U.S. patent application number 13/203281 was filed with the patent office on 2011-12-15 for grease composition.
This patent application is currently assigned to Total Rafinage Marketing. Invention is credited to Franck Bardin, Alain Bouffet.
Application Number | 20110306527 13/203281 |
Document ID | / |
Family ID | 41119926 |
Filed Date | 2011-12-15 |
United States Patent
Application |
20110306527 |
Kind Code |
A1 |
Bouffet; Alain ; et
al. |
December 15, 2011 |
GREASE COMPOSITION
Abstract
The disclosure relates to a grease composition comprising: (A) a
synthetic base oil in majority consisting of alkylaromatic(s); (B)
a thickener in majority consisting of at least one metal soap of
fatty acids; and (C) a solid lubricant in majority consisting of
nanoparticulate polytetrafluorethylene, at least 85% of the
particles of which have a size of less than one micron.
Inventors: |
Bouffet; Alain; (Taluyers,
FR) ; Bardin; Franck; (Vienne, FR) |
Assignee: |
Total Rafinage Marketing
Puteaux
FR
|
Family ID: |
41119926 |
Appl. No.: |
13/203281 |
Filed: |
February 26, 2010 |
PCT Filed: |
February 26, 2010 |
PCT NO: |
PCT/IB2010/050851 |
371 Date: |
August 25, 2011 |
Current U.S.
Class: |
508/182 |
Current CPC
Class: |
C10M 2205/223 20130101;
C10N 2010/08 20130101; C10M 2207/1225 20130101; F16C 2240/48
20130101; C10N 2040/045 20200501; C10M 2213/062 20130101; C10N
2010/04 20130101; C10M 169/02 20130101; C10M 2207/1206 20130101;
C10N 2040/02 20130101; C10N 2020/02 20130101; C10M 2203/065
20130101; C10M 2207/1256 20130101; C10N 2020/06 20130101; C10N
2010/02 20130101; C10M 2207/1265 20130101; C10N 2020/067 20200501;
C10N 2050/10 20130101; C10M 169/06 20130101; C10N 2030/06 20130101;
F16C 33/6688 20130101; C10N 2020/065 20200501; C10N 2040/044
20200501; C10M 2207/1285 20130101; C10M 2205/0285 20130101; C10N
2040/042 20200501; C10N 2010/06 20130101; C10N 2040/046 20200501;
C10M 2207/1216 20130101 |
Class at
Publication: |
508/182 |
International
Class: |
C10M 169/06 20060101
C10M169/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2009 |
FR |
FR 09/00898 |
Claims
1. A grease composition comprising: (A) a synthetic base oil in
majority consisting of alkylaromatic(s); (B) a thickener in
majority consisting of at least one metal soap of fatty acids; and
(C) a solid lubricant in majority consisting of nanoparticulate
polytetrafluoroethylene, at least 85% of the particles of which
have a size of less than one micron.
2. The composition according to the preceding claim, wherein the
oil in the form of alkylaromatics makes up at least 80% by weight
of the base oil in said composition.
3. The composition according to claim 1, wherein the metal soap(s)
make(s) up at least 80% by weight of the thickener in said
composition.
4. The composition according to claim 1, wherein the solid
lubricant consists of at least 80%, by weight of nanoparticulate
polytetrafluoroethylene.
5. The composition according to claim 1, wherein the solid
lubricant only consists of nanoparticulate
polytetrafluoroethylene.
6. The composition according to claim 1, wherein the thickener is
free of urea compounds.
7. The composition according to claim 1, wherein the composition is
free of calcium carbonate.
8. The composition according to claim 1, wherein the composition
comprises 0.1 to 10% by weight of solid lubricant in the form of
nanoparticulate polytetrafluoroethylene.
9. The composition according to claim 1, wherein the
polytetrafluoroethylene particles have an average size comprised
between 150 and 800 nm.
10. The composition according to claim 1, wherein the synthetic
base oils are selected from oils of the alkybenzene or
alkylnaphthalene type.
11. The composition according to claim 1, wherein the synthetic
base oil comprises at least one other mineral, synthetic or natural
base oil.
12. The composition according to claim 1, wherein the soaps are
simple metal soaps of either saturated or not, either hydroxylated
or not, fatty acids comprising from 14 to 28 carbon atoms, or
complex metal soaps of one or more either saturated or not, either
hydroxylated or not fatty acids comprising from 14 to 28 carbon
atoms, in a combination with one or more carboxylic acids with a
short hydrocarbon chain comprising from 6 to 12 carbon atoms.
13. The composition according to claim 1, wherein the metal soaps
of fatty acids are selected from titanium, aluminium, alkaline and
earth alkaline metal soaps, preferably lithium, calcium, sodium,
barium soaps.
14. The composition according to claim 1, wherein the composition
comprises one or more anti-wear and/or extreme pressure agents.
15. The grease composition according to claim 1, wherein the
composition comprises, based on the total weight of the
composition: from 50 to 90% by weight of the synthetic base oil;
from 1 to 15% by weight of the thickener in majority consisting of
at least one metal soap of fatty acids; from 0.1 to 10% by weight
of solid lubricant in the form of nanoparticulate
polytetrafluoroethylene powder with at least 85% of the particles
which have a size of less than one micron; and from 0 to 10% of one
or more anti-wear and/or extreme pressure additives.
16. The composition according to the preceding claim, wherein the
composition comprises 5 to 15% by weight based on the total weight
of the composition, of a synthetic oil of the polyalphaolefin
type.
17. The composition according to claim 1, wherein the composition
comprises a base oil having a kinematic viscosity at 40.degree. C.,
measured according to the ASTM D 445 standard, comprised between 10
and 120 mm.sup.2/s.
18. The composition according to claim 1, wherein the composition
has a consistency according to the ASTM D217 standard of more than
265 tenths of millimeters, and in that it has a consistency
according to the ASTM D217 standard of more than 400 tenths of
millimeters.
19. A method for preparing a grease, the method comprising:
dissolving one or more fatty acids in a fraction of the base oil or
of the base oil mixture adding metal compounds; saponifying fatty
acids with said metal compounds; and incorporating nanoparticulate
polytetrafluoroethylene, for which at least 85% of the particles
have a size of less than one micron.
20. The composition according to claim 1, wherein the grease is
adapted for use in automobile transmissions.
21. The composition according to claim 1, wherein the grease is
adapted for use in at least one automobile member selected from:
lubricated rolling bearings, machine tool slide rails or
centralized greasing systems.
22. The composition according to claim 1, wherein the solid
lubricant consists of at least 90% by weight of nanoparticulate
polytetrafluoroethylene.
23. The composition according to claim 1, wherein it comprises 2 to
7% by weight of solid lubricant in the form of nanoparticulate
polytetrafluoroethylene.
24. The composition according to claim 1, wherein the composition
has a consistency according to the ASTM D217 standard comprised
between 265 and 475 tenths of millimeters, and has a consistency
according to the ASTM D217 standard comprised between 400 and 475
tenths of millimeters.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a National Phase Entry of International
Application No. PCT/IB2010/050851, filed on Feb. 26, 2010, which
claims priority to French application Ser. No. 09/00898, filed on
Feb. 27, 2009, both of which are incorporated by reference
herein.
FIELD OF THE INVENTION
[0002] The present invention relates to grease compositions, in
particular which may be used for greasing rolling bearings.
BACKGROUND
[0003] There exist many applications where liquid lubricants are
not suitable because they "drift" relatively to the greasing point.
These are in particular rolling and sliding bearings, open gears,
metal cables and chain drives, and more generally applications
which do not include any sealing system. For these applications,
lubricant greases are used, which are solid or semi-fluid
substances resulting from the dispersion of a thickener in a liquid
lubricant, integrating additives which give them particular
properties.
[0004] The very large majority of lubricant greases are prepared
with thickeners of the fatty acid metal salt type. The fatty acid
is dissolved in the base oil at a relatively high temperature, and
then the suitable metal hydroxide is added. After having evaporated
the water by baking, which is formed during the reaction, it is
cooled during a defined period of time in order to form the soap
lattice.
[0005] Lithium, sodium, calcium, barium, titanium or aluminium
hydroxides are suitable as metal compounds for making the grease.
Fatty acids with a long chain of the order of C.sub.14 to C.sub.28,
mainly C.sub.18, are generally derived from vegetable oils (castor
oil for example) or animal oils (for example tallow). They may be
hydrogenated. The most known derivative is 12-hydroxystearic acid
derived from ricinoleic acid. It is also possible to use, in
combination with fatty acids with a long chain, short chain acids,
typically comprising between 6 and 12 carbon atoms, such as for
example azelaic acid, . . . . So-called complex greases are then
formed.
[0006] The soaps form a fibrous structure which retains the
lubricant oil. Aluminium soaps, them, have a spherical gel
structure. Other inorganic thickeners such as for example
bentonite, silica gel may be used. Polycarbamides (polyureas) are
also found among the thickeners. These thickeners are generally
used for special applications, for example high temperature
greases.
[0007] For certain applications, for example for lubricated rolling
bearings, but also for machine tool slide rails, or for centralized
greasing systems in automobiles, transmissions, it is desirable
that the greases have a low friction coefficient, so as to increase
the yield of the systems and possibly generate savings in fuel
(so-called "ecofuel" or "fuel saving" properties). These greases
should further remain sufficiently consistent so as not to run out
of the greasing point, and play their role of reducing wear and
preventing seizing.
[0008] Patent application JP 55082196 discloses certain grease
compositions incorporating as additives, solid lubricants in
particulate form in order to improve the friction coefficient and
to prevent seizing of the systems. It is known that solid
lubricants, in particular polytetrafluoroethylene (PTFE), should be
incorporated into the greases at high contents, above 5% or further
10% by mass, sometimes up to 40% by mass, so that an effect is
noticed.
[0009] It is also known that anti-friction and anti-wear properties
of these particulate solids are improved when the particles are of
nanometric size. Patent application WO 2008/069936 thus discloses
the use of solid lubricants in the form of nanoparticles with a
diameter of less than 500 nm in liquid lubricants or in greases, in
order to improve their anti-wear and lubrication properties. The
amounts of solid lubricants required for obtaining a significant
effect are still however very substantial, of the order of 20% by
mass, greater than 15% by mass. This poses problems of cost of the
formulations, and such a high content may also spoil other
properties of the lubricants and of the greases, notably having an
effect on their viscosity, or on their consistency as regards
greases.
[0010] Such nanoparticulate solid lubricants, for example in
polytetrafluorethylene (PTFE), may also be incorporated in motor
oils, in order to increase their lubricating power, for example at
contents comprised between 0.01 and 10% by mass, in combination
with compounds of the organomolybdenum, zinc dithiophosphate, boron
compound type, . . . as described in patent application US
2005/0124504. However, it seems that the whole of the parameters
with which a maximum antifriction effect of the solid nanoparticles
in the lubricants or in the greases may be attained, has not been
adjusted in the prior art, in particular the parameters which
determine the more or less proper dispersion of these particular
solids in said lubricants or grease. These parameters may prove to
be substantially different from one medium to the other, for
example between a grease and a liquid lubricant, and depend on the
respective nature of the particles, of the bases, of the thickeners
used.
[0011] Therefore there in particular exists a need for grease
compositions where the anti-friction effect of the solid
nanoparticles is improved. Accessorily, there exists a need for
such greases also having an improved anti-wear effect.
Surprisingly, the applicant noticed that a grease having a specific
combination of synthetic base oil, of fatty acid metal soaps and of
additives of the solid lubricant type in nanoparticulate form, had
very low friction coefficients, expressed by very high yields on
lubricated rolling bearing systems.
SUMMARY
[0012] The present invention relates to grease compositions
comprising: [0013] at least one synthetic base oil of the
alkylaromatic type, [0014] one or more fatty acid metal soaps,
[0015] a solid lubricant consisting of nanoparticulate
polytetrafluoroethylene where at least 80% of the particles have a
size of less than one micron.
[0016] An advantage of the invention is the obtaining of
significant ant-friction effects with low amounts of solid
nanoparticles, typically less than or equal to 10% by mass, or
further less than or equal to 5% by mass of nanoparticles based on
the total weight of the compositions. Thus, an economical means is
found for producing grease compositions with a low friction
coefficient, which may therefore lead to high yields on rolling
systems, or allow savings in energy on various systems, for example
transmissions, in particular automobile transmissions or
constant-velocity universal joints.
[0017] Another advantage of the invention is that this effect may
be obtained with inexpensive and available conventional thickeners
which are metal soaps of fatty acids. Certain thickeners, for
example polyureas, are expensive, difficult to make and not
accessible in large amounts. These soaps further have the advantage
of a very good mechanical strength, comparatively with other
thickeners, for example polyureas. Thus, the greases according to
the invention do not lose their structure when they are subject to
mechanical stresses, and may be used in applications where no
sealing system is provided, without any fear of leaks out of the
greasing point.
[0018] The invention relates to a grease composition comprising:
[0019] (A) a synthetic base oil in majority consisting of
alkylaromatic(s) (A1), [0020] (B) a thickener in majority
consisting of at least one fatty acid metal soap, [0021] (C) a
solid lubricant in majority consisting of nanoparticulate
polytetrafluoroethylene, at least 85% of the particles of which
have a size of less than one micron.
[0022] The oil in the form of alkylaromatics (A1) preferably makes
up at least 80% by weight of the base oil (A) in said composition.
The metal soap(s) (B) preferably makes up at least 80% by weight of
the thickener (B) in said composition. The solid lubricant (C)
preferably consists of at least 80%, notably at least 90% by weight
of nanoparticulate polytetrafluoroethylene.
[0023] According to an embodiment, a solid lubricant (C) only
consists of nanoparticulate polytetrafluoroethylene. Preferably,
the thickener (B) is free of urea compounds. Preferably, the
composition is free of calcium carbonate. Preferably, it comprises
from 0.1 to 10% by weight, notably 2 to 7% by weight of solid
lubricant in the form of nanoparticulate polytetrafluoroethylene.
Preferably the polytetrafluorethylene particles have an average
size comprised between 150 and 800 nm. The synthetic base oils may
be selected from oils of the alkyl benzene or alkyl naphthalene
type.
[0024] According to an embodiment, the synthetic base oil (A)
comprises at least one other mineral, synthetic or natural base oil
(A2), preferably a synthetic oil selected from polyalphaolefins.
Preferably, the soaps are simple metal soaps of either saturated or
not, either hydroxylated or not, fatty acids comprising from 14 to
28 carbon atoms, or complex metal soaps of one or more either
saturated or not, either hydroxylated or not, fatty acids
comprising from 14 to 28 carbon atoms, in combination with one or
more carboxylic acids with a short hydrocarbon chain comprising
from 6 to 12 carbon atoms.
[0025] The metal soaps of fatty acids may be selected from
titanium, aluminium soaps or from those of alkaline and earth
alkaline metals, preferably, lithium, calcium, sodium, barium. The
composition according to the invention may comprise one or more
anti-wear and/or extreme pressure agents.
[0026] The invention also relates to a grease composition which
comprises, based on the total weight of the composition: [0027]
from 50 to 90% by weight of the synthetic base oil (A), [0028] from
1 to 15% by weight of the thickener (B) in majority consisting of
at least one metal soap of fatty acids, [0029] from 0.1 to 10% by
weight of solid lubricant (C) in the form of nanoparticulate
polytetrafluoroethylene powder with at least 85% of the particles
having a size of less than one micron, [0030] from 0 to 10% of one
or more anti-wear and/or extreme pressure additives.
[0031] Preferably, the composition comprises 5 to 15% by weight,
based on the total weight of the composition, of a synthetic oil
(A2) of the polyalphaolefin type. Preferably, the composition has a
base oil (A) having a kinematic viscosity at 40.degree. C.,
measured according to the ASTM D 445 standard, comprised between 10
and 120 mm.sup.2/s. Preferably, the composition has a consistency
according to the ASTM D217 standard of more than 265, preferably
comprised between 265 and 475, or between 265 and 295, or between
310 and 340, or between 335 and 385 tenths of millimeters, or in
that it has a consistency according to the ASTM D217 standard of
more than 400 tenths of millimeters, preferably comprised between
400 and 475 or between 445 and 475 tenths of millimeters.
[0032] The invention also relates to a method for preparing a
grease as defined above and which comprises the following
steps:
[0033] dissolving one or more fatty acids in a fraction of the base
oil or of the base oil mixture,
[0034] adding metal compounds, preferably of the type: metal oxide,
hydroxide or carbonate or lime,
[0035] saponifying the fatty acids with said metal compounds,
[0036] incorporating nanoparticulate polytetrafluorethylene, at
least 85% of the particles of which have a size of less than one
micron.
[0037] The invention also relates to the use of the grease
composition as defined above as a grease for transmissions, in
particular automobile transmissions. The invention also relates to
the use of the grease composition as defined above as a grease for
lubricated rolling bearings, machine tool slide rails or
centralized greasing systems in automobiles.
[0038] By "in majority consisting of" is meant in the present text
that the content of this compound is of at least 50% by weight of
the targeted compound. The content in question may also attain at
least 80%, preferably at least 85 or 90 or 95% by weight, or even
substantially 100% by weight of the targeted compound.
DETAILED DESCRIPTION
[0039] Base Oils:
[0040] The grease compositions according to the invention contain
at least one synthetic base oil of the alkylaromatic type. These
oils are obtained by alkylation of aromatic compounds with
compounds such as olefins, monohalogenated or monohydroxylated
paraffins, or other alkylation agents, in the presence of an acid
catalyst, for example of the Friedel-Craft type or zeolites. The
aromatic compounds may for example be benzene, naphthalene or
anthracene, optionally substituted. The alkyl benzene or alkyl
naphthalene bases are preferred.
[0041] The resulting alkylaromatic synthetic bases may be mono- or
polyalkylaromatics, for example di- or tri-alkylaromatics (for
example mono-, di-, tri- or poly-alkyl benzene or naphthalene or
anthracene). The alkyl substituents may be linear or branched and
preferably include from 9 to 24 carbon atoms, preferentially from
12 to 24 carbon atoms. The presence of substituents including less
than 9, or less than 12 carbon atoms may lead, notably in bases of
the alkyl benzene type, to compounds which are too volatile, and
the substituents including more than 24 carbon atoms provide too
high viscosity for the target applications.
[0042] These different compounds may be present either alone or as
a mixture in the greases according to the invention. They have a
strong solvent power which should contribute to optimum dispersion
of the additives in the compositions according to the invention.
The kinematic viscosity at 40.degree. C. according to ASTM D445 of
these alkyklaromatic synthetic bases is preferentially comprised
between 10 and 120 cSt.
[0043] When applications such as lubricated bearings or centralized
greasing for automobiles are targeted, bases will be preferred for
which the kinematic viscosity at 40.degree. C. according to ASTM
D445 is comprised between 10 and 80 cSt, preferentially between 10
and 50 cSt, preferentially between 20 and 40 cSt, so as to
guarantee good operability, good pumpability, and good cold
properties, allowing use down to -20.degree. C., or even down to
-40.degree. C. When applications such as transmissions are
targeted, bases will be preferred for which the kinematic viscosity
at 40.degree. C. according to ASTM D445 is comprised between 70 and
110 cSt, preferentially between 30 and 40 cSt, preferentially
between 35 and 37 cSt, so as to guarantee an adequate oil film
under higher loads. These alkylaromatic bases are preferably
present at contents comprised between 50 and 90% by weight,
preferentially between 65 and 85% or between 70 and 80% in the
grease compositions according to the invention.
[0044] Other Base Oils:
[0045] The grease compositions according to the invention may
contain in addition to the alkylaromatic synthetic bases described
above, other base oils in a lesser amount. The other base oil(s)
used in the compositions according to the present invention may be
oils of mineral or synthetic origin of the groups I to VI according
to the classes defined in the API (American Petroleum Institute)
classification.
[0046] The mineral base oils according to the invention include all
types of bases obtained by atmospheric and vacuum distillation of
crude oil, followed by refining operations such as extraction with
a solvent, de-asphalting, de-waxing with a solvent, hydrotreatment,
hydrocracking and hydro-isomerization, hydrofinishing. The base
oils of the grease compositions according to the present invention
may also be synthetic oils, such as certain esters, silicones,
glycols, polybutene, polyalphaolefins (PAOs). The base oils may
also be oils of natural origin, for example esters of alcohol and
carboxylic acids which may be obtained from natural resources such
as sunflower, rapeseed, palm oil, . . . .
[0047] Preferentially, synthetic oils of the polyalphaolefin (PAO)
type combined with alkylaromatic synthetic bases as described above
are used in the compositions according to the invention. The
polyalphaolefins are for example obtained from monomers having from
4 to 32 carbon atoms (for example octene, decene). Their average
weight molecular mass is typically comprised between 250 and
3,000.
[0048] Mixtures of synthetic and mineral oils may also be used.
Preferably the base oils other than the alkylaromatic synthetic
bases described above, are present at contents comprised between 5
and 15% in the compositions according to the invention. The
kinematic viscosity at 40.degree. C. according to ASTM D445 of the
base oil or of the base oil mixture used in the compositions
according to the invention is preferentially comprised between 10
and 120 cSt.
[0049] When applications such as lubricated bearings or centralized
greasing for automobiles are targeted, a base oil or a base oil
mixture will be preferred, for which the kinematic viscosity at
40.degree. C. according to ASTM D445 is comprised between 10 and 80
cSt, preferentially between 10 and 50 cSt, preferentially between
20 and 40 cSt, so as to guarantee good operability, good
pumpability, and good cold properties, allowing use down to
-20.degree. C., or even down to -40.degree. C. When applications
such as transmissions are targeted, a base oil or a base oil
mixture will be preferred, the kinematic viscosity of which at
40.degree. C. according to ASTM D445 is comprised between 70 and
110 cSt, preferentially between 30 and 40 cSt, preferentially
between 35 and 37 cSt, so as to guarantee an adequate oil film
under higher loads.
[0050] Thickeners:
[0051] The greases according to the invention are thickened with
metal soaps of fatty acids, which may be prepared separately or in
situ during the making of the grease (in the latter case, the fatty
acid is dissolved in the base oil and the suitable metal hydroxide
is then added). These thickeners are easily available and
inexpensive products currently used in the field of greases.
Moreover, the thereby thickened greases have very good mechanical
stability, for example comparatively with greases based on
polyureas, this allows them to be easily used in applications where
the grease is found in a non-confined enclosure.
[0052] Long chain fatty acids are preferentially used, typically
comprising from 10 to 28 carbon atoms, either saturated or
unsaturated, optionally hydroxylated. The long chain fatty acids
(typically comprising from 10 to 28 carbon atoms) are for example,
capric, lauric, myristic, palmitic, stearic, arachidic, behenic,
oleic, linoleic, erucic acids and their hydroxylated derivatives.
12-hydroxystearic acid is the most well-known derivative of this
category, and preferred. These long chain fatty acids generally
derive from vegetable oils, for example palm, castor, rapeseed,
sunflower oil . . . or from animal fats (tallow, whale oil . . .
).
[0053] So-called simple soaps may be formed by using one or more
long chain fatty acids. It is also possible to form so-called
complex soaps by using one or more long chain fatty acids in
combination with one or more carboxylic acids with a short
hydrocarbon chain comprising at most 8 carbon atoms.
[0054] The saponification agent used for making the soap may be a
metal compound of lithium, sodium, calcium, barium, titanium,
aluminium, preferentially lithium and calcium, and preferably a
hydroxide, oxide or carbonate of these metals. One or more metal
compounds may be used, either having the same metal cation or not,
in the greases according to the invention. It is thereby possible
to associate lithium soaps combined with calcium soaps in a lesser
proportion.
[0055] The metal soaps are used at contents of the order of 1 to
15% by weight, preferentially from 2 to 10% or further from 4 to
10% or from 4.5 to 6% by weight in the greases according to the
invention. When applications such as lubricated bearings or
centralized greasing for automobiles are targeted, the use of 1 to
6%, preferentially 2 to 5% of metal soap(s) will be preferred, so
as to obtain fluid or semi-fluid greases of grade 000 or 00
according to the NLGI classification. When applications such as
transmissions are targeted, the use of 6.5% to 15%, preferentially
7 to 13% or 8 to 12% of metal soap(s) will be preferred, so as to
obtain greases of grade 0, grade 1 or grade 2 according to the NLGI
classification. In every case, these thickener contents are
relatively low in the greases according to the invention, so as to
obtain greases for which the consistency corresponds to a grade
comprised between 000, 00, 0, 1 or 2 according to the NLGI
classification, and to promote an increase in the yield, energy
savings or an ecofuel effect, for example on systems such as
lubricated rolling bearings, centralized greasing systems for
vehicles or transmissions.
[0056] Method for Preparing the Greases:
[0057] The greases according to the invention are preferentially
made by forming the metal soap in situ. One or more fatty acids are
dissolved in a fraction of the base oil or of the base oil mixture
at room temperature. This fraction is usually of the order of 40%
of the total amount of oil contained in the final grease. The fatty
acids may be long acids, comprising from 14 to 28 carbon atoms, in
order to form a simple soap, optionally combined with short fatty
acids, comprising from 6 to 12 carbon atoms, in order to form
complex soaps.
[0058] Metal compounds preferentially of the metal oxide, hydroxide
or carbonate type are added at a temperature of about 60.degree. C.
Thus, it is possible to add a single type of metal or to combine
several metals. The preferred metal of the compositions according
to the invention is lithium, optionally combined in a lesser
proportion with calcium.
[0059] The saponification reaction of the fatty acids by the metal
compounds is left to take place at a temperature of about
80.degree. C. The formed water is then evaporated by baking the
mixture at a temperature of about 100 to 200.degree. C. The grease
is then cooled by the remaining base oil fraction.
[0060] The nanoparticulate polytetrafluoroethylene and other
optional additives are then incorporated at about 80.degree. C.
Kneading is then carried out for sufficient time in order to obtain
a homogeneous grease composition.
[0061] Grade of the Greases:
[0062] The consistency of a grease measures its hardness or its
fluidity at rest. It is evaluated by the penetration depth of a
cone of given dimensions and mass. The grease is subject to
kneading beforehand. The conditions for measuring the consistency
of a grease are defined by the ASTM D 217 standard.
[0063] Depending on their consistency, the greases are distributed
in 9 classes or 9 NLGI (National Lubricating Grease Institute)
grades frequently used in the field of greases. These grades are
indicated in the table below.
TABLE-US-00001 Consistency according to ASTM D 217 NLGI Grade
(tenths of millimeters) 000 445-475 00 400-430 0 335-385 1 310-340
2 265-295 3 220-250 4 175-205 5 130-160 6 85-115
[0064] The greases according to the invention have a consistency of
more than 265 tenths of millimeters, preferentially comprised
between 275 and 475 tenths of millimeters according to the ASTM
D217 standard. Preferentially they are of NLGI grade 000, 00, 0, 1
or 2, i.e. their consistency is respectively comprised between 445
and 475, or between 400 and 300, or between 335 and 385, or between
310 and 340, or between 265 and 295 tenths of millimeters according
to ASTM D217.
[0065] When applications such as lubricated bearings or centralized
greasing for automobiles are targeted, the greases according to the
invention are preferentially fluid or semi-fluid greases, with a
consistency of, more than 400 tenths of millimeters, preferentially
comprised between 400 and 475 tenths of millimeters according to
ASTM D217. Preferentially, they are of NLGI grade 00 or 000, i.e.
their consistency is respectively comprised between 400 and 430, or
445 and 475 tenths of millimeters according to ASTM D217.
[0066] When applications such as transmission, constant-velocity
universal joints are targeted, the greases according to the
invention are preferentially fluid or semi-fluid greases with a
consistency of more than 265 tenths of millimeters, preferentially
comprised between 265 and 335 tenths of millimeters according to
ASTM D217. Preferentially, they are of NLGI grade 0, 1 or 2, i.e.
their consistency is respectively comprised between 335 and 385, or
310 and 340, or 265 and 295 tenths of millimeters according to ASTM
D217. Generally, the greases according to the invention tend to be
more fluid than the average of the greases used in the relevant
applications, so as to promote an increase in the yield, energy
savings or an "ecofuel" effect for example on systems such as
lubricated rolling bearings, centralized greasing systems for
vehicles or transmissions.
[0067] PTFE Nanoparticles:
[0068] The greases according to the invention contain
nanoparticulate polytetrafluoroethylene (PTFE). This PTFE may be
added in the dry powder condition or else in the form of a
concentrated dispersion, wherein the powder is dispersed in a
pre-dilution lubricant oil, for example a synthetic oil of the
polyalkylaromatic oil or PAO type as described above. The term of
nanoparticulate PTFE designates a powder or a dispersion of powder
in an oil, wherein at least 85%, preferentially at least 90%, still
more preferentially at least 95% (in number) of the particles have
a size of less than one micron. More preferably, 100% of the number
of particles has a size of less than one micron.
[0069] In the whole present text, the measurement of the size of
the PTFE nanoparticles is accomplished according to the teaching of
patent application WO 2004/067608 (corresponding to patent
application EP 1 594 682). Reference will be made to the
description of the measurements indicated in the application WO
2004/067608 more particularly:
[0070] to the passage of page 16, line 15 to page 17, line 13 for a
dry measurement
[0071] to the passage of page 17, line 14 to page 20, line 4 for a
measurement in isopropyl alcohol (IPA),
[0072] to the passage of page 20, line 5 to page 22, line 4 for a
measurement in an oily medium, a measurement method which is
preferred within the scope of the present invention,
[0073] to the passage of page 22, line 5 to page 24, line 4 for a
measurement in water.
[0074] Preferentially, at least 80%, or at least 80%, or even 95%
in number, or even more preferentially 100% of the PTFE particles
in these powders or dispersions have a size of more than 50 nm,
preferentially more than 100 nm. The presence of too small
particles may create problems of re-aggregation of the particles
with each other and penalize their dispersion in the grease. The
nanoparticulate PTFE of the greases according to the invention
preferably has an average size comprised between 150 and 800 nm, or
further between 200 and 700 nm or further between 400 and 600 nm.
By average size is meant the average of the distribution of the
sizes of particles.
[0075] As indicated above, this nanometric PTFE may be prepared
from methods described in the aforementioned patent application EP
1 594 682. Such powders or dispersions are marketed by Shamrock in
the Nanoflon.RTM. range. The distribution of the particle sizes of
the powders or dispersions of PTFE used in the grease compositions
according to the invention are measured with an analyzer of the
Malvern type, according to suitable methods described in the
aforementioned patent application WO 2004/067608 (EP 1 594
682).
[0076] For facilitating the application of the mixture,
incorporation of the PTFE nanoparticles as dispersions will be
preferred, preferentially in synthetic oils of the alkylaromatic or
PAO type, as described above. When a dispersion is used, it forms a
concentrate wherein the PTFE particles preferably account for about
20 to 50% by weight, preferentially 25 to 35% by weight or further
30% by weight of the dispersion. The nanometric PTFE is preferably
present in the grease compositions according to the invention at
contents comprised between 0.1 and 10%, preferentially between 2
and 7%, even more preferentially between 3 and 4.5% or further 3
and 5%. One of the advantages of the invention is to allow a
significant anti-friction effect with a small amount of
nanoparticles.
[0077] The anti-friction properties of PTFE are known. It is also
known that this type of solid lubricant has its properties improved
when the powders or dispersions containing them consist of
nanoparticles. However, it is also important to give the lubricants
and greases which contain them improved anti-friction properties,
that said nanoparticles are properly dispersed. It seems that with
the combination of PTFE nanoparticles with alkylaromatic base oils
and fatty acid metal soaps applied in the greases according to the
invention it is possible to obtain this good dispersion and
consequently excellent yields which have been observed on rolling
systems.
[0078] Other Performance Additives:
[0079] Anti-Wear and/or Extreme Pressure Additives
[0080] The grease compositions according to the present invention
may contain at least one sulfur, phosphorus or phospho-sulfur
anti-wear and/or extreme pressure agent, preferentially present at
contents comprised between 0.5 and 5% by weight based on total
weight of the composition. As an example of sulfur-containing
anti-wear and extreme pressure additives, mention may be made of
dithiocarbamates, thiadiazoles, and benzothiazoles,
sulfur-containing olefins. The phospho-sulfur anti-wear and extreme
pressure additives may for example be in a non-limiting way,
thiophosphoric acid, thiophosphorous acid, esters of these acids,
their salts, and dithiophosphates.
[0081] The lubricating compositions according to the present
invention may also contain phosphorus-containing anti-wear and
extreme pressure additives, such as for example alkyl phosphates or
alkyl phosphonates, phosphoric acid, phosphorous acid, mono-, di-,
and tri-esters of phosphorous acid and of phosphoric acid, and
their salts. Other additives: the grease compositions according to
the invention may also contain anti-rust additives, such as for
example sulfonates . . . (for example calcium, sodium, barium
sulfonates), naphthenates (typically zinc naphthenate), salicylates
(typically calcium salicylate) or oxidized waxes, antioxidant or
anti-corrosion additives . . . . These additives are typically
present at contents comprised between 0 and 10%, preferentially
between 0.5 and 2% by weight based on the total weight of the
composition. Finally, the compositions according to the invention
may also contain any type of additives suitable for their use, for
example coloring agents, at contents of the order of 0.05 to
0.5%.
EXAMPLES
Example 1
[0082] We have compared the performances of a bicycle wheel hub
including a bearing lubricated with different greases, with the
performances obtained with a Mavic hub (such as those mounted on
bicycle wheels of the Mavic Cosmic type) provided with ball
bearings, considered as an up market reference in the field. The
lubricated bearing hub used is of the type of those described in
patent application EP 1 719 641. The yield of the rolling bearing
system Mavic and of the lubricated bearing system is determined on
a test bench: [0083] A bicycle wheel provided with the hub to be
tested (a hub with a Mavic ball bearing, or a hub with bearings
lubricated with different greases) is driven by a motor, at an
initial speed of 70 km/hour, and then during a heating period of 5
minutes at 50 km/hour. [0084] During the whole duration of the
test, a load of 50 kg is applied to it. [0085] At the initial
instant, the power supply of the motor is switched off and then the
distance covered before stopping (or seizing) is measured.
[0086] The distance covered before stopping is a relative
measurement of the yield of the different rolling bearing systems.
It also allows a relative measurement of the anti-friction
properties of the different greases used for lubricating the
bearing of the hub. The bicycle wheel is the same for all the
tested tires, it is provided with a flexible pipe Hutchinson
initially inflated at a pressure of 10 bars.
[0087] All the tested greases are greases of grade 000 according to
the NLGI classification. [0088] The grease A is a grease comprising
a mineral base oil of group I of the 150 NS type, thickened with a
metal soap, lithium 12-hydroxystearate, of NLGI grade 000 [0089]
The grease B is a grease comprising a base oil of the polyglycol
type also thickened with lithium 12-hydroxystearate, of NLGI grade
000 [0090] The grease C is a grease comprising a base oil of the
alkyl benzene type thickened with lithium 12-hydroxystearate, of
NLGI grade 000 [0091] The grease D is a grease according to the
invention prepared by incorporating polyfluorotetraethylene
nanoparticles into the grease C, it is also of NLGI grade 000.
[0092] Grease D' is a grease prepared by incorporating tungsten
bisulfide WS.sub.2 nanoparticles into the grease C, it is also of
NLGI grade 000.
[0093] The mass compositions of the greases C and D and D' are
indicated in Table 1.
TABLE-US-00002 TABLE 1 Composition of the greases (in mass %)
Grease C Multi ZS EP Grease D Grease D' 000 31665 31663 Alkyl
benzene synthetic base 5.53 89.8% 76.9% 87.8% cSt at 100.degree. C.
PAD Base 10 cSt at 100.degree. C. -- 10.0% -- Lithium
12-hydroxystearate 5.9% 5.1% 5.8% Anti-wear/Extreme pressure agent
2.2% 1.9% 2.2% Anti-wear/antioxidant 0.8% 0.7% 0.8% Anti-rust 1.2%
1.0% 1.2% Coloring agent 0.1% 0.1% 0.1% Nanometric PTFE -- 4.3% --
Nanometric WS2 -- -- 2.25%
[0094] The rolling distances d (in meters) of the different tested
hubs are grouped in Table 2.
The last indicated distance d is the distance covered before
stopping.
TABLE-US-00003 TABLE 2 rolling distances Hub with a bearing
lubricated by a grease Mavic hub Grease A Grease B Grease C Grease
D Grease D' Time time time time time time (s) d (m) (s) d (m) (s) d
(m) (s) d (m) (s) d (m) (s) d (m) 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0
0 3.3 61 3.5 61 3.5 61 3.5 61 3.3 61 3.4 61 7.1 122 7.0 122 7.0 122
7.0 122 6.7 122 6.9 122 10.6 183 10.8 183 10.7 183 10.7 183 10.4
183 10.6 183 14.8 244 15.0 244 14.8 244 14.8 244 14.5 244 14.6 244
19.2 305 19.7 305 19.3 305 19.3 305 18.8 305 19.2 305 24.2 366 25.0
366 24.2 366 24.2 366 23.7 366 24.2 366 30.1 427 31.5 427 30.0 427
29.8 427 29.0 427 29.7 427 36.6 488 39.5 488 36.8 488 36.4 488 35.4
488 36.2 488 44.9 549 52.0 549 45.4 549 44.6 549 42.9 549 44.2 549
57.4 610 67.0 579 58.0 610 56.7 610 52.9 610 55.4 610 75.8 649 76.0
643 74.8 650 77.0 674 73.7 650
[0095] A yield (rolling distance before stopping) which is
significantly lower, is noted for the hub with a bearing lubricated
with grease A. The yield obtained with the hub with a bearing
lubricated by the greases B and C, is of the level of that of the
Mavic reference. In grease D', the incorporation of WS.sub.2
nanoparticles does not provide any improvement relatively to the
grease C. The performance level of the greases C and D' are
strictly identical.
[0096] An excellent yield, greater than that of the Mavic
reference, which however forms the up market of the cycling field,
and greater than that of the grease C, is obtained with the hub
with a bearing lubricated by the grease D according to the
invention. The incorporation of PTFE nanoparticles in the grease C
leads to notable improvement in its performances.
Example 2
Influence of the Base
[0097] Teflon nanoparticles identical with those used in the grease
D according to the invention were added into a grease (E) based on
synthetic base oil of the PAO type, thickened with the same lithium
metal soap (lithium 12-hydroxystearate). The anti-wear performances
in the 4-ball test ASTM D 2266 of the initial PAO+lithium grease
(grease E) were compared with those of greases E with nanometric
PTFE at 3% and 5% by mass respectively (greases F, G,
respectively), as well as with a grease E with 3% of micronic PTFE
with an average diameter of 5 .mu.m (grease H).
[0098] The results are grouped in the Table 3 below:
TABLE-US-00004 TABLE 3 anti-wear properties E F G H Solid -- 3% by
mass of 5% by mass of 3% by mass of lubricant nanometric PTFE
nanometric PTFE micronic PTFE Wear 830 790 810 530 diameter ASTMD
(.mu.m)
[0099] The greases E and F, G have performances of identical level:
no notable improvement in the anti-wear properties is provided by
adding nanometric PTFE into the grease based on PAO. At an
equivalent amount, micrometric PTFE provides a larger gain as
regards wear. Without having the intention of being bound by any
theory, it seems that in a grease thickened with lithium soap, the
base oil-nanoparticles interactions lead to a dispersion of the
nanoparticles which is less favorable than in the case of the alkyl
benzene base-PTFE nanoparticles pair, which may explain that their
incorporation does not give rise to any improvement in the
anti-wear or anti-friction performances.
* * * * *