Silver powder and method for producing same

Abstract

There is provided a method for a silver powder capable of decreasing the viscosity of a photosensitive paste using the silver powder and improving the film state, sensitivity and linearity of the paste even if the particle diameter of the silver powder is small. The surface of a silver powder produced by a wet reducing method is smoothed by a surface smoothing process for mechanically causing particles of the silver powder to collide with each other, and thereafter, silver agglomerates are removed by classification. The surface smoothing process is carried out by putting a dried silver powder into an apparatus, which is capable of mechanically fluidizing particles, e.g., a mixer or mill such as a cylindrical high-speed mixer, for mechanically causing the particles to collide with each other.

1 . A method for producing a silver powder, said method comprising the steps of: 
 producing a silver powder by a wet reducing method;    smoothing a surface of the produced silver powder by a surface smoothing process for mechanically causing particles to collide with each other; and    removing silver agglomerates by a classification.    
     
     
         2 . A method for producing a silver powder as set forth in  claim 1 , wherein said wet reducing method comprises the steps of: 
 adding an alkali or complexing agent to an aqueous silver salt containing solution to form a silver oxide containing slurry or an aqueous silver complex salt containing solution; and    thereafter, adding a reducing agent to the slurry or solution to deposit a silver powder by reduction.    
     
     
         3 . A method for producing a silver powder as set forth in  claim 1 , wherein said silver powder has a mean particle diameter of 0.1 to 10 μm after said classification.  
     
     
         4 . A method for producing a silver powder as set forth in  claim 1 , wherein said silver powder has a mean particle diameter of not greater than 5 μm after said classification.  
     
     
         5 . A method for producing a silver powder as set forth in  claim 1 , wherein said classification removes silver agglomerates having a size of greater than 15 μm.  
     
     
         6 . A method for producing a silver powder as set forth in  claim 1 , wherein said classification removes silver agglomerates having a size of greater than 11 μm.  
     
     
         7 . A method for producing a silver powder as set forth in  claim 1 , wherein said surface smoothing process is carried out by means of a high-speed mixer.  
     
     
         8 . A silver powder having a mean particle diameter of 0.1 to 10 μm and a maximum particle diameter of not greater than 15 μm, wherein said silver powder has a maximum particle diameter D max  measured by a grind gauge is not greater than 12.5 μm when said silver powder is used for preparing a paste, and 
 wherein a mixture, which is obtained by mixing and dispersing 80 wt % of said silver powder in 20 wt % of an epoxy resin having a viscosity of 0.2 to 0.6 Pa·sec at 25° C., has a viscosity of not greater than 135 Pa·sec when said viscosity is measured by an E-type viscometer at 25° C. and 1 rpm.    
     
     
         9 . A silver powder as set forth in  claim 8 , wherein said maximum particle diameter of said silver powder is not greater than 11 μm, and said maximum particle diameter D max  measured by said grind gauge is not greater than 7.5 μm.  
     
     
         10 . A silver powder as set forth in  claim 8 , wherein said means particle diameter of said silver powder is not greater than 5 μm.  
     
     
         11 . A silver powder having a mean particle diameter of 0.1 to 10 μm and a maximum particle diameter of not greater than 15 μm, wherein said silver powder has a maximum particle diameter D max  measured by a grind gauge is not greater than 12.5 μm when said silver powder is used for preparing a paste, and 
 wherein a mixture, which is obtained by mixing and dispersing 80 wt % of said silver powder in 20 wt % of an epoxy resin having a viscosity of 0.2 to 0.6 Pa·sec at 25° C., has a viscosity of not greater than 90 Pa·sec when said viscosity is measured by an E-type viscometer at 25° C. and 3 rpm.    
     
     
         12 . A silver powder as set forth in  claim 11 , wherein said maximum particle diameter of said silver powder is not greater than 11 μm, and said maximum particle diameter D max  measured by said grind gauge is not greater than 7.5 μm.  
     
     
         13 . A silver powder as set forth in  claim 11 , wherein said means particle diameter of said silver powder is not greater than 5 μm.  
     
     
         14 . A silver powder produced by a method as set forth in  claim 1 , wherein said silver powder has a maximum particle diameter D max  is not greater than 12.5 μm when said maximum particle diameter D max  is measured by a grind gauge if said silver powder is used for preparing a paste.  
     
     
         15 . A silver powder as set forth in  claim 14 , wherein said maximum particle diameter D max  measured by said grind gauge is not greater than 7.5 μm.