Hydrophobic precipitated silica for defoamer formulations
View Patent ↗A hydrophobic precipitated silica having a BET of less than 110 m 2 /g, a CTAB of less than 150 m 2 /g, a BET/CTAB ratio of less than 3, a carbon content of greater than 3.1%, a pH of 9.7 to 10.5, a DBP of less than 230 g/(100 g), and a methanol wettability of more than 50%. The hydrophobic precipitated silica is used in compositions including defoamers, silicone rubber and HTV crosslinkable silicone rubber compositions. The hydrophobic precipitated silica is also useful as a flow assistant and carrier or anti-blocking agent.
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 5-12%,
a pH of 9.7 -10.5,
a DBP of <230 g/(100 g), and
a methanol wettability of more than 50%.
2. The hydrophobic precipitated silica as claimed in claim 1 , having a modified Sears number of less than 6 ml/(5 g).
3. The hydrophobic precipitated silica as claimed in claim 1 , having a silanol group density of less than 0.05 ml/(5m 2 ), as measured by the ratio of the modified Sears number to BET.
4. The hydrophobic precipitated silica as claimed in claim 1 , having a mean particle size d 50 of less than 14 μm.
5. A defoamer formulation comprising the hydrophobic precipitated silica according to claim 1 .
6. The hydrophobic precipitated silica as claimed in claim 1 , having a pH of from 9.8 to 10.5.
7. The hydrophobic precipitated silica as claimed in claim 1 obtained by a process that includes precipitating a precipitation silica and isolating a silica filter cake, then forming a suspension of the silica filter cake in water and adjusting the pH to 9 with at least one basic agent to form an alkalified silica, then spray drying the alkalified silica to form a dried silica, then treating the dried silica with a hydrophobicization agent to form the hydrophobic precipitated silica.
8. A defoamer formulation, comprising:
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 5-12%,
a pH of 9.7-10.5,
a DBP of <230 g/(100 g), and
a methanol wettability of more than 50%; and
at least one of a mineral oil and a silicone oil.
9. The defoamer formulation according to claim 8 , comprising a mineral oil.
10. The defoamer formulation as claimed in claim 8 , wherein the hydrophobic precipitated silica has a pH of from 9.8 to 10.5.
11. The defoamer formulation as claimed in claim 8 , wherein the hydrophobic precipitated silica is obtained by a process that includes precipitating a precipitation silica and isolating a silica filter cake, then forming a suspension of the silica filter cake in water and adjusting the pH to 9 with at least one basic agent to form an alkalified silica, then spray drying the alkalified silica to form a dried silica, then treating the dried silica with a hydrophobicization agent to form the hydrophobic precipitated silica.