Fumed Silica

Abstract

Fumed silica having a BET surface area of 200±15 m2/g, a grindometer value of less than 30 μm and a median value by PCS of 65 to 85 nm is prepared by grinding a fumed silica having a surface area of 200±25 m2/g, and silicone rubber containing this silica.

1 . Fumed silica having the following physicochemical data: 
       
         
           
                 
                 
                 
                 
               
                     
                     
                 
                     
                   BET surface area 
                   200 ± 15 
                   m 2 /g 
                 
                     
                   Grindometer value 
                   less than 30 
                   μm 
                 
                     
                   Median value by PCS 
                   65 to 85 
                   nm 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
               
            
           
         
       
     
     
         2 . Process for preparing the fumed silica according to  claim 1 , comprising grinding fumed silica having a BET surface area of 200±25 m 2 /g. 
     
     
         3 . A composition comprising silicone rubber and the fumed silica according to  claim 1 . 
     
     
         4 . Silicone rubber composition comprising 0.5% to 60% by weight of a fumed silica having the following characteristic physicochemical data: 
       
         
           
                 
                 
                 
                 
               
                     
                     
                 
                     
                   BET surface area 
                   200 ± 15 
                   m 2 /g 
                 
                     
                   Grindometer value 
                   less than 30 
                   μm 
                 
                     
                   Median value by PCS 
                   65 to 85 
                   nm 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
               
            
           
         
         and 40% to 99.5% by weight of an organopolysiloxane of the formula Z n SiR 3-n —O—[SiR 2 O] x —SiR 3-n -Z 1   n    
         where R=alkenyl, alkoxy, aryl, oxime, acetoxy, alkyl radicals, having 1 to 50 carbon atoms, unsubstituted or substituted by O, S, F, Cl, Br, I, in each case identical or different, 
         and/or a polystyrene, polyvinyl acetate, polyacrylate, polymethacrylate and polyacrylonitrile radical having 40-10 000 repeater units, 
         Z=OH, Cl, Br, acetoxy, amino, amineoxy, oxime, alkoxyamido, alkenyloxy, acryloxy or phosphate radicals, wherein organic radicals contain up to 20 carbon atoms, and in each case identical or different, 
         Z′=oxime, alkoxy, acetoxy, amino, amido, 
         wherein 
         n=1-3, and 
         x=100-15, 000. 
       
     
     
         5 . The formed silica according to  claim 1  which has no particles in the range greater than 40 μm. 
     
     
         6 . The silicone rubber composition according to  claim 4  which is vulcanized. 
     
     
         7 . An article of manufacture made from the vulcanized composition of  claim 6 . 
     
     
         8 . The fumed silica according to  claim 1  which has a specific surface area in the range from 195 to 202 m 2 /g. 
     
     
         9 . The fumed silica according to  claim 1  which have a D50 of 12 to 14 nm weight distribution. 
     
     
         10 . The fumed silica of  claim 1  which has a total span of 5.260 to 34.700 nm in particle size. 
     
     
         11 . The fumed silica of  claim 1  which has an arithmetic mean of particle size of 11.5 to 13.5 nm.