WO2006001636A1

WO2006001636A1 - A manufacturing method of conductive electromagnetic wave absorptive powder

Info

Publication number: WO2006001636A1
Application number: PCT/KR2005/001941
Authority: WO
Inventors: Jongyoull Kim; Howook Kim
Original assignee: Jongyoull Kim; Howook Kim
Priority date: 2004-06-24
Filing date: 2005-06-23
Publication date: 2006-01-05
Also published as: KR100485513B1; KR20040063874A

Abstract

The present invention relates to a method for producing an electromagnetic wave-absorbing conductive powder material having a core of ferrite magnetic material plated with a conductive metal, such as copper, nickel or silver. The conductive powder material is applied on various electrical/electronic devices in the form of paints or synthetic resin composite materials so as to be able to achieve the effects of the shielding of unnecessary electromagnetic waves and the absorption of harmful electromagnetic waves. The invention allows the production of paints and synthetic resin composite materials, which can perform both the absorption of harmful electromagnetic waves and the shielding of unnecessary electromagnetic waves. Accordingly, the invention contributes to the simplification of a process for producing various electrical/electronic devices emitting electromagnetic waves, and at the same time, can achieve the effects of the improvement of product designs and the reduction of production cost.

Description

A MANUFACTURING METHOD OF CONDUCTIVE ELECTROMAGNETIC WAVE ABSORPTIVE POWDER

Technical Field The present invention relates to a method for producing an electromagnetic wave-absorbing conductive powder material, which has a core consisting of magnetic material plated with a conductive metal, such as copper, nickel or silver. The inventive conductive powder material is applied on electrical/electronic devices in the form of paints or synthetic resin composite materials so as to be able to achieve the effects of the shielding of unnecessary electromagnetic waves and the absorption of harmful electromagnetic waves.

Background Art Electromagnetic wave refers to a phenomenon where electromagnetic waves with periodically changing intensities are propagated through space. They have various frequencies, wavelengths and electromagnetic characteristics, and thus, are used in various fields and applications, including various electrical/electronic devices and communication devices. The effect of electromagnetic waves on the human body can be seen through various syndromes found to be caused by electromagnetic waves, such as the thermal effects caused by microwaves used in electronic ranges, mobile phones and the like, or video display terminal syndromes indicating syndromes, such as headaches or sight disturbance, which are caused by electromagnetic waves. In addition, there are a number of study results, such as an increase in the cancer development of residents in the vicinity of power transmission lines, or an attack of brain tumor in long-term users of mobile phones. In particular, due to the development of mobile communication technology and the public use of personal mobile communication, there are continued studies on the possibility of^* adverse effects on the human body and the suggestion of problems, for example, the defenseless exposure of users to high-frequency electromagnetic waves generated from mobile communication devices, such as mobile phones, and an increase in body temperature at cranial sites during the use of such mobile communication devices. For this reason, in highly developed countries where personal mobile communication is commonly used, the standards for the protection of the human body from electromagnetic waves are made and provided as recommendation standards by private organizations, such as associations or societies, on the assumption that electromagnetic waves are harmful to the human body. Some countries, these standards are in force. Also, the recognition of consumers is spread that judges not only the function of products but also the non-harmfulness of products to the human body as important quality factors. As concern and consciousness about the harmfulness of electromagnetic waves to the human body are increased as described above, research and development on either electrical/electronic devices with minimized generation of electromagnetic waves or materials for absorbing generated electromagnetic waves are now actively conducted. Particularly, various forms of electromagnetic wave-absorbing materials, which are attached to various electrical/electronic devices so as to absorb the generated harmful electromagnetic waves, are developed and applied as internal or external parts in antennas or monitors. Moreover, electromagnetic waves have an adverse health effect on the human body as described above and can also cause interference on electrical/electronic devices themselves. Particularly, as electrical/electronic devices become smaller in size and more integrated, the possibilities of interference and misoperation by not only external electromagnetic waves but also self-generated electromagnetic waves can still exist. In order to block the effect of electromagnetic waves on devices, there is generally used a method for shielding unnecessary electromagnetic waves by either providing electromagnetic wave-shielding means in the form of a conductive metal plate or metal network or applying a conductive paste on the external surface or main circuit of electrical/electronic devices. However, these harmful electromagnetic wave-absorbing material or unnecessary electromagnetic wave-shielding means according to the prior art are individually applied on the corresponding electromagnetic wave-emitting devices. Thus, these ■ materials- -or means are applied by an independent process, thus making a device manufacturing process complex and causing an increase in manufacturing cost. In precision devices, there is a serious problem in that the individual structure of the electromagnetic wave absorbing material and shielding means interferes with the miniaturization and integration of the devices.

Disclosure of Invention The present invention has been made in view of the above- described problems occurring in the prior art and it is an object of the present invention to provide 1 a method for producing a conductive powder material for absorbing electromagnetic waves, which has a core of magnetic material plated with a conductive metal, such as copper, nickel or silver, and is applied on electrical/electronic devices in the form of paints or synthetic resin composite materials so as to be able to achieve the effects of the shielding of unnecessary electromagnetic waves and the absorption of harmful electromagnetic waves. In plating the magnetic core with the conductive metal, two or more metals are sequentially plated on the magnetic core so as to form a multilayer plating structure. This prevents the inner plating film from oxidation and improves the ability to shield electromagnetic waves. After plating, the powder material is thermally treated in a reducing furnace having, for example a hydrogen atmosphere, thus making the plating films more strong and stable. Hereinafter, the present invention will be described in detail by a preferred embodiment with reference to the accompanying drawings . FIG . 1 is a representative cross-sectional view of the present invention, — which ■ shows ■ the structure of an electromagnetic wave absorbing and shielding powder . As shown in FIG . 1 , the first plating film 21 and the second plating film, each made of a conductive metal, are formed on the powder core 10 of magnetic material . Namely, the magnetic powder core 10 and the conductive plating films 21 and 22 will act as a harmful electromagnetic wave-absorbing material and an unnecessary electromagnetic wave- shielding material , respectively. The powder core 10 playing a role as a harmful electromagnetic wave-absorbing material is made of ferrite which is a solid solution formed by dissolving alloy elements or impurities in an iron compound of stable body-centered cubic crystal structure at less than 900 (C and will be manufactured into an electromagnetic wave-absorbing material mainly by sintering. Ferrites are classified according to additives, such as zinc, manganese, nickel, copper, barium or strontium, into various kinds. The present invention is not ferrite itself but rather an electromagnetic wave absorbing and shielding powder material consisting of the plating films 21 and 22 formed on a ferrite core, and thus, the kinds of ferrites will not be specifically limited in claims. The formation of the conductive plating films 21 and 22 is performed by an electroless plating process. For this purpose, as shown in FIGS. 2 to 4, a metal salt solution for electroless plating and a reducing agent solution are prepared, and the powder core 10 based on ferrite is added to the metal salt solution, followed by the addition of the reducing agent solution, so as to form the plating film 21. Then, the plated and precipitated powder is collected, washed with water and dried. Conductive metals plated oa the core powder include copper (Cu), nickel (Ni), and silver (Ag). In making the inventive powder, the powder core 10 is not plated with only one metal, but rather may also be plated sequentially with two or more metals as shown in FIG. 1, in which case the first plated powder will serve as the powder core 10 in the second plating step. Namely, when silver plating following copper plating is performed, the first plating film 21 will be made of copper and the second plating film made of silver. Since copper can also lose its conductivity due to oxidation when it is left to stand for a long period of time, the silver plating may also provide the effect of preventing copper from oxidation. In the process of forming the plating films 21 and 22 of conductive metals, the copper plating is performed in the following manner. 5-15% by weight of copper nitrate (Cu(NO3)2) and 15-85% by weight of solvent are mixed with each other to prepare a metal salt solution. Meanwhile, 4-6% by weight of potassium hydroxide (KOH), 22-30% by weight of 80% hydrazine (H2NNH2) hydrate and 64-74% by weight of solvent are mixed with each other to prepare a reducing agent solution. As the solvent, water, methyl alcohol or a mixture of water and methyl alcohol is used. The higher the content of methyl alcohol, the thickness of the plating film 21 becomes thinner. Thus, the thickness of the plating film 21 can be controlled by adjusting the content of methyl alcohol. To the metal salt solution, the powder core 10 based on ferrite is added, and the mixture is stirred and heated. As the temperature of the mixture reaches 40-60 (C, the reducing agent solution is added to the mixture. After completion of the plating, the precipitated powder is collected, washed and dried, thus producing an electromagnetic wave-absorbing conductive powder. The plating of nickel may be performed by two methods, a method including the use of nickel chloride (NΪC12) and a method including the use of nickel sulfate (NiSO4), each of the methods being performed in the following manner. The nickel plating by nickel chloride comprises: mixing 3-7% by weight of nickel chloride (NiC12) and 93-97% by weight of solvent, to prepare a metal salt solution; mixing 1-3% by weight of sodium hydroxide (NaOH), 3-7% by weight of 80% hydrazine (H2NNH2) hydrate and 90-96% by weight of solvent, to prepare a reducing agent solution; adding the powder core 10 to the metal salt solution, and stirring, and heating.the mixture; adding the reducing agent solution to the mixture as the temperature of the mixture reaches 50-70 (C; and collecting the plated and precipitated powder, and washing and drying the collected powder. The nickel plating by nickel sulfate (NΪSO4) comprises: mixing 2-6^Λ buy weight of nickel sulfate (NiSO4) and 94-98% by weight of solvent, to prepare a metal salt solution; 0.5-1.5% by weight of anhydrous sodium carbonate (Na2CO3), 1-2.5% by weight of sodium chloride (NaCl) and 96-98.5% by weight of solvent, to prepare a reducing agent solution; adding the powder core 10 to the metal salt solution and stirring and heating the mixture; adding the reducing agent solution to the mixture as the temperature of the mixture reaches 70-90 (C; and collecting the plated and precipitated powder and washing and drying the collected powder. Solvents used in the nickel plating include water, ethyl alcohol and a mixture of water and ethyl alcohol The higher the content of ethyl alcohol, the thickness of the plating film 21 formed becomes thinner. Thus, the thickness of the plating film 21 can be controlled by adjusting the content of ethyl alcohol. Also, the process of plating silver on the core powder is performed in the following manner. 5-15% by weight of silver nitrate (AgNO3) and 85-95% by weight of water are mixed with each other to prepare a silver nitrate solution, to which ammonia water is then added until the dark brown suspension becomes transparent. Next, an 8- 12-fold higher amount of water than the weight of the silver nitrate solution existing before the addition of ammonia water is added to the transparent solution, to prepare a metal salt solution. To the metal salt solution, the powder core 10 is added. To the powder solution, a reducing agent solution made by mixing 1-3% by weight of formaldehyde (HCHO) with 97-99% by weight of water at room temperature is added. Then, the plated and precipitated powder is collected, washed and dried. In this regard, the amount of formaldehyde is two times the weight of silver nitrate in the metal salt solution. By the above-described process, the plating films 21 and 22 as shown in FIG. 1 are formed on the-surface of the powder coreJLQ. based on ferrite. The plated powder. is. thermally treated under a reducing atmosphere (e.g., hydrogen, argon or nitrogen), so that a very small amount of conductive metal (e.g., copper, nickel or silver) oxides mixed in an unreduced state may also be reduced, thus maximizing the conductivity of the powder. This thermal treatment process is carried out in the following manner. The plated powder is introduced into a reducing furnace where it is heated while introducing nitrogen. As the temperature of the powder reaches 100-200 (C, the powder is heated while introducing a mixed gas of argon (Ar) and hydrogen (H2) into the reducing furnace. As the temperature within the furnace reaches 580 (C, this temperature is kept for 30 minutes and the heating is stopped. The furnace is cooled while continuing to introduce the gas mixture. As the temperature within the furnace reaches 90 (C, the introduction of the mixed gas is stopped, and the furnace is cooled to 60 (C while introducing nitrogen (N2). The electromagnetic wave-absorbing power rendered conductive by the plating and thermal treatment as described above is applied to various electrical/electronic devices in various forms, such as paints or synthetic resin additives, so that it will show the effects of the shielding of unnecessary electromagnetic waves and the absorption of harmful electromagnetic waves.

Brief Description of Drawings FIG. 1 is a representative cross-sectional view of a conductive powder produced according to the present invention. FIG. 2 is a flow chart showing an electroless plating process according to the present invention. FIG. 3 is a flow chart showing a double-plating process according to the present invention. FIG. 4 is a flow chart showing one embodiment of the present invention, which additionally comprises a heating process by a reducing furnace. FIG. 5 shows a portion of a mobile phone, which has been painted with the inventive conductive powder paint. FIG. 6 is a graphic diagram showing test results for CDMA- mode phones painted with the inventive conductive powder paints. FIG. 7 is a graphic diagram showing test results for PCS- mode mobile phones painted with the inventive conductive powder paints.

Best Mode for Carrying Out the Invention Hereinafter, the process and effects of the present invention will be described in detail by examples. Example 1: Electromagnetic wave-absorbing conductive powder having ferrite powder core 10, first plating film 21 of copper (Cu) and second plating film 22 of silver (Ag) 40 g of copper nitrate and 400 cc of water are mixed with each other to prepare a metal salt solution, and 28 g of potassium hydroxide, 150 g of 80% hydrazine hydrate and 400 cc of water are mixed with each other to prepare a reducing agent solution. To the metal salt solution, 20 g of the Mn-Zn ferrite powder cores 10 with a particle size of 0.5-1 μm and a magnetic permeability of 7,000 is added. A mixture of the powder cores 10 and the metal salt solution is stirred and heated. As the temperature of the mixture reaches 50 °C, the reducing agent solution is added to the mixture. After the first plating film 21 is formed, the precipitated powder is collected, washed and dried. Then, the dried powder is subjected to a process for forming the second plating film 22 and a thermal treatment process, in the following manner. 20 g of silver nitrate and 200 cc of water are mixed with each other, to which ammonia water is added. The mixture of silver.-nitrate, water and .ammonia water, which has become...a_ dark brown suspension by the addition of ammonia water, is continuously added with ammonia water until it becomes transparent. Then, 2,000 cc of water is added to the transparent solution, thus preparing a metal salt solution. To the metal salt solution, the powder having the first plating film 21 formed thereon is added. To the powder solution, a reducing agent solution consisting of a mixture of 40 cc of formaldehyde and 1,960 cc of water is added so as to form the second plating film 22. After the second plating film is formed, the precipitated powder is collected, washed and dried. The powder having the second plating film 22 formed thereon is loaded in an alumina vessel to small thickness and introduced into a reducing furnace where it is heated while introducing nitrogen. As the temperature of the powder reaches 100 ⁰C, the material is heated at a rate of 5 °C/minute while introducing a mixed gas of 10% by volume of argon and 90% by volume of hydrogen is introduced at a flow rate of 9 liters/minute. As the temperature within the furnace reaches 580 °C, the furnace is maintained at an isothermal condition for 30 minutes without a further increase in temperature while continuing to introduce the mixed gas. Then, the heating is stopped and the inside of the furnace is cooled while continuing to introduce the mixed gas into the furnace. As the temperature within the furnace reaches 90 ⁰C, the introduction of the mixed gas is stopped and the inside of the furnace is cooled to 60 ⁰C while introducing nitrogen. This yields an electromagnetic wave- absorbing conductive powder. Example 2 : Electromagnetic wave-absorbing conductive powder having ferrite powder core 10, first plating film 21 of nickel (Ni) and second plating film of silver (Ag) 40 g of nickel chloride and 800 cc of water are mixed with each—other to prepare a metaJL-aali—solution, .and__~l£__g of sodium hydroxide, 40 g of 80% hydrazine hydrate and 800 cc of water are mixed with each other to prepare a reducing agent solution. To the metal salt solution, 20 g of the Mn-Zn ferrite powder core with a particle size of 0.5-1 μm and a magnetic permeability of 7,000 is added. The mixture of the powder core 10 and the metal salt solution is stirred and heated. As the temperature of the mixture reaches 60 ⁰C, the reducing agent solution is added. After the first plating film 21 is formed on the powder core, the precipitated powder is collected, washed and dried. Then, the powder is subjected to a process for forming the second plating film 22 and a thermal treatment process in the same manner as described in Example 1. This yields an electromagnetic wave-absorbing conductive powder. Example 3: Electromagnetic wave-absorbing conductive powder having ferrite powder core 10 and first plating film 21 of silver (Ag) 28 g of silver nitrate and 280 cc of water are mixed with each other, to which ammonia water is added. The mixture of silver nitrate, water and ammonia water, which has become a dark brown suspension as a result of the addition of ammonia water, is continuously added with ammonia water until it becomes transparent. Then, 3,000 cc of water is added to the transparent solution, thus preparing a metal salt solution. To the metal salt solution, 20 g of the Mn-Zn ferrite powder cores 10 with a particle size of 0.5-1 μm and a magnetic permeability of 7,000 are added. To the powder solution, a reducing agent solution prepared by mixing 60 cc of formaldehyde and 2,940 cc of water is added so as to form the first plating film 21. After the plating film is formed, the precipitated powder is collected, washed and dried. The powd_er__having__the first plating film 2I_nformed thereon is loaded in an alumina vessel to small thickness and introduced into a reducing furnace where it is heated while introducing nitrogen. As the temperature of the powder reaches 100 ⁰C, the powder is heated at a rate of 5 °C/minute while introducing a mixed gas of 10% by volume of argon and 90% by volume of hydrogen is introduced at a flow rate of 9 liters/minute. As the temperature within the furnace reaches 580 ⁰C, the inside of the furnace is maintained at an isothermal condition for 30 minutes without a further increase in temperature while continuing to introduce the gas mixture. Then, the heating is stopped and the inside of the furnace is cooled while continuing to introduce the mixed gas into the furnace. As the temperature within the furnace reaches 90 °C, the introduction of the mixed gas is stopped and the inside of the furnace is cooled to 60 °C while introducing nitrogen. This yields an electromagnetic wave- absorbing conductive powder. The electromagnetic wave-absorbing conductive powders produced by Examples as described above are either applied to various electrical/electronic devices in the form of paints or mixed with synthetic resin in a process for injection-molding cases for electrical/electronic devices, thus exhibiting the effects of the shielding of unnecessary electromagnetic waves and the absorption of harmful electromagnetic waves. In Comparative Examples for use in verifying the effects of the present invention, a conductive paint based on silver and an electromagnetic wave-absorbing paint based on Mn-Zn ferrite powder were selected. Each of the powders produced by Examples 1-3 and Comparative Examples was used to produce paints. These paints are applied to the inner surface of cases for mobile phone terminals, and then the cases were subjected to tests for measuring specific absorption rates, surface resistance and the like. As shown in FIG. 5, concrete locations of the mobile ^' plϊohe case, applied with the paints, were the inner surfaces of the folder upper, folder assembly, front case and rear case of folder-type mobile phones. In Comparative Example 1, a conductive silver paint commercially available from Polychem Co. , Ltd. under the tradename ^ΛN599-B3730", and in Comparative Example 2 and Examples 1-3, Mn-Zn ferrite powder commercially available from Yulim Ferrite Co., Ltd. in the tradename "YM-9ul2" was used as the powder core. For the production of paints, the following components were mixed with each other: 25% by weight of the powder produced in each of Comparative Example 1 and Examples 1- 3, 35% by weight of methyl alcohol, 25% by weight of an urethane dispersion binder, 8% by ^' weight of N-methylpyrrolidone (CH₃NCOCH₂CH₂CH₂) , 5.5% by weight of ethyl acetate, and 1.5% by weight of ethoxylated nonylphenol phosphate, a dispersing agent commercially available from the tradename "RE-610". Each of the paints was applied to the inner surface of cases for CDMA-mode mobile phone terminals (Model: C-5) and PCS- mode mobile phone terminals (Model: X-40) to a coating thickness of 15 μm after drying at 50 ⁰C for 1 hour, and subjected to various measurements in a state where the folder of the mobile phone terminals has been unfolded. Channel 779 and channel 559 were used in the CDMA terminals and the PCS terminals, respectively. The measurement results are shown in Table 1 below and FIGS. 6 and 7. (Table 1)

As can be seen in Table 1 and FIGS. 6 and 7, the specific absorption rates (SAR) of Examples 1-3 were significantly improved as compared to Comparative Example 1. Also in surface and relative gain, Examples 1-3 were comparable with Comparative Example 1. As a result, the technical substance of the present invention is a method for producing an electromagnetic wave- absorbing conductive powder characterized in that the plating film 21 of conductive metal is formed on the surface of the powder core 10 consisting of ferrite powder. Accordingly, one embodiment of the present invention provides a method for producing an electromagnetic wave-absorbing conductive powder, comprising the steps of: (SIl) mixing 5-15% by weight of copper nitrate (Cu (NO₃)2 with 85-95% by weight of a solvent selected from the group consisting of water, methyl alcohol and a mixture of water and methyl alcohol, so as to prepare a metal salt solution; (S12) mixing 4-6% by weight of potassium hydroxide (KOH), 22-30% by weight of hydrazine (H₂NNH₂) hydrate and 64-74% by weight of solvent so as to prepare a reducing agent solution; (S13) adding the ferrite-based powder core 10 to the metal salt solution and stirring and heating the mixture; (S14) adding the reducing agent solution to the mixture as the temperature of the mixture reaches 40-60 ⁰C; and (S15) collecting the plated and precipitated powder and washing and drying the collected powder. In another embodiment, the present invention provides a method for producing an electromagnetic wave-absorbing conductive powder, comprising the steps of: (SIl) mixing 3-7% by weight of nickel chloride ^"(NiCl₂) and 93-97% by weight of a solvent selected from water, ethyl alcohol and a mixture of water and ethyl alcohol, so as to prepare a metal salt solution; (S12) mixing 1-3% by weight of sodium hydroxide (NaOH) , 3-7% by weight of 80% hydrazine (H₂NNH₂) hydrate and 90-96% by weight of solvent so as to prepare a reducing agent solution; (S13) adding the ferrite-based powder core 10 to the metal salt solution and stirring and heating the mixture; (S14) adding the reducing agent solution to the mixture as the temperature of the mixture reaches 50-70 °C; and (S15) collecting the plated and precipitated powder and washing and drying the collected powder. In still another aspect, the present invention provides a method for producing an electromagnetic wave-absorbing conductive powder, comprising the steps of: (SIl) mixing 2-6% by weight of nickel sulfate (NiSO₄) and 94-98% by weight of solvent so as to prepare a metal salt solution; (S12) mixing 0.5-1.5% by weight of anhydrous sodium carbonate (Na₂Cθ₃) , 1-2.5% by weight of sodium chloride and 96-98.5% by weight of solvent so as to prepare a reducing agent solution; (S13) adding the ferrite- based powder core 10 to the metal salt solution and stirring and heating the mixture; (S14) adding the reducing agent solution to the mixture as the temperature of the mixture reaches 50-70 °C; and (S15) collecting the plated and precipitated powder and washing and drying the collected powder. In still another embodiment, the present invention provides a method for producing an electromagnetic wave-absorbing conductive powder, comprising the steps of: (SIl) 5-15% by weight of silver nitrate (AgNOa) and 85-95% by weight of water so as to prepare a silver nitrate solution, adding ammonia water to the silver nitrate solution until the dark brown suspension becomes transparent, and adding to the transparent solution an 8-12-fold higher amount of water than the weight of the silver nitrate solution existing before the addition of ammonia water; (S12) mixing 1-3% by weight of formaldehyde (HCHO) and 97-99% by weight of water so as to prepare a reducing agent solution; (S13) adding the ferrite-based powder core 10 to the metal salt solution and stirring and heating the mixture; (S14) adding the reducing agent solution to the mixture as the temperature of the mixture reaches 50-70 ⁰C; and (S15) collecting the plated and precipitated powder, and washing and drying the collected powder. Each of the above-described methods may additionally comprise the steps of: (S21) introducing the powder from the step (S15) into a reducing furnace and initially heating the introduced powder to a temperature of 100-200 °C while introducing nitrogen into the furnace; (S22) additionally heating the powder to 580 °C while introducing a mixed gas of hydrogen (H₂) and argon (Ar) into the furnace; (S23) stopping the heating of the powder and initially cooling the inside of the furnace to 90 ⁰C while continuing to introduce the gas mixture; and (S24) stopping the introduction of the mixed gas as the temperature within the furnace reaches 90 °C, and additionally cooling the inside of the furnace to 60 ⁰C while introducing nitrogen (N2) into the furnace.

Industrial Applicability As described above, the use of the electromagnetic wave absorbing and shielding powder according to the present invention makes it possible to produce paints and synthetic resin composite materials, which can perform both the absorption of harmful electromagnetic waves and the shielding of unnecessary electromagnetic waves. Accordingly, the present invention contributes to the simplification of a process for producing various electrical/electronic devices emitting electromagnetic waves, and at the same^ time, can -achieve ,:the effects of the improvement of product designs and the reduction of production cost.

Claims

What Is Claimed Is:

1. A method for producing an electromagnetic wave-absorbing conductive powder in which a plating film (21) of conductive metal is formed on the surface of a powder core (10) consisting of ferrite powder, the method comprising the steps of: (SIl) mixing 5-15% by weight of copper nitrate (Cu(NOs) 2 and 85-95% by weight of solvent so as to prepare a metal salt solution; (S12) mixing 4-6% by weight of potassium hydroxide (KOH) , 22-30% by weight of hydrazine (H₂NNH₂) hydrate and 64-74% by weight of solvent so as to prepare a reducing agent solution; (S13) adding the ferrite-based powder core (10) to the metal salt solution and stirring and heating the mixture; (S14) adding the reducing agent solution to the mixture as the temperature of the mixture reaches 40-60 ⁰C; and (S15) collecting the plated and precipitated- powder, and washing and drying the collected powder.

2. A method for producing an electromagnetic wave-absorbing conductive powder in which a plating film (21) of conductive metal is formed on the surface of a powder core (10) consisting of ferrite powder, the method comprising the steps of: (511) mixing 3-7% by weight of nickel chloride (NiCIa) and 93-97% by weight of solvent so as to prepare a metal salt solution; (512) mixing 1-3% by weight of sodium hydroxide (NaOH), 3- 7% by weight of 80% hydrazine (H₂NNH₂) hydrate and 90-96% by weight of solvent so as to prepare a reducing agent solution; (S13) adding the ferrite-based powder core (10) to the metal salt solution and stirring and heating the mixture; (S14) adding the reducing agent solution to the mixture as the temperature of the mixture reaches 50-70 ⁰C; and (S15) collecting the plated and precipitated powder and, washing and drying the collected powder.

3. A method for producing an electromagnetic wave-absorbing conductive powder in which a plating film (21) of conductive metal is formed on the surface of a powder core (10) consisting of ferrite powder, the method comprising the steps of: (511) mixing 2-6% by weight of nickel sulfate (NiSO₄) and 94-98% by weight of solvent so as to prepare a metal salt solution; (512) mixing 0.5-1.5% by weight of anhydrous sodium carbonate (Na₂Cθ₃) , 1-2.5% by weight of sodium chloride and 96- 98.5% by jweight of solvent so as to prepare a reducing agent solution; (513) adding the ferrite-based powder core (10) to the metal salt solution and stirring and heating the mixture; (514) adding the reducing agent solution to the mixture as the temperature of the mixture reaches 50-70 ⁰C; and (S15) collecting the plated and precipitated powder and washing and drying the collected powder.

4. A method for producing an electromagnetic wave-absorbing conductive powder in which a plating film (21) of conductive metal is formed on the surface of a powder core (10) consisting of ferrite powder, the method comprising the steps of: (SIl) mixing 5-15% by weight of silver nitrate (AgNOs) and 85-95% by weight of water so as to prepare a silver nitrate solution, adding ammonia water to the silver nitrate solution until the dark brown suspension becomes transparent, and adding to the transparent solution an 8-12-fold higher amount of water than the weight of the silver nitrate solution existing before the addition of ammonia water; (S12) mixing 1-3% by weight of formaldehyde (HCHO) and 97- 99% by weight of water so as to prepare a reducing agent solution; (S13) adding the ferrite-based powder core 10 to the metal salt solution and stirring and heating the mixture; (514) adding the reducing agent solution to the mixture as the temperature of the mixture reaches 50-70 ⁰C; and (515) collecting the plated and precipitated powder and washing and drying the collected powder.

5. The method of any one of Claims 1 to 4, which additionally comprises the steps of: (521) introducing the powder from the step (S15) into a reducing furnace and performing the first heating of the introduced powder to a temperature of 100-200 ⁰C while introducing nitrogen into the furnace; (522) additionally heating the powder to 580 °C while introducing a mixed gas of hydrogen (H₂) and argon (Ar) into the furnace; (523) stopping the heating of the powder and initially cooling the inside of the furnace to 90 °C while continuing to introduce the gas mixture; and (524) stopping the introduction of the mixed gas as the temperature within the furnace reaches 90 ⁰C, and additionally cooling the inside of the furnace to 60 ⁰C while introducing nitrogen (N₂) into the furnace.

6. The method of Claim 1, wherein the solvent is one selected from the group consisting of water, methyl alcohol and a mixture of water and methyl alcohol.

7. The method of Claim 2 or 3, wherein the solvent is one selected from the group consisting of water, ethyl alcohol and a mixture of water and ethyl alcohol.