Lubricant composition

The present invention relates to a lubricant composition, and more particularly to a lubricant composition with a distinguished rust inhibition, particularly even after having been subjected to heat hysteresis.

Lubricants such as grease, etc. are widely used in lubrication of various machines including automobiles, construction machines, industrial machines, machine tools, etc., and also various parts as members of the machines. The machines have a possibility of water intrusion, depending on the locations where they are used, and thus requirements for the rust inhibition thereof are more and more strict. Furthermore, recent trends towards higher speed, much more size reduction, higher performance, lighter weight, etc. have made service temperatures of these peripheral equipment higher and higher, so the rust inhibition after having been subjected to such heat hysteresis has been also an important requirement.

To improve the rust inhibition use of some of additives have been studied. A grease composition for ball-and-roller bearings, which comprises a grease composition containing silicone oil- or fluorocarbon oil-based lubricating oil as a base oil, and a rust inhibitor comprising a magnesium compound and a volatile rust inhibitor as essential components has been so far proposed, where triazole-based compound such as benzotriazole, methylbenzotriazole, etc., or dicyclohexyl ammonium nitrite have been recommended as preferable volatile rust inhibitors.

Patent Literature 1: JP-A-9-59664

The proposed grease composition for ball-and-roller bearings is said to have a distinguished rust inhibitive action in addition to a high durability at elevated temperatures, but it contains a volatile rust inhibitor as one of rust inhibitor components, so a long term rust inhibition at elevated temperatures is not satisfactory, and as to the alkaline component such as magnesium oxide, etc., their influence on the environments must be taken into consideration.

A heat-resistant grease composition, which comprises fluoro-silicone oil, a fluororesin-based thickener, and an additive such as calcium alkylsulfonate, etc., and which can also contain other well known thickeners such as calcium stearate, etc. has been also proposed, where it is shown by evaporation tests or engine tests that the heat resistance is distinguished and also stable for a long time, but no mention is made of the rust inhibition, particularly even after having been subjected to heat resistance tests.

Patent Literature 2: JP-A-8-143883

The present applicant has previously proposed a lubricating grease composition, which comprises perfluoropolyether base oil, and a metal salt of aliphatic dicarboxylic acid as a thickener, where the applicant shows that the composition can further contain a powdery fluororesin to attain improvements of abrasion resistance of mating material, leakage resistance, detergency, etc.

Patent Literature 3: JP-A-2001-354986

It is recommended that in the proposed lubricating grease composition a mixing proportion of the metal salt of aliphatic dicarboxylic acid used as a thickener is about 1 to about 50% by weight, preferably 3 to 35% by weight, on the basis of the composition. In the disclosed Examples 1 to 14 relate to lubricating grease compositions consisting of two components, i.e. the thickener and perfluoropolyether oil, the thickener is used in such preferable mixing proportions.

As to the powdery fluororesin as an admixable component, it is recommended that the admixing proportion is not more than about 50% by weight, preferably about 3 to about 35% by weight, on the basis of the composition. In the disclosed Examples 15 to 17 relate to lubricating grease composition consisting of these three components, it is recommended that the admixing proportion of powdery fluororesin is 5% by weight, whereas that of metal salt of aliphatic dicarboxylic acid as a thickener is 15-25% by weight. As is known from such results, an increase in the admixing proportion of metal salt of aliphatic dicarboxylic acid as a thickener will inhibit any increase the admixing proportion of powdery fluororesin.

An object of the present invention is to provide a lubricant composition with a distinguished rust inhibition, particularly even after having been subjected to heat hysteresis, which comprises a fluoro-oil and an appropriate admixing proportion of powdery fluororesin as a thickener.

The object of the present invention can be attained by a lubricant composition, which comprises a fluoro-oil, a powdery fluororesin thickener, and a Ca salt or a Na salt of aromatic sulfonic acid or saturated aliphatic dicarboxylic acid as a rust-inhibitive additive, where the proportion of the thickener is 10-40% by weight, and that of the additive is 0.3-10% by weight, on the basis of the total weight of the composition, the balance being the fluoro-oil. In general, perfluoropolyether oils are used as a fluoro-oil.

The present lubricant composition has a distinguished rust inhibition, particularly even after having been subjected to heat hysteresis, and thus can be used widely in lubrication of machines and their parts to be used particularly outdoors, and specifically used in effective lubrication of bearings requiring substantial rust inhibition, heat resistance, low-temperature characteristics, load-carrying capacity, etc. in automobile auxiliary equipment such electric fan motors, fuel injector equipments, alternators, etc. of automobiles. Furthermore, the present lubricant composition can be used for lubrication of solid-solid contacts such as sliding parts of ball-and-roller bearings, slide bearings, sintered bearings, gears, valve, cocks, oil seals, rolls, electric contacts, etc.