Note: Descriptions are shown in the official language in which they were submitted.
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GREASE COMPOSITION
The present invention relates to a grease
composition, in particular to a low friction grease
composition whereby wear generated in lubricated parts
such as bearings or gears is suppressed.
Greases having excellent frictional wear
characteristics are required in, for example, bearings or
gears of mechanical devices in the automobile, iron and
steel, railway and other industries.
In particular, this is important for lubrication
applications such as constant velocity joints of
automobiles, in which both rolling friction and sliding
friction are present and ball screws of driving gears in
an injection moulding machine or an electric pressing
machine.
Conventionally, greases having excellent lubricating
properties were prepared by adding molybdenum disulphide
to a lithium soap-thickened grease composition. Later in
the art, greases have been prepared by simultaneously
adding an organic molybdenum compound and zinc
dithiophosphate to a urea-thickened grease. Such urea-
thickened greases have been used with a view to reducing
frictional wear characteristics. For example, laid-open
Japanese Patent Application No. 62-207397 describes a
grease composition which comprises a sulphur-phosphorus
type extreme-pressure additive in which (a) molybdenum
dialkyl dithiocarbamate sulphide and (b) at least one
member selected from the group consisting of a sulfurized
oil, a sulfurized olefin, tricresyl phosphate, trialkyl
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dithiophosphate, and a zinc dialkyl dithiophosphate are
combined with each other as essential components.
Further, laid-open Japanese Patent Application No.
63-046299 discloses a grease composition in which
additives, namely, molybdenum dialkyl dithiocarbamate
sulphide and molybdenum dithiophosphate and, optionally,
zinc dithiophosphate are simultaneously blended in a
urea-thickened grease.
However, in some jurisdictions such as Japan, common
molybdenum-containing grease additives such as those
described above are defined as restricted substances.
These chemical substances are restricted in view of the
danger of harmful effects on human health or ecological
systems (e.g. Japanese PRTR Law: Pollutant Release
Transfer Register; Law for promotion of Chemical
Management) and submission of an MSDS (Material Safety
Data Sheet) on a product which contains a specified
amount or more of any of these substances may be required
by the laws of such jurisdictions.
Lead compounds and antimony compounds, which are
also defined as PRTR restricted substances, were used in
grease compositions for many years. However, such
compounds have been almost entirely replaced by sulphur
type extreme-pressure additives or the like which are
free of these problems.
However, the afore-mentioned molybdenum compounds,
in particular, molybdenum dialkyl dithiocarbamate
sulphide, have an excellent effect in reducing friction
and wear and it is hard to find a replacement for
molybdenum dialkyl dithiocarbamate. Furthermore, even if
such a replacement is added to the grease, a considerable
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amount thereof may be required in order to secure a
sufficiently low coefficient of friction.
Tungsten disulphide, is known as a solid lubricant
and is a substance which is not defined as a PRTR
restricted substance. Laid-open Japanese Patent
Application No. 2003-301188 discloses that by adding
tungsten disulphide to a lithium soap grease which
contains polyoxypropylene and glyceryl ether as a base
oil, a powder for density adjustment is prepared such
that, when the grease that is used is liberated in water,
this grease floats or sinks.
It is highly desirable to develop a grease
composition imposing little environmental load which has
excellent friction and wear characteristics and better
safety by avoiding the use of molybdenum compounds that
are the subject of the afore-mentioned PRTR restrictions
and/or being able to reduce the amount thereof that is
used in such a grease composition.
A grease composition has now been surprisingly
developed which has low friction properties and excellent
wear resistance by blending tungsten disulphide and zinc
dithiophosphate and/or molybdenum dithiocarbamate with a
urea-thickened grease.
Accordingly, the present invention provides a grease
composition, comprising base oil, one or more urea
thickeners, (A) in the range of from 0.1 to 5 weight% of
tungsten disulphide and (B) in the range of from 0.1 to
5 weight% of one or more zinc dithiophosphates and/or one
or more molybdenum dithiocarbamates, based on the total
weight of the grease composition.
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In a preferred embodiment of the present invention,
the grease composition may further comprise (C) one or
more molybdenum dithiophosphates.
According to the present invention, molybdenum
compounds designated as PRTR restricted substances are
not used, or the amount thereof which is used can be
relatively reduced, and a grease composition having
excellent performance in terms of friction and wear
characteristics and high stability can thereby be
obtained.
The base oil in the grease composition according to
the present invention may be conveniently selected from
mineral oils, vegetable oils and synthetic oils such as
ester oil, ether oil or hydrocarbon oil, or mixtures
thereof.
The one or more urea thickeners in the grease
composition of the present invention may be selected from
urea compounds such as monourea, diurea, triurea,
tetraurea or other polyureas.
Diurea compounds are easily obtained by the reaction
of diisocyanate and monourea; tetraurea compounds can be
obtained by reaction of diisocyanate, monourea and
diamines.
Examples of diisocyanates that may be used to make
said urea compounds include: diphenylmethane
diisocyanate, tolylene diisocyanate, bitolylene
diisocyanate and naphthylene diisocyanate.
Also, examples of monoamines that may be used to
make said urea compounds include octylamine,
dodecylamine, stearylamine, oleylamine, aniline,
paratoluidine and cyclohexylamine. Also, examples of
diamines that may be used to make said urea compounds
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include ethylene diamine, propane diamine, butane diamine
and phenylene diamine.
In a preferred embodiment, the grease composition of
the present invention may comprise a total amount in the
range of from 1 to 25 weight% of said one or more urea
thickeners, based on the total weight of said grease
composition.
The grease composition of the present invention may
further comprise one or more additional thickeners such
as metallic soaps, organic substances or inorganic
substances, for example, lithium soaps, lithium complex
soaps, sodium terephthalate, urea/urethane compounds and
clays.
The tungsten disulphide which is employed as the
afore-mentioned component (A) in the grease composition
of the present is preferably a powder having an average
particle size of less than 10 pm obtained by the Fisher
method (Fisher Sub-sieve Sizer). More preferably, the
tungsten disulphide which is employed is a powder having
an average particle size of about 0.6 pm obtained by the
afore-mentioned method.
The one or more zinc dithiophosphates which may be
employed as the afore-mentioned component(B) in the
grease composition of the present invention may be
conveniently selected from zinc dialkyl dithiophosphates
and/or zinc diaryl dithiophosphates. Preferably, said one
or more zinc dithiophosphates may be selected from
compounds of formula (I),
R'0 P~ S Zn S P OR'
R'0~ ~S~ ~S~ ~OR'
(I)
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wherein R' indicates primary or secondary alkyl groups or
aryl groups, which may be the same or different.
Preferably, primary or secondary alkyl groups are
employed as R'.
Specific examples of the above R' include a methyl
group, ethyl group, propyl group, isopropyl group, butyl
group, secondary butyl group, isobutyl group, pentyl
group, 4-methyl pentyl group, hexyl group, 2-ethyl hexyl
group, heptyl group, octyl group, nonyl group, decyl
group, isodecyl group, dodecyl group, tetradecyl group,
hexadecyl group, octadecyl group, eicosyl group, docosyl
group, tetracosyl group, cyclopentyl group, cyclohexyl
group, methyl cyclohexyl group, ethyl cyclohexyl group,
dimethyl cyclohexyl group, cycloheptyl group, phenyl
group, tolyl group, xylyl group, ethyl phenyl group,
propyl phenyl group, butyl phenyl group, pentyl phenyl
group, hexyl phenyl group, heptyl phenyl group, octyl
phenyl group, nonyl phenyl group, decyl phenyl group,
dodecyl phenyl group, tetradecyl phenyl group, hexadecyl
phenyl group, octadecyl phenyl group, benzyl group and
phenethyl group.
Specific examples of the above primary alkyl zinc
dithiophosphate include zinc diisopropyl dithiophosphate
and zinc diisobutyl dithiophosphate and zinc diisodecyl
dithiophosphate.
Also, specific examples of the above secondary
dialkyl zinc dithiophosphate include zinc mono or di-sec-
butyl dithiophosphate, zinc mono or di-sec-pentyl
dithiophosphate and zinc mono or di-4-methyl-2-pentyl
dithiophosphate.
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Specific examples of the above zinc aryl
dithiophosphate include zinc di-para-dodecyl phenol
dithiophosphate, zinc di-heptyl phenol dithiophosphate
and zinc di-para-nonyl phenol dithiophosphate.
Preferred examples of the one or more molybdenum
dialkyl dithiocarbamates, which may be employed as
component (B) in the grease composition of the present
invention may be selected from compounds of formula (II),
( R1R2N-CS-S ) ZMo2OmSn ( I I )
wherein R' and R2 respectively, may be independently
selected from alkyl groups having a carbon number in the
range of from 1 to 24, preferably in the range of from
3 to 18, m is an integer in the range of from 0 to 3, n
is an integer in the range of from 1 to 4 and m+n=4.
Specific examples of the afore-mentioned one or more
molybdenum dialkyl dithiocarbamates include molybdenum
diethyl dithiocarbamate sulphide, molybdenum dipropyl
dithiocarbamate sulphide, molybdenum dibutyl
dithiocarbamate sulphide, molybdenum dipentyl
dithiocarbamate sulphide, molybdenum dihexyl
dithiocarbamate sulphide, molybdenum dioctyl
dithiocarbamate sulphide, molybdenum didecyl
dithiocarbamate sulphide, molybdenum didodecyl
dithiocarbamate sulphide, molybdenum di(butylphenyl)
dithiocarbamate sulphide, molybdenum di(nonylphenyl)
dithiocarbamate disulphide, oxy-molybdenum diethyl
dithiocarbamate sulphide, oxy-molybdenum dipropyl
dithiocarbamate sulphide, oxy-molybdenum dibutyl
dithiocarbamate sulphide, oxy-molybdenum dipentyl
dithiocarbamate sulphide, oxy-molybdenum dihexyl
dithiocarbamate sulphide, oxy-molybdenum dioctyl
dithiocarbamate sulphide, oxy-molybdenum didecyl
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dithiocarbamate sulphide, oxy-molybdenum didodecyl
dithiocarbamate sulphide, oxy-molybdenum (butylphenyl)
dithiocarbamate sulphide, oxy-molybdenum di(nonylphenyl)
dithiocarbamate sulphide, and mixtures thereof.
Specific examples of the afore-mentioned one or more
molybdenum dithiophosphates that may be employed as
optional component (C) in the grease composition of the
present invention include molybdenum diethyl
dithiophosphate sulphide, molybdenum dipropyl
dithiophosphate sulphide, molybdenum dibutyl
dithiophosphate sulphide, molybdenum dipentyl
dithiophosphate sulphide, molybdenum dihexyl
dithiophosphate sulphide, molybdenum dioctyl
dithiophosphate sulphide, molybdenum didecyl
dithiophosphate sulphide, molybdenum didodecyl
dithiophosphate sulphide, molybdenum di(butylphenyl)
dithiophosphate sulphide, molybdenum di(nonylphenyl)
dithiophosphate disulphide, oxy-molybdenum diethyl
dithiophosphate sulphide, oxy-molybdenum dipropyl
dithiophosphate sulphide, oxy-molybdenum dibutyl
dithiophosphate sulphide, oxy-molybdenum dipentyl
dithiophosphate sulphide, oxy-molybdenum dihexyl
dithiophosphate sulphide, oxy-molybdenum dioctyl
dithiophosphate sulphide, oxy-molybdenum didecyl
dithiophosphate sulphide, oxy-molybdenum didodecyl
dithiophosphate sulphide, oxy-molybdenum (butylphenyl)
dithiophosphate sulphide and oxy-molybdenum
di(nonylphenyl) dithiophosphate sulphide.
The afore-mentioned components (A) tungsten
disulphide; and (B) one or more zinc dithiophosphates
and/or one or more molybdenum dithiocarbamates are
respectively blended in the grease composition of the
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present invention in an amount in the range of from 0.1
to 5 weight%. Preferably, the afore-mentioned components
(A) and (B) are each blended in the grease composition of
the present invention in an amount in the range of from
0.2 to 3 weight%, based on the total weight of the grease
composition. If the afore-mentioned components (A) and
(B) are each blended in an amount of less than 0.1
weight%, based on the total weight of the grease
composition, a low coefficient of friction cannot be
obtained and frictional wear is insufficiently improved.
Furthermore, if the afore-mentioned components (A) and
(B) are blended in an amount exceeding 5 weight%, based
on the total weight of the grease composition, then no
further increase in beneficial effect is seen.
The one or more molybdenum dithiophosphates (C) may
be present in the grease composition of the present
invention in an amount in the range of from 0.1 to
5 weight%, more preferably in the range of from 0.2 to
3 weight%.
The grease composition of the present invention may
further comprise various types of known additives such as
antioxidants, for example, aminic and/or phenolic
antioxidants, extreme pressure additives, for example,
olefin sulphides and/or oil sulphides, viscosity
increasing agents, for example, polybutenes and/or
polymethacrylates, solid lubricants, for example,
molybdenum disulphide and/or boron nitride, metallic
salts, for example, sulfonates, salicylates and/or
phenates capable of being used as antirust agents or
structure stabilisers and phosphites and/or phosphates
capable of being used as extreme pressure/wear reducing
agents.
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The present invention further provides a method of
reducing friction and/or wear in the bearings, gears
and/or joints of mechanical devices, wherein said method
comprises lubricating said bearings, gears and/or joints
with a grease composition as hereinbefore described.
In addition, the present invention also provides a
bearing, gear and joint, characterised in that the grease
composition as hereinbefore described is used therein as
the lubricant.
Furthermore, the present invention also provides the
use of a grease composition as hereinbefore described to
lubricate a bearing, a gear and/or a joint.
The present invention is described below with
reference to the following Examples, which are not
intended to limit the scope of the invention in any way.
EXAMPLES
The grease compositions of Examples 1 to 7 and
Comparative Examples 1 to 8 were obtained by processing
in a three-roll mill the base greases and additives shown
below with the blending compositions shown in Table 1 to
Table 4.
[1] Base grease
[1-1] Diurea grease
Diphenyl methane-4,4'-diisocyanate (295.2 g)
and octylamine (304.8 g) were reacted in
refined mineral oil (5400 g) having a
kinematic viscosity of about 15 mm2/s at
100 C, and the diurea compound produced was
uniformly dispersed to obtain a base grease.
The content of urea compound in the base
grease was 10 weight%. The consistency of
this diurea grease (25 C, 60 W) according
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to JS-K2220 was 283 and its dropping point
was 263 C.
[1-2] Tetraurea grease
Diphenyl methane-4,4'-diisocyanate
(382.7 g), stearylamine (411.4 g) and
ethylene diamine (46.0 g) were reacted in
refined mineral oil (5160 g) having a
kinematic viscosity of about 15 mm2/s at
100 C, and the urea compound produced was
uniformly dispersed to obtain a base grease.
The content of the urea compound in the base
grease was 14 weight%. The consistency of
this tetraurea grease (25 C, 60 W)
according to JS-K2220 was 285 and its
dropping point was 202 C.
[2] Additives
[2-1] Tungsten disulphide (indicated in the Tables
as WS2) : a tungsten disulphide powder having
an average particle size of 0.6 pm,
available under the trade designation of
"Tanmik B" from Nippon Lubricants Ltd. was
employed.
[2-2] Zinc dithiophosphate (indicated in the
Tables as Zn-DTP): additive available under
the trade designation "Lubrizol 1395" from
Lubrizol Inc. was employed.
[2-3] Molybdenum dithiocarbamate (indicated in the
Tables as Mo-DTC): additive available under
the trade designation "Molyvan A" from
Vanderbilt Inc. was employed.
[2-4] Molybdenum dithiophosphate (indicated in the
Tables as Mo-DTP): additive available under
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the trade designation "Sakuralube 300" from
Asahi Electrochemical Industries Ltd. was
employed.
[2-5] Molybdenum disulphide (indicated in the
Tables as MoS2): Molybdenum disulphide
having an average particle size of 0.7 pm as
manufactured by CLIMAX MOLYBDENUM UK Ltd was
employed.
[2-6] Graphite (indicated in the Tables as
graphite): graphite as manufactured under
the trade name "FAHN" by Fuji Graphite Ltd
was employed.
Falex Wear Resistance Test
Evaluation was conducted by carrying out the Falex
Wear Resistance Test for checking performance of the
grease compositions obtained according to the Examples
and Comparative Examples, and measuring the wear
coefficient and wear resistance (surface roughness of the
test sample) in respect of these grease compositions.
The Falex wear resistance test is based on IP 241
(IP: Institute of Petroleum, UK); tests are carried out
in accordance with the following conditions, to obtain a
wear coefficient after completion of the test. Also, the
Rmax (pm) (maximum surface roughness) of a reference test
sample was measured.
Test conditions
Rotational speed: 290 10 rpm
Temperature: room temperature (about 25 C)
Load: 890N (200 lbf)
Time: 15 min
Amount of grease applied: about 1 gram applied to
the test sample
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Test results
The results of the Falex wear resistance test are
listed in Table 1 to Table 4.
Table 1
Example 1 2 3 4
Composition Base Diurea 96.0 98.0 96.0 95.0
(weight%) grease grease
Tetraurea - - - -
grease
Additives WS2 3.0 1.0 2.0 2.0
Zn-DTP 1.0 - - 1.0
Mo-DTC - 1.0 1.0 1.0
Mo-DTP - - 1.0 1.0
Total 100.0 100.0 100.0 100.0
Falex test Coefficient 0.081 0.082 0.056 0.057
of
friction, p
Surface 9.3 10.1 6.6 5.9
roughness,
Rmax ( pm )
Table 2
Example 5 6 7
Composition Base Diurea - - -
(weight%) grease grease
Tetraurea 96.0 96.0 96.0
grease
Additives WS2 2.0 2.0 3.0
Zn-DTP 1.0 1.0 -
Mo-DTC 1.0 - 1.0
Mo-DTP - 1.0 -
Total 100.0 100.0 100.0
Falex test Coefficient 0.060 0.070 0.083
of
friction, p
Surface 7.8 5.9 8.1
roughness,
Rmax (pm)
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Table 3
Comparative Example 1 2 3 4
Composition Base Diurea 97.0 97.0 97.0 97.0
(weight%) grease grease
Tetraurea - - - -
grease
Additives WS2 3.0 - - -
Zn-DTP - 3.0 - -
Mo-DTC - - 3.0 -
Mo-DTP - - - 3.0
Mo-Sz - - - -
Graphite - - - -
Total 100.0 100.0 100.0 100.0
Falex test Coefficient 0.116 0.090 0.079 0.072
of
friction, p
Surface 36.2 21.9 35.0 17.2
roughness,
Rmax (pm)
Table 4
Comparative Example 5 6 7 8
Composition Base Diurea 98.0 - 96.0 -
(weight%) grease grease
Tetraurea - 98.0 - 96.0
grease
Additives WS2 - - - -
Zn-DTP 1.0 1.0 - 1.0
Mo-DTC 1.0 1.0 1.0 -
Mo-DTP - - 1.0 -
Mo-S2 - - 2.0 -
Graphite - - - 3.0
Total 100.0 100.0 100.0 100.0
Falex test Coefficient 0.094 0.103 0.090 0.123
of
friction, p
Surface 12.1 11.3 14.0 31.2
roughness,
Rmax (pm)
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As is clear from Table 1 and Table 2, Examples 1 to
7 show excellent wear resistance, displaying low friction
properties, with a frictional coefficient of approx.
0.056 to 0.083 in the Falex test, the maximum surface
roughness of the test sample being approx. 5.9 to
10.1 pm.
In contrast, as is clear from Table 3 and Table 4,
the products of Comparative Examples 1 to 8 show in each
case results that are unsatisfactory as regards both the
coefficient of friction and wear resistance properties.
Specifically, the products of Comparative Examples
1, 2, 5, 7 and 8 have a high coefficient of friction and
show large values of the maximum surface roughness of the
test sample. The products of Comparative Examples 3 and 4
show comparatively low values of the coefficient of
friction, but display large values of the maximum surface
roughness of the test sample; it is inferred that in
these cases the low coefficient of friction is displayed
due to lowering of the contact area pressure due to
increased wear. In the case of the product of Comparative
Example 6, the maximum surface roughness of the test
sample is comparatively close to that of the practical
examples, but this product shows a high value of the
coefficient of friction.
Also, as can be seen by comparing the Examples and
Comparative Examples 7, 8, in the case of molybdenum
disulphide or graphite, which are substances of the same
layer lattice structure as the tungsten disulphide used
in the present invention, results satisfying both the
requirement to provide an excellent low coefficient of
friction and good wear resistance as in the case of the
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practical examples are not obtained even when these are
used together with for example Mo-DTC, Mo-DTP or Zn-DTP.
Thus, with the grease composition according to the
present invention, an excellent lubricating effect can be
obtained without using molybdenum compounds such as
molybdenum dialkyl dithiocarbamate sulphide, or a
reduction in the amount of use of such molybdenum
compounds can be achieved.
