Preparation method for electromagnetic wave shield composite material using copper- and nickel-plated carbon fiber prepared by electroless and electrolytic continuous processes, and electromagnetic wave shield composite material

Abstract

The present invention relates to a preparation method for an electromagnetic wave shield composite material and the electromagnetic wave shield composite material prepared by the method. The present invention uses a highly conductive carbon fiber prepared by electroless and electrolytic continuous processes, and thus is suitable for an EMI shield due to having an excellent conductivity and low surface resistance, and is capable of providing the electromagnetic wave shield composite material having an excellent productivity and economic value. Furthermore, the electromagnetic wave shield composite material of the present invention can be used for blocking electromagnetic waves by being inserted into a cell phone cover and a cell phone pouch, and can also be applied to a bracket for protecting an LCD of a portable display product.

Claims

1. A method for preparing an electromagnetic shielding composite comprising: (a) copper plating a carbon fiber by passing the carbon fiber through an electroless plating liquid, wherein the electroless plating liquid contains 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), 25% NaOH 8-12 mL/L and 0.008-0.15 g/L 2,2-bipyridine on the basis of the volume of pure water, wherein the electroless plating liquid has pH 12-13 and a temperature of 36-45 C.; (b) nickel plating the copper-plated carbon fiber by passing the copper-plated carbon fiber through an electrolytic plating liquid, wherein the electrolytic plating liquid contains 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, and wherein the electrolytic plating liquid has pH 4.0-4.2 and a temperature of 50-60 C.; (c) mixing 50-90 wt % of a thermosetting resin and 10-50 wt % of the copper- and nickel-plated carbon fibers; and (d) performing discharge molding on the product in step (c) to obtain an electromagnetic shielding composite, wherein the copper- and nickel-plated carbon fiber in step (c) has a chopped shape with a length of 3 mm to 500 mm.

2. The method of claim 1, wherein the thermosetting resin in step (a) is at least one thermosetting resin selected from the group consisting of polyurethane-based resins, epoxy-based resins, phenol-based resins, urea resins, melamine resins and unsaturated polyester-based resins.

3. The method of claim 1, wherein the discharge molding in step (d) further comprises: (d-1) discharging the product in step into a mold or a conveyor; (d-2) setting the discharged product in step (d-1); and (d-3) releasing the set product in step (d-2).

4. The method of claim 3, wherein the setting in step (d-2) is performed by applying heat, pressure or UV.

5. The method of claim 1, wherein the product in step (c) further comprises a conductive material selected from the group consisting of ferrite, graphite and metal-plated graphite.

6. The method of claim 5, wherein the product in step (c) comprises 40-89.5 wt % of the thermosetting resin, 10-50 wt % of the copper- and nickel-plated carbon fibers and 0.5-10 wt % of the conductive material.

7. The method of claim 5, wherein a metal of the metal-plated graphite is at least one metal selected from the group consisting of aluminum, iron, chromium, stainless, copper, nickel, black nickel, silver, gold, platinum, palladium, tin, cobalt, and an alloy of two or more thereof.

8. The method of claim 1, wherein the mixing in step (c) is performed by mixing the thermosetting resin and the copper- and nickel-plated carbon fibers with at least one additive selected from the group consisting of a carbon filler, a flame retardant, a plasticizer, a coupling agent, a heat stabilizer, a light stabilizer, an inorganic filler, a releasing agent, a dispersing agent, an anti-dropping agent and a weathering stabilizer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block diagram showing a process for preparing an electromagnetic shielding composite according to an embodiment of the present invention.

(2) FIG. 2 is a cross-sectional image of a highly conductive carbon fiber plated by continuous electroless and electrolytic processes.

(3) FIG. 3 is an image showing a surface in which highly conductive carbon fibers in a chopped shape are dispersed in a network form with contact points.

(4) FIG. 4 is an image showing that highly conductive carbon fibers plated by continuous electroless and electrolytic processes are processed in a chopped shape.

(5) FIG. 5 is a graph showing an electromagnetic shielding effect of a molded product using carbon fibers prepared by the continuous processes.

(6) FIG. 6 is a view showing a sample for the electromagnetic shielding test.

(7) FIG. 7 is a block diagram showing a process for preparing an electromagnetic shielding composite using a thermosetting resin according to another embodiment of the present invention.

(8) FIG. 8 shows an apparatus for surface treatment of carbon fibers, used in the present invention.

MODE FOR CARRYING OUT THE INVENTION

(9) 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.

(10) 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

(11) Materials and Methods

(12) The respective components used in examples and comparative examples were as follows:

(13) (A) As a thermoplastic resin, BJ700 from Samsung Total was used for polypropylene (PP), KN120 from Kolon was used for polyimide 6 (PA6), LUPOY PC1201-22 from LG Chemical was used for polycarbonate (PCT), and ABS XR401 from LG Chemical was used for an acrylonitrile-butadiene-styrene (ABS) resin. (B) As a thermosetting resin, UP 395 from Kukdo Chemical was used for polyurethane (PU), and KBR1753 from Kukdo Chemical was used for epoxy. In addition, (C) as carbon fibers, CuNi-plated carbon fibers through continuous electroless and electrolytic processes, which were prepared by Bulsone Material were used. The carbon fibers were cut into chopped shapes with 6 mm, 12 mm, and 30 mm. In addition, as other additives, a product from Novamet was used for nickel-plated graphite.

(14) Meanwhile, the electromagnetic shielding test, that is, EMI shielding property (dB) was determined by measuring the electromagnetic shielding performance according to ASTM D 4935.

Example 1: Manufacturing of Electromagnetic Shielding Sheets by Injection Molding and Evaluation Thereof

(15) Molding was performed while the contents of the respective components were shown in table 1. Injection molded products were manufactured in a sheet form with a thickness of 0.7 mm. Specifically, thermoplastic resins, PP (grade BJ 700, melting index: 25, density: 0.91 g/cm.sup.3, heat deflection temperature: 105 C., Samsung Total), PC (grade LUPOY PC 1201-22, melting index: 22, density: 1.2 g/cm.sup.3, heat deflection temperature: 147 C., LG Chemical), and ABS (grade ABS XR401, melting index: 9, density: 1.05 g/cm.sup.3, heat deflection temperature: 105 C., LG Chemical) were, respectively, dried for 6 hours in a vacuum oven at 80 C. After that, the dried thermoplastic resins were mixed in contents thereof shown in table 1. Then, each 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 cases of the PP mixture, the temperature section was divided into five, which was set to 215 C., 220 C., 220 C., 220 C., and 230 C., respectively, and working was performed under 55 rpm, 60 bars, and a mold cooling time of 8 seconds. In cases of the PC mixture and the ABS mixture, the temperature was set to 255 C., 265 C., 265 C., 265 C., and 275 C. in the same machine, and working was performed under 55 rpm, 60 bars, and a mold cooling time of 8 seconds.

(16) The manufactured sheets were subjected to an electromagnetic shielding test, and the result values are shown (table 1).

(17) TABLE-US-00001 TABLE 1 Highly EMI SE conductive Thermoplastic (dB) (at carbon fibers Additive resin 1.0 GHz) Cu + Ni PP 70 wt % 72 carbon fibers Ferrite 2 wt % PP 68 wt % 72 (6 mm, Ni-plated graphite 2 wt % PP 68 wt % 82 30 wt %) PC 70 wt % 67 Ferrite 2 wt % PC 68 wt % 70 Ni-plated graphite 2 wt % PC 68 wt % 81 PC/ABS 70 wt % 68 Ferrite 2 wt % PC/ABS 68 wt % 72 Ni-plated graphite 2 wt % PC/ABS 68 wt % 81 PA6 70 wt % 81 Ferrite 2 wt % PA6 68 wt % 80 Ni-plated graphite 2 wt % PA6 68 wt % 84

Example 2: Manufacturing of Molded Products by Injection and Extrusion Molding Processes and Evaluation Thereof

(18) Molded products were manufactured from the above components by injection and extrusion processes shown in tables 2 and 3, respectively, and the electromagnetic shielding performance thereof was tested. For the manufacturing of the injection molded products shown in table 2 below, 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. Then, the dried PP was mixed with copper- and nickel-plated carbon fibers (6 mm) in contents thereof shown in table 2 below. In addition, sheets were manufactured by injecting the mixtures into injected products with a size specified by ASTM D4935 in the same conditions as in example 1.

(19) TABLE-US-00002 TABLE 2 Manufacturing of molded product through injection molding EMI SE (dB) Composite (at 1.0 GHz) PP/CuNi carbon fibers (90/10 wt %) 16.4 PP/CuNi carbon fibers (80/20 wt %) 54 PP/CuNi carbon fibers (70/30 wt %) 72 Injection molding, fiber length 6 mm chopped

(20) Meanwhile, for the manufacturing of the extrusion molded products shown in table 3 below, PA6 (KOPA KN120, melting point: 222 C., density: 1.14 g/cm.sup.3, relative viscosity (RV): 2.75, KOLON Ltd) was dried for 6 hours in a vacuum oven at 80 C. The dried PA6 was mixed with copper- and nickel-plated carbon fibers (12 mm) in contents thereof shown in table 3 below. In addition, the mixtures were fed into an extruder for pellet manufacturing (twin screw compounding extruder; Bowtech, Korea, BA-11) while the temperature section was divided into five, which was set to 230 C., 245 C., 245 C., 245 C., and 255 C., respectively, and then discharged at 100 rpm, followed by a water cooling process, thereby manufacturing composite pellets. The manufactured pellets were made into sheet form molded products with a thickness of 0.7 mm, using T-dice in an extruder for sheet manufacturing, self-manufactured by Ecogreen at temperature sections of 230 C., 255 C., 255 C., 255 C., and 265 C., at a speed of 45 rpm.

(21) TABLE-US-00003 TABLE 3 Manufacturing of molded product through extrusion molding EMI SE (dB) Composite (at 1.0 GHz) PA 6/CuNi carbon fibers (90/10 wt %) 25.4 PA 6/CuNi carbon fibers (80/20 wt %) 58.2 PA 6/CuNi carbon fibers (70/30 wt %) 81 Extrusion molding, fiber length 12 mm chopped

Example 3: Manufacturing Molded Products Using Thermosetting Resins and Evaluation Thereof

(22) In table 4, sheets were manufactured by immersing highly conductive Cu- and Ni-plated carbon fibers in a polyurethane resin and an epoxy resin, which are representative thermosetting resins, and the electromagnetic shielding performance thereof was measured.

(23) Polyurethane PU (grade UP 395, viscosity: 1500 cps, specific gravity: 1, one-component urethane, Korea, Kukdo Chemical) and copper- and nickel-plated carbon fibers (6 mm chop) were quantified at a weight ratio of 80:20 in a beaker, and then mixed at 1000 rpm in a mixer for 1 minute, thereby preparing a mixture liquid. 20 g of the prepared mixture liquid was drawn off on a glass substrate that was subjected to release treatment (an appropriate amount of WD-40 from 3M was sprayed on a 5 mm-thick glass substrate, which was then uniformly rubbed with a cotton cloth, and then kept in an oven at 70 C. for 3 minutes, thereby inducing the sufficient stabilization of the releasing agent, and then the surface is wiped with a smooth tissue, and the pollutants were finally removed), and was pushed to have a thickness of 0.7 mm by a glass rod, thereby molding a sheet form. The molded glass substrate was dried and hardened in an oven at 50 C. for 24 hr, thereby obtaining a final molded product.

(24) An epoxy resin (KBR-1753, viscosity: 800 cps, Korea, Kukdo Chemical) and a hardener (KBH-1089, Acid Anhydride-based, Korea, Kukdo Chemical) were mixed at a weight ratio of 100:92 to prepare a mixed epoxy solution. The mixed solution and the copper- and nickel-plated carbon fibers (12 mm chop) were quantified at a weight ratio of 80:20 in a beaker, and mixed in a mixer at 100 rpm for 1 minute, thereby preparing a mixture liquid. 20 g of the prepared mixture liquid was drawn off on a glass substrate that was subjected to release treatment, and was pushed to have a thickness of 0.7 mm by a glass rod, thereby molding a sheet form. The molded glass substrate was dried and cured in an oven at 150 C. for 24 hr, thereby obtaining a final molded product.

(25) TABLE-US-00004 TABLE 4 EMI SE (dB) Composite (at 1.0 GHz) Polyurethane/CuNi carbon fibers (80/20 wt %) (6 mm) 56.7 Mixed epoxy solution/CuNi carbon fibers 57.3 (80/20 wt %) (12 mm)

Comparative Example 1: Manufacturing of Injection and Extrusion Molded Products Using Non-Plated Carbon Fibers and Evaluation Thereof

(26) In comparative example 1, the non-plated carbon fibers were subjected to injection molding and extrusion molding, respectively, and the shielding performance thereof was measured. Specifically, the non-treated carbon fiber chops with a length of 6 mm or 12 mm were subjected to molding in contents thereof shown in table 5 under the same conditions as in examples 1 and 2, thereby obtaining molded products. In cases of the extrusion molding, the pellets were first prepared, and dried in a drying furnace, and then manufactured into continuous type sheets with a thickness of 0.7 mm in an extruder.

(27) TABLE-US-00005 TABLE 5 EMI SE (dB) Composite (at 1.0 GHz) Molding method PP/carbon fibers (80/20 wt %) (6 mm) 13 Injection molding PA 6/carbon fibers (80/20 wt %) 14 Extrusion (12 mm) molding

(28) It can be seen that, in examples 1, 2, and 3 above, the electromagnetic shielding performance is different depending on the content of highly conductive carbon fibers regardless of the kind of resin. In addition, when the nickel-coated graphite was added at the compositional ratio of the same content of the highly conductive carbon fibers, the electromagnetic shielding effect slightly increased.

(29) It seems that the reason why the shielding efficiency slightly increased in the injection molding rather than in the extrusion molding is that the surface of the molded product has an integral skin due to the mold in cases of the extrusion molding.

(30) The reason why example 3 had a slight increase in the shielding efficiency compared with the extrusion molded product using the thermoplastic resin is that the mutual contact points between carbon fibers were formed more stably in example 3 rather than the injection molded product.

(31) In comparative example 1, the injection and extrusion molded products using the metal-non-plated carbon fibers showed a half level of the electromagnetic shielding efficiency compared with the same content of the highly conductive carbon fibers.

(32) Therefore, the present invention shows that the electromagnetic shielding effect is very excellent when a predetermined content of highly conductive carbon fibers obtained by continuous electroless and electrolytic processes are contained.

(33) Meanwhile, the CuNi double-plated carbon fibers obtained by continuous electroless and electrolytic processes, which were manufactured by Bulsone Material and used in examples 1 to 3 above, were pretreated and prepared through the following process.

Example 4: Pretreatment Procedure of Carbon Fibers

(34) 1) Degreasing and Softening Processes

(35) First, the epoxy or urethane that has been sized to the carbon fibers was removed using an organic solvent, and a process of swelling to soften the surfaces of the fibers was performed at the same time.

(36) The degreasing and softening processes were performed by allowing carbon fibers (12K, purchased from Toray, Hyosung, or Taekwang (TK)) to pass through a pretreatment bath containing 25 wt % of a solution in which pure water and NaOH were mixed at a weight ratio of 47:3, as a surfactant; 65 wt % of diethyl propanediol and 10 wt % of dipropylene glycol methyl ether, as an organic solvent; and 500 ppm ethoxylated linear alcohol as a non-ionic surfactant (low foam). The degreasing and softening processes were performed at a temperature of 50 C. for 2 minutes.

(37) 2) Etching Process

(38) An etching process was performed, in order to neutralize strong alkali components of NaOH using sulfuric acid (H.sub.2SO.sub.4), reducing the load of a sensitizing process as a next process, and helping a washing action and performing a conditioning action using ammonium peroxysulfate ((NH.sub.4).sub.2S.sub.2O.sub.8) to enhance the adsorption of palladium.

(39) Specifically, an etching process was performed by allowing the carbon fibers, which were subjected to 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), 5 wt % of ammonium persulfate ((NH.sub.4).sub.2S.sub.2O.sub.8), 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.

(40) 3) Sensitizing Process (Catalyst Imparting Process)

(41) A sensitizing process was performed by treating the carbon fibers, which were subjected to 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 allow metal ions to be adsorbed on surfaces of the surface-modified carbon fibers.

(42) 4) Activating Process

(43) 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 for the prevention of Pd oxidation.

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

Examples 5 and 6: Copper- and Nickel-Plated Carbon Fibers Obtained by Electroless and Electrolytic Continuous Plating Processes

(45) The carbon fibers (12K, purchased from Toray) pretreated in example 4 and the carbon fibers (12K, purchased from Taekwang (TK)) pretreated in example 4 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 shown in the accompanying FIG. 8, thereby preparing copper- and nickel-plated carbon fibers, which were then used for examples 5 and 6. Hereinafter, the contents of components of the plating liquids are on the basis of 1 L of pure water.

(46) TABLE-US-00006 TABLE 6 Electroless copper plating iquid 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 (triethanol 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

(47) TABLE-US-00007 TABLE 7 Electrolytic Ni plating liquid Component Content (Conditions) Electrolytic Nickel metal salt Ni(NH.sub.2SO.sub.3).sub.2 300 g/l plating liquid 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 7: Copper- and Nickel-Plated Carbon Fibers Obtained by Electroless and Electrolytic Continuous Plating Processes

(48) The carbon fibers pretreated in example 4 were subjected to an electroless copper plating process in the compositions and conditions shown in table 8, and then continuously subjected to an electrolytic nickel plating process in the compositions and conditions shown in table 9, using a plating apparatus in the accompanying FIG. 8, thereby preparing copper- and nickel-plated carbon fibers.

(49) TABLE-US-00008 TABLE 8 Electroless copper plating liquid 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 (triethanol 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

(50) TABLE-US-00009 TABLE 9 Electrolytic Ni plating liquid Component Content (Conditions) Electrolytic Nickel metal salt Ni(NH.sub.2SO.sub.3).sub.2 280-320 g/l plating liqud 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.

Example 8: Copper- and Nickel-Plated Carbon Fibers Obtained by Electroless and Electrolytic Continuous Plating Processes

(52) The carbon fibers pretreated in example 4 were subjected to an electroless copper plating process in the compositions and conditions shown in table 10, and then continuously subjected to an electrolytic nickel plating process in the compositions and conditions shown in table 11, using a plating apparatus in the accompanying FIG. 8, thereby preparing copper- and nickel-plated carbon fibers.

(53) TABLE-US-00010 TABLE 10 Electroless copper plating liquid 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 (triethanol 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

(54) TABLE-US-00011 TABLE 11 Electrolytic Ni plating liquid Component Content (Conditions) Electrolytic Nickel metal salt Ni(NH.sub.2SO.sub.3).sub.2 280-320 g/l plating liquid 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

(55) 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 1: Measurement on Change in Current Density and Linear Resistance Value of Plated Carbon Fiber

(56) 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 7.

(57) While 25% NaOH varies 8, 9, 10, 11, and 12 ml/l, and HCHO varies 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 (/30 cm) of the finally obtained products (copper- and nickel-plated carbon fibers) was evaluated, and the results were summarized in table 12 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 13 and 14 below.

(58) TABLE-US-00012 TABLE 12 Resistance Period of use HCHO NaOH Current density (A) (/30 cm) of plating liquid 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

(59) In table 11 above, 1 turn expresses 1 make-up amount of electroless copper plating.

(60) TABLE-US-00013 TABLE 13 Electroless copper plating liquid 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 (triethanol 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

(61) TABLE-US-00014 TABLE 14 Electrolytic plating liquid Component Content (Conditions) Electrolytic Nickel metal salt Ni(NH.sub.2SO.sub.3).sub.2 300 g/l plating liquid Nickel metal 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

(62) As can be confirmed from table 12 above, as the amounts of the reducing agent and NaOH increased, the plating rate increased, but the lifespan 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 the amount of NaOH at the maximum.

Test Example 2: Test on Plating Rate and Liquid Stability

(63) For the plating rate and the liquid stability test 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 15) 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 16 and 17 below.

(64) TABLE-US-00015 TABLE 15 Metal salt Reducing agent Complexing Plating thickness (Cu) (HCHO) agent (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

(65) TABLE-US-00016 TABLE 16 Electroless copper plating liquid 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 (triethanol 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

(66) TABLE-US-00017 TABLE 17 Electrolytic plating liquid Component Content (Conditions) Electrolytic Nickel metal salt Ni(NH.sub.2SO.sub.3).sub.2 300 g/l plating liquid 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

(67) As can be seen from table 15 above, it was verified that, as the concentrations of copper and HCHO were higher, the high-rate plating was possible, and the thickness of the plating layer was increased (plating thickness: 0.7 microns 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.

(68) 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 3: Comparison of Physical Properties and Electrical Conductivity

(69) Table 18 shows comparison of physical properties, electrical conductivity, and the like, between copper- and nickel-plated carbon fibers in examples 5 and 6 and nickel-plated carbon fibers on the market prepared by an electroless plating process, as comparative example 2.

(70) TABLE-US-00018 TABLE 18 Comparative example 2 Example 5 Example 6 Note Strand strength 280 380 338 (kgf/mm.sup.2) (Range) (367~405) (325~353) Elastic modulus (tons/mm.sup.2) 22.0 20.0 22.5 Strain (%) 1.2 1.9 1.5 Specific gravity (g/cm.sup.3) 2.70 2.7277 2.7894 Diameter (m) 7.5 7.828 7.705 Tex 1420 1575 1561 (Fiber thickness) Electric resistance (/m) 0.8 0.7 Electric resistance (cm) 7.5 10.sup.5 4.62 10.sup.5 4.05 10.sup.5 Electric resistance compared 32-fold 37-fold General with general CF reduction reduction CF: 1.50 10.sup.3 cm Coating thickness (nm) 250 240 350 (210~271) (305~392)

(71) As can be seen from table 18 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.

(72) 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.