This invention relates to lubricating oil compositions containing less than 1000 ppm phosphorus, comprising or resulting from the admixing of A) one or more base oil(s), B) one or more dispersant(s), wherein said one or more dispersants comprise at least 2.0 mass %, based on the total mass of the lubricating oil composition, of one or more unborated poly(alkenyl)succinimides, in which the polyalkenyl is derived from polyisobutylene and the imide is derived from polyamine (PIBSA-PAM); and C) one or more detergent(s), wherein said one or more detergent(s) together provide soap to the lubricating oil composition in an amount of 0.1 to 0.9 mass %, based on the total mass of the lubricating oil composition; wherein the ratio of mass %, based on the total mass of the lubricating oil composition, of the one or more unborated PIBSA-PAM(s) to soap of the lubricating oil composition is 6.65 or more.

Object

To provide a fluid dynamic pressure bearing oil and a fluid dynamic pressure bearing filled with the fluid dynamic pressure bearing oil, and to provide a spindle motor and a disk drive device including the spindle motor in which the fluid dynamic pressure bearing oil and the bearing are used, thereby suppressing adhesion of a volatile component to a magnetic disk or the like even when the fluid dynamic pressure bearing oil is volatilized, so that occurrence of HDD read/write errors can be suppressed.

Solution

A fluid dynamic pressure bearing oil contains at least one compound selected from the group consisting of a monoester compound represented by the following Formula (1) and a diester compound represented by the following Formula (2): R.sub.1C(O)OR.sub.2 (1) (where R.sub.1 is an alkyl group having 10 or more carbon atoms in total, R.sub.2 is an alkyl group having 9 or more carbon atoms in total, and R.sub.3-E.sub.1-R.sub.4-E.sub.2-R.sub.5 (2) (where R.sub.3 and R.sub.5 are each independently an alkyl group having 8 or more carbon atoms in total, R.sub.4 is an alkylene group having 4 or more carbon atoms in total, and E.sub.1 and E.sub.2 are each independently C(O)O or OC(O).

A lubricant composition comprising an oil-soluble polyalkylene glycol; an ester compound selected from the group of natural esters and synthetic esters, and combinations thereof; and an additive mixture comprising an antioxidant and an anticorrosive, wherein the anticorrosive is selected from neutral alkali metal and alkaline earth metal salts of sulfonic acids, carboxylic acids, naphthoic acids, naphthenic acids, benzoic acids and phosphoric acids, and derivatives and combinations thereof.