Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Nitrogen and heavy metal – or nitrogen and aluminum – in the...
Reexamination Certificate
1997-12-12
2001-02-13
Medley, Margaret (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Nitrogen and heavy metal, or nitrogen and aluminum, in the...
C508S365000, C508S377000, C508S378000, C508S438000, C508S440000
Reexamination Certificate
active
06187723
ABSTRACT:
This invention relates to a lubricant composition containing a combination of additives providing antiwear properties, and to the antiwear additive combination contained therein.
It is well-known to include an antiwear additive in lubricating oils such as engine oils. Wear results mainly from the rubbing together of two metal surfaces, i.e., in boundary lubrication regimes, such as is found in valve trains in internal combustion engines. It is believed that the antiwear additive acts to provide a protective film over the metal surfaces. One well-known class of antiwear additives is the metal alkylphosphate, especially zinc dialkyldithiophosphate (“ZDDP”). Generally ZDDP is employed at treat levels of 1 to 2 wt % based on the total weight of the lubricant, which gives a phosphorus level in the lubricant typically in the range of from 0.05 to 0. 15 wt %, and a zinc level of from 0.1 to 0.2 wt %.
In recent years there has been increasing concern that lubricant ash levels, such as that produced by the zinc in ZDDP, contribute to particulate emissions from internal combustion engines. There is also concern that the phosphorus fiom the lubricant tends to poison catalysts used in catalytic converters, thereby preventing them fiom functioning to full effect. However, any reduction in ZDDP treat levels has the disadvantage that it will reduce the antiwear properties of the lubricant.
There is therefore a need for an effective antiwear additive with reduced zinc and phosphorus levels.
We have found that a phosphoius-free organo-molybdenum compound and an ashless sulfur-containing organo-phosphorus compound act together synergistically to provide improved antiwear performance when used in a lubricant composition. By using this combination of compounds it becomes possible to achieve the same or better performance than that achieved with ZDDP, with significantly lower levels of phosphorus.
Sulfur-containing organic phosphorus compounds are known to be used as “extreme pressure compounds” in heavy duty applications such as greases for constant velocity joints. It is also known to use sulfur-containing organic compounds of heavy metals such as molybdenum, tungsten and lead in such applications. Thus GB-A-2255346 describes an additive for grease used in constant velocity joints comprising in combination molybdenum sulfide dialkyldithiocarbamate, zinc dithiophosphate, a sulfur-phosphorus series extreme pressure compound, and lead dialkyldithiocarbamate. It is stated that the presence of the lead compound is essential to achieve the desired performance.
U.S. Pat. No. 4,648,985 describes a lead-free extreme pressure additive, generally for lubricants based on asphalt, utilizing an organic phosphate in combination with copper or molybdenum compounds selected from carboxylate, phosphate, thiophosphate and thiocarbamate, optionally with a metal-free thiocarbamate or in combination with a metal thiocarbamate (numerous metals being described). The preferred metals are copper and zinc.
Organic phosphorus compounds are also used as ashless dispersants. Thus EP-A-0516461 describes a dispersant additive for lubricating oils showing improved compatibility with elastomeric seal material which comprises in combination a metal dihydrocarbyl dithiocarbamate or dithiocarbamate and a phosphorylated ashless dispersant. Various metal compounds are described including molybdenum dithiophosphate.
EP-A-0316610 describes a multipurpose antiwear, antiseizure and corrosion inhibiting additive for lubricating oils utilizing a combination of an organo-phosphorus compound selected from various phosphines and phosphites and an organo-molybdenum compound selected from oxysulphide alkylphosphorodithioates and oxysulphide alkyl dithiocarbamates.
GB-A-1373588 describes an antiwear, antioxidant additive combination comprising a metal dialkyldithiocarbamate and/or a metal alkyl, aryl or aralkyl dithiophosphate and a metal-free phosphorus compound selected from sulfurized sperm oil esterified with dithiophosphate, sulfurized terpene esterified with dithiophosphate, sulfurized and phosphated sperm oil and phosphorus polysulfide. Many metals are mentioned including molybdenum, zinc and lead.
In one aspect the present invention provides a lubricant composition comprising a base oil of viscosity from 3 to 26 cSt (mm
2
/s) at 100° C. and an antiwear additive combination comprising
(a) an oil soluble or oil-dispersible phosphorus-free organo-molybdenum compound wherein the organo group of the molybdenum compound is selected from carbamate, carboxylate and xanthate groups and mixtures thereof, and
(b) an ashless, sulfur-containing organo phosphorus compound selected from:
(i) a phosphorothiolothionate of the formula:
wherein R
5
, R
6
and R
7
are each independently an unsubstituted branched or straight chain hydrocarbyl group or a branched or straight chain hydrocarbyl group substituted with one or more sulfur, oxygen, or nitrogen containing functional groups,
(ii) a phosphorothionate of the formula:
wherein R
8
, R
9
, and R
10
are as defined for R
5
, R
6
, and R
7
above; and
(iii) a mixture of (i) and (ii).
Furthermore, we have found surprisingly that compounds (a), (b) when used in combination with reduced levels of a selected zinc thiophosphate, act synergistically to provide better wear protection than that achieved using a comparable amount (i.e., an amount providing a similar total level of phosphorus) of the zinc thiophosphate alone.
Accordingly in a preferred lubricant composition the combination includes, in addition to (a) and (b), a zinc thiophosphate compound (c) selected from one or more of zinc dialkyldithiophosphate, zinc diaryldithiophosphate, zinc alkylaryldithiophosphate and zinc arylalkyldithiophosphate.
This provides the advantage that the organo-molybdenum compound can replace some of the zinc thiophosphate compound used in lubricant compositions with the effect that the phosphorus level in the lubricant is reduced without substantially reducing, indeed increasing the antiwear performance of the lubricant.
The organo-molybdenum compound may comprise a molybdenum carbamate, preferably a dicarbamate and more preferably a dithiocarbamate (MoDTC) the organo group(s) of which may be substituted with hydrocarbyl groups, with the proviso that the organo group selected results in an organo-molybdenum compound that is oil-soluble or oil-dispersible, preferably oil-soluble.
However it is known that MoDTC decomposes when heated in use to decomposition products which include free amine and carbon disulfide. Both such products are aggressive towards copper, which is present in the engine bearings. Wear in bearings is particularly objectionable since repair involves complete dismantling of the engine. Carbon disulfide tends to boil off fairly rapidly and does not constitute a special problem. However even small amounts of free amine can cause damage.
We have found that the synergisms described above extend not only to carbamates of molybdenum but also to molybdenum compounds which are nitrogen free and which therefore do not decompose to free amine. Organo-molybdenum compound which are also free from sulfur are also known.
Accordingly, while from a performance perspective, in a preferred combination of (a) and (b) together optionally with (c) the organo-molybdenum compound is a carbamate, in those situations wherein it is desirable to have an oil with low sulfur and/or nitrogen content, then organo-molybdenum compounds that are sulfur and/or nitrogen-free, e.g., carboxylate and xanthate or mixtures thereof, the organo group(s) of which may be substituted with a hydrocarbyl group, are preferred, again with the proviso that the organo group selected results in an organo-molybdenum compound that is oil-soluble or oil-dispersable, preferably oil-soluble.
While the preferred organo-molybdenum compound from a performance viewpoint is carbamate, those compounds which do not contain sulfur and/or nitrogen or phosphorus have an advantage in that they are relatively cheap and contain a higher proportion of molybdenum than the more
Atherton John Ian
Holt David Gary Lawton
Vernon Patrick Desmond Fraser
Allocca Joseph J.
Exxon Research and Engineering Company
Medley Margaret
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