Hydrophobic precipitated silica for defoamer formulations

Abstract

Hydrophobic precipitated silicas with a high pH and low silanol group density, a process for preparing them and their use, particularly in deformer formulations.

1 . A hydrophobic precipitated silica having 
 a BET of <110 m 2 /g,    a CTAB of <150 m 2 /g,    a BET/CTAB ratio of <3,    a carbon content of >3.1%, and    a pH of >9.    
     
     
         2 . The hydrophobic precipitated silica as claimed in  claim 1 , having a DBP of <230 g/(100 g).  
     
     
         3 . The hydrophobic precipitated silica as claimed in  claim 1 , having a modified Sears number of less than 6 ml/(5 g).  
     
     
         4 . The hydrophobic precipitated silica as claimed in  claim 1 , having a silanol group density of less than 0.05 ml/(5 m 2 ), as measured by the ratio of the modified Sears number to BET.  
     
     
         5 . The hydrophobic precipitated silica as claimed in  claim 1 , having a methanol wettability of more than 50%.  
     
     
         6 . The hydrophobic precipitated silica as claimed in  claim 1 , having a mean particle size d 50  of less than 14 μm.  
     
     
         7 . A defoamer formulation comprising the hydrophobic precipitated silica according to  claim 1 .  
     
     
         8 . A silicone rubber comprising a reinforcing filler comprising the hydrophobic precipitated silica according to  claim 1 .  
     
     
         9 . An HTV peroxidically crosslinking silicone rubber composition comprising the hydrophobic precipitated silica as claimed in  claim 1 .  
     
     
         10 . A flow assistant comprising the hydrophobic precipitated silica according to  claim 1 .  
     
     
         11 . A carrier comprising the hydrophobic precipitated silica according to  claim 1 .  
     
     
         12 . An anti-blocking agent comprising the hydrophobic precipitated silica as claimed in  claim 1 .  
     
     
         13 . A process for preparing a hydrophobic precipitated silica, comprising: 
 a) precipitating a precipitation silica,    b) filtering,    c) liquefying the filtercake by adding water,    d) drying the suspension,    h) heat treating at more than 150° C., and    i) milling the hydrophobic precipitated silica,    which further comprises    e) alkalifying the precipitated silica by adding at least one basic agent and coating the precipitated silica with a hydrophobicizer by    f) preparing a mixture of at least one hydrophobicizer and a precipitated silica, a precipitated silica dispersion or a precipitated silica filtercake.    
     
     
         14 . The process as claimed in  claim 13 , wherein 
 a) the precipitating is carried out to form a precipitation silica,    b) the filtering is carried out on the precipitation silica to form a filtercake,    c) the liquefying is carried out to form a suspension,    d) the suspension is dried to form a dried precipitation silica, and    h) the heat treating is carried out on the dried precipitation silica to form the hydrophobic precipitated silicae.    
     
     
         15 . The process as claimed in  claim 13 , wherein a) comprises: 
 aa) heating an initial charge of water, or of water mixed with waterglass, to a temperature of between 60 and 100° C.,    ab) simultaneously adding waterglass and an acid to the initial charge, and    ac) lowering the pH by adding an acidifier.    
     
     
         16 . The process as claimed in  claim 15 , further comprising, after ac), ad) aging the precipitation suspension at 10° C. to 95° C. for 0 to 72 hours.  
     
     
         17 . The process as claimed in  claim 15 , wherein the pH in ab) is between 7 and 11.  
     
     
         18 . The process as claimed in  claim 15 , wherein the temperature of the reaction solution in ab) is between 60 and 100° C.,  
     
     
         19 . The process as claimed in  claim 15 , wherein the simultaneous addition of waterglass and acidifier is continued to a solids concentration of 40 to 70 g/l and then stopped.  
     
     
         20 . The process as claimed in  claim 15 , further comprising: 
 adjusting the pH in ac) to from 2 to 8 by adding an acidifier.    
     
     
         21 . The process as claimed in  claim 13 , wherein e) is carried out simultaneously with c).  
     
     
         22 . The process as claimed in  claim 13 , wherein e) is carried out after c) but before d).  
     
     
         23 . The process as claimed in  claim 13 , wherein e) is carried out after d).  
     
     
         24 . The process as claimed in  claim 13 , further comprising: 
 adjusting the pH of the precipitated silica or of the suspension in e) to from 7 to 11 by adding the basic agent.    
     
     
         25 . The process as claimed in  claim 13 , wherein the basic agent is at least one selected from the group consisting of an alkali metal hydroxide, an alkali metal carbonate, an alkaline earth metal hydroxide, an alkaline earth metal carbonate, an alkali metal oxide, an alkaline earth metal oxide, an alkali metal silicate, an alkaline earth metal silicate, an ammonia metal aluminate, an alkali metal aluminate, an aqueous solution thereof or a mixture thereof.  
     
     
         26 . The process as claimed in  claim 13 , wherein the mixing of the hydrophobicizer with the precipitated silica in f) is carried out by adding the hydrophobicizer to a precipitated silica having a water content of 1.0 to 80% by weight.  
     
     
         27 . The process as claimed in  claim 13 , wherein the mixing of the hydrophobicizer with the precipitated silica in f) is carried out by adding the hydrophobicizer to a precipitated silica having a water content of 70 to 99% by weight.  
     
     
         28 . The process as claimed in  claim 13 , wherein the mixing of the hydrophobicizer with the precipitated silica in f) is carried out by simultaneously passing the hydrophobicizer and the precipitated silica into a spin-flash dryer.  
     
     
         29 . The process as claimed in  claim 13 , wherein the mixing of the hydrophobicizer with the precipitated silica in f) takes place by adding the hydrophobicizer to a suspension or dispersion of the precipitated silica.  
     
     
         30 . The process as claimed in  claim 13 , wherein the mixing of the hydrophobicizer with the precipitated silica in f) is carried out by mixing a precipitated silica, dried beforehand, with the hydrophobicizer.  
     
     
         31 . The process as claimed in  claim 26 , wherein the hydrophobicizer is mixed with a precipitated silica which has already been alkalified.  
     
     
         32 . The process as claimed in  claim 26 , wherein the alkalifying in e) is carried out after the hydrophobicizer has been mixed with the precipitated silica.  
     
     
         33 . The process as claimed in  claim 13 , wherein the hydrophobicizer is one or more of an organopolysiloxane derivative or a silicon compound which reacts with the organopolysiloxanes.  
     
     
         34 . The process as claimed in  claim 13 , further comprising 
 subjecting the precipitated silica coated with the hydrophobicizer, or the mixture of the precipitated silica with the hydrophobicizer, to g) conditioning at 10 to 150° C. for a period of 0.5 to 72 h.    
     
     
         35 . The process as claimed in  claim 34 , wherein conditioning takes place at 100 to 150° for a period of 0.5 to 2 hours.  
     
     
         36 . The process as claimed in  claim 13 , wherein g) is followed by h).  
     
     
         37 . The process as claimed in  claim 13 , wherein the mixing of the hydrophobicizer with the precipitated silica in f) is carried out by mixing an already conditioned precipitated silica obtained after g) with a hydrophilic precipitated silica.  
     
     
         38 . The process as claimed in  claim 37 , wherein the conditioned precipitated silica is mixed with a filtercake or suspension or dispersion of the hydrophilic precipitated silica.  
     
     
         39 . The process as claimed in  claim 13 , wherein one of f), g) or h) is carried out repeatedly in succession.  
     
     
         40 . The process as claimed in  claim 13 , wherein f) and h) are carried out repeatedly in succession.  
     
     
         41 . The process as claimed in  claim 13 , wherein f), g) and h) are carried out repeatedly in succession.  
     
     
         42 . The precipitated silica prepared as claimed in  claim 13 .  
     
     
         43 . The process as claimed in  claim 13 , wherein the heating in aa) is carried out at a temperature between 70° C. and 90° C.  
     
     
         44 . The process as claimed in  claim 16 , wherein the aging is carried out at a temperature of from 40° C. to 60° C. for a time of from 0 to 12 hours.