Abstract:
The present invention relates to a method for manufacturing copper nanoparticles and copper nanoparticles thus manufactured, in particular, to a method for manufacturing copper nanoparticles, wherein the method includes producing mixture by mixing one or more copper salt selected from a group consisting of CuCl 2 , Cu(NO 3 ) 2 , CuSO 4 , (CH 3 COO) 2 Cu and Cu(acac) 2  (copper acetyloacetate) with fatty acid and dissociating; and reacting the mixture by heating and copper nanoparticle. 
     According to the present invention, copper nanoparticles can be synthesized in a uniform size and a high concentration using general copper salt as a copper precursor material in non-aqueous system without designing precursor material. The present invention is not only environment-friendly, but also economical as highly expensive equipment is not demanded.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2006-0098315 filed on Oct. 10, 2006, with the Korea Intellectual Property Office, the contents of which are incorporated here by reference in their entirety. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a method for manufacturing copper nanoparticles and copper nanoparticles manufactured using the same. 
         [0004]    2. Description of the Related Art 
         [0005]    Noncontact direct writing technology applying inkjet offers advantages of material and manufacturing time reduction since it allows discharging an exact amount of ink on an exact position. To introduce this inkjet method in industrial applications, corresponding inks should be developed. However, to the present, there is no metal ink for metal wiring, except a silver nanoink. 
         [0006]    Silver nanoparticles, which is a major component for the silver nanoink, has not only a chemical stability but also an excellent electrical conductance so that it has got paid attention as an ink material for the metal wiring. Also, noble metal nanoparticles including silver nanoparticles are easy to be synthesized and their industrial applicability is enhanced as many synthetic methods are known. In spite of these advantages, it is known that, in case of silver, atomic migration or ion migration or electrochemical migration is easily occurred. This ion migration is affected by temperature, humidity, and strength of electric field, etc. In general, ion migration is occurred in high temperature, high humidity, which further induces short circuit between wires and increases defect rate. As strength of electric field is enhanced by micro-wiring, possibility of ion migration is increased. 
         [0007]    Experimentally, tendency of ion migration is Ag + &gt;Pb 2+ &gt;Cu 2+ &gt;Sn 2+ &gt;Au + . Considering the tendency of ion migration, gold can be the best alternative, but its cost is very high. On the other hand, considering electrical conductivity and cost, copper can be another good alternative. Presently, wires of electrical units consist of bulk cooper. Therefore, the ion migration of silver nanoink can be solved if cooper nanoink is developed. 
         [0008]    Conventional synthetic methods of copper nanoparticles provide several tens of nm particles. These synthetic methods use mainly high temperature vapor-phase processes such as thermal evaporation or thermal plasma. Even though they easily synthesize copper and other metals, the surface of synthesized copper particles cannot be treated with an organic dispersing agent. Thus, it requires re-dispersion and results in a lowered dispersibility so that it cannot be used as nanoink. Also, the high temperature vapor-phase method can synthesize only particles with the size more than several tens of nm and a broad range of size distribution of particles. 
         [0009]    Recently, a copper nanoparticle synthetic method using solution synthesis has been suggested. In case of aqueous system, this method includes methods using micelles or PVP. However, in case of using micelles, it is impossible to produce copper nanoparticles in mass production since a copper precursor concentration which can be used per batch is low. 
         [0010]    As methods of preparing copper nanoparticles with the size less than several tens of nm, TDMA (thermal decomposition of metal acetate) suggested by O&#39;Brein et al. has been well-known. This method is a thermal decomposition of metal acetates such as Mn(CH 3 CO 2 ) 2 , Cu(CH 3 CO 2 ) in an oleic acid, in which the oleic acid functions as a solvent and a capping molecule. In case of copper nanoparticles, the example using trioctylamine simultaneously was published in J. Am. Chem. Soc. 2005. Also, Hyeon group published that copper particle synthesis using the thermal decomposition of copper acetyloacetate (Cu(acac) 2 ) in oleylamine. These methods are examples that use the high temperature thermal decomposition in solution. 
         [0011]    Recently, methods for manufacturing copper nanoparticles using the thermal decomposition have been reported after designing a copper precursor using the CVD precursor design technique (KR Patent No. 10-2005-35606). It has an advantage that copper nanoparticles can be synthesized by the thermal decomposition at a low temperature of less than 200° C. It, however, requires a new precursor design and high manufacturing costs. 
         [0012]    Conventional high temperature vapor-phase process is advantageous for particle synthesis with several tens of nm, however, particles having dispersing ability cannot be synthesized and high-cost vacuum equipment is also required. Also, conventional liquid-phase method requires bulk energy consumption through high temperature process so that it is not proper in mass production. In case of using CVD system precursor, commercialized metal salts cannot be used which is further disadvantage in mass production as high-cost precursor is used. 
       SUMMARY 
       [0013]    The present invention was accomplished taking into account of the problems as described above. The present invention provides a method for manufacturing copper nanoparticles including: producing a mixture by dissociating one or more copper salt selected from a group consisting of CuCl 2 , Cu(NO 3 ) 2 , CuSO 4 , (CH 3 COO) 2 Cu and Cu(acac) 2  (copper acetyloacetate) in fatty acid; and reacting the mixture by heating. 
         [0014]    According to an embodiment of the invention, the fatty acid may include one or more compounds selected from a group consisting of saturated fatty acids (C n H 2n O 2 ), oleic acids (C n H 2n-2 O 2 ), lynolic acid (C n H 2n-4 O 2 ), lynolene acids (C n H 2n-6 O 2 ), and high unsaturated acids (C n H 2n-3 O 2 , C n H 2n-10 O 2 , C n H 2n-12 O 2 ) (n is an integer of 10-18). 
         [0015]    Also here, the fatty acid may include one or more compounds selected from a group consisting of dodecarnoic acid (C 11 H 23 COOH), oleic acid (C 17 H 33 COOH), hexadecanoic acid (C 15 H 33 COOH), and tetradecanoic acid (C 13 H 27 COOH). 
         [0016]    Here, the fatty acid may be mixed in a mole ratio of 2 to 10 with respect to the copper salt. 
         [0017]    According to an embodiment of the invention, a primary aliphatic amine having carbon numbers of 3 to 18 may be further added to the mixture. Here, the primary aliphatic amine may be oleylamine or butylamine. Also here, the primary aliphatic amine may be added in a mole ratio of 1 to 10 with respect to the copper salt. 
         [0018]    According to an embodiment of the invention, one or more nonpolar solvents selected from a group consisting of toluene, xylene, chloroform, dichloromethane, hexane, tetradecane and octadecene may be further added to the mixture. Here, the nonpolar solvent may be added in 200 to 1000 parts by weight with respect to 100 parts by weight of the copper salt. 
         [0019]    Here, the heating temperature may be 50 to 300° C. Also here, the heating temperature may be 150 to 300° C. when a thermo-reduction is performed without using a reducing agent. 
         [0020]    Here, after the reaction of the mixture, adding at least one reducing agent selected from group consisting of NaBH 4 , LiBH 4 , KBH 4 , tetrabutylammonium borohydride, N 2 H 4 , PhHNNH 2 , NH 3 —BH 3 , (CH 3 ) 3 N—BH 3 , formate and NaHPO 2  into the mixture, and reacting the mixture by heating may be further included. 
         [0021]    Here, prior to adding the reducing agent, the heating temperature may be 50 to 110° C. 
         [0022]    Here, the reducing agent may be added in a mole ratio of 1 to 6 with respect to the copper salt. 
         [0023]    Here, the heating temperature of the final mixture may be 50 to 150° C. 
         [0024]    Here, the cooper nanoparticles has size of 5 to 40 nm. 
         [0025]    Another aspect of the invention may provide copper nanoparticles manufactured by the method for manufacturing copper nanoparticles set for the above, wherein the surface of the copper nanoparticles includes fatty acid as a capping molecule. 
         [0026]    Here, the fatty acid may be 5 to 40 weight % with respect to the total weight. 
         [0027]    Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    These and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0029]      FIG. 1  is a graph representing PXRD (powder X-ray diffraction) of the copper nanoparticles manufactured according to example 1 of the invention; 
           [0030]      FIG. 2  is a graph representing PXRD (powder X-ray diffraction) of the copper nanoparticles manufactured according to example 2 of the invention; and 
           [0031]      FIG. 3  is a TEM image of the copper nanoparticles manufactured according to example 2 of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Hereinafter, preferred embodiments will be described in detail of the method for manufacturing copper nanoparticles and the copper nanoparticles thus manufactured according to the present invention. 
         [0033]    In the invention, to produce copper nanoparticles without designing a precursor material, copper nanoparticles is synthesized in a high concentration and a uniform size of copper nanoparticles using a general copper salt as a copper precursor material in a non-aqueous system. 
         [0034]    According to an embodiment of the present invention, the present invention provides a method for producing copper nanoparticles including: producing a mixture by dissociating one or more copper salts selected from a group consisting of CuCl 2 , Cu(NO 3 ) 2 , CuSO 4 , (CH 3 COO) 2 Cu and Cu(acac) 2  (copper acetyloacetate) in fatty acid; and reacting the mixture by heating. 
         [0035]    The copper precursor material in the present invention may be a commercialized CuCl 2 , Cu(NO 3 ) 2 , CuSO 4 , (CH 3 COO) 2 Cu, or Cu(acac) 2 , etc. 
         [0036]    The fatty acid in the present invention may be a component that functions as a dispersion stabilizer or a capping molecule and control the size of copper nanoparticles produced finally and further guarantee the dispersion stability. The fatty acid may be saturated fatty acid system (C n H 2n O 2 ), oleic acid system (C n H 2n-2 O 2 ), linoleic acid system, linolenic acid system, or high degree unsaturated system (C n H 2n-2 O 2 , C n H 2n-10 O 2 , C n H 2n-12 O 2 ). Here, n in the above formula is a positive number of 10-18. Examples of the fatty acid may be one or more selected from a group consisting of dodecanoic acid (C 11 H 23 COOH), oleic acid (C 17 H 33 COOH), hexadecanoic acid (C 15 H 33 COOH) and tetradecanoic acid (C 13 H 27 COOH), however, it is not limited to these examples. 
         [0037]    In the dissociation after adding the copper salt to the fatty acid, the fatty acid may be mixed in a mole ratio of 2 to 10 with respect to the copper salt. If the content of the fatty acid is less than 2 mole ratio, the copper salt cannot be perfectly dissociated. If the content of the fatty acid is more than 10 mole ratio, productivity is reduced. 
         [0038]    According to one embodiment of the present invention, in the dissociation of the copper salt, amine compounds can be further added. 
         [0039]    In the forming of the mixture, examples of the amine compounds may be a primary aliphatic amine having carbon numbers of 3 to 18. The oleyl amine is used in an example of the present invention, however, it is not limited to this. The primary aliphatic amine may be used in a molar ratio of 1 to 10 with respect to the copper salt. If the content of the primary aliphatic amine is less than 1 mole ratio, it cannot dissociate the copper salt efficiently. If the content is more than 10 mole ratio, it may not isolated and remains with the capping molecule. The amine compounds dissociate the copper salt in the organic-phase, as well as, control a reaction velocity. 
         [0040]    According to one embodiment of present invention, in the dissociation step, the copper salt is mixed directly to the fatty acid by dissociating without using another organic solvent, however, a nonpolar solvent may be further added for stable reaction. The nonpolar solvent may be added independently or as a mixture of two solvents or more of toluene, xylene, chloroform, dichloromethane, hexane, tetradecane and octadecene etc. The nonpolar solvent is added 200 to 1000 parts by weight with respect to 100 parts by weight of the copper salt. If the content of the nonpolar solvent is less than 200 parts by weight, the effect of stable reaction cannot be obtained. If the content of the nonpolar solvent is more than 1000 parts by weight, productivity is not preferable. 
         [0041]    The mixture of the copper salt dissociated into the fatty acid has a green color system. 
         [0042]    After preparing the mixture in which the copper salt is dissociated, the mixture was heated. 
         [0043]    In the present invention, the reaction temperature and reaction time can be properly controlled according to the desired oxidation state of nanoparticles, size of nanoparticles and reaction condition. The reaction temperature of the mixture in the heat-reacting is 50 to 300° C. If the temperature is less than 50° C., reduction of copper ions cannot be properly performed. If the temperature is more than 300° C., available fatty acids are limited. Furthermore, if the reaction temperature is low, reaction time is excessively elongated. So, heat reduction is performed in a high temperature, if a reducing agent is not used, which will be mentioned later. In other words, among the above range of temperature, high temperature, 150 to 300° C., is preferable. In case of less than 150° C., a reaction time cannot be reduced efficiently. 
         [0044]    In the method for manufacturing copper nanoparticles according to the present invention, to facilitate reduction of copper ions, a reducing agent can be further added. If the reaction is performed using the reducing agent, copper ions can be reduced in a lower temperature within a short period of time. 
         [0045]    According to one embodiment of present invention, the present invention further includes, after reacting the mixture by heating, adding at least one reducing agent selected from a group consisting of NaBH 4 , LiBH 4 , KBH 4 , tetrabutylammonium borohydride, N 2 H 4 , PhHNNH 2 , NH 3 —BH 3 , (CH 3 ) 3 N—BH 3 , formate and NaHPO 2 ; and reacting the mixture by heating. 
         [0046]    When the reducing agent is further added, before adding the reducing agent, the reaction is heated at a lower temperature, 50 to 110° C., and stirred gently sufficient to dissociate the copper salt. 
         [0047]    The available reducing agent in the present invention may be borohydrazines, boranes, hydrazines, formate, sodium hydrophosphate, etc. More specifically, it may be at least one compound selected from group consisting of NaBH 4 , LiBH 4 , KBH 4 , tetrabutylammonium borohydride, N 2 H 4 , PhHNNH 2 , NH 3 —BH 3 , (CH 3 ) 3 N—BH 3 , formate and NaHPO 2 , however, it is not limited to these. 
         [0048]    After preparing the mixture in which the copper salt is dissociated, the reducing agent is added to it and the mixture is heated. The content of the reducing agent is 1 to 6 mole ratio with respect to the copper salt. If the content of the reducing agent is less than 1 mole ratio, reducing power is too weak to obtain the desired effect. If the content of the reducing agent is more than 6 mole ratio, the reaction is too explosive to control the reaction. The content of reducing agent may be determined according to reaction time, reaction temperature, desirable oxidation state of copper nanoparticles. 
         [0049]    The temperature in heat reaction after adding the reducing agent may be 50 to 150° C. 
         [0050]    If the reaction temperature is less than 50° C., it is difficult to reduce a reaction time. If the reaction temperature is more than 150° C., the reaction cannot be controlled. 
         [0051]    As the copper ions in the mixture is reduced, color has changed. The reaction is completed when the color of the mixture turns to brown or dark red. 
         [0052]    The copper nanoparticles thus manufactured may be obtained in powder by general filtration, washing and drying processes. For example, after methanol, acetone or mixture of methanol/acetone is added, the copper nanoparticles may be obtained by centrifugation. According to the present invention, the size of copper nanoparticles is 5 to 40 nm. 
         [0053]    The copper nanoparticles according to another aspect of the present invention may be manufactured by the above method and the surface of the copper nanoparticle may include fatty acid as a capping molecule. The fatty acid forms 5 to 40 weight % among the total weight. 
         [0054]    The method for manufacturing copper nanoparticles and copper nanoparticles thus manufactured were set forth above in detail, and hereinafter, explanations will be given in greater detail with specific examples. While the embodiment of the present invention provides the production of copper nanoparticles, the invention is not limited to the examples stated below and may be used for production of another copper nanoparticles. It is also apparent that more changes may be made by those skilled in the art without departing from the principles and spirit of the present invention. 
       EXAMPLE 1 
       [0055]    After Cu(NO 3 ) 2  0.5 mol was added to 2 mol of oleic acid, 1 mol of butylamine was further added to dissociate. The color of the reaction solution was changed to green. The reaction solution was heated to 200° C. with stirring. Then reduction reaction was processed and color of the reaction solution was further changed to brown, and copper metal color was appeared at the wall of a glass reactor. After 2 hours of the reaction, re-precipitation was performed using a polar solvent a mixture of acetone and methanol. The copper nanoparticles was recovered using centrifugation. 
       EXAMPLE 2 
       [0056]    After 0.5 mol of Cu(CH 3 CO 2 ) 2  was added to 1 mol of oleic acid and 300 g of xylene, the mixture was heated to 90° C. while stirring. The color of the reaction solution was changed to green color. After 1 mol of oleylamine was added to it and the mixture was further gently mixed, 1 mol of formic acid was added to it. The mixture was heated to 130° C. and as the reduction reaction processed, the color of the solution was changed to brown, and the copper metal color was appeared at the wall of glass reactor. 
         [0057]    PXRD (powder X-ray diffraction) of the copper nanoparticles prepared in Example 1 was shown in  FIG. 1 . From Scherrer-Debye formula,  FIG. 1  ensures that copper nanoparticle with a size of 30 nm was generated. 
         [0058]    PXRD (powder X-ray diffraction) results of the copper nanoparticles prepared in Example 2 was shown in  FIG. 2  and TEM photo is shown in  FIG. 3 . From Scherrer-Debye formula,  FIG. 2  ensures that the copper nanoparticles with a size of 10 nm was generated. TEM analysis of  FIG. 3  also ensures it.