Lubricant composition for ball joints
The invention provides a grease composition for a ball joint which has a low friction coefficient under a load from normal temperatures to high temperatures, a small difference between static friction and dynamic friction, and little change in the friction coefficient even after repeated operation. TO this end, the invention provides a grease composition for a ball joint comprising: (i) a polyisoprene rubber and/or (ii) a polyisoprene rubber viscous material; a specific aliphatic amide and/or a specific aliphatic bisamide; and a specific urea compound.
1. A grease composition for a ball joint, said composition comprising:
(A) (i) a polyisoprene rubber and/or (ii) a polyisoprene rubber viscous material wherein the total amount of (A) is from 30 to 70 parts by mass per 100 parts by mass of the entire composition;
(B) an aliphatic amide represented by General Formula (1)
R 1 CONH 2 (1)
wherein R 1 represents a saturated or unsaturated alkyl group having from 15 to 21 carbon atoms; and/or an aliphatic bisamide represented by General Formula (2)
R 2 CONHR 3 NHCOR 2 (2)
wherein R 2 represents a saturated or unsaturated alkyl group having from 15 to 17 carbon atoms and R 3 represents a methylene group or an ethylene group wherein the total amount of (B) is from 10 to 50 parts by mass per 100 parts by mass of the entire composition; and
(C) at least one compound selected from among the compounds represented by the general formulae (3), (4) and (5)
R 4 NHCONHR 5 NHCONHR 4 (3)
R 6 NHCONHR 5 NHCONHR 6 (4)
R 4 NHCONHR 5 NHCONHR 6 (5)
wherein R 5 is a diphenylmethane group, R 4 is an alkyl group having 8 carbon atoms, and R 6 is an unsaturated hydrocarbon group having from 14 to 20 carbon atoms, wherein the total amount of urea compound in (C) is from 1 to 15 parts by mass per 100 parts by mass of the entire composition and
wherein the molar ratio (R 6 /R 4 ) of R 6 to R 4 is from 0.10 to 3.00.
2. The grease composition for a ball joint according to claim 1 , wherein component (i) in (A) is a polyisoprene rubber having a weight average molecular weight in a range from 20,000 to 50,000, and component (ii) is a polyisoprene rubber viscous material obtained by mixing a mineral oil and/or a synthetic oil and adjusting the viscosity at 25° C. to 3×10 3 to 3×10 5 centipoises.