Making rubber blends of diene rubber & EPR or EPDM

DETAILED DESCRIPTION I claim: 1.
The process of producing a rubber blend by masticating a mixture of (A) monoolefin copolymer rubber which is a largely non-crystalline, rubbery copolymer of two or more alpha monoolefins and, optionally, a lesser quantity of a non-conjugated diene, which rubber has been modified to engraft functional groups thereto which provide selective vulcanization cites, (B) high-diene hydrocarbon rubber which is selected from homopolymers of diolefin monomers or copolymers containing a major portion of diolefin monomers and a vulcanizing agent capable of vulcanizing (A) but not (B), said masticating being performed at vulcanizing temperature for (A) until (A) is vulcanized but (B) is not, the ratio of (A) to (B) in the mixture not being so high as to produce an unprocessable blend.
2.
The process of claim 1 wherein the weight ratio of (A) to (B) is between 1:10 and 5:1 and wherein A is functionalized.
3.
The process of claim 2, wherein the weight ratio of (A) to (B) is between 1:4 and 3:2 and (A) is maleic functionalized.
4.
The process of claim 2, wherein the mixture is masticated in an internal mixer.
5.
The process of claim 2, and the additional step of admixing vulcanizing agent for (B).
6.
The process of claim 5 and the subsequent steps of shaping the blend and vulcanizing (B).




Description:
BACKGROUND OF THE INVENTION This invention relates to a process for making blends of monoolefin rubber and high-diene hydrocarbon rubber and to blends produced thereby.
Monoolefin rubber, typified by terpolymers of ethylene, propylene and a minor portion of diene monomer (EPDM rubber) has particularly good resistance to the degrading effects of oxygen or ozone, among other good properties.
In other respects, however, unvulcanized monoolefin rubber has poor tack properties and is consequently unsuited to the production of built-up molded articles such as tires wherein assembly of uncured components requires good tack.
A high-diene hydrocarbon rubber, such as natural and synthetic polyisoprene, polybutadiene and copolymers of butadiene with other monomers such as styrene, has better tack, but is comparatively more susceptible to oxygen and ozone degradation, probably because of the relatively high number of double-bonds in its molecular backbone