Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic -co- compound
Reexamination Certificate
1999-03-24
2004-03-30
Medley, Margaret (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic -co- compound
C508S485000, C508S492000, C508S496000, C508S499000, C508S591000, C208S018000, C208S019000, C208S020000, C208S021000, C585S009000, C585S010000, C585S011000, C585S012000, C585S013000
Reexamination Certificate
active
06713438
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to engine oils useful in internal combustion engines and more particularly to engine oils having good antiwear and viscometric properties as well as other desirable properties including resistance to oxidation under conditions of high temperature, high speed and high load. The preferred engines oils of this type are synthetic oils but the advantages of the invention may be extended to oils containing base stocks of mineral origin.
BACKGROUND OF THE INVENTION
Multi-grade engine oils, derived from a combination of low viscosity basestocks and high molecular weight thickeners, viscosity index improvers, and other components have been used for a long time. Synthetic engine oils based on polyalphaolefins (PAOs) have been shown to demonstrate performance benefits together with cost effectiveness in automotive and other engine applications. In these synthetic oils, as with conventional oils of mineral origin, the viscosity-temperature relationship of the oil is one of the critical criteria which must be considered when selecting the lubricant for a particular application. The viscosity requirements for qualifications as multi-grade engine oils are described by the SAE Engine Oil Viscosity Classification-SAE J300. The low temperature (WA) viscosity requirements are determined by ASTM D 5293, Method of Test for Apparent Viscosity of Motor Oils at Low Temperature Using the Cold Cranking Simulator (CCS), and the results are reported in centipoise (cP). The higher temperature (100° C.) viscosity is measured according to ASTM D445, Method of Test for kinematic Viscosity of Transparent and Opaque Liquids, and the results are reported incentistokes (cSt). Table 1 below outlines the high and low temperature requirements for the recognized SAE grades for engine oils.
TABLE 1
Engine Oil Viscosity Grade Specifications (SAE J300)
Cranking
Kinematic
SAE
Viscosity (cP) at
Viscosity (cSt.)
Viscosity
Temperature (° C.)
at 100 ° C.
Grade
Max.
Min.
Max.
0 W
3250 at −30°
3.8
5 W
3500 at −25°
3.8
10 W
3500 at −20°
4.1
15 W
3500 at −15°
5.6
20 W
4500 at −10°
5.6
25 W
6000 at −5°
9.3
20
5.6
<9.3
30
9.3
<12.5
40
12.5
<16.3
50
16.3
<21.9
60
21.9
<26.1
The SAE J300 viscosity grade definitions end at SAE 60 but the scale may be extrapolated in a simple linear manner using the following correlation, which is used in this specification in reference to viscosity grades beyond J300:
TABLE 1a
Extended High-Temperature Viscosity Grades
Kinematic
Kinematic
Viscosity
Viscosity (cSt)
Viscosity (cSt)
Grade
Minimum
Maximum
(Extrapolation beyond SAE J300)
70
26.1
<30
80
30
<35
90
35
<40
100
40
<45
110
45
<50
120
50
<55
130
55
<60
140
60
<65
150
65
<70
In a similar manner, SAE J306c describes the viscometric qualifications for axle and manual transmission lubricants. High temperature (100° C.) viscosity measurements are performed according to ASTM D445. The low temperature viscosity values are determined according to ASTM D2983, Method of Test for Apparent Viscosity at Low Temperature Using the Brookfield Viscometer and these results are reported in centipoise (cP). Table 2 summarizes the high and low temperature requirements for qualification of axle and manual transmission lubricants.
TABLE 2
Axle/Transmission Oil Viscosity Specifications
SAE
Maximum Temperature
Kinematic Viscosity at
Viscosity
for Viscosity
100 ° C., cSt.
Grade
of 150,000 cP., ° C.
Min
Max
70 W
−55
—
75 W
−40
4.1
80 W
−26
7.0
85 W
−12
11.0
90
—
13.5
<24.0
140
—
24.0
<41.0
250
—
In addition to the viscosity temperature relationship, other properties are, of course, required for an engine oil including resistance to oxidation under the high temperatures encountered in the engine, resistance to hydrolysis in the presence of the water produced as a combustion product (which may enter the lubricating circulation system as a result of ring blow-by) and since the finished oil is a combination of basestock together with additives, these properties should be achieved in the final, finished lubricant so that it possesses the desired balance of properties over its useful life
In recent years, considerable attention has been given to the tribological behavior of lubricants under conditions of high shear rate and high pressure. At high shear rates, as in a lubrication contact zone, considerable shear thinning may occur, which results in a decrease in the thickness of the lubricant film separating the relatively moving surfaces with the possibility that inadequate film thickness may be maintained under these conditions. As a counter to this tendency, it would be desirable to provide lubricant compositions which can function effectively under high temperature conditions and which possess good Theological properties to provide adequate. film thickness and wear protection by resisting shear thinning under conditions of high temperature and high shear rate as well as high contact pressure.
As noted above, various combinations of additives with lubricants have been used in the past for the improvement of lubricant properties and in particular, the use of polymeric materials for altering the viscosity or viscosity index of base stocks of mineral and synthetic origin has been well known for a number of years. Polymeric thickeners which are commonly used in the production of multi-grade lubricants typically include hydrogenated styrene-isoprene block copolymers, rubbers based on ethylene and propylene (OCP), polymers produced by polymerization of esters of the acrylate or methacrylate series, polyisobutylene and the like. These polymeric thickeners are added to bring the viscosity of the base fluid up to the level required for the desired grade (high temperature specification) and possibly to increase the viscosity index of the fluid, allowing for the production of multi-grade oils.
The use of high molecular weight thickeners and VI improvers in the production of multi-grade lubricants has, however, some serious drawbacks. First, these improvements are more sensitive to oxidation than the basestocks in which they are used, which may result in a progressive loss of viscosity index and thickening power with use and frequently in the formation of unwanted deposits. In addition, these materials tend to be sensitive to high shear rates and stresses as well as to a high degree of temporary shear the result of which is that temporary or permanent viscosity losses, or reduction of film thickness in bearings may occur. Temporary viscosity losses occurring from shear forces are the result of the non-Newtonian viscometrics associated with the solutions of high molecular weight polymers. As the polymer chains align with the shear field under high shear rates, a decrease in viscosity occurs, reducing film thickness and the wear protection associated with the elastohydrodynamic film. By contrast, Newtonian fluids maintain their viscosity regardless of shear rate. From the point of view of lubricant performance at high temperatures and under the influence of a shear rate condition, it would be desirable to maintain Newtonian rheological properties for the lubricant.
U.S. Pat. No. 4,956,122 (Watts/Uniroyal) discloses lubricating compositions based on combination of low and high molecular weight PAOs which are stated to provide high viscosity index coupled with improved resistance to oxidative degradation and resistance to viscosity losses caused by permanent or temporary shear conditions. According to the invention description in this patent, the lubricating composition comprises a high viscosity PAO or other synthetic hydrocarbon together with a low viscosity mineral derived oil or PAO or other synthetic hydrocarbon such as alkyl benzene. Optionally, a low viscosity ester and an additive package may be included in the lubricants. While the combination of PAO components of varying molecular weight has been effective in a variety of different applications, further improvements in reducing shear thinning charac
Baillargeon David J.
Bergstra Raymond J.
Jackson Andrew
Johnston G. James
Maxwell William L.
Keen Malcolm D.
Medley Margaret
Mobil Oil Corporation
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