Particulate compositions of particulate metal and polymer binder

Abstract

A particulate composition wherein each particle thereof includes a first metal (e.g., tungsten), an optional second metal (e.g., tin), and a polymer binder (e.g., thermoplastic polyvinyl alcohol) is described. The first metal has a particle size of less than or equal to 10 μm, and the second metal has a particle size of less than or equal to 20 μm. The polymer binder is typically present in each particle of the particulate composition in an amount of from 0.5 to 2.5 percent by weight, based on the total weight of the particulate composition. The particulate composition has an average particle size of 25 to 300 μm, and is free flowing. The particles of the particulate composition are preferably substantially spherical. Also described is a method of preparing the particulate composition by means of spray drying. The particulate compositions may be used to prepare molded articles, such as frangible projectiles (e.g., frangible bullets).

1 . A particulate composition comprising: 
 (a) a first metal selected from the group consisting of tungsten, tungsten carbide, ferro-tungsten, bismuth, stainless steel, tantalum, molybdenum, combinations thereof, and alloys of at least two metals thereof, said first metal having an average particle size of less than or equal to 10 μm;    (b) optionally a second metal selected from the group consisting of tin, zinc, iron, copper, aluminum, combinations thereof, and alloys of at least two metals thereof, said second metal having an average particle size of less than or equal to 20 μm;    (c) a binder selected from the group consisting of thermosetting resins, thermoplastic resins and combinations thereof,    wherein each particle of said particulate composition substantially comprises,    said first metal in an amount of from 30 percent by weight to 99 percent by weight, based on the total weight of said particulate composition,    said second metal in an amount of from 0 percent by weight to 70 percent by weight, based on the total weight of said particulate composition, and    said binder in an amount of 0.5 percent by weight to 2.5 percent by weight, based on the total weight of said particulate composition,    said particulate composition has an average particle size of from 25 μm to 300 μm, and said particulate composition is substantially free flowing.    
   
   
       2 . The particulate composition of  claim 1  wherein the particles of said particulate composition are substantially spherical.  
   
   
       3 . The particulate composition of  claim 1  wherein said first metal comprises tungsten, and said second metal comprises tin.  
   
   
       4 . The particulate composition of  claim 1  wherein said binder is a thermoplastic resin selected from the group consisting of polyvinyl alcohol, poly(C 2 -C 5 -alkylene glycol), hydroxyalkylcellulose, polyacrylate, polymethacrylate, polyurethane, polyolefin, polyester, polyamide and combinations thereof.  
   
   
       5 . The particulate composition of  claim 1  wherein said first metal is tungsten, said second metal is tin, said binder is thermoplastic polyvinyl alcohol, and said particles of said particulate composition are substantially spherical.  
   
   
       6 . The particulate composition of  claim 5  wherein said particulate composition has a tungsten to tin weight ratio of 4 to 1.  
   
   
       7 . A method of preparing a particulate composition comprising: 
 (a) forming a substantially homogenous particulate metal mixture comprising, 
 (i) a first metal selected from the group consisting of tungsten, tungsten carbide, ferro-tungsten, bismuth, stainless steel, tantalum, molybdenum, combinations thereof, and alloys of at least two metals thereof, said first metal having an average particle size of less than or equal to 10 μm, and  
 (ii) optionally a second metal selected from the group consisting of tin, zinc, iron, copper, aluminum, combinations thereof, and alloys of at least two metals thereof, said second metal having an average particle size of less than or equal to 20 μm,  
 said first metal being present in said particulate metal mixture in an amount of from 30 percent by weight to 100 percent by weight, based on the total weight of said particulate metal mixture,  
 said second metal being present in said particulate metal mixture in an amount of from 0 percent by weight to 70 percent by weight, based on the total weight of said particulate metal mixture, and said particulate metal mixture being substantially dry;  
   (b) preparing a slurry comprising, 
 (i) said homogenous particulate metal mixture,  
 (ii) water,  
 (iii) a binder selected from the group consisting of thermosetting  
  resins, thermoplastic resins and combinations thereof, and  
 (iv) optionally a defoamer,  
 wherein said slurry contains,  
 said first metal in an amount of from 24 to 89 percent by weight, based on the total weight of said slurry,  
 said second metal in an amount of from 0 to 63 percent by weight, based on the total weight of said slurry,  
 water in an amount of from 10 to 25 percent by weight, based on the total weight of said slurry,  
 binder in an amount of from 0.4 to 2.2 percent by weight, based on the total weight of said slurry, and  
 defoamer in an amount of from 0 percent by weight to 0.05 percent by weight, based on the total weight of said slurry; and  
   (c) passing said slurry through a spray drier, thereby forming said particulate composition,    wherein each particle of said particulate composition substantially comprises,    said first metal in an amount of from 30 percent by weight to 99 percent by weight, based on the total weight of said particulate composition, said second metal in an amount of from 0 percent by weight to 70 percent by weight, based on the total weight of said particulate composition, and    said binder in an amount of 0.5 percent by weight to 2.5 percent by weight, based on the total weight of said particulate composition,    said particulate composition has an average particle size of from 25 μm to 300 μm, the particles of said particulate composition are substantially spherical, and said particulate composition is substantially free flowing.    
   
   
       8 . The method of  claim 7  wherein said spray drier is operated at an inlet temperature of from 200° C. to 300° C., and an outlet temperature of 100° C. to 165° C.  
   
   
       9 . The method of  claim 7  wherein said first metal comprises tungsten, and said second metal comprises tin.  
   
   
       10 . The method of  claim 7  wherein said binder is a thermoplastic resin selected from the group consisting of polyvinyl alcohol, poly(C 2 -C 5 -alkylene glycol), hydroxyalkylcellulose, polyacrylate, polymethacrylate, polyurethane, polyolefin, polyester, polyamide and combinations thereof.  
   
   
       11 . The method of  claim 7  wherein said first metal is tungsten, said second metal is tin, and said binder is thermoplastic polyvinyl alcohol.  
   
   
       12 . The method of  claim 11  wherein said particulate composition has a tungsten to tin weight ratio of 4 to 1.  
   
   
       13 . The particulate composition prepared by the process of  claim 7 .  
   
   
       14 . A molded article comprising the particulate composition of  claim 13 .  
   
   
       15 . A molded article comprising the particulate composition of  claim 1 .  
   
   
       16 . The molded article of  claim 15  wherein said molded article is substantially non-sintered, and said molded article is a projectile.  
   
   
       17 . The molded article of  claim 16  wherein said projectile has a density of from 11.0 to 11.5 g/cm 3 .  
   
   
       18 . The molded article of  claim 17  wherein said projectile is a frangible bullet.