Rubber composition

Abstract

A rubber composition comprising (i) an incompatible polymer blend of at least two diene rubbers selected from rubbers containing a conjugated diene and, optionally, an aromatic vinyl monomer and forming two polymer phases (A) and (B), and (ii) 0.1 to 20 parts by weight, based upon 100 parts by weight of the total polymer component including the block copolymer, of a block copolymer having at least two mutually incompatible blocks (a) and (b), wherein the block (a) is compatible with the polymer phase (A) and incompatible with the polymer phase (B) and the block (b) is compatible with the polymer phase (B) and incompatible with the polymer phase (A), and composed of a conjugated diene and, optionally, an aromatic vinyl monomer, and wherein the molecular weights of the polymers forming the polymer phases (A) and (B) satisfy the specified equations (I) and (II) mentioned in the specification.

1 . A method for producing a rubber composition having an improved abrasion resistance and tensile strength by controlling a molecular weight distribution of a rubber composition comprising (i) an incompatible polymer blend comprising at least two diene rubbers selected from the group consisting of rubbers containing at least one conjugated diene monomer and, optionally, at least one aromatic vinyl monomer and forming two incompatible polymer phases (A) and (B) and (ii) 0.1 to 20 parts by weight, based upon 100 parts by weight of the total polymer component including the block copolymer, of a block copolymer having at least two mutually incompatible blocks (a) and (b) in which the block (a) is compatible with the polymer phase (A) and incompatible with the polymer phase (B) and the block (b) is compatible with the polymer phase (B) and incompatible with the polymer phase (A), and comprising at least one conjugated diene monomer and, optionally, at least one aromatic vinyl monomer, such that the polymers forming the polymer phases (A) and (B) satisfy the following equations (I) and (II):  
         Mw   30 ( A )/ Mw ( a )≦1.2  (I)  Mw   30 ( B )/ Mw ( b )≦1.2  (II)  
       wherein 
 Mw 30 (A): a value of molecular weight corresponding to 30% of the cumulative area when converting the curve of the distribution of the molecular weight measured by GPC to the integrated molecular weight curve of the polymer forming the polymer phase (A),  
 Mw30(B): a value of molecular weight corresponding to 30% of the cumulative area when converting the curve of the distribution of the molecular weight measured by GPC to the integrated molecular weight curve of the polymer forming the polymer phase (B),  
 Mw(a): weight average molecular weight of block (a) of block copolymer, and  
 Mw(b): weight average molecular weight of block (b) of block copolymer.  
 
     
     
         2 . A method as claimed in  claim 1 , wherein (iii) 5 to 200 parts by weight, based upon 100 parts by weight of the block copolymer of polymer (α) compatible with the block (a) and the polymer phase (A) and/or polymer (β) compatible with the block (b) and polymer phase (B) are further blended and the weight average molecular weights of the polymer (α) and (β) satisfy the following equations (III) and (IV):  
         S   α   =Mw (α)/ Mw ( a )≦1.2  (III)  S   β   =Mw (β)/ Mw ( b )≦1.2  (IV)  
       wherein 
 Mw(α): weight average molecular weight of polymer (α),  
 Mw(β): weight average molecular weight of polymer (β)  
 Mw(a): weight average molecular weight of block (a) of block copolymer, and  
 Mw(b): weight average molecular weight of block (b) of block copolymer.  
 
     
     
         3 . A method as claimed in  claim 1 , wherein said diene rubbers are NR, IR, BR, SBR, SIR and SIBR.  
     
     
         4 . A method as claimed in  claim 3 , wherein a weight ratio of polymer phase (A)/polymer phase (B) is 90/10 to 10/90.  
     
     
         5 . A method as claimed in  claim 1 , wherein said block copolymer contains at least two blocks selected from the group consisting of BR block, SBR block, IR block, SIR block, BIR block and SBIR block.  
     
     
         6 . A method as claimed in  claim 5 , wherein a weight ratio of block (a)/block (b) is 80/20 to 20/80.  
     
     
         7 . A method as claimed in  claim 2 , wherein said polymers (α) and (β) are selected from IR, BR, SBR and SIBR.