Copper nano-particles, method of preparing the same, and method of forming copper coating film using the same

Abstract

The present invention relates to copper nano-particles having controlled particle size, high monodispersity, and oxidation stability, a method of preparing the copper nano-particles, and a method of forming a copper coating film using the copper nano-particles. The present invention provides a method of preparing copper nano-particles, comprising mixing a copper salt solution with a mixture of a reducing agent and a solvent; where the copper salt solution is added to the mixture at a temperature of 300° C. or less so that the copper salt solution can react with the mixture. It is thus possible to obtain copper nano-particles with controlled particle size and monodispersity by inducing uniform nucleation and nucleus growth through control of the reaction rate and/or the amount of copper ions during synthesis of the copper nano-particles. Moreover, the copper nano-particles of the present invention employ capping organic molecules, which provide oxidation stability by forming a protective dispersant shell around the copper nano-particles.

1 . A method of preparing copper nano-particles, comprising:
 mixing a reducing agent with a solvent to provide a mixture; and   adding a copper salt solution comprising a copper salt and a solvent to the mixture at a temperature of 300° C. or less such that the copper salt is reduced.   
     
     
         2 . The method as claimed in  claim 1 , wherein the copper salt comprises copper acetate, copper chloride, copper carbonate, copper nitrate, copper sulfate, or a combination comprising at least one of the foregoing copper salts. 
     
     
         3 . The method as claimed in  claim 1 , wherein the reducing agent comprises sodium phosphinate monohydrate, sodium azide, hydrazine hydrate, sodium borohydride, lithium aluminum hydride, or a combination comprising at least one of the foregoing reducing agents. 
     
     
         4 . The method as claimed in  claim 1 , wherein the solvent comprises ethylene glycol, diethylene glycol, triethylene glycol, or a combination comprising at least one of the foregoing solvents. 
     
     
         5 . The method as claimed in  claim 1 , wherein mixing the reducing agent with the solvent further comprises mixing a dispersant with the mixture. 
     
     
         6 . The method as claimed in  claim 5 , wherein the dispersant is a capping organic molecule. 
     
     
         7 . The method as claimed in  claim 6 , wherein the dispersant comprises polyvinylpyrrolidone, thioglycolic acid, trioctylphosphine, trioctylphosphine oxide, cetyltrimethylammonium bromide, or a combination comprising at least one of the foregoing dispersants. 
     
     
         8 . The method as claimed in  claim 1 , wherein adding the copper salt solution to the mixture is performed by injecting the copper salt solution into the mixture using a syringe pump. 
     
     
         9 . Copper nano-particles having a particle size of 20 to 300 nm and comprising capping organic molecules adsorbed onto surfaces of the copper nano-particles. 
     
     
         10 . The copper nano-particles as claimed in  claim 9 , wherein the capping organic molecules comprise polyvinylpyrrolidone (PVP), thioglycolic acid, trioctylphosphine, trioctylphosphine oxide, or cetyltrimethylammonium bromide. 
     
     
         11 . The copper nano-particles as claimed in  claim 9 , wherein the copper nano-particles are prepared using a polyol method. 
     
     
         12 . A method of forming a copper coating film, comprising:
 preparing a coating solution by dispersing copper nano-particles prepared by a polyol method into a solvent;   coating the coating solution on a substrate; and   heat-treating the coating solution coated on the substrate.   
     
     
         13 . The method as claimed in  claim 12 , wherein the coating solution further comprises capping organic molecules adsorbed onto the copper nano-particles. 
     
     
         14 . The method as claimed in  claim 12 , wherein the solvent comprises a primary solvent comprising ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, hexylene glycol, glycerol, or a combination comprising at least one of the foregoing primary solvents. 
     
     
         15 . The method as claimed in  claim 14 , wherein the solvent further comprises a cosolvent comprising ethyl alcohol, methyl alcohol, acetone, isopropanol, toluene, hexane, heptane, methyl ethyl ketone, ethyl lactate, or a combination comprising at least one of the foregoing cosolvents. 
     
     
         16 . The method as claimed in  claim 12 , wherein the coating is performed by spin coating, dip coating, droplet casting, inkjet printing, or screen printing. 
     
     
         17 . The method as claimed in  claim 12 , wherein the heat treatment step is performed at a temperature of 200 to 350° C. 
     
     
         18 . The method as claimed in  claim 12 , wherein the heat treatment step is performed under vacuum, in a reducing atmosphere using hydrogen gas, or in an inert atmosphere. 
     
     
         19 . The method as claimed in  claim 12 , wherein the substrate is a flexible substrate. 
     
     
         20 . The method as claimed in  claim 12 , wherein the copper nano-particles are prepared by adding a copper salt solution to a mixture of a reducing agent and a solvent at a temperature of 300° C. or less so that the copper salt solution reacts with the reducing agent in the mixture. 
     
     
         21 . Copper nano-particles comprising the reaction product of:
 a copper salt,   a reducing agent, and   a dispersant comprising capping organic molecules,   
       wherein the copper nano-particles have a particle size of 20 to 300 nm, and the capping organic molecules are adsorbed onto surfaces of the copper nano-particles.