1.  Field of the Invention
The present invention relates to ethylene-alpha-olefin-polyene random copolymer rubber having excellent extrudability and physical properties and a method for the production thereof.  It also relates to vulcanizate obtained from the ethylene-alpha-olefin-polyene random copolymer rubber. 
2.  Description of the Prior Art
Ethylene-alpha-olefin-polyene terpolymer rubber such as ethylene-propylene-polyene terpolymer rubber ("copolymer rubber" hereinbelow) generally has excellent weathering resistance, ozone resistance, heat aging characteristic, and other characteristics and, therefore, is widely used as materials for automobiles, electric wires, buildings, and other various industrial products.  For these purposes, copolymer rubber having, for example, excellent extrudability, a fast cure rate, and excellent tensile strength of the vulcanizate is desired.  However, copolymer rubber having all these desirable characteristics is not commercially available.  For example, typical copolymer rubber, ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber has advantages of a fast cure rate and high tensile strength of the vulcanizate.  However, since ethylene-propylene-5-ethylidene-2-norbornene has poor extrudability, it is difficult to obtain molded articles having a good surface appearance of the extrudate.  Another typical copolymer rubber, ethylene-propylene-dicyclopentadiene copolymer, has excellent extrudability, but the cure rate thereof is slow and the tensile strength of the vulcanizate is not good. 
Various attempts have been made to improve various characteristics of copolymer rubber by using two or more polyene components, as disclosed in, for example, U.S. Pat.  Nos.  3,594,348 and 3,554,988, and Japanese Unexamined Patent Publication (Kokai) Nos.  49-62582 and 49-62583.  However, copolymer rubber having all the above-mentioned desirable characteristics have not been developed.  For example, although U.S. Pat.  No.  3,554,988 discloses the combined use of 5-ethylidene-2-norbornene and dicyclopentadiene, copolymer rubber having the desired balance of the extrudability, cure rate, and tensile stength of the vulcanizate cannot be obtained, i.e., one of the above-mentioned desirable characteristics is not satisfactory depending upon the proportion of 5-ethylidene-2-norbornene and dicyclopentadiene contained in the copolymer rubber.