Note: Descriptions are shown in the official language in which they were submitted.
CA 02447567 2003-10-31
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LUBRICATING OIL COMPOSITION
The present invention relates to lubricating oil compositions. More
particularly,
the present invention relates to lubricating oil compositions exhibiting
improved
antioxidant properties with reduced phosphorus and sulfur content.
BACKGROUND OF THE INVENTION
to Lubricating oil compositions used to lubricate internal combustion engines
contain base oil of lubricating viscosity, or a mixture of such oils, and
additives used to
improve the performance characteristics of the oil. For example, additives are
used to
improve detergency, reduce engine wear, to provide stability against heat and
oxidation,
to reduce oil consumption, to inhibit corrosion, to act as a dispersant, and
reduce friction
15 loss. Some additives provide multiple benefits, such as a
dispersant/viscosity modifier.
Other additives, while improving one characteristic of the lubricating oil,
have an adverse
effect on other characteristics. Thus, to provide a lubricating oil having
optimal overall
performance, it is necessary to characterize and understand all the effects of
the various
additives available, and carefully balance the additive content of the
lubricant.
To provide improved low temperature valve train wear performance, conventional
lubricants are formulated with an antiwear additive. Metal hydrocarbyl
dithiophosphates,
particularly zinc dialkyldithiophosphates (ZDDP), are the primary antiwear
additive used
in lubricating oils for internal combustion engines. ZDDP provides excellent
wear
protection at a comparatively low cost and also functions as an antioxidant.
However,
there is some evidence that phosphorus in lubricants can shorten the effective
life of
automotive emission catalysts. Accordingly, industry has limited the amount of
phosphorus that lubricants can contain. The proposed category (ILSAC GF-4) is
expected to require not more than 0.08 wt. % P and 0.5 wt. % S in the finished
oil, and it
CA 02447567 2003-10-31
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is expected that future categories will require that the phosphorus content of
lubricants be
further reduced to below 0.06 wt. %.
U.5. Patent Nos. 5,346,635 and 5,439,605 describe lubricating oils completely
free of phosphorus-containing antiwear additives containing a complex blend of
ashless
friction reducers, ashless antiwear/extreme pressure additives, antioxidants,
metal
detergents and polymeric viscosity modifiers and flow improvers, which
compositions
purportedly provide acceptable properties. These compositions may also contain
a
molybdenum-containing additive, as a friction modifier.
Each of WO 96/37,582 and EP 0 855 437 describes lubricating oil formulations
that contain, in addition to other specified and required additives, an amount
of ZDDP
that may provide 600 ppm or less of phosphorus, together with a molybdenum-
based
friction modifier.
It has been proposed in many patents and articles (for example, U.S. Patent
No.
4,164,473; 4,176,073; 4,176,074; 4,192,757; 4,248,720; 4,201,683; 4,289,635;
and
4,479,883) that oil soluble molybdenum compounds are useful as lubricant
additives. In
particular, molybdenum compounds provide enhanced fuel economy in gasoline or
diesel
fueled engines (spark- and compression-ignited engines, respectively),
including both
short and long term fuel economy (i.e., fuel economy retention properties).
Oil soluble copper compounds are known to be effective antioxidants, as
described in U.S. Patent No. 4,867,890.
It is desirable to formulate reduced phosphorus lubricating oils providing
acceptable antioxidative properties, without the use of substantial amounts of
relatively
expensive ashless (metal-free) antioxidants.
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SUMMARY OF THE INVENTION
In accordance with this invention, there is provided a lubricating oil
composition
comprising a major amount of oil of lubricating viscosity, an oil soluble
molybdenum
compound in an amount sufficient to provide the composition with 0.001 to 0.10
mass
of molybdenum; and an oil soluble copper antioxidant in an amount providing
the
composition with from about 0.001 to 0.02 mass % copper, which composition
contains
an amount of metal hydrocarbyl dithiophosphate, such as ZDDP, that introduces
from
l0 100 ppm to 550 ppm of phosphorus to the lubricating oil composition.
Preferably, the lubricating oil composition contains no more than 0.5 wt. % of
sulfur.
Preferably, the lubricating oil composition is substantially free (less than
about 1
wt. %, preferably less than 0.5 wt. %, more preferably 0 to 0.25 wt. %) of
ashless
antioxidant.
Also preferably, the oil of lubricating viscosity has a viscosity of between
about
4.0 mm2/sec and 5.5 mm2/sec at 100°C and/or the lubricating oil
composition (the fully
formulated oil) has a Noack volatility of no more than 15 wt. %.
The present invention is based on the discovery that the combination of
molybdenum compound and copper compound, in lubricating oil compositions
formulated with relatively low amounts of ZDDP, provides an unexpected
cooperative
antioxidative effect.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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To provide a low cost, commercially acceptable product providing excellent
overall properties, especially oxidation resistance, the lubricating oil
compositions of the
present invention comprise a major amount of oil of lubricating viscosity, an
amount of a
dihydrocarbyl dithiophosphate metal salt, preferably an amount providing 200
to 550
ppm by mass of phosphorus; a molybdenum compound in an amount providing the
composition with from about 0.005 to 0.1 mass % molybdenum and an oil soluble
copper
antioxidant in an amount providing the composition with from about 0.001 to
0.02 mass
copper, wherein all mass percentages and ppm are based on the total mass of
the
lubricating oil composition or finished oil.
The oil of lubricating viscosity useful in the context of the present
invention is
selected from the group consisting of Group I, Group II, or Group III, Group
IV or Group
V base stocks or base oil blends of the aforementioned base stocks. Generally,
the
viscosity of such oils ranges from about 2 mm2/sec (centistokes) to about 40
mmz/sec at
100°C. Preferred are base stocks or base stock mixtures having an
intrinsic viscosity of
from about 4.0 to about 5.5 mm2/sec at 100°C. Further preferable are
base stocks and
base stock mixtures having a volatility, as measured by the Noack test
(measured by
determining the evaporative loss in mass percent of an oil after 1 hour at
250°C according
to the procedure of ASTM D5880), of less than 15%, more preferably less than
12%,
2o most preferably less than 10%. The most preferred oils for both fuel
economy retention
and low temperature valve train antiwear performance are:
(a) Base oil blends of Group III, IV or V base stocks with Group I or Group II
base stocks, where the combination has a viscosity index of at least 110;
and
(b) Group III, IV or V base stocks or base oil blends of more than one Group
III, IV and/or V base stock, where the viscosity index is between about
120 to about 140.
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Definitions for the base stocks and base oils in this invention are the same
as those
found in the American Petroleum Institute (API) publication "Engine Oil
Licensing and
Certification System", Industry Services 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.
l0 b.) Group II base stocks contain greater than or equal to 90 percent
saturates
and less than or equal to 0.03 percent sulfi~r and have a viscosity index
greater than or equal to 80 and less than 120.
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.
d.) Group IV base stocks are polyalphaolefins (PAO).
e.) Group V base stocks include all other base stocks not included in Group I,
II, III, or IV.
2o Table 1 - Analytical Methods for Base Stock
Property Test Method
Saturates ASTM D 2007
Viscosity IndexASTM D 2270
Sulfur ASTM D 2622
ASTM D 4294
ASTM D 4927
ASTM D 3120
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The metal dihydrocarbyl dithiophosphate antiwear agents comprise dihydrocarbyl
dithiophosphate metal salts wherein 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. Although the present specification hereafter
makes
express mention of ZDDP, dihydrocarbyl dithiophosphate metal salts based on
these
other metals should be considered equivalent.
Dihydrocarbyl dithiophosphate metal salts may be prepared in accordance with
known techniques by first forming a dihydrocarbyl dithiophosphoric acid
(DDPA),
to usually by reaction of one or more alcohol or a phenol with PISS and then
neutralizing the
formed DDPA with a zinc compound. For example, 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
15 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.
2o The preferred zinc dihydrocarbyl dithiophosphates are oil soluble salts of
dihydrocarbyl dithiophosphoric acids and may be represented by the following
formula:
S
RO
P S Zn
R'O
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,
CA 02447567 2003-10-31
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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 can therefore comprise zinc dialkyl
dithiophosphates. The
zinc dialkylthiophosphate compound can be primary zinc, secondary zinc, or
mixtures
thereof.
to
ZDDP (or other dihydrocarbyl dithiophosphate metal salt) is added to
lubricating
oil compositions of this invention in an amount within a limited range to gain
the
beneficial effects and yet comply with low phosphorus regulations. To provide
the
antiwear advantages of ZDDP but limit phosphorus to a minimum of 100 ppm and a
15 maximum of 550 ppm by mass (calculated as elemental phophorus), the amount
of ZDDP
should be limited to an amount of from about 0.12 to about 0.7 wt.%,
preferably from
about 0.24 to about 0.63 wt. %, based on the total weight of the lubricating
oil
composition (finished oil).
2o Lubricating oil compositions of this invention contain an amount of a
molybdenum
compound, or combination of molybdenum compounds, providing the composition
with
from about 0.001 to 0.1, preferably from about 0.005 to 0.05 mass % of
molybdenum. Any
suitable soluble organo-molybdenum compound having anti-wear properties in
lubricating
oil compositions having reduced phosphorus contents may be employed. The oil-
soluble
25 or oil-dispersible molybdenum compound suitable for use in the present
invention is
typically in the form of a molybdenum additive comprising one or more oil-
soluble or
oil-dispersible molybdenum compounds. In a preferred embodiment, the
molybdenum
compound is a molybdenum-sulfur compound.
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The molybdenum-sulfur compounds useful in the present invention may be
mononuclear or polynuclear. 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. To enable
the
molybdenum-sulfur compound to be oil-soluble or oil-dispersible, one or more
ligands
are 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
1o and another ligand may be electrostatically bonded.
Preferably, the or each ligand is monoanionic and examples of such ligands are
dithiophosphates, dithiocarbamates, xanthates, carboxylates, thioxanthates,
phosphates
and hydrocarbyl, preferably alkyl, derivatives thereof. 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.
2o The oil-solubility or oil-dispersibility of the molybdenum-sulfur compound
may
be influenced by the total number of carbon atoms present among a,11 of the
compound
ligands. The total number of carbon atoms present among all of the hydrocarbyl
groups of
the compound 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 molybdenum-sulfur compounds include dinuclear molybdenum-
sulfur compounds and trinuclear molybdenum-sulfur compounds.
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An example of a dinuclear molybdenum-sulfur compound is represented by the
formula:
Rl ,s X~ Xz X4 S R3
\N / \ ~ ~ / \ ( ~ / w., /
C, M\ /Mo\ ~ N\
/ \ / ,,
R2 S X3 S R4
where R1 to R4 independently denote a straight chain, branched chain or
aromatic
hydrocarbyl group having 1 to 24 carbon atoms; and X, to X4 independently
denote an
oxygen atom or a sulfur atom. The four hydrocarbyl groups, R, to Rq, may be
identical or
different from one another.
In a preferred embodiment, the molybdenum-sulfur compound is an oil-soluble or
oil-dispersible trinuclear molybdenum-sulfur compound. Examples of trinuclear
molybdenum-sulfur compounds are disclosed in W098126030, W099131113,
W099/66013, EP-A-1 138 752, EP-A-1 138 686 and European patent application no.
02078011. Preferably the trinuclear molybdenum-sulfur compound has a core of
the
structures depicted in (I) or (II):
S' Mo 'S
S
Mo- _Mo
S (i)
or
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S~M ~~'IS
S S
S
Mo- _Mo
~' S~
S
(II);
wherein each core has a net electrical charge of +4.
Preferably, the trinuclear molybdenum-sulfur compounds are represented by the
formula Mo3SkExL"ApQZ, 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 recognize that formation of the trinuclear molybdenum-
sulfur compound requires selection of appropriate ligands (L) and other anions
(A),
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.
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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 one
embodiment of the present invention, 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 another embodiment, k is 4 or
7, L is a
monoanionic ligand, n is 4 and each of p, x and z is 0.
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
2o atom, to form oligomers. Molybdenum-sulfur additives comprising such
oligomers are
considered to fall within the scope of this invention. Other examples of
molybdenum
compounds include molybdenum carboxylates and molybdenum nitrogen complexes,
both of which may be sulfurised,
The lubricating oil compositions of the invention contain an oil soluble
copper
antioxidant in an amount providing the composition with from about 0.001 to
0.02 mass %,
preferably from about 0.008 to about 0.016 wt. %, of copper (calculated as
elemental
copper).
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Examples of suitable copper-containing antioxidants include oil soluble copper
compounds mentioned in published European Patent Application Nos. EP 0 024 146
B, EP
0 280 579 A, EP 0 280 580 A and U.S. 4,867,890. Thus, for example, the copper
may be
blended into the oil as an oil-soluble copper salt of a synthetic or natural
carboxylic acid.
s Examples of carboxylic acids from which suitable copper salts may be derived
include CZ to
C,8 fatty acids (e.g., acetic acid, stearic acid and palinitic acid),
unsaturated acids (e.g., oleic
acid), branched carboxylic acids (e.g., naphthenic acids of molecular weight
of from 200 to
500, neodecanoic acid and 2-ethylhexanoic acid), and alkyl- or alkenyl-
substituted
dicarboxylic acids (e.g., polyalkenyl-substituted succinic acids such as
octadecenyl succinic
to acids, dodecenyl succinic acids and polyisobutenyl succinic acids). In some
cases, suitable
compounds may be derived from an acid anhydride, for example, from a
substituted
succinic anhydride.
The copper antioxidant may be, for example, a copper dithiocarbamate or copper
15 dithiophosphate. Other copper and sulfur-containing antioxidant compounds,
for example,
copper mercaptides, xanthates, thioxanthates, are also suitable for use in
accordance with
the invention, as are copper sulfonates, phenates (optionally sulfurized) and
acetylacetonates. Other copper compounds which may be used in accordance with
the
invention are overbased copper compounds. Examples of such compounds, and of
2o processes for their preparation, are given in U.S. Patent No. 4,664,822 and
European
Specification No. 0 425 367 A. The copper compound may be in cuprous or cupric
form.
The amount of phosphorus, molybdenum and copper present in any composition
is measured in accordance with the procedures of ASTM D5185.
2s
Preferably, the lubricating oil compositions of the present invention are
substantially
free (contain less than about 1 wt. %, preferably less than 0.5 wt. %, more
preferably 0 to
CA 02447567 2003-10-31
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0.25 wt.%) of ashless, or metal-free, supplemental oxidation inhibitors.
Typical
commercial ashless antioxidants include both phenolic and aminic antioxidants.
Ashless phenolic antioxidants include hindered phenols, alkaline earth metal
salts of
alkylphenolthioesters having preferably CS to C,z alkyl side chains,
nonylphenol sulfide
(NPS), ashless oil soluble phenates and sulfurized phenates and
phosphosulfurized or
sulfurized hydrocarbons.
Ashless aminic antioxidants include aromatic amines having at least two
aromatic
1o groups attached directly to the nitrogen. 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-,
15 SOz- or alkylene group) and two are directly attached to one amine nitrogen
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.
Additional additives may be incorporated into the compositions of the
invention
to enable particular performance requirements to be met. Examples of
additional
additives that may be included in the lubricating oil compositions of the
present invention
are ashless dispersants, ash-forming detergents, metal rust inhibitors,
viscosity index
2s improvers, corrosion inhibitors, anti-foaming agents, and pour point
depressants. Some
are discussed in further detail below.
Dispersants maintain in suspension materials resulting from oxidation during
use
that are insoluble in oil, thus preventing sludge flocculation and
precipitation, or
CA 02447567 2003-10-31
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deposition on metal parts. 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. Such ashless dispersants comprises an oil soluble
polymeric
hydrocarbon backbone having functional groups that are capable of associating
with
particles to be dispersed. Typically, such dispersants comprise amine,
alcohol, amide, or
ester polar moieties attached to the polymer backbone often via a bridging
group. The
ashless dispersant may, for example, be 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. Also suitable are Mannich condensation products formed by condensing
a long
chain substituted phenol with formaldehyde and polyalkylene polyamine.
Dispersants can be used in the lubricating oil compositions of the present
invention in amounts of from about 0.5 to 10.0 wt.%, preferably from about 1
to 3 wt.%.
Preferred are polyisobutenyl succinimide dispersants wherein the
polyisobutenyl moiety
has an Mn of about 500 to 3,000, preferably about 900 to 2,500. A preferred
embodiment
utilizes polyisobutenyl succinimide dispersants prepared using polyisobutylene
prepared
2o 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
Glissopal~ (from BASF) and UltravisTM (from BP-Amoco).
Metal-containing or ash-forming detergents function both as detergents to
reduce or
remove deposits and as acid neutralizers or rust inhibitors, thereby reducing
wear and
CA 02447567 2003-10-31
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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.
The salts may contain a substantially stoichiometric amount of the metal in
which they are
usually described as normal or neutral salts, and would typically have a total
base number
(TBN), as may be measured by ASTM D-2896 of from 0 to 80. It is possible to
include
large amounts of a metal base by reacting an excess of a metal compound such
as an oxide
or hydroxide with an acid gas such a such as carbon dioxide. The resulting
overbased
detergent comprises neutralized detergent as the outer layer of a metal base
(e.g., carbonate)
micelle. Such overbased detergents may have a TBN of 150 or greater, and
typically from
250 to 450 or more.
Known detergents include oil-soluble neutral and overbased sulfonates,
phenates,
sulfurized phenates, thiophosphonates, salicylates, and naphthenates and other
oil-soluble
carboxylates of a metal, particularly the alkali or alkaline earth metals,
e.g., sodium,
potassium, lithium, calcium, and magnesium. The most commonly used metals are
calcium
and magnesium, which may both be present in detergents used in a lubricant,
and mixtures
of calcium and/or magnesium with sodium. Particularly convenient metal
detergents are
neutral and overbased calcium sulfonates having TBN of from 20 to 450 TBN, and
neutral
and overbased calcium phenates and sulfurized phenates having TBN of from 50
to 450.
In the present invention, overbased detergents are preferred, and when used,
may
be used in amounts of from about 0.5% to 5% weight percent based on the total
weight of
the composition. The total base number of the overbased sulfonate detergent is
preferably between about 150 to 450. Further preferably, the overbased
detergent is
2s overbased calcium sulfonate.
The viscosity modifier (VM) functions to impart high and low temperature
operability to lubricating oil. The VM used may have that sole function, or
may be
multifunctional. Representative examples of suitable viscosity modifiers are
CA 02447567 2003-10-31
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polyisobutylene, copolymers of ethylene and propylene, polymethacrylates,
methacrylate
copolymers, copolymers of an unsaturated dicarboxylic acid and a vinyl
compound,
interpolymers of styrene and acrylic esters, and partially hydrogenated
copolymers of
styrene/ isoprene, styrene/butadiene, and isoprene/butadiene, as well as the
partially
hydrogenated homopolymers of butadiene and isoprene. Multifunctional viscosity
modifiers that fiurther function as dispersants are also known.
Rust inhibitors selected from the group consisting of nonionic polyoxyalkylene
polyols and esters thereof, polyoxyalkylene phenols, and anionic alkyl
sulfonic acids may
1o be used.
Copper and lead bearing corrosion inhibitors may be used, but are typically
not
required with the formulation of the present invention. Typically such
compounds are the
thiadiazole polysulfides containing from 5 to 50 carbon atoms, their
derivatives and
is polymers thereof. Derivatives of 1,3,4 thiadiazoles such as those described
in U.S. Patent
Nos. 2,719,125; 2,719,126; and 3,087,932; are typical. Other similar materials
are
described in U.S. Patent Nos. 3,821,236; 3,904,537; 4,097,387; 4,107,059;
4,136,043;
4,188,299; and 4,193,882. Other additives are the thio and polythio
sulfenamides of
thiadiazoles such as those described in UK Patent Specification No. 1,560,830.
2o Benzotriazoles derivatives also fall within this class of additives. When
these compounds
are included in the lubricating composition, they are preferably present in an
amount not
exceeding 0.2 wt. % active ingredient.
A small amount of a demulsifying component may be used. A preferred
25 demulsifying component is described in EP 330,522. It is obtained by
reacting an alkylene
oxide with an adduct obtained by reacting a bis-epoxide with a polyhydric
alcohol. The
demulsifier should be used at a level not exceeding 0.1 mass % active
ingredient. A treat
rate of 0.001 to 0.05 mass % active ingredient is convenient.
CA 02447567 2003-10-31
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Pour point depressants, otherwise known as tube oil flow improvers, lower the
minimum temperature at which the fluid will flow or can be poured. Such
additives are well
known. Typical of those additives which improve the low temperature fluidity
of the fluid
are C8 to C,8 dialkyl fiunarate/vinyl acetate copolymers,
polyalkylmethacrylates and the
like.
Foam control can be provided by many compounds including an antifoamant of the
polysiloxane type, for example, silicone oil or polydimethyl siloxane.
1 o The individual additives may be incorporated into a base stock in any
convenient
way. Thus, each of the components can be added directly to the base stock or
base oil blend
by dispersing or dissolving it in the base stock or base oil blend at the
desired level of
concentration. Such blending may occur at ambient temperature or at an
elevated
temperature.
Preferably, all the additives except for the viscosity modifier and the pour
point
depressant are blended into a concentrate or additive package described herein
as the
additive package, that is subsequently blended into base stock to make the
finished
lubricant. The concentrate will typically be formulated to contain the
additives) in proper
2o amounts to provide the desired concentration in the final formulation when
the concentrate
is combined with a predetermined amount of a base lubricant.
The concentrate is preferably made in accordance with the method described in
US
4,938,880. That patent describes making a pre-mix of ashless dispersant and
metal
detergents that is pre-blended at a temperature of at least about
100°C. Thereafter, the pre-
mix is cooled to at least 85°C and the additional components are added.
CA 02447567 2003-10-31
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The final crankcase lubricating oil formulation may employ from 2 to 20
mass %, preferably 4 to 18 mass %, and most preferably about S to 17 mass % of
the
concentrate or additive package with the remainder being base stock. The
compositions
can be used in the formulation of crankcase lubricating oils (i.e., passenger
car motor oils,
heavy duty diesel motor oils, and passenger car diesel oils) for spark-ignited
and
compression-ignited engines.
Preferably, the lubricating oil compositions of the present invention contain
no
more than 0.5 wt. % of sulfur.
This invention will be further understood by reference to the following
examples,
wherein all percentages are by weight of active ingredient, unless otherwise
noted, and
which include preferred embodiments of the invention.
is EXAMPLES
The following lubricating oils were prepared and the antioxidative properties
were
tested using MHT-4 (Medium High Temperature-4) TEOST (Thermal Engine Oil
Stability Test) in accordance with the procedures of ASTM 06335. Each of the
lubricating oil samples contained identical amounts of identical mineral oil
base stock,
dispersant, detergent, organic friction modifier and antifoam agent. Each
sample
contained 0.64 wt. % of ZDDP, which provided each sample with a phosphorus
content
of 510 ppm. The amount of copper compound (copper oleate), molybdenum compound
(molybdenum dithiocarbamate) and supplemental ashless antioxidant (nonylphenol
sulfide or "NPS").
The amount of copper compound and molybdenum compound are reported as
wt.% of elemental copper and molybdenum introduced, respectively. MHT-4 TEOST
results are reported as mg of weight gain (of deposit). Lower weight gain
indicates
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improved antioxidative properties. The GF-3 lubricating oil specification
allows a
maximum limit of 45 mg. The GF-4 lubricating oil specification has a proposed
maximum limit of 25 mg.
Table 2
Example C 1 C2 I1 C3 C4 CS
Cu (mass 0 0.016 0.008 0.016 0 0
%)
Mo (mass 0 0 0.011 0.011 0 0.019
%)
nr>?s (wt. 0 0 0 1.1 s 1.1 s o
i)
DescriptionBaselineCu Cu/Mo Cu/NPS NPS Mo
TEOST (mg) 68.9 63.5 46.9 65.8 63.7 51.2
Example I1 represents the lubricating oil compositions of the present
invention.
As shown by the data presented in Table 2, in lubricating oil compositions
having a
reduced phosphorus content, a combination of a copper compound and a
molybdenum
compound provided antioxidative properties that were superior to those
provided by an
equivalent amount of either the copper compound or the molybdenum compound
used
individually, as well as a combination of a molybdenum compound and an ashless
phenolic antioxidant.
It should be noted that the lubricating oil compositions of this invention
comprise
defined, individual, i.e., separate, components that may or may not remain the
same
chemically before and after mixing. Thus, it will be understood that various
components
of the composition, essential as well as optional and customary, may react
under the
conditions of formulation, storage or use and that the invention also is
directed ta, and
encompasses, the product obtainable, or obtained, as a result of any such
reaction.
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The principles, preferred embodiments and modes of operation of the present
invention have been described in the foregoing specification. What applicants
submit is
their invention, however, is not to be construed as limited to the particular
embodiments
disclosed, since the disclosed embodiments are regarded as illustrative rather
than
limiting. Changes may be made by those skilled in the art without departing
from the
spirit of the invention.
