Flaky Copper Powder, Method For Producing The Same, And Conductive Paste

Abstract

It is an object of the present invention to provide a flaky copper powder composed of fine particles having a sharp distribution particle size, a large crystallite diameter and high oxidation resistance. The flaky copper powder of the present invention contains P and has a crystallite diameter/D 1A ratio of 0.01 or more to achieve the object. The method for producing the flaky copper powder comprises four steps: a first step of preparing an aqueous solution containing a copper salt and complexing agent; a second step of adding an alkali hydroxide to the aqueous solution to prepare a first slurry containing cupric oxide; a third step of adding a first reducing agent which can reduce the cupric oxide into cuprous oxide to the first slurry to prepare a second slurry containing cuprous oxide; and a fourth step of adding a second reducing agent which can reduce the cuprous oxide into copper to the second slurry to provide a flaky copper powder, wherein phosphoric acid and its salt are added in at least one of the first to third steps and/or in the second slurry in the fourth step.

1 . A flaky copper powder which is characterized in that comprising P.  
   
   
       2 . The flaky copper powder according to  claim 1  which is characterized in that comprising P at 10 to 200 ppm.  
   
   
       3 . The flaky copper powder according to  claim 1 , which is characterized in that an average particle diameter D 50  of the powder is in the range from 0.3 μm to 7 μm.  
   
   
       4 . The flaky copper powder according to  claim 1 , which is characterized in that crystallite diameter of the powder is 25 nm or more.  
   
   
       5 . The flaky copper powder according to  claim 1  which is characterized in that an aspect ratio D 1A /t of the powder, which is calculated by dividing an average particle diameter D 1A  (μm) by a flaky copper particle thickness t (μm), the average particle diameter D 1A  (μm) and the thickness t (μm) are measured from analyzing SEM images directly observed by a scanning electron microscope, is in the range from 2 to 50.  
   
   
       6 . The flaky copper powder according to  claim 1  characterized by having an SD/D 50  ratio of 0.45 or less, (where D 50  is a median diameter (μm) calculated as 50% of volume cumulative distributions examined by a laser diffraction scattering particle size distribution measuring method).  
   
   
       7 . The flaky copper powder according to  claim 1  which is characterized in that D 90 /D 10  ratio of 3.0 or less, (where D 10  is diameter (μm) at 10% of volume cumulative distributions and D 90  is diameter (μm) at 90% of volume cumulative distributions examined by a laser diffraction scattering particle size distribution measuring method, and SD is a standard deviation (μm) of a particle size distribution examined by the same measuring method respectively).  
   
   
       8 . A method for producing a flaky copper powder comprising four steps: a first step of preparing an aqueous solution comprising a copper salt and a complexing agent; a second step of adding an alkali hydroxide to the aqueous solution to prepare a first slurry comprising cupric oxide; a third step of adding a first reducing agent which can reduce cupric oxide into cuprous oxide to the first slurry to prepare a second slurry comprising cuprous oxide; and a fourth step of adding a second reducing agent which can reduce the cuprous oxide into copper to the second slurry to provide a flaky copper powder, which is characterized in that phosphoric acid and its salt are added in at least one of the first to third steps and/or phosphoric acid and its salt are added in the second slurry in the fourth step.  
   
   
       9 . The method for producing a flaky copper powder according to  claim 8 , which is characterized in that the phosphoric acid and its salt are added in at least one of the first to third steps and/or in the second slurry in the fourth step to be a total amount of 0.001 to 3 moles as P per 1 mole of copper which present in the above described aqueous solution, the first slurry or the second slurry.  
   
   
       10 . The method for producing a flaky copper powder according to  claim 8 , which is characterized in that the first slurry contains the alkali hydroxide at 1.05 to 1.50 equivalents per equivalent of the copper salt.  
   
   
       11 . The method for producing a flaky copper powder according to  claim 8 , which is characterized in that the complexing agent is an amino acid.  
   
   
       12 . The method for producing a flaky copper powder according to  claim 8 , which is characterized in that the first reducing agent is a reducing sugar.  
   
   
       13 . The method for producing a flaky copper powder according to  claim 8 , which is characterized in that the second reducing agent is at least one selected from the group consisting of hydrazine, hydrated hydrazine, hydrazine sulfate, hydrazine carbonate and hydrazine chloride.  
   
   
       14 . The method for producing a flaky copper powder according to  claim 8 , which is characterized in that the aqueous solution comprises the complexing agent at 0.005 to 10 moles per 1 mole of copper present in the aqueous solution itself, the first slurry or the second slurry.  
   
   
       15 . The flaky copper powder according to  claim 1 , which is characterized in that an organic surface treatment layer is formed on the surface.  
   
   
       16 . The flaky copper powder according to  claim 15 , which is characterized in that a coating rate of the organic surface treatment layer is 0.05 to 2 wt % based on the flaky copper powder.  
   
   
       17 . A conductive paste comprising the flaky copper powder according to  claim 1  and a resin.