Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic -co- compound
Patent
1998-10-05
2000-10-03
Johnson, Jerry D.
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic -co- compound
508221, 508242, 508452, 508454, 508468, 508470, 508472, 525223, 525231, C10M14522, C10M14524, C10M14518, C08L 3314, C08L 2900
Patent
active
061273252
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a viscosity index improver to be added to lubricating oils such as engine oils, gear oils, transmission oils and hydraulic oils, a process for producing the same and a lubricating oil composition. More particularly, the present invention relates to a viscosity index improver which has excellent viscosity index improving property, thickening property, low-temperature fluidity and shear stability and which does not undergo separation in a lubricating oil, to a process for producing the same and to a lubricating oil composition prepared by incorporating the viscosity index improver into a lubricating oil.
BACKGROUND ART
It is practically preferred that lubricating oils employable as engine oils, hydraulic oils, etc. undergo least viscosity change over a wide temperature range from low temperatures to high temperatures. Viscosity index is employed as a measure of this property, and the greater the viscosity index is, the higher is the stability to temperature changes. It is known that viscosity index of an oil can be improved by adding to it a certain kind of polymer. As such polymers, for example, polymethacrylates (PMA) (Japanese Unexamined Patent Publication No. Hei 7-62372), olefin copolymers (OCP) (Japanese Patent Publication No. Sho 46-34508), hydrogenated styrene/diene copolymers (SDC) (Japanese Patent Publication No. Sho 48-39203) and polyisobutylenes (PIB) are employed. SDCs assuming polymeric forms of block copolymer (Japanese Unexamined Patent Publication No. Sho 49-47041) and star-shaped polymer (Japanese Unexamined Patent Publication No. Sho 52-96695) have been developed in addition to SDCs assuming a form of random copolymer.
Lubricating oils incorporated with these polymers exhibit characteristics of their own. More specifically, although PMAs have excellent viscosity index improving properties and also have pour point-lowering actions, they have poor thickening effects. In order to improve the thickening effects, the molecular weight of PMAs may be increased. However, PMAs having increased molecular weights come to have extremely low stability to shear forces to be caused by stirring etc. of lubricating oils. PIBs have high thickening effects but poor viscosity index improving properties. OCPs and SDCs have high thickening effects and have low viscosity at low temperatures, but their viscosity index improving properties are inferior to those of PMAs. Meanwhile, those PMAs which are copolymerized with polar monomers can impart to lubricating oils detergent dispersing performance of dispersing sludge in the lubricating oils easily compared with other improvers (Japanese Patent Publication No. Sho 51-20273 and Japanese Unexamined Patent Publication No. Hei 5-222389).
While multi-grade oils having excellent viscosity index improving performances are now generally used as lubricating oils, viscosity index improvers having higher performance are now in demand so as to comply with recent requirements including reduction of energy consumption. It can be contemplated to use a mixture of PMA and OCP or SDC as a composition which satisfies such requirements. However, these compounds have poor compatibility with each other, so that if a mere mixture of such compounds is added to a lubricating oil, the lubricating oil separates into two phases. Therefore, in order to avoid such separation, there are proposed graft copolymers consisting of two different kinds of polymers (Japanese Patent Publication Nos. Sho 59-40194, Sho 62-16997 and Hei 4-50328; Japanese Unexamined Patent Publication No. Hei 6-346078, etc.).
However, the processes for producing such graft copolymers each employ a conventional radical polymerization initiator to carry out graft copolymerization of a methacrylate monomer in the presence of an oil-soluble olefin copolymer. The graft copolymerization in this case takes place based on olefin copolymer chain radicals to be formed when the radical polymerization initiator extracts hydrogen atoms from the olefin copolymer. However, a homopolymer
Higuchi Yoshiki
Ohmura Hiroshi
Suyama Shuji
Tochigi Hidefumi
Johnson Jerry D.
NOF Corporation
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