Rubber composition for dynamic parts
View Patent ↗A rubber composition having (A) an elastomer component in which the primary elastomer constituent is an ethylene-propylene elastomer polymerized in the gas phase with a metallocene catalyst and having a molecular weight of at least about 250,000; (B) a silicon-modified olefinic elastomer in an amount of from about 5 to about 50 parts per hundred parts of the elastomer component; (C) ground mica in an amount of from about 2.5 to about 30 parts per hundred parts of the elastomer component; and (D) a peroxide curative. The composition may be used in a vibration isolator which may be used in a belt drive system.
1. A rubber composition comprising:
100 parts of elastomer comprising as its primary elastomer constituent an ethylene-propylene elastomer polymerized in the gas phase with a metallocene catalyst and having a molecular weight of at least about 250,000;
a silicon-modified olefinic elastomer in an amount of from about 5 to about 50 parts per hundred parts of the elastomer;
ground mica in an amount of from about 2.5 to about 30 parts per hundred parts of the elastomer; and
a peroxide curative, or the crosslinked reaction product of the foregoing.
2. The rubber composition of claim 1 wherein the olefinic elastomer is silicone-modified ethylene-propylene elastomer.
3. The rubber composition of claim 1 wherein the molecular weight is in the range from about 300,000 to about 350,000.
4. The rubber composition of claim 1 wherein the ground mica has a particle size such that the majority of particles pass through a number 325 mesh screen.
5. The rubber composition of claim 2 wherein the amount of the mica is from about 2.5 to about 10 parts per hundred parts of the elastomer and the amount of the silicone-modified ethylene-propylene elastomer is from about 5 to about 20 parts per hundred parts of the elastomer.
6. The rubber composition of claim 1 wherein the elastomer further comprises a minor amount of low-molecular-weight ethylene-propylene elastomer.
7. The rubber composition of claim 1 further comprising:
from about 20 to about 150 parts per hundred parts of the elastomer of reinforcing filler;
from about 20 to about 100 parts per hundred parts of the elastomer of process oil; and
from about 1 to about 20 parts per hundred parts of the elastomer of process aid.
8. The rubber composition of claim 1 having a cured tear strength of at least about 45 kN/m as determined by the method of ASTM D624 using die C at room temperature.
9. The rubber composition of claim 7 having a cured hardness of at least about 75 on the Shore A scale.
10. A dynamic article comprising a structural member and a crosslinked rubber member comprising the reaction product of:
100 parts of elastomer comprising as its primary elastomer constituent an ethylene-propylene elastomer polymerized in the gas phase with a metallocene catalyst and having a molecular weight of at least about 250,000;
a silicon-modified olefinic elastomer in an amount of from about 5 to about 50 parts per hundred parts of the elastomer;
ground mica in an amount of from about 2.5 to about 30 parts per hundred parts of the elastomer; and
a peroxide curative.
11. The dynamic article of claim 10 wherein the olefinic elastomer is silicone-modified ethylene-propylene elastomer.
12. The dynamic article of claim 10 wherein the ground mica has a particle size such that the majority of particles pass through a number 325 mesh screen.
13. The dynamic article of claim 10 wherein the elastomer further comprises a minor amount of low-molecular-weight ethylene-propylene elastomer.
14. The dynamic article of claim 11 wherein the molecular weight is in the range from about 300,000 to about 350,000.
15. The dynamic article of claim 14 wherein the amount of the mica is from about 2.5 to about 10 parts per hundred parts of the elastomer and the amount of the silicone-modified ethylene-propylene elastomer is from about 5 to about 20 parts per hundred parts of the elastomer.
16. The dynamic article of claim 15 further comprising:
from about 20 to about 150 parts per hundred parts of the elastomer of reinforcing filler;
from about 20 to about 100 parts per hundred parts of the elastomer of process oil; and
from about 1 to about 20 parts per hundred parts of the elastomer of process aid.
17. The dynamic article of claim 16 having a cured tear strength of at least about 45 kN/m as determined by the method of ASTM D624 using die C at room temperature.
18. The dynamic article of claim 17 having a cured hardness of at least about 75 on the Shore A scale.
19. The dynamic article of claim 10 in the form of a cush drive, vibration isolator, vibration damper, vibration absorber, or shock absorber.
20. The dynamic article of claim 10 wherein said rubber member has a surface portion in contact with, but not bonded to, a surface portion of said structural member.
21. A system comprising a dynamic article and a power transmission system in driving engagement with said dynamic article, wherein the dynamic article comprises a structural member and a crosslinked rubber member comprising the reaction product of:
100 parts of elastomer comprising as its primary elastomer constituent an ethylene-propylene elastomer polymerized in the gas phase with a metallocene catalyst and having a molecular weight of at least about 250,000;
a silicon-modified olefinic elastomer in an amount of from about 5 to about 50 parts per hundred parts of the elastomer;
ground mica in an amount of from about 2.5 to about 30 parts per hundred parts of the elastomer; and
a peroxide curative.
22. The system of claim 21 wherein the power transmission system comprises a toothed belt and the dynamic article is a vibration isolator in driving engagement with said belt.
23. The system of claim 21 in the form of a cush drive.
24. The composition of claim 1 wherein said 100 parts of elastomer consists of said primary elastomer.
25. The composition of claim 1 wherein said 100 parts of elastomer consists of from 70% to 99% said primary elastomer and from 1% to 30% low-molecular-weight ethylene-propylene elastomer.
26. The composition of claim 1 wherein said ethylene-propylene elastomer is polymerized in the gas phase in granular form and is coated with carbon black.
27. The composition of claim 26 wherein said ethylene-propylene elastomer exhibits a Mooney viscosity ML1+4 at 125° C. of at least about 130.
28. The rubber composition of claim 27 wherein the elastomer further comprises a minor amount of low-molecular-weight ethylene-propylene elastomer.
29. The composition of claim 28 wherein said molecular weight is in the range from about 300,000 to about 350,000 and said Mooney viscosity is about 130, and wherein said 100 parts of elastomer consists of from 70% to 99% said primary elastomer and from 1% to 30% low-molecular-weight ethylene-propylene elastomer having a Mooney viscosity in the range of from about 15 to about 30.