Note: Descriptions are shown in the official language in which they were submitted.
1
USE OF A MOLYBDENUM-CONTAINING ADDITIVE AND A
BORON-CONTAINING ADDITIVE IN A LUBRICATING COMPOSITION FOR
REDUCING LOW-SPEED PRE-IGNITION (LSPI) EVENTS IN A
DIRECT-INJECTION SPARK-IGNITION COMBUSTION ENGINE
Field of the Invention
The present invention concerns a method of reducing low-speed pre-ignition
(LSPI) events in a direct-injection spark-ignition combustion engine
comprising
lubricating the crankcase of the engine with a lubricating composition
comprising a
combination of a molybdenum-containing additive and a boron-containing
additive.
Background of the Invention
Market demand, as well as governmental legislation, has led automotive
manufacturers to continuously improve fuel economy and reduce CO2 emissions
across
engine families, while simultaneously maintaining perfoimance (horsepower).
Using
smaller engines providing higher power densities, increasing boost pressure,
by using
turbochargers or superchargers to increase specific output and down-speeding
the engine
by using higher transmission gear ratios allowed by higher torque generation
at lower
engine speeds have allowed engine manufacturers to provide excellent
performance while
reducing frictional and pumping losses. However, higher torque at lower engine
speeds
has been found to cause random pre-ignition in engines at low speeds, a
phenomenon
known as Low Speed Pre-Ignition, or LSPI, resulting in extremely high cylinder
peak
pressures, which can lead to catastrophic engine failure. The possibility of
LSPI prevents
engine manufacturers from fully optimizing engine torque at lower engine speed
in such
smaller, high-output engines.
While not wishing to be bound by any specific theory, it is believed that LSPI
may be caused, at least in part, by auto-ignition of droplets, e.g. comprising
engine oil, or
a mixture of engine oil, fuel and/or deposits, that enter the engine
combustion chamber
from the piston crevice (space between the piston ring pack and cylinder
liner) under high
pressure, during periods in which the engine is operating at low speeds, and
compression
Date Recue/Date Received 2022-09-20
2
stroke time is longest (e.g., an engine having a 7.5 msec compression stroke
at 4000 rpm
may have a 24 msec compression stroke when operating at 1250 rpm). Therefore,
it
would be advantageous to identify and provide lubricating oil compositions
that are
resistant to auto-ignition and therefore prevent or ameliorate the occurrence
of LSPI.
Some attempts have been made in the art to address this problem. For example,
SAE 2013-01-2569 ("Investigation of Engine Oil Effect on Abnormal Combustion
in
Turbocharged Direct Injection-Spark Ignition Engines (Part 2)", Hirano et al.)
concludes
that increasing calcium concentration leads to greater LSPI frequency. It is
also
concluded that increasing zinc dihydrocarbyl dithiophosphate (ZDDP)
concentration can
reduce LSPI frequency. SAE 2014-01-2785 ("Engine Oil Development for
Preventing
Pre-Ignition in Turbocharged Gasoline Engine", Fujimoto et al.) concludes that
reducing
the amount of calcium detergent in a lubricating oil formulation is the most
effective
approach at reducing LSPI events. It is also concluded that increasing the
amount of
ZDDP can be effective in reducing LSPI frequency. SAE 2015-01-2027 ("Engine
Oil
Formulation Technology to Prevent Pre-Ignition in Turbocharged Direct
Injection Spark
Ignition Engines", Onodera et al.) concludes that (a) reducing calcium content
together
with increasing molybdenum content in engine oil formulations, and (b)
substitution of
calcium with magnesium in detergents for engine oil formulations, were both
effective in
reducing the frequency of LSPI events. A method of reducing LSPI frequency by
using a
lubricating oil having a reduced sodium content and containing certain
molybdenum-
containing compounds is disclosed in W02017/011683. W02015/171980 discloses a
method of reducing LSPI frequency by including in a lubricating oil
formulation at least
one boron-containing compound, such as a borated dispersant or a mixture of a
boron-
containing compound and a dispersant. However, according to the examples
disclosed in
W02015/171980, it was necessary to replace a substantial amount, or even all
of, the
calcium detergent with a magnesium detergent in order to obtain significant
improvements in LSPI frequency.
The prior art has further recognised that reducing the calcium content, and/or
increasing the ZDDP content, of a lubricating oil formulation can lead to a
reduction in
LSPI events. However, detergents are often considered to be necessary
additives for
CA 3018827 2018-09-27
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maintaining basic engine oils performance. Thus, recent efforts in providing
lubricating
oil formulations that reduce LSPI events have focused on replacing calcium
detergents
with alternative detergents. However, alternative detergents capable of
providing
appropriate detergent activity and adequate total base number (TBN) can be
challenging
to develop. Furthermore, increased ZDDP contents in lubricating oil
formulations can
lead to other, less desirable, effects. In particular, increasing ZDDP
concentration often
leads to an increase in ash formation and can lead to damage of catalysts in
engine
exhaust systems. EP 3 101 095 discloses a lubricating oil composition for
reducing LSPI
frequency, the composition comprising a compound containing calcium and/or
magnesium, a compound containing molybdenum and/or phosphorus, and an ashless
dispersion containing nitrogen. According to the disclosure of EP 3 101 095,
LSPI event
frequency can be reduced by controlling the relative amounts of calcium,
magnesium,
molybdenum and phosphorus in the lubricating oil composition.
Thus, there remains a need for a lubricating oil composition suitable for use
in
modern direct injection-spark ignition engines that reduces occurrences of
LSPI events.
Summary of the Invention
The present inventors have surprisingly found that the use of both molybdenum-
containing and boron-containing additives in a lubricating oil composition
significantly
reduces in the frequency of LSPI events in direct injection-spark ignition
internal
combustion engines when the crankcase of the engine is lubricated with said
lubricating
oil composition. More particularly, the present inventors have surprisingly
found a
synergistic improvement in LSPI reduction when using such a lubricating
composition as
compared to using a lubricating oil composition comprising only molybdenum-
containing additives and not boron-containing additives, and vice versa.
Thus, the present invention provides, according to a first aspect, a method of
reducing LSPI events in a direct-injection spark-ignition internal combustion
engine
comprising lubricating the crankcase of the engine with a lubricating oil
composition, the
composition comprising a boron-containing additive and a molybdenum-containing
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additive, having a molybdenum content of at least 150 ppm by weight, based on
the
weight of the lubricating oil composition, and having a boron content of at
least 150 ppm
by weight, based on the weight of the lubricating oil composition.
According to a second aspect, the present invention provides the use of a
combination of the composition a boron-containing additive and a molybdenum-
containing additive in a lubricating oil composition to reduce LSPI events,
when the
composition lubricates the crankcase of a direct injection-spark ignition
internal
combustion engine, wherein, the molybdenum-containing additive provides the
lubricating oil composition with a molybdenum content of at least 150 ppm by
weight,
based on the weight of the lubricating oil composition, and the boron-
containing additive
provides the lubricating oil composition with a boron content of at least 150
ppm by
weight, based on the weight of the lubricating oil composition.
In this specification, the following words and expressions, if and when used,
have
the meanings ascribed below:
"hydrocarbyl" means a chemical group of a compound that normally contains
only hydrogen and carbon atoms and that is bonded to the remainder of the
compound
directly via a carbon atom but that may contain hetero atoms provided that
they do not
detract from the essentially hydrocarbyl nature of the group;
"oil-soluble" or "oil-dispersible", or cognate terms, do not necessarily
indicate
that the compounds or additives are soluble, dissolvable, miscible, or are
capable of being
suspended in the oil in all proportions. These do mean, however, that they
are, for
example, soluble or stably dispersible in oil to an extent sufficient to exert
their intended
effect in the environment in which the oil in employed. Moreover, the
additional
incorporation of other additives may also permit incorporation of other
additives may
also permit incorporation of higher levels of a particular additive, if
desired;
"major amount" mean in excess of 50 mass % of a composition;
"minor amount" means 50 mass % or less of a composition;
"antifoam" is a chemical additive that reduces and hinders the formation of
foam
in the lubricating oil composition, examples of commonly used antifoams are
polydimethylsiloxanes and other silicones, certain alcohols, stearates and
glycols;
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"TBN" means total base number as measured by ASTM D2896 in units of
mg KOHg-1;
"phosphorus content" is measured by ASTM D5185;
"molybdenum content" is measured by ASTM D5185;
"boron content" is measured by ASTM D5185;
"sulfur content" is measured by ASTM D2622; and,
"sulphated ash content" is measured by ASTM D874.
Also, it will be understood that various components used, essential as well as
optimal and customary, may react under conditions of formulation, storage or
use and
that the invention includes the use of the product obtainable or obtained as a
result of any
such reaction. Further, it is understood that any upper and lower quantity,
range and ratio
limits set forth herein may be independently combined. Furthermore, the
constituents of
this invention may be isolated or be present within a mixture and remain
within the scope
of the invention.
It will of course be appreciated that features described in relation to one
aspect of
the present invention may be incorporated into other aspects of the present
invention. For
example, the use of the invention may incorporate any of the features
described with
reference to the method of the invention and vice versa.
Brief Description of the Figures
Fig. 1 shows the LSPI test results of Example 3 in matrix format.
Detailed Description
Several terms exist for various forms of abnormal combustion in spark ignited
internal combustion engines including knock, extreme knock (sometimes referred
to as
super-knock or mega-knock), surface ignition, and pre-ignition (ignition
occurring prior
to spark ignition). Extreme knock occurs in the same manner as traditional
knock, but
with increased knock amplitude, and can be mitigated using traditional knock
control
CA 3018827 2018-09-27
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methods. LSPI occurs at low speeds and high loads. In LSPI, initial combustion
is
relatively slow and similar to noinial combustion, followed by a sudden
increase in
combustion speed. LSPI is not a runaway phenomenon, unlike some other types of
abnormal combustion. Occurrences of LSPI are difficult to predict, but are
often cyclical
in nature.
LSPI is most likely to occur in direct-injected, boosted (turbocharged or
supercharged), spark-ignited (gasoline) internal combustion engines that, in
operation,
generate a brake mean effective pressure level of greater than about 1,500 kPa
(15 bar)
(peak torque), such as at least about 1,800 kPa (18 bar), particularly at
least about 2,000
kPa (20 bar) at engine speeds of from about 1000 to about 2500 rotations per
minute
(rpm), such as at engine speeds of from about 1000 to about 2000 rpm. As used
herein,
brake mean effective pressure (BMEP) is the mean effective pressure calculated
from
measured brake torque. The word "brake" denotes the actual torque or power
available at
the engine flywheel, as measured on a dynamometer. Thus, BMEP is a measure of
the
useful power output of the engine. BMEP is defined as the work accomplished
during
an engine cycle, divided by the engine swept volume; the engine torque
normalized by
engine displacement and can be calculated using the following formula:
BMEP = 27cTneNd
where T is torque (Nm), tic is the number of revolutions per cycle, Vd is
displacement
(m3). For a 4 stroke engine ric is 2, for a 2 stroke engine tic is 1.
SAE 2014-01-2785 has concluded that LSPI event frequency is strongly
influenced by the calcium content of the lubricating oil composition, and that
it is
preferable to avoid lubricating composition calcium contents of greater than
0.11 wt.%,
based on the weight of the lubricating oil composition, in order to avoid
excessive LSPI
event frequency.
Surprisingly, the present inventors have found that the presence of a
combination
of molybdenum and boron in a lubricating oil formulation is effective at
reducing the
occurrence of LSPI events. Unexpectedly, it has been found that the
combination of both
molybdenum and boron provides a synergistic improvement in LSPI event
reduction, the
frequency reduction being greater than expected from analysing the performance
of
CA 3018827 2018-09-27
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lubricating oil compositions comprising only molybdenum and compositions
comprising
only boron. It has now been found that the occurrence of LSPI in engines can
be reduced
by lubricating the crankcase with lubricating oil compositions comprising at
least 150
ppm by weight molybdenum and at least 150 ppm by weight boron, based on the
weight
of the lubricating oil composition, compared to lubricating the crankcase with
lubricating
oil compositions comprising less than 150 ppm by weight molybdenum and less
than 150
ppm by weight boron. Surprisingly, the present inventors have found that the
method and
use of the first and second aspects of the invention is effective at reducing
LSPI event
frequency even when the lubricating oil composition comprises a significant
amount of
calcium, for example when the lubricating oil composition additionally
comprises at least
0.08 wt.% calcium, based on the weight of the lubricating oil composition.
Preferably, the engine of the method of the first aspect of the invention,
and/or the
use of the second aspect of the invention, is an engine that generates a break
mean
effective pressure level of greater than 1,500 kPa, optionally greater than
2,000 kPa, at engine speeds of from 1,000 to 2,500 rotations per minute (rpm),
optionally
from 1,000 to 2,000 rpm.
Optionally, the lubricating oil composition of all aspects of the invention
comprises at least 175 ppm molybdenum, preferably at least 300 ppm molybdenum,
optionally at least 350 ppm molybdenum, such as at least 500 ppm molybdenum,
for
example at least 700 ppm molybdenum, by weight, based on the weight of the
lubricating
oil composition. Optionally, the lubricating oil composition comprises no more
than
1500 ppm molybdenum, preferably no more than 1400 ppm molybdenum, such as no
more than 1200 ppm molybdenum, for example no more than 1100 ppm molybdenum,
optionally no more than 1000 ppm molybdenum, by weight, based on the weight of
the
lubricating oil composition. Optionally, the lubricating oil composition
comprises from
150 to 1500 ppm molybdenum, preferably from 175 to 1500 ppm molybdenum,
optionally from 300 to 1400 ppm molybdenum, such as from 350 to 1200 ppm
molybdenum, for example from 500 to 1100 ppm molybdenum, optionally from 700
to
1000 ppm molybdenum, by weight, based on the weight of the lubricating oil
composition.
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Optionally, the lubricating oil composition comprises at least 200 ppm boron,
preferably at least 300 ppm boron, such as at least 400 ppm boron, by weight,
based on
the weight of the lubricating oil composition. Optionally, the lubricating oil
composition
comprises no more than 1500 ppm boron, preferably no more than 1000 ppm boron,
such
as no more than 800 ppm boron, by weight, based on the weight of the
composition.
Optionally, the lubricating oil composition comprises from 150 to 1500 ppm
boron,
preferably from 200 to 1000 ppm boron, optionally from 400 to 800 ppm boron,
by
weight, based on the weight of the lubricating oil composition.
It will be understood that the boron-containing additive may be any suitable
oil-
soluble compound or oil-dispersible compound. Boron-containing additives may
be
prepared by reacting a boron compound with an oil-soluble or oil-dispersible
additive or
compound. Boron compounds include boron oxide, boron oxide hydrate, boron
trioxide,
boron trifluoride, boron tribromide, boron trichloride, boron acid such as
boronic acid,
boric acid, tetraboric acid and metaboric acid, boron hydrides, boron amides
and various
esters of boron acids. For example, the boron-containing additive may be one
or more of
a borated dispersant; a borated dispersant viscosity index improver; an alkali
metal or a
mixed alkali metal or an alkaline earth metal borate; a borated overbased
metal detergent;
a borated epoxide; a borate ester; a sulfurised borate ester; and a borate
amide.
Preferably, the boron-containing additive is one or more of a borated
dispersant, a borate
ester or a borated overbased metal detergent. Optionally, the borated
overbased metal
detergent, if present, is a borated overbased metal detergent having a TBN of
at least150,
such as a borated overbased calcium detergent having a TBN of at least 150.
Borated dispersants may be prepared by boration of succinimide, succinic
ester,
benzylamine and their derivatives, each of which has an alkyl or alkenyl group
of
molecular weight of 700 to 3000. Processes for manufacture of these additives
are
known to those skilled in the art. A preferred amount of boron contained in
these
dispersants is 0.1 to 5 mass % (especially 0.2 to 2 mass %). A particularly
preferable
borated dispersant is a succinimide derivative of boron, for example borated
polyisobutenyl succinimide. An example of a borated dispersant is a borated
polyisobutenyl succinimide wherein the average number molecular weight (Mn) of
the
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polybutenyl backbone is in the range from 700 to 1250. Additionally or
alternatively,
borated dispersants are made by borating the ashless dispersants described
below, using
known borating means and techniques.
Ashless dispersants are non-metallic organic materials that form substantially
no
ash on combustion, in contrast to metal-containing, and hence ash-forming,
materials.
They comprise a long chain hydrocarbon with a polar head, the polarity being
derived
from inclusion of, e.g. an 0, P or N atom. The hydrocarbon is an oleophilic
group that
confers oil-solubility, having, for example 40 to 500 carbon atoms. Thus,
ashless
dispersants may comprise an oil-soluble polymeric hydrocarbon backbone having
functional groups that are capable of associating with particles to be
dispersed.
Typically, dispersants comprise amine, alcohol, amide, or ester polar moieties
attached to
the polymer backbone often via a bridging group. Ashless dispersants may be,
for
example, selected from oil-soluble salts, esters, amino-esters, amides,
imides, and
oxazolines of long chain hydrocarbon-substituted mono- and dicarboxylic acids
or their
anhydrides; thiocarboxylate derivatives of a long chain of hydrocarbons; long
chain
aliphatic hydrocarbons having a polyamine attached directly thereto, and
Mannich
condensation products formed by condensing a long chain substituted phenol
with
formaldehyde and alkylene polyamine, such as described in US-A-3, 442, 808.
The oil-
soluble polymeric hydrocarbon backbone is typically an olefin polymer or
polyene,
especially a polymer comprising a major molar amount (i.e. greater than 50
mole %) of a
C2 to Cis olefin (e.g. ethylene, propylene, butylenes, isobutylene, pentene,
octane-1,
styrene), and typically a C2 to C5 olefin. The oil-soluble polymeric
hydrocarbon
backbone may be homopolymeric (e.g. comprising a copolymer of ethylene and an
alpha-
olefin such as propylene or butylenes, or a copolymer of two different alpha-
olefins). A
preferred class of olefin polymers comprises polybutenes, specifically
polyisobutenes
(PIB) or poly-n-butenes, such as may be prepared by polymerization of a C4
refinery
stream. Other classes of olefin polymers include ethylene alpha-olefin (EAO)
copolymers and alpha-olefin homo- and copolymers.
Ashless dispersants include, for example, derivatives of long chain
hydrocarbon-
substituted carboxylic acids, examples being derivatives of high molecular
weight
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hydrocarbyl-substituted succinic acid. A noteworthy group of dispersants are
hydrocarbon- substituted succinimides, made, for example, by reacting the
above acids
(or derivatives) with a nitrogen-containing compound, advantageously a
polyalkylene
polyamine, such as polyethylene polyamine. Particularly preferred are the
reaction
products of polyalkylene polyamines with alkenyl succinic anhydrides, such as
described
in US-A-3, 202, 678; -3, 154, 560; -3, 172,892; -3, 024, 195, -3, 024, 237; -
3,219,666;
and -3,216,936; and BE-A-66,875. Preferred dispersants are polyalkene-
substituted
succinimides wherein the polyalkene group has a number-average molecular
weight in
the range of 900 to 5,000. The number-average molecular weight is measured by
gel
permeation chromatography (GPC). The polyalkene group may comprise a major
molar
amount (i.e. greater than 50 mole %) of a C2 to C18 alkene, e.g. ethene,
propene, butene,
isobutene, pentene, octane-1 and styrene. Preferably, the alkene is a C2 to CS
alkene;
more preferably it is butene or isobutene, such as may be prepared by
polymerisation of a
C4 refinery stream. Most preferably, the number average molecular weight of
the
polyalkene group is in the range of 950 to 2,800.
The above ashless dispersants are post-treated with boron to form a borated
dispersant in ways known in the art, such as described in US-A-3,087,936, US-A-
3,254,025 and US-A-5,430,105. Boration may for example be accomplished by
treating
an acyl nitrogen-containing dispersant with a boron compound selected from
boron
oxide, boron halides, boron acids and esters of boron acids, in an amount
sufficient to
provide from about 0.1 to about 20 atomic proportions of boron for each mole
of ashless
dispersant.
Alkali metal and alkaline earth metal borates are generally hydrated
particulate
metal borates, which are known in the art. Alkali metal borates include mixed
alkali and
alkaline earth metal borates. These metal borates are available commercially.
Representative patents describing suitable alkali metal and alkaline earth
metal borates
and their methods of manufacture include U.S. 3,997,454; 3,819,521; 3,853.772;
3,907,601; 3,997,454; and 4,089,790.
Borated amines may be prepared by reacting one or more of the above boron
compounds with one or more of fatty amines, e.g., an amine having from four to
eighteen
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carbon atoms. They may be prepared by reacting the amine with the boron
compound at
a temperature in the range of from 50 to 300 C, preferably from 100 to 250 C,
and at a
ratio from 3:1 to 1:3 equivalents of amine to equivalents of boron compound.
Borated epoxides are generally the reaction product of one or more of the
above
boron compounds with at least one epoxide. The epoxide is generally an
aliphatic
epoxide having from 8 to 30, preferably from 10 to 24, more preferably from 12
to 20,
carbon atoms. Examples of useful aliphatic epoxides include heptyl epoxide and
octyl
epoxide. Mixtures of epoxides may also be used, for instance commercial
mixtures of
epoxides having from 14 to 16 carbon atoms and from 14 to 18 carbon atoms. The
borated fatty epoxides are generally known and are described in U.S. Patent
4,584,115.
Borate esters may be prepared by reacting one or more of the above boron
compounds with one or more alcohols of suitable oleophilicity. Typically, the
alcohols
contain from 6 to 30, or from 8 to 24, carbon atoms. The methods of making
such borate
esters are known in the art. The borate esters can be borated phospholipids.
Such
compounds, and processes for making such compounds, are described in EP-A-0
684
298. Examples of sulfurised borated esters are also known in the art: see EP-A-
0 285
455 and US-B-6,028,210. Alternatively, it may be that a borate ester is
substantially
absent in the lubricating oil compositions of the method or use of the present
invention.
Borated overbased metal detergents are known in the art where the borate
substitutes the carbonate in the core either in part or in full. Borated
detergents may be
prepared by any conventional method, for example, a borated detergent may be
prepared
by treating a metal detergent with boric acid. Suitable borated detergents and
methods of
preparing them are disclosed in US 3,480,548, US 3,679,584, US 3,829,381, US
3,909,691 and US 4, 965,004.
Preferably, at least a portion of the boron content of the lubricating oil
composition is provided by a boron-containing dispersant additive, such as a
major
portion. In an embodiment of the invention, 100 wt.% of the boron in the
lubricating oil
composition, based on the weight of the boron in the lubricating oil
composition, is
provided by one or more boron-containing dispersant additives.
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Alternatively or in addition, at least a portion of the boron content of the
lubricating oil composition is provided by a borated detergent.
Additionally or alternatively, at least a portion of the boron content of the
lubricating oil composition is provided by a borate ester.
In an embodiment of the invention, at least a portion of the boron content of
the
lubricating oil composition is provided by a boron-containing compound that is
not a
dispersant, such as a major portion.
Optionally, 100 wt.% of the boron in the lubricating oil composition, based on
the
weight of the boron in the lubricating oil composition is provided by one or
more non-
dispersant boron-containing compounds, such as a borated detergent and/or a
borate
ester. Optionally, from 20 wt.% to 100 wt.%, preferably from 40 wt.% to 80
wt.%, such
as from 50 wt.% to 70 wt.%, of the boron in the lubricating oil composition,
based on the
weight of the boron in the lubricating oil composition, is provided by one or
more borated
detergent(s) and/or borate ester(s).
It will be understood that the molybdenum-containing additive may be any
suitable oil-soluble or oil-dispersible organo-molybdenum compound.
Preferably, 100
wt.% of the molybdenum content of the lubricating oil composition is provided
by an
organo-molybdenum compound, based on the weight of the lubricating oil
composition.
Such molybdenum-containing additives generally exhibit friction modifying
properties
when present in a lubricating oil composition. Additionally or alternatively,
such
molybdenum-containing additives may also provide antioxidant and anti-wear
credits to a
lubricating oil composition.
To enable the molybdenum compound to be oil-soluble or oil-dispersible, one or
more ligands are typically bonded to a molybdenum atom in the compound. The
bonding
of the ligands includes bonding by electrostatic interaction as in the case of
a counter-ion
and forms of bonding intermediate between covalent and electrostatic bonding.
Ligands
within the same compound may be differently bonded. For example, a ligand may
be
covalently bonded and another ligand may be electrostatically bonded.
Preferably, the or
each ligand is monoanionic and examples of such ligands are dithiophosphates,
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dithiocarbamates, xanthates, carboxylates, thioxanthates, phosphates and
hydrocarbyl,
preferably alkyl, derivatives thereof.
The molybdenum-containing additive may be mono-, di-, tri- or tetra-nuclear.
Di-
nuclear and tri-nuclear molybdenum compounds are preferred. In the event that
the
compound is polynuclear, the compound contains a molybdenum core consisting of
non-
metallic atoms, such as sulfur, oxygen and selenium, preferably consisting
essentially of
sulfur.
In a preferred embodiment, the molybdenum compound is a molybdenum-sulfur
compound. Preferably, the ratio of the number of molybdenum atoms, for
example, in
the core in the event that the molybdenum-sulfur compound is a polynuclear
compound,
to the number of monoanionic ligands, which are capable of rendering the
compound oil-
soluble or oil-dispersible, is greater than 1 to 1, such as at least 3 to 2.
The molybdenum-
sulfur compound's oil-solubility or oil-dispersibility may be influenced by
the total
number of carbon atoms present among all of the compound's ligands. The total
number
of carbon atoms present among all of the hydrocarbyl groups of the compound's
ligands
typically will be at least 21, e.g. 21 to 800, such as at least 25, at least
30 or at least 35.
For example, the number of carbon atoms in each alkyl group will generally
range
between 1 to 100, preferably 1 to 40, and more preferably between 3 and 20.
Examples of suitable organo-molybdenum compounds include molybdenum
dithiocarbamates, molybdenum dithiophosphates, molybdenum dithiophosphinates,
molybdenum xanthates, molybdenum thioxanthates, molybdenum sulfides, and the
like,
and mixtures thereof. Particularly preferred are molybdenum dithiocarbamates,
molybdenum dialkyldithiophosphates, molybdenum alkyl xanthates and molybdenum
alkylthioxanthates. An especially preferred organo-molybdenum compound is a
molybdenum dithiocarbamate. In an embodiment of the present invention the oil-
soluble
or oil-dispersible molybdenum compound consists of either a molybdenum
dithiocarbamate or a molybdenum dithiophosphate or a mixture thereof, as the
sole
source of molybdenum atoms in the lubricating oil composition. In an
alternative
embodiment of the present invention the oil-soluble or oil-dispersible
molybdenum
CA 3018827 2018-09-27
14
compound consists of a molybdenum dithiocarbamate, as the sole source of
molybdenum
atoms in the lubricating oil composition.
Suitable dinuclear or dimeric molybdenum dialkyldithiocarbamate are
represented
by the following formula:
RiS Xi s , x4
I A2 I
/R3
N
C, MO MO ,C ¨N
/
R2 X3 R4
Ri through R4 independently denote a straight chain, branched chain or
aromatic
hydrocarbyl group having 1 to 24 carbon atoms; and X1 through X4 independently
denote
an oxygen atom or a sulfur atom. The four hydrocarbyl groups, RI through R4,
may be
identical or different from one another.
Other molybdenum-containing additives useful in the compositions of this
invention are organo-molybdenum compounds of the formulae Mo(ROCS2)4 and
Mo(RSCS2)4, wherein R is an organo group selected from the group consisting of
alkyl,
aryl, aralkyl and alkoxyalkyl, generally of from 1 to 30 carbon atoms, and
preferably 2 to
12 carbon atoms and most preferably alkyl of 2 to 12 carbon atoms. Especially
preferred
are the dialkyldithiocarbamates of molybdenum.
In a preferred embodiment, the molybdenum-containing additive is an oil-
soluble
or oil-dispersible trinuclear molybdenum-sulfur compound. Examples of
tinuclear
molybdenum-sulfur compounds are disclosed in W098/26030, W099/31113,
W099/66013, EP-A-1 138 752, EP-A-1 138 686 and European patent application no.
02078011, particularly with respect to the characteristics of the molybdenum
compound
or additive disclosed therein.
Suitable tri-nuclear organo-molybdenum compounds include those of the formula
Mo3SkLnQz and mixtures thereof wherein L are independently selected ligands
having
organo groups with a sufficient number of carbon atoms to render the compound
soluble
or dispersible in the oil, n is from 1 to 4, k varies from 4 through 7, Q is
selected from the
Date Recue/Date Received 2022-09-20
15
group of neutral electron donating compounds such as water, amines, alcohols,
phosphines, and ethers, and z ranges from 0 to 5 and includes non-
stoichiometric values.
At least 21 total carbon atoms should be present among all the ligands' organo
groups,
such as at least 25, at least 30, or at least 35 carbon atoms.
The ligands are independently selected from the group of:
¨X¨ R 1,
XI\
R 2,
X2
\ zR
X2
and mixtures thereof, wherein X, Xi, X2, and Y are independently selected from
the group of oxygen and sulfur, and wherein RI, R2, and R are independently
selected
from hydrogen and organo groups that may be the same or different. Preferably,
the
organo groups are hydrocarbyl groups such as alkyl (e.g., in which the carbon
atom
attached to the remainder of the ligand is primary or secondary), aryl,
substituted aryl and
ether groups. More preferably, each ligand has the same hydrocarbyl group.
Importantly, the organo groups of the ligands have a sufficient number of
carbon atoms
to render the compound soluble or dispersible in the oil. For example, the
number of
carbon atoms in each group will generally range between about 1 to about 100,
preferably
from about 1 to about 30, and more preferably between about 4 to about 20.
Preferred
ligands include dialkyldithiophosphate, alkylxanthate, and
dialkyldithiocarbamate, and of
these dialkyldithiocarbamate is more preferred. Organic ligands containing two
or more
of the above functionalities are also capable of serving as ligands and
binding to one or
more of the cores. Those skilled in the art will realize that formation of the
compounds
of the lubricating oil composition of the present invention requires selection
of ligands
having the appropriate charge to balance the core's charge.
CA 3018827 2018-09-27
16
Particularly suitable molybdenum-containing additives include compounds having
the formula Mo3SkLnQz, having cationic cores surrounded by anionic ligands and
being
represented by structures such as
8 ¨T
le, v 8
Mo ./1 >
and
and having net charges of +4. Consequently, in order to solubilize these cores
the
total charge among all the ligands must be -4. Four mono-anionic ligands are
preferred.
Without wishing to be bound by any theory, it is believed that two or more tri-
nuclear
cores may be bound or interconnected by means of one or more ligands and the
ligands
may be multidentate. This includes the case of a multidentate ligand having
multiple
connections to a single core. It is believed that oxygen and/or selenium may
be
substituted for sulfur in the core(s).
Additionally or alternatively, particularly suitable trinuclear molybdenum-
containing additives may be represented by the formula Mo3SkE,LnAnQz, wherein:
k is an integer of at least 1;
E represents a non-metallic atom selected from oxygen and selenium;
x can be 0 or an integer, and preferably k + x is at least 4, more preferably
in the
range of 4 to 10, such as 4 to 7, most preferably 4 or 7;
L represents a ligand that confers oil-solubility or oil-dispersibility on the
molybdenum-sulfur compound, preferably L is a monoanionic ligand;
n is an integer in the range of 1 to 4;
A represents an anion other than L, if L is an anionic ligand;
p can be 0 or an integer;
Q represents a neutral electron-donating compound; and
z is in the range of 0 to 5 and includes non-stoichiometric values.
Those skilled in the art will realise that formation of the trinuclear
molybdenum-
sulfur compound will require selection of appropriate ligands (L) and other
anions (A),
CA 3018827 2018-09-27
17
depending on, for example, the number of sulfur and E atoms present in the
core, i.e. the
total anionic charge contributed by sulfur atom(s), E atom(s), if present, L
and A, if
present, must be ¨12. Examples of Q include water, alcohol, amine, ether and
phosphine.
It is believed that the electron-donating compound, Q, is merely present to
fill any vacant
coordination sites on the trinuclear molybdenum-sulfur compound. Examples of A
can
be of any valence, for example, monovalent and divalent and include disulfide,
hydroxide, alkoxide, amide and, thiocyanate or derivative thereof; preferably
A
represents a disulfide ion. Preferably, L is monoanionic ligand, such as
dithiophosphates,
dithiocarbamates, xanthates, carboxylates, thioxanthates, phosphates and
hydrocarbyl,
preferably alkyl, derivatives thereof. When n is 2 or more, the ligands can be
the same or
different. In an embodiment, independently of the other embodiments, k is 4 or
7, n is
either 1 or 2, L is a monoanionic ligand, p is an integer to confer electrical
neutrality on
the compound based on the anionic charge on A and each of x and z is 0.
In a further embodiment, independently of the other embodiments, k is 4 or 7,
L is
a monoanionic ligand, n is 4 and each of p, x and z is 0.
In another embodiment, the molybdenum-containing additive comprises trinuclear
molybdenum core and bonded thereto a ligand, preferably a mono-anionic ligand,
such as
a dithiocarbamate, capable of rendering the core oil-soluble or oil-
dispersible. For the
avoidance of doubt, the molybdenum-containing additive may also comprise
either
negatively charged molybdenum species or positively charged molybdenum species
or
both negatively and positively charged molybdenum species.
The molybdenum-sulfur cores, for example, the structures depicted in (I) and
(II)
above, may be interconnected by means of one or more ligands that are
multidentate, i.e.
a ligand having more than one functional group capable of binding to a
molybdenum
atom, to form oligomers. Molybdenum-sulfur additives comprising such oligomers
are
considered to fall within the scope of the lubricating oil compositions of
this invention.
Oil-soluble or oil-dispersible tri-nuclear molybdenum-containing additives can
be
prepared by reacting in the appropriate liquid(s)/solvent(s) a molybdenum
source such as
(NI-14)2Mo3S n.n(H20), where n varies between 0 and 2 and includes non-
stoichiometric
values, with a suitable ligand source such as a tetralkylthiuram disulfide.
Other oil-
CA 3018827 2018-09-27
18
soluble or dispersible tri-nuclear molybdenum-containing additives can be
formed during
a reaction in the appropriate solvent(s) of a molybdenum source such as of
(NH4)2Mo3Si3.n(H20), a ligand source such as tetralkylthiuram disulfide,
dialkyldithiocarbamate, or dialkyldithiophosphate, and a sulfur abstracting
agent such as
cyanide ions, sulfite ions, or substituted phosphines. Alternatively, a tri-
nuclear
molybdenum-sulfur halide salt such as [M12[Mo3S7A61, where M' is a counter
ion, and A
is a halogen such as Cl, Br, or I, may be reacted with a ligand source such as
a
dialkyldithiocarbamate or dialkyldithiophosphate in the appropriate
liquid(s)/solvent(s) to
form an oil-soluble or dispersible trinuclear molybdenum compound. The
appropriate
liquid/solvent may be, for example, aqueous or organic.
A compound's oil solubility or dispersibility may be influenced by the number
of
carbon atoms in the ligand's organo groups. Preferably, at least 21 total
carbon atoms
should be present among all the ligands' organo groups. Preferably, the ligand
source
chosen has a sufficient number of carbon atoms in its organo groups to render
the
compound soluble or dispersible in the lubricating composition.
Other examples of molybdenum compounds include molybdenum carboxylates
and molybdenum nitrogen complexes, both of which may be sulfurised.
Alternatively, the molybdenum-containing additive may be an acidic
molybdenum compound. These compounds will react with a basic nitrogen compound
as
measured by ASTM test D-664 or D-2896 titration procedure and are typically
hexavalent. Included are molybdic acid, ammonium molybdate, sodium molybdate,
potassium molybdate, and other alkaline metal molybdates and other molybdenum
salts,
e.g., hydrogen sodium molybdate, Mo0C14, MoO2Br2, Mo203C16, molybdenum
trioxide
or similar acidic molybdenum compounds.
Alternatively, the lubricating oil compositions of the present invention can
be
provided with molybdenum by molybdenum/sulfur complexes of basic nitrogen
compounds as described, for example, in U.S. Patent Nos. 4,263,152; 4,285,822;
4,283,295; 4,272,387; 4,265,773; 4,261,843; 4,259,195 and 4,259,194; and WO
94/06897.
CA 3018827 2018-09-27
19
Optionally, the lubricating oil composition comprises one or more molybdenum-
containing compounds that is not a friction modifier additive (for example
that is not used
as a friction modifier additive). Optionally, at least a portion of the
molybdenum content
of the lubricating oil composition is provided by a molybdenum-containing
compound
that is not a friction modifier, such as a major portion.
Optionally, the lubricating oil composition of all embodiments of the present
invention has a calcium content of at least 0.08 wt.%, based on the weight of
the
lubricating oil composition. The lubricating oil composition of all aspects of
the
invention may have a calcium content of at least 0.10 wt.%, preferably at
least 0.15 wt.%,
for example at least 0.18 wt.%, based on the weight of the lubricating oil
composition.
Optionally, the lubricating oil composition of all aspects of the invention
has a calcium
content of from 0.08 wt.% to 0.8 wt.%, preferably from 0.10 wt.% to 0.6 wt.%,
for
example from 0.15 wt.% to 0.5 wt.%, such as from 0.18 wt.% to 0.3 wt.%, based
on the
weight of the lubricating oil composition. It will be appreciated that it is
particularly
advantageous to utilise LSPI-reducing additives in lubricating oil
compositions
containing higher concentrations of calcium.
Optionally, the lubricating oil composition has a magnesium content of no more
than 0.12 wt.%, such as no more than 0.6 wt.%, for example no more than 0.03
wt.%,
based on the weight of the lubricating oil composition. Optionally, the
lubricating oil
composition is substantially free from magnesium, for example having a
magnesium
content of about 0.0 wt.%, based on the weight of the lubricating oil
composition.
Lubricating oil compositions suitable for use as passenger car motor oils
conventionally comprise a major amount of oil of lubricating viscosity and
minor
amounts of performance enhancing additives, including detergents. Metal-
containing or
ash-forming detergents function as both detergents to reduce or remove
deposits and as
acid neutralizers or rust inhibitors, thereby reducing wear and corrosion and
extending
engine life. Detergents generally comprise a polar head with a long
hydrophobic tail.
The polar head comprises a metal salt of an acidic organic compound. The salts
may
contain a substantially stoichiometric amount of the metal in which case they
are usually
described as normal or neutral salts, and have a total base number or TBN (as
can be
CA 3018827 2018-09-27
20
measured by ASTM D2896) of from 0 to less than 150, such as 0 to about 80 or
100. A
large amount of a metal base may be incorporated by reacting excess metal
compound
(e.g., an oxide or hydroxide) with an acidic gas (e.g., carbon dioxide). The
resulting
overbased detergent comprises neutralized detergent as the outer layer of a
metal base
(e.g carbonate) micelle. Such overbased detergents have a TBN of 150 or
greater, and
typically will have a TBN of from 250 to 450 or more.
Optionally, the lubricating oil composition comprises a detergent, for example
a
calcium detergent. Optionally, the detergent is a borated calcium detergent.
Examples of
suitable borated calcium detergents include, but are not limited to, one or
more borated
calcium sulfonate detergent, one or more borated calcium salicylate detergent,
or a
mixture thereof. Preferably, such borated calcium detergents are overbased
borated
calcium detergents. Such borated calcium detergents may be prepared by any
conventional method. For example, it may be that the borated calcium detergent
is
prepared by treating a calcium detergent with boric acid. Suitable borated
calcium
detergents and methods of preparing such borated calcium detergents are
disclosed in US
3,480,548, US 3,679,584, US 3,829,381, US 3,909,691 and US 4, 965,004.
Optionally,
the detergent is an overbased calcium detergent, for example having a Total
Base
Number (TBN) of at least 150, preferably at least 200. Preferably, the
overbased calcium
detergent has a TBN of from 200 to 450. It will be appreciated that the
composition
optionally includes one or more additional detergents, such as a detergent
that is not an
overbased calcium detergent having a TBN of at least 150. For example, it may
be that
the composition comprises a detergent package comprising the overbased calcium
detergent. The detergent is preferably used in an amount providing the
lubricating oil
composition with a TBN of from about 4 to about 10 mg KOH/g, preferably from
about 5
to about 8 mg KOH/g. Preferably, overbased detergents based on metals other
than
calcium are present in amounts contributing no greater than 60%, such as no
greater than
50% or no greater than 40% of the TBN of the lubricating oil composition
contributed by
overbased detergent. Preferably, lubricating oil compositions of the present
invention
contain non-calcium-based overbased ash-containing detergents in amounts
providing no
greater than about 40% of the total TBN contributed to the lubricating oil
composition by
CA 3018827 2018-09-27
21
overbased detergent. Combinations of overbased calcium detergents may be used
(e.g.,
comprising two or more of an overbased calcium phenate, an overbased calcium
salicylate and an overbased calcium sulfonate; or comprising two or more
calcium
detergents each having a different TBN of greater than 150). Preferably, the
detergent
will have, or have on average, a TBN of at least about 200, such as from about
200 to
about 500; preferably at least about 250, such as from about 250 to about 500;
more
preferably at least about 300, such as from about 300 to about 450.
Calcium detergents that may be used in all aspects of the present invention
include, oil-soluble neutral and overbased sulfonates, phenates, sulfurized
phenates,
thiophosphonates, salicylates, and naphthenates and other oil-soluble
carboxylates of
calcium. It will be appreciated that suitable calcium detergents may also
comprise other
metals, particularly alkali or alkaline earth metals, e.g., barium, sodium,
potassium,
lithium, calcium, and/or magnesium. The most commonly used additional metals
are
magnesium and sodium, either of which or both may be present in the calcium
detergent
and/or the borated calcium detergent. The detergent may optionally comprise
combinations of detergents, whether overbased or neutral or both.
Sulfonates may be prepared from sulfonic acids which are typically obtained by
the sulfonation of alkyl substituted aromatic hydrocarbons such as those
obtained from
the fractionation of petroleum or by the alkylation of aromatic hydrocarbons.
Examples
include those obtained by alkylating benzene, toluene, xylene, naphthalene,
diphenyl or
their halogen derivatives such as chlorobenzene, chlorotoluene and
chloronaphthalene.
The alkylation may be carried out in the presence of a catalyst with
alkylating agents
having from about 3 to more than 70 carbon atoms. The alkaryl sulfonates
usually
contain from about 9 to about 80 or more carbon atoms, preferably from about
16 to
about 60 carbon atoms per alkyl substituted aromatic moiety.
The oil soluble sulfonates or alkaryl sulfonic acids may be neutralized with
oxides, hydroxides, alkoxides, carbonates, carboxylate, sulfides,
hydrosulfides, nitrates,
borates and ethers of the metal. The amount of metal compound is chosen having
regard
to the desired TBN of the final product but typically ranges from about 100 to
220 mass
% (preferably at least 125 mass %) of that stoichiometrically required.
CA 3018827 2018-09-27
22
Metal salts of phenols and sulfurized phenols are prepared by reaction with an
appropriate metal compound such as an oxide or hydroxide and neutral or
overbased
products may be obtained by methods well known in the art. Sulfurized phenols
may be
prepared by reacting a phenol with sulfur or a sulfur containing compound such
as
hydrogen sulfide, sulfur monohalide or sulfur dihalide, to final products
which are
generally mixtures of compounds in which 2 or more phenols are bridged by
sulfur
containing bridges.
Carboxylate detergents, e.g., salicylates, can be prepared by reacting an
aromatic
carboxylic acid with an appropriate metal compound such as an oxide or
hydroxide and
neutral or overbased products may be obtained by methods well known in the
art. The
aromatic moiety of the aromatic carboxylic acid can contain hetero-atoms, such
as
nitrogen and oxygen. Preferably, the moiety contains only carbon atoms; more
preferably the moiety contains six or more carbon atoms; for example benzene
is a
preferred moiety. The aromatic carboxylic acid may contain one or more
aromatic
moieties, such as one or more benzene rings, either fused or connected via
alkylene
bridges. The carboxylic moiety may be attached directly or indirectly to the
aromatic
moiety. Preferably the carboxylic acid group is attached directly to a carbon
atom on the
aromatic moiety, such as a carbon atom on the benzene ring. More preferably,
the
aromatic moiety also contains a second functional group, such as a hydroxy
group or a
sulfonate group, which can be attached directly or indirectly to a carbon atom
on the
aromatic moiety.
Preferred examples of aromatic carboxylic acids are salicylic acids and
sulfurized
derivatives thereof, such as hydrocarbyl substituted salicylic acid and
derivatives thereof.
Processes for sulfurizing, for example a hydrocarbyl-substituted salicylic
acid, are known
to those skilled in the art. Salicylic acids are typically prepared by
carboxylation, for
example, by the Kolbe-Schmitt process, of phenoxides, and in that case, will
generally be
obtained, normally in a diluent, in admixture with uncarboxylated phenol.
Preferred substituents in oil-soluble salicylic acids are alkyl substituents.
In alkyl-
substituted salicylic acids, the alkyl groups advantageously contain 5 to 100,
preferably 9
to 30, especially 14 to 20, carbon atoms. Where there is more than one alkyl
group, the
CA 3018827 2018-09-27
23
average number of carbon atoms in all of the alkyl groups is preferably at
least 9 to
ensure adequate oil solubility.
Detergents generally useful in the formulation of lubricating oil compositions
of
the invention also include "hybrid" detergents formed with mixed surfactant
systems,
e.g., phenate/salicylates, sulfonate/phenates, sulfonate/salicylates,
sulfonates/phenates/salicylates, as described, for example, in U.S. Patent
Nos. 6,153,565;
6,281,179; 6,429,178; and 6,429,178.
Optionally, the detergent comprises a calcium phenate, a calcium sulfonate
and/or
a calcium salicylate. Optionally, the detergent comprises a borated calcium
phenate, a
borated calcium sulfonate and/or a borated calcium salicylate, preferably a
borated
calcium salicylate.
Optionally, the detergent comprises a plurality of calcium detergents.
Optionally,
each calcium detergent is independently a calcium phenate, a calcium sulfonate
or a
calcium salicylate. Preferably, the detergent is substantially free from any
detergent that
is not a calcium detergent. In other words, it may be that the detergent
consists of one or
more calcium detergents. It will be appreciated that where a detergent is said
to be
substantially free from anything other than a particular type of detergent, or
is said to
consist of that particular type of detergent, the detergent may nevertheless
comprise trace
amounts of another material. For example, it may be that the detergent
comprises a trace
amount of another material left over from the preparation process used to make
the
detergent.
Optionally, at least 75 %, for example at least 90 %, such as at least 95 %,
of the
calcium content of the lubricating oil composition is provided by the
detergent. It may be
that when the calcium content of the lubricating composition is provided
principally by
the detergent, the detergent and LSPI characteristics of the composition can
be controlled
particularly effectively.
Optionally, the composition additionally comprises a further detergent.
Preferably, the further detergent is substantially free of calcium.
Optionally, the further
detergent comprises one or more phenate, sulfonate and/or salicylate
detergents. The
further detergent may be an overbased or neutral detergent. Optionally, the
further
CA 3018827 2018-09-27
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detergent comprises one or more neutral metal-containing detergents (having a
TBN of
less than 150). These neutral metal-based detergents may be magnesium salts or
salts of
other alkali or alkali earth metals, except calcium. Optionally, 100 % of the
metal
introduced into the lubricating oil composition by detergent is calcium. The
further
detergent may also contain ashless (metal-free) detergents such as oil-soluble
hydrocarbyl
phenol aldehyde condensates described, for example, in US 2005/0277559 Al.
Preferably, detergent in total is used in an amount providing the lubricating
oil
composition with from 0.2 to 2.0 mass %, such as from 0.35 to 1.5 mass % or
from 0.5 to
1.0 mass %, more preferably from about 0.6 to about 0.8 mass % of sulfated ash
(SASH).
Optionally, the composition comprises one or more additives from the list
consisting of: dispersants, corrosion inhibitors, antioxidants, pour point
depressants,
antifoaming agents, supplemental anti-wear agents, friction modifiers, and
viscosity
modifiers.
The oil of lubricating viscosity useful in the formulation of lubricating oil
compositions suitable for use in the practice of the invention may range in
viscosity from
light distillate mineral oils to heavy lubricating oils such as gasoline
engine oils, mineral
lubricating oils and heavy duty diesel oils. Generally, the viscosity of the
oil ranges from
about 2 mm2/sec (centistokes) to about 40 mm2/sec, especially from about 3
mm2/sec to
about 20 mm2/sec, most preferably from about 9 mm2/sec to about 17 mm2/sec,
measured
at 100 C.
Natural oils include animal oils and vegetable oils (e.g., castor oil, lard
oil); liquid
petroleum oils and hydrorefined, solvent-treated or acid-treated mineral oils
of the
paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of
lubricating
viscosity derived from coal or shale also serve as useful base oils.
Synthetic lubricating oils include hydrocarbon oils and halo-substituted
hydrocarbon oils such as polymerized and interpolymerized olefins (e.g.,
polybutylenes,
polypropylenes, propylene- isobutylene copolymers, chlorinated polybutylenes,
poly(1-
hexenes), poly(1-octenes), poly(1-decenes)); alkylbenzenes (e.g.,
dodecylbenzenes,
tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes); polyphenyls
(e.g.,
CA 3018827 2018-09-27
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biphenyls, terphenyls, alkylated polyphenols); and alkylated diphenyl ethers
and
alkylated diphenyl sulfides and derivatives, analogs and homologs thereof.
Alkylene oxide polymers and interpolymers and derivatives thereof where the
terminal hydroxyl groups have been modified by esterification, etherification,
etc.,
constitute another class of known synthetic lubricating oils. These are
exemplified by
polyoxyalkylene polymers prepared by polymerization of ethylene oxide or
propylene
oxide, and the alkyl and aryl ethers of polyoxyalkylene polymers (e.g., methyl-
polyiso-
propylene glycol ether having a molecular weight of 1000 or diphenyl ether of
poly-
ethylene glycol having a molecular weight of 1000 to 1500); and mono- and
polycarboxylic esters thereof, for example, the acetic acid esters, mixed C3-
C8 fatty acid
esters and C13 Oxo acid diester of tetraethylene glycol.
Another suitable class of synthetic lubricating oils comprises the esters of
dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids
and alkenyl
succinic acids, maleic acid, azelaic acid, suberic acid, sebasic acid, fumaric
acid, adipic
acid, linoleic acid dimer, malonic acid, alkylmalonic acids, alkenyl malonic
acids) with a
variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-
ethylhexyl
alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol).
Specific
examples of such esters includes dibutyl adipate, di(2-ethylhexyl) sebacate,
di-n-hexyl
fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl
phthalate,
didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester of linoleic
acid dimer, and
the complex ester formed by reacting one mole of sebacic acid with two moles
of
tetraethylene glycol and two moles of 2-ethylhexanoic acid. Also useful are
synthetic oils
derived from a gas to liquid process from Fischer-Tropsch synthesized
hydrocarbons,
which are commonly referred to as gas to liquid, or "GTL" base oils.
Esters useful as synthetic oils also include those made from C5 to C12
monocarboxylic acids and polyols and polyol esters such as neopentyl glycol,
trimethylolpropane, pentaerythritol, dipentaerythritol and tripentaerythritol.
Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- or
polyaryloxysilicone oils and silicate oils comprise another useful class of
synthetic
lubricants; such oils include tetraethyl silicate, tetraisopropyl silicate,
tetra-(2-
CA 3018827 2018-09-27
26
ethylhexyl)silicate, tetra-(4-methyl-2-ethylhexyl)silicate, tetra-(p-tert-
butyl-phenyl)
silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl)siloxanes and
poly(methylphenyl)siloxanes. Other synthetic lubricating oils include liquid
esters of
phosphorous-containing acids (e.g., tricresyl phosphate, trioctyl phosphate,
diethyl ester
of decylphosphonic acid) and polymeric tetrahydrofurans.
The oil of lubricating viscosity may comprise a Group I, Group II, Group III,
Group IV or Group V base stocks or base oil blends of the aforementioned base
stocks.
Preferably, the oil of lubricating viscosity is a Group II, Group III, Group
IV or Group V
base stock, or a mixture thereof, or a mixture of a Group I base stock and one
or more a
Group II, Group III, Group IV or Group V base stock. The base stock, or base
stock
blend preferably has a saturate content of at least 65%, more preferably at
least 75%,
such as at least 85%. Preferably, the base stock or base stock blend is a
Group III or
higher base stock or mixture thereof, or a mixture of a Group II base stock
and a Group
III or higher base stock or mixture thereof. Most preferably, the base stock,
or base stock
blend, has a saturate content of greater than 90 %. Preferably, the oil or oil
blend will
have a sulfur content of less than 1 mass %, preferably less than 0.6 mass %,
most
preferably less than 0.4 mass %, such as less than 0.3 mass %. In one
preferred
embodiment, at least 30 mass %, preferably at least 50 mass %, more preferably
at least
80 mass % of the oil of lubricating viscosity used in lubricating oil
compositions of the
present invention is Group III base stock, a Group IV base stock, or a mixture
of Group II
and Group IV base stocks.
Preferably the volatility of the oil or oil blend, as measured by the Noack
test
(ASTM D5800), is less than or equal to 30 mass %, such as less than about
25 mass %, preferably less than or equal to 20 mass %, more preferably less
than or equal
to 15 mass %, most preferably less than or equal 13 mass %. Preferably, the
viscosity
index (VI) of the oil or oil blend is at least 85, preferably at least 100,
most preferably
from about 105 to 140.
Definitions for the base stocks and base oils in the lubricating oil
compositions of
this invention are the same as those found in the American Petroleum Institute
(API)
publication "Engine Oil Licensing and Certification System", Industry Services
CA 3018827 2018-09-27
27
Department, Fourteenth Edition, December 1996, Addendum 1, December 1998. Said
publication categorizes base stocks as follows:
a) Group I base stocks contain less than 90 percent saturates and/or greater
than
0.03 percent sulfur and have a viscosity index greater than or equal to 80 and
less than
120 using the test methods specified in Table 1;
b) Group II base stocks contain greater than or equal to 90 percent saturates
and
less than or equal to 0.03 percent sulfur and have a viscosity index greater
than or equal
to 80 and less than 120 using the test methods specified in Table 1;
c) Group III base stocks contain greater than or equal to 90 percent saturates
and
less than or equal to 0.03 percent sulfur and have a viscosity index greater
than or equal
to 120 using the test methods specified in Table 1;
d) Group IV base stocks are polyalphaolefins (PAO); and,
e) Group V base stocks include all other base stocks not included in Group I,
II,
III, or IV.
Table 1 - Analytical Methods for Base Stock
Property Test Method
Saturates ASTM D 2007
Viscosity Index ASTM D 2270
Sulfur ASTM D 2622; ASTM D 4294; ASTM D 4927; ASTM D 3120
The lubricating oil compositions of all aspects of the present invention may
further comprise a phosphorus-containing compound.
A suitable phosphorus-containing compound includes dihydrocarbyl
dithiophosphate metal salts, which are frequently used as anti-wear and
antioxidant
agents. The metal may be an alkali or alkaline earth metal, or aluminum, lead,
tin,
molybdenum, manganese, nickel or copper. The zinc salts are most commonly used
in
lubricating oil in amounts of 0.1 to 10, preferably 0.2 to 2 mass %, based
upon the total
weight of the lubricating oil composition. They may be prepared in accordance
with
known techniques by first forming a dihydrocarbyl dithiophosphoric acid
(DDPA),
CA 3018827 2018-09-27
28
usually by reaction of one or more alcohol or a phenol with P2S5 and then
neutralizing the
formed DDPA with a zinc compound. For example, a dithiophosphoric acid may be
made by reacting mixtures of primary and secondary alcohols. Alternatively,
multiple
dithiophosphoric acids can be prepared where the hydrocarbyl groups on one are
entirely
secondary in character and the hydrocarbyl groups on the others are entirely
primary in
character. To make the zinc salt, any basic or neutral zinc compound could be
used but
the oxides, hydroxides and carbonates are most generally employed. Commercial
additives frequently contain an excess of zinc due to the use of an excess of
the basic zinc
compound in the neutralization reaction.
The preferred zinc dihydrocarbyl dithiophosphates are oil soluble salts of
dihydrocarbyl dithiophosphoric acids and may be represented by the following
formula:
RO
\
P ¨ S Zn
R.0
¨2
wherein R and R' may be the same or different hydrocarbyl radicals containing
from 1 to
18, preferably 2 to 12, carbon atoms and including radicals such as alkyl,
alkenyl, aryl,
arylalkyl, alkaryl and cycloaliphatic radicals. Particularly preferred as R
and R' groups
are alkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, for example,
be ethyl, n-
propyl, i-propyl, n-butyl, i-butyl, sec-butyl, amyl, n-hexyl, i-hexyl, n-
octyl, decyl,
dodecyl, octadecyl, 2-ethylhexyl, phenyl, butylphenyl, cyclohexyl,
methylcyclopentyl,
propenyl, butenyl. In order to obtain oil solubility, the total number of
carbon atoms (i.e.
R and R') in the dithiophosphoric acid will generally be about 5 or greater.
The zinc
dihydrocarbyl dithiophosphate (ZDDP) preferably comprises zinc dialkyl
dithiophosphates.
Lubricating oil compositions useful in the practice of the present invention
will
preferably contain a phosphorus-containing compound, in an amount introducing
from
0.01 to 0.12 wt.% of phosphorus, such as from 0.04 to 0.10 wt.% of phosphorus,
preferably, from 0.05 to 0.08 wt.% of phosphorus, based on the total mass of
the
CA 3018827 2018-09-27
29
lubricating oil composition into the lubricating oil composition. Optionally,
the
lubricating oil composition has a phosphorus content of no more than 0.1 wt.%
(1000ppm), for example no more than 0.09 wt.% (900ppm), preferably no more
than 0.08
wt.% (800ppm), based on the weight of the lubricating oil composition. In a
preferred
embodiment of the present invention, the lubricating oil composition has a
phosphorous
content of no greater than 0.06 wt.% (600 ppm).
Oxidation inhibitors or antioxidants reduce the tendency of mineral oils to
deteriorate in service. Oxidative deterioration can be evidenced by sludge in
the
lubricant, varnish-like deposits on the metal surfaces, and by viscosity
growth. Such
oxidation inhibitors include hindered phenols, alkaline earth metal salts of
alkylphenolthioesters having preferably C5 to C12 alkyl side chains, calcium
nonylphenol
sulfide, oil soluble phenates and sulfurized phenates, phosphosulfurized or
sulfurized
hydrocarbons or esters, phosphorous esters, metal thiocarbamates, oil soluble
copper
compounds as described in U.S. Patent No. 4,867,890, and molybdenum-containing
compounds.
Aromatic amines having at least two aromatic groups attached directly to the
nitrogen constitute another class of compounds that is frequently used for
antioxidancy.
Typical oil soluble aromatic amines having at least two aromatic groups
attached directly
to one amine nitrogen contain from 6 to 16 carbon atoms. The amines may
contain more
than two aromatic groups. Compounds having a total of at least three aromatic
groups in
which two aromatic groups are linked by a covalent bond or by an atom or group
(e.g., an
oxygen or sulfur atom, or a -CO-,
-S02- or alkylene group) and two are directly attached to one amine nitrogen
are also
considered aromatic amines having at least two aromatic groups attached
directly to the
nitrogen. The aromatic rings are typically substituted by one or more
substituents
selected from alkyl, cycloalkyl, alkoxy, aryloxy, acyl, acylamino, hydroxy,
and nitro
groups. The amount of any such oil soluble aromatic amines having at least two
aromatic
groups attached directly to one amine nitrogen should preferably not exceed
0.4 mass %.
Dispersants maintain in suspension materials resulting from oxidation during
use
that are insoluble in oil, thus preventing sludge flocculation and
precipitation, or
CA 3018827 2018-09-27
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deposition on metal parts. Optionally, the lubricating oil compositions used
according to
the present invention comprise at least one dispersant, and may comprise a
plurality of
dispersants. The dispersant or dispersants are preferably nitrogen-containing
dispersants
and preferably contribute, in total, from 0.05 to 0.19 mass %, such as from
0.06 to 0.18
mass %, most preferably from 0.07 to 0.16 mass % of nitrogen to the
lubricating oil
composition.
Dispersants useful in the context of the present invention include the range
of
nitrogen-containing, ashless (metal-free) dispersants known to be effective to
reduce
formation of deposits upon use in gasoline and diesel engines, when added to
lubricating
oils and comprise an oil soluble polymeric long chain backbone having
functional groups
capable of associating with particles to be dispersed. Typically, such
dispersants have
amine, amine-alcohol or amide polar moieties attached to the polymer backbone,
often
via a bridging group. The ashless dispersant may be, for example, selected
from oil
soluble salts, esters, amino-esters, amides, imides and oxazolines of long
chain
hydrocarbon-substituted mono- and poly-carboxylic acids or anhydrides thereof;
thiocarboxylate derivatives of long chain hydrocarbons; long chain aliphatic
hydrocarbons having polyamine moieties attached directly thereto; and Mannich
condensation products formed by condensing a long chain substituted phenol
with
formaldehyde and polyalkylene polyamine.
Generally, each mono- or di-carboxylic acid-producing moiety will react with a
nucleophilic group (amine or amide) and the number of functional groups in the
polyalkenyl-substituted carboxylic acylating agent will determine the number
of
nucleophilic groups in the finished dispersant.
The polyalkenyl moiety of dispersants useful in the present invention has a
number average molecular weight of from 700 to 3000, preferably between 950
and
3000, such as between 950 and 2800, more preferably from about 950 to 2500,
and most
preferably from 950 to 2400. In one embodiment of the invention, the
dispersant of the
lubricating oil composition comprises a combination of a lower molecular
weight
dispersant (e.g., having a number average molecular weight of from 700 to
1100) and a
high molecular weight dispersant having a number average molecular weight of
from at
CA 3018827 2018-09-27
31
least 1500, preferably between 1800 and 3000, such as between 2000 and 2800,
more
preferably from 2100 to 2500, and most preferably from 2150 to 2400. The
molecular
weight of a dispersant is generally expressed in terms of the molecular weight
of the
polyalkenyl moiety as the precise molecular weight range of the dispersant
depends on
numerous parameters including the type of polymer used to derive the
dispersant, the
number of functional groups, and the type of nucleophilic group employed.
The polyalkenyl moiety from which the high molecular weight dispersants are
derived preferably have a narrow molecular weight distribution (MWD), also
referred to
as polydispersity, as determined by the ratio of weight average molecular
weight (Mw) to
number average molecular weight (Mn). Specifically, polymers from which
dispersants
useful in the practice of the present invention are derived have a Mw/Mn of
from 1.5 to
2.0, preferably from 1.5 to 1.9, most preferably from 1.6 to 1.8.
Suitable hydrocarbons or polymers employed in the formation of dispersants
useful in the practice of the present invention include homopolymers,
interpolymers or
lower molecular weight hydrocarbons. One family of such polymers comprise
polymers
of ethylene and/or at least one C3 to C28 alpha-olefin having the formula
H2C=CHR1
wherein R' is straight or branched chain alkyl radical comprising 1 to 26
carbon atoms
and wherein the polymer contains carbon-to-carbon unsaturation, preferably a
high
degree of teiminal ethenylidene unsaturation. Preferably, such polymers
comprise
interpolymers of ethylene and at least one alpha-olefin of the above formula,
wherein R1
is alkyl of from 1 to 18 carbon atoms, and more preferably is alkyl of from 1
to 8 carbon
atoms, and more preferably still of from 1 to 2 carbon atoms. Therefore,
useful alpha-
olefin monomers and comonomers include, for example, propylene, butene-1,
hexene-1,
octene-1, 4-methylpentene-1, decene-1, dodecene-1, tridecene-1, tetradecene-1,
pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nonadecene-1, and
mixtures
thereof (e.g., mixtures of propylene and butene-1, and the like). Exemplary of
such
polymers are propylene homopolymers, butene-1 homopolymers, ethylene-propylene
copolymers, ethylene-butene-1 copolymers, propylene-butene copolymers and the
like,
wherein the polymer contains at least some telminal and/or internal
unsaturation.
Preferred polymers are unsaturated copolymers of ethylene and propylene and
ethylene
CA 3018827 2018-09-27
32
and butene-1. The interpolymers may contain a minor amount, e.g. 0.5 to 5 mole
% of a
C4 to Cu non-conjugated diolefin comonomer. However, it is preferred that the
polymers
used in the practice of the present invention comprise only alpha-olefin
homopolymers,
interpolymers of alpha-olefin comonomers and interpolymers of ethylene and
alpha-
olefin comonomers. The molar ethylene content of the polymers employed in this
invention is preferably in the range of 0 to 80 %, and more preferably 0 to 60
%. When
propylene and/or butene-1 are employed as comonomer(s) with ethylene, the
ethylene
content of such copolymers is most preferably between 15 and 50 %, although
higher or
lower ethylene contents may be present.
These polymers may be prepared by polymerizing alpha-olefin monomer, or
mixtures of alpha-olefin monomers, or mixtures comprising ethylene and at
least one C3
to C28 alpha-olefin monomer, in the presence of a catalyst system comprising
at least one
metallocene (e.g., a cyclopentadienyl-transition metal compound) and an
alumoxane
compound. Using this process, a polymer in which 95 % or more of the polymer
chains
possess terminal ethenylidene-type unsaturation can be provided. The
percentage of
polymer chains exhibiting terminal ethenylidene unsaturation may be determined
by
FTIR spectroscopic analysis, titration, or 13C NMR. Interpolymers of this
latter type may
be characterized by the formula POLY-C(RI)=CH2 wherein IV is CI to C26 alkyl,
preferably C1 to C18 alkyl, more preferably CI to Cs alkyl, and most
preferably CI to C2
alkyl, (e.g., methyl or ethyl) and wherein POLY represents the polymer chain.
The chain
length of the RI alkyl group will vary depending on the comonomer(s) selected
for use in
the polymerization. A minor amount of the polymer chains can contain terminal
ethenyl,
i.e., vinyl, unsaturation, i.e. ,POLY-CH=CH2, and a portion of the polymers
can contain
internal mono-unsaturation, e.g.
POLY-CH=CH(RI), wherein RI is as defined above. These terminally unsaturated
interpolymers may be prepared by known metallocene chemistry and may also be
prepared as described in U.S. Patent Nos. 5,498,809; 5,663,130; 5,705,577;
5,814,715;
6,022,929 and 6,030,930.
Another useful class of polymers is polymers prepared by cationic
polymerization
of isobutene, styrene, and the like. Common polymers from this class include
CA 3018827 2018-09-27
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polyisobutenes obtained by polymerization of a C4 refinery stream having a
butene
content of 35 to 75 mass %, and an isobutene content of 30 to 60 mass %, in
the presence
of a Lewis acid catalyst, such as aluminum trichloride or boron trifluoride. A
preferred
source of monomer for making poly-n-butenes is petroleum feedstreams such as
Raffinate II. These feedstocks are disclosed in the art such as in U.S. Patent
No.
4,952,739. Polyisobutylene is a most preferred backbone of the polymers useful
in the
practice of the present invention because it is readily available by cationic
polymerization
from butene streams (e.g., using A1C13 or BF3 catalysts). Such
polyisobutylenes generally
contain residual unsaturation in amounts of about one ethylenic double bond
per polymer
chain, positioned along the chain. A preferred embodiment utilizes
polyisobutylene
prepared from a pure isobutylene stream or a Raffinate I stream to prepare
reactive
isobutylene polymers with terminal vinylidene olefins. Preferably, these
polymers,
referred to as highly reactive polyisobutylene (HR-PIB), have a terminal
vinylidene
content of at least 65%, e.g., 70%, more preferably at least 80%, most
preferably, at least
85%. The preparation of such polymers is described, for example, in U.S.
Patent No.
4,152,499. HR-PIB is known and HR-PIB is commercially available under the
tradenames GlissopalTM (from BASF).
Polyisobutylene polymers that may be employed are generally based on a
hydrocarbon chain of from 700 to 3000. Methods for making polyisobutylene are
known. Polyisobutylene can be functionalized by halogenation (e.g.
chlorination), the
thermal "ene" reaction, or by free radical grafting using a catalyst (e.g.
peroxide), as
described below.
The hydrocarbon or polymer backbone can be functionalized, e.g., with
carboxylic acid producing moieties (preferably acid or anhydride moieties)
selectively at
sites of carbon-to-carbon unsaturation on the polymer or hydrocarbon chains,
or
randomly along chains using any of the three processes mentioned above or
combinations
thereof, in any sequence.
Processes for reacting polymeric hydrocarbons with unsaturated carboxylic
acids,
anhydrides or esters and the preparation of derivatives from such compounds
are
disclosed in U.S. Patent Nos. 3,087,936; 3,172,892; 3,215,707; 3,231,587;
3,272,746;
CA 3018827 2018-09-27
34
3,275,554; 3,381,022; 3,442,808; 3,565,804; 3,912,764; 4,110,349; 4,234,435;
5,777,025;
5,891,953; as well as EP 0 382 450 Bl; CA-1,335,895 and GB-A-1,440,219. The
polymer or hydrocarbon may be functionalized, for example, with carboxylic
acid
producing moieties (preferably acid or anhydride) by reacting the polymer or
hydrocarbon under conditions that result in the addition of functional
moieties or agents,
i.e., acid, anhydride, ester moieties, etc., onto the polymer or hydrocarbon
chains
primarily at sites of carbon-to-carbon unsaturation (also referred to as
ethylenic or
olefinic unsaturation) using the halogen assisted functionalization (e.g.
chlorination)
process or the thermal "ene" reaction.
Selective functionalization can be accomplished by halogenating, e.g.,
chlorinating or brominating the unsaturated a-olefin polymer to about 1 to 8
mass %,
preferably 3 to 7 mass % chlorine, or bromine, based on the weight of polymer
or
hydrocarbon, by passing the chlorine or bromine through the polymer at a
temperature of
60 to 250 C, preferably 110 to 160 C, e.g., 120 to 140 C, for about 0.5 to 10,
preferably
1 to 7 hours. The halogenated polymer or hydrocarbon (hereinafter backbone) is
then
reacted with sufficient monounsaturated reactant capable of adding the
required number
of functional moieties to the backbone, e.g., monounsaturated carboxylic
reactant, at 100
to 250 C, usually about 180 C to 235 C, for about 0.5 to 10, e.g., 3 to 8
hours, such that
the product obtained will contain the desired number of moles of the
monounsaturated
carboxylic reactant per mole of the halogenated backbones. Alternatively, the
backbone
and the monounsaturated carboxylic reactant are mixed and heated while adding
chlorine
to the hot material.
While chlorination normally helps increase the reactivity of starting olefin
polymers with monounsaturated functionalizing reactant, it is not necessary
with some of
the polymers or hydrocarbons contemplated for use in the present invention,
particularly
those preferred polymers or hydrocarbons which possess a high terminal bond
content
and reactivity. Preferably, therefore, the backbone and the monounsaturated
functionality
reactant, e.g., carboxylic reactant, are contacted at elevated temperature to
cause an initial
thermal "ene" reaction to take place. Ene reactions are known.
CA 3018827 2018-09-27
35
The hydrocarbon or polymer backbone can be functionalized by random
attachment of functional moieties along the polymer chains by a variety of
methods. For
example, the polymer, in solution or in solid form, may be grafted with the
monounsaturated carboxylic reactant, as described above, in the presence of a
free-radical
initiator. When performed in solution, the grafting takes place at an elevated
temperature
in the range of about 100 to 260 C, preferably 120 to 240 C. Preferably, free-
radical
initiated grafting would be accomplished in a mineral lubricating oil solution
containing,
e.g., 1 to 50 mass %, preferably 5 to 30 mass % polymer based on the initial
total oil
solution.
The free-radical initiators that may be used are peroxides, hydroperoxides,
and
azo compounds, preferably those that have a boiling point greater than about
100 C and
decompose thermally within the grafting temperature range to provide free-
radicals.
Representative of these free-radical initiators are azobutyronitrile, 2,5-
dimethylhex-3-
ene-2, 5-bis-tertiary-butyl peroxide and dicumene peroxide. The initiator,
when used,
typically is used in an amount of between 0.005% and 1% by weight based on the
weight
of the reaction mixture solution. Typically, the aforesaid monounsaturated
carboxylic
reactant material and free-radical initiator are used in a weight ratio range
of from 1.0:1
to 30:1, preferably 3:1 to 6:1. The grafting is preferably carried out in an
inert
atmosphere, such as under nitrogen blanketing. The resulting grafted polymer
is
characterized by having carboxylic acid (or ester or anhydride) moieties
randomly
attached along the polymer chains: it being understood, of course, that some
of the
polymer chains remain un-grafted. The free radical grafting described above
can be used
for the other polymers and hydrocarbons useful in the practice of the present
invention.
The preferred monounsaturated reactants that are used to functionalize the
backbone comprise mono- and di-carboxylic acid material, e., acid, anhydride,
or acid
ester material, including (i) monounsaturated C4 to Cio dicarboxylic acid
wherein (a) the
carboxyl groups are vicinyl, (i.e., located on adjacent carbon atoms) and (b)
at least one,
preferably both, of said adjacent carbon atoms are part of said mono
unsaturation; (ii)
derivatives of (i) such as anhydrides or CI to C5 alcohol derived mono- or
diesters of (i);
(iii) monounsaturated C3 to C10 monocarboxylic acid wherein the carbon-carbon
double
CA 3018827 2018-09-27
36
bond is conjugated with the carboxy group, i.e., of the structure -C¨C-00-;
and (iv)
derivatives of (iii) such as C1 to C5 alcohol derived mono- or diesters of
(iii). Mixtures of
monounsaturated carboxylic materials (i)-(iv) also may be used. Upon reaction
with the
backbone, the monounsaturation of the monounsaturated carboxylic reactant
becomes
saturated. Thus, for example, maleic anhydride becomes backbone-substituted
succinic
anhydride, and acrylic acid becomes backbone-substituted propionic acid.
Exemplary of
such monounsaturated carboxylic reactants are fumaric acid, itaconic acid,
maleic acid,
maleic anhydride, chloromaleic acid, chloromaleic anhydride, acrylic acid,
methacrylic
acid, crotonic acid, cinnamic acid, and lower alkyl (e.g., Ci to C4 alkyl)
acid esters of the
foregoing, e.g., methyl maleate, ethyl fumarate, and methyl fumarate.
To provide the required functionality, the monounsaturated carboxylic
reactant,
preferably maleic anhydride, typically will be used in an amount ranging from
equimolar
amount to about 100 mass % excess, preferably 5 to 50 mass % excess, based on
the
moles of polymer or hydrocarbon. Unreacted excess monounsaturated carboxylic
reactant can be removed from the final dispersant product by, for example,
stripping,
usually under vacuum, if required.
The functionalized oil-soluble polymeric hydrocarbon backbone is then
derivatized with a nitrogen-containing nucleophilic reactant, such as an
amine,
aminoalcohol, amide, or mixture thereof, to form a corresponding derivative.
Amine
compounds are preferred. Useful amine compounds for derivatizing
functionalized
polymers comprise at least one amine and can comprise one or more additional
amine or
other reactive or polar groups. These amines may be hydrocarbyl amines or may
be
predominantly hydrocarbyl amines in which the hydrocarbyl group includes other
groups,
e.g., hydroxy groups, alkoxy groups, amide groups, nitriles, imidazoline
groups, and the
like. Particularly useful amine compounds include mono- and polyamines, e.g.,
polyalkene and polyoxyalkylene polyamines of 2 to 60, such as 2 to 40 (e.g., 3
to 20)
total carbon atoms having 1 to 12, such as 3 to 12, preferably 3 to 9, most
preferably form
6 to about 7 nitrogen atoms per molecule. Mixtures of amine compounds may
advantageously be used, such as those prepared by reaction of alkylene
dihalide with
ammonia. Preferred amines are aliphatic saturated amines, including, for
example, 1,2-
CA 3018827 2018-09-27
37
diaminoethane; 1,3-diaminopropane; 1,4-diaminobutane; 1,6-diaminohexane;
polyethylene amines such as diethylene triamine; triethylene tetramine;
tetraethylene
pentamine; and polypropyleneamines such as 1,2-propylene diamine; and di-(1,2-
propylene)triamine. Such polyamine mixtures, known as PAM, are commercially
available. Particularly preferred polyamine mixtures are mixtures derived by
distilling the
light ends from PAM products. The resulting mixtures, known as "heavy" PAM, or
HPAM, are also commercially available. The properties and attributes of both
PAM
and/or HPAM are described, for example, in U.S. Patent Nos. 4,938,881;
4,927,551;
5,230,714; 5,241,003; 5,565,128; 5,756,431; 5,792,730; and 5,854,186.
Other useful amine compounds include: alicyclic diamines such as
1,4-di(aminomethyl) cyclohexane and heterocyclic nitrogen compounds such as
imidazolines. Another useful class of amines is the polyamido and related
amido-amines
as disclosed in U.S. Patent Nos. 4,857,217; 4,956,107; 4,963,275; and
5,229,022. Also
usable is tris(hydroxymethyl)amino methane (TAM) as described in U.S. Patent
Nos.
4,102,798; 4,113,639; 4,116,876; and UK Patent No. 989,409. Dendrimers, star-
like
amines, and comb-structured amines may also be used. Similarly, one may use
condensed
amines, as described in U.S. Patent No. 5,053,152. The functionalized polymer
is reacted
with the amine compound using conventional techniques as described, for
example, in
U.S. Patent Nos. 4,234,435 and 5,229,022, as well as in EP-A-208,560.
A preferred dispersant composition is one comprising at least one polyalkenyl
succinimide, which is the reaction product of a polyalkenyl substituted
succinic
anhydride (e.g., PIBSA) and a polyamine (PAM) that has a coupling ratio of
from 0.65 to
1.25, preferably from 0.8 to 1.1, most preferably from 0.9 to 1. In the
context of this
disclosure, "coupling ratio" may be defined as a ratio of the number of
succinyl groups in
the PIBSA to the number of primary amine groups in the polyamine reactant.
Another class of high molecular weight ashless dispersants comprises Mannich
base condensation products. Generally, these products are prepared by
condensing about
one mole of a long chain alkyl-substituted mono- or polyhydroxy benzene with
about 1 to
2.5 moles of carbonyl compound(s) (e.g., formaldehyde and paraformaldehyde)
and
about 0.5 to 2 moles of polyalkylene polyamine, as disclosed, for example, in
U.S. Patent
CA 3018827 2018-09-27
38
No. 3,442,808. Such Mannich base condensation products may include a polymer
product of a metallocene catalyzed polymerization as a substituent on the
benzene group,
or may be reacted with a compound containing such a polymer substituted on a
succinic
anhydride in a manner similar to that described in U.S. Patent No. 3,442,808.
Examples
of functionalized and/or derivatized olefin polymers synthesized using
metallocene
catalyst systems are described in the publications identified supra.
The dispersant(s) are preferably non-polymeric (e.g., are mono- or bis-
succinimides). The dispersant(s), particularly the lower molecular weight
dispersants,
may optionally be borated. Such dispersants can be borated by conventional
means, as
generally taught in U.S. Patent Nos. 3,087,936, 3,254,025 and 5,430,105.
Boration of the
dispersant is readily accomplished by treating an acyl nitrogen-containing
dispersant with
a boron compound such as boron oxide, boron halide, boron acids, and esters of
boron
acids, in an amount sufficient to provide from 0.1 to 20 atomic proportions of
boron for
each mole of acylated nitrogen composition.
Dispersants derived from highly reactive polyisobutylene have been found to
provide lubricating oil compositions with a wear credit relative to a
corresponding
dispersant derived from conventional polyisobutylene. This wear credit is of
particular
importance in lubricants containing reduced levels of ash-containing anti-wear
agents,
such as ZDDP. Thus, in one preferred embodiment, at least one dispersant used
in the
lubricating oil compositions of the present invention is derived from highly
reactive
polyisobutylene.
Additional additives may be incorporated into the lubricating oil composition
to
enable particular performance requirements to be met. Examples of additives
which may
be included in the lubricating oil compositions of the present invention are
metal rust
inhibitors, viscosity index improvers, corrosion inhibitors, oxidation
inhibitors, friction
modifiers, antifoaming agents, anti-wear agents and pour point depressants.
Some are
discussed in further detail below.
Friction modifiers and fuel economy agents that are compatible with the other
ingredients of the final oil may also be included. Examples of such materials
include
glyceryl monoesters of higher fatty acids, for example, glyceryl mono-oleate;
esters of
CA 3018827 2018-09-27
39
long chain polycarboxylic acids with diols, for example, the butane diol ester
of a
dimerized unsaturated fatty acid; oxazoline compounds; and alkoxylated
alkyl-substituted mono-amines, diamines and alkyl ether amines, for example,
ethoxylated tallow amine and ethoxylated tallow ether amine.
The viscosity index of the base stock is increased, or improved, by
incorporating
therein certain polymeric materials that function as viscosity modifiers (VM)
or viscosity
index improvers (VII). Generally, polymeric materials useful as viscosity
modifiers are
those having number average molecular weights (Mn) of from about 5,000 to
about
250,000, preferably from about 15,000 to about 200,000, more preferably from
about
20,000 to about 150,000. These viscosity modifiers can be grafted with
grafting
materials such as, for example, maleic anhydride, and the grafted material can
be reacted
with, for example, amines, amides, nitrogen-containing heterocyclic compounds
or
alcohol, to form multifunctional viscosity modifiers (dispersant-viscosity
modifiers).
Polymer molecular weight, specifically Mn, can be determined by various known
techniques. One convenient method is gel permeation chromatography (GPC),
which
additionally provides molecular weight distribution information (see W. W.
Yau, J. J.
Kirkland and D. D. Bly, "Modern Size Exclusion Liquid Chromatography", John
Wiley
and Sons, New York, 1979). Another useful method for determining molecular
weight,
particularly for lower molecular weight polymers, is vapor pressure osmometry
(see, e.g.,
ASTM D3592).
One class of diblock copolymers useful as viscosity modifiers has been found
to
provide a wear credit relative to, for example, olefin copolymer viscosity
modifiers. This
wear credit is of particular importance in lubricants containing reduced
levels of ash-
containing anti-wear agents, such as ZDDP. Thus, in one preferred embodiment,
at least
one viscosity modifier used in the lubricating oil compositions of the present
invention is
a linear diblock copolymer comprising one block derived primarily, preferably
predominantly, from vinyl aromatic hydrocarbon monomer, and one block derived
primarily, preferably predominantly, from diene monomer. Useful vinyl aromatic
hydrocarbon monomers include those containing from 8 to about 16 carbon atoms
such
as aryl-substituted styrenes, alkoxy-substituted styrenes, vinyl naphthalene,
alkyl-
CA 3018827 2018-09-27
40
substituted vinyl naphthalenes and the like. Dienes, or diolefins, contain two
double
bonds, commonly located in conjugation in a 1,3 relationship. Olefins
containing more
than two double bonds, sometimes referred to as polyenes, are also considered
within the
definition of "diene" as used herein. Useful dienes include those containing
from 4 to
about 12 carbon atoms, preferably from 8 to about 16 carbon atoms, such as 1,3-
butadiene, isoprene, piperylene, methylpentadiene, phenylbutadiene, 3,4-
dimethy1-1,3-
hexadiene, 4,5-diethy1-1,3-octadiene, with 1,3-butadiene and isoprene being
preferred.
As used herein in connection with polymer block composition, "predominantly"
means that the specified monomer or monomer type that is the principle
component in
that polymer block is present in an amount of at least 85 % by weight of the
block.
Polymers prepared with diolefins will contain ethylenic unsaturation, and such
polymers are preferably hydrogenated. When the polymer is hydrogenated, the
hydrogenation may be accomplished using any of the techniques known in the
prior art.
For example, the hydrogenation may be accomplished such that both ethylenic
and
aromatic unsaturation is converted (saturated) using methods such as those
taught, for
example, in U.S. Pat. Nos. 3,113,986 and 3,700,633 or the hydrogenation may be
accomplished selectively such that a significant portion of the ethylenic
unsaturation is
converted while little or no aromatic unsaturation is converted as taught, for
example, in
U.S. Pat. Nos. 3,634,595; 3,670,054; 3,700,633 and U.S. Re 27,145. Any of
these
methods can also be used to hydrogenate polymers containing only ethylenic
unsaturation
and which are free of aromatic unsaturation.
The block copolymers may include mixtures of linear diblock polymers as
disclosed above, having different molecular weights and/or different vinyl
aromatic
contents as well as mixtures of linear block copolymers having different
molecular
weights and/or different vinyl aromatic contents. The use of two or more
different
polymers may be preferred to a single polymer depending on the rheological
properties
the product is intended to impart when used to produce formulated engine oil.
Examples
of commercially available styrene/hydrogenated isoprene linear diblock
copolymers
include Infineum SV14OTM, Infineum SV1SOTM and Infineum SV16OTM, available
from
Infineum USA L.P. and Infineum UK Ltd.; Lubrizol 7318, available from The
Lubrizol
CA 3018827 2018-09-27
41
Corporation; and Septon 1001TM and Septon 1020T", available from Septon
Company of
America (Kuraray Group). Suitable styrene/1, 3-butadiene hydrogenated block
copolymers are sold under the tradename GlissoviscalTM by BASF.
Pour point depressants (PPD), otherwise known as lube oil flow improvers
(LOFIs) lower the temperature. Compared to VM, LOFIs generally have a lower
number
average molecular weight. Like VM, LOFIs can be grafted with grafting
materials such
as, for example, maleic anhydride, and the grafted material can be reacted
with, for
example, amines, amides, nitrogen-containing heterocyclic compounds or
alcohol, to
form multifunctional additives.
In the lubricating oil compositions of the present invention it may be
necessary to
include an additive which maintains the stability of the viscosity of the
blend. Thus,
although polar group-containing additives achieve a suitably low viscosity in
the pre-
blending stage it has been observed that some compositions increase in
viscosity when
stored for prolonged periods. Additives which are effective in controlling
this viscosity
increase include the long chain hydrocarbons functionalized by reaction with
mono- or
dicarboxylic acids or anhydrides which are used in the preparation of the
ashless
dispersants as hereinbefore disclosed. In another preferred embodiment, the
lubricating
oil compositions of the present invention contain an effective amount of a
long chain
hydrocarbons functionalized by reaction with mono- or dicarboxylic acids or
anhydrides.
When lubricating compositions contain one or more of the above-mentioned
additives, each additive is typically blended into the base oil in an amount
that enables
the additive to provide its desired function. Representative effective amounts
of such
additives, when used in crankcase lubricants, are listed below. All the values
listed (with
the exception of detergent values) are stated as mass percent active
ingredient (A.I.). As
used herein, A.I. refers to additive material that is not diluent or solvent.
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42
ADDITIVE MASS % (Broad) MASS % (Preferred)
Dispersant 0.1 - 20 1 - 8
Metal Detergents 0.1 - 15 0.2 - 9
Corrosion Inhibitor 0 - 5 0 - 1.5
Metal Dihydrocarbyl Dithiophosphate 0.1 - 6 0.1 - 4
Antioxidant 0 - 5 0.01 - 2.5
Pour Point Depressant 0.01 -5 0.01 -1.5
Antifoaming Agent 0 - 5 0.001 - 0.15
Supplemental Anti-wear Agents 0 - 1.0 0 - 0.5
Friction Modifier 0 - 5 0 - 1.5
Viscosity Modifier 0.01 - 10 0.25 - 3
Base stock Balance Balance
It may be desirable, although not essential to prepare one or more additive
concentrates comprising additives (concentrates sometimes being referred to as
additive
packages) whereby several additives can be added simultaneously to the oil to
form the
lubricating oil composition.
The final composition may employ from 5 to 25 mass %, preferably 5 to 22 mass
%, typically 10 to 20 mass % of the concentrate, the remainder being oil of
lubricating
viscosity.
Preferably, the Noack volatility of the fully formulated lubricating oil
composition (oil of lubricating viscosity plus all additives) will be no
greater than 20
mass %, such as no greater than 15 mass %, preferably no greater than 13 mass
%.
Lubricating oil compositions useful in the practice of the present invention
may
have an overall sulfated ash content of from 0.3 to 1.2 mass %, such as from
0.4 to 1.1
mass %, preferably from 0.5 to 1.0 mass %.
This invention will be further understood by reference to the following
examples,
wherein all parts are parts by mass, unless otherwise noted and which include
preferred
embodiments of the invention.
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43
Description of the Examples
Whilst the present invention has been described and illustrated with reference
to
particular embodiments, it will be appreciated by those of ordinary skill in
the art that the
invention lends itself to many different variations not specifically
illustrated herein. By
way of example only, certain possible variations will now be described.
The amounts of additives provided are additive amounts including diluent oil,
amounts unless otherwise indicated.
Example 1
Two SAE OW-20 grade lubricating oil compositions representing typical
European mid-SAPS passenger car motor oils were prepared. The formulation of
these
compositions is shown in Table 2 below.
Table 2
Constituent Type Oil 1 Oil 2
Borated Dispersant 1 (B,
0.0057 0.0195
mass%)
Mg Salicylate Detergent 2
0.02 0.02
(Mg, mass%)
Ca Salicylate Detergent 3
0.15 0.15
(Ca, mass%)
Molybdenum Compound 4
0 0.0198
(Mo, mass%)
Additive Package 5
8.053 8.053
(mass%)
SN150 Diluent (mass%) 1.82 1.9
Pour Point Depressant6
0.3 0.3
(mass%)
Viscosity
9.5 9.5
Modifier7(mass%)
Base Stock8(mass%) 77.5 76
SASH, mass% 0.73 0.75
P %, mass% 0.085 0.085
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S %, mass% 0.2 0.2
I The borated dispersant was a borated polyisobutenyl succinimide dispersant
available from
Infineum UK Limited.
2 The magnesium detergent was a magnesium salicylate detergent having a total
base number of 342
available from Infineum UK Limited.
The calcium detergent was the same for each oil and comprised a mixture of a
calcium salicylate
detergent having a total base number of 225 available from Infineum UK Limited
and a calcium
salicylate detergent having a total base number of 64 available from Infineum
UK Limited.
4 The molybdenum dithiocarbamate is a trimeric molybdenum dithiocarbamate
available from
Infineum UK Limited.
The additive package was the same for each oil and included non-borated
dispersant, zinc
dialkyldithiophosphate, aminic antioxidant and silicon antifoam.
6 The pour point depressant was Infineum V385 available from Infineum UK Ltd.
The viscosity modifier was Infineum SV603 available from Infineum UK Ltd.
The base stock comprised API Group III base oil.
Oil 1, being a comparative example, includes a typical dose of a borated
dispersant, the oil composition having a boron content of 57 ppm, and no
molybdenum-
containing additive. Oil 2, being an example of the invention, includes a
higher dose of a
borated dispersant, the oil composition having a boron content of 195 ppm, and
a
molybdenum containing compound providing the oil composition with 198 ppm of
molybdenum.
The oils were tested for LSPI event occurrence according to the GM LSPI test
for
approvals against DeXoSTM specifications, the results being presented in Table
3. The test
limit for the Dexos test for five runs is 0 0 0 2 2, meaning that a
composition achieving
zero LSPI events in runs 1, 2 and 3 and two or fewer LSPI events in runs 4 and
5, passes
the test, whereas a composition with more than zero LSPI events in runs 1, 2
and/or 3
and/or more than two LSPI events in runs 4 and 5 fails the test.
Table 3
Run LSPI Events Per Run
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Oil 1 0i12
1 1 0
2 1 0
3 3 0
4 3 0
5 4 1
Across all five runs with each composition, Oil 2 showed a lower LSPI event
frequency, passing the DexosTM test, whereas Oil 1 failed the DexosTM test.
These results
indicate that a combined increase in both boron and molybdenum contents
provides a
reduction in LSPI event frequency.
Example 2
Two further SAE OW-20 grade lubricating oil compositions representing typical
European mid-SAPS passenger car motor oils with a phosphorous content of 0.09
mass%
were prepared. The formulation of these compositions is shown in Table 4
below.
Table 4
Constituent Type Amount Oil 3 Oil 4
Borated Dispersant9 B, mass% 0.0037 0.0198
Ca Salicylate Detergent 1 Ca, mass% 0.18 0.18
Molybdenum compound" Mo, mass% 0.0027 0.0330
Additive package 12 mass% 8.254 8.254
APP150DIL Diluent mass% 2.485 2.485
Pour Point Depressant13 mass% 0.300 0.300
Viscosity Modifier" mass% 9.000 9.000
Base Stock15 mass% 77.376 75.586
9 The borated dispersant was a borated polyisobutenyl succinimide dispersant
available from
Infineum UK Limited.
19 The calcium detergent comprised a calcium salicylate detergent having a
total base number of 225
available from Infineum UK Limited.
11 The molybdenum dithiocarbamate is a trimeric molybdenum dithiocarbamate
available from
Infineum UK Limited.
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12 The additive package was the same for each oil and included non-borated
dispersant, zinc
dialkyldithiophosphate, aminic antioxidant, hindered phenol antioxidant,
ashless friction modifier
and silicon antifoam.
" The pour point depressant was Infineum V385 available from Infineum UK Ltd.
14 The viscosity modifier was Infineum SV603 available from Infineum UK Ltd.
15 The base stock comprised GTL base oil.
It can be seen from Table 4 that Oil 3 has a lower boron content and a lower
molybdenum content than Oil 4 composition.
The compositions were tested for LSPI event occurrence according to the ASTM
(Ford) LSPI test for applications claiming GF-6 / API SP, the results being
presented in
Table 6.
Table 5
LSPI Events Per Run
Run
0i13 0i14
1 7 4
2 17 2
3 12 4
4 10 4
Across all four runs with each composition, Oil 4 showed a significantly lower
LSPI event frequency than Oil 3, indicating that a increase in both boron and
molybdenum content provides a reduction in LSPI event frequency.
Example 3
Constituent
Amount Oil 5 Oil 6 Oil 7 Oil 8 Oil 9
Type
Borated
B, mass% 0.000 0.000 0.040 0.040 0.020
Dispersant
16
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Non-Borated
mass% 2.75 2.75 1.30 1.30 2.00
DispersantI7
Ca Sulfonate Ca,
0.151 0.151 0.151 0.151 0.151
Detergent 18 mass /o
MgSulfonate Mg,
0.030 0.030 0.030 0.030 0.030
Detergent 19 mass /o
Molybdenum Mo,
0.000 0.070 0.000 0.070 0.035
Compound" mass%
Additive
mass% 3.103 3.103 3.103 3.103 3.103
Package2I
Group H
mass% 1.00 1.00 1.00 1.00 1.00
Diluent
Pour Point
mass% 0.30 0.30 0.30 0.30 0.30
Depressantn
Viscosity
mass% 8.20 8.20 8.20 8.20 8.20
Modifier23
Base Stock34 mass% balance balance balance balance balance
SASH mass% 0.72 0.72 0.75 0.75 0.73
P % mass% 0.06 0.06 0.06 0.06 0.06
S% mass% 0.1 0.3 0.1 0.3 0.2
Five 5W-30 grade lubricating oil representing typical European mid-SAPS
passenger car motor oils were prepared. The formulation of these compositions
is shown
in Table 6 below.
Table 6
16 The borated dispersant was a borated polyisobutenyl succinimide dispersant
available from
Infineum UK Limited.
'7 The non-borated dispersant was a polyisobutylene succinimide dispersant
available from Infineum
UK Limited. The amount of non-borated dispersant varies in order to balance
the varied amount of
borated dispersant used to vary the amount of boron present in the oils.
18The calcium detergent comprised a calcium sulfonate detergent having a total
base number of 300
available from Infineum UK Limited.
19 The magnesium detergent is a magnesium sulfonate detergent having a total
base number of 400
available from Infineum UK Limited.
20 The molybdenum dithiocarbamate is a trimeric molybdenum dithiocarbamate
available from
Infineum UK Limited.
2' The additive package was the same for each oil and included zinc
diallcyldithiophosphate, aminic
antioxidant, hindered phenol antioxidant, ashless friction modifier, diluent
oil and silicon antifoam.
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22 The pour point depressant was Infineum V387 available from Infineum UK Ltd.
23 The viscosity modifier was Paratone 68530 available from Chevron Oronite.
The base stock comprised an API Group II base stock.
Oils 5 and 6 include no boron (in order to maintain equivalent dispersant
functionality in the compositions, boron-free dispersants are included in the
compositions). Oils 5 and 7 contain no molybdenum. Thus, Oil 5 contains
neither boron
nor molybdenum, Oil 6 contains a relatively high molybdenum dose but no boron,
and
Oil 7 contains a relatively high boron dose but no molybdenum. Oils 8 and 9
include
boron and molybdenum. Oil 8 containing the same relatively high boron dose and
a
relatively high molybdenum dose as Oils 7 and 6, respectively, and Oil 9
including half
the amount of boron and molybdenum.
The compositions were tested for LSPI event occurrence according to the ASTM
(Ford) LSPI test for applications claiming GF-6 / API SP, the results being
presented in
Table 7. The tests were run in a matrix fashion in a random order, with a
reference oil
run every five tests.
Table 7
Average LSPI Event Occurance
Oil 5 Oil 6 Oil 7 Oil 8 Oil 9
14 8 16 4 6
The LSPI test results set out in Table 7 are also shown in matrix format in
Fig. 1.
The test results indicate no reduction in LSPI frequency through substantially
increasing
the boron content of the composition from 0 ppm to 400 ppm in the absence of
molybdenum, and a modest reduction in LSPI frequency (43% reduction) through
substantially increasing molybdenum content of the composition from 0 ppm to
700 ppm
in the absence of boron. In contrast, the test results show a significantly
more substantial
reduction in LSPI frequency (57% reduction) through only moderately increasing
both
the boron content and the molybdenum content from 0 ppm to 200 ppm and 350
ppm,
respectively. Furthermore, the test results show an even more significant
reduction in
LSPI frequency (71% reduction) through substantially increasing both the boron
content
CA 3018827 2018-09-27
49
and the molybdenum content from 0 ppm to 400 ppm and 700 ppm, respectively.
Surprisingly, the test results of Example 3 show a synergistic effect on LSPI
frequency
reduction resulting from the combination of both boron and molybdenum in a
lubricating
oil composition.
Where in the foregoing description, integers or elements are mentioned which
have known, obvious or foreseeable equivalents, then such equivalents are
herein
incorporated as if individually set forth. Reference should be made to the
claims for
determining the true scope of the present invention, which should be construed
so as to
encompass any such equivalents. It will also be appreciated by the reader that
integers or
features of the invention that are described as preferable, advantageous,
convenient or the
like are optional and do not limit the scope of the independent claims.
Moreover, it is to
be understood that such optional integers or features, whilst of possible
benefit in some
embodiments of the invention, may not be desirable, and may therefore be
absent, in
other embodiments.
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