Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a friction modifier comprising a metal
sulfonate and to a lubricating oil composition with the metal sulfonate added
therein, and more specifically to a friction modifier comprising a metal
sulfonate
containing a specific chain hydrocarbon group and to a lubricating oil composi-
tion with the metal sulfonate added therein.
Description of the Prior Art
From the need for resource and energy saving measures in all the
industrial fields in view of environmental conservation, reductions in
friction
and wear through improvements in lubricating oils have also been investigated
in
the field of lubricating oils from a variety of viewpoints in recent years
with a
view to lowering fuel consumption rates. As a result, it has already become in-
dispensable to incorporate additives in base stocks for lubricating oils so
that the
base stocks can be provided with desired friction characteristics.
Accordingly, a
number of friction modifiers have been proposed to date, resulting in the use
of
fatty acids and their metal salts, esters, amines and the like - all of which
are of
the oiliness improver type - and phosphate esters, phosphite esters, zinc
dithio-
phosphate and the like - all of which are of the extreme pressure agent type -
in
wet brake oils, automatic transmission fluids, sliding surface oils, plastic
work-
ing oils and the like and also in the use of phosphate esters, phosphite
esters,
acidic phosphite ester amine salts, molybdenum dithiophosphate, molybdenum
dithiocarbamate and the like - all of which are of the extreme pressure agent
type
- in engine oils, gear oils, cutting oils and the like.
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Meanwhile, an automatic transmission oil was disclosed, which
had been obtained by adding magnesium sulfonate, which is used as a metallic
detergent, for example, for the dispersion of sludge occurring in lubricating
oils,
the solubilization of a precursor and the neutralization of an acid,
especially
over-based magnesium sulfonate having a base number of 300 mg-KOH/g or
greater in a base stock, in order to improve friction characteristics (see JP
Kokai
62-84190). Further, a lubricating oil making combined use of a metallic
detergent, such as calcium sulfonate, barium sulfonate or magnesium sulfonate,
with a molybdenum dialkyldithiocarbamate was also proposed (see JP Kokai
62-215697).
These metal sulfonates, when employed singly, are however still
insufficient in friction reducing effects, so that they are merely friction
modifier
adjuvants for use in combination with friction modifiers such as phosphate
esters
and molybdenum dithiocarbamate. If a metal sulfonate having still higher
friction reducing ability is identified, it is therefore believed it will find
utility in
a much wider range of fields and hence to have a significantly-increased
industrial value. There is accordingly an outstanding intense desire for the
development of such a metal sulfonate.
In view of the circumstances of development of friction modifiers
as described above, the present invention has as objects thereof the provision
of
a novel metal sulfonate having friction reducing ability and also the
provision of
a lubricating oil composition with the metal sulfonate added.
Present Invention
It has been discovered that a metal sulfonate having an alkyl group,
which has a specific linear portion determinable by carbon nuclear magnetic
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resonance measurement (13 C-NMR measurement) (hereinafter referred to as
13C-NMR measurement, as needed), has excellent friction reducing ability.
Having been interested in its effectiveness as a friction modifier, it has
also been
found that its addition to a base stock for lubricating oil makes it possible
to
furnish a lubricating oil composition having improved friction characteristics
and
utility in a variety of technical fields. Based on these findings, the present
invention has now been completed.
The present invention relates in a first aspect thereof to a friction
modifier comprising a metal sulfonate composed of an organic sulfonic group,
which contains a hydrocarbon group, and a metal, characterized in that said
hydrocarbon group is a chain hydrocarbon group or an aromatic group with at
least one chain hydrocarbon group bonded thereto, and said chain hydrocarbon
group has an alkyl chain linearity of 20% or higher as determined by 13C-NMR
measurement.
The present invention also relates in a second aspect thereof to a
lubricating oil composition characterized in that said lubricating oil
composition
comprises:
a base stock; and
a metal sulfonate composed of an organic sulfonic group, which
contains a hydrocarbon group, and a metal, said hydrocarbon group being a
chain hydrocarbon group or an aromatic group with at least one chain hydro-
carbon group bonded thereto, said chain hydrocarbon group having an alkyl
chain linearity of 20% or higher as determined by 13C-NMR measurement, and
said metal sulfonate having been added in a proportion of from 1 ppm to 10,000
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ppm in terms of the metal thereof based on a whole weight of said lubricating
oil
composition.
The present invention will hereinafter be described in detail.
The metal sulfonate which is used as the friction modifier accord-
mg to the present invention is composed of an organic sulfonic group, which
contains a hydrocarbon group, and a metal, and is a compound which can be
represented, for example, by the following formula (1):
(RSO3)xM (I)
It may consist of one type of the compound or may be a mixture of two or more
compounds having different hydrocarbon groups. In the formula (I), R in the
organic sulfonic group RSO3 is a hydrocarbon group, which is a chain hydro-
carbon group or an aromatic group with at least one chain hydrocarbon group
bonded thereto. Illustrative of the chain hydrocarbon group can be alkyl
groups,
each of which has 12-40 carbon atoms on average per organic sulfonic group as
measured by 13C-NMR and calculated supposing that there is one carbon atom
bonded to a sulfonic group. It is particularly preferred to contain at least
one or
more alkyl groups having 12-30 carbon atoms. Specific examples of the alkyl
group can include dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,
heptadecyl, octadecyl, nonadecyl, eicosyl, tetracosyl, pentacosyl, hexacosyl,
heptacosyl, octacosyl, nonacosyl, triacontyl, pentatriacontyl, and
octatriacontyl.
As the metal sulfonate according to the present invention, one
having an alkyl chain linearity of 20% or higher, especially of from 30% to
80%
as determined by a 13C-NMR measurement is preferred.
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Here, the term "alkyl chain linearity" is based on a unique concept
established by the present inventors as a result of repetition of numerous
experi-
ments, and means the ratio of the number of carbon atoms in a linear portion
located 5 or more atoms apart from an end of the alkyl group or 4 or more
atoms
apart from a branched site of the alkyl group to the total number of carbon
atoms
in the alkyl group. Its value is dependent on the bonding site of an aromatic
group and the site of branching of the alkyl group.
In the present invention, the alkyl chain linearity has been deter-
mined specifically by the following formula from a 13C-NMR measurement.
Alkyl chain linearity (%) =
Integral intensity over a chemical shift range
of from 29 ppm to 31 ppm
Sum of all integral intensity over a chemical x l00
shift range of from 5 ppm to 60 ppm
Incidentally, the 13C-NMR measurement was conducted by
converting the metal sulfonate into its corresponding sulfonic acid.
The present inventors recognized the existence of a correlation
between the alkyl chain linearity and the friction reducing effects of its
metal
sulfonate, and have ascertained that the metal sulfonate exhibits better
friction
reducing effects as the linearity becomes higher and also that a linearity
lower
than 20% cannot exhibit the effects fully although a linearity of 20% or
higher,
especially of from 30% to 80% shows particularly marked effects.
Even when the metal sulfonate contains two or more chain hydro-
carbon groups per organic sulfonic group or is a mixture of two or more
different
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compounds (metal sulfonates), the metal sulfonate exhibits friction reducing
effects and is effective as a metal sulfonate according to the present
invention
provided that the alkyl chain linearity as determined by a 13C-NMR measure-
ment is 20% or higher. In particular, a metal sulfonate, the chain hydrocarbon
groups of which are each an alkyl group having 12 or more carbon atoms and a
linearity of 20% or higher, is preferred from the viewpoint of making it
possible
to substantially increase friction reducing ability. The aromatic group bonded
to
the chain hydrocarbon groups can be either monocyclic or fused polycyclic.
Those represented by the following structural formulas (a) to (g),
respectively,
are effective, with a phenyl group being particularly preferred.
(a)
(b)
(c)
(d)
(e)
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O l'/
0 0 (g)
The metal component represented by M in the above-described
metal sulfonate (formula (I)) (RSO3)xM can be an alkali metal or an alkaline
earth metal. Further, a metal of an atomic number in a range of from 12 to 56
is
also suited. Specific examples can include sodium, potassium, lithium,
calcium,
magnesium and barium. In addition, aluminum, zinc, tin, chromium, copper,
cobalt and the like are also effective. Of these, calcium, magnesium, barium
and
the like are particularly preferred.
In the above formula (I), x is a value corresponding to the valence
of the metal component M.
Typical illustrative compounds of the metal sulfonate according to
the present invention can be represented by the following formula (II):
O 0
1) 11
A S O M O S B (II)
11 11
0 0
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In the above formula (II), A and B may be the same or different
and are each (i) an alkyl group or (ii) an aromatic group with at least one
alkyl
group bonded thereto, and the alkyl groups are those capable of providing 20%
or higher as an average linearity of the whole alkyl groups as determined by a
13C-NMR measurement. Further, the aromatic group can be at least one
aromatic group selected from the group consisting of the above-described
structural formulas (a) to (g). In addition, M in the formula represents the
above-
described divalent metal, with an alkaline earth metal being preferred.
Accordingly, more specific illustrative examples of the metal
sulfonate according to the present invention can be represented by the
following
formulas (III) to (VII):
O 0
1 11 11 2
R S O M O S R (III)
11 11
0 0
O O R4)n
3 II II
R S O M O S (IV)
11 11
0 0
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( R S ) n O O R 11 1
S O M O S (V)
11 11
O O
(R)n 0 O (Rg)n
b~I I
S-O M-O-S (V
I)
11 1O O
(R9)n O O (R 1 o)n
1 11
S-O-M-O-S (VII)
O O
In the above formulas (III) to (VII), R' to R10 are alkyl groups and
as already described, the average total carbon numbers of Rl, R2, R3, R4, R5,
R6,
R7, Rg, R9 and R10, said average total carbon numbers being equivalent to the
numbers of carbon atoms per the corresponding organic sulfonic acids, may
preferably be from 12 to 40, and R' to R10 have alkyl chain linearities of 20%
or
higher as determined by 13C-NMR measurement.
In each of the above formulas (III) to (VII), each n represents the
number of alkyl groups bonded to the associated aromatic group and may stand
for an integer of I to 5, preferably of 1 to 3. In each formula, two n values
can
be the same or different.
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Further, Ms in the fonnulas (III) to (VII) are preferably alkaline
earth metals, although they can be other divalent metals described above.
No particular limitation is imposed on a process for the preparation
of a metal sulfonate according to the present invention, which contains one or
more alkyl groups which are large in chain length and high in linearity. It is
possible to adopt, for example, a process in which a sulfonic acid available
by
sulfonation of an alkyl-substituted aromatic hydrocarbon obtained from a
petroleum fraction or of an alkyl-substituted aromatic hydrocarbon, which is
an
alkylation product of an aromatic hydrocarbon by an olefinic hydrocarbon, is
neutralized with an alkali metal oxide, hydroxide, alkoxide or the like,
followed
by the adjustment of a quantity of a metal.
Further, a metal sulfonate according to the present invention,
which has a specific alkyl chain linearity, can be prepared by mixing various
metal sulfonates of different alkyl chain linearities so that the overall
alkyl chain
linearity is controlled to fall within the above-descried particular range.
In the present invention, the metal sulfonate can be a basic salt or
over-based salt in addition to a neutral salt. Its salt type can be chosen as
desired
depending on its application. A basic salt can be one prepared by a
conventional
process, and can be prepared, for example, by dispersing M(OH)2 or MCO3
(wherein M represents an alkaline earth metal or the like) in a colloidal form
in a
sulfonate. A conventionally-adopted preparation process can be relied upon.
As has been described above, the present invention provides a
friction modifier, especially a friction modifier for lubricating oils, which
is
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composed of a particular metal sulfonate. This friction modifier is oil-
soluble. It
can be used by dissolving it in a hydrocarbon or another solvent and diluting
the
resultant concentrate as needed or as a component of an additive package in
combination with other additives.
A description will next be made about the lubricating oil composi-
tion according to the present invention.
No particular limitation is imposed on the base stock employed in
the lubricating oil composition according to the present invention. The base
stock can be any one of mineral base stocks, synthetic base stocks and
vegetable
base stocks, or can be a blended base stock of two or more of these base
stocks.
As a mineral base stock, it is possible to use, for example, a
mineral oil obtained by the treatment of a lubricating oil fraction, which is
in
turn available by vacuum distillation of an atmosphere distillation residue of
paraffm-base, neutral or naphthene-base crude oil, through a refining step
such
as solvent refining, hydrocracking, hydro-refining, catalytic dewaxing,
solvent
dewaxing or clay treatment; a mineral oil obtained by subjecting a vacuum
distillation residue to solvent deasphalting and then treating the resulting
deasphalted oil through the above-described refining step; a mineral oil
obtained
by isomerizing wax components; or a blended oil thereof. In the above solvent
refming, an aromatic extraction solvent such as phenol, furfural or N-methyl-
pyrrolidone can be used, whereas as a solvent for the solvent dewaxing,
liquefied
propane, MEK/toluene, MEK/MIBK, or the like can be used. Among the above-
described mineral base stocks, hydro-refined oil is preferred from the
standpoint
of oxidation stability and the like, and one containing, for example, 2 wt% or
less of aromatic hydrocarbons and 90 wt% or more of saturated hydrocarbons
can be used.
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Examples of synthetic base stocks, on the other hand, can include
poly(a-olefin) oligomers of lubricating viscosity; polybutene; alkylbenzenes;
polyol esters such as trimethylolpropane esters and pentaerythritol esters;
poly-
oxyalkylene glycols; polyoxyalkylene glycol esters; polyoxyalkylene glycol
ethers; dibasic acid esters; phosphate esters; and silicone oils. These base
stocks
can be used either singly or in combination. Further, usable examples of
vegetable base stocks can include rape seed oil, soybean oil, coconut oil,
olive
oil and sunflower oil.
The lubricating base stock employed in the lubricating oil
composition according to the present invention can be produced by suitably
preparing a blended base stock so that the blended base stock has properties
desired for the intended application of the lubricating oil composition.
Concerning viscosity, for example, it is preferred to control the kinematic
viscosity at 100 C in a range of from 2 mm2/s to 30 mm2/s, especially from
3 mm2/s to 10 mm2/s for a lubricating oil for internal combustion engines, the
kinematic viscosity at 100 C in a range of from 2 mm2/s to 30 mm2/s,
especially
from 3 nun2/s to 15 mm2/s for an automatic transmission fluid, and the
kinematic
viscosity at 40 C in a range of from 10 mm2/s to 1,000 mm2/s, especially from
20 mm2/s to 500 mm2/s.
The metal sulfonate according to the present invention can exhibit
sufficient friction reducing effects when added to the lubricating base stock
in a
proportion of from 0.01 to 10 wt%, preferably from 0.05 to 5 wt% based on the
whole weight of the lubricating oil composition or in a proportion of from 1
ppm
to 10,000 ppm, preferably from 50 ppm to 5,000 ppm in terms of the metal,
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although the proportion varies depending on the application field of the
lubricat-
ing oil.
To the lubricating oil composition according to the present
invention, it is possible to add selected ones of viscosity index improvers,
ashless
dispersants, oxidation inhibitors, extreme pressure agents, wear inhibitors,
metal
deactivators, pour-point depressants, rust inhibitors, other friction
modifiers and
other additives as needed.
Illustrative usable examples of the viscosity index improvers can
include polymethacrylates, polyisobutylenes, ethylene-propylene copolymers,
and hydrogenated styrene-butadiene copolymers. These viscosity index
improvers are used generally in a proportion of from 3 wt% to 35 wt%.
Illustrative of the ashless dispersants can be polybutenyl-
succinimides, polybutenylsuccinamides, benzylamines, and succinate esters.
They can be used generally in a proportion of from 0.05 wt% to 7 wt%.
Illustrative examples of the oxidation inhibitors can include amine-
type oxidation inhibitors such as alkylated diphenylamines, phenyl-a-naphthyl-
amine and alkylated phenyl-a-naphthylamines; phenolic oxidation inhibitors
such as 2,6-di-t-butylphenol and 4,4'-methylene-bis(2,6-di-t-butyl-phenol);
and
zinc dithiophosphate. They can be used generally in a proportion of from
0.05 wt% to 5 wt%.
Illustrative of the extreme pressure agents can be dibenzyl sulfide
and dibutyl disulfide. They can be used generally in a proportion of from
0.05 wt% to 3 wt%.
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Illustrative examples of the metal deactivators can include benzo-
triazole, benzotriazole derivatives, and thiadiazole. They can be used
generally
in a proportion of from 0.01 wt% to 3 wt%.
Illustrative of the pour-point depressants can be ethylene-vinyl
acetate copolymers, chlorinated paraffin-naphthalene condensation products,
polymethacrylates, and polyalkylstyrenes. They can be used generally in a
proportion of from 0.1 wt% to 10 wt%.
Illustrative of the wear inhibitors can be phosphate esters, zinc
thiophosphate, and sulfur compounds. They can be used generally in a
proportion of from 0.01 wt% to 5 wt%.
As preferred embodiments of the present invention, it is possible to
provide:
(i) A friction modifier for lubricating oils, which comprises a
metal sulfonate composed of an organic sulfonic group, which contains a
hydrocarbon group, and a metal, in which the hydrocarbon group is a chain
hydrocarbon group or an aromatic group with at least one chain hydrocarbon
group bonded thereto, and wherein the chain hydrocarbon group is an alkyl
group having an average carbon number of from 12 to 40 per organic sulfonic
group and an alkyl chain linearity of 20% or higher as determined by a
13C-NMR measurement.
(ii) A friction modifier for lubricating oils, which comprises metal
sulfonate composed of an organic sulfonic group, which contains a hydrocarbon
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group, and a metal, in which the hydrocarbon group is a chain hydrocarbon
group or an aromatic group with at least one chain hydrocarbon group bonded
thereto, and wherein the chain hydrocarbon group is an alkyl group having an
average carbon number of from 12 to 40 per organic sulfonic group and has an
alkyl chain linearity of 30% or higher as determined by a 13C-NMR measure-
ment.
(iii) A lubricating oil composition comprising:
a lubricating base stock;
a metal sulfonate composed of an organic sulfonic group, which
contains a hydrocarbon group, and a metal, said hydrocarbon group being a
chain hydrocarbon group or an aromatic group with at least one chain hydro-
carbon group bonded thereto, said chain hydrocarbon group being an alkyl
group, which has an average carbon number of from 12 to 40 per organic
sulfonic group, and having an alkyl chain linearity of 20% or higher as deter-
mined by a 13C-NMR measurement, and said metal sulfonate having been added
in a proportion of from 1 ppm to 10,000 ppm in terms of the metal thereof
based
on a whole weight of the lubricating oil composition.
(iv) A lubricating oil composition comprising:
a lubricating base stock;
a metal sulfonate composed of an organic sulfonic group, which
contains a hydrocarbon group, and a metal, said hydrocarbon group being a
chain hydrocarbon group or an aromatic group with at least one chain hydro-
carbon group bonded thereto, said chain hydrocarbon group being an alkyl
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group, which has an average carbon number of from 12 to 40 per organic
sulfonic group, and having an alkyl chain linearity of 20% or higher as deter-
mined by a 13C-NMR measurement, and said metal sulfonate having been added
in a proportion of from 1 ppm to 10,000 ppm in terms of the metal thereof
based
on a whole weight of the lubricating oil composition; and
at least one additive selected from the group consisting of viscosity
index improvers, ashless dispersants, oxidation inhibitors, extreme pressure
agents, metal deactivators, pour-point depressants and wear inhibitors.
As a more preferable embodiment of the lubricating oil composi-
tion according to the present invention, there is provided a lubricating oil
composition comprising as a base stock a hydro-refined oil, which contains
2 wt% or less of aromatic hydrocarbons and 90 wt% or more of saturated
hydrocarbons, and a calcium sulfonate containing 1 to 2 C 14-24 alkyl groups
per
organic sulfonic group and having an alkyl chain linearity of 40% or higher as
determined by a 13C-NMR measurement, said calcium sulfonate having been
added in a proportion of from 50 ppm to 5,000 ppm in terms of calcium based on
the whole weight of the lubricating oil composition.
As has been described above, the metal sulfonate according to the
present invention can be used as a friction modifier in hydraulic working
oils,
wet brake oils, sliding surface oils, plastic working oils, cutting oils and
the like
in addition to lubricating oils for internal combustion engines, automatic
trans-
mission fluids and gear oils. Without being limited to them, the metal
sulfonate
can be used without limitations in any other oils insofar as it can exhibit
its
friction reducing effects.
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Examples
The present invention will next be described specifically by
Examples and Comparative Examples. It is however to be noted that the
Examples and the like are to primarily demonstrate the unique effects of the
alkyl group or groups in the metal sulfonate according to the present
invention
and that the present invention shall not be limited by these Examples and the
like.
The alkyl chain linearities of the metal sulfonates employed in the
following Examples and the performance evaluation of the lubricating oil
compositions were measured or conducted by the following methods.
(i) Measuring method of alkyl chain linearity
Each metal sulfonate was converted into its corresponding sulfonic acid,
and under the following measuring conditions, its 13C-NMR spectrum was
measured. Further, its alkyl chain linearity was calculated in accordance
with the below-described formula.
Measuring conditions
Used instrument EX400 (manufactured by JEOL Ltd.)
Observed nucleus 13 C
Observing frequency 100.50 MHz
Measuring mode Inverse gated 'H decoupling
Internal standard TMS (= 0 ppm)
Relaxation reagent Cr(acac)3
Solvent CDC13
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Quantity of sample 300 mg
Temperature 30 C
Alkyl chain linearity (%) =
Integral intensity over the chemical shift range
of from 29 ppm to 31 ppm
Sum of all integral intensity over the chemical x 100
shift range of from 5 ppm to 60 ppm
(ii) Performance evaluation
Measuring method of friction coefficients
Concerning lubricating oil compositions with corresponding metal
sulfonates added in predetermined proportions, their friction coefficients
were measured under the following conditions by using "LFW-1 " as a
testing machine.
Friction materials: steel/steel
Load: 2001b.
Oil temperature: 80 C
Revolution speed: 600 rpm
Measuring period: 30 minutes
Example 1
Provided was Calcium Sulfonate 1 of the following characteristics:
- Average number of alky 1 carbons per organic 31
sulfonic group
- Alkyl chain linearity 47.2%
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- Calcium content 2.8 wt%
- Total base number 25 mg-KOH/g
A lubricating oil composition was formulated by adding the
sulfonate to a solvent-refined mineral oil " 100N" (kinematic viscosity at 100
C:
4.2 mm 2/s) in a proportion of 140 ppm in terms of calcium based on the whole
weight of the lubricating oil composition. The friction coefficient of the
resultant lubricating oil composition was measured by the above-described
method. It was found to be 0.09.
Example 2
A lubricating oil composition was formulated in exactly the same
manner as in Example 1 except that the proportion of Calcium Sulfonate 1 was
increased from 140 ppm to 560 ppm in terms of calcium. The resultant lubricat-
ing oil composition was subjected to a performance evaluation. Its friction
coefficient was found to be 0.08, thereby indicating an improvement in
friction
characteristics.
Example 3
Provided was Calcium Sulfonate 2 of the following characteristics:
- Average number of alky 1 carbons per 35
organic sulfonic group
- Alkyl chain linearity 39.9%
- Calcium content 12 wt%
- Total base number 300 mg-KOH/g
A lubricating oil composition was formulated by adding the
sulfonate to the same lubricating base stock as that employed in Example I in
a
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proportion of 1,200 ppm in terms of calcium based on the whole weight of the
lubricating oil composition. The resultant lubricating oil composition was
subjected to the above-described performance evaluation. Its friction
coefficient
was found to be 0.10.
Example 4
A lubricating oil composition was formulated in exactly the same
manner as in Example 3 except that the proportion of Calcium Sulfonate 2 was
increased from 1,200 ppm to 2,400 ppm in terms of calcium. The resultant
lubricating oil composition was subjected to a performance evaluation. Its
friction coefficient was found to be 0.08.
Example 5
Provided was Calcium Sulfonate 3 of the following characteristics:
- Average number of alky 1 carbons per 26
organic sulfonic group
- Alkyl chain linearity 31.0%
- Calcium content 11.8 wt%
- Total base number 295 mg-KOH/g
A lubricating oil composition was formulated by adding the
sulfonate to the same lubricating base stock as that employed in Example 1 in
a
proportion of 2,400 ppm in terms of calcium based on the whole weight of the
lubricating oil composition. The resultant lubricating oil composition was
subjected to the above-described performance evaluation. Its friction
coefficient
was found to be 0.09.
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Example 6
A lubricating oil composition was formulated in exactly the same
manner as in Example 5 except that the proportion of Calcium Sulfonate 3 was
increased from 2,400 ppm to 4,800 ppm in terms of calcium. The resultant
lubricating oil composition was subjected to a performance evaluation. Its
friction coefficient was found to be 0.08.
Comparative Example 1
Provided was Calcium Sulfonate 4 of the following characteristics:
- Average number of alky 1 carbons per 33
organic sulfonic group
- Alkyl chain linearity 17.2%
- Calcium content 12 wt%
- Total base number 300 mg-KOH/g
A lubricating oil composition was formulated by adding the
sulfonate to the same lubricating base stock as that employed in Example 1 in
a
proportion of 2,400 ppm in terms of calcium based on the whole weight of the
lubricating oil composition. As a result of a performance evaluation, its
friction
coefficient was found to be 0.13.
Comparative Example 2
Provided was Calcium Sulfonate 5 of the following characteristics:
- Average number of alky 1 carbons per 31
organic sulfonic group
- Alkyl chain linearity 12.6%
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- Calcium content 11.7 wt%
- Total base number 295 mg-KOH/g
A lubricating oil composition was formulated by adding the
sulfonate to the same lubricating base stock as that employed in Example 1 in
a
proportion of 2,400 ppm in terms of calcium based on the whole weight of the
lubricating oil composition. The friction coefficient of the resultant
lubricating
oil composition was found to be 0.14.
Comparative Example 3
A lubricating oil composition was formulated in exactly the same
manner as in Comparative Example 2 except that the proportion of Calcium
Sulfonate 5 was increased from 2,400 ppm to 4,800 ppm in terms of calcium. Its
friction coefficient was found to be 0.13. The calcium sulfonate, the alkyl
chain
linearity of which is low, was also found to be unable to bring about any sub-
stantial advantageous effects on friction characteristics despite the increase
in its
proportion.
Comparative Example 4
The solvent-refined mineral oil "100N" (kinematic viscosity at
100 C: 4.2 mm2/s), which was employed as a lubricating base stock in Example
1, was subjected by itself to a performance evaluation. Its friction
coefficient
was found to be 0.14.
The measurement results of the friction coefficients in the above
Examples and Comparative Examples and the calcium sulfonates employed
therein are summarized in Table I and Table 2, respectively. From these
results,
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it is appreciated that an alkyl chain linearity of 20% or higher in a metal
sulfonate provides a low friction coefficient even if the metal sulfonate is
added
in a small proportion (Examples 1 and 2) whereas a lower alkyl chain linearity
cannot provide a low friction coefficient even if the proportion of the metal
sulfonate is increased (Comparative Example 3). From a comparison between
Comparative Example 2 and Comparative Example 4, it is indicated that use of a
metal sulfonate having a linearity lower than 20% results in a lubrication oil
composition the friction coefficient of which is the same as that of the base
stock
alone. It has therefore been elucidated that the alkyl chain linearity is a
primary
element governing friction characteristics.
TABLE 1
Example Comparative Example
1 2 3 4 5 6 1 2 3 4
Base stock Refined Mineral Oil
Additive (Ca concentration, ppm)
Ca-sulfonate 1 140
Ca-sulfonate 1 560
Ca-sulfonate 2 1,200
Ca-sulfonate 2 2,400
Ca-sulfonate 3 2,400
Ca-sulfonate 3 4,800
Ca-sulfonate 4 2,400
Ca-sulfonate 5 2,400
Ca-sulfonate 5 4,800
Performance evaluation
Friction coefficient 0.09 0.08 0.10 0.08 0.09 0.08 0.13 0.14 0.13 0.14
TABLE 2
Average Alkyl Carbon Number Total Base Number
Kind Per Organic Sulfonic Group Alkyl Chain Linearity Ca Content (TBN)
Ca-sulfonate 1 31 47.2% 2.8% 25 mg-KOH/g
Ca-sulfonate 2 35 39.9% 12% 300 mg-KOH/g L~
Ca-sulfonate 3 26 31.0% 11.8% 295 mg-KOH/g
Ca-sulfonate 4 33 17.2% 12% 300 mg-KOH/g
Ca-sulfonate 5 31 12.6% 11.7% 295 mg-KOH/g
CA 02235701 1998-05-25
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From this it is readily seen that a metal sulfonate having an alkyl
chain linearity of 20% or higher is useful as a friction modifier for
lubricating
oils, and can improve the friction characteristics of lubricating oil
compositions.
