Rubber composition and method for producing same

Abstract

A rubber composition obtained by dry-mixing a natural rubber wet master batch yielded by mixing at least a natural rubber latex and a carbon-black-containing slurry solution with each other in a liquid phase and drying the resultant mixture, a dry rubber made mainly of a polybutadiene rubber, and an oil, wherein when the total amount of rubber components in the rubber composition is regarded as 100 parts by mass, the natural rubber is contained in an amount of 50 parts or more by mass, and the polybutadiene rubber is contained in an amount of 20 to 50 parts by mass, and the oil has a pour point of −10 C or lower, and an aniline point of 90 C or higher, and the blend amount of the oil is from 15 to 40 parts by mass for 100 parts by mass of the rubber components.

1 . A rubber composition obtained by dry-mixing a natural rubber wet master batch yielded by mixing at least a natural rubber latex and a carbon-black-containing slurry solution with each other in a liquid phase and drying the resultant mixture, a dry rubber made mainly of a polybutadiene rubber, and an oil,
 wherein when the total amount of rubber components in the rubber composition is regarded as 100 parts by mass, the natural rubber is contained in an amount of 50 parts or more by mass, and the polybutadiene rubber is contained in an amount of 20 to 50 parts by mass, and   the oil has a pour point of −10 C or lower, and an aniline point of 90 C or higher, and the blend amount of the oil is from 15 to 40 parts by mass for 100 parts by mass of the rubber components.   
     
     
         2 . The rubber composition according to  claim 1 , wherein the natural rubber wet master batch is a master batch produced through the following steps:
 step (I) in which when a carbon black is dispersed into a dispersing solvent to prepare the carbon-black-containing slurry solution, at least one portion of the natural rubber latex is added thereto, thereby producing a slurry solution containing the carbon black to which natural rubber latex particles adhere,   step (II) of mixing this slurry solution with the rest of the natural rubber latex to produce a natural rubber latex solution containing the just-above described natural-rubber-latex-particle-adhering carbon black, and   step (III) of solidifying and drying the natural rubber latex solution containing the natural-rubber-latex-particle-adhering carbon black.   
     
     
         3 . The rubber composition according to  claim 1 , wherein the natural rubber wet master batch contains the carbon black in an amount of 40 to 70 parts by mass for 100 parts by mass of the rubber components of the master batch. 
     
     
         4 . The rubber composition according to according to  claim 1 , wherein the carbon black contained in the natural rubber wet master batch has a nitrogen adsorption specific surface area (N2SA) of 100 m2/g or less. 
     
     
         5 . The rubber composition according to according to  claim 1 , wherein when the total amount of the rubber components in the rubber composition is regarded as 100 parts by mass, at least one of a plant granular material, a grain granular material, and a granular region of a grain core material is further contained in an amount of 0.5 to 10 parts by mass.