Lubricant composition

A lubricating oil composition, comprising, based on a total composition weight:

• (A) a base oil (A) comprising a polyalkylene glycol (A1), in an amount of greater than 20 wt. %, and a polyol ester (A2) comprising a hindered ester of a hindered polyol comprising a quaternary carbon atom with 1 to 4 methylol groups bonded thereto, with an aliphatic monocarboxylic acid;
• (B) 0.02 to 0.5 wt. % of a phosphorus-based rust inhibitor (B);
• and
• (C) 0.05 to 2.4 wt. % of an antioxidant (C) comprising an amine-based antioxidant (C1),
• wherein an [(A1)/(A2)] mass content ratio of the base oil is in a range of from more than 20/80 to 49/51,
• wherein the phosphorus-based rust inhibitor (B) comprises the amine salt of acidic phosphate ester (B2), which comprises an amine salt (B21) of a compound of formula (b2-1) and/or an amine salt (B22) of a compound of formula (b2-2):
• Ra and Rb each independently being an alkyl group having 3 to 12 carbon atoms,
• wherein the hindered polyol has a formula (a-2):
• RA11 and RA12 being independently a monovalent hydrocarbon group having 1 to 6 carbon atoms or a methylol group, and n being an integer in a range of from 0 to 4, and
• wherein the polyalkylene glycol (A1) is of formula (a-1), and is sealed on at least one end with a substituent:
• wherein
• RA1 is a hydrogen atom, a monovalent hydrocarbon group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, a divalent to hexavalent hydrocarbon group having 1 to 10 carbon atoms, or a heterocyclic group having 3 to 10 ring atoms,
• RA2 is an alkylene group having 2 to 4 carbon atoms,
• RA3 is a hydrogen atom, a monovalent hydrocarbon group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, or a heterocyclic group having 3 to 10 ring atoms, and
• b is an integer in a range of from 1 to 6, a is a number of 1 or more.