Patent ID: 7696139

Claim:
A grease composition for a pivot assembly bearing, which comprises: a thickener of 10 to 20% by mass; and a base oil of 90 to 79% by mass with respect to the total mass of the thickener and the base oil, wherein the thickener comprising two or more ureas selected from the group consisting of: urea A comprising diurea compounds having at least one of an aliphatic substituent and an alicyclic substituent; urea B comprising diurea compounds having at least one of an alicyclic substituent and an aromatic substituent; and urea C comprising diurea compounds having at least one of an aromatic substituent and an aliphatic substituent, wherein the base oil is a poly α-olefin mixture having a kinematic viscosity at 40° C. of 40 to 70 mm 2 /s, wherein the poly α-olefin mixture is prepared by mixing poly α-olefin having a kinematic viscosity at 40° C. of 350 to 450 mm 2 /s with poly α-olefin having a kinematic viscosity at 40° C. of 25 to 40 mm 2 /s in a mass ratio of 15:85 to 30:70; and wherein urea A comprises a mixture of diurea compounds represented by formulae (1), (2) and (3): wherein R 1 represents an aliphatic hydrocarbon group having 8 to 22 carbon atoms, and R 2 represents an alicyclic hydrocarbon group having 6 to 12 carbon atoms; urea B comprises a mixture of diurea compounds represented by formulae (2), (4) and (5): wherein R 2 represents an alicyclic hydrocarbon group having 6 to 12 carbon atoms, and R 3 represents an aromatic hydrocarbon group having 6 to 20 carbon atoms; and urea C comprises a mixture of diurea compounds represented by formulae (1), (4) and (6): wherein R 1 represents an aliphatic hydrocarbon group having 8 to 22 carbon atoms, and R 3 represents an aromatic hydrocarbon group having 6 to 20 carbon atoms.