Note: Descriptions are shown in the official language in which they were submitted.
Lubricating Oil Compositions Comprising Dual Dispersants
This application claims priority to Japanese Patent Application number JP 2011-
214116 which
was tiled on September 29, 2011.
Field of Invention
The present invention relates to a lubricating oil composition favorably
employable for
lubricating internal combustion engines such as diesel engines and gasoline
engines. In
particular, the invention relates to a lubricating oil composition having a
low sulfur content of
about 0.5 wt.% or less, particularly about 0.2 wt.% or less, which reduces
friction occurring in
the internal combustion engines mounted to land-travelling automotives using
low sulfur
hydrocarbon fuel and shows good high temperature detergency.
Background of Invention
The sulfur contained in fuels such as gasolines or diesel fuels employed for
operating
internal combustion engines is oxidized when it burns in the engine to give
sulfur oxide such as
sulfuric acid. A portion of the sulfur oxide enter the lubricating oil
employed for lubricating the
engine, and the remaining portion is exhausted with other exhaust gases. The
sulfur oxide ex-
hausted with other exhaust gases causes environmental pollution. Hence, the
sulfur content in
the fuel has been heretofore under severe regulation. The regulation on the
sulfur content was
initially applied to gasolines (fuels for gasoline engines). However, the
regulation on the sulfur
content has been also applied recently to diesel fuels having a higher sulfur
content. The sulfur
content in the diesel fuels has been recently regulated to be not higher than
0.0010 wt.%.
As a result of the decrease of the sulfur content, the lubricating oil is less
contaminated
with sulfur oxide such as sulfuric acid which is produced when the fuel burns.
This means that
the amount of the overbasic metal-containing detergent in the lubricating oil
can be reduced.
The basic metal-containing detergent serves for neutralizing the sulfur oxide
in the lubricating
oil.
When the fuel burns in the engine, not only the fuel, but also a portion of
the lubricating
3 0 oil burns in the engine. A gas produced by burnt lubricating oil is
also exhausted with other
exhaust gas. Therefore, it is desirable to reduce the amount of the sulfur
content of the
lubricating oil.
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By the way, the recently employed lubricating oils for internal combustion
engines
comprise a base oil (hydrocarbon oil having lubricating viscosity) and a
variety of additives
(i.e., lubricating oil additives) such as a basic metal-containing detergent
for neutralizing the
emigrated sulfur oxide, an oxidation inhibitor for keeping the base oil
functioning at elevated
temperature from deteriorating, a dispersant for dispersing soots produced by
burning of fuels
and residues produced by deterioration of the base oil and metal-containing
detergent in the
base oil, an extreme pressure agent for preventing of seizure of the piston
and cylinder, a fric-
tion-reducing agent (friction modifier) for reducing friction occurring
between the piston and
cylinder.
Therefore, the phosphorus component and metal component contained in the
additive
placed in the lubricating oil composition are decomposed when the lubricating
oil composition
burns and enter the exhaust gas in the form of phosphorus oxides and metal
oxides. The
phosphorus oxides and metal oxides contained in the exhaust gas, are brought
into contact with
oxidative catalyst or reductive catalyst placed in the exhaust gas-cleaning
apparatus and
1 5 inactivate the catalyst.
For the reasons described above, it has been demanded to reduce the sulfated
ash
content, phosphorus content and sulfur content of the lubricating oil
composition.
Patent publication 1 (JP 2002-53888 A) discloses a lubricating oil composition
favorably employable for lubricating internal combustion engines operated
using a fuel having
.. a low sulfur content, particularly, diesel engines. The disclosed
lubricating oil composition
comprises a base oil having a sulfur content of 0.1 wt.% or less (preferably
0.03 wt.% or less)
and the following additives:
a) an ashless dispersant comprising an alkenyl- or alkyl-succinimide or a
derivative
thereof in an amount of 0.01-0.3 wt.% in terms of the nitrogen content;
b) a metal-containing detergent having a sulfur content of 3 wt.% or less and
a TBN of
10-350 mg=KOH/g in an amount of 0.1-1 wt.% in terms of the sulfated ash
content;
c) a zinc dialkyldithio phosphate in an amount of 0.01-0.12 wt.% in terms of
the
phosphorus content;
d) an oxidation-inhibiting phenolic compound and/or an oxidation-inhibiting
amine
compound in an amount of 0.01-5 wt.%,
the lubricating oil composition having a sulfated ash content of 0.1-1 wt.%, a
phosphorus content of 0.01-0.1, a sulfur content of 0.01-0.3 wt.%, a chlorine
content of 40
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CA 02791202 2012-09-28
wt.ppm or less, and an organic acid salt derived from the metal-containing
detergent in an
amount of 0.2 to 7 wt.% (preferably 0.5-5 wt.%, more preferably 1.0-3 wt.%),
wherein the above-mentioned contents and amounts are expressed based on the
total
amount of the lubricating oil composition.
Patent Publication 1 further discloses in the working examples that the
disclosed
lubricating oil compositions show good high temperature detergency in the
internal combustion
engines.
Patent Publication 1 furthermore discloses that the lubricating oil
composition may
contain a molybdenum-containing compound which can serve as a friction
modifier, an oxida-
tion inhibitor as well as an anti-wear agent. The molybdenum-containing
compound can be one
of known molybdenum-containing compounds such as sulfoxymolybdenum
dithiocarbamate,
sulfoxymolybdenum dithiophosphate and molybdenum complexes of succinimide
possibly con-
taining sulfur.
Patent Publication 2 (JP 2004-149802 A) discloses a lubricating oil
composition having
a low sulfated ash content, a low phosphorus content and a low sulfur content,
preferably em-
ployable for lubricating internal combustion engines (that is, engine oil),
which comprises a
base oil, an ethylene carbonate post-treated ashless dispersant, a borated
ashless dispersant, an
overbased metal-containing detergent and a phosphorus compound. Patent
Publication 2
further discloses that the disclosed lubricating oil composition may contain a
molybdenum-
2 0 succinimide complex. In the working examples of Patent Publication 2,
it is shown by
experimental data that the lubricating oil composition shows good oxidation
stability as well as
good anti-wear performance.
Patent Publication 3 discloses a low sulfated ash, low phosphorus, low sulfur
engine oil
(engine oil composition) comprising a low sulfur base oil, a boron-containing
ashless disper-
2 5 sant, a molybdenum-containing friction modifier, a metal-containing
detergent such as sul-
fonate, phenate or salicylate, and a zinc dithiophosphate. The molybdenum-
containing friction
modifier can be molybdenum diorgano-dithiocarbamate, molybdenum diorgano-
dithiophosphate, molybdenum carboxylate, and a trinuclear molybdenum compound
such as
Mo3S7(dtc)4 or Mo3S4(dtc)4. In the working examples, it is shown by the
experimental data that
30 the lubricating oil composition employing the above-mentioned trinuclear
molybdenum com-
pound has particularly good high temperature oxidation stability and a good
friction reductive
performance.
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As is described above, it has been known that the molybdenum-containing
compound is
particularly effective as a friction modifier to be incorporated into
lubricating oil compositions.
As the known molybdenum-containing compounds, molybdenum diorgano
dithiocarbamate and molybdenum diorgano dithiophosphate are most generally
employed.
However, both compounds have disadvantage problems, in that the former
contains sulfur (S)
in its molecular structure and the latter contains phosphorous (P) in its
molecular structure, and
hence both produce poisonous gases such as sulfur oxide gas and phosphorus
oxide gas when
the lubricating oil burns in the internal combustion engine, resulting in
inactivation of the
catalysts of the exhaust gas-clearing apparatus. As is explained above, Patent
Publication 3
describes that a trinuclear molybdenum compound such as Mo3S7(dtc)4 or
Mo3S4(dtc)4 shows a
good friction-modifying function (friction-reducing function). However, these
trinuclear
molybdenum compounds contains sulfur atoms in the molecular structure of its
ligand moiety,
i.e., dithiocarbamate, dtc, and further contains other sulfur atoms directly
attached to the molyb-
denum atom, and hence, the trinuclear molybdenum compounds contains a
relatively large
amount of sulfur in the compound per se. Therefore, the trinuclear molybdenum
compound is
not favorably employed for incorporation into the lubricating oil composition
if reduction of the
sulfur content in the oil composition is intended.
Summary of Invention
Accordingly, it is the object of the invention to provide a molybdenum-
containing
friction-reducing agent having no or a relatively less amount of sulfur and
phosphorus which is
favorably employable in place of the conventionally employed friction-reducing
agents
containing sulfur and phosphorus in relatively large amounts, such as
molybdenum diorgano-
dithiocarbamate, molybdenum diorgano-dithiophosphate, molybdenum carboxylatc,
and a tri-
2 5 nuclear molybdenum compound such as Mo3S7(dtc)4 or Mo3S4(dtc)4.
The present inventors have found that the friction-reducing function of the
known
molybdenum complex of a basic nitrogen-containing compound such as a
molybdenum-
suceinimide complex is prominently enhanced if the molybdenum complex is
incorporated into
lubricating oil compositions in combination with specifically selected amounts
of an alkenyl- or
alkyl-succinimide or its derivative (which is known as an ashless dispersant)
and an alkenyl- or
alkyl-succinic acid ester (succinate) or its derivative (which is also known
as an ashless
dispersant).
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The present invention has been made on the above-mentioned inventors' new
finding. It
has been further found out that the lubricating oil compositions containing
the above-mentioned
molybdenum complex of a basic nitrogen-containing compound but not containing
the
succinimide or its derivative (and further not containing the succinate or its
derivative) show
improved resistance to oxidation at high temperatures but the oil compositions
show little
reduction of the friction coefficient.
Accordingly, the present invention provides a lubricating oil composition for
lubricating
internal combustion engines which has a sulfur content of 0.5 wt.% or less and
which comprises
a base oil having a lubricating viscosity and at least the following additive
components a) to e):
a) an ashless dispersant in an amount of 0.5-5.0 wt.% which comprises an
alkenyl- or
alkyl-succinimide or a derivative thereof;
b) an ashless dispersant in an amount of 0.5-5.0 wt.% which comprises an
alkenyl- or
alkyl-succinic ester or a derivative thereof;
c) a molybdenum complex of a basic nitrogen-containing compound in an amount
of
50-1,200 wt.ppm in terms of a molybdenum content thereof;
d) an alkaline earth metal-containing detergent having a TBN in the range of
10 to 400
mg=KOH/g in an amount of 0.05-1.0 wt.% in ternis of an alkaline earth metal
content thereof-,
and
e) an anti-wear agent in an amount of 0.05-5.0 wt.%.
The present invention further provides a method for operating internal engines
mounted
to land-travelling vehicles using a fuel having a sulfur content of 0.001 wt.%
or less under
lubrication with the above-mentioned lubricating oil composition according to
the invention.
Preferred embodiments of the invention are stated below.
(1) The lubricating oil composition has the sulfur content in the range of
0.01 to 0.2
wt.%.
(2) The lubricating oil composition has the sulfur content in the range of
0.05 to
0.12 wt.%.
(3) The lubricating oil composition is a multi-grade engine oil further
comprising a
viscosity index improver, whereby being classified to 0W5, OW10, OW15, 0W20,
0W30,
5W20, 5W30, 10W20, or 10W30.
5
(4) The lubricating oil composition contains the component a), namely, an
alkenyl-
or alkyl-succinimide or a derivative thereof, in an amount of 1.0-4.0 wt.%.
(5) The lubricating oil composition contains the component b), namely, an
alkenyl-
or alkyl-succinic ester or a derivative thereof, is contained in an amount of
1.0-4.0 wt.%.
(6) The lubricating oil composition wherein a ratio of the component a) to
the
component b) is in the range of 1:4 to 4:1.
(7) The component c), namely, a molybdenum complex of a basic nitrogen-
containing compound, contains a sulfur not larger than 1 wt.%.
(8) The component c), namely, the molybdenum complex of a basic nitrogen-
containing compound, contains a sulfur in the range of 0.05 to 0.5 wt.%.
(9) The component c) is a molybdenum complex of a succinimide.
(10) The component d) comprises an alkaline earth metal salicylate.
(11) The anti-wear agent is a zinc dialkyldithiophosphate.
(12) The lubricating oil composition further comprises an oxidation inhibitor.
(13) The lubricating oil composition is used for lubricating internal
combustion engines
operated using a fuel oil having a sulfur content of 0.001 wt.% or less.
In an aspect, there is provided a lubricating oil composition for lubricating
internal
combustion engines which has a sulfur content of 0.5 wt.% or less and which
comprises a base
oil having a lubricating viscosity and at least the following additive
components a) to e):
a) an ashless dispersant in an amount of 0.5-5.0 wt.% which is an alkenyl- or
alkyl-succinimide;
b) an ashless dispersant in an amount of 0.5-5.0 wt.% which is an alkenyl- or
alkyl-succinic ester;
c) a molybdenum complex of a basic nitrogen-containing compound in an
amount of 50-1,200 wt ppm in terms of the molybdenum content thereof;
d) an alkaline earth metal-containing detergent having a TBN in the range of
10
to 400 rrig=KOH/g in an amount of 0.05-1.0 wt.% in terms of an alkaline earth
metal content
thereof; and
e) an anti-wear agent in an amount of 0.05-5.0 wt.%;
wherein the anti-wear agent is a sulfur-containing anti-wear agent or a
phosphorus-containing
anti-wear agent; wherein the sulfur-containing anti-wear agent is selected
from the
CA 2791202 2018-12-20
group consisting of a sulfurized olefin, a polysulfide compound, a sulfurized
ester, a sulfurized
alcohol, a sulfurized amide, a sulfurized oil, a sulfurized fat, an ashless
dithiocarbamate, a metal
dithiocarbamate, a mercapto thiadiazole, a mercapto benzothiadiazole, and a
mercapto
thiazoline; wherein the phosphorus-containing anti-wear agent is selected from
the group
consisting of a phosphoric acid ester, a phosphorous acid ester, a
thiophosphoric acid ester, a
thiophosphoric amine salt, zinc dialkyldithiophosphate, and zinc
dialkylphosphate; and wherein
the metal dithiocarbamate is other than molybdenum dithiocarbamate.
The lubricating oil composition of the invention contains a molybdenum complex
of a
basic nitrogen-containing compound (serving as a friction-modifier) in
combination of a
.. mixture of known dispersants, that is, an alkenyl- or alkyl-succinimide or
a derivative thereof
and an alkenyl- or alkyl-succinic acid ester (succinate) or a derivative
thereof both in specific
amounts. Therefore, the lubricating oil composition can be prepared to contain
sulfur at a low
level. Nevertheless, the lubricating oil composition of the invention shows a
prominently good
friction-reducing function.
Detailed Description of Invention
The base oil and additives employable for the preparation of the lubricating
oil
composition of the invention are described below in more detail.
2 0 Base Oil
The base oil generally is a mineral oil or a synthetic oil showing a kinematic
viscosity of
2 to 50 mm2/s at 100 C. There are no specific limitations on the natures and
other properties of
6a
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=
the mineral oil and synthetic oil. However, the sulfur content of the base oil
should be 0.1 wt.%
or less. The sulfur content preferably is 0.03 wt.% or less, and more
preferably is 0.005 wt.%
or less.
The mineral oil preferably is an oil which is obtained by processing a
lubricating oil
distillate of a mineral oil by solvent refining, hydrogenation, or their
combination. Particularly
preferred is a highly hydrogenated refined oil (corresponding to a
hydrocracked oil, typically
has a viscosity index of 100 to 150, an aromatic component content of 5 wt.%
or less, a
nitrogen content of 50 wt.ppin or less, and a sulfur content of 50 wt. ppm or
less. Particularly
preferred is a high viscosity index base oil for instance having a viscosity
index of 140-160
which is obtained by hydroisomerization of slack wax or GTL wax (Gas-To-
Liquid).
Examples of the synthetic oils (synthetic lubricating base oils) include poly-
a-olefin
such as a polymerized compound of a-olefin having 3 to 12 carbon atoms; a
dialkyl ester of a
di-basic acid such as sebacic acid, azelaic acid or adipic acid and an alcohol
having 4 to 18
carbon atoms, typically dioctyl sebacate; a polyol ester which is an ester of
1,1,1-
trimethylolpropane or pentaerythritol and a mono-basic acid having 3 to 18
carbon atoms; and
alkylbenzene having an alkyl group of 9 to 40 carbon atoms. The synthetic oil
generally
contains essentially no sulfur, shows good stability to oxidation and good
heat resistance, and
gives less residual carbon and soot when it is burned. Therefore, the
synthetic oil is preferably
employed for the lubricating oil composition of the invention. Particularly
preferred is poly-a-
olefin, from the viewpoint of the object of the invention.
Each of the mineral oil and synthetic oil can be employed singly. If desired,
however,
two or more mineral oils can be employed in combination, and two or more
synthetic oils can
be employed in combination. The mineral oil and synthetic oil can be employed
in combination
at an optional ratio.
Ashless Dispersant
The lubricating oil composition of the invention comprises at least two
different ashless
dispersants, that is, an alkenyl- or alkyl-succinimide or a derivative thereof
(component a) and
an alkenyl- or alkyl-succinic ester or a derivative thereof (component b), in
an amount of 0.5-
5.0 wt.%, preferably 1.0-4.0 wt.%, for each (the amount is based on the total
amount of the
7
CA 02791202 2012-09-28
lubricating oil composition). The component a) and component b) are preferably
contained in a
weight ratio of 1:4 to 4:1, more preferably 1:2 to 2:1.
The component a), namely, the alkenyl- or alkyl-succinimide or a derivative
thereof,
may be a known alkenyl- or alkyl-succinimide or a derivative thereof. For
example, the
alkenyl- or alkyl-succinimide derived from a polyolefin or its derivative may
be employed. A
representative succinimide can be prepared by the reaction between succinic
anhydride
substituted with a high molecular weight alkenyl or alkyl and a polyalkylene
polyamine
containing average 4 to 10 (preferably 5 to 7) nitrogen atoms in one molecule.
The high
molecular weight alkenyl or alkyl is preferably derived from a polybutene
(particularly a high
reactivity polybutene having a vinylidene telininal) having a number average
molecular weight
of about 900 to 3,000.
The process for obtaining the polybutenyl-succinic anhydride by the reaction
of
polybutene and maleic anhydride is generally performed by the chlorination
process using a
chloride compound. The chlorination process is advantageous in its reaction
yield. However,
the reaction product obtained by the chlorination process contains a large
amount (for instance,
approx. 2,000-3,000 wt.ppm) of chlorine. In contrast, if the thermal reaction
process using no
chloride compound is employed, the reaction product contains only an extremely
small chlorine
(for instance, 0-30 ppm). Accordingly, it is preferred that the succinimide be
prepared from a
polybutenyl succinic anhydride which is produced by the thermal reaction,
whereby the
chlorine content of the resulting succinimide is in the range of 0 to 30
wt.ppm. The
succinimide can be reacted with boric acid, alcohol, aldehyde, ketone,
alkylphenol, cyclic
carbonate, organic acid or the like, to give a modified succinimide.
Particularly, a borated
alkenyl(or alkyl)-succinimide which is obtained by the reaction with boric
acid or a boron com-
pound is advantageous from the viewpoints of thermal and oxidation stability.
The component b), namely, the alkenyl- or alkyl-succinic ester or a derivative
thereof,
may be a known
alkenyl- or alkyl-succinic ester or a derivative thereof For example, the
alkenyl- or alkyl-
succinic ester derived from a polyolefin or its derivative may be employed. A
representative
succinic ester can be prepared by the reaction between succinic anhydride
substituted with a
high molecular weight alkenyl or alkyl and an alcohol containing average 1 to
6 hydroxyl
groups in one molecule. The high molecular weight alkenyl or alkyl is
preferably derived from
8
CA 02791202 2012-09-28
a polybutene (particularly a high reactivity polybutene having a vinylidene
terminal) having a
number average molecular weight of about 900 to 3,000.
The lubricating oil composition of the invention may contain other ashless
dispersants
such as an alkenylbenzylamine ashless dispersant in addition to the ashless
dispersant a) (i.e.,
component a)) and ashless dispersant b) (i.e., component b)).
Molybdenum complex of basic nitrogen-containing compound
The lubricating oil composition of the invention further comprises a
molybdenum
complex of a basic nitrogen-containing compound in an amount of 50-1,200
wt.ppm in terms of
a molybdenum content thereof This molybdenum complex is already known as a
multifunctional addi-tive. The molybdenum complex of a basic nitrogen-
containing compound
may contain a small amount of sulfur.
The molybdenum complex of basic nitrogen-containing compound functions mainly
as
an oxidation inhibitor, an anti-wear agent or a friction modifier in the
lubricating oil
composition.
A preferred molybdenum complex of a basic nitrogen-containing compound is an
oxymolybdenum complex produced by reaction of an acidic molybdenum compound
and a
basic nitrogen-containing compound. Examples of the acidic molybdenum
compounds include
molybdic acid, ammonium molybdate, and alkali metal salts of molybdate.
Examples of the
basic nitrogen-containing compounds include succinimide, carboxylic amide,
hydrocarbylamine and a Mannich basic compound. Examples of the molybdenum
complex of
basic nitrogen-containing compounds include a molybdenum complex of
succinimidc and a
molybdenum complex of a secondary aliphatic amine.
The molybdenum complex of a basic nitrogen-containing compound can be employed
after reaction with a small amount of sulfur or a sulfur-containing compound.
Specifically, a
reaction product obtained by sulfurization of a molybdenum complex of
succinimide at low
temperatures. The reaction product preferably contains sulfur in a relatively
small amount such
as 10 wt.% or less. The sulfoxymolybdenum complex can be prepared in the
manner described
in Examples C to H of United States Patent 6,562,765 B.
The lubricating oil composition of the invention can further contain other
molybdenum-
containing compounds such as sulfoxymolybdenum dithiocarbamate,
sulfoxymolybdenum
dithiophosphate, and oxymolybdenum monoglyceride.
9
CA 02791202 2012-09-28
=
Alkaline earth metal-containing Detergent
The lubricating oil composition of the invention further comprises an alkaline
earth
metal-containing detergent having a TBN in the range of 10 to 400 mgeKOH/g in
an amount of
0.05-1.0 wt.% in tet ins of an alkaline earth metal content thereof The
known alkaline earth
metal-containing detergent having a TBN in the range of 10 to 400 mg=KOH/g is
employable.
Preferred is a calcium alkylsalicylate detergent. The calcium alkylsalicylate
detergent
preferably contains an organic acid salt in an amount of 0.2-7 wt.%, more
preferably 0.5-5
wt.%, most preferably 1.0-3 wt.%. The calcium alkylsalicylate detergent
preferably comprises
an unsulfurized calcium alkylsalicylate detergent having an alkyl group
containing 14-18
carbon atoms. The unsulfurized calcium alkylsalicylate detergent having an
alkyl group
containing 14-18 carbon atoms can be employed in combination with an
unsulfurized calcium
alkylsalicylate detergent having an alkyl group containing 20-28 carbon atoms.
In the speci-
fication, the unsulfurized calcium alkylsalicylate detergent having an alkyl
group containing 14-
18 carbon atoms means an unsulfurized calcium alkylsalicylate detergent having
an alkyl group
in which 90 mole % or more of the alkyl groups contain 14-18 carbon atoms. The
unsulfurized
calcium alkylsalicylate detergent having an alkyl group containing 20-28
carbon atoms has the
same meaning, that is, the unsulfurized calcium alkylsalicylate detergent
having an alkyl group
containing 20-28 carbon atoms means an unsulfurized calcium alkylsalicylate
detergent having
an alkyl group in which 90 mole % or more of the alkyl groups contain 20-28
carbon atoms.
The unsulfurized calcium alkylsalicylate preferably is a calcium salt of an
alkylsalicylic
acid which can be prepared from an alkylphenol (which is produced by the
reaction of a-olefin
having the desired number of carbon atoms and phenol) by the Kolbe-Schmidt
reaction.
Generally, the calcium salt of an alkylsalicylic acid can be overbased by the
use of lime and
carbon dioxide, to give an overhased calcium salicylate.
The calcium salt of an alkylsalicylate can be prepared by the steps of
neutralizing
phenol to give its calcium salt and subsequent carbonation.
The calcium alkylsalicylate detergent is preferably incorporated into the
lubricating oil
composition under such conditions that the amount of the organic acid salt
(contained in the
calcium alkylsalicylate detergent) is in the range of 0.2 to 7 wt.%,
preferably 0.5 to 5 wt.%,
more preferably 1.0 to 3 wt.%, based on the total amount of the lubricating
oil composition. In
more detail, the calcium alkylsalicylate detergent is an oily dispersion which
comprises an
organic acid metal salt (generally called a soap component) and basic
inorganic salt micro-
CA 02791202 2012-09-28
=
particles (e.g., calcium carbonate particles) aggregated around the organic
acid metal salt in an
oily medium. Generally, the dispersion contains the oily medium in an amount
of 30 to 50
wt.%. Even if the amount of the calcium alkylsalicylate detergent is reduced,
the high tem-
perature detergency (i.e., power for keeping the inside space of an engine
operated at high
temperatures) of the lubricating oil composition does not substantially lower
provided that the
amount of the organic acid metal salt is kept at or above a certain level.
The alkaline earth metal-containing detergent can be an alkaline earth metal
salt of an
organic acid having a carbon-nitrogen bonding or a phenol derivative. This
detergent can have
a high TBN regardless of a sulfated ash content, if it is treated with an
amine compound. The
amine compound brings a base number originating from the basic nitrogen atoms.
For
example, a metal salt of an aminocarboxylic acid can be employed. Particularly
preferred is an
unsulfurized alkylphenate (i.e., alkaline earth metal salt) having a Mannich
base structure. This
compound can be obtained by Mannich reaction using an alkylphenol,
formaldehyde, and an
amine or an amine compound to give an aminomethylated phenol, and subsequent
neutralization of the reaction product by a base such as calcium hydroxide.
Alternatively, the alkaline earth metal-containing detergent can be an
alkaline earth
metal salt of a sulfonic acid (i.e., sulfonate) obtained from a petroleum
sulfonic acid, an
alkylbenzenesulfonic acid, or an alkyltoluenesulfonic acid.
Alternatively, the alkaline earth metal-containing detergent can be a
sulfurized phenate,
.. namely, an alkaline earth metal salt of a sulfurized alkyl phenol
Anti-wear agent
The lubricating oil composition of the invention further comprises an anti-
wear agent
(component e)) in an amount of 0.05-5.0 wt.%. There are no specific limitation
on the anti-
wear agent, and the known sulfur-containing anti-wear agent as well as the
known phosphorus-
containing anti-wear agent can be employed. Examples of the sulfur-containing
anti-wear
agents include sulfurized olefin, polysulfide compound, sulfurized ester,
sulfurized alcohol,
sulfurized amide, sulfurized oil/fat, ashless dithiocarbamate, metal (other
than molybdenum)
dithiocarbamate, mercapto thiadiazole, mercapto benzothiadiazole, and mercapto
thiazoline.
Examples of the phosphorus-containing anti-wear agents include phosphoric acid
ester,
phosphorous acid ester, thiophosphoric acid ester, their amine salts, and
their metal salts such as
zinc dialkyldithiophosphate, zinc dialkyldithiophosphate, and zinc
dialkylphosphate.
11
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The anti-wear agent, i.e., component e), preferably is zinc
dialkyldithiophosphate or
zinc dihydrocarbylphosphate. These zinc phosphate anti-wear agents are well
known and easily
produced by the known procedures. The zinc phosphate anti-wear agent can be
employed in an
amount of 0.01-0.12 wt.%, but preferably in an amount of 0.01-0.06 wt.%, in
consideration of
the desired low phosphorus content and sulfur content.
The zinc dialkyldithiophosphate preferably contains an alkyl group having 3-18
carbon
atoms or an alkylaryl group having C3.18 alkyl group. Most preferred is a zinc
dialkyldithiophosphate containing an alkyl group derived from a secondary
alcohol having 3-18
carbon atoms or a zinc dialkyldithiophosphate containing a mixture of alkyl
groups derived
from a mixture of a primary alcohol having 3-18 carbon atoms and a secondary
alcohol having
3-18 carbon atoms. Both are particularly effective for reducing wear. A zinc
dialkyldithiophosphate derived from a primary alcohol shows high thermal
resistance. These
zinc dialkyldithiophosphates can be employed alone or in combination in the
form of a mixture
mainly comprising one derived from the secondary alcohol and/or one derived
from the primary
alcohol.
Oxidation Inhibitor
The lubricating oil composition of the invention preferably contains an
oxidation inhibi-
tor in an amount of 0.01-5 wt.%, preferably 0.1-3 wt.%. The oxidation
inhibitor can be the phe-
2 0 .. nolic oxidation inhibitor and the amine oxidation inhibitor. A
lubricating oil composition
having a low sulfated ash content, a low phosphorus content and a low sulfur
content is apt to
show a relatively low high-temperature detergency, oxidation-inhibiting
perfoimance and anti-
wear performance due to decrease of the amounts of the metal-containing
detergent and zinc
dithiophosphate. Therefore, the lubricating oil composition of the invention
preferably contains
an oxidation inhibitor so as to keep these performances high.
Preferred oxidation inhibitors are a cliarylamine oxidation inhibitor and a
hindered
phenol oxidation inhibitor. These oxidation inhibitors also function for
improving high-
temperature detergency. The diarylamine oxidation inhibitor is advantageous in
giving a base
number originating from the nitrogen atoms. The hindered phenol oxidation
inhibitor is
advantageous in producing no NO gas.
Examples of the hindered phenol oxidation inhibitors include 2,6-di-t-butyl-p-
cresol,
4,4'-methylenebis(2,6-di-t-butylphenol), 4,4'-methylenebis(6-t-butyl-o-
cresol), 4,4'-
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CA 02791202 2012-09-28
isopropylidenebis(2,6-di-t-butylphenol), 4,4'-bis(2,6-di-t-butylphenol), 2,2'-
methylenebis(4-
methy1-6-t-butylphenol), 4,4'-thiobis(2-methyl-6-t-butylphenol), 2,2-thio-
diethylenebis[3-(3,5-
di-t-buty1-4-hydoxyphenyl)propionate], octyl 3-(3,5-di-t-buty1-4-
hydroxyphenyl)propionate,
octadecyl 3-(3,5-di-t-buty1-4-hydroxyphenyl)propionate, and oetyl 3-(3,54-
buty1-4-hydroxy-3-
methylphenyl)propionatc.
Examples of the diarylamine oxidation inhibitors include alkyldiphenylamine
having a
mixture of alkyl groups of 4 to 9 carbon atoms, p,p'-dioetyldiphenylamine,
phenyl-a-
naphthylamine, phenyl-a-naphthylamine, alkylated 13-naphthylamine, and
alkylated phenyl-cc-
naphthylamine.
Each of the hindered phenol oxidation inhibitor and diarylamine oxidation
inhibitor can
be employed alone or in combination. If desired, other oil soluble oxidation
inhibitors can be
employed in combination with the above-mentioned oxidation inhibitor(s).
Other Additives
The lubricating oil composition of the invention may further contain an alkali
metal
borate hydrate for increasing stability at high temperatures and a base
number. A representative
alkali metal borate hydrate can be prepared in the manner described in United
States Patents
3,929,650 and 4,089,790. For example, the alkali metal borate hydrate can be
in the form of a
dispersion containing micro-particles of an alkali metal borate hydrate which
is produced by
carbonizing a neutral alkali metal or alkaline earth metal sulfonate in the
presence of an alkali
metal hydroxide to yield an overbased sulfonate and reacting the overbased
sulfonate with boric
acid. In the carbonizing procedure, it is desired to incorporate an ashless
dispersant such as
succinimide into the reaction mixture. The alkali metal preferably is
potassium or sodium. The
alkali metal borate hydrate can be a dispersion of KB305=1-120 particles
having a particle size of
about 0.3 pim or less which is dispersed in the presence of a neutral calcium
sulfonate and
succinimide. From the viewpoint of resistance to hydrolysis, potassium is
preferably replaced
with sodium.
The lubricating oil composition of the invention preferably contains a
viscosity index
improver in an amount of 20 wt.% or less, preferably 1 to 20 wt.%. Examples of
the viscosity
index improvers are polymers such as polyalkyl methacrylate, ethylene-
propylene copolymer,
styrene-butadiene copolymer, and polyisoprene. A dispersant viscosity index
improver and a
13
CA 02791202 2012-09-28
multi-functional viscosity index improver which are produced by providing
dispersing
properties to the above-mentioned polymer are preferably employed. The
viscosity index
improvers can be used alone or in combination.
The lubricating oil composition of the invention may further contain a small
amount of
various auxiliary additives. Examples of the auxiliary additives are described
below.
benzotriazol compounds and thiadiazol compounds functioning as metal
deactivating
agent; nonionic polyoxyalkylene surface active agents such as
polyoxyethylenealkylphenyl
ether and copolymers of ethylene oxide and propylene oxide functioning as an
anti-rust agent
and an anti-emulsifying agent. In addition, various compounds functioning as
an anti-foaming
1 0 agent and a pour point depressant can be incorporated.
The above-mentioned auxiliary additives may be incorporated into the
lubricating oil
composition in an amount of 3 wt.% or less, particularly in an amount of 0.001-
3 wt.%.
Examples
.. (1) Preparation of lubricating oil composition (test oil)
Lubricating oil compositions having a low sulfur content (0.5 wt.% or less)
for evalua-
tion on the oil performance were prepared in the below-described manner using
the below-
mentioned base oil and additives. The lubricating oil compositions were
formulated to show a
viscosity grade (SAE viscosity grade) of 5W30 by addition of a viscosity index
improver.
(2) Base oil and additives
1) Base oil (mixture of the below-mentioned base stock A and base stock B in
the weight ratio
of 46:54)
Base stock A: Hydrocracked base stock showing a kinematic viscosity of 6.4
mm2/s (at
.. 100 C), a viscosity index of 132, a saturated component content of 92 wt.%
and a sulfur content
of less than 0.001 wt.%.
Base stock B: Hydrocracked base stock showing a kinematic viscosity of 4.1
mm2/s (at
100 C), a viscosity index of 127, a saturated component content of 92 wt.% and
a sulfur content
of less than 0.001 wt.%.
2) Additives
Ashless dispersant A: Ethylene carbonate post-treated succinimide dispersant
(nitrogen
content: 0.85 wt.%) prepared by the steps of thermally reacting polybutene
(number average
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CA 02791202 2012-09-28
molecular weight: about 2,200) and maleic anhydride to give
polyisobutenylsuccinic anhydride,
reacting about 2 moles of the polyisobutenylsuccinic anhydride and
polyalkylene polyamine
containing 6.5 nitrogen atoms (average) in one molecule to give a bis-type
succinimide, and
finally treating the bis-type succinimide with ethylene carbonate under
reaction.
Ashless dispersant B: Alkenylsuccinic ester (TAN: 5 mg=KOH/g) prepared by the
steps
of thermally reacting polybutene (number average molecular weight: about
1,000) and maleic
anhydride to give polyisobutenylsuccinic anhydride, reacting about 1.14 moles
of the
polyisobutenylsuccinic anhydride and one mole of pentaerythritol.
Mo complex of succinimide: A product (Mo content: 4.5 wt.%, N content: 2.1
wt.%, S
content: 0.16 wt.%) obtained by the steps of reacting a mono-type
alkenylsuccinimide derived
from polyisobutene having a number average molecular weight of about 1,000 and
molybdic
acid to give a molybdenum complex and reacting the molybdenum complex with a
small
amount of sulfur.
MoDTC: Sulfoxymolybdenum dialkyldithiocarbamate (Mo content: 10 wt.%, S
content: 11 wt.%)
Ca-containing detergent A: Calcium monoalkylsalicylate (alkyl containing about
14-18
carbon atoms, overbase degree: 2.0, Ca content: 6.2 wt.%, S content: 0.12
wt.%)
Ca-containing detergent B: Calcium monoalkylsalicylate (alkyl containing about
20-28
carbon atoms, overbase degree: 8.2, Ca content: 11.4 wt.%, S content: 0.17
wt.%)
Ca-containing detergent C: Calcium sulfonate (neutral type, Ca content: 2.4
wt.%,
sulfur content: 2.7 wt.%)
ZnDTP: zinc dialkyldithiophosphate (P content: 7.2 wt.%, S content: 14.4 wt.%,
derived from a mixture of a secondary alcohol having 4 carbon atoms and a
secondary alcohol
having 6 carbon atoms)
Oxidation inhibitor: Mixture of dialkyldiphenylamine oxidation inhibitor and
hindered
phenol propionate oxidation inhibitor.
Viscosity index improver (VII): Non-dispersant type ethylene-propylene
copolymer
(Paratone 8057)
.. (3) Determination of friction coefficient
The friction coefficient was determined by means of High Frequency
Reciprocating Rig
(HFRR) under the below-described conditions:
CA 02791202 2012-09-28
Oil temperature: 105 C, Load: 400 g, Friction length: 1,0001_im, Reciprocating
frequency: 20 Hz, Test Period: one hour.
(4) Evaluation of inhibition of production of high-temperature deposit
The power inhibiting production of a high-temperature deposit (Deposit) was
evaluated
by means a hot tube tester (HTT) under the below described conditions:
In a heater block was placed vertically a glass tube (inner diameter: 2 mm).
The test oil
and air were supplied into the tube from its bottom at supply rates of 0.31
cc/h and 10 cc/min.,
respectively. These procedures were performed under keeping the temperature of
the heater
element at 280 C for 16 hours. Thereafter, the glass tube was taken out from
the heater block,
washed with petroleum ether, and dried. The deposit attached to the inner
surface of the glass
tube was observed and marked according to the merit rating.
The merit rating was done in the known manner on the basis of 10 points. The
higher
point means that the power of inhibiting production of deposit is high.
(5) Compositions of the test oils and results of determination and evaluation
The test results of the test oils are set forth in Table 1 below.
16
CA 02791202 2012-09-28
Table 1
Base oil/ Example 1 Com.Ex.1 Com.Ex.2
Additives
Ashless disper-
sant A (wt.%) 3.0 5.5 3.0
Ashless disper-
sant B (wt.%) 2.5 2.5
Succinimide Mo-
complex(Mo wt.ppm) 220 220
MoDTC
(Mo wt.ppm) 220
Ca detergent A
(Ca wt.%) 0.19 0.19 0.19
Ca detergent B
(Ca wt.%) 0.06 0.06 0.06
Ca detergent C
(Ca wt.%) 0.01 0.01 0.01
ZnDTP (P wt.%) 0.04 0.04 0.04
Oxidation in-
hibitor (wt.%) 1.0 1.0 1.0
VII (wt.%) 5.0 5.0 5.0
Base oil remainder remainder remainder
S content (wt.%) 0.11 0.11 0.13
________________________________________________________________
Friction
coefficient 0.05 0.12 0.05
HIT merit point 7.5 7.5 5.5
17
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Remarks:
The test results set forth in Table 1 indicate the following:
The lubricating oil composition of the invention comprising succinimide-Mo
complex,
succinimide dispersant (Ashless dispersant A) and succinic ester dispersant
(Ashless dispersant
B) in combination (Test oil of Example 1) shows the same high-temperature
deposit produc-
tion-inhibiting power but markedly low friction coefficient as compared with
the lubricating oil
composition (Test oil of Comparison Example 1) comprising the succinimide-Mo
complex and
succinimide dispersant (Ashless dispersant A) in combination but containing no
succinic ester
dispersant (Ashless dispersant B). Test oil of Comparison Example 2 prepared
by replacing the
succinimide-Mo complex with the same amount of MoDTC (sultbxy molybdenum
dialkyldithiocarbamate) shows the same friction coefficient but poor power of
inhibiting
production of high-temperature deposit.
18
