Lubricating oil compositions

Abstract

Lubricating oil compositions and viscosity index (VI) improver concentrates containing combinations of first polymers that are amorphous ethylene α-olefin copolymers; and second polymers that are star polymers, the arms of which are derived from diene, and optionally vinyl aromatic hydrocarbon monomer, wherein the star polymers have a Shear Stability Index (SSI) of from about 1% to about 35% (30 cycle).

Description

FIELD OF THE INVENTION[0001]The invention is directed to lubricating oil compositions formulated with blended viscosity index improver compositions. More specifically, the present invention is directed to lubricating oil compositions comprising a major amount of oil of lubricating viscosity and a viscosity index improver composition containing at least two polymeric viscosity index improvers, which lubricating oil compositions provide simultaneously improved viscometric properties, particularly at low temperatures, and shear stability performance.BACKGROUND OF THE INVENTION[0002]Lubricating oil compositions for use in crankcase engine oils comprise a major amount of base oil and minor amounts of additives that improve the performance and increase the useful life of the lubricant. Crankcase lubricating oil compositions conventionally contain polymeric components that are used to improve the viscometric performance of the engine oil, i.e., to provide multigrade oils such as SAE 5W-30,...

AI Technical Summary

Benefits of technology

[0014]In accordance with a fourth aspect of the invention, there is provided a lubricating oil composition, as in the first, second or thirds aspects, wherein the base oil of the lubricating oil composition has a saturates content of at least about 80%, and said lubricating oil composition contains less than about 0.4 mass % of sulfur, less than about 0.12 mass % phosphorus and less than about 1.2 mass % of sulfated ash.

[0015]In accordance with a fifth aspect of the invention, there is provided a VI improver concentrate comprising diluent oil, a first polymer that is an amorphous ethylene α-olefin copolymer having a crystallinity of less than 1.0%; and a second polymer comprising a star polymer, the arms of which are derived from diene, and optionally vinyl aromatic hydrocarbon monomer, wherein the star polymer has a Shear Stability Index (SSI) of from about 1% to about 35% (30 cycle), wherein the total amount of polymer in the concentrate (including at least the first polymer and the second polymer) is at least 5 mass %, based on the total mass of the concentrate.

Problems solved by technology

Some polymers are excellent in some of the above properties, but are deficient in one or more of the others.

However, amorphous OCP provide relatively poor thickening efficiency (TE) in oil for a given shear stability index (30-cycle SSI).

Semi-crystalline OCP show improved TE in oil for a given SSI, however, the crystalline nature of such copolymers causes both intermolecular and intramolecular interactions, which leads to network formations.

Formation of such networks causes difficulties in handling of copolymer concentrates, even at room temperature, and interactions between such copolymers and base stocks can lead to poor low temperature viscometric properties, such as high MRV viscosities and scanning Brookfield gelation index values.

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