Grease composition for ball joint

Abstract

An object is to provide a grease composition for a ball joint capable of reducing the starting torque, reducing the operating torque, and improving the low temperature property as compared with the related art. The grease composition for a ball joint according to the present invention contains a silicone oil as a base oil and an additive, and contains an amino-modified silicone and a modified polyolefin as the additive. The silicone oil preferably includes at least one of dimethyl silicone oil and phenyl-modified silicone oil.

1 . A grease composition for a ball joint, comprising:
 a silicone oil as a base oil;   an additive; and   an amino-modified silicone and a modified polyolefin as the additive.   
     
     
         2 . The grease composition for a ball joint according to  claim 1 , comprising at least one of dimethyl silicone oil and phenyl-modified silicone oil as the silicone oil. 
     
     
         3 . The grease composition for a ball joint according to  claim 1 , wherein the amino-modified silicone is represented by a following general formula (1) or (2): 
       
         
           
           
               
               
           
         
         Organic group is —RNH 2 , R represents an alkyl group, and n represents number of repetitions. 
       
       
         
           
           
               
               
           
         
         Organic group is selected from any 
       
       
         
           
           
               
               
           
         
         R and R′ represent an alkyl group, and m and n represent number of repetitions. 
       
     
     
         4 . The grease composition for a ball joint according to  claim 1 , comprising at least one of oxidized polyethylene, oxidized polypropylene, acid-modified polyethylene, and acid-modified polypropylene, as the modified polyolefin. 
     
     
         5 . The grease composition for a ball joint according to  claim 1 , wherein a content of the amino-modified silicone is more than 0 parts by mass and 30 parts by mass or less. 
     
     
         6 . The grease composition for a ball joint according to  claim 1 , wherein a content of the modified polyolefin is more than 0.1 parts by mass and 20 parts by mass or less. 
     
     
         7 . The grease composition for a ball joint according to  claim 1 , wherein a content of the amino-modified silicone with respect to the modified polyolefin is in a range of a following formula (3):
   0.5≤(mass of amino-modified silicone/mass of modified polyolefin)≤30.0  (3).
   
     
     
         8 . The grease composition for a ball joint according to  claim 1 , wherein an acid value of the modified polyolefin is more than 0.1 (mgKOH/g) and 100.0 (mgKOH/g) or less. 
     
     
         9 . The grease composition for a ball joint according to  claim 1 , wherein a static friction coefficient of the grease composition is 0.050 or less. 
     
     
         10 . The grease composition for a ball joint according to  claim 1 , comprising at least one of hindered phenol, alkylated diphenylamine, or a hindered amine light stabilizer as an antioxidant.