Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic -co- compound
Reexamination Certificate
2001-07-09
2002-10-01
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic -co- compound
C508S470000
Reexamination Certificate
active
06458749
ABSTRACT:
BACKGROUND
This invention involves a method for improving overall low temperature fluidity properties of a broad range of lubricating oil compositions based on the addition of mixtures of selected high molecular weight and low molecular weight polymer additives, in particular alkyl (meth)acrylate polymer additives.
The behavior of petroleum oil formulations under cold flow conditions is greatly influenced by the presence of paraffins (waxy materials) that crystallize out of the oil upon cooling; these paraffins significantly reduce the fluidity of the oils at low temperature conditions. Polymeric flow improvers, known as pour point depressants, have been developed to effectively reduce the “pour point” or solidifying point of oils under specified conditions (that is, the lowest temperature at which the formulated oil remains fluid). Pour point depressants are effective at very low concentrations, for example, between 0.05 and 1 percent by weight in the oil. It is believed that the pour point depressant material incorporates itself into the growing paraffin crystal structure, effectively hindering further growth of the crystals and the formation of extended crystal agglomerates, thus allowing the oil to remain fluid at lower temperatures than otherwise would be possible.
One limitation of the use of pour point depressant polymers is that petroleum base oils from different sources contain varying types of waxy or paraffin materials and not all polymeric pour point depressants are equally effective in reducing the pour point of different petroleum oils, that is, a polymeric pour point depressant may be effective for one type of oil and ineffective for another. As existing oil fields become depleted, lower grade oil reservoirs are being used resulting in the supply of base oils (or base stocks) having an overall lower quality than previously encountered; these base oils are more difficult to handle, thus making it more difficult for conventional pour point depressant polymers to satisfy the multiple low temperature requirements of lubricating oil compositions derived from a wide variety of base oils.
One approach to solving this problem is disclosed in “Depression Effect of Mixed Pour Point Depressants for Crude Oil” by B. Zhao,
J. Shenyang, Inst. Chem. Tech.,
8(3), 228-230 (1994), where improved pour point performance on two different crude oil samples was obtained by using a physical mixture of two different conventional pour point depressants when compared to using the pour point depressants individually in the oils. Similarly, U.S. Pat. No. 5,281,329 and European Patent Application EP 140,274 disclose the use of physical mixtures of different polymeric additives to achieve improved pour point properties when compared to using each polymer additive alone in lubricating oils. U.S. Pat. No. 5,149,452 discloses combinations of low and high molecular weight polyalkylmethacrylates useful for reducing the pour points of wax isomerates compared to using the low or high molecular weight polyalkylmethacrylates alone. GB Patent No. 1559952 discloses combinations of viscosity index (VI) improving polyalkyl(meth)acrylates having greater than 75% (C
12
-C
15
)alkyl (meth)acrylate units with pour point depressing polyalkyl(meth)acrylates having less than 75% (C
12
-C
15
)alkyl (meth)acrylate units and 10-90% (C
16
+)alkyl (meth)acrylate units; the polymer combinations were useful for reducing the pour points of hydrocracked lubricating oils compared to using each type of polyalkyl(meth)acrylate alone.
A 37/63 weight ratio mixture of poly(65 dodecyl-pentadecyl methacrylate/35 cetyl-stearyl methacrylate) having weight average molecular weight of approximately 500,000 and poly(85 dodecyl-pentadecyl methacrylate/15 cetyl-eicosyl methacrylate) having weight average molecular weight of approximately 100,000 was a commercially available pour point depressant additive formulation; the polymers were prepared by conventional solution polymerization processes.
It would be desirable for a pour point depressant polymer or mixture of pour depressant polymers to be useful in a wide variety of petroleum oils and also simultaneously satisfy more than one aspect of low temperature fluidity requirements, that is, other than pour point depression. Recent advances in measuring low temperature properties of oils have led to the need to satisfy multiple performance requirements, for example, low-shear rate viscosity, yield stress and gel index (used to predict low temperature pumpability in equipment), in addition to conventional pour point depression.
None of these previous approaches provides good low temperature fluidity when a polymer additive or combination of additives is used in a wide range of lubricating oil formulations. It is an object of the present invention to provide an improved method for treating a broad range of lubricating oils such that different aspects of low temperature fluidity are satisfied simultaneously.
SUMMARY OF INVENTION
The present invention provides a method for maintaining low temperature fluidity of a lubricating oil composition comprising adding from 0.03 to 3 percent, based on total lubricating oil composition weight, of a first [P
1
] and a second [P
2
] polymer to the lubricating oil composition wherein (a) the first polymer [P
1
] comprises zero to 15 percent monomer units selected from one or more (C
1
-C
6
)alkyl (meth)acrylates, 30 to 75 percent monomer units selected from one or more (C
7
-C
15
)alkyl (meth)acrylates and 25 to 70 percent monomer units selected from one or more (C
16
-C
24
)alkyl (meth)acrylates, based on total first polymer weight, and has a weight average molecular weight from 250,000 to 1,500,000; (b) the second polymer [P
2
] comprises zero to 15 percent monomer units selected from one or more (C
1
-C
6
)alkyl (meth)acrylates, 75 to 100 percent monomer units selected from one or more (C
7
-C
15
)alkyl (meth)acrylates and zero to 25 percent monomer units selected from one or more (C
16
-C
24
)alkyl (meth)acrylates, based on total second polymer weight, and has a weight average molecular weight from 10,000 to 1,500,000; (c) the first polymer [P
1
] has a weight average molecular weight at least 50,000 greater than that of the second polymer [P
2
]; and (d) the first and second polymers are combined in a weight ratio ([P
1
]/[P
2
]) of 5/95 to 75/25.
In another embodiment the present invention provides a method for maintaining low temperature fluidity of a lubricating oil composition wherein the first [P
1
] and second [P
2
] polymers are selected and combined in a weight ratio such that the lubricating oil composition has (a) a “gel index” of less than 12, and (b) a “low-shear rate viscosity” of less than 60 pascal·seconds with a “yield stress” of less than 35 pascals.
In another aspect the present invention provides concentrate and lubricating oil compositions comprising the first [P
1
] polymer described above and a second [P
2
] polymer, wherein the second polymer [P
2
] comprises zero to 15 percent monomer units selected from one or more (C
1
-C
6
)alkyl (meth)acrylates, 90 to 100 percent monomer units selected from one or more (C
7
-C
15
)alkyl (meth)acrylates and zero to 10 percent monomer units selected from one or more (C
6
-C
24
)alkyl (meth)acrylates, based on total second polymer weight, and has a weight average molecular weight from 10,000 to 1,500,000; the first polymer [P
1
] has a weight average molecular weight at least 50,000 greater than that of the second polymer [P
2
]; and the first and second polymers are combined in a weight ratio ([P
1
]/[P
2
]) of 5/95 to 75/25.
DETAILED DESCRIPTION
The process of the present invention is useful for improving different aspects of low temperature fluidity simultaneously for a broad range of lubricating oils. We have found that combinations of selected low and high molecular weight polymers are effective for this purpose a
Kinker Bernard G.
Mc Gregor Thomas A.
Souchik Joan Marie
Howard Jacqueline V.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
RohMax Additives GmbH
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