Disclosed is a lubricating oil composition. The lubricating oil composition contains a lubricating base oil including mineral base oil, 4 to 15 mass % of an ester compound of a monovalent or polyvalent aliphatic carboxylic acid and a monovalent or polyvalent aliphatic alcohol, 400 to 1200 mass ppm of zinc dialkyl dithiophosphate in terms of a phosphorus element, 500 to 3000 mass ppm of a calcium-based detergent in terms of a calcium element, and 50 to 1000 mass ppm of a boron-modified succinimide-based dispersant in terms of a boron element, on the basis of the total amount of the lubricating oil composition.

The present disclosure provides a lubricating oil composition which is excellent in metal fatigue life, wear resistance and electrical insulating properties, even when the composition has a reduced viscosity. The lubricating oil composition according to the present disclosure comprises: (A) a lubricating base oil; (B) from 0.6 to 4.0% by weight, based on the total weight of the lubricating oil composition, of a polydiene having a number average molecular weight of from 500 to 3,000 and containing a functional group on at least one end thereof; and (C) at least one selected from a phosphorus-based anti-wear agent and a phosphorus-based extreme pressure agent, the at least one agent being contained in such an amount that the content of phosphorus is from 50 to 500 ppm by weight based on the total weight of the lubricating oil composition.

Provided is a lubricant composition for plastic working of a ferrous material, the lubricant composition being excellent in lubricity and releasability and not staining the work environment black. A lubricant composition for plastic working of a ferrous material is used, the lubricant composition containing (a) an alkali metal salt of an organic acid, (b) water-based resin particles, (c) a water-soluble polymer, and (d) water, the (b) water-based resin particles including particles having a particle diameter of not more than 0.1 μm in an amount of more than 5% by weight relative to a total amount of the (b) water-based resin particles.

A lubricating oil composition for an internal combustion engine includes: (A) a lubricating base oil including at least one mineral oil-based base oil and having a kinematic viscosity at 100° C. of from 2.0 mm.sup.2/s or more and 4.3 mm.sup.2/s or less, and (B) a calcium borate-containing metallic detergent in an mount of 500 mass ppm or more and less than 1500 mass ppm in terms of calcium, based on a total amount of the composition. The composition has an evaporation loss by NOACK method (250° C., 1 h) of from 10 mass % or more and 40 mass % or less, and the composition has a viscosity index of from 140 or more and 350 or less. The lubricating oil composition is provided, wherein even in the case of using a highly evaporative base oil to make the viscosity low, the friction characteristic of the lubricating oil composition can be kept low.

A novel process can be used for the preparation of polyalkyl (meth)acrylate polymers with improved compositional distribution, which leads to better producibility, solubility, and improved performance of the polymers in lubricant compositions, especially in engine oil formulations.

The disclosed technology relates to an automotive or industrial gear oil for automotive or industrial gears, as well as axles and bearings, the automotive or industrial gear oil containing an oil of lubricating viscosity, an optional phosphate and/or thiophosphate compound, a particular sulfurized olefin, and a metal thiophosphate compound, such as zinc dialkyldithiophosphate, as well as a method of improving automotive or industrial gear operating efficiency and temperature by lubricating such automotive or industrial gears with the automotive or industrial gear oil.

A water-based lubricating grease composition includes at least 40 wt % water; a salt-based thickener; a polymer-based thickener; and optionally, an inorganic solid-based thickener. A process for preparing the water-based lubricating grease composition may include blending a suitable amount of water with a salt-based thickener to provide a thickened water-based grease, wherein the salt-based thickener is obtained from contacting a base with a fat; and adding a polymer-based thickener to the thickened water-based grease.

A lubricant composition of an oil of lubricating viscosity and a phosphite ester reaction product of a monomeric phosphorous acid or an ester thereof with a first alkylene diol having two hydroxy groups in a 1,4 or 1,5 or 1,6 relationship and a second, alkyl-substituted, diol being a substituted 1,3-propylene diol, exhibits good wear and frictional performance.

A lubricating oil composition prepared by blending a base oil (A) containing a compound (A1) that is an ester or ether and has two or more aromatic rings, with a polyalkylene glycol (B) is provided. The lubricating oil composition has a high density (i.e., a high bulk modulus), a high viscosity index, and excellent shear stability.

An aspect of the present invention provides a refrigerating machine oil containing: a lubricating base oil; and a polymer containing an unsaturated carboxylic acid ester as a monomer unit, wherein the unsaturated carboxylic acid ester contains an ester of an unsaturated carboxylic acid and an alcohol having a hydrocarbon group represented by the following formula (1):

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wherein x represents an integer of 5 to 18, and y represents an integer of 3 to 18.