Method for producing rubber composition
A method for producing a rubber composition, which comprises kneading 20 parts by mass or more of silica with 100 parts by mass of diene rubber, and adding from 3 to 20 parts by mass of syndiotactic-1,2-polybutadiene to the kneaded mixture obtained, followed by kneading is disclosed. This method brings out characteristics of syndiotactic-1,2-polybutadiene and can improve wet grip performance.
1. A method for producing a rubber composition, comprising kneading 20 parts by mass or more of silica with 100 parts by mass of diene rubber to form a kneaded mixture, and adding from 3 to 20 parts by mass of syndiotactic-1,2-polybutadiene to the kneaded mixture obtained, followed by kneading.
2. The method for producing a rubber composition according to claim 1 , wherein the syndiotactic-1,2-polybutadiene has a melting point of 110° C. or lower.
3. The method for producing a rubber composition according to claim 1 , wherein the diene rubber is such that the content of a vinyl bond unit in the entire polymer constituting the diene rubber is from 10 to 25 mass %.
4. The method for producing a rubber composition according to claim 1 , wherein the kneaded mixture is prepared by kneading the entire amount of silica to be contained in the rubber composition with the diene rubber.
5. The method for producing a rubber composition according to claim 1 , wherein the diene rubber comprises a modified diene rubber modified with a functional group having an interaction with a silanol group on a silica surface.
6. The method for producing a rubber composition according to claim 1 , wherein the syndiotactic-1,2-polybutadiene has a 1,2-vinyl bond content of 70 mol % or more and the degree of crystallinity of from 5 to 50%.
7. The method for producing a rubber composition according to claim 1 , wherein the kneaded mixture is prepared without adding syndiotactic-1,2-polybutadiene in the step of kneading the silica with the diene rubber.
8. The method for producing a rubber composition according to claim 1 , further comprising adding a vulcanizing agent and a vulcanization accelerator to a second kneaded mixture obtained by adding the syndiotactic-1,2-polybutadiene to the kneaded mixture.
9. The method for producing a rubber composition according to claim 1 , wherein a vulcanizing agent and a vulcanization accelerator are added to the kneaded mixture together with the syndiotactic-1,2-polybutadiene followed by kneading.
10. The method for producing a rubber composition according to claim 1 , wherein the syndiotactic-1,2-polybutadiene is phase-separated as a disperse phase from the diene rubber constituting a continuous phase in the rubber composition obtained.
11. A method for manufacturing a pneumatic tire, comprising:
kneading 20 parts by mass or more of silica with 100 parts by mass of diene rubber to form a kneaded mixture,
adding from 3 to 20 parts by mass of syndiotactic-1,2-polybutadiene to the kneaded mixture obtained, followed by kneading to obtain a rubber composition,
manufacturing an unvulcanized tire using the rubber composition, and vulcanization-molding the unvulcanized tire.