Note: Descriptions are shown in the official language in which they were submitted.
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LUBRICATING OIL COMPOSITION
BACKGROUND OF THE INVENTION
The present invention relates to a novel lubricating oil composi-
tion. More specifically, the present invention relates to a lubricating oil
composition having excellent antiwear properties and friction-reducing
properties, capable of maintaining the friction-reducing properties, for a
prolonged period of time, useful as a lubricating oil for internal-combustion
engines, automatic transmission gearboxes, dampers, power steering units and
the like, particularly useful as a lubricating oil for internal-combustion
engines.
DISCUSSION OF THE RELATED OIL
Lubricating oils have been used for internal-combustion engines,
and for driving units and gears such as automatic transmission gearboxes,
dampers and power steerings in order to smoothly operate them. In particular,
lubricating oils for internal-combustion engines not only lubricate various
sliding
portions, but also cool the inside of the engines, clean and disperse those
products which are produced by combustion, and furthermore prevent the rusting
and corrosion of the engines.
In order to meet this requirement, various additives such as an
antiwear agent, a metallic detergent, a nonash dispersant and an antioxidant
are
incorporated into the lubricating oils for internal-combustion engines.
It is particularly important that the lubricating oils ensure the
smooth operation of the engines under all operating conditions to prevent the
wear and seizure of the engines. The lubricated parts of the engines are, in
most
cases, under the fluid lubrication condition. However, valve-trains and the
top
and bottom dead centers of a piston tend to be under the boundary lubrication
condition. Antiwear properties under the boundary lubrication condition are
generally imparted by the addition of zinc dithiophosphate or zinc dithio-
carbamate.
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In order to reduce energy lost to friction and to increase fuel
economy, a friction modifier is added to lubricating oils. For example, an
extreme pressure agent such as a molybdenum compound or a phosphoric ester,
or a compound which is an oily agent such as a fatty ester or an alkylamine
has
been generally used as the friction modifier.
However, while lubricating oil containing such a friction modifaer
shows the effect of the friction modifier at the outset of the use thereof, it
loses
the effect when it undergoes oxidative degradation. Namely, the friction-
reducing effect of the friction modifier is greatly affected by additives
other than
the friction modifier, so that it has been difficult for the lubricating oil
to main-
tain, for a long period of time, friction-reducing properties which are shown
at
the beginning of the operation of an engine.
The present invention has accomplished the objective of develop-
ing a lubricating oil (engine oil) which can maintain the effect of reducing
friction in engines for a long period of time under these circumstances.
SUMMARY OF THE INVENTION
It has been discovered that a lubricating oil composition having the
above described properties is obtained by blending, sulfoxymolybdenum dithio-
carbamate having a specific alkyl group, zinc dialkyldithiophosphate having a
specific alkyl group, zinc dialkyldithiophosphate having a specific alkyl
group,
specific alkylsalicylate(s), and, if desired, succinimide containing boron,
each in
a predetermined amount infra lubricating oil base stock. The present invention
has been accomplished on the basis of the above finding.
Namely, the present invention relates to the following lubricating
oil compositions:
(1) a lubricating oil composition characterized by comprising a
lubricating base oil and additives consisting essentially o~
(a) sulfoxymolybdenum dithiocarbamate containing a hydro-
carbon group having 8 to 18 carbon atoms,
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(b) zinc dialkyldithiophosphate selected from the group consist-
ing of zinc dialkyldithiophosphate containing a primary alkyl group having 1
to
18 carbon atoms, and a mixture of zinc dialkyldithiophosphate containing a
primary alkyl group having 1 to 18 carbon atoms and zinc
dialkyldithiophosphate
containing a secondary alkyl group having 1 to 18 carbon atoms, and
(c) a mixture of 100 to 50% by weight of calcium alkylsalicylate
and 0 to 50% by weight of magnesium alkylsalicylate,
the amount of molybdenum derived from the sulfoxymolybdenum
dithiocarbamate being from 200 to 1000 ppm (weight basis) of the total weight
of the composition,
the amount of phosphorus derived from the zinc diallcyldithio-
phosphate being from 0.04 to 0.15% by weight of the total weight of the
composition, and
the total amount of the calcium alkylsalicylate and the magnesium
alkylsalicylate being from 1 to 10% by weight of the total weight of the
composition; and
(2) a lubricating oil composition characterized by comprising a
lubricating base oil and additives consisting essentially of:
(a) sulfoxymolybdenum dithiocarbamate containing a hydro-
carbon group having 8 to 18 carbon atoms,
(b) zinc dialkyldithiophosphate selected from the group
consisting of zinc dialkyldithiophosphate containing a primary alkyl group
having 1 to 18 carbon atoms, and a mixture of zinc dialkyldithiophosphate
containing a primary alkyl group having 1 to 18 carbon atoms and zinc dialkyl-
dithiophosphate containing a secondary alkyl group having 1 to 18 carbon
atoms,
(c) a mixture of 100 to 50% by weight of calcium alkylsalicylate
and 0 to 50% by weight of magnesium alkylsalicylate, and
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(d) succinimide containing boron,
the amount of molybdenum derived from the sulfoxyrnolybdenum
dithiocarbamate being from 200 to 1000 ppm (weight basis) of the total weight
of the composition,
the amount of phosphorus derived from the zinc dialkyldithio-
phosphate being from 0.04 to 0.15% by weight of the total weight of the
composition,
the total amount of the calcium alkylsalicylate and the magnesium
alkylsalicylate being from 1 to 10% by weight of the total weight of the
composition, and
the amount of boron derived from the succinimide containing
boron being from 0.005 to 0.06% by weight of the total weight of the
composition.
DETAILED DESCRIPTION OF THE INVENTION
There is no particular limitation on the lubricating base stock oil
which is used in the lubricating oil composition of the present invention, and
any
base oil, such as mineral oil or synthetic oil, which is commonly used for the
conventional lubricating basic oils can be used.
Examples of the mineral oil include raffinates which can be
obtained by subjecting raw materials for lubricating oils to solvent refining,
using an aromatic extraction solvent such as phenol or furfural, hydrogenated
oils which can be obtained by subjecting raw materials for lubricating oils to
hydrogenation treatment, using a hydrogenation catalyst such as cobalt or
molybdenum with a silica-alumina Garner, and lubricating oil fractions which
can be obtained by the isomerization of waxes. Suitable base stocks include 60
neutral oil, 100 neutral oil, 150 neutral oil, 300 neutral oil, 500 neutral
oil and
bright stocks.
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Examples of the synthetic oil include poly alpha-olefin oligomers,
polybutenes, alkylbenzenes, polyol esters, polyglycol esters, dibasic esters,
phosphoric esters and silicone oils. These base oils belonging to mineral oil
or
synthetic oil can be used either singly or in combination of two or more.
Further, a mixture of mineral oil and synthetic oil can also be used.
Those oils which have a viscosity at 100°C of 3 to 20 cSt are
preferable as the base oils for use in the lubricating oil composition of the
present invention. Of these, hydrocracked oils and wax-isomerized oils which
contain 3% by weight or less of aromatics, 50 ppm or less of sulfur and 50 ppm
or less of nitrogen are particularly preferred.
As the sulfoxymolybdenum dithiocarbamate to be incorporated
into the lubricant oil composition in accordance with the present invention,
use
may be made of a compound having the following formula [ 1 ]:
Rlv
R2~1-C-S- -Mo2SmOn [1]
2
wherein R1 and R2, are independently a hydrocarbon group with 8 to 18 carbon
atoms and may or may not be the same, m and n are a positive integer provided
thatm+n=4.
Examples of the hydrocarbon group having 8 to 18 carbon atoms,
represented by R1 and R2 in the general formula [I] include hydrocarbon groups
such as an alkyl group having 8 to 18 carbon atoms, an alkenyl group having 8
to
18 carbon atoms, a cycloalkyl group having 8 to 18 carbon atoms, an aryl group
having 8 to 18 carbon atoms, an alkylaryl group and an arylalkyl group. The
above alkyl and alkenyl groups may be linear or branched. In the lubricating
oil
composition of the present invention, it is particularly preferable that the
hydro-
carbon group represented by Rl and R2 have 8 carbon atoms.
Specific examples of the hydrocarbon group represented by R1 and
R2 include octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, octenyl, noneyl,
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decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, hexadecenyl,
octadecenyl, dimethylcyclohexyl, ethylcyclohexyl, methylcyclohexylinethyl,
cyclohexylethyl, propylcyclohexyl, butylcyclohexyl, heptylcyclohexyl, di-
methylphenyl, methylbenzyl, phenethyl, naphthyl and dimethylnaphthyl groups.
In the lubricating oil composition of the present invention, either
one or two or more sulfoxymolybdenum dithiocarbamates can be used. Further,
the sulfoxymolybdenum dithiocarbamate is incorporated into the composition so
that the amount of molybdenum derived from the sulfoxymolybdenum dithio-
carbamate can be from 200 to 1000 ppm (weight basis), preferably from 300 to
800 ppm (weight basis) of the total weight of the composition. When the
sulfoxymolybdenum dithiocarbamate is incorporated in such an amount that the
amount of molybdenum derived from the sulfoxymolybdenum dithiocarbamate is
less than 200 ppm (weight basis) of the total weight of the composition, the
effect of improving friction-reducing properties cannot be sufficiently
obtained.
On the other hand, when the sulfoxymolybdenum dithiocarbamate is in-
corporated in such an amount that the amount of molybdenum derived from the
sulfoxymolybdenum dithiocarbamate is in excess of 1000 ppm (weight basis) of
the total weight of the composition, the effect which is expected from such an
amount of the sulfoxymolybdenum dithiocarbamate cannot be obtained, and
sludge or the like tends to be brought about.
As the zinc dialkyldithiophosphate to be incorporated into the
lubricant oil composition in accordance with the present invention, use may be
made of a compound having the following formula [2]:
R3-O\~ -
R4-O S -Zn [2]
2
wherein R3 and R4 are independently a primary and secondary allcyl group with
1 to 18, preferably 3 to 18 carbon atoms and may or may not be the same.
In the lubricating oil composition of the present invention, any of
the following ones can be used as the zinc dialkyldithiophosphate: zinc
dialkyl-
dithiophosphate represented by the general formula [2] in which all of the
alkyl
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groups are primary; a mixture of zinc dialkyldithiophosphate in which all of
the
alkyl groups are primary and zinc dialkyldithiophosphate in which all of the
alkyl groups is primary and the other alkyl group is secondary; zinc dialkyl-
dithiophosphate in which one of the alkyl groups are secondary; and a mixture
thereof.
The primary and secondary alkyl groups represented by R3 and R4
in the general formula [2] are propyl, butyl, pentyl, hexyl, heptyl, octyl,
nonyl,
decyl, undecyl and dodecyl groups. However, zinc dialkyldithiophosphate
containing a primary or secondary alkyl group having 3 to 12 carbon atoms is
preferably used in the lubricating oil composition of the present invention.
In the lubricating oiI composition of the present invention, the zinc
dialkylditl>iophosphate is incorporated so that the amount of phosphorus
derived
from the zinc dialkyldithiophosphate can be from 0.04 to 0.15% by weight,
preferably from 0.06 to 0.12% by weight of the total weight of the
composition.
When the zinc dialkyldithiophosphate is incorporated into the composition in
such an amount that the amount of phosphorus derived from the zinc dialkyl-
dithiophosphate is less than 0.04% by weight of the total weight of the
composition, the resulting composition is poor in antiwear properties, in addi-
tion, cannot have a satisfactorily low coefficient of friction under the
operating
conditions of high oil temperatures and low rotational speeds. On the other
hand, when the zinc dialkyldithiophosphate is incorporated in such an amount
that the amount of phosphorus derived from the zinc dialkyldithiophosphate is
in
excess of 0.15% by weight of the total weight of the composition, the effect
which is expected from such an amount of the zinc dialkyldithiophosphate
cannot be obtained.
As the calcium or magnesium alkylsalicylate to be used in the
lubricant oil composition in accordance with the present invention, use may be
made of a compound having the following formula [3]:
\ /C-O-M-O-C~
RS~~ I ~R6
/ \OH HO
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wherein M is calcium or magnesium, and RS and R6 are independently alkyl
group with 8 to 30 carbon atoms and may or may not be the same.
T'he alkyl group having 8 to 30 carbon atoms represented by RS
and R6 in the general formula [3J may be linear, branched or cyclic one.
Examples of such an allcyl group include octyl, nonyl, decyl, dodecyl,
pentadecyl, octadecyl, eicosyl, docosyl, tricosyl, hexacosyl, triacontyl,
dimethylcyclohexyl, ethylcyclohexyl, methylcyclohexylinethyl and cyclo-
hexylethyl groups.
In the lubricating oil composition of the present invention, the
alkylsalicylate is incorporated as a mixture of 100 to 50% by weight of
calcium
alkylsalicylate and 0 to 50% by weight of magnesium alkylsalicylate. The
mixture is incorporated in such an amount that the total amount of the calcium
alkylsalicylate and the magnesium alkylsalicylate is from 0.5 to 10% by
weight,
preferably from 1 to 6% by weight of the total weight of the composition. When
the total amount of the calcium alkylsalicylate and the magnesium
alkylsalicylate
is less than 0.5% by weight of the total weight of the composition, cleaning
effect cannot be su~ciently obtained. On the other hand, when the total amount
of the calcium alkylsalicylate and the magnesium alkylsalicylate is in excess
of
10% by weight of the total weight of the composition, the effect which is
expected from such an amount of the mixture cannot be obtained, and ash
content is rather increased. Such an amount is therefore unfavorable.
In the lubricating oil composition of the present invention, it is
preferable to adjust the total base number of the composition to 3 to 10,
preferably 4 to 7. The base number of the composition can be determined in
accordance with JIS K2501. The total base number of the composition can be
adjusted by selecting calcium alkylsalicylate and magnesium alkylsalicylate,
each having a proper base number.
Succinimide containing boron can be incorporated into the
lubricating oil composition of the present invention, if desired.
The boron/nitrogen ratio regarding the number of the atoms
contained in the succinimide containing boron which is used in the lubricating
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oil composition of the present invention is from 0.05 to 1.5, preferably from
0.1
to 0.8. VVhen the boron/nitrogen ratio is less than 0.05, the resulting
composition
cannot have sufficiently-improved friction-reducing properties. On the other
hand, when the boron/nitrogen ratio exceeds 1.5, the friction-reducing
properties
of the resulting composition are impaired.
In the lubricating oil composition of the present invention, the
succinimide containing boron is incorporated so that the amount of boron
derived from the succinimide containing boron can be from 0.005 to 0.06% by
weight, preferably from 0.01 to 0.04% by weight of the total weight of the
composition. When the succinimide containing boron is used in such an amount
that the amount of boron derived from the succinimide containing boron is less
than 0.005% by weight of the total weight of the composition, the resulting
composition cannot have sufficiently-improved friction-reducing properties. On
the other hand, when the succinimide containing boron is used in such an
amount that the amount of boron derived from the succinimide containing boron
is in excess of 0.06% by weight of the total weight of the composition, the
effect
which is expected from such an amount of the succinimide containing boron
cannot be obtained.
Various additives which have been usually incorporated into the
conventional lubricating oils, such as a metallic detergent, another friction
modifier., an antioxidant, a viscosity index improver, a pour point
depressant, an
anti-foaming agent, other antiwear agent(s), a rust preventive, an ashless
dispersant and a corrosion inhibitor, can be added, if necessary, to the
lubricating
oil composition of the present invention within such a limit that the object
of the
present invention can be fully attained.
Examples of the metallic detergent include calcium sulfonate,
magnesium sulfonate, barium sulfonate, calcium phenate, barium phenate,
calcium salicylate and magnesium salicylate. In general, the metallic
detergent is
used in the composition in an amount of 0.1 to 5% by weight.
Examples of the friction modifier include partial esters of poly-
valent alcohols, amines, amides and ester sulfides.
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Examples of the antioxidant include amine antioxidants such as
alkylated diphenylamines, phenyl-alpha-naphthylamines and alkylated alpha-
naphthylamines, and phenolic antioxidants such as 2,6-di-t-butyl-4-
methylphenol
and 4,4'-methylene-bis(2,6-di-t-butylphenol). In general, such an antioxidant
is
used in the composition in an amount of 0.05 to 2% by weight.
Examples of the viscosity index improver include those of poly-
methacrylate type, polyisobutylene type, ethylene-propylene copolymer type and
stryene-butadiene hydrogenated copolymer type. In general, such an improver is
used in the composition in an amount of 0.5 to 35% by weight.
Examples of the pour point depressant include polyalkyl-
methacrylate, a condensation product of chlorinated paraffin and naphthalene
and alkylated polystyrene.
Examples of the anti-foaming agent include dimethyl polysiloxane
and polyacrylic acid.
Examples of the antiwear agent include metallic salts of
thiophosphoric acid, metallic salts of thiocarbamic acid, sulfur compounds,
phosphoric esters and phosphorous esters. In general, this agent is used in
the
composition in an amount of 0.05 to 5.0% by weight.
Examples of the rust preventive additive include fatty acids, partial
esters of allcenyl succinates, fatty acid soaps, alkylsulfonates, fatty
polyvalent
alcohol esters, fatty amines, paraffin oxides and alkyl polyoxyethylene
ethers.
Examples of the ashless dispersant include those of succinimide
type, succinamide type, benzylamine type and ester type. In general, such a
dispersant is used in the composition in an amount of 0.5 to 7% by weight.
Examples of the corrosion inhibitor include benzotriazole and
benzoimidazole.
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Examples
a
The present invention will now be explained more specifically by
referring to the following Examples. However, the present invention is not
limited by these examples in any way.
The coefficients of friction of the lubricating oil compositions were
determined by a reciprocating sliding friction tester [SRV Friction Tester]
under
the conditions of a frequency of 50 Hz, an amplitude of 3 mm, a load of 25 N,
a
temperature of 80°C and a test time of 25 minutes.
Examples 1 to 9 and Comparative Examples 1 and 2
The lubricating oil compositions of these examples are those which
contain sulfoxymolybdenum dithiocarbamate, zinc dialkyldithiophosphate and
alkylsalicylate. Each lubricating oil composition was prepared by blending the
components whose type and amount are shown in Table 1 with a base oil ( 100
neutral ail having a viscosity at 100°C of 4.4 mm/s2). The coefficient
of friction
of each composition thus obtained was determined right after the composition
was prepared, and after the composition was oxidized by being held at
150°C for
72 hours. The results are shown in Table 1.
A
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WO 96/37582 PCT/US95/06620
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c, o o ~o .n
p
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z
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WO 96/37582 PCT/US95/06620
-13-
When the lubricating oil compositions of Examples 1 to 9 accord-
ing to the present invention were used for the determination of the
coefficient of
friction thereof, it was found that all of the compositions had a low
coefficient of
friction and excellent friction-reducing properties. Moreover, almost no
change
was found in the coefficient of friction even after the compositions were
heated
at 150°C for 72 hours and oxidized. Therefore, it can be understood
that the
lubricatW g oil compositions of the invention are excellent in heat
resistance. In
contrast, in the case of the lubricating oil composition of Comparative
Example
1, which was prepared by using only zinc dialkyldithiophosphate having a
secondary alkyl group as the zinc dialkyldithiophosphate, the coefficient of
friction determined right after the composition was prepared was already high.
Moreover, the coe~cient of fi-iction became higher after the composition was
heated at 150°C for 72 hours and oxidized. It can thus be seen that
this
comparative composition is poor in both friction-reducing properties and heat
resistance. In the case of the lubricating oil composition of Comparative
Example 2, which was prepared by using calcium sulfonate instead of alkyl-
salicylate, the coefficient of friction became higher after the composition
was
heated at 150°C for 72 hours and oxidized. It can thus be known that
this
comparative composition is poor in heat resistance.
Examples 10 to 18 and Comparative Examples 3 and 4
The lubricating oil compositions of these examples are those which
contain sulfoxymolybdenum dithiocarbamate, zinc dialkyldithiophosphate, alkyl-
salicylate and succinimide containing boron. Each lubricating oil composition
was prepared by blending the components whose type and amount are shown in
Table 2 with a base oil (100 neutral oil having a viscosity at 100°C
of 4.4
mm/s2). The coefficient of friction of each composition thus obtained was
determined right after the composition was prepared, and after the composition
was oxidized by being held at 150°C for 72 hours. The results are shown
in
Table 2.
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WO 96/37582 PCT/ITS95/06620
- 14 -
: ~ o ~ .no o -r
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CA 02218811 1997-11-07
WO 96!37582 PCT/US95/06620
-15-
The lubricating oil compositions of Examples 10 to 18 according
to the present invention, into which succinimide containing boron was
incorporated, had a coeffident of fi-iction lower than that of any of the
lubricat-
ing oil compositions of Examples 1 to 9 which contain no succinimide contain-
ing boron, and showed excellent friction-reducing properties. Moreover, almost
no change was found in the coefficient of friction even after the compositions
were heated at 150°C for 72 hours and oxidized. Therefore, it can be
seen that
the lubricating oil compositions of the present invention are excellent in
heat
resistance. In contrast, in the case of the lubricating oil composition of
Comparative Example 3, which was prepared by using only zinc dialkyldithio-
phosphate having a secondary alkyl group as the zinc dialkyldithiophosphate,
the
coefficient of friction determined right after the composition was prepared
was
already high, even though succinimide containing boron was incorporated into
the composition. Moreover, the coefficient of fiiction became higher after the
composition was heated at 150°C for 72 hours and oxidized. It can thus
be seen
that this comparative composition is poor in both friction-reducing properties
and heat resistance. In the case of the lubricating oil composition of Compara-
tive Example 4, which was prepared by using calcium sulfonate instead of
alkylsalieylate, the coefficient of fi-iction became higher after the
composition
was heated at 150°C for 72 hours and oxidized, even though succinimide
containing boron was incorporated into the composition. It can thus be known
that this comparative composition is poor in heat resistance.
The lubricating oil compositions of the present invention prepared
by blending sulfoxymolybdenum dithiocarbamate having a specific structure,
zinc dialkyldithiophosphate, alkylsalicylate, and, if desired, succinimide
contain-
ing boron with a base oil, therefore, have excellent antiwear properties, can
maintain fi-iction-reducing properties for a prolonged period of time, and are
excellent in both fi-iction-reducing properties and heat resistance. The
lubricat-
ing oil compositions of the present invention are thus useful as lubricating
oils
for internal-combustion engines, automatic transmission gearboxes, dampers,
power steering units and the like, particularly useful as lubricating oils for
internal-combustion engines.
