Grease composition

Abstract

A grease composition containing a base oil (A), a urea-based thickener (B), an antioxidant (C), and a rust inhibitor (D), wherein in a particle size distribution curve obtained by measuring the particle size of particles containing the urea-based thickener (B) in the grease composition on a volume basis with light scattering, a peak indicating the maximum frequency satisfies the following Requirements (I) and (II): (I) a particle size indicating the maximum frequency of the peak is 1.0 μm or less; and (II) a half width of the peak is 1.0 μm or less.

1 : A grease composition comprising: a base oil (A), a urea-based thickener (B), an antioxidant (C), and a rust inhibitor (D),
 wherein in a particle size distribution curve obtained by measuring the particle size of particles containing the urea-based thickener (B) in the grease composition on a volume basis with light scattering, a peak indicating the maximum frequency satisfies the following Requirements (I) and (II):   (I) a particle size indicating the maximum frequency of the peak is 1.0 μm or less; and   (II) a half width of the peak is 1.0 μm or less.   
     
     
         2 : The grease composition according to  claim 1 , wherein the content of component (B) is from 1 to 40% by mass based on the whole amount of the grease composition. 
     
     
         3 : The grease composition according to  claim 1 , wherein the content of component (C) is from 0.01 to 15% by mass based on the whole amount of the grease composition. 
     
     
         4 : The grease composition according to  claim 1 , wherein the content of component (D) is from 0.01 to 5% by mass based on the whole amount of the grease composition. 
     
     
         5 : The grease composition according to  claim 1 , wherein the kinematic viscosity of the base oil (A) at 40° C. is from 10 to 130 mm 2 /s. 
     
     
         6 : The grease composition according to  claim 1 , wherein the urea-based thickener (B) is a compound represented by the following general formula (b1):
   R 1 —NHCONH—R 3 —NHCONH—R 2   (b1)
   wherein R 1  and R 2  each independently represent a monovalent hydrocarbon group having 6 to 24 carbon atoms, and R 1  and R 2  may be the same as or different from each other, and R 3  represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.   
     
     
         7 : The grease composition according to  claim 1 , wherein the antioxidant (C) contains one or more kinds selected from an amine antioxidant (C1) and a phenol-based antioxidant (C2). 
     
     
         8 : The grease composition according to  claim 1 , wherein the rust inhibitor (D) contains an alkenyl succinic acid polyhydric alcohol ester. 
     
     
         9 : The grease composition according to  claim 1 , which is used in a bearing portion of a hub unit, an electric power steering, a driving electric motor flywheel, a ball joint, a wheel bearing, a spline portion, a constant velocity joint, a clutch booster, a servo motor, a blade bearing, or a generator.