plated carbon nanofibers, which correspond to a resultant product in step (c), and the nonwoven fabric strength reinforcing agent.

4. The method of claim 2, wherein the low-melting thermoplastic resin is low-melting polyethylene terephthalate (LMPET).

5. The method of claim 1, wherein the mixing in step (d) is performed by further adding: as a magnetic and ferromagnetic additive, one metal or an alloy of two or more metals selected from the group consisting of iron, nickel, and cobalt; or as a carbon-based additive, an additive selected from the group consisting of carbon nanotubes, graphite, carbon block or metal-plated carbon-based additives thereof, ferrites, and inorganic-based additives.

6. The method of claim 1, wherein in step (e), a water-soluble adhesive or a water-soluble polymer is further added in 0.1-50 wt % on the basis of the total weight of the resultant product in step (c).

7. The method of claim 1, further comprising (g) after step (f), immersing the nonwoven fabric, which is a resultant product in step (f), in a mixture solution in which a thermoplastic resin is dissolved in a solvent selected from the group consisting of toluene, acetone, alcohol, tetrahydrofurane (THF), cyclohexane, and xylene, the content of the thermoplastic resin being 0.1-10 wt % on the basis of the total weight of the solvent, or spraying the mixture solution on the nonwoven fabric, which is a resultant product in step (f).

8. The method of claim 1, further comprising (h) drying the resultant product in step (f) or (g) at 50-150 C. for 10 minutes to 3 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an enlarged cross-sectional image of metal-plated carbon fibers manufactured by continuous electroless and electrolytic processes.

(2) FIG. 2 is an image showing a nonwoven fabric (wet laid) manufactured using metal-plated carbon fibers according to an example of the present invention.

(3) FIG. 3 shows a diagram for manufacturing a sticker type of nonwoven composite material for shielding and absorption of electromagnetic waves according to another example of the present invention.

(4) FIG. 4 is an image showing a metal-plated carbon fiber nonwoven fabric manufactured according to an example of the present invention, and a decoration film.

(5) FIG. 5 is an image of test samples for comparison between a metal-plated carbon fiber nonwoven fabric manufactured according to an example of the present invention and an injected or extruded material containing fibers for electromagnetic waves shield.

(6) FIG. 6 is an image of a chopped sample resulting from the cutting of the metal-plated carbon fibers used in the present invention.

(7) FIG. 7 is an image of a nonwoven fabric manufacturing machine for manufacturing an experimental nonwoven fabric (wet laid).

(8) FIG. 8 is a graph showing measurement results of electromagnetic waves specific absorption rate.

(9) FIG. 9 shows an apparatus for surface treatment of carbon fibers, used in the present invention.

DETAILS FOR CARRYING OUT THE INVENTION

(10) 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.

(11) 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.

EXAMPLES

Example 1

Manufacturing of Copper and Nickel-plated Carbon Fiber Nonwoven Fabric by Continuous Electroless and Electrolytic Processes

(12) Metal (copper and nickel)-plated carbon fibers prepared by continuous electroless and electrolytic processes were cut into 3 mm, 6 mm, or 12 mm, and each 1 g of metal-plated carbon fibers, which were processed in a chopped form, were dispersed in 500 g of water, followed by high-speed dispersion at 5,000 rpm for 1 minute in a mixer. The mixture solution having the metal-plated carbon fibers dispersed therein was put in a sheet former machine (self-production) filled with 7 L of water, and, after 3 seconds, the water was discharged through a mesh net to obtain a remaining carbon fiber nonwoven fabric. The carbon fiber nonwoven fabric filtered on the mesh net was dried in an oven at 70 C. for 2 hours. Finally, it obtains a metal-plated carbon fiber nonwoven fabric having a weight of 30 g/m.sup.2.

(13) For the metal-plated fibers used in example 1 and examples 2 to 5 below, CuNi double-plated carbon fibers, which were prepared through continuous electroless and electrolytic processes by Bullsone Material CO. Ltd., were used, and the carbon fibers were chopped into 3 mm, 6 mm, or 12 mm.

Example 2

Manufacturing of LMPET-added Composite Nonwoven Fabric for Strength Reinforcement

(14) For strength reinforcement, 0.1 g, 0.2 g, or 0.3 g of low-melting polyethylene terephthalate (LMPET) was added to chopped metal (copper and nickel)-plated carbon fibers, thereby manufacturing a composite nonwoven fabric for strength reinforcement, to which LMPET was added in 10 wt %, 20 wt %, or 30 wt % on the basis of the total weight of the metal-plated carbon fibers and LMPET. The composite nonwoven fabric containing 10 wt % of LMPET was manufactured by dispersing 0.9 g of the metal-plated carbon fibers and 0.1 g of LMPET in 500 g of water, carrying out high-speed dispersion at 5,000 rpm for 1 minute in a mixer, putting the mixture solution in a sheet former machine (self-production) filled with 7 L of water, and, after 3 seconds, discharging the water through a mesh net, thereby obtaining a remaining carbon fiber nonwoven fabric. In the same manner, the composite nonwoven fabric containing 20 wt % of LMPET was manufactured by using 0.8 g of the metal-plated carbon fibers and 0.2 g of LMPET, and the composite nonwoven fabric containing 30 wt % of LMPET was manufactured by using 0.7 g of the metal-plated carbon fibers and 0.3 g of LMPET. The carbon fiber nonwoven fabric filtered on the mesh net was dried in an oven at 120 C. for 2 hours to obtain a metal-plated carbon fiber nonwoven fabric. The obtained nonwoven fabric was pressed in a hot press at 150 C. for 7 seconds. Finally, it obtains a final product with 30 g/m.sup.2.

Example 3

Manufacturing of Metal-plated Carbon Fiber Nonwoven Fabrics of 60 g/m2 and 90 g/m2

(15) The method described in examples 1 and 2 was used to obtain samples with a basis weight of 30 g/m.sup.2. Because the effectiveness of electromagnetic wave shield may vary depending on the content of the metal-plated carbon fibers, nonwoven fabrics with 60 g/m.sup.2 and 90 g/m.sup.2 were manufactured in order to measure the efficiency of electromagnetic waves shield depending on the content. The nonwoven fabrics with 60 g/m.sup.2 and 90 g/m.sup.2 were manufactured by the same method as in example 1 except that the total weight of the fibers was 2 g and 4.5 g for the respective fabrics.

Example 4

Manufacturing of Nonwoven Composite Material Using Metal-plated Carbon Fiber Nonwoven Fabric

(16) Hot-melt films were laid on both surfaces of each of the nonwoven fabrics with 30 g/m.sup.2, 60 g/m.sup.2 and 90 g/m.sup.2, and upper and lower surfaces thereof were finished with UV-printed PET films. The binding process was carried out by press-molding using a hot press at 100 C. for 10 seconds.

(17) As an adhesive film used in example 4 and examples 5 and 6, a hot-melt type adhesive film was used in order to allow the metal-plated carbon fiber nonwoven fabric and the PET decoration film to adhere to each other. Meanwhile, the adhering manner may employ normal adhesives without limitation to the hot-melt type adhesive film.

(18) In addition, The UV-printed PET film, as a decoration film used in example 4 and examples 5 and 6, used SW84G product of SKC company, printed with a design through UV printing, but the printing of the design was not particularly limited to UV printing.

Example 5

Manufacturing of Nonwoven Composite Material Using LMPET-added Composite Nonwoven Fabric for Strength Reinforcement

(19) Hot-melt films were laid on both surfaces of the nonwoven fabric containing 10 wt %, 20 wt %, or 30 wt % of LMPET, and upper and lower surfaces thereof were finished with UV-printed PET films. The binding process was carried out by press-molding using a hot press at 100 C. for 10 seconds.

Example 6

Manufacturing of Sticker Using Nonwoven Composite Material

(20) Hot-melt films were laid on both surfaces of the metal (copper and nickel)-plated carbon fiber nonwoven fabric of examples 1 and 3, or the LMPET-added composite nonwoven fabric for strength reinforcement of example 2, and an upper surface thereof was finished with a UV-printed PET film, and a double-sided tape with a release film was laid on a lower surface thereof, followed by binding. The binding process was carried out by press-molding using a hot press at 100 C. for 10 seconds. The obtained sample was conveniently attachable, like a sticker, through the removal of the release film.

Comparative Example 1

Manufacturing of Composite Material for Electromagnetic Waves Shield

(21) For the comparative example, composite materials for electromagnetic waves shield were manufactured by injection-molding PP(Polypropylene) as a thermoplastic resin and copper/nickel-plated carbon fibers. The contents thereof are shown in table 1 below. Injection-molded products were manufactured in sheet forms with thicknesses of 0.5 mm and 0.7 mm. Specifically, polypropylene (PP, grade BJ 700, melting index: 25, density: 0.91 g/cm.sup.3, heat deflection temperature: 105 C., Samsung Total) was dried in a vacuum oven at 80 C. for 6 hours, and then 80 wt % of the dried PP was mixed with 20 wt % of copper and nickel-plated carbon fibers (6 mm). In addition, the mixture was fed into an extruder (twin injection machine; manufactured by Woojin, Korea, GT-1 9300), and injected through a mold with a standard specified by ASTM D4935. In this case, the temperature section was divided into five, which was set to 215 C., 220 C., 220 C., 220 C., and 230 C., respectively, and a molding operation was conducted under 55 rpm, 60 bars, and a mold cooling time of 8 seconds.

Test Example 1

Test on Electromagnetic Waves Specific Shielding Rate and Absorbing Rate (Specific Absorption Test, SAR)

(22) The nonwoven fabrics of examples 1 to 3 and the plastic composite materials of the comparative example were subjected to a specific absorption rate (SAR) test, and the results are shown in table 1 below.

(23) TABLE-US-00001 TABLE 1 A Test on attenuation of Electromagnetic waves in cellular phone Efficiency of SAR Electromagnetic result wave shield value (ASTM D4935) Thick- (reduction EMI SE(dB) Item ness (%)) (at 1.0 GHz) Example 1 (nonwoven 0.18 mm 84 65 fabric 30 g/m.sup.2) Example nonwoven 0.35 mm 91 67 3 fabric 60 g/m.sup.2 nonwoven 0.51 mm 95 68 fabric 90 g/m.sup.2 Example metal-plated 0.35 mm 90 66 2 carbon fibers + LMPET 10% (60 g/m.sup.2) metal-plated 0.35 mm 87 65 carbon fibers + LMPET 20% (60 g/m.sup.2) metal-plated 0.35 mm 85 65 carbon fibers + LMPET 30% (60 g/m.sup.2) Com- Plastic composite 0.5 mm 85 54 parative material example 20 wt % 1 Plastic composite 0.7 mm 86 54 material 20 wt %

(24) As shown from table 1 above, it was verified that the more the amount (generally referred to as basis weight) of the metal-plated carbon fibers used in the manufacturing of the nonwoven fabrics of examples 1 and 3 above, the higher the SAR and the shielding and absorbing effectiveness. In addition, the nonwoven fabrics of the examples exhibited the same, or a more excellent, shielding effect with even about 30% of the thickness of the plastic composite material of the comparative example, and thus are suitable for slimmer electronic devices.

(25) In addition, as a result of the test according to ASTM D 4935 for measuring efficiency of intrinsic electromagnetic waves shield for a raw material, examples 1 to 3 exhibited similar effects of electromagnetic waves shield regardless of the type. The samples were manufactured by laminating 10 nonwoven fabrics and the samples were processed, and thus the difference in the effect of electromagnetic waves shield was not great depending on the basis weight.

(26) However, it can be seen that the samples manufactured from the nonwoven fabrics of examples 1 to 3 exhibited more excellent performance of electromagnetic waves shield by at least about 10 dB compared with the samples manufactured from the plastic nonwoven fabrics of the comparative example, and the reason is that the fiber length is longer and the fiber network structure is denser in the nonwoven fabrics of examples 1 to 3 than that in the plastic composite materials.

(27) Meanwhile, FIG. 8 is a graph showing measurement results of electromagnetic waves specific absorption rates of materials. The absorption rates of the nonwoven fabric and the plastic composite material were about 60-70%, but a shielding material obtained by metal-plating the woven organic fabric showed an intrinsic absorption rate of about 10%, indicating that the shielding effect of the shielding material is mainly due to reflection. This absorption rate is similar to that of a copper sheet that blocks electromagnetic waves by only a reflection action, and thus the metal-plating of densely woven fibers is far from electromagnetic waves extinction through absorption. Therefore, the nonwoven fabric and the plastic composite material used in the present invention exhibited a material intrinsic electromagnetic waves shield rate of 99.99% or higher, of which the electromagnetic waves absorption and extinction accounts for about 60-70% and the shielding rate by reflection accounts for about 29-39%.

(28) Therefore, the present invention shows that it can manufacture a high efficient electromagnetic waves shield film or sticker that is economical and highly productive can be produced by manufacturing a nonwoven fabric using highly conductive carbon fibers prepared through continuous electroless and electrolytic processes, and laminating a finish film with an aesthetic appearance or a double-sided film on upper and lower surfaces of the nonwoven fabric, which was used as a core for blocking electromagnetic waves.

(29) Meanwhile, the Cu/Ni double-plated carbon fibers obtained by continuous electroless and electrolytic processes, which were prepared by Bullsone Material Co. Ltd. used in examples 1 to 6, were pretreated and prepared through the following process.

Example 7

Pretreatment Step of Carbon Fibers

(30) 1) Degreasing and Softening Process

(31) At first, a process was performed that degreases the epoxy or urethane sized on the carbon fibers and softens the surfaces of the fibers through swelling, by using an organic solvent.

(32) The degreasing and softening process was conducted by allowing carbon fibers (12K, purchased from Toray, Hyosung, or Taekawng (TK)) 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.

(33) 2) Etching Process

(34) An etching process was performed, in order to neutralize a strong alkali component of NaOH using sulfuric acid (H.sub.2SO.sub.4), reduce the load of a sensitizing process as a next process, and help a cleaning process and function a conditioning action using ammonium peroxysulfate ((NH.sub.4).sub.2S.sub.2O.sub.8), and to enhance the adsorption of palladium.

(35) Specifically, an etching process for neutralization, cleaning, and conditioning was performed by allowing the carbon fibers, which had gone through the degreasing and softening processes, to pass through a pretreatment bath containing 1 wt % of sodium bisulfate (NaHSO.sub.3), 0.5 wt % of sulfuric acid (H.sub.2SO.sub.4), 15 wt % of ammonium persulfate ((NH.sub.4).sub.2S.sub.2O.sub.8), and 83.5 wt % of pure water. The etching process was performed at a temperature of 20-25 C. for 2 minutes.

(36) 3) Sensitizing Process (Catalyst Imparting Process)

(37) A sensitizing process was performed by treating the carbon fibers, which had gone through the etching process, with 20% PdCl.sub.2 at a temperature of 30 C. for 2 minutes. The sensitizing process is performed in order to adsorb metal ions on the surfaces of the surface-modified carbon fibers.

(38) 4) Activating Process

(39) An activating process is performed together with the sensitizing process. The carbon fibers were treated with 10% sulfuric acid (H.sub.2SO.sub.4) at a temperature of 50 C. for 2 minutes in order to remove Sn, that has been colloidized, and to prevent oxidation of Pd.

(40) The carbon fibers were pretreated by the above processes.

Examples 8 and 9

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

(41) The carbon fibers (12K, purchased from Toray) pretreated in example 7 and the carbon fibers (12K, purchased from Taekwang (TK)) pretreated in example 7 were subjected to an electroless copper plating process in the compositions and conditions shown in table 2, and then continuously subjected to an electrolytic nickel plating process in the compositions and conditions shown in table 3, using a plating apparatus shown in the accompanying FIG. 9, thereby preparing copper- and nickel-plated carbon fibers, which were then used for examples 8 and 9. Hereinafter, the contents of components of the plating solution are on the basis of 1 L of pure water.

(42) TABLE-US-00002 TABLE 2 Electroless copper plating solution Component Content (conditions) Metal salt Cu ion 3 g/l Complexing agent EDTA 30 g/l Reducing agent Formalin 3.0 g/l Stabilizer TEA (triethanolamine) 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

(43) TABLE-US-00003 TABLE 3 Electroytic Ni plating solution Component Content (conditions) Electrolytic plating Nickel metal Ni(NH.sub.2SO.sub.3).sub.2 300 g/l solution salt NiCl.sub.2 20 g/l pH buffer H.sub.3BO.sub.3 40 g/l Temperature 55 C. pH 4.2 Treatment time 1 min

Example 10

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

(44) The carbon fibers pretreated in example 7 were subjected to an electroless copper plating process in the compositions and conditions shown in table 4, and then continuously subjected to an electrolytic nickel plating process in the compositions and conditions shown in table 5, using a plating apparatus in the accompanying FIG. 9, thereby preparing copper- and nickel-plated carbon fibers.

(45) TABLE-US-00004 TABLE 4 Electroless copper plating solution Component 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 (triethanolamine) 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

(46) TABLE-US-00005 TABLE 5 Electrolytic Ni plating solution Component Content (conditions) Electrolytic plating Nickel metal Ni(NH.sub.2SO.sub.3).sub.2 280-320 g/l solution salt NiCl.sub.2 15-25 g/l pH buffer H.sub.3BO.sub.3 35-45 g/l Temperature 50-55 C. pH 4.0-4.2 Treatment time 1-3 min

(47) 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 11

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

(48) The carbon fibers pretreated in example 7 were subjected to an electroless copper plating process in the compositions and conditions shown in table 6, and then continuously subjected to an electrolytic nickel plating process in the compositions and conditions shown in table 7, using a plating apparatus in the accompanying FIG. 9, thereby preparing copper- and nickel-plated carbon fibers.

(49) TABLE-US-00006 TABLE 6 Electroless copper plating solution Component 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 (triethanolamine) 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

(50) TABLE-US-00007 TABLE 7 Electrolytic Ni plating solution Component Content (conditions) Electrolytic plating Nickel metal Ni(NH.sub.2SO.sub.3).sub.2 280-320 g/l solution salt NiCl.sub.2 15-25 g/l pH buffer H.sub.3BO.sub.3 35-45 g/l Temperature 50-55 C. pH 4.0-4.2 Treatment time 1-3 min

(51) 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.

Test Example 2

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

(52) 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, among the compositions and conditions for preparing copper- and nickel-plated carbon fibers in example 10.

(53) 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) that flows through the carbon fibers was measured, and the linear resistance (/30 cm) of the finally obtained products (copper and nickel-plated carbon fibers) was evaluated, and the results were summarized in table 8 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 9 and 10 below.

(54) TABLE-US-00008 TABLE 8 Current Resistance Plating sol. HCHO NaOH density (A) (/30 cm) period of use 2.5 8 100 0.8 10 turn 9 110 0.6 10 120 0.4 11 130 0.3 12 140 0.2 2.7 8 110 0.7 8 turn 9 120 0.6 10 130 0.5 11 140 0.3 12 150 0.2 2.9 8 120 0.6 6 turn 9 130 0.5 10 140 0.4 11 150 0.3 12 160 0.2 3.1 8 130 0.6 4 turn 9 140 0.5 10 150 0.4 11 160 0.3 12 170 0.2 3.3 8 140 0.5 2 turn 9 150 0.4 10 160 0.3 11 170 0.2 12 180 0.1

(55) In table 8 above, 1 turn represents 1 make-up amount of electroless copper plating.

(56) TABLE-US-00009 TABLE 9 Electroless copper plating solution Component 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 (triethanolamine) 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

(57) TABLE-US-00010 TABLE 10 Electrolytic plating solution Component Content (conditions) Electrolytic plating Nickel metal Ni(NH.sub.2SO.sub.3).sub.2 300 g/l solution salt NiCl.sub.2 20 g/l pH buffer H.sub.3BO.sub.3 40 g/l Temperature 55 C. pH 4.2 Treatment time 1 min Constant voltage (Cv) 7 V

(58) As can be confirmed from table 8 above, as the amounts of the reducing agent and NaOH were increased, the plating rate increased, but the lifespan of the plating solution 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 3

Test on Plating Rate and Solution Stability

(59) For the test on plating rate and stability to solution 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 11) when the copper ions and the complexing agent were increased at the same ratio, and the other conditions that were uniformly maintained were summarized in tables 12 and 13 below.

(60) TABLE-US-00011 TABLE 11 Metal salt Reducing agent Complexing agent Plating thickness (Cu) (HCHO) (EDTA) NaOH (m) 2.5 2.5 25 12 0.2-0.3 3.5 3.0 35 0.3-0.5 4.5 3.5 45 0.4-0.6 5.5 4 55 0.5-0.8

(61) TABLE-US-00012 TABLE 12 Electroless copper plating solution Component 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(triethanolamine) 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

(62) TABLE-US-00013 TABLE 13 Electrolytic plating solution Component Content (conditions) Electrolytic plating Nickel metal Ni(NH.sub.2SO.sub.3).sub.2 300 g/l solution salt NiCl.sub.2 20 g/l pH buffer H.sub.3BO.sub.3 40 g/l Temperature 55 C. pH 4.2 Treatment time 1 min C.V 7 V

(63) As can be seen from table 11 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 m or more). For a preferable plating thickness, 0.3 m, of the carbon fiber, 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.

(64) As the plating thickness of the carbon fiber increases, the specific gravity increases and the strength, elastic modulus, and strain deteriorate, and thus carbon fibers with excellent electrical conductivity were 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 4

Comparison of Physical Properties and Electrical Conductivity

(65) Table 12 shows comparison of physical properties, electrical conductivity, and the like, between copper and nickel-plated carbon fibers in examples 8 and 9 and nickel-plated carbon fibers on the market prepared by an electroless plating process, as comparative example 2.

(66) TABLE-US-00014 TABLE 12 Com- parative example Example Example 2 8 9 Note Strand strength 280 380 338 (kgf/mm.sup.2)(Range) (367~405) (325~353) elastic modulus 22.0 20.0 22.5 (tons/mm.sup.2) Strain (%) 1.2 1.9 1.5 Specific gravity 2.70 2.7277 2.7894 (g/cm.sup.3) Diameter (m) 7.5 7.828 7.705 Tex (fiber 1420 1575 1561 thickness) Electric resistance 0.8 0.7 (/m) Electric resistance 7.5 10.sup.5 4.62 10.sup.5 4.05 10.sup.5 ( cm) Electric resistance 32-fold 37-fold Normal CF: compared with reduction reduction 1.50 normal CF 10.sup.3 cm Coating thicknss 250 240 350 (nm) (210~271) (305~392)

(67) As can be seen from table 12 above, the copper and nickel-plated carbon fibers had excellent physical properties and exhibited excellent electrical conductivity values due to the low electric conductivity values, compared with comparative example 2 prepared by the electroless plating process.

(68) 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 example 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.