Note: Descriptions are shown in the official language in which they were submitted.
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LUBRICATING OIL COMPOSITION
BACKGROUND OF THE INVENTION
1. Technical Field
[0001] The present invention generally relates to lubricating oil compositions
for
reducing wear in engines.
2. Description of the Related Art
[0002] Automobile spark ignition and diesel engines have valve train systems
including, for example, valves, cams and rocker arms, which present special
lubrication
concerns. It is extremely important that the lubricant, i.e., the engine oil,
protects these parts
from wear. It is also important for the engine oils to suppress the production
of deposits in
the engines. Such deposits are produced from non-combustibles and incomplete
combustion
of hydrocarbon fuels (e.g., gasoline and diesel fuel oil) and by the
deterioration of the engine
oil employed.
[0003] Engine oils typically use a mineral oil or a synthetic oil as a base
oil.
However, simple base oils alone do not provide the necessary properties to
provide the
necessary wear protection, deposit control, etc., required to protect internal
combustion
engines. Thus, base oils are formulated with various additives, for imparting
auxiliary
functions, such as ashless dispersants, metallic detergents (i.e., metal-
containing detergents),
antiwear agents, antioxidants (i.e., oxidation inhibitors), viscosity index
improvers and the
like to give a formulated oil (i.e., a lubricating oil composition).
[0004] A number of such engine oil additives are known and employed in
practice.
For example, zinc dialkyldithiophosphates are usually contained in the
commercially
available internal composition engine oils, especially those used for
automobiles, because of
their favorable characteristics as an antiwear agent and performance as an
oxidation inhibitor.
[0005] However, a problem associated with the use of zinc
dialkyldithiophosphate is
that their phosphorus and sulfur derivatives poison the catalyst components of
the catalytic
converters. This is a major concern as effective catalytic converters are
needed to reduce
pollution and to meet governmental regulation designed to reduce toxic gases
such as, for
example, hydrocarbons, carbon monoxide and nitrogen oxides, in internal
combustion engine
exhaust emissions. Such catalytic converters generally use a combination of
catalytic metals,
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e.g., platinum and metal oxides, and are installed in the exhaust streams,
e.g., the exhaust
pipes of automobiles, to convert the toxic gases to nontoxic gases. As
previously mentioned,
these catalyst components are poisoned by the phosphorus and sulfur
components, or the
phosphorus and sulfur decomposition product of the zinc
dialkyldithiophosphate; and
accordingly, the use of engine oils containing phosphorus and sulfur additives
may
substantially reduce the life and effectiveness of catalytic converters.
[0006] There is also governmental and automotive industry pressure towards
reducing
the phosphorus and sulfur content. For example, current GF-4 motor oil
specifications
require a finished oil to contain less than 0.08 wt % and 0.7 wt % phosphorus
and sulfur,
respectively, and CJ-4 motor oil specifications, the most current generation
heavy duty diesel
engine oil, require an oil to contain less than 0.12 wt % and 0.4 wt %
phosphorus and sulfur,
respectively, and 1.0 wt % sulfated ash. It is widely believed that lowering
these limits may
have a serious impact on engine performance, engine wear, and oxidation of
engine oils.
This is because historically a major contributor to the phosphorus content in
engine oils has
been zinc dialkyldithiophosphates. Accordingly, it would be desirable to
eliminate the
amount of zinc dialkyldithiophosphate in lubricating oils, thus reducing
catalyst deactivation
and hence increasing the life and effectiveness of catalytic converters while
also meeting
future industry standard proposed phosphorus and sulfur contents in the engine
oil. However,
simply decreasing the amount of zinc dialkyldithiophosphate presents problems
because this
necessarily lowers the antiwear properties and oxidation inhibition properties
of the
lubricating oil. Therefore, it is necessary to find a way to reduce or
eliminate phosphorus and
sulfur content while still retaining the antiwear properties of the higher
phosphorus and sulfur
content engine oils.
[0007] Accordingly, as demand for further decrease of the phosphorus content
and a
limit on the sulfur content of lubricating oils is very high, this reduction
cannot be satisfied
by the present measures in practice and still meet the severe antiwear
properties required of
today's engine oils. Thus, it would be desirable to develop lubricating oil
compositions
having relatively low levels of phosphorus and sulfur but which still provide
the needed wear
protection now provided by lubricating oils containing zinc dialkyl
dithiophosphate. It would
therefore be desirable to develop improved lubricating oil compositions which
exhibit
improved wear when used in an internal combustion engine while containing no
zinc therein
and relatively low levels or free of any phosphorus and/or sulfur content.
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SUMMARY OF THE INVENTION
[0008] In accordance with one embodiment of the present invention, a
lubricating oil
composition is provided comprising (a) a major amount of an oil of lubricating
viscosity, (b)
an ashless dispersant, (c) at least one metal-containing detergent, (d) an
antioxidant, and (e)
an anti-wear agent, wherein the lubricating oil composition is free of any
zinc dialkyl
dithiophosphate compound and further wherein the lubricating oil composition
is
substantially free of any phosphorus content.
[0009] In accordance with a second embodiment of the present invention, a
lubricating oil composition is provided comprising (a) a major amount of an
oil of lubricating
viscosity, (b) an ashless dispersant, (c) at least one metal-containing
detergent, (d) an
antioxidant, and (e) an anti-wear agent, wherein the lubricating oil
composition is free of any
zinc dialkyl dithiophosphate compound and is substantially free of any
phosphorus content,
and further wherein the lubricating oil composition has a wear reducing
property greater than
that of a corresponding lubricating oil composition in which a zinc dialkyl
dithiophosphate
compound is present therein.
[0010] In accordance with a third embodiment of the present invention, a
method for
improving the wear reducing properties of a lubricating oil composition is
provided
comprising the step of forming a lubricating oil composition comprising (a) a
major amount
of an oil of lubricating viscosity, (b) an ashless dispersant, (c) at least
one metal-containing
detergent, (d) an antioxidant, and (e) an anti-wear agent, wherein the
lubricating oil
composition is free of any zinc dialkyl dithiophosphate compound and is
substantially free of
any phosphorus content.
[0011] In accordance with a fourth embodiment of the present invention, there
is
provided a method of reducing wear in an internal combustion engine which
comprises
operating the internal combustion engine with a lubricating oil composition
comprising (a) a
major amount of an oil of lubricating viscosity, (b) an ashless dispersant,
(c) at least one
metal-containing detergent, (d) an antioxidant, and (e) an anti-wear agent,
wherein the
lubricating oil composition is free of any zinc dialkyl dithiophosphate
compound and is
substantially free of any phosphorus content.
[0012] In accordance with a fifth embodiment of the present invention, there
is
provided an internal combustion engine lubricated with a lubricating oil
composition
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comprising (a) a major amount of an oil of lubricating viscosity, (b) an
ashless dispersant, (c)
at least one metal-containing detergent, (d) an antioxidant, and (e) an anti-
wear agent,
wherein the lubricating oil composition is free of any zinc dialkyl
dithiophosphate compound
and is substantially free of any phosphorus content.
[0013] The lubricating oil composition of the present invention advantageously
possesses improved wear reducing properties while containing no zinc dialkyl
dithiophosphate compound as compared to a corresponding lubricating oil
composition in
which a zinc dialkyl dithiophosphate compound is present therein. This is
unexpected as zinc
dialkyl dithiophosphate is a known antiwear agent typically used in
lubricating oil
compositions. In addition, the improved wear reducing properties can be
achieved with the
lubricating oil compositions of the present invention while also employing
relatively low
levels or free of any phosphorus content and relatively low levels of sulfur.
BRIEF DESCRIPTION OF THE DRAWING
[0014] Figure 1 is a bar graph comparing the wear performance of the
lubricating oil
composition of Example 1 versus the lubricating oil compositions of
Comparative Examples
A and B.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The present invention is directed to a lubricating oil composition
containing at
least (a) a major amount of an oil of lubricating viscosity; (b) an ashless
dispersant; (c) at
least one metal-containing detergent; (d) an antioxidant; and (e) an anti-wear
agent other than
a zinc dialkyl dithiophosphate compound, wherein the lubricating oil
composition is free of
any zinc dialkyl dithiophosphate compound and is substantially free of any
phosphorus
content, e.g., a phosphorus content not exceeding 0.08 wt. %, more preferably
not exceeding
0.05 wt. % and most preferably 0 wt. %, based on the total weight of the
lubricating oil
composition. In another embodiment, the lubricating oil composition of the
present invention
contains relatively low levels of sulfur, i.e., not exceeding 0.7 wt. % and
preferably not
exceeding 0.2 wt. %. The amount of phosphorus and sulfur in the lubricating
oil composition
of the present invention is measured according to ASTM D495 1.
[0016] The oil of lubricating viscosity for use in the lubricating oil
compositions of
this invention, also referred to as a base oil, is typically present in a
major amount, e.g., an
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amount of greater than 50 wt. %, preferably greater than about 70 wt. %, more
preferably
from about 80 to about 99.5 wt. % and most preferably from about 85 to about
98 wt. %,
based on the total weight of the composition. The expression "base oil" as
used herein shall
be understood to mean a base stock or blend of base stocks which is a
lubricant component
that is produced by a single manufacturer to the same specifications
(independent of feed
source or manufacturer's location); that meets the same manufacturer's
specification; and that
is identified by a unique formula, product identification number, or both. The
base oil for use
herein can be any presently known or later-discovered base oil of lubricating
viscosity used in
formulating lubricating oil compositions for any and all such applications,
e.g., engine oils,
marine cylinder oils, functional fluids such as hydraulic oils, gear oils,
transmission fluids,
etc. Additionally, the base oils for use herein can optionally contain
viscosity index
improvers, e.g., polymeric alkylmethacrylates; olefinic copolymers, e.g., an
ethylene-
propylene copolymer or a styrene-butadiene copolymer; and the like and
mixtures thereof.
[0017] As one skilled in the art would readily appreciate, the viscosity of
the base oil
is dependent upon the application. Accordingly, the viscosity of a base oil
for use herein will
ordinarily range from about 2 to about 2000 centistokes (cSt) at 100
Centigrade (C).
Generally, individually the base oils used as engine oils will have a
kinematic viscosity range
at 100 C of about 2 cSt to about 30 cSt, preferably about 3 cSt to about 16
cSt, and most
preferably about 4 cSt to about 12 cSt and will be selected or blended
depending on the
desired end use and the additives in the finished oil to give the desired
grade of engine oil,
e.g., a lubricating oil composition having an SAE Viscosity Grade of OW, OW-
20, OW-30,
OW-40, OW-50, OW-60, 5W, 5W-20, 5W-30, 5W-40, 5W-50, 5W-60, 10W, IOW-20, lOW-
30, IOW-40, 10W-50, 15W, 15W-20, 15W-30 or 15W-40. Oils used as gear oils can
have
viscosities ranging from about 2 cSt to about 2000 cSt at 100 C.
[0018] Base stocks may be manufactured using a variety of different processes
including, but not limited to, distillation, solvent refining, hydrogen
processing,
oligomerization, esterification, and rerefining. Rerefined stock shall be
substantially free
from materials introduced through manufacturing, contamination, or previous
use. The base
oil of the lubricating oil compositions of this invention may be any natural
or synthetic
lubricating base oil. Suitable hydrocarbon synthetic oils include, but are not
limited to, oils
prepared from the polymerization of ethylene or from the polymerization of 1-
olefins to
provide polymers such as polyalphaolefin or PAO oils, or from hydrocarbon
synthesis
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procedures using carbon monoxide and hydrogen gases such as in a Fischer-
Tropsch process.
For example, a suitable base oil is one that comprises little, if any, heavy
fraction; e.g., little,
if any, lube oil fraction of viscosity 20 cSt or higher at 100 C.
[0019] The base oil may be derived from natural lubricating oils, synthetic
lubricating
oils or mixtures thereof. Suitable base oil includes base stocks obtained by
isomerization of
synthetic wax and slack wax, as well as hydrocracked base stocks produced by
hydrocracking
(rather than solvent extracting) the aromatic and polar components of the
crude. Suitable
base oils include those in all API categories I, II, III, IV and V as defined
in API Publication
1509, 14th Edition, Addendum I, Dec. 1998. Group IV base oils are
polyalphaolefins (PAO).
Group V base oils include all other base oils not included in Group I, II,
III, or IV. Although
Group II, III and IV base oils are preferred for use in this invention, these
base oils may be
prepared by combining one or more of Group I, II, III, IV and V base stocks or
base oils.
[0020] Useful natural oils include mineral lubricating oils such as, for
example, liquid
petroleum oils, solvent-treated or acid-treated mineral lubricating oils of
the paraffinic,
naphthenic or mixed paraffinic-naphthenic types, oils derived from coal or
shale, animal oils,
vegetable oils (e.g., rapeseed oils, castor oils and lard oil), and the like.
[0021] Useful synthetic lubricating oils include, but are not limited to,
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), and the like
and mixtures
thereof; alkylbenzenes such as dodecylbenzenes, tetradecylbenzenes,
dinonylbenzenes, di(2-
ethylhexyl)-benzenes, and the like; polyphenyls such as biphenyls, terphenyls,
alkylated
polyphenyls, and the like; alkylated diphenyl ethers and alkylated diphenyl
sulfides and the
derivative, analogs and homologs thereof and the like.
[0022] Other useful synthetic lubricating oils include, but are not limited
to, oils made
by polymerizing olefins of less than 5 carbon atoms such as ethylene,
propylene, butylenes,
isobutene, pentene, and mixtures thereof. Methods of preparing such polymer
oils are well
known to those skilled in the art.
[0023] Additional useful synthetic hydrocarbon oils include liquid polymers of
alpha
olefins having the proper viscosity. Especially useful synthetic hydrocarbon
oils are the
hydrogenated liquid oligomers of C6 to C12 alpha olefins such as, for example,
1-decene
trimer.
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[0024] Another class of useful synthetic lubricating oils include, but are not
limited
to, alkylene oxide polymers, i.e., homopolymers, interpolymers, and
derivatives thereof
where the terminal hydroxyl groups have been modified by, for example,
esterification or
etherification. These oils are exemplified by the oils prepared through
polymerization of
ethylene oxide or propylene oxide, the alkyl and phenyl ethers of these
polyoxyalkylene
polymers (e.g., methyl poly propylene glycol ether having an average molecular
weight of
1,000, diphenyl ether of polyethylene glycol having a molecular weight of 500
to 1000,
diethyl ether of polypropylene glycol having a molecular weight of 1,000 to
1,500, etc.) or
mono- and polycarboxylic esters thereof such as, for example, the acetic
esters, mixed C3 to
Cg fatty acid esters, or the C13 oxo acid diester of tetraethylene glycol.
[0025] Yet another class of useful synthetic lubricating oils include, but are
not
limited to, the esters of dicarboxylic acids e.g., phthalic acid, succinic
acid, alkyl succinic
acids, alkenyl succinic acids, maleic acid, azelaic acid, suberic acid,
sebacic acid, fumaric
acid, adipic acid, linoleic acid dimer, malonic acids, alkyl malonic acids,
alkenyl malonic
acids, etc., with a variety of alcohols, e.g., butyl alcohol, hexyl alcohol,
dodecyl alcohol, 2-
ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene
glycol, etc.
Specific examples of these esters include 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, the
complex ester formed by reacting one mole of sebacic acid with two moles of
tetraethylene
glycol and two moles of 2-ethylhexanoic acid and the like.
[0026] Esters useful as synthetic oils also include, but are not limited to,
those made
from carboxylic acids having from about 5 to about 12 carbon atoms with
alcohols, e.g.,
methanol, ethanol, etc., polyols and polyol ethers such as neopentyl glycol,
trimethylol
propane, pentaerythritol, dipentaerythritol, tripentaerythritol, and the like.
[0027] Silicon-based oils such as, for example, polyalkyl-, polyaryl-,
polyalkoxy- or
polyaryloxy-siloxane oils and silicate oils, comprise another useful class of
synthetic
lubricating oils. Specific examples of these include, but are not limited to,
tetraethyl silicate,
tetra-isopropyl silicate, tetra-(2-ethylhexyl) silicate, tetra-(4-methyl-
hexyl)silicate, tetra-(p-
tert-butylphenyl) silicate, hexyl-(4-methyl-2-pentoxy)disiloxane,
poly(methyl)siloxanes,
poly(methylphenyl)siloxanes, and the like.
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[0028] The lubricating oil may be derived from unrefined, refined and
rerefined oils,
either natural, synthetic or mixtures of two or more of any of these of the
type disclosed
hereinabove. Unrefined oils are those obtained directly from a natural or
synthetic source
(e.g., coal, shale, or tar sands bitumen) without further purification or
treatment. Examples of
unrefined oils include, but are not limited to, a shale oil obtained directly
from retorting
operations, a petroleum oil obtained directly from distillation or an ester
oil obtained directly
from an esterification process, each of which is then used without further
treatment. Refined
oils are similar to the unrefined oils except they have been further treated
in one or more
purification steps to improve one or more properties. These purification
techniques are
known to those of skill in the art and include, for example, solvent
extractions, secondary
distillation, acid or base extraction, filtration, percolation, hydrotreating,
dewaxing, etc.
Rerefined oils are obtained by treating used oils in processes similar to
those used to obtain
refined oils. Such rerefined oils are also known as reclaimed or reprocessed
oils and often
are additionally processed by techniques directed to removal of spent
additives and oil
breakdown products.
[0029] Lubricating oil base stocks derived from the hydroisomerization of wax
may
also be used, either alone or in combination with the aforesaid natural and/or
synthetic base
stocks. Such wax isomerate oil is produced by the hydroisomerization of
natural or synthetic
waxes or mixtures thereof over a hydroisomerization catalyst.
[0030] Natural waxes are typically the slack waxes recovered by the solvent
dewaxing of mineral oils; synthetic waxes are typically the wax produced by
the Fischer-
Tropsch process.
[0031] The ashless dispersant compounds employed in the lubricating oil
composition
of the present invention are generally used to maintain in suspension
insoluble materials
resulting from oxidation during use, thus preventing sludge flocculation and
precipitation or
deposition on metal parts. The lubricating oil composition of the present
invention may
contain one or more ashless dispersants. Nitrogen-containing ashless (metal-
free) dispersants
are basic, and contribute to the total base number or TBN (as can be measured
by ASTM
D2896) of a lubricating oil composition to which they are added, without
introducing
additional sulfated ash. The term "Total Base Number" or "TBN" as used herein
refers to the
amount of base equivalent to milligrams of KOH in one gram of sample. Thus,
higher TBN
numbers reflect more alkaline products, and therefore a greater alkalinity.
TBN was
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determined using ASTM D 2896 test. An ashless dispersant generally comprises
an oil
soluble polymeric hydrocarbon backbone having functional groups that are
capable of
associating with particles to be dispersed. Many types of ashless dispersants
are known in the
art.
[0032] Representative examples of ashless dispersants include, but are not
limited to,
amines, alcohols, amides, or ester polar moieties attached to the polymer
backbones via
bridging groups. An ashless dispersant of the present invention 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 long chain 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 polyalkylene
polyamine.
[0033] Carboxylic dispersants are reaction products of carboxylic acylating
agents
(acids, anhydrides, esters, etc.) comprising at least about 34 and preferably
at least about 54
carbon atoms with nitrogen containing compounds (such as amines), organic
hydroxy
compounds (such as aliphatic compounds including monohydric and polyhydric
alcohols, or
aromatic compounds including phenols and naphthols), and/or basic inorganic
materials.
These reaction products include imides, amides, and esters.
[0034] Succinimide dispersants are a type of carboxylic dispersants. They are
produced by reacting hydrocarbyl-substituted succinic acylating agent with
organic hydroxy
compounds, or with amines comprising at least one hydrogen atom attached to a
nitrogen
atom, or with a mixture of the hydroxy compounds and amines. The term
"succinic acylating
agent" refers to a hydrocarbon-substituted succinic acid or a succinic acid-
producing
compound, the latter encompasses the acid itself. Such materials typically
include
hydrocarbyl-substituted succinic acids, anhydrides, esters (including half
esters) and halides.
[0035] Succinic-based dispersants have a wide variety of chemical structures.
One
class of succinic-based dispersants may be represented by the formula:
H
H O O
Rl-C C/ C C-R'
/N_ R2_ N+ R2- N
H i \ X C C-H
H O H
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wherein each R1 is independently a hydrocarbyl group, such as a polyolefin-
derived group.
Typically the hydrocarbyl group is an alkyl group, such as a polyisobutyl
group.
Alternatively expressed, the R1 groups can contain about 40 to about 500
carbon atoms, and
these atoms may be present in aliphatic forms. R2 is an alkylene group,
commonly an
ethylene (C2H4) group. Examples of succinimide dispersants include those
described in, for
example, U.S. Patent Nos. 3,172,892, 4.234,435 and 6,165,235.
[0036] The polyalkenes from which the substituent groups are derived are
typically
homopolymers and interpolymers of polymerizable olefin monomers of 2 to about
16 carbon
atoms, and usually 2 to 6 carbon atoms. The amines which are reacted with the
succinic
acylating agents to form the carboxylic dispersant composition can be
monoamines or
polyamines.
[0037] Succinimide dispersants are referred to as such since they normally
contain
nitrogen largely in the form of imide functionality, although the amide
functionality may be
in the form of amine salts, amides, imidazolines as well as mixtures thereof.
To prepare a
succinimide dispersant, one or more succinic acid-producing compounds and one
or more
amines are heated and typically water is removed, optionally in the presence
of a
substantially inert organic liquid solvent/diluent. The reaction temperature
can range from
about 80 C up to the decomposition temperature of the mixture or the product,
which
typically falls between about 100 C to about 300 C. Additional details and
examples of
procedures for preparing the succinimide dispersants of the present invention
include those
described in, for example, U.S. Patent Nos. 3,172,892, 3,219,666, 3,272,746,
4,234,435,
6,165,235 and 6,440,905.
[0038] Suitable ashless dispersants may also include amine dispersants, which
are
reaction products of relatively high molecular weight aliphatic halides and
amines, preferably
polyalkylene polyamines. Examples of such amine dispersants include those
described in, for
example, U.S. Patent Nos. 3,275,554, 3,438,757, 3,454,555 and 3,565,804.
[0039] Suitable ashless dispersants may further include "Mannich dispersants,"
which
are reaction products of alkyl phenols in which the alkyl group contains at
least about 30
carbon atoms with aldehydes (especially formaldehyde) and amines (especially
polyalkylene
polyamines). Examples of such dispersants include those described in, for
example, U.S.
Patent Nos. 3,036,003, 3,586,629. 3,591,598 and 3,980.569.
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[0040] Suitable ashless dispersants may also be post-treated ashless
dispersants such
as post-treated succinimides, e.g., post-treatment processes involving borate
or ethylene
carbonate as disclosed in, for example, U.S. Patent Nos. 4,612,132 and
4,746,446; and the
like as well as other post-treatment processes. The carbonate-treated alkenyl
succinimide is a
polybutene succinimide derived from polybutenes having a molecular weight of
about 450 to
about 3000, preferably from about 900 to about 2500, more preferably from
about 1300 to
about 2300, and most preferably from about 2000 to about 2400, as well as
mixtures of these
molecular weights. Preferably, it is prepared by reacting, under reactive
conditions, a
mixture of a polybutene succinic acid derivative, an unsaturated acidic
reagent copolymer of
an unsaturated acidic reagent and an olefin, and a polyamine, such as
disclosed in U.S. Patent
No. 5,716,912, the contents of which are incorporated herein by reference.
[0041] Suitable ashless dispersants may also be polymeric, which are
interpolymers
of oil-solubilizing monomers such as decyl methacrylate, vinyl decyl ether and
high
molecular weight olefins with monomers containing polar substitutes. Examples
of
polymeric dispersants include those described in, for example, U.S. Patent
Nos. 3,329,658;
3,449,250 and 3,666,730.
[0042] In a preferred embodiment of the present invention, an ashless
dispersant for
use in the lubricating oil composition is an ethylene, carbonate-treated
bissuccinimide derived
from a polyisobutenyl group having a number average molecular weight of about
2300. The
dispersant(s) for use in the lubricating oil compositions of the present
invention are
preferably non-polymeric (e g., are mono- or bissuccinimides).
[0043] Generally, the ashless dispersant is present in the lubricating oil
composition
in an amount ranging from about 3 to about 10 wt. %, and preferably from about
4 to about 8
wt. %, based on the total weight of the lubricating oil composition.
[0044] The at least one metal-containing detergent compound employed in the
lubricating oil composition of the present invention functions both as a
detergent to reduce or
remove deposits and as an acid neutralizer or rust inhibitor, thereby reducing
wear and
corrosion and extending engine life. Detergents generally comprise a polar
head with long
hydrophobic tail, with the polar head comprising a metal salt of an acid
organic compound.
[0045] The lubricating oil composition of the present invention may contain
one or
more detergents, which are normally salts, and especially overbased salts.
Overbased salts,
or overbased materials, are single phase, homogeneous Newtonian systems
characterized by a
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metal content in excess of that which would be present according to the
stoichiometry of the
metal and the particular acidic organic compound reacted with the metal. The
overbased
materials are prepared by reacting an acidic material (typically an inorganic
acid or lower
carboxylic acid such as carbon dioxide) with a mixture comprising an acidic
organic
compound, in a reaction medium comprising at least one inert, organic solvent
(such as
mineral oil, naphtha, toluene, xylene) in the presence of a stoichiometric
excess of a metal
base and a promoter.
[0046] Useful acidic organic compounds for making the overbased compositions
include carboxylic acids, sulfonic acids, phosphorus-containing acids, phenols
and mixtures
thereof. Preferably, the acidic organic compounds are carboxylic acids or
sulfonic acids with
sulfonic or thiousulfonic groups (such as hydrocarbyl-substituted
benzenesulfonic acids), and
hydrocarbyl-substituted salicylic acids.
[0047] 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.
Neutral or overbased products may then be obtained by methods well known in
the art. The
aromatic moiety of the aromatic carboxylic acid can contain one or more
heteroatoms such as
nitrogen and oxygen. Preferably, the moiety contains only carbon atoms. More
preferably,
the moiety contains six or more carbon atoms, such as a benzene moiety. The
aromatic
carboxylic acid may contain one or more aromatic moieties, such as one or more
benzene
rings, optionally fused together or otherwise connected via alkylene bridges.
Representative
examples of aromatic carboxylic acids include 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. In that case, salicylic acids are generally
obtained in a
diluent in admixture with an uncarboxylated phenol.
[0048] Metal salts of phenols and sulfurized phenols are prepared by reaction
with an
appropriate metal compound such as an oxide or hydroxide. Neutral or overbased
products
may be obtained by methods well known in the art. For example, 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 form products that are
mixtures of
compounds in which 2 or more phenols are bridged by sulfur-containing bridges.
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[0049] The metal compounds useful in making the overbased salts are generally
any
Group I or Group II metal compounds in the Periodic Table of the Elements.
Group I metals
of the metal base include Group la alkali metals (e.g., sodium, potassium,
lithium) as well as
Group lb metals such as copper. Group I metals are preferably sodium,
potassium, lithium
and copper, more preferably sodium or potassium, and particularly preferably
sodium. Group
II metals of the metal base include Group IIa alkaline earth metals (e.g.,
magnesium, calcium,
strontium, barium) as well as Group IIb metals such as zinc or cadmium.
Preferably, the
Group II metals are magnesium, calcium, barium, or zinc, more preferably
magnesium or
calcium, and most preferably calcium.
[0050] Examples of the overbased detergents include, but are not limited to,
calcium
sulfonates, calcium phenates, calcium salicylates, calcium stearates and
mixtures thereof.
Overbased detergents suitable for use in the lubricating oil compositions of
the present
invention may be low overbased (e.g., an overbased detergent having a TBN
below about
100). The TBN of such a low-overbased detergent may be from about 5 to about
50, or from
about 10 to about 30, or from about 15 to about 20. Alternatively, the
overbased detergents
suitable for use in the lubricating oil compositions of the present invention
may be high
overbased (e.g., an overbased detergent having a TBN above about 100). The TBN
of such a
high-overbased detergent may be from about 150 to about 450, or from about 200
to about
350, or from about 250 to about 280. A low-overbased calcium sulfonate
detergent with a
TBN of about 17 and a high-overbased sulfurized calcium phenate with a TBN of
about 400
are two exemplary overbased detergents for use in the lubricating oil
compositions of the
present invention. The lubricating oil compositions of the present invention
may contain
more than one overbased detergent, which may be all low-TBN detergents, all
high-TBN
detergents, or a mixture thereof. For example, the lubricating oil
compositions of the present
invention may contain a first metal-containing detergent which is an overbased
alkaline earth
metal sulfonate detergent having a TBN of about 150 to about 450 and a second
metal-
containing detergent which is an overbased alkaline earth metal sulfonate
detergent having a
TBN of about 10 to about 50.
[0051] Suitable detergents for the lubricating oil compositions of the present
invention also include "hybrid" detergents such as, for example,
phenate/salicylates,
sulfonate/phenates, sulfonate/salicylates, sulfonates/phenates/salicylates,
and the like.
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Examples of hybrid detergents include those described in, for example, U.S.
Patent Nos,
6,153,565, 6,281,179, 6,429,178, and 6,429,179.
[0052] Generally, the metal-containing detergent is present in the lubricating
oil
composition in an amount ranging from about 0.25 to about 3 wt. %, and
preferably from
about 0.5 to about 2 wt. %, based on the total weight of the lubricating oil
composition.
[0053] The antioxidant compounds employed in the lubricating oil composition
of the
present invention reduce the tendency of base stocks to deteriorate in
service, which
deterioration can be evidenced by the products of oxidation such as sludge and
varnish-like
deposits on the metal surfaces and by viscosity growth. Such oxidation
inhibitors include
hindered phenols, ashless oil soluble phenates and sulfurized phenates, alkyl-
substituted
diphenylamine, alkyl-substituted phenyl and naphthylamines and the like and
mixtures
thereof. Suitable diphenylamine antioxidants include, but are not limited to,
monoalkylated
diphenylamine, dialkylated diphenylamine, trialkylated diphenylamine, and the
like and
mixtures thereof. Representative examples of diphenylamine antioxidants
include
butyldiphenylamine, di-butyldiphenylamine, octyldiphenylamine, di-
octyldiphenylamine,
nonyldiphenylamine, di-nonyldiphenylamine, t-butyl-t-octyldiphenylamine, and
the like and
mixtures thereof.
[0054] Generally, the antioxidant compound is present in the lubricating oil
composition in an amount ranging from about 0.2 to about 4 wt. %, and
preferably from
about 0.3 to about 1 wt. %, based on the total weight of the lubricating oil
composition.
[0055] The anti-wear agent compounds other than a zinc dialkyl dithiophosphate
compound employed in the lubricating oil composition of the present invention
include
molybdenum-containing complexes such as, for example, a molybdenum/nitrogen-
containing
complex. Such complexes are known in the art and are described, for example,
in U.S. Patent
No. 4,263,152, the content of which is incorporated by reference herein.
[0056] The structure of the molybdenum/nitrogen complexes is not known with
certainty. However, the molybdenum/nitrogen complexes are believed to be
compounds in
which molybdenum, whose valences are satisfied with atoms of oxygen or sulfur,
is either
complexed by, or the salt of, one or more nitrogen atoms of the basic nitrogen
containing
compound used in the preparation of these compositions. The molybdenum
compounds used
to prepare the molybdenum and molybdenum/nitrogen complexes are acidic
molybdenum
compounds. By acidic is meant that the molybdenum compounds will react with a
basic
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nitrogen compound as measured by ASTM test D-664 or D-2896 titration
procedure.
Typically, these molybdenum compounds are hexavalent. Suitable molybdenum
compounds
include molybdic acid, ammonium molybdate, sodium molybdate, potassium
molybdate and
other alkaline metal molybdates and other molybdenum salts such as hydrogen
salts, e.g.,
hydrogen sodium molybdate, MoOC14, MoO2Br2, MozO3C16, molybdenum trioxide and
the
like and mixtures thereof. Preferred acidic molybdenum compounds are molybdic
acid,
ammonium molybdate, and alkali metal molybdates. Particularly preferred are
molybdic acid
and ammonium molybdate.
[0057] The basic nitrogen-containing compound used to prepare the
molybdenum/nitrogen complexes have at least one basic nitrogen and are
preferably oil-
soluble. Representative examples of basic nitrogen-containing compounds
include
succinimides, carboxylic acid amides, hydrocarbyl monoamines, hydrocarbon
polyamines,
Mannich bases, phosphoramides, thiophosphoramides, phosphonamides, dispersant
viscosity
index improvers, and the like and mixtures thereof. Any of the nitrogen-
containing
compounds may be post-treated with, e.g., boron, using procedures well known
in the art so
long as the compositions continue to contain basic nitrogen. The post-
treatments are
particularly applicable to succinimides and Mannich base compositions.
[0058] The succinimides that can be used to prepare the molybdenum complexes
described herein are disclosed in numerous references and are well known in
the art. Certain
fundamental types of succinimides and the related materials encompassed by the
term of art
"succinimide" are taught in U.S. Patent Nos. 3,172,892; 3,219,666 and
3,272,746, the content
of which is incorporated by reference herein. The term "succinimide" is
understood in the art
to include many of the amide, imide, and amidine species which may also be
formed. The
predominant product however is a succinimide and this term has been generally
accepted as
meaning the product of a reaction of an alkenyl substituted succinic acid or
anhydride with a
nitrogen-containing compound. Preferred succinimides, because of their
commercial
availability, are those succinimides prepared from a hydrocarbyl succinic
anhydride, wherein
the hydrocarbyl group contains from about 24 to about 350 carbon atoms, and an
ethylene
amine. Examples of ethylene amines include ethylene diamine, diethylene
triamine,
triethylene tetramine, tetraethylene pentamine and the like. Particularly
preferred are those
succinimides prepared from polyisobutenyl succinic anhydride of about 70 to
about 128
carbon atoms and tetraethylene pentamine or triethylene tetramine and mixtures
thereof.
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[0059] Also included within the term "succinimide" are the cooligomers of a
hydrocarbyl succinic acid or anhydride and a poly secondary amine containing
at least one
tertiary amino nitrogen in addition to two or more secondary amino groups.
Ordinarily this
composition has between about 1,500 and about 50,000 average molecular weight.
A typical
compound would be that prepared by reacting polyisobutenyl succinic anhydride
and
ethylene dipiperazine.
[0060] Carboxylic acid amide compounds are also suitable starting materials
for
preparing the molybdenum complexes. Examples of such compounds include those
disclosed
in, for example, U.S. Patent No. 3,405,064, the content of which is
incorporated by reference
herein. These compounds are ordinarily prepared by reacting a carboxylic acid
or anhydride
or ester thereof, having at least about 12 to about 350 aliphatic carbon atoms
in the principal
aliphatic chain and, if desired, having sufficient pendant aliphatic groups to
render the
molecule oil soluble with an amine or a hydrocarbyl polyamine, such as an
ethylene amine, to
give a mono or polycarboxylic acid amide. Preferred are those amides prepared
from (1) a
carboxylic acid of the formula R'COOH, wherein R1 is C12 to C20 alkyl or a
mixture of this
acid with a polyisobutenyl carboxylic acid in which the polyisobutenyl group
contains from
about 72 to about 128 carbon atoms and (2) an ethylene amine, especially
triethylene
tetramine or tetraethylene pentamine or mixtures thereof.
[0061] Another class of basic nitrogen-compounds which are useful in preparing
the
molybdenum/nitrogen complex is hydrocarbyl monoamines and hydrocarbyl
polyamines,
e.g., as disclosed in U.S. Pat. No. 3,574,576, the content of which is
incorporated by
reference herein. The hydrocarbyl group, e.g., an alkyl group or olefinic
group having one or
two sites of unsaturation, usually contains from about 9 to about 350 carbon
atoms, and
preferably from about 20 to about 200 carbon atoms. Particularly preferred
hydrocarbyl
polyamines are those which are derived, e.g., by reacting polyisobutenyl
chloride and a
polyalkylene polyamine, such as an ethylene amine, e.g., ethylene diamine,
diethylene
triamine, tetraethylene pentamine, 2-aminoethylpiperazine, 1,3-propylene
diamine, 1,2-
propylenediamine, and the like.
[0062] Another class of basic nitrogen-compounds useful for supplying basic
nitrogen
is the Mannich base compound. These compounds are prepared from a phenol or C9
to C200
alkylphenol, an aldehyde, such as formaldehyde or formaldehyde precursor such
as
paraformaldehyde, and an amine compound. The amine may be a mono or polyamine
and
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typical compositions are prepared from an alkylamine, such as methylamine or
an ethylene
amine, e.g., diethylene triamine or tetraethylene pentamine, and the like. The
phenolic
material may be sulfurized and preferably is dodecylphenol or a Cso to Cioo
alkylphenol.
Typical Mannich bases are disclosed in U.S. Patent Nos. and 3,368,972;
3,539,663;
3,649,229 and 4,157,309, the content of which is incorporated by reference
herein. The
Mannich base can be prepared by reacting an alkylphenol having at least about
50 carbon
atoms, preferably about 50 to about 200 carbon atoms with formaldehyde and an
alkylene
polyamine H2N(ANH)eH where A is a saturated divalent alkyl hydrocarbon of
about 2 to
about 6 carbon atoms and e is 1 to about 10 and where the condensation product
of the
alkylene polyamine may be further reacted with urea or thiourea. The utility
of these
Mannich bases as starting materials for preparing lubricating oil additives
can often be
significantly improved by treating the Mannich base using conventional
techniques to
introduce boron into the compound.
[0063] The molybdenum-containing complexes can be sulfurized or non-
sulfurized.
Representative sulfur sources for preparing the molybdenum/sulfur complexes
include sulfur,
hydrogen sulfide, sulfur monochloride, sulfur dichloride, phosphorus
pentasulfide, R2Sf
wherein R2 is a hydrocarbyl such as a Ci to C40 alkyl, and f is at least 2,
inorganic sulfides
and polysulfides such as (NH4)2Sg, where g is at least 1, thioacetamide,
thiourea, and
mercaptans of the formula R2SH wherein R2 is as defined above. Also useful as
sulfurizing
agents are traditional sulfur-containing antioxidants such as wax sulfides and
polysulfides,
sulfurized olefins, sulfurized carboxylic and esters and sulfurized ester-
olefins, and sulfurized
alkylphenols and the metal salts thereof.
[0064] Generally, the molybdenum/nitrogen-containing complex can be made with
an
organic solvent comprising a polar promoter during a complexation step and
procedures for
preparing such complexes are described, for example, e.g., in U.S. Pat. Nos.
4,259,194;
4,259,195; 4,261,843; 4,263,152; 4,265,773; 4,283,295; 4,285,822; 4,369,119;
4,370,246;
4,394,279; 4,402,840; and 6,962,896 and U.S. Patent Application Publication
No.
2005/0209111, the contents of which are incorporated by reference herein. As
shown in
these references, the molybdenum/nitrogen-containing complex can further be
sulfurized.
[0065] In one embodiment, the anti-wear agent compounds for use herein are
substantially free of any phosphorus and/or sulfur content. In another
embodiment, the anti-
wear agent compounds for use herein are free of any phosphorus and/or sulfur
content.
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[0066] Generally, the anti-wear agent compounds other than a zinc dialkyl
dithiophosphate compound are present in the lubricating oil composition in an
amount
ranging from about 0.25 to about 5 wt. %, and preferably from about 0.3 to
about 2 wt. %,
based on the total weight of the lubricating oil composition.
[0067] The lubricating oil compositions of the present invention can be
conveniently
prepared by simply blending or mixing the ashless dispersant, at least one
metal-containing
detergent, antioxidant and anti-wear agent other than a zinc dialkyl
dithiophosphate
compound, optionally with other additives, with the oil of lubricating
viscosity. The ashless
dispersant, metal-containing detergent, antioxidant and anti-wear agent other
than a zinc
dialkyl dithiophosphate compound may also be preblended as a concentrate or
package with
various other additives, if desired, in the appropriate ratios to facilitate
blending of a
lubricating composition containing the desired concentration of additives. The
ashless
dispersant, at least one metal-containing detergent, antioxidant and anti-wear
agent other than
a zinc dialkyl dithiophosphate compound are blended with the base oil using a
concentration
at which they provide improved antiwear effect and are both soluble in the oil
and compatible
with other additives in the desired finished lubricating oil. Compatibility in
this instance
generally means that the present compounds as well as being oil soluble in the
applicable
treat rate also do not cause other additives to precipitate under normal
conditions. Suitable
oil solubility/compatibility ranges for a given compound of lubricating oil
formulation can be
determined by those having ordinary skill in the art using routine solubility
testing
procedures. For example, precipitation from a formulated lubricating oil
composition at
ambient conditions (about 20 C to 25 C) can be measured by either actual
precipitation from
the oil composition or the formulation of a "cloudy" solution which evidences
formation of
insoluble wax particles.
[0068] The lubricating oil compositions of the present invention may also
contain
other conventional additives for imparting auxiliary functions to give a
finished lubricating
oil composition in which these additives are dispersed or dissolved. For
example, the
lubricating oil compositions can be blended with friction modifiers, rust
inhibitors, dehazing
agents, demulsifying agents, metal deactivating agents, pour point
depressants, antifoaming
agents, co-solvents, package compatibilisers, corrosion-inhibitors, dyes,
extreme pressure
agents and the like and mixtures thereof. A variety of the additives are known
and
commercially available. These additives, or their analogous compounds, can be
employed
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for the preparation of the lubricating oil compositions of the invention by
the usual blending
procedures.
[0069] Examples of friction modifiers include, but are not limited to,
alkoxylated
fatty amines; borated fatty epoxides; fatty phosphites, fatty epoxides, fatty
amines, borated
alkoxylated fatty amines, metal salts of fatty acids, fatty acid amides,
glycerol esters, borated
glycerol esters; and fatty imidazolines as disclosed in U.S. Patent No.
6,372,696, the contents
of which are incorporated by reference herein; friction modifiers obtained
from a reaction
product of a C4 to CAS, preferably a C6 to C24, and most preferably a C6 to
C20, fatty acid ester
and a nitrogen-containing compound selected from the group consisting of
ammonia, and an
alkanolamine and the like and mixtures thereof. The friction modifier can be
incorporated in
the lubricating oil composition in an amount ranging of from about 0.02 to
about 2.0 wt. % of
the lubricating oil composition, preferably from about 0.05 to about 1.0 wt.
%, and more
preferably from about 0.1 to about 0.5 wt. %.
[0070] Examples of rust inhibitors include, but are not limited to, nonionic
polyoxyalkylene agents, e.g., polyoxyethylene lauryl ether, polyoxyethylene
higher alcohol
ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether,
polyoxyethylene octyl stearyl ether, polyoxyethylene oleyl ether,
polyoxyethylene sorbitol
monostearate, polyoxyethylene sorbitol monooleate, and polyethylene glycol
monooleate;
stearic acid and other fatty acids; dicarboxylic acids; metal soaps; fatty
acid amine salts;
metal salts of heavy sulfonic acid; partial carboxylic acid ester of
polyhydric alcohol;
phosphoric esters; (short-chain) alkenyl succinic acids; partial esters
thereof and nitrogen-
containing derivatives thereof; synthetic alkarylsulfonates, e.g., metal
dinonylnaphthalene
sulfonates; and the like and mixtures thereof.
[0071] Examples of antifoaming agents include, but are not limited to,
polymers of
alkyl methacrylate; polymers of dimethylsilicone and the like and mixtures
thereof.
[0072] The lubricating composition of the present invention may also contain a
viscosity index improver. Examples of the viscosity index improvers include
poly-(alkyl
methacrylate), ethylene-propylene copolymer, styrene-butadiene copolymer, and
polyisoprene. Viscosity index improvers of the dispersant type (having
increased
dispersancy) or multifunction type are also employed. These viscosity index
improvers can
be used singly or in combination. The amount of viscosity index improver to be
incorporated
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into an engine oil varies with desired viscosity of the compounded engine oil,
and generally
in the range of about 0.5 to about 20 wt. % per total amount of the engine
oil.
[0073] The lubricating oil composition of the present invention possesses a
wear
reducing property greater than that of a corresponding lubricating oil
composition in which a
zinc dihydrocarbyl dithiophosphate such as a zinc dialkyl dithiophosphate
compound is
present therein. In one embodiment of the present invention, the lubricating
oil composition
of the present invention possesses a wear reducing property at least about 20%
greater than
that of a corresponding lubricating oil composition in which a zinc
dihydrocarbyl
dithiophosphate such as a zinc dialkyl dithiophosphate compound is present
therein. In
another embodiment of the present invention, the lubricating oil composition
of the present
invention possesses a wear reducing property at least about 25% greater than
that of a
corresponding lubricating oil composition in which a zinc dialkyl
dithiophosphate compound
is present therein.
[0074] The final application of the lubricating oil compositions of this
invention may
be, for example, in marine cylinder lubricants in crosshead diesel engines,
crankcase
lubricants in automobiles and railroads and the like, lubricants for heavy
machinery such as
steel mills and the like, or as greases for bearings and the like. In one
embodiment, the
lubricating oil compositions of this invention are used to lubricate an
internal combustion
engine such as a spark ignition engine, a compression ignition diesel engine,
e.g., a heavy
duty diesel engine or a compression ignition diesel engine equipped with at
least one of an
exhaust gas recirculation (EGR) system; a catalytic converter; and a
particulate trap.
[0075] Whether the lubricating oil composition is fluid or solid will
ordinarily depend
on whether a thickening agent is present. Typical thickening agents include
polyurea acetates,
lithium stearate and the like.
[0076] The following non-limiting examples are illustrative of the present
invention.
EXAMPLE 1
[0077] A lubricating oil composition was formed containing 3.858 wt. % of an
ethylene carbonate post-treated bis-succinimide prepared from a 2300 average
molecular
weight polyisobutenyl succinic anhydride with a heavy polyamine, 0.286 wt. %
borated
glycerol monooleate friction modifier, 0.487 wt. % molybdenum succinimide
dispersant/wear
inhibitor, 0.490 wt. % diphenylamine antioxidant, 0.593 wt. % 17 TBN calcium
sulfonate
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detergent, 1.141 wt. % 410 TBN calcium sulfonate detergent, 0.050 wt. %
silicone-based
foam inhibitor, 0.537 wt. % Exxon 100 N diluent oil and 4.800 wt. % ethylene-
propylene
copolymer viscosity index improver, in 87.46 wt. % Group II base oil. The
resulting
lubricating oil composition had a phosphorus content of 0 wt. % and a sulfur
content of 0.051
wt. %.
COMPARATIVE EXAMPLE A
[0078] To the lubricating oil composition of Example 1 was added 0.64 wt. % of
zinc
dihydrocarbyl dithiophophate. The resulting lubricating oil composition had a
phosphorus
content of 0.048 wt. % and a sulfur content of 0.151 wt. %.
COMPARATIVE EXAMPLE B
[0079] A lubricating oil composition was formed containing 2.35 wt. %
succinimide
dispersant, 6 wt. % borated succinimide dispersant, 2.84 wt. % 260 TBN
sulfurized calcium
phenate detergent, 1.02 wt. % 17 TBN calcium sulfonate detergent, 0.22 wt. %
410 TBN
calcium sulfonate detergent, 0.3 wt. % diphenyl amine antioxidant, 0.6 wt. %
hindered
phenol antioxidant, 0.4 wt. % terephthalic acid salt of a bis-succinimide
(derived from 1300
MW PIBSA and heavy polyamine) dispersant, 0.5 wt. % molybdenum succinimide
complex
dispersant/wear inhibitor, 10 ppm foam inhibitor, 5.75 wt. % functionalized
viscosity index
improver, 0.3 wt. % pour point depressant, 0.75 wt. % non-functionalized
viscosity index
improver, and 1.89 wt. % zinc dihydrocarbyl dithiophophate in 76.17 wt. % base
oil
consisting of 24.5 wt. % base oil consisting of 24.5% Group II base oil having
a kinematic
viscosity (kv) at 100 C of 4.7 to 4.9 cSt and 75.5 wt. % Group II base oil
having a kv at
100 C of 7.8 to 7.9 cSt. The resulting lubricating oil composition had a
phosphorus content
of 0.150 wt. % and a sulfur content of 0.445 wt. %.
[0080] Testing
[0081] Mini-traction Machine Evaluation
[0082] The lubricating oil composition of Example 1 and the lubricating oil
compositions of Comparative Examples A and B were evaluated using a PCS
Instruments
Ltd., London UK, Mini-Traction Machine (MTM) bench test. The PCS MTM
instrument
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was modified so that a 1/4-in. diameter Falex 52100 steel test ball (with
special holder) was
substituted for the pin holder that came with the instrument (see, e.g.,
Yamaguchi, E. S.,
"Friction and Wear Measurements Using a Modified MTM Tribometer," IP.com
Journal 7,
Vol. 2, 9, pp 57-58 (August 2002), No. IPCOM000009117D; and Yamaguchi, E. S.,
"Soot
Wear in Diesel Engines", Journal of Engineering Tribology, Proceedings of the
Institution of
Mechanical Engineers Part J, Vol. 220, No. J5, pp. 463-469 (2006)). The
instrument was
used in the pin-on-disk mode and run under sliding conditions. It is achieved
by fixing the
ball rigidly in the special holder, such that the ball stays still while the
disk slides under it.
The conditions are shown in Table 1.
TABLE 1
Test Conditions for MTM
Load 14 N
Initial Contact Pressure 1.53 GPa
Temperature 116 C
Tribocouple 52100/52100
Speed mm/Sec. Min.
3800 10
2000 10
1000 10
100 10
20 10
10
5 10
Length of Timer 70 Min. Test
Diesel Engine Soot 9%
[0083] Engine soot obtained from the overhead recovery system of an engine
testing
facility was used for this test. Mineral oil was added to the soot before it
was shipped.
Therefore, the soot has to be washed prior to the test. It was made into a
thin slurry with
pentane. The slurry was stirred for a few minutes before it was filtered
through a Whatman
Number 2 filter paper over a Buchner funnel. The precipitate was made into a
thin slurry
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again and filtered through a Whatman Number 2 filter paper again. The
precipitate was then
dried in a vacuum oven at 20 inch vacuum and 90 C for more than 16 hours. The
dried soot
was then sieved through a 50 mesh (300 gm maximum) before use. The objective
of this
operation was to remove the oil and other impurities so that reproducible
particles are made
and they would give rise to abrasive wear as seen in modem exhaust gas
recirculation (EGR)
engines.
[0084] To prepare the test specimens, the anti-corrosion coating of the PCS
Instruments 52100 smooth (0.02 micron Ra), steel discs was removed using
heptane, hexane,
and isooctane. Then, the discs were wiped clean with a soft tissue and
submersed in a beaker
of the cleaning solvent until the film on the disc track had been removed, and
the track of the
disc appeared shiny. The discs and test balls were placed in individual
containers and
submerged in Chevron 450 thinner. Lastly, the test specimens were
ultrasonically cleaned by
placing them in a sonicator for 30 minutes.
[0085] The results of this evaluation are set forth in Figure 1, which show
the wear
scar diameter (WSD) and standard deviation (STD) of the lubricating oil
compositions of
Example 1 and Comparative Examples A and B. As the data show, the lubricating
oil
composition of Example 1 containing no zinc dihydrocarbyl dithiophophate
provided a
significantly improved MTM wear result as compared to the same lubricating oil
composition
of Comparative Example A treated with a zinc dihydrocarbyl dithiophophate.
This was
unexpected as zinc dihydrocarbyl dithiophophate is a known antiwear agent and
would be
expected to improve the wear result of the lubricating oil composition. In
fact, the MTM
wear result of the lubricating oil composition of Example 1 is lower than the
lubricating oil
composition of Comparative Example B, which is a standard lubricant containing
a relatively
high amount of zinc dihydrocarbyl dithiophophate.
[0086] It will be understood that various modifications may be made to the
embodiments disclosed herein. Therefore the above description should not be
construed as
limiting, but merely as exemplifications of preferred embodiments. For
example, the
functions described above and implemented as the best mode for operating the
present
invention are for illustration purposes only. Other arrangements and methods
may be
implemented by those skilled in the art without departing from the scope and
spirit of this
invention. Moreover, those skilled in the art will envision other
modifications within the
scope and spirit of the claims appended hereto.
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