Propylene copolymers in elastomeric compositions
Disclosed is an ethylene-propylene copolymer having isotactic polypropylene crystallinity compounded with a halobutyl rubber in an amount effective to improve one or more of aged tensile strength retention, fatigue resistance, and dimensional stability. Also disclosed is an elastomer composition wherein the copolymer can have at least 60 wt % propylene-derived units and at least 6 wt % ethylene-derived units, and a tire inner tube or tire innerliner composition comprising from 1 to 10 phr copolymer. Also disclosed is a vulcanizate of the elastomer composition, and articles, tire innerliners, tires, and tire inner tubes comprising the vulcanizate. Further disclosed are processes for making molded articles, tire inner tubes and tires.
1. An elastomer composition comprising a blend of:
from 70 to 100 phr of a halobutyl rubber;
a cure system comprising 0.1 to 2 phr sulphur and 2 to 5 phr accelerators; and
from 1 to less than 10 phr of a saturated ethylene-propylene copolymer comprising at least 60 wt % propylene-derived units, and at least 6 wt % ethylene-derived units, based on the total weight of the copolymer, wherein the copolymer has isotactic polypropylene crystallinity, a melting point equal to or less than 110° C., a heat of fusion from 5 J/g to 50 J/g, an isotactic propylene triad tacticity of from 65 to 95%, and a Mooney viscosity ML (1+4) at 100° C. in the range of 40 to 60;
wherein the composition has a Mooney viscosity ML (1+4) at 100° C. less than 55.
2. The elastomer composition of claim 1 , wherein the copolymer comprises from 75 to 94 wt % of the propylene-derived units.
3. The elastomer composition of claim 1 , wherein the copolymer comprises from 6 to 30 wt % of the ethylene-derived units.
4. The elastomer composition of claim 1 , wherein the copolymer has a tacticity index of from 6 to 8.
5. The elastomer composition of claim 1 , wherein the blend comprises from 3 to 6 phr of the copolymer.
6. The elastomer composition of claim 1 , wherein the halobutyl rubber is selected from bromobutyl rubber, chlorobutyl rubber and mixtures thereof.
7. The elastomer composition of claim 1 , further comprising a filler selected from carbon black, modified carbon black, silica, precipitated silica, and blends thereof.
8. The elastomer composition of claim 1 , further comprising processing oil, resin, or a combination thereof.
9. The elastomer composition of claim 1 , wherein the cure system comprises metal oxide.
10. The elastomer composition of claim 1 , wherein the cure system comprises from 1 to 5 phr zinc oxide, from 0.4 to 0.8 phr sulfur and from 2 to 5 phr accelerators.
11. The vulcanizate obtained by curing the elastomer composition of claim 1 .
12. An article comprising the vulcanizate of claim 11 .
13. The article of claim 12 , wherein the halobutyl rubber comprises chlorobutyl and the article is a tire inner tube.
14. The article of claim 12 , wherein the halobutyl rubber comprises bromobutyl and the article is a tire innerliner.
15. A process for making a molded article, the process comprising:
melt mixing the elastomeric composition of claim 1 ;
shaping the mixture into a green article; and
curing the green article to vulcanize the halobutyl rubber.
16. The process of claim 15 , wherein the green article comprises an innerliner and further comprising assembling the innerliner in a tire build, wherein the innerliner is cured in the tire build.
17. The elastomer composition of claim 1 , wherein the blend comprises from 5 to 50 phr of at least one processing aid, the processing aid selected from polyolefin copolymer plastomers, polybutene process oils, paraffinic oils, naphthenic oils, and aromatic oils.