Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-03-15
2004-06-22
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S313000, C508S110000, C585S012000
Reexamination Certificate
active
06753381
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polymer blend containing a high ethylene content ethylene-propylene copolymer and a lower ethylene content ethylene-propylene copolymer. The polymer blend of the present invention is useful for the preparation of viscosity index improvers with improved lower temperature properties relative to conventional viscosity index improvers.
BACKGROUND OF THE INVENTION
Ethylene-propylene polymers have long been known, and used for a variety of applications. For example, such copolymers, frequently referred to in the art as olefin copolymers, or OCPs, have long been recognized as viscosity index improvers in engine lubricating oils. In addition to that application, such polymers have also been widely used as impact modifiers for plastic compositions.
As used in lubricating oil compositions, ethylene-propylene polymers have the ability to provide a high thickening contribution to the lubricating oil composition with which the OCP is mixed to provide increases in the viscosity index of the overall composition. Thickening power is often defined as the difference in the kinematic viscosities of a dilute solution of an OCP mixed with oil and the diluent oil. For example, an oil solution containing from 1 to 2 percent of an OCP which provides a thickening power of 6 to 7 centistokes measured at 100° C. generally indicates acceptable viscosity index improvement performance.
For a given class of polymers, the higher the molecular weight, the higher is the viscosity of a lubricating oil containing the OCP. However, higher molecular weight polymers exhibit a greater tendency to break down under the shear and high temperature conditions normally found in engine operation, frequently resulting in the loss of viscosity. Accordingly, viscosity index improvement often depends on the balance between the thickening contribution of the OCP and its tendency to degrade, referred to as shear stability. Shear stability is typically defined as a percent viscosity breakdown on shear under a standard set of conditions. A value below 30 percent viscosity breakdown in an OCP is generally an indication that the viscosity index improver OCP is shear stable as that term is understood in the art.
Another important characteristic required for a viscosity index improver is viscosity at low temperatures, which relates to the ease of engine cranking during start-up in cold climates. An ideal viscosity index improver exhibits a negligible viscosity contribution at low temperatures while providing a large viscosity contribution at engine operating temperatures. At the same time, an ideal viscosity index improver exhibits a low tendency to degrade, and consequently a high shear stability under engine operating conditions.
Accordingly, in formulating lubricating oils to satisfy the varying conditions desired, it has generally been the practice to select those polymers which provide at the lowest cost the best overall balance of properties including viscosity at performance temperatures, shear stability and low temperature viscosity.
In the past, the art has employed as viscosity index improvers, solid amorphous ethylene-propylene polymers. When selecting ethylene-propylene polymers, a molecular weight was chosen so that the polymer would provide shear stable viscosity index improvement after the oil dispersion process.
The prior art has recognized the need to improve low temperature performance of such viscosity index improvers. For example, U.S. Pat. No. 4,507,515 describes blends of polymer compositions in which the major component has a low ethylene content and the minor component has a higher ethylene content, the minor component generally containing less than 10 percent by weight based on the weight of the blend. Similarly, U.S. Pat. No. 3,697,429 likewise describes the use of blends of high and low ethylene content polymers to achieve improvement in low temperature properties of a lubricating oil composition. One of the shortcomings of both prior art patents is that they do not describe any technique by which the major and minor components can be handled as solids.
U.S. Pat. No. 5,391,617 discloses a polymer blend with a high ethylene content ethylene-propylene polymer and a lower ethylene content ethylene-propylene polymer. That U.S. Patent does not teach or suggest the ratios of polymers of the present invention.
U.S. Pat. No. 3,697,429 discloses a mixture of two copolymers, but does not teach or suggest the ratios of polymers of the present invnetion.
Texaco Corporation developed a lubricating oil product, TXA 6070 (shear stable product) and TLA 6718 (non-shear stable product), which was a 40:60 blend of a high-ethylene:low ethylene copolymer, wherein the high-ethylene polymer of the blend had a 78.9 mol percent ethylene content.
In Canadian Patent No. 911792, there is disclosed a process for shearing high molecular weight polymers to produce a polymer having a desired molecular weight without altering the molecular weight distribution for use as a viscosity index improver. That Canadian patent does not, however, address the need for a solid shear stable polymer formed by shearing the polymer to reduce its molecular weight and its molecular weight distribution.
All patents, patent applications, and publications disclosed herein are fully incorporated by reference.
It is accordingly an object of the present invention to provide an ethylene-propylene polymer blend which overcomes the shortcomings of the prior art.
It is a more specific object of the invention to provide an ethylene-propylene polymer blend and a method for its preparation which can be used to improve the viscosity index of lubricating oil compositions as well as an impact modifier for plastic compositions in which the blend is subjected to simultaneous blending and shearing to reduce the molecular weight and sometimes the molecular weight distribution of each of the ethylene-propylene polymer components.
It is furthermore an object of the present invention to provide an ethylene-propylene polymer blend which can be prepared in conventional plastic processing equipment.
These and other objects and advantages of the present invention will appear more fully by way of the following description.
SUMMARY OF THE INVENTION
The present invention addresses the need to provide an ethylene-propylene polymer blend having the capability of functioning as a viscosity index improver. According to the concepts of the invention, the ethylene-propylene copolymer blend of the invention is the product of simple blending or a simultaneously blended and sheared blend containing a high ethylene content ethylene-propylene polymer (HEOCP) and a lower ethylene content ethylene-propylene polymer, whereby the physical properties of the sheared blend allows it to be recovered by means of conventional plastics processing equipment. The composition of the present invention in which the two components are blended or simultaneously blended and sheared can thus be used as a viscosity index improver exhibiting improved low temperature properties.
In an embodiment, the present invention resides in a blend and a process for producing that blend in which a high ethylene content ethylene-propylene polymer and a lower ethylene content ethylene-propylene polymer are subjected to blending or simultaneous blending and shearing to yield a product that can be recovered as a solid, using conventional plastic processing equipment.
In carrying out the simultaneous blending and shearing in accordance with one embodiment of the present invention, the two ethylene-propylene components undergo shearing to reduce molecular weights and sometimes molecular weight distribution (MWD), resulting in an intimate admixture exhibiting increased viscosity at ambient temperatures.
A feature of an embodiment of the present invention is to provide a polymer (also referred to herein as a copolymer) blend containing (a) an essentially amorphous low ethylene content ethylene-propylene polymer containing an ethylene to propylene mole ratio within the range of 35/65
Mishra Munmaya K.
Salazar Luis C.
Saxton Raymond G.
Spedale Gary J.
Ethyl Corporation
Nutter Nathan M.
Rainear Dennis H.
Robinson Leah O.
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