Rubber composition for tire, and pneumatic tire

Abstract

The present invention provides a rubber composition for a tire, which has an increased rate of reaction between a silane coupling agent and silica so that its performances including fuel economy and abrasion resistance can be enhanced; and a pneumatic tire formed from the rubber composition. The present invention relates to a rubber composition for a tire, containing: diene rubber; silica; a silane coupling agent; and a carbonate salt and/or a hydrogen carbonate salt, wherein the rubber composition has a total content of the carbonate salt and the hydrogen carbonate salt of 0.3 to 25 parts by mass relative to 100 parts by mass of the silica.

1 . A rubber composition for a tire, comprising: diene rubber; silica; a silane coupling agent; and at least one of a carbonate salt and a hydrogen carbonate salt,
 wherein the rubber composition has a total content of the carbonate salt and the hydrogen carbonate salt of 0.3 to 25 parts by mass relative to 100 parts by mass of the silica.   
     
     
         2 . The rubber composition for a tire according to  claim 1 , wherein the carbonate salt is at least one selected from the group consisting of sodium carbonate, potassium carbonate, ammonium carbonate, lithium carbonate, calcium carbonate and magnesium carbonate, and
 the hydrogen carbonate salt is at least one selected from the group consisting of sodium hydrogen carbonate, potassium hydrogen carbonate and ammonium hydrogen carbonate.   
     
     
         3 . The rubber composition for a tire according to  claim 1 , wherein the carbonate salt is at least one selected from the group consisting of sodium carbonate, ammonium carbonate, lithium carbonate, calcium carbonate and magnesium carbonate, and
 the hydrogen carbonate salt is ammonium hydrogen carbonate.   
     
     
         4 . The rubber composition for a tire according to  claim 1  or  2 , wherein the potassium carbonate has an average particle size of 40 μm or smaller. 
     
     
         5 . The rubber composition for a tire according to  claim 1 , wherein the silane coupling agent is at least one selected from the group consisting of a sulfide-type silane coupling agent, a silane coupling agent represented by formula (1): 
       
         
           
           
               
               
           
         
         wherein R 1  is a group represented by —O—(R 5 —O) m —R 6  in which m pieces of R 5  are the same or different and each denote a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms, R 6  denotes a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms, and m is an integer between 1 and 30; R 2  and R 3  are the same or different and each denote a group as defined for R 1 , a branched or unbranched alkyl group having 1 to 12 carbon atoms, or a group represented by —O—R 7  in which R 7  denotes a hydrogen atom, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms; and R 4  denotes a branched or unbranched alkylene group having 1 to 30 carbon atoms, and 
         a silane coupling agent comprising linking units A and B respectively represented by formulae (2) and (3): 
       
       
         
           
           
               
               
           
         
       
       wherein x is an integer of 0 or higher; y is an integer of 1 or higher; R 8  denotes a hydrogen atom, a halogen atom, a branched or unbranched alkyl or alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenyl or alkenylene group having 2 to 30 carbon atoms, a branched or unbranched alkynyl or alkynylene group having 2 to 30 carbon atoms, or a group in which a terminal of the alkyl or alkenyl group is substituted with a hydroxyl or carboxyl group; R 9  denotes a hydrogen atom, a branched or unbranched alkylene or alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenylene or alkenyl group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene or alkynyl group having 2 to 30 carbon atoms; and R 8  and R 9  may together form a ring structure. 
     
     
         6 . The rubber composition for a tire according to  claim 1 , wherein 5 to 150 parts by mass of the silica is contained relative to 100 parts by mass of the diene rubber, and
 2 to 20 parts by mass of the silane coupling agent is contained relative to 100 parts by mass of the silica.   
     
     
         7 . The rubber composition for a tire according to  claim 1 , which is obtained by a production method comprising:
 a step (A) of kneading diene rubber, silica, a silane coupling agent, and at least one of a carbonate salt and a hydrogen carbonate salt, and discharging the resulting kneaded mixture A;   a step (B) of kneading the kneaded mixture A discharged in the step (A), stearic acid and zinc oxide, and discharging the resulting kneaded mixture B; and   a step (C) of kneading the kneaded mixture B discharged in the step (B), a vulcanizing agent and a vulcanization accelerator.   
     
     
         8 . The rubber composition for a tire according to  claim 1 , which is obtained by a production method comprising:
 a step (a) of kneading diene rubber, silica, a silane coupling agent, and at least one of a carbonate salt and a hydrogen carbonate salt, adding thereto stearic acid and zinc oxide, further kneading them, and discharging the resulting kneaded mixture a; and   a step (b) of kneading the kneaded mixture a discharged in the step (a), a vulcanizing agent and a vulcanization accelerator.   
     
     
         9 . A pneumatic tire formed from the rubber composition according to  claim 1 .