Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~
~~'~~22~
Lubricating Oil Composition
Field of the Invention
The present invention relates to a lubricating oil composition,
and more specifically, one excellent in wear-resistant properties and
frictional characteristics. The lubricating oil composition of the
present invention can be used as a lubricating oil for automotive
internal combustion engines (engine oil), and also ,in a wide range of
fields as gear oils, automatic transmission fluids (ATF), power-
steering oils (PS oil), spindle oils, hydraulic fluids, and
industrial lubricating oils.
Background of the Invention
Since zinc dithiophosphates (below called "Zn-DTP") such as zinc
dialkyldithiophosphates show an excellent wear-inhibiting
performance, besides acting as an antioxidant and a corrosion
inhibitor, they have been generally used as an additive for engine
oils.
However, since phosphorus (P) contained in Zn-DTP poisons any
automotive exhaust emission purification catalyst and any automotive
oxygen sensor, an engine oil to which Zn-DTP is added has had a
problem in that the performance of any exhaust-gas emission control
system decreases significantly. Conventionally to resolve this
problem a method of decreasing the added amount of Zn-DTP to lower
the amount of phosphorus in the engine oil has been adopted.
However, when the amount of Zn-DTP decreases, problems are caused
such that the wear-resistant properties of the lubricating oil
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~2~.'~~4222
decrease and in that the engine durability decreases due to the wear
of the valve-gear system. Thus while decreasing the added amount of
Zn-DTP, other additives, such as an ash-free detergent dispersant and
a metal detergent have been used with Zn-DTP to maintain performances
necessary for an engine oil.
However, when both Zn-DTP and an ash-free detergent dispersant
such as a polyalkenyl succinimide are used, a problem arises such
that both compounds are the first to react in a base oil to result in
the effects of Zn-DTP'being masked and its activity being impaired.
Accordingly, to attain sufficient wear-resistant properties, Zn-DTP
must be used in a relatively high amount, and thus it has been
difficult to decrease the phosphorus content.
Summary of the Invention
1. Disclosure of the Invention
The object of the present invention resides in providing a
lubricating oil composition excellent in Wear-resistant properties
and frictional characteristics.
2. Means to Resolve the Problems
As a result of the extensive study by the inventors of the
present invention to resolve the above problems, they found that
besides the wear-resistant properties of a lubricating oil being
improved, the coefficient of friction of the oil significantly
decreased by (1) adding to a lubricating base oil a complex of a
metallic salt of dithiophosphoric acid (below called "M-DTC") with a
primary alkylamine having a short chain and (2) containing in a
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~ ~ ~ ~1°~422~
lubricating base oil at least one kind of compound selected from the
group consisting of an oxymolybdenum sulfide dithiocarbamate (below
called "Mo-DTC"), an oxymolybdenum sulfide organophosphorodithioate
(below called "Mo-DTP"), a fatty ester, and an organic amide
compound.
Based on this finding they accomplished the present invention.
Thus according to the present invention a lubricating oil
composition is provided by containing in a lubricating base oil (A) a
complex obtained by reacting a metallic salt of dithiophosphoric acid
having lipophilic groups, the average number of the carbon atoms of
which is 4 or more, with a primary alkylamine having 8 or less carbon
atoms, and (B) at least one kind of compound selected from the group
consisting of an oxymolybdenum sulfide dithiocarbamate, an
oxymolybdenum sulfide organophosphorodithioate, a fatty ester, and an
organic amide.
Detailed Description of Embodiment
The present invention will be described in detail below.
(Lubricating Base Oil)
Lubricating base oils used in the present invention are not
specifically limited, and various kinds of conventionally-known
mineral oils and synthetic lubricating oils can be used. Exemplified
as the mineral oils are raffinates obtained by solvent-refining a
lubricating oil material with an aromatic extraction solvent such as
phenol or furfural, a hydrogenation-treated oil obtained by
hydrogenation treatment with a catalyst for hydrogenation treatment
- 3 -
~ ~ ~2~'~4222
such as cobalt or molybdenum supported on silica-alumina as a
carrier, and a mineral oil such as a lubricating oil distillate
obtained by the isomerization of wax, as, for example, 60 Neutral
Oil, 100 Neutral Oil, 150 Neutral Oil, 300 Neutral Oil, 500 Neutral
Oil, Bright Stock, etc. As the synthetic lubricating oils, poly- a -
olefins, polybutene, alkylbenzenes, polyol esters, and dibasic acid
esters, are exemplified. Such a base oil can be used alone or as a
mixture of two or more kinds. When such a lubricating base oil is
used in an engine oil,, its kinetic viscosity i~s ordinarily 3 to 20
cSt at 100 °C .
(Metallic Salts of Dithiophosphoric Acid)
The metallic salts of dithiophosphoric acid (M-DTP) used in the
present invention are compounds represented by following general
formula ( I )
RIO\ P _ S ORg
RZO/ M _ P ~O~ ( I
wherein M is a metal atom selected from zinc, copper, nickel,
iron, cadmium, silver, lead, antimony, tin, and bismuth, and each of
R~ to R4 is independently selected from lipophilic groups having 1 to
30 carbon atoms provided that the average number of the carbon atoms
of the four lipophilic groups is 4 or more.
Each of these M-DTPs may be used alone, or two or more kinds of
the M-DTPs may be used together.
As the lipophilic group, saturated and unsaturated alkyl groups,
- 4 -
alkylaryl groups, and arylalkyl groups, are exemplified. The four
lipophilic groups can be varied from those in which four of the
lipophilic groups are all the same to those in which each of them is
different. When the average number of the carbon atoms of the four
lipophilic groups of this M-DTP is less than 4, even if the M-DTP is
used with a primary alkylamine, it is difficult to obtain a uniform
lubricating oil composition, since the solubility of M-DTP in a
lubricating oil is poor. Since.an organic metal-based wear-resistant
agent generally fulfills its function by being adsorbed on the
surface of metals, it is necessary to have an appropriate solubility
in the oil.
In contrast, when an M-DTP is used in which the average number
of the carbon atoms of the four lipophilic groups exceeds 13,
although the solubility of the M-DTP in a lubricating oil is good,
the wear-resistant properties decrease. From the aspect of the
functionality of wear-resistant properties etc., the upper limit of
the average number is preferably 13.
From the aspect of the functionalities such as the ease of their
synthesis and wear-resistant properties, usually M-DTPs in which four
lipophilic groups are alkyl groups having 4 or more carbon atoms are
especially preferred.
As the metal atoms (M), zinc, copper, nickel, iron, cadmium,
silver, lead, antimony, tin, and bismuth, are exemplified. Among
others, from the aspect of functionalities such as the ready
availability and wear-resistant properties, zinc (Zn) is especially
preferred.
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~1~4222
(Primary Alkylamine)
As the primary alkylamines used in the present invention,
relatively short-chain alkylamines such as n-propylamine, n-
butylamine, n-pentylamine, n-hexylamine, n-heptylamine, and n-
octylamine, are exemplified.
When preparing a complex with an alkylamine, the amount used of
M-DTP is adjusted such that the compounding ratio in a lubricating
oil composition based on the total amount of the composition becomes
usually 0.05 to 7 ~ by weight, preferably 0.2 to 5~ by weight, more
preferably 0.3 to 2~ by weight. If the compounding ratio of the M-
DTP is too low, the effect in imparting wear-resistant properties is
insufficient, and if the ratio is too high the wear-resistant
properties do not increase above a certain degree and corrosion of
metals can be caused.
The compounding ratio of the primary alkylamine is 0.001 to 0.5~
by weight, preferably 0.01 to 0.3~ by weight. If the compounding
ratio of the primary alkylamine compound is too low, the effect
obtained by the compound is insufficient, and if the ratio is too
high the wear-resistant properties often decrease rather than
increase.
It is preferable to first form a complex of M-DTP with a primary
alkylamine, and then to add the cpmplex to a lubricating oil, since
the preferential reaction of M-DTP with an ash-free detergent
dispersant is depressed, and thus a lubricating oil composition
having excellent wear-resistant properties can be obtained. To first
form a complex of M-DTP with a primary alkylamine, a preferable
process is to add them to a lubricating base oil such that the
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. ~~-'4222
concentration of the complex is high, and then to heat the obtained
composition. For example, M-DTP is added and mixed with a primary
alkylamine in a given ratio, and, if desired, the obtained mixture is
diluted with the base oil to an amount equaling several times the
amount of the mixture, and the obtained mixture is stirred,
preferably at 40 to 120 °C , more preferably at 60 to 100 °C ,
preferably for 1 to 60 minutes, more preferably for 5 to 30 minutes,
to form a complex. The higher the heating temperature is, the
shorter is the time required to form a complex which is uniformly
solubilized in a base oil. The resmltin~ cn~"tinn of +ho ..~~",iw ,~
used as a lubricating oil composition as such, or it is further
diluted with a lubricating oil and used as a uniform lubricating oil
composition containing M-DTP and a primary alkylamine in a desired
ratio.
(Additives Used Together)
In the present invention, to a lubricating base oil, together
with a complex of a metallic salt of dithiophosphoric acid and a
primary alkylamine, is added at least one kind of compound selected
from the group consisting of oxymolybdenum sulfide dithiocarbamates,
oxymolybdenum sulfide organophosphorodithioates, fatty esters, and
organic amide compounds.
Mo-DTC and Mo-DTP
The oxymolybdenum sulfide dithiocarbamates (Mo-DTC) and
oxymolybdenm sulfide organophosphorodithioates (Mo-DTP) are organic
molybdenum compounds represented by following general formulas (II)
and (III ) respectively:
RS S Xi Y ~z S R7
R6>N-C-S-MoCYa>Ivlo-S-C-N<R8 (h )
RS- O S xt y.i xa S Q -R7
R6 ~>P S lvlo <~a>IVIo S P'~ _Re , . (~ )
in which formulas (II) and (111) Rg to R8, which may be the same
or different, are each a hydrogen atom, an alkyl group having 1 to 20
carbon atoms, a cycloalkyl group having 6 to 26 carbon atoms, an
aryl, alkylaryl, or arylalkyl group having 6 to 26 carbon atoms, or a
hydrocarbon group containing an ester bond, ether bond, alcohol
group, or carboxyl group. X1 and X2, which may be the same or
different, are each an oxygen atom or a sulfur atom. Y1 and Ya ,
which may be the same or different, are each an oxygen atom or a
sulfur atom.
In general formulas ( II ) and ( III ) Rg to R$ are each preferably a
saturated or unsaturated alkyl group having 6 to 18 carbon atoms, a
cycloalkyl group having 12 to 24 carbon atoms, or an alkylaryl group
having 12 to 24 carbon atoms. As the preferred examples of these
substituents are alkyl groups or unsaturated alkyl groups (alkenyl
groups) having 6 to 18 carbon atoms such as n-hexyl, 2-ethylhexyl, n-
octyl, nonyl, decyl, lauryl, tridecyl, oleyl, and linoleyl, and
alkylaryl groups substituted by an alkyl group having 3 to 18 carbon
- g
atoms, such as nonylphenyl.
Not only when Mo-DTC or Mo-DTP is used alone, but also when they
are used together, is the compounding ratio of Mo-DTC and/or Mo-DTP
based on the total composition of 0.01 to 10~ by weight, preferably
0.05 to 5~ by weight, more preferably 0.1 to 13~ by weight. If the
compounding ratio is less than 0.01 by weight, the wear-decreasing
effect of the composition is low, and if it is too high, a problem
such as the occurence of copper-corrosive properties tends to appear.
To aim to lower the'phosphorus content in a lubricating oil, as the
organic molybdenum compound, it is preferred to use Mo-DTC alone, or
when Mo-DTP is used it is used such that its compounding ratio is as
low as 0.2~ by weight or less. By using a combination of specified
additives, even if the ratio used of the organic molybdenum compound
is relatively low, an excellent effect in regards to the coefficient
of friction can be obtained.
Fatty Ester
As the fatty esters used in the present invention, monoesters
and diesters of a fatty acid and glycerine yr sorbitan are
exemplified.
The fatty glyceride is a monoester represented by following
general formula (IV) or a diester represented by following general
formula ( V )
CHZOCOR 9
t
CHOH
t ( IV )
CHZOH
- 9 -
. 21'42
22
CHa0C0 R i o
I
CHaOCOR ~ ~
I (V )
CHaOH
in which formulas (IV ) and (V ) R9 to R11 are each a saturated
or unsaturated alkyl group having 8 to 22 carbon atoms.
The fatty ester.may be used alone or as a mixture of two or more
kinds of the esters. Based on the total composition its compounding
ratio is 0.01 to 109 by weight, preferably 0.05 to 5~ by weight. If
the compounding ratio is too low any improved effect in the
frictional characteristics is too low, and if it is too high the wear-
resistant properties worsen.
Organic amide compound
An organic amide compound used in the present invention is a
compound represented by following general formula (VI):
O
(I Ria
R~, C-N< (~ )
R~3
in Which formula (VI) R12 and R13, which may be the same or
different, are each a hydrogen atom, an alkyl group having 1 to 20
carbon atoms, a cycloalkyl group having 6 to 26 carbon atoms, or an
aryl, alkylaryl, or arylalkyl group having 6 to 26 carbon atoms, an
alkylene oxide group having 2 to 30 carbon atoms, and R14 is a
- 10 -
hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an
cycloalkyl group having 6 to 26 carbon atoms, an aryl, alkylaryl, or
arylalkyl group having 6 to 26 carbon atoms, or a hydrocarbon group
having an ester bond, an ether bond, or a carboxyl group.
The alkylene oxide group used here is a group represented by
following general formula (VB ) or (V~ )
-(CHZCHO~H . .
I (
R'
-( i HCHZO~H
R'
in which formulas (Vd) and (V~) R' is a hydrogen atom or a
methyl group, and n is an integer of 1 to 10.
In general formula (VI) R12 and R13 are preferably each a
hydrogen atom, an alkyl group having 2 to 8 carbon atoms, a
cycloalkyl group having 8 to 14 carbon atoms, an alkylaryl group
having 8 to 14 carbon atoms, or an alkylene oxide in which n is 1 to
5, and R14 is preferably a saturated or unsaturated alkyl group
having 6 to 18 carbon atoms, a cycloalkyl group having 12 to 24
carbon atoms, or an alkylaryl group having 12 to 24 carbon atoms.
As such organic amides, oleic amide and lauric amide are
exemplified.
The compounding ratio of the organic amide compound is 0.01 to
- 11 -
10~ by weight, preferably 0.01 to 5~ by weight, more preferably 0.05
to 29~ by weight. By adding the organic amide compound, while copper-
corrosive properties are lowered, the coefficient of friction can be
decreased from the beginning. If the compounding ratio is too small,
the effect in decreasing friction is low, and if too high the effect
does not increase above a certain degree.
(Lubricating Oil Composition)
The lubricating'oil composition of the present invention can be
prepared by adding said various ingredients to a lubricating base
oil. M-DTP and a primary alkyl amine are first reacted to form a
complex, and then the complex is added to the lubricating oil.
To a lubricating~oil composition of the present invention, if
required, a wear-resistant agent, a friction-decreasing agent, an ash-
free detergent dispersant, an anti-oxidant, a metal detergent, a
viscosity index-improving agent, a pour-point lowering agent, a rust-
preventive agent, a defoaming agent, a corrosion-preventive agent,
etc., may be suitably added.
As wear-resistant agents, zinc salt of dithiocarbamic acid,
phosphoric esters, and amine salts of phosphoric esters, are
exemplified.
As ash-free detergent dispersants, polyalkenyl succinic imides,
polyalkenyl succinic amides, alkylbenzyl amines, boron derivatives of
polyalkenyl succinic imides, and boron derivatives of alkylbenzyl
amines, are exemplified.
As the anti-oxidant agents, amine-based anti-oxidant agents such
as alkylated diphenylamines, phenyl- a -naphtylamine, and alkylated
- 12 -
a -naphtylamine, and phenol-based anti-oxidant agents such as 2,6-di-
t-butylphenol and 4,4'-methylene-bis-(2,6-di-t-butylphenol), are
exemplified. The agent is usually used in a ratio of 0.05 to 2~ by
weight.
Exemplified as the metal detergents are Ca-sulfonate, Mg-
sulfonate, Ba-sulfonate, Ca-phenate, Ba-phenate, Mg-phenate, Ca-
salicylate, Mg-salicylate, and Ba-salicylate. They are usually used
in a ratio of 0.1-59b by weight.
Exemplified as the viscosity-index improving agents are
polymethylmethacrylate-type, polyisobutyrene-type, ethylene-propylene-
copolymer-type, and hydrogenated styrene-butadiene copolymer-type
agents. They are usually used in a ratio of 1-35~ by weight.
Exemplified as the rust-preventive agents are alkenyl succinic
acids and partially esterified alkenyl succinic acids.
As the defoaming agents, dimethyl polysiloxane and polyacrylate
are exemplified.
By adopting the above constitution the lubricating oil
compositions of the present invention can significantly decrease the
coefficient of friction, besides showing superior wear-resistant
properties. Also, by using zinc dithiocarbamate (Zn-DTC) with M-DTP,
the ratio of M-DTP can be significantly decreased, to obtain a
lubricating oil composition with a lower content of phosphorus than
those conventionally used.
Because of the use of a combined system of M-DTP and a primary
alkylamine, the lubricating oil compositions of the present invention
have properties, such as oxidation stability and anti-coking
properties, besides wear-resistant and extreme-pressure properties.
- 13 -
. c
Although the reason why the lubricating oil compositions of the
present invention show excellent wear-resistant properties is
unclear, it is considered that due to the formation of a complex of M-
DTP and a primary alkylamine, the reaction of M-DTP with an ash-free
detergent dispersant is depressed, thus making the adsorption of M-
DTP on the surface of metals easy.
The lubricating oil compositions are used for automotive engine
oils, gear oils, automatic transmission fluids, power-steering oils,
spindle oils, hydraulic fluids, and industrial lubricating oils.
The present invention is especially illustrated by the following
Examples and Comparative Examples, but it is not limited to those
Examples.
Examples 1 to 8, and Comparative Examples 1 to 4
Lubricating oil compositions were prepared by adding the various
ingredients listed in Table 1. In the Table the ratios of the
various ingredients are represented by ~ by weight. The remaining
portion is the ratio of a lubricating base oil. Zn-DTP, in which the
number of carbon atoms of a lipophilic group is 6, is first reacted
with n-hexylamine to form a complex, and then the complex is used.
Various ingredients are shown below.
(1) Lubricating base oil
150 Neutral mineral oil (The kinetic viscosity at 100 °C is 5.1
cSt.)
(2) Zn-DTP
A commercially available Zn-DTP: a Zn-DTP having four s-hexyl
groups
- 14 -
i d
CA 02174222 2004-04-15
After the Zn-DTP is reacted with n-hexylamine in a mineral oil
to form a complex, the complex was further diluted with a mineral
oii.
(3) Mo-DTC
(2EH)\ S ~ S 10t S {2EH)
(2EH)/N C-S-Mo<S>Mo-S-C-N<(~EH)
wherein 2EH is.a 2-ethylhexyl group.
(4) Mo-DTP
S O O S
(2EH)-0'P-S-Mo ~O~Mo--S-P<O (2EH)
(2EH)- 0 0 O - {ZEH)
wherein 2EH is a 2-ethylhexyl group.
(5) Fatty glyceride
CHZOCOR CHzOCOR
50i by weight of I + 50% by weight of I
CHOH CHOCOR
I t
CHZOH CHZOH
wherein R is an oleyl group.
(6) Organic amide compound
Oleic amide
Treatment for Forming a Complex
zn-DTP in which the number of carbon atoms of a lipophilic group
is 6, n-hexylamine, and a mineral oil, were mixed in a weight ratio
- 15 -
21'~~222
of 1:0.28:1 in a reactor equipped with a stirrer, and the obtained
mixture was heated at 60 °C for 5 minutes With stirring. The
resulting solution containing the formed complex was further diluted
with a mineral oil to be prepared such that the content of Zn-DTP was
0.5~ by weight or 1.0~ by weight.
For the obtained lubricating oil compositions, the wear-
resistant properties and coefficients of friction were evaluated.
The results are listed in Table 1. The method of measuring was as
shown below.
Method of Measuring Frictional Characteristics and Wear-resistant
Properties
By using the Shell four-ball-type test, the coefficients of
friction and ball diameters after wear (mm) were measured. The
conditions were as follows:
Load : 40 kg
Oil temperature: 90 °C
Number of revolutions: 1,800 rpm
Test time: 30 minutes
- 16 -
0 1 I I
1 I
U
0 0
p
I I I
I I ~
0 0
.r., ~ p
o ~ I I C O
I I c
r~
0 0
0
~--a I I
I I O o
U
O o 0 0
c~
00 LCJ -~-i ~ o
, . O .I ,
-~ crJ
o O o 0 o O o
LCJ ,-~ .-~ 1 o C'rJ o
O o 0 0 0 o p
cn
I '~--i O I o
O o O o 0 0
r-i
tt~~ ~ ~ i o
N i c~
r., U o 0 0 o O o
H
E ~r tra ,--.i ,-~ I ~cJ I o
0 0 0 ,-i O o
W
I o I
o
o O ,-i o 0 0
L_
O
Gw o c~ ,-t 1 p I p
o O O o 0
c~
'"'i~ ,--i .-i I o I
O
0 0 0 0 0 0
cps
,..a n
E
U
~ i-w ~O :r
' r-I O S-~
ir
,~ ~ i~ ,--~ N c~
V
--~ ,-~ U U +-~ ~-~
v1 +-~ U
E U t7 ~ U U 9~
,--y..cC ~ O
E3 . c~ i.-i
U H ~ -~
i-i
C7 ~C U fs. ,-a
p U
.-i L -E-~
O DC H H p, U 4-a ~
l 4
-~ H
8 N +-~ ,-i 4-i .--~
O d
..~ +-~ U d7 .-,
~ ~ ~ _
U G~ O U
~ x'74222
- 17 -
As is clear from the results as listed in Table 1, any
lubricating oil composition of the present invention shows, besides a
significantly low coefficient of friction and good low-friction
properties, that the ball diameter after wear is small and that the
wear-resistant properties are good. In contrast, when only the
combination system of Zn-DTP and n-hexylamine is used (comparative
Examples 1 and 2), the effect in decreasing the coefficient of
friction was insufficient. When n-hexylamine was not used
(Comparative Examples 3 and 4) the coefficient of friction was
further increased, and the frictional characteristics were
insufficient.
According to the present invention, lubricating oil compositions
excellent in wear-resistant properties and frictional characteristics
are provided. Although any lubricating oil composition of the
present invention has a Iow phosphorus content, it shows excellent
wear-resistant properties and a low coefficient of friction, and thus
it is especially suitable for internal combustion engines.
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