Micronized barium sulfate

Abstract

Micronized barium sulfate (BaSO 4 ) and methods for the production and use thereof. The micronized barium sulfate of the invention is particularly suitable for use as an additive or filler for adhesives, colorants, rubber articles and/or cosmetics.

What is claimed is:  
     
         1 . A method for producing particulate barium sulfate in which at least 90% of the particles have a primary grain diameter of less than 0.1 μm, said method comprising: 
 combining a barium salt solution with an alkali sulfate salt solution to form a reaction mixture in a continuously operating mixing reactor, in which shear, displacement and frictional forces of intermeshing tools act at high relative speed on the reaction mixture formed, whereby resulting barium sulfate is precipitated, and  
 after passage of the reaction mixture through the reactor, separating and drying the resulting barium sulfate;  
 wherein the concentration of barium salt and sulfate in the salt solutions is at least 80% of the maximum possible concentration.  
 
     
     
         2 . A method according to  claim 1 , wherein the concentration of barium salt and sulfate in the salt solutions is at least 90% of the maximum possible concentration.  
     
     
         3 . A method according to  claim 1 , further comprising washing the separated barium sulfate at least once with water before drying.  
     
     
         4 . A method according to  claim 1 , wherein the barium sulfate is precipitated at a temperature between 0° C. and 100° C.  
     
     
         5 . A method according to  claim 4 , wherein the barium sulfate is precipitated at a temperature between 20° C. and 50° C.  
     
     
         6 . A method according to  claim 1 , wherein at least some of said intermeshing tools are mounted on at least one rotor which rotates at a rotational speed of from 2000 rpm to 8000 rpm.  
     
     
         7 . A method according to  claim 1 , wherein the reaction mixture has a residence time in the mixing reactor in the millisecond range.  
     
     
         8 . A method according to  claim 1 , wherein said barium salt solution and said alkali sulfate solution are aqueous solutions.  
     
     
         9 . A method according to  claim 1 , wherein the barium salt solution is a solution of barium chloride.  
     
     
         10 . A method according to  claim 9 , wherein the barium chloride solution has a BaCl2 concentration of at least 0.9 mole/liter.  
     
     
         11 . A method according to  claim 1 , wherein the alkali sulfate solution is a solution of sodium sulfate.  
     
     
         12 . A method according to  claim 11 , wherein the sodium sulfate solution has a Na 2 SO 4  concentration of at least 0.9 mole/liter.  
     
     
         13 . A method according to  claim 1 , wherein a wetting agent or a dispersing agent is added during or after precipitation of the resulting barium sulfate.  
     
     
         14 . A particulate, coated BaSO 4 , wherein at least 95% of the particles have a primary grain diameter ≦0.1 μm, produced according to the method of  claim 13 .  
     
     
         15 . A particulate, coated BaSO4 according to  claim 14 , wherein at least 99% of the particles have a primary grain diameter ≦0.1 μm.  
     
     
         16 . A particulate, coated BaSO4 according to  claim 15 , wherein 100% of the particles have a primary grain diameter ≦0.1 μm.