Olefinic rubber composition

A process for producing a thermoplastic olefinic rubber composition comprising (A) 1 to 99 parts by weight of an ethylene-α-olefin copolymer having ethylene units and C3-C20 α-olefin units, and (B) 1 to 99 parts by weight of a thermoplastic olefinic resin, the total amount of (A) and (B) being 100 parts by weight, said (A) having a degree of crosslinking of 50% or more and a degree of swelling of 5 to 40, wherein said thermoplastic olefinic resin (B) is selected from the group consisting of polyethylenes, isotactic homopolypropylenes and isotactic (block and random) copolymers of propylene and other α-olefin selected from the group consisting of ethylene, butane-1, pentene-1 and hexane-1;

• the process comprising the steps of
• using a radical initiator (D) having a one-minute half-life temperature T1 of 100 to 250° C. in an amount of 0.02 to 3 parts by weight based on 100 parts by weight of total amount of (A) and (B),
• setting an extruder zone with a length of 0.1 L to 0.5 L at a melting temperature T2 and an extruder zone with a length of 0.5 L to 1.0 L at a melting temperature T3, wherein L is extruder length in die direction with material supply section as datum point, so as to satisfy the following requirements;
• T1−100<T2<T1+40
• T2+1<T3<T2+200
• and
• controlling degree of mixing M defined as
• M=(Π2/2) (L/D)D3 (N/Q)
• in a range of 10×106≦M≦1,000×106
• wherein L is extruder length (mm), D is inner diameter (mm) of extruder barrel, Q is discharge rate (kg/h) and N is screw rotation speed (rpm).