Silica reinforced rubber
The subject invention is based upon the unexpected discovery that the use of a very specific combination of hydrophobating silanes and sulfur crosslinkable silanes can be used to attain outstanding performance characteristics in silica reinforced rubber formulations. More specifically, these rubber formulations provide a highly desirable combination of both improved abrasion characteristics and reduced hysteresis without compromising other important rubber characteristics. The present invention more specifically discloses a sulfur cured rubber formulation which is the reaction product of (1) at least one rubbery polymer, (2) sulfur, (3) silica, (4) 2 phf to 12 phf of a hydrophobating silane, and (5) 0.5 phf to 3 phf of a crosslinkable silane. The weight ratio of the hydrophobating silane to the crosslinkable silane will typically be within the range of about 2:1 to about 20:1.
1. A sulfur curable rubber formulation which is comprised of (1) at least one rubbery polymer, (2) sulfur, (3) 50 to 150 phr of pre-reacted silica, and (4) 2 phr to 10 phr of carbon black, wherein the pre-reacted silica is comprised of a silica which is pre-reacted with (a) a hydrophobating silane, and (b) a crosslinkable silane, wherein the crosslinkable silane is of the structural formula: HS—(CH 2 ) n —Si—[(O—(CH 2 ) m CH 3 )] 3 , wherein n represents an integer from 1 to 6, wherein m represents an integer from 0 to 6, wherein the weight ratio of the hydrophobating silane to the crosslinkable silane is within the range of about 2:1 to about 20:1, wherein the total weight of the hydrophobating silane and the crosslinkable silane is within the range of 2.5 phf to 15 phf, wherein the level of hydrophobating silica is within the range of 2 phf to 12 phf, wherein the level of the crosslinkable silane is within the range of 0.5 phf to 3 phf, and wherein the sulfur curable rubber formulation is void of titanium compounds.
2. The sulfur curable rubber formulation of claim 1 wherein the carbon black is present at a level which is within the range of 2 phr to 5 phr.
3. The sulfur curable rubber formulation of claim 1 wherein the weight ratio of hydrophobating silane to crosslinkable silane is within the range of 6:1 to 12:1.
4. The sulfur curable rubber formulation of claim 1 wherein total level of the hydrophobating silane and the crosslinkable silane is within the range of 8 phf to 10 phf.
5. The sulfur curable rubber formulation of claim 1 wherein the level of crosslinkable silane is within the range of 0.5 phf to 2.5 phf.
6. The sulfur curable rubber formulation of claim 1 wherein n represents the integer 3 and wherein m represents the integer 1.
7. The sulfur curable rubber formulation of claim 1 wherein the hydrophobating silica is of the structural formula:
CH 3 —(CH 2 ) n —Si—[(O—(CH 2 ) m CH 3 )] 3
wherein n represents an integer from 0 to 18 and wherein m represents an integer from 0 to 6.
8. The sulfur curable rubber formulation of claim 7 wherein n represents the integer 7 and wherein m represents the integer 1.
9. A sulfur cured rubber formulation which is the reaction product of sulfur and the sulfur curable rubber formulation of claim 1 .
10. A tire which is comprised of a generally toroidal-shaped carcass with an outer circumferential tread which is adapted to be ground contacting, two spaced beads, at least one ply extending from bead to bead and sidewalls extending radially from and connecting said tread to said beads, wherein the circumferential tread is comprised of the sulfur cured rubber formulation of claim 9 .
11. A pre-reacted silica which is comprised of a silica which is pre-reacted with (1) a hydrophobating silane, and (2) a crosslinkable silane, wherein the crosslinkable silane is of the structural formula: HS—(CH 2 ) n —Si—[(O—(CH 2 ) m CH 3 )] 3 , wherein n represents an integer from 1 to 6, wherein m represents an integer from 0 to 6, wherein the hydrophobating silica is of the structural formula: CH 3 —(CH 2 ) x —Si—[(O—(CH 2 ) y CH 3 )] 3 , wherein x represents an integer from 0 to 18 and wherein y represents an integer from 0 to 6, wherein the weight ratio of the hydrophobating silane to the crosslinkable silane is within the range of about 2:1 to about 20:1, wherein the total weight of the hydrophobating silane and the crosslinkable silane is within the range of 2.5 phf to 15 phf, wherein the maximum level of the crosslinkable silane is 3 phf, and wherein the pre-reacted silica is void of titanium compounds.
12. The pre-reacted silica of claim 11 wherein the weight ratio of hydrophobating silane to the crosslinkable silane is within the range of 6:1 to 12:1.
13. A rubber formulation which is comprised of (1) at least one rubbery polymer, and (2) the pre-reacted silica as specified in claim 11 .
14. The pre-reacted silica of claim 12 wherein x represents the integer 7 and wherein y represents the integer 1.
15. A sulfur curable rubber formulation which is comprised of (1) at least one rubbery polymer, (2) sulfur, (3) 50 to 150 phr of pre-reacted silica, and (4) 2 phr to 10 phr of carbon black, wherein the pre-reacted silica consists of a silica which is pre-reacted with (a) a hydrophobating silane, and (b) a crosslinkable silane, wherein the crosslinkable silane is of the structural formula: HS—(CH 2 ) n —Si—[(O—(CH 2 ) m CH 3 )] 3 , wherein n represents an integer from 1 to 6, wherein m represents an integer from 0 to 6, wherein the weight ratio of the hydrophobating silane to the crosslinkable silane is within the range of about 2:1 to about 20:1, wherein the total weight of the hydrophobating silane and the crosslinkable silane is within the range of 2.5 phf to 15 phf, wherein the level of hydrophobating silica is within the range of 2 phf to 12 phf, and wherein the level of the crosslinkable silane is within the range of 0.5 phf to 3 phf.
16. The sulfur curable rubber formulation of claim 15 wherein the carbon black is present at a level which is within the range of 2 phr to 5 phr and wherein the weight ratio of hydrophobating silane to crosslinkable silane is within the range of 6:1 to 12:1.
17. The sulfur curable rubber formulation of claim 15 wherein total level of the hydrophobating silane and the crosslinkable silane is within the range of 8 phf to 10 phf and wherein the level of crosslinkable silane is within the range of 0.5 phf to 2.5 phf.
18. The sulfur curable rubber formulation of claim 15 wherein n represents the integer 3 and wherein m represents the integer 1.
19. A sulfur cured rubber formulation which is the reaction product of sulfur and the sulfur curable rubber formulation of claim 15 .
20. A tire which is comprised of a generally toroidal-shaped carcass with an outer circumferential tread which is adapted to be ground contacting, two spaced beads, at least one ply extending from bead to bead and sidewalls extending radially from and connecting said tread to said beads, wherein the circumferential tread is comprised of the sulfur cured rubber formulation of claim 19 .