FLAME-RETARDANT POLYESTER-BASED LUBRICATING OIL COMPOSITION

PROBLEM TO BE SOLVED: To obtain a composition having a kinematic viscosity in a specified range and improved flame retardancy, by making the composition contain a synthetic polymeric compound in a base oil comprising an unsaturated fatty acid polyol ester in a specified ratio. SOLUTION: The base oil contains an unsaturated fatty acid polyol ester, 0.1-15 mass % at least one synthetic polymeric compound having a weight- average molecular weight of 20,000-1,500,000 and selected from among polymethyacrylates and polyisobutylenes, etc., and optionally 0.8-5 mass % antioxidant such as a phenol/α-naphthylamine dehydration condensate, 0.01-30 mass % rust preventive, 0.01-5 mass % corrosion preventive, etc., to obtain the lubricating oil composition having a kinematic viscosity (at 40 deg.C) of 10-150 mm /s. The unsaturated fatty acid polyol ester has a kinematic viscosity (at 40 deg.C) of 20-100 mm /g and is exemplified by an ester obtained by reacting an 8-32C unsaturated monocarboxylic acid with a 2-10C polyol or a complex ester obtained by reacting an 8-54C unsaturated monocarboxylic acid with a polyol.