Polyol-based method for producing ultra-fine copper powders

Abstract

The present invention provides a metallic composition, which contains a plurality of ultra-fine metallic particles (e.g., ultra-fine copper, nickel, or silver particles) having at least one desirable feature, such as, tight size distribution, low degree of agglomeration, and high degree of crystallinity and oxidation resistance. The present invention further provides a method for forming the ultra-fine metallic particles. Also provided are a substance or substrate coated with the ultra-fine metallic particles and a method of coating a substance or substrate with the ultra-fine metallic particles. Furthermore, the present invention provides a method of controlling the size of ultra-fine metal particles formed in a reducing reaction in a liquid. Also provided is a method for producing ultra-fine metallic particles, which utilizes a concentrated reaction system.

1 . A metallic composition comprising a plurality of ultra-fine copper particles, wherein the plurality of ultra-fine copper particles is resistant to oxidation.  
     
     
         2 . The metallic composition of  claim 1 , wherein the plurality of ultra-fine copper particles undergoes minimal oxidation for 12 months in ambient environment, wherein oxidation is minimal when the oxygen content of the ultra-fine copper particles is less than about 5-10% at the end of such period of time.  
     
     
         3 . The metallic composition of  claim 1 , wherein the plurality of ultra-fine copper particles undergoes minimal oxidation when the plurality of ultra-fine copper particles is exposed to a temperature up to 100° C. for 120 minutes in air.  
     
     
         4 . The metallic composition of  claim 1 , wherein the plurality of ultra-fine copper particles undergoes minimal oxidation when the plurality of ultra-fine copper particles is heated in air at 20° C./minute up to 200-220° C.  
     
     
         5 . The metallic composition of  claim 1 , wherein oxidation is characterized by a weight gain in the plurality of ultra-fine copper particles and wherein the weight gain of the plurality of ultra-fine copper particles does not exceed about 80% of a theoretical weight gain for the plurality of ultra-fine copper particles when the plurality of ultra-fine copper particles is heated in air at 20° C./minute to 800° C.  
     
     
         6 . The metallic composition of  claim 1 , wherein the plurality of ultra-fine copper particles has a tight size distribution.  
     
     
         7 . The metallic composition of  claim 6 , wherein the plurality of ultra-fine copper particles has a tight size distribution when at least about 80% of the plurality of ultra-fine copper particles has a diameter within the range of N±15% N, wherein N is an average diameter of the plurality of ultra-fine copper particles.  
     
     
         8 . The metallic composition of  claim 1 , wherein the plurality of ultra-fine copper particles has a high degree of crystallinity.  
     
     
         9 . The metallic composition of  claim 8 , wherein at least about 80-95% of the plurality of ultra-fine copper particle is highly crystalline.  
     
     
         10 . The metallic composition of  claim 1 , wherein the plurality of ultra-fine copper particles has a low degree of agglomeration.  
     
     
         11 . The metallic composition of  claim 10 , wherein the degree of agglomeration is measured with an I aggl  value and wherein the I aggl  of the plurality of ultra-fine copper particles is less than about 1.2.  
     
     
         12 . A metallic composition comprising a plurality of ultra-fine copper particles, wherein the plurality of ultra-fine copper particles is obtained in accordance with the process comprising the steps of: 
 (a) forming a reaction mixture comprising a precursor of copper, a branched dispersing agent, and an alcoholic agent;    (b) adjusting the temperature of the reaction mixture to a reaction temperature suitable for reducing the precursor of copper to copper particles;    (c) maintaining the reaction mixture under the reaction temperature for a time sufficient to reduce the precursor of copper to copper particles; and optionally,    (d) isolating the copper particles.    
     
     
         13 . The metallic composition of  claim 12 , wherein the branched dispersing agent is a branched polyol.  
     
     
         14 . The metallic composition of  claim 13 , wherein the branched polyol is pentaerythritol.  
     
     
         15 . The metallic composition of  claim 12 , wherein the reaction mixture further comprises at least one other dispersant selected from the group consisting of a linear polyol dispersant and a salt of polynaphtalene sulphonic/formaldehyde co-polymer.  
     
     
         16 . The metallic composition of  claim 12 , wherein the alcoholic agent is at least one polyol selected from the group consisting of 1,2-propylene glycol, 1,3-propylene glycol, and diethyleneglycol.  
     
     
         17 . The metallic composition of  claim 16 , wherein the alcoholic agent is the mixture of 1,2-propylene glycol and diethyleneglycol.  
     
     
         18 . The metallic composition of  claim 12 , wherein the precursor of copper is copper carbonate.  
     
     
         19 . The metallic composition of  claim 12 , wherein the precursor of copper is a mixture of copper carbonate and at least one of copper acetate and copper salycilate.  
     
     
         20 . The metallic composition of  claim 12 , wherein the reaction temperature is about 180-185° C.  
     
     
         21 . The metallic composition of  claim 12 , wherein the process further comprises adjusting pH of the reaction mixture.  
     
     
         22 . The metallic composition of  claim 21 , wherein the pH of the reaction mixture is adjusted by introducing a buffering agent into the reaction mixture.  
     
     
         23 . The metallic composition of  claim 22 , wherein the buffering agent is triethanolamine.  
     
     
         24 . The metallic composition of  claim 12 , wherein the reaction mixture further comprises an agent which releases an organic counter ion.  
     
     
         25 . The metallic composition of  claim 24 , wherein the organic counter ion is at least one of an acetate and a salycilate.  
     
     
         26 . A method for forming a plurality of ultra-fine copper particles comprising the steps of: 
 (a) forming a reaction mixture comprising a precursor of copper, a branched dispersing agent, and an alcoholic agent;    (b) adjusting the temperature of the reaction mixture to a reaction temperature suitable for reducing the precursor of copper to copper particles;    (c) maintaining the reaction mixture under the reaction temperature for a time sufficient to reduce the precursor of copper to copper particles; and optionally,    (d) isolating the copper particles.    
     
     
         27 . The method of  claim 26 , wherein the branched dispersing agent is a branched polyol.  
     
     
         28 . The method of  claim 27 , wherein the branched polyol is pentaerythritol.  
     
     
         29 . The method of  claim 26 , wherein the reaction mixture further comprises at least one other dispersant selected from the group consisting of a linear polyol dispersant and a salt of polynaphtalene sulphonic/formaldehyde co-polymer.  
     
     
         30 . The method of  claim 26 , wherein the alcoholic agent is at least one polyol selected from the group consisting of 1,2-propylene glycol, 1,3-propylene glycol, and diethyleneglycol.  
     
     
         31 . The method of  claim 30 , wherein the alcoholic agent is the mixture of 1,2-propylene glycol and diethyleneglycol.  
     
     
         32 . The method of  claim 26 , wherein the precursor of copper is copper carbonate.  
     
     
         33 . The method of  claim 26 , wherein the precursor of copper is a mixture of copper carbonate and at least one of copper acetate and copper salycilate.  
     
     
         34 . The method of  claim 26 , wherein the reaction temperature is about 180-185° C.  
     
     
         35 . The method of  claim 26 , further comprising adjusting pH of the reaction mixture.  
     
     
         36 . The method of  claim 26 , wherein the pH of the reaction mixture is adjusted by introducing a buffering agent into the reaction mixture.  
     
     
         37 . The method of  claim 36 , wherein the buffering agent is triethanolamine.  
     
     
         38 . The method of  claim 26 , wherein the reaction mixture further comprises an agent which releases an organic counter ion.  
     
     
         39 . The method of  claim 38 , wherein the organic counter ion is at least one of an acetate and a salycilate.