Silicone rubber
View Patent ↗A composition containing a silicone and one or more silanized, structure-modified, pyrogenic silicas which contain groups fixed to their surface is described. The silicone containing silanized, structure-modified, pyrogenic silicas exhibit advantageous rheological properties, such as lowered crepe hardening, which facilitates the processing operations even after storage or transport of the silicone composition.
1. A composition, comprising:
a silicone; and
one or more silanized, structure-modified, pyrogenic silicas;
wherein:
the one or more silanized, structure-modified, pyrogenic silicas comprise at least one of dimethylsilyl and monomethylsilyl groups fixed on a surface of the silicas;
the one or more silanized, structure-modified, pyrogenic silicas are prepared by:
flame-hydrolyzing one or more vaporizable silicon compounds to obtain a pyrogenic silica;
treating the pyrogenic silica with at least one member selected from the group consisting of dimethylchlorosilane and monomethyltrichlorosilane to obtain a silanized, pyrogenic silica; and
structure-modifying the silanized, pyrogenic silica to obtain the silanized, structure-modified, pyrogenic silica;
the one or more silanized, structure-modified, pyrogenic silicas are present in the composition in an amount of at least 40% by weight based on a total weight of the composition; and
the silicone is a polydimethylsiloxane having a molecular weight of from 400,000 to 600,000.
2. The composition according to claim 1 , wherein said one or more silanized, structure-modified, pyrogenic silicas have the following physico-chemical characteristics:
BET surface area m 2 /g:
25-400
mean primary particle size nm:
3-50
pH value:
3-10
carbon content %:
0.1-10
DBP number %:
<200.
3. The composition according to claim 1 , wherein said silica has a tamped density of from 100 to 280 g/l.
4. The composition according to claim 1 , wherein said structure-modifying is carried out using a ball mill or by a continuously operating ball mill.
5. The composition according to claim 1 , wherein said silanized, structure-modified, pyrogenic silica is further milled by an air jet mill or a pinned disk mill.
6. The composition according to claim 1 , wherein said silanized, structure-modified, pyrogenic silica is further tempered in a drying cabinet or in a fixed or fluidized bed.
7. The composition according to claim 1 , wherein said silicone is a water-clear, self-deliquescing silicone polymer having a viscosity of from 15 to 30 kPa-s.
8. The composition according to claim 1 , wherein said composition further comprises at least one member selected from the group consisting of a crosslinker, a filler, a catalyst, a coloring pigment, an antiadhesive, a plasticizer, and an adhesion promoter.
9. The composition according to claim 1 , wherein said silicone is crosslinked.
10. The composition according to claim 9 , wherein said silicone is crosslinked by peroxidic crosslinking, addition crosslinking or condensation crosslinking.
11. The composition according to claim 9 , wherein said silicone is crosslinked by peroxidic crosslinking with a diaroyl peroxide or a dialkyl peroxide.
12. The composition according to claim 8 , wherein said filler is a non-reinforcing filler, a reinforcing filler, a filler having both a non-reinforcing and reinforcing properties, or a filler which increases the heat stability of said composition.
13. The composition according to claim 1 , wherein said composition further comprises one or more low molecular weight or monomeric silanol-containing compounds.
14. The composition according to claim 1 , wherein said composition further comprises one or more organic polymers.
15. A method of producing said composition according to claim 1 , said method comprising:
incorporating said one or more silanized, structure-modified, pyrogenic silica into said silicone.
16. An article comprising said composition according to claim 1 .