| abstract |
An additive composition is provided for a lubricating oil that is easy to produce, does not have adverse effects, such as causing rubber seals to swell, and is excellent in storage stability. The additive composition contains a metal salt of a phosphorus-containing compound represented by formula (1) in an amount of 10 to 90 percent by mass of the composition, contained in a hydrocarbon solvent selected from a mineral oil, a hydrocarbon synthetic oil and a mixture thereof, the hydrocarbon solvent having a 100° C. kinematic viscosity of 0.5 to 4.5 mm 2 /s, a % C A of 3 or less, and a sulfur content of 0.05 percent by mass or less: n n n n n n n n n n n n wherein X 1 and X 2 are each independently oxygen or sulfur, R 1 , R 2 , R 3 , and R 4 are each independently a straight-chain alkyl group having 3 to 12 carbon atoms, the average of the carbon number is 5 or greater, and M is a divalent metal atom. |