Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LUBRICATING OIL COMPOSITION
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a novel lubricating oil composition, and
more specifically to a lubricating oil composition having high heat
resistance, high
oxidation stability and excellent lubricating properties, useful as a
lubricating oil for
internal-combustion engines, automatic transmission gearboxes, dampers, power
steer-
ing units and the like, particularly useful as a lubricating oil for internal
combustion
engines.
DESCRIPTION OF THE RELATED ART
Lubricating oils have been used for internal combustion engines, and for
driving units and gears such as automatic transmission gearboxes, dampers and
power
steering unit in order to smoothly operate them. In particular, lubricating
oils for
internal-combustion engines (engine oils) not only lubricate various sliding
portions such
as a piston ring, a cylinder liner, bearings for a crank shaft and a
connecting rod, and a
valve-operating mechanism including a cam and a valve lifter, but also cool
the inside of
the engines, clean and disperse those products which are produced by
combustion, and
prevent the rusting and corrosion of the engines.
Thus, the lubricating oils for internal-combustion engines have been
required to have a great variety of properties. Moreover, due to the recent
trend toward
high-performance, high-output internal-combustion engines and more severe
operating
conditions, the lubricating oils are required to have higher quality. 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 as the essential function of the lubricating oils
for internal-combustion engines that the lubricating oils can ensure the
smooth operation
of the engines under every condition to prevent the wear and seizure of the
engines.
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The parts of the engines to be lubricated are, in most cases, under the fluid
lubrication
condition. However, the valve train, 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
dithio-
phosphate (ZnDTP) or zinc dithiocarbamate (ZnDTC).
Energy loss at the friction parts of internal-combustion engines which are
lubricated by lubricating oils is great. For this reason, a lubricating oil to
which various
additives including a friction modifier (F'Ni] are added has been used in
order to reduce
the friction loss and to decrease the fuel cost (e.g., Japanese Laid-Open
Patent Publica-
tion No. 23595/1991). Lubricating oils for automotive internal-combustion
engines are
used at various temperatures, at various revolutions per minute and under
various loads.
Therefore, in order to further improve the rate of fuel consumption, it is
necessary that
the lubricating oils be excellent in friction properties under a wide range of
conditions
under which they are used.
Besides the above-described properties, high heat resistance, high
oxidation stability and moderate viscosity characteristics can be mentioned as
the
properties required for the lubricating oils for internal-combustion engines.
The present invention is directed to meeting these requirements. An
object ofthe present invention is therefore to provide a lubricating oil
composition
having excellent lubricating properties, high heat resistance, high oxidation
stability and
moderate viscosity characteristics, particularly useful as a lubricating oil
for internal-
combustion engines.
DESCRIPTION OF THE FIGURE
Figure 1 is a diagrammatic view of an apparatus used in the LFW-1
friction test in which 1 is the S-test ring, 2 is the R-type block, and 3 is a
distortion
meter.
SUMMARY OF THE 1NVENTION
After intensive investigations made for the purpose of developing a
lubricating oil composition having the above-described advantageous
properties, it has
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been discovered that the object can be attained by a composition which is
obtainable by
adding a predetermined amount of a specific amine antioxidant, and a
predetermined
amount of oxymolybdenum sulfide dithiocarbamates (MoDTC), oxymolybdenum
sulfide
organophosphorodithioates (MoDTP) or oxymolybdenum sulfide dithioxanthogenates
(MoDT~ to a lubricating base oil containing a small amount of aromatics, and
having
other specific characteristics. The present invention has been accomplished on
the basis
of the above finding.
Namely, the present invention relates to:
(1) a lubricating oil composition characterized by comprising:
(A) a lubricating base oil containing 3% by weight or less of aromatics, 20%
by weight or more of monocyclic naphthenes, 50 ppm by weight or less of
sulfur and 50 ppm by weight or less of nitrogen, having a viscosity of 2 to
50 mm2/s at 100°C;
(B) at least one compound selected from diarylamines of the general formula:
Rl 3
[lJ
R2 ~t4
wherein R1, R2, R3 and R4, which may be the same or different, each
represent hydrogen atom or a hydrocarbon group having 3 to 18 carbon
atoms, provided that at least one of them is the hydrocarbon group, or of
the general formula:
R5 NFi R6 [2)
wherein RS and R6 are hydrogen atom or a hydrocarbon group having
to 18 carbon atoms, in an amount of 0.05 to 3% by weight of the total
weight of the composition; and
CA 02218809 1997-11-07
t~l~~ ~ 5 i 0 5 I ~ 2
r
IP~j~S ~2 C ",a, Tna7
-4-
(C) at least one compound selected from oxymolybdenum sulfide dithio-
carbamates of the general formula:
R\
/N C- S Mo2SmOn [3]
R$
2
wherein R' and R8, which may be the same or different, each represent a
hydrocarbon group having 5 to 23 carbon atoms, and m and n are a posi-
tive integer, provided that the total number of m and n is 4, oxymoly-
bdenum sulfide organophosphorodithioates of the general formula:
R9
P S Mo2SxOy [q,
Rio
2
wherein R9 and R1°, which may be the same or different, each represent
a
hydrocarbon group having 1 to 18 carbon atoms, and x and y are a
positive integer, provided that the total number of x and y is 4, and
w oxymolybdenum sulfide dithioxanthogenates of the general formula:
S
R~ ~ O IC
Mo-X-Mo Y [5]
R~2 O C/
2
S
wherein Rt 1 and RI2, which may be the same or different, each represent
a hydrocarbon group having 1 to 30 carbon atoms, and X and Y, which
may be the same or different, each represent oxygen or sulfur atom, in
such an amount that the amount of molybdenum is 50 to 2000 ppm by
weight of the total weight of the composition.
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Further, preferred embodiments of the present invention are as follows:
(2) the lubricating oil composition as set forth in the above item (1),
wherein the
lubricating base oil is a hydrogenated oil containing 3% by weight or less of
aromatics, 20% by weight or more of monocyclic naphthenes, and 97% by weight
or more of saturated compounds;
(3) the lubricating oil composition as set forth in the item (1) or (2),
wherein the
lubricating base oil is a hydrogenated oil, the diarylamines are
alkyldiphenylamines
containing at least one alkyl group having 3 to 18 carbon atoms or phenyl-a-
naphthylamines containing an alkyl group having 3 to 18 carbon atoms, and
containing the oxymolybdenum sulfide dithiocarbamate;
(4) the lubricating oil composition as set forth in the item (1), (2) or (3),
containing
the oxymolybdenum sulfide organophosphorodithioates, having an alkyl group
having 8 to 18 carbon atoms;
(5) the lubricating oil composition as set forth in the item (1), (2), (3) or
(4),
containing the oxymolybdenum sulfide dithioxanthogenates, having an alkyl
group
having 8 to 18 carbon atoms; and
(6) a method for reducing fuel consumption by the use of the lubricating oil
composi-
tion described above in internal-combustion engines.
DETAILED DESCRIPTION OF THE INVENTION
In the lubricating oil composition of the present invention, an oil contain-
ing 3% by weight or less of aromatics, 20% by weight or more of monocyclic
naphthenes, 50 ppm by weight or less of sulfur and 50 ppm by weight or less of
sulfur
and 50 ppm by weight or less of nitrogen, having a viscosity of 2 to 50 mm2/s
at 100°C
is used as the lubricating base oil, the component (A). The preferable amount
of the
monocyclic naphthenes is in the range of 25 to 40% by weight. When the amount
of the
aromatics exceeds 3% by weight, the resulting lubricating oil composition
undergoes
deterioration in heat resistance, oxidation stability and lubricating
properties. In the case
where the amount of the monocyclic naphthenes is less than 20% by weight, the
result-
ing composition cannot have su~ciently high adaptability to sealing rubber.
Further,
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when the lubricating base oil has a viscosity of lower than 2 mm2/s, the
resulting
composition is poor in the oil-film-forming properties, and has a shortcoming
in that it
undergoes a great evaporation loss. A base oil having a viscosity of higher
than
50 mm2/s is also unfavorable because the power loss of the resulting
composition
caused by viscosity resistance is too great. Furthermore, when either sulfur
or nitrogen
content exceeds 50 ppm by weight, the oxidation stability and lubricating
properties of
the resulting composition become poor.
Either mineral or synthetic oil can be used as the lubricating base oil as
long as it has the aforementioned properties. Specific examples of the base
oil include
raffnates which can be obtained by subjecting starting materials for
lubricating oils
derived from naphthene base or paraffin base crude oil by evaporation under
normal or
reduced pressure to solvent refining, using an aromatic extraction solvent
such as
phenol, furfural or N-methylpyrrolidone, and hydrogenated oils which can be
obtained
by subjecting starting materials for lubricating oils to hydrogenation
treatment including
hydrocracking reaction. In either production process, such processes as
dewaxing,
hydrorefining and clay treatment processes may be optionally adopted in
accordance
with the conventional manner. Particularly preferable base oils are
hydrocracked oils
and wax-isomerized oils.
In the composition of the present invention, at least one compound
selected from diarylamines of the general formula [ 1 ]:
Rl 3
[1]
NH
R2 R4
or of the general formula [2]:
2
R5 NH R6 [ ]
is used as the amine oxidant, the component (B).
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In the above general formula [1], R1, R2, R3 and R4 each represent
hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. Further,
although
R1, R2, R3 and R4 each represent hydrogen atom or a hydrocarbon group having 1
to
18 carbon atoms. Further, although R1, R2, R3 and R4 may be the same or
different
.,
from one another, it is necessary that at least one of them be an alkyl group
having 3 to
18 carbon atoms. The alkyl group having 3 to 18 carbon atoms may be any of
linear,
branched and cyclic ones. Examples of such an alkyl group include propyl,
butyl, amyl,
hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl,
pentadecyl,
hexadecyl, heptadecyl and octadecyl groups of all types, and cyclohexyl,
cyclooctyl and
cyclododecyl groups.
In the above general formula [2], RS and R6 are hydrogen atom or a
hydrocarbon group having 1 to 18 carbon atoms. A preferable hydrocarbon group
is an
alkyl group having 3 to 18 carbon atoms, which may be any of linear, branched
and
cycllic ones. Examples of such an alkyl group include the same groups as those
enumerated in the explanation ofRl, R2, R3 and R4 in the above general formula
[1).
Specifically, the following compounds can be mentioned as the diarylamines:
p,p'-
dibutyl-diphenylamine, p,p'-dipentyldiphenylamine, p,p'-dihexyl-diphenylamine,
p,p'-
diheptyldiphenylamine, p,p'-dioctyl-diphenylamine, p,p'-dinonyldiphenylamine,
mono-
octyldiphenyl-amine, monononyldiphenylamine, tetrabutyldiphenylamine,
tetrahexyl-
diphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine, a mixture of
alkyldiphenylamines having 4 to 9 carbon atoms, phenyl-oc-naphthylamine,
phenyl-[i-
naphthylamine, butylphenyl-a.-naphthylamine, butylphenyl-(3-naphthylamine,
pentyl-
phenyl-a-naphthylamine, pentylphenyl-(3-naphthylamine, hexylphenyl-a-
naphthylamine,
hexylphenyl-[3-naphthylamine, heptylphenyl-a-naphthylamine, heptylphenyl-(3-
naphthyl-
amine, octylphenyl-oc-naphthylamine, octylphenyl-(3-naphthylamine, nonylphenyl-
oc-
naphthylamine and nonylphenyl-[3-naphthylamine. Particularly preferable
diarylamines
are p,p'-dioctyldiphenylamine, phenyl-a,-naphthylamine and alkylphenyl-a.-
naphthyl-
amines.
In the composition of the present invention, one or two or more of the
alkyldiphenylamines represented by the above general formula [ 1 ], or one or
two or
more of the phenyl-oc-naphthylamines represented by the above general formula
[2] may
be used as the amine oxidant, the component (B). Moreover, one or more of the
alkyldiphenylamines represented by the general formula [ 1 ], and one or more
of the
CA 02218809 1997-11-07 ~~ Q
,i
_g_
phenyl-a.-naphthylamines represented by the general formula [2] may also be
used
in combination as the amine oxidant.
In the present invention, it is necessary to incorporate the amine
oxidant, the component (B), into the composition in an amount of 0.05 to 3% by
weight, preferably 0.2 to 2% by weight of the total weight of the composition.
When the amount of the amine oxidant is less than 0.05% by weight, the
resulting
composition cannot have sufficiently high oxidation stability. On the other
hand,
when the amount is in excess of 3% by weight, the effects of the oxidant
expected
from such an amount cannot be obtained.
In the composition of the present invention, at least one compound
selected from oxymolybdenum sulfide dithiocarbamates (MoDTC) of the general
formula [3]:
R\
/N C-S Mo2Sm0~ [3]
R$
2
oxymolybdenum sulfide organophosphorodithioates (MoDTP) of the general
formula [4]:
R9 ~ IP S Mo S O
2 x y [4]
Rio
2
and oxymolybdenum sulfide dithioxanthogenates (MoDTX)of the general
formula [5]:
S
R~ ~ O ~C
Mo-X-Mo Y [5]
R~ 2 O C/
I- II 2
S
is used as the friction modifier, the component (C).
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In the above general formula [3], R~ and R8 each represent a hydro-
carbon group having 5 to 23 carbon atoms, and they may be the same or
different from
each other. Examples of the hydrocarbon group having 5 to 23 carbon atoms
include a
linear or branched alkyl or alkenyl group having 5 to 23 carbon atoms, and a
cycloalkyl,
aryl, alkylaryl or arylalkyl group having 6 to 23 carbon atoms. Preferable
hydrocarbon
groups are those having 8 to 23 carbon atoms. Specific examples of such
hydrocarbon
groups include 2-ethylhexyl, n-octyl, nonyl, decyl, lauryl, tridecyl,
palmityl, stearyl,
oleyl, eicosyl, butylphenyl and nonylphenyl groups. Further, m and n are a
positive
integer, provided that the total number of m and n is 4.
In the above general formula [4], R9 and R10 each represent a hydro-
carbon group having 1 to 18 carbon atoms, and they may be the same or
different from
each other. Preferable hydrocarbon groups are those having 3 to 18 carbon
atoms, most
preferably 8 to 18 carbon atoms. Examples of the hydrocarbon groups having 3
to 18
carbon atoms include a linear or branched alkyl or alkenyl group having 3 to
18 carbon
atoms, a cycloalkyl group having 6 to 18 carbon atoms, an aryl group having 6
to 18
carbon atoms,- and an alkylaryl-or arylalkyl-group -having 7 fo 18 carbon
atoms. Specific
examples of such groups include isopropyl, n-propyl, n-butyl, isobutyl, sec-
butyl, amyl,
hexyl, cyclohexyl, 2-ethylhexyl, n-octyl, nonyl, decyl, lauryl, tridecyl,
palmityl, stearyl,
oleyl, butylpheyl and nonylphenyl groups. Further, x and y are a positive
intetger,
provided that the total number of x and y is 4.
In the above general formula [5], R11 and R12 each represent a hydro-
carbon group having 1 to 30 carbon atoms, and they may be the same or
different from
each other. Preferable hydrocarbon groups are those having 3 to 20 carbon
atoms, most
preferably 8 to 18 carbon atoms. Examples of such hydrocarbon groups include a
linear
or branched alkyl or alkenyl group having 5 to 20 carbon atoms, a cycloalkyl
group
having 6 to 20 carbon atoms, and an aryl, alkylaryl or arylalkyl group having
6 to 20
carbon atoms. Specific examples of such groups include isopropyl, n-propyl,
isobutyl,
n-butyl, sec-butyl, amyl, hexyl, cyclohexyl, 2-ethylhexyl, n-octyl, nonyl,
decyl, lauryl,
tridecyl, palmityl, stearyl, oleyl, butylpheyl and nonylphenyl groups.
Further, X and Y
are oxygen or sulfur atom, and may be the same or different from each other.
In the composition of the present invention, the MoDTC represented by
the above general formula [3] may be used either singly or in combination of
two or
more. The MoDTP represented by the general formula [4] may also be used either
CA 02218809 1997-11-07
WO 96!37583 PCT/LTS95/05142
-10-
singly or in combination of two or more. Further, the MoDTX represented by the
general formula [5] may also be used either singly or in combination of two or
more.
In the composition of the present invention, it is necessary to incorporate
the friction modifier, the component (C), into the composition in such an
amount that
the amount of molybdenum will be 50 to 2000 ppm by weight, preferably 100 to
1000
ppm by weight of the total weight of the composition. When the amount of
molybdenum is less than 50 ppm by weight, lubricating properties cannot be
sufficiently
obtained. On the other hand, when the amount of molybdenum is in excess of 200
ppm
by weight, lubricating properties expected from such an amount cannot be
obtained.
Those additives which have been usually incorporated into the con-
ventional lubricating oils, such as a metallic detergent, a nonash detergent-
dispersant, an
antiwear agent, a viscosity index improver, a pour point depressant, a rust
preventive, a
corrosion inhibitor, an anti-foaming agent and other antioxidants, 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 incorporated into
the
composition in an amount of 0.1 to 5% by weight. Examples of the nonash
detergent-
dispersant include those of succinimide type, succinamide type, benzylamine or
its boron
derivative type and ester type. In general, such a detergent is incorporated
into the
composition in an amount of 0.5 to 7% by weight.
Examples of the antiwear agent include metallic (Zn, Pb, Sb, Mo, etc.)
salts of thiophosphoric acid, metallic (Zn, etc.) salts of thiocarbamic acid,
sulfur
compounds, phosphoric esters and phosphorous esters. In general, this agent is
incorporated into the composition in an amount of 0.05 to 5.0% by weight.
Examples of the viscosity index improver include those of poly-
methacrylate type, polyisobutylene type, ethylene-propylene copolymer type and
styrene-butadiene hydrogenated copolymer type. In general, such an improver is
incorporated into the composition in an amount of 0.5 to 35% by weight.
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WO 96137583 PCT/US95105142
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Examples of the rust preventive include alkenyl succinates and partial
esters thereof. Examples of the corrosion inhibitor include benzotriazole and
benzoimidazole. Examples of the anti-foaming agent include dimethyl
polysiloxane and
polyacrylate. These agents may be incorporated into the composition, when
necessary.
EXAMPLES
The present invention will now be explained more specifically by
refernng to the following Examples. However, the present invention is not
limited by
these examples in any way.
The oxidation-induction time and coefficient of friction of the lubricating
oil compositions were obtained in the following respective manners.
(1) Coefficient ofFriction (u)
LFW-1 friction test was carried out by using an LFW-I tester shown in
Figure 1 equipped with an R-type block (made of iron) manufactured by Falex
Corporation and an S-10 test ring (made of iron) manufactured by Falex
Corporation
under the following conditions: the number of revolutions was 270 rpm, the
load was
30 kgf, the temperature ofthe oil was 120°C, and the time was 10
minutes. In Figure 1,
reference numeral 1 indicates the S-10 test ring, reference numeral 2
indicates the R-
type block and reference numeral 3 indicates a distortion meter. Load is
applied to the
R-type block, and the resistance caused by the rotation of the ring is
measured by the
distortion meter. The coe~cient of friction is calculated from the resistance
measured.
It is noted that approximately half of the ring is immersed in the oil to be
tested.
(2) Oxidation-Induction Time (minutes)
The oxidatipn-induction time was determined by means of differential
thermal analysis which was conducted under oxygen atmosphere, by applying a
load of
a 20 kgf/cm2 and heating the sample to 200°C.
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EXAMPLES 1 TO 8 AND COMPARATIVE EXAMPLES 1 TO 7
By the use of a base oil shown in Table 1, a lubricating oil composition
having a formulation shown in Table 2 was prepared. The coefficient of
friction (~) and
oxidation-induction time (minutes) of the composition were obtained. The
results are
shown in Table 2.
CA 02218809 1997-11-07
WO 96/37583 PCTlUS95/05142
- 13 -
z~,~
O ~ ~~ M "" ~ O O O
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t~~.., w ø~'"., o ~n c~ °.
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CA 02218809 1997-11-07
WO 96137583 PCT/US95/05142
- 14 -
a3 v ~. .~r '~?
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CA 02218809 1997-11-07
WO 96/37583 PCT/US95/05142
- 15 -
U 01
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CA 02218809 1997-11-07
WO 96/37583 PCT/US95/05142
-16-
All of the lubricating oils of Examples 1 to 8, which are the compositions
of the present invention, have a low coefficient of friction and a long
oxidation-induction
time. In contrast, the lubricating oil of Comparative Example 1 has a low
coe~cient of
friction but has a short oxidation-induction time. The lubricating oils of
Comparative
Examples 2 to 7 are remarkably inferior to those of Examples of the present
invention in
both the coefficient of friction and the oxidation-induction time.
The lubricating oil compositions of the present invention have high heat
resistance, high oxidation stability and excellent lubricating properties, and
are
particularly useful for lubricating oils for internal-combustion engines and
the like.
