Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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WO 99114292 PCT/EP98105859 _ ._
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LUBRICATING COMPOSITIONS
The present invention relates to lubricating
compositions, particularly to lubricating greases
containing such compositions, and more particularly to
lubricating greases for use in constant velocity joints
of all types, e.g. to constant velocity fixed ball
joints and to the plunging type constant velocity
joint.
The primary purpose of lubrication is separation of
solid surfaces moving relative to one another, to
minimise friction and wear. The materials most
frequently used for this purpose are oils and greases.
The choice of lubricant is mostly determined by the
particular application.
Lubricating greases are employed where heavy
pressures exist, where oil drip from the bearings is
undesirable or where the motion of the contacting
surfaces is discontinuous so that it is difficult to
maintain a separating film in the bearing. Because of
design simplicity, decreased sealing requirements and
less need for maintenance, greases are almost
universally given first consideration far lubricating
ball and roller bearings in electric motors, household
appliances, automotive wheel bearings, machine tools or
aircraft accessories. Greases are also used for the
lubrication of small gear drives and for many slow-
speed sliding applications.
Lubricating greases consist primarily of a fluid
lubricant, such as an oil, and a thickener.
Essentially, the same type of oil is employed in
compounding a grease as would normally be selected for
oil lubrication. Fatty acid soaps of lithium, calcium,
sodium, aluminium and barium are most commonly used as
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thickeners. However, thickeners may be one of a
variety of solid materials, including clays, soaps and
complexes such as those of lithium, and urea-type
compounds.
The base oil may be of mineral or synthetic origin.
Base oils of mineral origin may be mineral oils, for
example produced by solvent refining or hydro-
processing. Base oils of synthetic origin may
typically be mixtures of C10_50 hydrocarbon polymers,
for example liquid polymers of alpha-olefins. They may
also be conventional esters, for example polyol esters.
The base oil may also be a mixture of these oils.
Preferably the base oil is that of mineral origin sold
by the Royal Dutch/Shell Group of Companies under the
designations "HVI" or "MVIN", is a polyalphaolefin, or
is a mixture of the two. Synthetic hydrocarbon base
oils, for example those sold by the Royal Dutch/Shell
Group of Companies under the designation "XHVI" (trade
mark) may also be used.
A lubricating grease preferably contains 5 to 20$
by weight of thickener.
Lithium soap thickened greases have been known for
many years. Typically, the lithium soaps are derived
from C10-24~ Preferably CIS_Ig, saturated or
unsaturated fatty acids or derivatives thereof. One
particular derivative is hydrogenated castor oil, which
is the glyceride of 12-hydroxystearic acid.
I2-Hydroxystearic acid is a particularly preferred
fatty acid.
Greases thickened with complex thickeners are well
known. In addition to a fatty acid salt, a complexing
agent is incorporated into the thickener, which is
commonly a low to medium molecular weight acid or
dibasic acid or one of its salts, such as benzoic acid
or boric acid or a lithium borate.
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Urea compounds used as thickeners in greases
include the urea group (-NHCONH-) in their molecular
structure. These compounds include mono-, di- or
polyurea compounds, depending upon the number of urea
linkages.
Various conventional grease additives may be
incorporated into the lubricating greases, in amounts
normally used in this field of application, to impart
certain desirable characteristics to the grease, such
t0 as oxidation stability, tackiness, extreme pressure
properties and corrosion inhibition. Suitable
additives include one or more extreme pressure/antiwear
agents, for example zinc salts such as zinc dialkyl or
diaryl dithiophosphates, borates, substituted
IS thiadiazoles. polymeric nitrogen/phosphorus compounds
made, for example, by reacting a dialkoxy amine with a
substituted organic phosphate, amine phosphates,
sulphurised sperm oils of natural or synthetic origin,
sulphurised lard, sulphurised esters, sulphurised fatty
20 acid esters, and similar sulphurised materials, organo-
phosphates for example according to the formula
(OR)3P=0 where R is an alkyl, aryl or aralkyl group,
and triphenyl phosphorothionate~ one or more overbased
metal-containing detergents, such as calcium or
25 magnesium alkyl salicylates or alkylarylsulphonates:
one or more ashless dispersant additives, such as
reaction products of polyisobutenyl succinic anhydride
and an amine or ester; one or more antioxidants, such
as hindered phenols or amines, for example phenyl alpha
30 naphthylamine; one or more antirust additives; one or
more friction-modifying additives; one or more
viscosity-index improving agents one or more pour
point depressing additives; and one or more tackiness
agents. Solid materials such as graphite, finely
35 divided molybdenum disulphide, talc, metal powders, and
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various polymers such as polyethylene wax may also be
added to impart special properties.
Zinc dithiocarbamates are sometimes used as
antioxidants and also as corrosion inhibitors in some
lubricants such as diesel and gasoline engine oils and
industrial oils.
In lubricants generally, the reduction of friction
(i.e. the increase of slideability) combined with the
reduction of wear (i.e. the reduction of surface damage
caused by mechanical and/or corrosive action) is highly
desirable.
There have been a number of proposals to reduce
friction levels using a variety of additives, usually
incorporating organic molybdenum-based formulations.
Often the friction reducing effect is thickener
dependent, i.e. an additive will work well with one
thickener type but not with another.
Molybdenum disulphide (a non-organic molybdenum
compound) is a known highly wear resistant solid
lubricant and is used in a wide variety of lubricants.
Equally common is the use of metal (dialkyl or diaryl)
dithiophophates in lubricants as extreme pressure or
anti wear agents.
Tribology Transactions, vol 33, no. 3, (1990) pages
345 to 354 reviews the effects of organic molybdenum
compounds (such as molybdenum dialkyl dithiocarbamates
(MoDTC) and molybdenum dithiophosphates (MoDTP)) on
wear and friction with zinc dialkyl
dithiophosphate(ZnDTP)-containing lubricant blends. In
the early part of the review, tests on various
components in a lubricating oil establishes inter alia
that zinc compounds, including a zinc dithiocarbamate,
exhibited similar high load antiwear performance to a
molybdenum dithiocarbamate. Later in the review, a
number of products commonly speculated to be
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decomposition products of MoDTC or MoDTP and ZnDTP
additives, were suspended into a reference grease for
independent evaluation to determine whether indeed any
of those products gave good friction and antiwear
properties. Molybdenum disulphide, thought by some to
be such a decomposition product, was tested in a
reference grease thickened with a lithium I2-hydroxy
stearate soap and containing 0.5o mass zinc dibutyl
dithiocarbamate as an oxidation inhibitor. The
resulting grease exhibited high (i.e. undesirable)
friction and only moderate anti-wear properties; zinc
compounds tested separately in the same reference
grease also showed no reduced friction.
In WO 97/03152, a friction reducing additive
IS combination has been described comprising molybdenum
disulphide, zinc naphthenate and metal dithiophosphate
optionally in combination with metal dithiocarbamates.
In Example 22 it is shown that the presence of zinc
naphthenate is essential.
It has now surprisingly been found that molybdenum
disulphide, zinc dithiocarbamate and a metal
dithiophosphate in combination work synergistically as
a friction reducing agent in lubricating compositions,
especially greases, whilst retaining goad, low anti-
wear properties. It has been found that zinc
naphthenate does not need to be present in this
combination. Furthermore such combination is not
thickener dependent. Tested against the use of
molybdenum disulphide alone or in combination with one
of the two other components, the friction reduction is
shown to be quite unexpected.
The use of lubricating oil compositions containing
molybdenum disulphide, molybdenum dithiocarbamate and
metal dithiophosphate has been described in WO 94/11470
and GB-A-2 255 103. WO 94/11470 or GB-A-2 255 103
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neither teach nor hint that the molybdenum
dithiocarbamate might be replaced by another metal
dithiocarbamate.
The present invention accordingly provides a
lubricating composition which comprises a base oil of
mineral and/or synthetic origin and a combination of
molybdenum disulphide, one or more zinc
dithiocarbamates and one or more metal dithiophosphates
which composition contains no substantial amount of
zinc naphthenate.
The composition of the present invention contains
no substantial amount of zinc naphthenate. This means
that the composition contains less than 0.3$ by weight
of zinc naphthenate, based on total weight of
lubricating composition. The amount of zinc
naphthenate is the amount of compound per se, excluding
further compounds which may be present in a commercial
product e.g. mineral oil. The composition preferably
contains less than 0.05$ by weight of zinc naphthenate,
more preferably less than 0.01$ wt. Most preferably,
the composition does not contain zinc naphthenate.
Preferred is the use of the friction reducing
additive combination in a lubricating grease which
comprises a base oil of mineral and/or synthetic origin
and a thickener, which is preferably a lithium soap,
either simple or complex, or a urea compound.
Such a lubricating grease preferably contains
molybdenum disulphide in an amount of from 0.5 to 10$
by weight, more preferably 1 to 4$ by weight.
Independently, the grease preferably contains zinc
dithiocarbamate in an amount of from 0.01 to 5~ by
weight, more preferably 0.3 to 2.4$ by weight, for a
urea thickened grease and a complex lithium soap
thickened greases, and an amount of from 0.5 to 10$ by
weight, more preferably 1 to 4$ by weight, for a simple
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lithium soap thickened grease. A lubricating grease of
the invention further preferably contains said one or
more metal dithiophosphates in a total amount of from
0.15 to 10~ by weight; more preferably 1 to 3$ by
weight. All amounts are based on total weight of the
grease composition.
It is especially useful if the three components are
present in an interrelated or 3-way proportion such
that, for a urea thickened grease and for a complex
lU lithium soap thickened grease the weight ratio of
molybdenum disulphide to metal dithiophosphate is in
the range of from 1:0.15 to 1:1, the weight ratio of
metal dithiophosphate to zinc dithiocarbamate is in the
range of from 1:0.25 to 1:1.5, and the weight ratio of
l5 molybdenum disulphide to zinc dithiocarbamate is in the
range of from 1:0.4 to 1:1.5. For a simple lithium
soap thickened grease the weight ratio of molybdenum
disulphide to metal dithiophosphate preferably is in
the range of from 1:0.15 to 1:1, the weight ratio of
20 metal dithiophosphate to zinc dithiocarbamate is in the
range of from 1:1 to 1:4.5 and the weight ratio of
molybdenum disulphide to zinc dithiocarbamate is in the
range of from 1:0.4 to 1:1.5.
Preferably, the one or more metal dithiophosphates
25 is/are selected from zinc dialkyl-, diaryl- or
alkylaryl-dithiophosphates, and the one or more zinc
dithiocarbamates is/are selected from zinc dialkyl-,
diaryl- or alkylaryl-dithiocarbamates, in which
dithiophosphates and/or dithiocarbamates usefully any
30 alkyl moiety is straight chain or branched and
preferably contains from 1 to 12 carbon atoms.
The thickener of lubricating greases, as mentioned
hereinbefore, preferably comprises a urea compound, a
simple lithium soap or a complex lithium soap. A
35 preferred urea compound is a polyurea compound. Such
*rB
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thickeners are well known in lubricant grease
technology. Surprisingly effective compositions of the
invention use simple lithium soaps as thickeners.
Lubricating compositions of the invention may be
prepared by incorporating the additive combination into
a base oil in conventional manner. For greases this
may be via hot or cold mixing followed by
homogenisation to ensure uniform dispersion of the
additive components. Other additives, e.g.
antioxidants, may be included if necessary or desired.
In accordance with the present invention there is
further provided a method of lubricating a constant
velocity joint comprising packing it with a lubricating
grease according to the present invention.
In accordance with the present invention there is
still further provided a constant velocity joint packed
with a lubricating grease according to the present
invention.
The present invention will now be described by
reference to the following Examples, in which all
percentages are given by weight.
Example 1
A lithium soap grease was prepared by adding a
slurry of 1.12 w Li0H.H20 and water in the proportions
of 1 part LiOH.H20 to 5 parts water to 9.15$ w
hydrogenated castor oil fatty acid in cold base oil (a
blend of MVIN and HVI oils) and heating the mix in a
sealed autoclave to 150°C. The steam was vented off
and heating continued to 220°C before the reaction mass
was quick cooled (at a rate of 6 to 7°C per minute) and
the product homogenised. Additives were incorporated
into the grease. In all cases, as antioxidant, 0.5~ w
of an aromatic amine was used.
A grease of the present invention and a number of
comparison greases were prepared and tested. For each
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grease the amount of molybdenum disulphide, ZnDTC (zinc
diamyl dithiocarbamate) and ZnDTP (4-methyl-2-pentyl
zinc dithiophosphate) was varied as shown in Table 1.
The friction coefficient and wear scar diameter
were evaluated for each grease; the results are also
given in Table 1.
The friction and wear measurements were made using
an oscillating SRV friction tester. For friction
measurements the oscillating SRV friction tester (from
Optimol Instruments) was used with a 10 mm ball on a
flat lapped surface as test geometry. An oscillation
frequency of 50 Hertz and a stroke of 1.5 mm was used
throughout. The friction coefficient was recorded
after two hours of operation under the test conditions
IS of a load of 300 Newtons at a temperature of 100°C.
Wear was assessed by measuring the diameter of the wear
scar on the ball at the end of the two hour test using
an optical graticule.
A grease of the present invention was compared with
lithium greases having only molybdenum disulphide or
molybdenum disulphide plus zinc dithiocarbamate or
molybdenum disulphide plus zinc dithiophosphate all
with the same base grease plus thickener plus
antioxidant. It can be clearly seen from the results
that the grease of the present invention has a
significantly lower friction coefficient and wear scar
diameter than any of the comparison greases.
Example 2
A urea grease C was prepared by heating 5$ w of
4,4'-diphenylmethane diisocyanate in base oiI (a
mixture of 75$ w HVI 160B and 25$ w HVI 650) to 70°C and
then adding 10.8$ w stearylamine. The mixture was then
further heated to 150°C before being cooled to 80°C.
The other additives to be included in the formulation
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were then added. The formulated grease was then
homogenised at ambient temperature.
A grease of the present invention and a number of
comparison greases were prepared and tested.
Again in all cases, an antioxidant, 0.5~ w of an
aromatic amine, was added and for each grease the
amount of molybdenum disulphide, ZnDTC (zinc diamyl
dithiocarbamate) and ZnDTP (4-methyl-2-pentyl zinc
dithiphosphate) were varied. The friction coefficient
and wear for each grease was evaluated as in Example 1.
Results are given in Table 2.
It can be seen that also for a urea-thickened
grease a significantly low friction coupled with low
wear is exhibited, but with a lower proportion of ZnDTC
than for the lithium soap thickened grease of
Example 1.
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CA 02303345 2000-03-09
WO 99114292 PCT/EP98/05859
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WO 99/14292 PCTIEP98/05859
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Example 3
A lithium complex grease was prepared by adding a
50$w slurry of LiOH.H~O and boric acid in water to
hydrogenated castor oil fatty acid, calcium alkyl
salicylate, and calcium octoate, in conventional
proportions, in base oil, (a mixture of HVI oils)
together with conventional antioxidants, and then
heating the charge to 210°C with stirring. After slowly
cooling the mixture to 160°C a quinoline and a
hydroxyphenyl were added as additional antioxidants.
The whole was then slowly cooled to ambient temperature
and molybdenum disulphide, ZnDTC (zinc diamyl
dithiocarbamate and ZnDTP (4-methyl-2-pentyl zinc
dithiophosphate) were added; the resulting grease was
then homogenised.
The grease obtained contained 3$ w molybdenum
disulphide, 1.5$ w ZnDTC and 1.5$ w ZnDTP as friction
reducing additive.
Using the same test methods as described in Example
1 above, the friction coefficient and wear for the
grease were measured at 300N and 100°C as 0.058 and
0.48 nm respectively. Thus the surprising low friction
coefficient coupled with low wear properties are also
given when using a lithium complex thickened grease.
