LUBRICATING OIL COMPOSITION HAVING IMPROVED OXIDATION STABILITY AT HIGH TEMPERATURES

COMPOSITION D'HUILE LUBRIFIANTE POSSEDANT UNE STABILITE A L'OXYDATION ACCRUE A HAUTE TEMPERATURE

English Abstract

A lubricating oil composition having a TBN in the range of 5 to 55 mg KOH/g
and containing a major amount of a base oil of lubricating viscosity and
a) 0.19 to 2.10 wt %, based on the total amount of the lubricating oil
composition, of an overbased calcium carboxylate having a TBN of
100 mg KOH/g or more, wherein the wt % is expressed in terms of
the calcium content;
b) 0 002 to 0.06 wt %, based on the total amount of the lubricating oil
composition, of a bis-succinimide compound, wherein the wt % is
expressed in terms of the nitrogen content; and
c) 0.007 to 0.15 wt %, based on the total amount of the lubricating oil
composition, of a zinc dialkyldithiophosphate having a secondary
alkyl group, wherein the wt % is expressed in terms of the
phosphorus content.

French Abstract

Une composition d'huile lubrifiante ayant un indice de base entre 5 et 55 mg KOH/g et contenant une grande quantité d'une huile de base de viscosité lubrifiante et a) 0,19 à 2.10 % en poids en fonction de la quantité totale de composition d'huile lubrifiante, d'un carboxylate de calcium surbasique ayant un indice de base de 100 mg KOH/g ou plus, où le % en poids est exprimé en termes de contenu de calcium; b) de 0,002 à 0,06 % en poids en fonction de la quantité totale de composition d'huile lubrifiante d'un composé bis-succinimide, où le % en poids est exprimé en termes de contenu en azote; et c) de 0,007 à 0,15 % en poids en fonction de la quantité totale de composition d'huile lubrifiante, d'un dialkyldithiophosphate de zinc ayant un groupe alkyle secondaire, où le % en poids est exprimé en termes de contenu phosphoreux.

Claims

WHAT IS CLAIMED IS:
1. A lubricating oil composition having a total base number (TBN) in the
range
of 5 to 55 mg KOH/g comprising a major amount of a base oil of lubricating
viscosity and
a) 0.19 to 2.10 wt %, based on the total amount of the lubricating oil
composition, of an overbased calcium carboxylate having a TBN of
100 mg KOH/g or more comprising each of the following compound
A and the following compound B, wherein the wt % is expressed in
terms of the calcium content, and wherein the overbased calcium
carboxylate having a TBN of 100 mg KOH/g or more comprises
more than 50 wt % of the following compound A and less than 50
wt% of the following compound B:
<IMG>
in which R is an alkyl group having 12 to 28 carbon atoms,
b) 0.002 to 0.06 wt %, based on the total amount of the lubricating oil
composition, of a bis-succinimide compound, wherein the wt % is
expressed in terms of the nitrogen content; and
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c) 0.007 to 0.15 wt %, based on the total amount of the lubricating
oil
Composition, of a zinc dialkyldithiophosphate having a secondary
alkyl group, wherein the wt % is expressed in terms of the
phosphorus content.
2. The lubricating oil composition according to claim 1, wherein the amount
of
the overbased calcium carboxylate having a TBN of 100 mg.cndot.KOH/g or
more is in the range of 0.38 to 1.15 wt %, based on the total amount of the
lubricating oil composition and expressed in terms of the calcium content.
3. The lubricating oil composition according to claim 1, wherein the amount
of
the bis-succinimide compound is in the range of 0.014 to 0.02 wt %, based
on the total amount of the lubricating oil composition and expressed in
terms of the nitrogen content.
4. The lubricating oil composition according to claim 1, wherein the amount
of
the zinc dialkyldithiophosphate having a secondary alkyl group is in the
range of 0.036 to 0.072 wt %, based on the total amount of the lubricating
oil composition and expressed in terms of the phosphorus content.
5. The lubricating oil composition according to claim 1, wherein the bis-
succinimide compound is prepared by a thermal reaction between a poly-
butene compound containing 50% or more methylvinylidene structure and
maleic anhydride, followed by further reaction of the resulting polybutenyl,
succinic anhydride with a polyalkylenepolyamine containing 4 to 10
nitrogen atoms per molecule.
6. The lubricating oil composition according to claim 1, wherein the zinc
dialkyldithiophosphate having a secondary alkyl group comprises alkyl
groups independently having 3 to 8 carbon atoms.
7. A method comprising operating an internal combustion engine with a
13

lubricating oil composition having a total base number (TBN) in the range
of 5 to 55 mg KOH/g comprising a base oil of lubricating viscosity and
a) 0.19 to 2.10 wt %, based on the total amount of the lubricating oil
composition, of an overbased calcium carboxylate having a TBN of
100 mg KOH/g or more comprising each of the following compound
A and the following compound B, wherein the wt % is expressed in
terms of the calcium content and wherein the overbased calcium
carboxylate having a TBN of 100 mg KOH/g or more comprises
more than 50 wt % of the following compound A and less than 50
wt% of the following compound B:
<IMG>
in which R is an alkyl group having 12 to 28 carbon atoms;
b) 0.002 to 0.06 wt %, based on the total amount of the lubricating oil
composition, of a bis-succinimide compound, wherein the wt % is
expressed in terms of the nitrogen content; and
c) 0.007 to 0.15 wt %, based on the total amount of the lubricating oil
14

composition, of a zinc dialkyldithiophosphate having a secondary
alkyl group, wherein the wt % is expressed in terms of the
phosphorus content.
8. The
method according to claim 7, wherein the internal combustion engine
is a four stroke trunk piston diesel engine.

Description

CA 02531433 2005-12-23
LUBRICATING OIL COMPOSITION HAVING IMPROVED OXIDATION
STABILITY AT HIGH TEMPERATURES
The present invention relates to a lubricating oil composition. More
particularly,
the present invention relates to a lubricating oil composition having improved
oxidation stability at high temperatures when employed in an internal
combustion
engines.
BACKGROUND OF THE INVENTION
Diesel engines, particularly four stroke trunk piston diesel engines, are
generally
employed as internal combustion engines for generation of electric power and
operation of marine vessels. These internal combustion engines are operated
smoothly using a lubricating oil composition which contains various additives.
Generally, most additives employed in lubricating oil compositions are metal-
containing detergents. Specifically, an over-based metal-containing detergent
which neutralizes sulfur oxide produced by the combustion of fuel and
disperses
combustion deposits such as sludge is generally employed. Particularly, a
lubri-
cating oil composition for marine diesel engines which is operated using high
sulfur content fuel such as A-heavy oil or C-heavy oil should contain over-
based
metal-containing detergents. Most metal-containing detergents are alkaline
earth
metal sulfonates, alkaline earth metal phenates, and alkaline earth metal
salicylates. An ashless dispersant such as succinimide is also generally
employ-
ed. Examples of other generally employable additives include a zinc
dialkyldithio-
phosphate compound which serves as an anti-oxidation agent and an extreme-
pressure agent and an organic anti-oxidation agent such as phenol compound
and amine compound.
Recently, the operation conditions of diesel engines for generation of
electric
power and operation of marine vessel have been getting severe. In addition,
these diesel engines are forced to employ a low grade fuel having increased
sulfur content. Moreover, the recent demand for economical operation and
increase of maintenance efficiency requires extended service periods for using
a
1

CA 02531433 2005-12-23
lubricating oil with no substantial exchange. Therefore, the load applied to
the
lubricating oil has increased recently.
The lubricating oil is consumed during the operation of engines. Although a
fresh
lubricating oil is supplemented periodically to compensate the consumed
portion,
and Japanese Provisional Patent Publication 2000-87066 disclose a metal-
containing overbased calcium carboxylate (i.e., overbased calcium hydrocarbyl-
salicylate carboxylate) having high thermal stability and high detergency. It
can
be prepared with low production costs. These publications describe a variety
of
SUMMARY OF THE INVENTION
As previously mentioned, the present invention relates to a lubricating oil
Accordingly, the present invention relates to a lubricating oil composition
having a TBN in the range of 5 to 55 mg KOH/g comprising a base oil of
lubricating viscosity and
a) 0.19 to 2.10 wt %, based on the total amount of the lubricating oil
composition, of an overbased calcium carboxylate having a TBN of
100 mg KOH/g or more, wherein the wt is expressed in terms of
the calcium (Ca) content;
9

CA 02531433 2013-02-11
b) 0.002 to 0.06 wt %, based on the total amount of the lubricating oil
composition, of a bis-succinimide compound wherein, the wt % is
expressed in terms of the nitrogen (N) content; and
c) 0.007 to 0.15 wt %, based on the total amount of the lubricating oil
composition, of a zinc dialkyldithiophosphate having a secondary
alkyl group, wherein the wt % is expressed in terms of the
phosphorus (P) content.
In a further embodiment the present invention relates to a method of improving
the oxidation stability at high temperatures of an internal combustion engine,
particularly a four stroke trunk piston diesel engine, by operating the
internal
combustion engine with the lubricating oil composition of the present
invention.
Among other factors, the present invention is based on the surprising
discovery
that a certain lubricating oil composition provides improved high temperature
oxidation stability when employed in internal combustion engines such as
diesel
engines and gasoline engines.
In accordance with another aspect, there is provided a lubricating oil
composition
having a total base number (TBN) in the range of 5 to 55 mg KOH/g comprising a
major amount of a base oil of lubricating viscosity and
a) 0.19 to 2.10 wt /0, based on the total amount of the
lubricating oil
composition, of an overbased calcium carboxylate having a TBN of
100 mg KOH/g or more comprising each of the following compound
A and the following compound B, wherein the wt % is expressed in
terms of the calcium content, and wherein the overbased calcium
carboxylate having a TBN of 100 mg KOH/g or more comprises
more than 50 wt % of the following compound A and less than 50
wt% of the following compound B:
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CA 02531433 2013-02-11
Ca
0 0
0
Compound A
OH
0
- C¨OCaOH
Compound B
in which R is an alkyl group having 12 to 28 carbon atoms;
b) 0.002 to 0.06 wt %, based on the total amount of the lubricating oil
composition, of a bis-succinimide compound, wherein the wt c'/0 is
expressed in terms of the nitrogen content; and
c) 0.007 to 0.15 wt %, based on the total amount of the lubricating oil
Composition, of a zinc dialkyldithiophosphate having a secondary
alkyl group, wherein the wt % is expressed in terms of the
phosphorus content.
In accordance with a further aspect, there is provided a method comprising
operating an internal combustion engine with a lubricating oil composition
having
a total base number (TBN) in the range of 5 to 55 mg KOH/g comprising a base
oil
of lubricating viscosity and
3a

CA 02531433 2013-02-11
a) 0.19 to 2.10 wt %, based on the total amount of the lubricating oil
composition, of an overbased calcium carboxylate having a TBN of
100 mg KOH/g or more comprising each of the following compound
A and the following compound B, wherein the wt % is expressed in
terms of the calcium content and wherein the overbased calcium
carboxylate having a TBN of 100 mg KOH/g or more comprises
more than 50 wt % of the following compound A and less than 50
wt% of the following compound B:
Ca
0 0
0
Compound A
OH
0
C¨OCaOH
Compound B
in which R is an alkyl group having 12 to 28 carbon atoms;
b) 0.002 to 0.06 wt %, based on the total amount of the lubricating oil
composition, of a bis-succinimide compound, wherein the wt % is
expressed in terms of the nitrogen content; and
c) 0.007 to 0.15 wt %, based on the total amount of the
lubricating oil
composition, of a zinc dialkyldithiophosphate having a secondary
3b

CA 02531433 2013-02-11
alkyl group, wherein the wt % is expressed in terms of the
phosphorus content.
DETAILED DESCRIPTION OF THE INVENTION
In its broadest aspect, the present invention relates to a lubricating oil
composition having a major amount of base oil of lubricating viscosity and an
overbased calcium carboxylate, bis-succinimide compound and a zinc
dialkylthidiophosphate, wherein the TBN of the lubricating oil composition is
in the
range of 5 to 55 mg KOH/g.
Base Oil of Lubricating Viscosity
The base oil of lubricating viscosity employed in the lubricating oil
composition of
the present invention generally is a mineral oil or a synthetic oil having a
dynamic
viscosity in the range of 22 to 300 mm2/s at 40 C. There are no specific
limitations with respect to the nature and other characteristics of the
mineral oil
and synthetic oil. However, the sulfur content of the base oil is preferably
not
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CA 02531433 2005-12-23
less than 0.1 wt %, more preferably less than 0.03 wt %, most preferably less
than 0.005 wt
The mineral oil is preferably prepared by processing a mineral oil of
lubricating oil
distillate by an appropriate combination of solvent purification and
hydrogenation
processing. Most preferred is a mineral oil having been subjected to high
hydrogenation processing (i.e., hydrogenation cracking) that advantageously
shows a viscosity index in the range of 100 to 150 and has an aromatic
component content of less than 5 wt %, a nitrogen content of less than 50 ppm,
and a sulfur content of less than 50 ppm. The above-identified most preferred
mineral oil can be a high viscosity index base oil which is prepared by
processing
synthetic wax by isomerization and hydrogenation cracking. The synthetic wax
was prepared by mineral slack was (crude wax) or natural gas.
The synthetic oil (synthetic base oil) can be poly-a-olefin (polymer prepared
from
a-olefin having 3 to 12 carbon atoms), a sebacic acid compound such as dioctyl
sebacate, a dialkyl diester prepared from a dibasic acid such as azelaic acid
or
adipic acid and an alcohol having 4 to 18 carbon atoms, a polyol ester
prepared
from 1-trimethylolpropane or pentaerythritol and a monobasic acid, or an
alkylbenzene having alkyl of 9 to 40 carbon atoms.
The synthetic oil generally contains no sulfur compound and shows high thermal
stability and high heat resistance. Moreover, the synthetic oil produces
little soot
and carbonaceous deposit. Therefore, the synthetic oil is preferred as the
base
oil for the lubricating oil composition of the present invention.
Each of the mineral base oil and synthetic base oil can be employed singly.
However, if desired, two or more of mineral base oils or two or more of
synthetic
base oils can be employed in combination. Further, if desired, one or more
mineral base oils and one or more synthetic base oils can be employed in
combination.
It is preferred to use a major amount of base oil of lubricating viscosity in
the
lubricating oil composition of the present invention. A major amount of base
oil of
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CA 02531433 2005-12-23
lubricating viscosity as defined herein comprises 40 wt % or more. Preferred
amounts of base oil comprise 40 wt % to 97 wt %, preferably greater than 50 wt
% to 97 wt %, more preferably 60 wt % to 97 wt % and most preferably 80 wt %
to 95 wt % of the lubricating oil composition. (When weight percent is used
herein, it is referring to weight percent of the lubricating oil composition
unless
otherwise specified.)
Overbased Calcium Carboxylate
The overbased calcium carboxylate employed in the lubricating oil of the
present
invention has a TBN of 100 mg KOH/g or more and can be prepared in the
manner described in the aforementioned references cited in the Background of
the Invention. The overbased calcium carboxylate will be in the amount of 0.19
to 2.10 wt %, preferably 0.38 to 1.15 wt %, based on the total amount of the
lubricating oil composition and expressed in terms of the calcium content. A
representative example of the overbased calcium carboxylate comprises a rela-
tively large amount (more than 50 wt %) of the following compound A and a
relatively small amount (less than 50 wt %) of the following compound B:
Compound A Compound B
Ca OH 0
0 11
C¨OCaOH
,CO
in which R is an alkyl group having 12 to 28 carbon atoms.
The lubricating oil composition of the present invention can contain other
metal-
containing detergents in addition to the overbased calcium carboxylate.
Examples of other metal-containing detergents employable in combination with
the overbased calcium carboxylate include sulfurized phenate (e.g., sulfurized
5

CA 02531433 2005-12-23
calcium phenate), petroleum sulfonates or synthetic sulfonates (e.g., calcium
sulfonate), and salicylate (e.g., calcium salicylate).
Bis-Succinimide Compound
The lubricating oil composition of the present invention contains a bis-
succinimide
compound (i.e., succinimide or its derivatives) in the amount of 0.002 to 0.06
wt
%, preferably 0.014 to 0.02 wt %, based on the total amount of the lubricating
oil
composition and expressed in terms of the nitrogen content. The bis-
succinimide
compound preferably is an alkenylsuccinimide or an alkylsuccinimide derived
from a polyolefin compound or its derivatives. The bis-succinimide can be
prepared, for example, by a reaction between succinic anhydride and a high
molecular weight alkenyl or alkyl, followed by further reaction with a
polyalkylenepolyamine containing 4 to 10, preferably 5 to 7, nitrogen atoms
per
molecule. For example, the bis-succinimide compound can be prepared by a
thermal reaction between a polybutene compound containing 50% or more
methylvinylidene structure and maleic anhydride, followed by reaction of the
resulting polybutenyl succinic anhydride with a polyalkylenepolyamine
containing
4 to 10, preferably 5 to 7, nitrogen atoms per molecule. The high molecular
weight alkenyl or alkyl group preferably is polybutene having a number-average
molecular weight in the range of approximately 900 to 5,000.
The bis-succinimide can be employed in the form of a modified succinimide
which
is obtained by reacting succinimide with boric acid, alcohol, aldehyde,
ketone,
alkylphenol, cyclic carbonate (e.g., ethylene carbonate), or an organic acid.
Preferred is a boron-containing alkenyl- or alkylsuccinimide which is obtained
by
reaction with boric acid or a boron compound. The resulting modified
succinimide
compound exhibits high thermal stability and high anti-oxidation property.
The lubricating oil composition of the present invention can contain other
ashless
dispersants such as nitrogen-containing ashless dispersants (e.g., mono-
structure type alkenyl- or alkylsuccinimide, and an alkenylbenzylamine) and/or
dispersants containing no nitrogen atoms such as an alkenyl succinic ester in
addition to the bis-structure alkenyl or alkyl succinimide.
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CA 02531433 2005-12-23
Zinc Dialkyldithiophosphate
The zinc dialkyldithiophosphate employed in the lubrication oil composition of
the
present invention has a secondary alkyl group and will be in the amount of
0.007
to 0.15 wt %, preferably 0.036 to 0.072 wt %, based on the total amount of the
lubricating oil composition and expressed in terms of the phosphorus content.
The alkyl group preferably contains 3 to 18 carbon atoms. All of the two alkyl
groups of the zinc dialkyldithiophosphate can be secondary alkyl groups.
Otherwise, a portion (e.g., a relatively small portion such as less than 48
mole %)
of the alkyl groups of the zinc dialkyldithiophosphate can be a primary alkyl
group. The secondary-alkyl type zinc dialkyldithiophosphate can be employed in
combination with a zinc dialkyldithiophosphate having a primary alkyl group.
In
this case, the former zinc dialkyldithiophosphate is generally employed in an
amount of 52 to 98 mole %, and the latter zinc dialkyldithiophosphate can be
employed in an amount of 2 to 48 mole %.
Other Additives
The lubricating oil composition of the present invention can further contain
other
oxidation inhibitors, such as phenol oxidation inhibitors and/or amine
oxidation
inhibitors, in an amount of 0.01 to 5 wt %, preferably 0.1 to 3 wt %.
The lubrication oil composition of the present invention can further contain a
multi-functional molybdenum-containing compound in an amount of 0.01 to 5 wt
%, preferably 0.1 to 3 wt %. The molybdenum-containing compound mainly
serves as friction-modifier, oxidation inhibitor and anti-wear agent in the
lubricating oil composition of the present invention. The molybdenum-
containing
compound further provides effective high temperatures detergency. The
molybdenum-containing compound can be incorporated into the lubricating oil
composition of the present invention in an amount of 10 to 2,500 ppm in terms
of
the molybdenum metal content. Examples of the molybdenum-containing
compounds include, but not limited to, a sulfur-containing molybdenum complex
compound of succinimide, sulfurized oxymolybdenum dithiocarbamate, sulfurized
7

CA 02531433 2005-12-23
oxymolybdenum dithiophosphate, an amine-molybdenum complex compound,
oxymolybdenum diethylateamide, and oxymolybdenum monoglyceride. The
sulfur-containing molybdenum complex compound of succinimide is particularly
effective to increase detergency at high temperatures.
The lubricating oil composition of the present invention can further contain a
viscosity index improver in an amount of less than 20 wt A, preferably in an
amount of 1 to 20 wt %. Examples of the viscosity index improvers are such
polymers as poly(alkyl methacrylate), ethylene-propylene copolymer, styrene-
butadiene copolymer, and polyisoprene. Dispersant-type viscosity index
improvers and multi-functional viscosity index improvers which are obtained by
adding dispersancy to the above-mentioned polymers are also employable. The
viscosity index improvers can be employed singly or in combination.
The lubricating oil composition of the present invention can further contain a
variety of subsidiary additives. Examples of the subsidiary additives include,
but
not limited to, oxidation inhibitors/anti-wear agents (e.g., zinc
dithiocarbamate,
methylene-bis(dibutyldithiocarbamate), oil-soluble copper compounds, sulfur-
containing compounds such as sulfurized olefins, sulfurized esters and
polysulfides, phosphate esters, phosphite esters, and organic amide compounds
such as oleylamide. Metal-deactivating compounds such as benzotriazol
compounds and thiaziazol compounds also can be employed. Anti-rust agents
and de-emulsifiers such as nonionic surfactants (e.g., polyoxyethylene
alkylphenyl ether, and copolymer of ethylene oxide and propylene oxide) also
can
be employed. Friction modifiers such as amines, amides, amine salts, their
derivatives, and fatty acid esters of polyhydric alcohols and their
derivatives also
can be employed. Anti-foaming agents and pour point depressants also can be
employed. Each of the subsidiary additives is generally contained in the
lubricating oil composition of the present invention in an amount of less than
3 wt
%, preferably in the range of 0.001 to 3 wt
8

CA 02531433 2005-12-23
EXAMPLES
The invention will be further illustrated by the following examples, which set
forth
particularly advantageous method embodiments. While the Examples are
provided to illustrate the present invention, they are not intended to limit
it.
Example 1
A lubricating oil composition (TBN: 30 mg=KOH/g, SAE viscosity grade: SAE 40)
was prepared using the following additives and base oil:
a) overbased calcium carboxylate (TBN: 145 mg=KOH/g, a mixture of a
compound of the aforementioned formula in which R has 12 to 18 carbon atoms
and a compound of the formula in which R has 20 to 28 carbon atoms, in a
weight ratio of 50:50 in an amount of 1.15 wt % in terms of Ca content;
b) bis-structure succinimide dispersant (nitrogen content 0.018 wt %,
prepared by reaction between polyalkylene polyamine (containing nitrogen atoms
of 5.0 (mean number) in a molecule) and a product produced by thermal reaction
of polybutene (number average molecular weight: approx. 1,000, having at least
50 mole % of methylvinylidene structure) and maleic anhydride) in an amount of
0.018 wt % in terms of N content;
c) zinc di(secondary)alkyldithiophosphate (P 0.049 wt %, Zn 0.054 wt %, S
0.14 wt `)/0, prepared using a secondary alcohol containing 3 to 8 carbon
atoms)
in an amount of 0.05 wt % in terms of P content;
d) base oil (dynamic viscosity at 40 C: 140 mm2/sec.) of the remaining
amount.
Comparative Example A
A lubricating oil composition having the same composition of Example 1 except
for containing no bis-succinimide (component b) was prepared.
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CA 02531433 2005-12-23
Comparative Example B
A lubricating oil composition having the same composition of Example 1 except
for containing neither bis-structure succinimide (component b) nor zinc
di(secondary)alkyldithiophosphate (component c) was prepared.
Comparative Example C
A lubricating oil composition having the same composition of Example 1 except
for replacing the zinc di(secondary)alkyldithlophosphate (component c) with a
zinc di(primary)alkyldithiophosphate was prepared. The phosphorus content of
the latter di(primary)alkyldithiophosphate was the same as that of the former
zinc
di(secondary)alkyldithiophosphate.
Comparative Example D
A lubricating oil composition having the same composition of Example 1 except
for replacing the bis-succinimide (component b) with a mono-succinimide
dispersant was prepared.
Evaluation of Thermal Stability at High Temperatures
The thermal stability of the lubrication oil compositions at high temperatures
was
evaluated using the JIS (Japanese Industrial Standard) K2514 ISOT (Indiana
Stirred Oxidation Test). This test is used to determine the oxidation
stability of a
lubricating oil composition in the presence of copper, steel and heat.
(1) ISOT test was performed under the following conditions:
Amount of oil: 250 mL
Temperature of the test oil: 165.5 C
Test period: continuous operation for 96 hours
Test results are determined and expressed as follows:

CA 02531433 2005-12-23
Viscosity increase: determined at 40 C after the continuous operation,
expressed as a relative value to the viscosity (as "1") of the test oil before
the operation;
TBN retention (HCI): in terms of %, measured using HCI, and
TBN retention (ASTM D2896): determined according to ASTM D2896.
(2) Test results
Test results are set forth in the following Table:
Example Comparative Example
1 A
Viscosity
increase 0.97 1.21 1.19 1.18 1.16
TBN retention
(HCI) 65.0 61.5 60.7 60.5 60.8
TBN retention
(ASTM D2896) 92.4 89.9 86.3 87.1 88.8
Remarks: The lubricating oil composition of Example 1 gave a viscosity
increase
of 1.02 after additional 24 hours ISOT test (total: 120 hours).
The lubricating oil composition of the present invention provides low
viscosity
increase and shows high TBN retention. Accordingly, it is clear that the
lubricating oil composition of the present invention has high anti-thermal
oxidation
property at high temperatures.
11