Note: Descriptions are shown in the official language in which they were submitted.
CA 02287726 1999-10-28
LUBRICANT COMPOSITIONS EXHIBITING
EXTENDED OXIDATION STABILITY
The present invention relates to the use of certain additives to extend the
thermal stability and oxidation stability of lubricant compositions, and to
lubricant
compositions exhibiting extended thermal stability and oxidation stability.
Lubricating compositions for antiwear hydraulic and industrial applications
typically contain additive components to impart antiwear performance.
Hydraulic
grade zinc dialkyldithiophosphates are typically used in this respect. The
compositions usually also contain antioxidant components. The compositions
have
conventionally been formulated using Group I base oils. However, the use of
hydrocracked and catalytically dewaxed Group II and Group III base oils is on
the
increase. The hydrogenation and dewaxing processes involved result in base
oils of
exceptionally low aromaticity and sulphur level. These Group II and Group III
bases
have been found to exhibit an improved response to antioxidant components when
compared with Group I basestocks. This has led to the thinking that use of
Group II
and Group III bases could allow the level of antioxidants to be decreased
without
detriment to the level of antioxidant performance required by end users.
However,
rather than leading to reduced amounts of antioxidants being used, the advent
of
Group II and Group III base oils has prompted end users to demand a higher
level of
antioxidant performance, irrespective of the kind of base oil which is
actually used.
For example, whereas a performance level of 2000 to 4000 hours in the ASTM
D943
thermal oxidation test was previously acceptable, extended performance is now
commonly required, for instance a result of 10,000 hours in the ASTM D943
test.
In accordance with the present invention it has now been found that specific
antioxidant components, and combinations thereof, can be blended in lubricant
compositions containing hydraulic antiwear components to achieve extended
thermal
and oxidative stability without formation of sludge. More particularly, the
combinations have been found to give improved thermal stability, and thus
reduced
levels of sludge, when used in Group I, II and III basestocks and increased
oxidation
stability in Group II, or higher basestocks. These advantageous results
enables a
CA 02287726 1999-10-28
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variety of base oils to be are used in formulating the lubricant composition
and, in
turn, this allows industrial formulators enhanced flexibility whilst also
meeting the
now extended performance requirements of end users.
Accordingly, the present invention provides the use in a lubricant
composition comprising a hydraulic antiwear component and a base oil of an
additive
comprising at least one amine antioxidant and at least one additional
antioxidant
selected from ashless dithiocarbamate, sulphurised olefin and phenolic,
antioxidants
to provide a lubricant having improved thermal stability and oxidative
stability in all
basestock types.
The performance of the combinations of antioxidants used in accordance with
the present invention will vary depending, amongst other things, on the base
oil type,
the specific combination and the concentration of additive(s), used. In terms
of
thermal stability the additives used in accordance with the present invention
enable
formulation of lubricants which may avoid excessive sludge formation after a
period
of 10 days when the lubricant is tested in accordance with the NOC test and
when the
base oil used is a Group I basestock. In a preferred embodiment the amount of
sludge produced after 10 days in this test is not more than 100 mg/100 ml,
preferably
not more than 25 mg/ 100 ml. A 10 day sludge result of less than 10 mg/100 ml
is
particularly preferred. In terms of oxidation stability the additives used in
accordance
with the present invention typically enable formulation of lubricants which
use a
Group II or higher basestock and which give a result of at least 500 minutes,
preferably at least 600 minutes, in the RBOT thermal stability test. Thus, the
present
invention relates to combinations of antioxidants which may be used to achieve
good
oxidation performance in Group II or higher basestock without derating thermal
stability performance when Group I or higher basestock is used, and vice
versa.
The amine used in the present invention is selected from optionally alkylated
diphenylamines, phenyl-naphthylamines and mixtures thereof. Examples of such
components that may be used in this invention include, but are not limited to,
diphenylamine, phenyl-a-naphthylamine, phenyl-beta-naphthylamine,
butyldiphenylamine, dibutyldiphenylamine, octyldiphenylamine,
dioctyldiphenylamine, nonyldiphenylamine, dinonyldiphenylamine,
CA 02287726 1999-10-28
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dioctyldiphenylamine, nonyldiphenylamine, dinonyldiphenylamine,
heptyldiphenylamine, diheptyldiphenylamine, methylstyryldiphenylamine, mixed
butyl/octyl alkylated diphenylamines, mixed butyl/styryl alkylated
diphenylamines,
mixed nonyl/ethyl alkylated diphenylamines, mixed octyl/styryl alkylated
diphenylamines, mixed ethyl/methylstyryl alkylated diphenylamines, octyl
alkylated
phenyl-a-naphthylamines and mixed alkylated phenyl-a-naphthylamines. 2,6-di-t-
butyl-a-dimethylamino-p-cresol may also be used.
Useful amine antioxidants are generally characterized by their nitrogen
content and TBN as determined by ASTM D 2896. It is preferred that the
nitrogen
l0 content of the amine antioxidants be between 3.0 and 7.0 wt% and the TBN be
between 100 and 250 mg KOH/g of the neat, i.e. undiluted, component.
The concentration of amine antioxidants) in the finished composition varies
depending upon the basestock used, customer requirements and applications.
Typically, the total amount of amine antioxidant present in the finished
composition
is from 0.04 wt% to 0.4 wt%, preferably, from 0.05 wt% to 0.2 wt %.
The sulphur-containing compounds of the present invention are selected from
the group consisting of sulphurized olefins, sulphurized fatty acids, ashless
dithiocarbamates, tetraalkylthiuram disulphides and mixtures thereof. The
sulphurized olefins suitable for use in the present invention may be prepared
by a
number of known methods. They are typically characterized by the type of
olefin
used in their production and their final sulphur content. High molecular
weight
olefins (e.g., those having an average molecular weight (Mn) of from about 112
to
about 351 g/mole) are preferred. Examples of olefins that may be used include
a-
olefins, isomerized a-olefins, branched olefins, cyclic olefins, polymeric
olefins and
mixtures thereof. Examples of a-olefins that may be used include 1-butene, 1-
pentene, I-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-
dodecene, I-tridecene, 1-tetradecene, 1-pentadecene, I-hexadecene, 1-
heptadecene,
1-octadecene, 1-nonadecene, 1-eicosene, 1-heneicosene, 1-docosene, I-
tricosene, 1-
tetracosene, I-pentacosene and mixtures thereof. a-Olefins may be isomerized
before the sulphurization reaction or during the sulphurization reaction.
Structural
and/or conformational isomers of the a-olefins that contain internal double
bonds or
CA 02287726 1999-10-28
-4-
branching may also be used. For example, isobutylene is the branched olefin
counterpart of the a-olefin 1-butene.
Sulphur sources that may be used in the sulphurization reaction can include,
for example, elemental sulphur, sulphur monochloride, sulphur dichloride,
sodium
sulphide, sodium polysulphide, and mixtures thereof added together or at
different
stages of the sulphurization process.
Unsaturated fatty acids and oils, because of their unsaturation, may also be
sulphurized and used in this invention. Examples of fatty acids that may be
used
include lauroleic acid, myristoleic acid, palmitoleic acid, oleic acid,
elaidic acid,
vaccenic acid, linoleic acid, linolenic acid, gadoleic acid, arachidonic acid,
erucic
acid, and mixtures of these. Examples of oils or fats that may be used include
corn
oil, cottonseed oil, grapeseed oil, olive oil, palm oil, peanut oil, rapeseed
oil,
safflower seed oil, sesame seed oil, soybean oil, sunflower oil, sunflower
seed oil,
and combinations thereof.
1 S Examples of ashless dithiocarbamates that may be used include, but are not
limited to, methylene-bis(dialkyldithiocarbamate), ethylene-
bis(dialkyldithiocarbamate), and isobutyl disulphide-2,2'-
bis(dialkyldithiocarbamate),
where the alkyl groups of the dialkyldithiocarbamate can preferably have from
1 to
16 carbons. Examples of preferred ashless dithiocarbamates are methylene-
bis(dibutyldithiocarbamate), ethylene-bis (dibutyldithiocarbamate), and
isobutyl
disulphide-2,2'-bis(dibutyldithiocarbamate). Examples of preferred
tetraalkylthiuram
disulphides that may be used include tetrabutylthiuram disulphide and
tetraoctylthiuram disulphide.
The concentration of the sulphur-containing compound in the finished
composition can vary depending upon the customers' requirements and
applications.
The compound is typically used in an amount of upto 0.1% by weight, preferably
upto 0.05% by weight based on the total weight of the lubricant composition.
An
important criteria for selecting the concentration of the compound is the
sulphur
content. The compound should typically deliver between 0.005 wt. % and 0.07
wt.
% of sulphur to the finished composition. For example, a sulphurized olefin
having
12 wt. % sulphur content should be used between 0.04 wt. % and 0.58 wt. % to
CA 02287726 1999-10-28
deliver between 0.005 wt. % and 0.07 wt. % sulphur to the tinished
composition. An
ashless dithiocarbamate having 30 wt. % sulphur content should be used between
0.02 wt. % and 0.23 wt. % to deliver between 0.005 wt. % and 0.07 wt. '%
sulphur to
the finished composition.
Another criterion usefiU for selecting the sulphur-containing compound is the
content of active sulphur as determined by ASTM D 1662. The presence of high
levels of active sulphur can lead to significant corrosion and sludge problems
in the
finished lubricant. In a preferred embodiment of the present invention, the
level of
active sulphur in the compound is below 1.5 wt. % as determined by ASTM D
1662.
An example of a sulphurized olefin that may be used in this invention would
contain approximately 12 wt. % total sulphur content and <1 wt. % active
sulphur.
Examples of commercially available sulphurized fatty oils or mixtures of
sulphurized fatty oils and olefins, that may be used in this invention include
those
having approximately 9.5 wt. % sulphur content and 1 wt. % active sulphur,
approximately 12.5 wt. % sulphur content and 1.5 wt. % active sulphur, and
approximately 10 wt. % sulphur content and < I wt. % active sulphur. An
example of
an ashless dithiocarbamate that may be used in this invention would be one
which
has approximately 30 wt. % sulphur from a practical standpoint the sulphur-
containing compound should contain a minimum of 8.0 wt% sulphur in order to
minimize the amount of additive needed to deliver the required amount of
sulphur.
Mixtures of sulphurized olefins, ashless dithiocarbamates and
tetraalkylthiuram disulphides, in varying proportions, may also be used, as
long as
the desired total sulphur content, and active sulphur content are satisfied.
Examples of phenolic antioxidants which may be used include hindered
phenolics such as 2,6-di-butylphenol, 4-methyl-2,6-di-t-butylphenol, 2,4,6-tri-
butylphenol, 2-t-butylphenol, 2,6-diisopropylphenol, 2-methyl-6-t-butylphenol,
2,4-
dimethyl-6-t-butylphenol, 4-(N,N-dimethylaminomethyl)-2,6-di-t-butylphenol, 4-
ethyl-2,6-di-t-butylphenol, 2-methyl-6-styrylphenol, 2,6-di-styryl-nonylphenol
and
mixtures thereof. Also useful are methylene bridged alkyl phenols and these
may be
used singly or in combination with each other or with sterically hindered
unbridged
phenols. Examples include 4,4'-methylene-bis(2,6-di-butylphenol), 4,4'-
methylene-
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bis(6-t-butyl-o-cresol), 4,4'-methylene-bis(2-t-amyl-o-cresol), 2,2'-methylene-
bis(4-
methyl-6-t-butylphenol), methylene bridged t-butylphenol mixtures, iso-octyl-
3,5-di-
butyl-4-hydroxy hydrocinnamate and thiodiethylene-bis (3,5-di-butyl-4-
hydroxy)hydrocinnamate. Also useful are mixtures of methylene bridged alkyl
phenols such as described in USP 3,21 1,652. Typically, the phenolic
antioxidant will
be present in the finished lubricant in an amount of upto 0.4% by weight,
preferably
upto 0. l5% by weight.
The present invention also provides lubricant compositions, as described
herein, comprising a hydraulic antiwear component, a base oil, at least one
amine
antioxidant and at least one additional antioxidant.
The antioxidants useful in the present invention are commercially available or
may be prepared by the application or adaptation of known techniques.
Usually, the hydraulic antiwear additive used in the composition of the
invention is a hydraulic grade zinc dialkyldithiophosphate (ZDDP). "Hydraulic
grade" means that the antiwear component is suitable for use in hydraulic
applications, particularly with respect to their thermal stability. (ZDDPs)
which have
insufficient thermal stability tend to degrade rapidly to breakdown products
which
can be corrosive, in particular towards copper. This is a serious problem as
certain
hydraulic system components are made of this metal. Furthermore, the breakdown
products can cause sludge formation which in turn can result in filter
blocking. Thus,
not all types of ZDDPs are suitable for use in the present invention. Zinc
dihydrocarbyl dithiophosphates which may be used in the present invention are
well-
known in the art (see for example U.S. Pat. No. 4,101,429). Suitably the zinc
dihydrocarbyl dithiophosphate is a zinc dialkyl dithiophosphate typically
containing
about 4 to about 12 carbon atoms and more commonly about 6 to about 12 carbon
atoms in each alkyl group. Preferably each alkyl group contains about 8 to
about 12
carbon atoms. Examples of suitable alkyl moieties include butyl, sec-butyl,
isobutyl,
tert-butyl, pentyl, n-hexyl, sec-hexyl, n-octyl, 2-ethylhexyl, decyl and
dodecyl.
Preferably each alkyl moiety is 2-ethylhexyl. Zinc dialkyl dithiophosphates of
this
type are described in European patent application no. 95306722.0 and are
commercially available.
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_7_
The ZDDP may be used in the lubricant over a broad weight range. It is usual
however that the lubricant contains about 0.4 to about 0.9% by weight ZDDP.
Preferably, the fluid comprises 0.6% by weight ZDDP.
It is generally possible to characterise those ZDDPs which are useful in the
present invention by reference to their overbased to neutral ratio or by their
titratable
base number (TBN). Useful ZDDPs typically exhibit an overbased to neutral
ratio of
from 0.3:1 to 2:1, preferably 0.5:1 to 2: I. ZDDPs having an overbased to
neutral
ratio of about 1:1 are more commonly used. The ratio in question is determined
by
"P nmr. In terms of TBN, useful ZDDPs generally exhibit a minimum value of
about 10 mgKOH/g and preferably about 12 mgKOH/g. ZDDPs having a TBN of
about 15 mgKOH/g are more commonly used. TBN is determined in accordance
with ASTM D664.
Alternatively, it is generally possible to characterise ZDDPs which may be
used by reference to the thermal stability of the finished hydraulic fluid in
which they
are included. Here reference may be made to the ASTM D2619 and CCM "A"
thermal stability tests. To meet the requirements of the ASTM D2619 test the
finished fluid should give a maximum copper loss of 0.2 mg. To pass the CMC
"A"
test the finished fluid should give a maximum copper rod rating of 5 and a
maximum
sludge deposit of 25 mg/100 ml. The ASTM D2619 and CCM "A" tests are well
known in the art.
It is possible to further improve the thermal stability of the lubricant
composition by post-treatment of the ZDDP component using a zinc alkanoate.
Typically the alkanoate is branched on its (3-carbon atom. Such components are
also
described in European patent application no. 95306722Ø The use of zinc
octanoate
is preferred, especially an overbased zinc octanoate such as zinc octanoate
22%
which is commercially available under this designation.
In an embodiment of the invention the amine antioxidant is phenyl-a-
naphthylamine or 2,6-di-t-butyl-a-dimethylamino-p-cresol, alone or each in
combination with diphenylamine. Combinations based on phenyl-a-naphthylamine
and diphenylamine are preferred.
Preferred combinations of antioxidants include: phenyl-a-naphthylamine,
CA 02287726 1999-10-28
-8-
diphenylamine and an ashless dithiocarbamate, such as methylene-
bis(dibutyldithiocarbamate); phenyl-a-naphthylamine, diphenylamine and a
phenolic
antioxidant, such as 2,6-di-t-butylphenol; and phenyl-a-naphthylamine,
diphenylamine and a sulphurised olefin, such as one derived from a mixture of
C,~_n
isomerised a-olet7ns. In these combinations the phenyl-a-naphthylamine may be
replaced by 2,6-di-t-butyl-a-dimethylamino-p-cresol.
Lubricating oils contemplated for use in this invention include natural
lubricating oils, synthetic lubricating oils and mixtures thereof. Suitable
lubricating
oils also include basestocks obtained by isomerization of synthetic wax and
slack
wax, as well as basestocks produced by hydrocracking (rather than solvent
extracting) the aromatic and polar components of crude oil. In general, both
the
natural and synthetic lubricating oils will each have a kinematic viscosity
ranging
from about 1 x 10-6 m'-/s to about 40 x 10-6 m2/s (about 1 to about 40 cSt) at
100°C,
although typical applications will require each oil to have a viscosity
ranging from
about 2 x 10'6 m2/s to about 8 x 10'6 mz/s (about 2 to about 8 cSt) at
100°C.
Natural base oils include animal oils, vegetable oils (e.g., castor oil and
lard
oil), petroleum oils, mineral oils, and oils derived from coal or shale. The
preferred
natural base oil is mineral oil.
The mineral oils useful in this invention include all common mineral oil base
stocks. This would include oils that are naphthenic or paraffinic in chemical
structure. Oils that are refined by conventional methodology using acid,
alkali, and
clay or other agents such as aluminum chloride, or they may be extracted oils
produced, for example, by solvent extraction with solvents such as phenol,
sulphur
dioxide, furfural, dichlordiethyl ether, etc. They may be hydrotreated or
hydro-
refined, dewaxed by chilling or catalytic dewaxing processes, or hydrocracked.
The
mineral oil may be produced from natural crude sources or be composed of
isomerized wax materials or residues of other refining processes.
Typically the mineral oils will have kinematic viscosities of from 2 x 10-6
mz/s to 12 x 10-6 m2/s (2 cSt to 12 cSt) at 100°C. The preferred
mineral oils have
kinematic viscosities of from 3 x 10'6 mz/s to 10 x 10-6 mz/s (3 to 10 cSt),
and most
preferred are those mineral oils with viscosities of 5 x 10-6 mz/s to 9 x 10'6
mz/s (5 to
CA 02287726 1999-10-28
_y_
9 cSt) at 100°C.
Synthetic lubricating oils useful in this invention include hydrocarbon oils
and halo-substituted hydrocarbon oils such as oligomerized, polymerized, and
interpolymerized olefins [e.g., polybutylenes, polypropylenes, propylene,
isobutylene
copolymers, chlorinated polylactenes, poly(1-hexenes), poly(1-octenes), and
mixtures thereof]; alkylbenzenes [e.g., polybutylenes, polypropylenes,
propylene,
isobutylene copolymers, chlorinated polylactenes, poly( 1-hexenes), poly ( 1-
octenes)
and mixtures thereof]; alkylbenzenes [e.g., dodecyl-benzenes,
tetradecylbenzenes,
dinonyl-benzenes and di(2-ethylhexyl)benzene]; polyphenyls [e.g., biphenyls,
terphenyls, alkylated polyphenyls]; and alkylated diphenyl ethers, alkylated
diphenyl
sulphides, as well as their derivatives, analogs, and homologs thereof, and
the like.
The preferred synthetic oils are oligomers of a-olefins, particularly
oligomers of 1-
decene, also known as polyalpha olefins or PAO's.
Synthetic lubricating oils also include alkylene oxide polymers,
1 S interpolymers, copolymers, and derivatives thereof where the terminal
hydroxyl
groups have been modified by esterification or etherification. This class of
synthetic
oils is exemplified by: polyoxyalkylene polymers prepared by polymerization of
ethylene oxide or propylene oxide; the alkyl and aryl ethers of these
polyoxyalkylene
polymers (e.g., methyl-polyisopropylene glycol ether having an average
molecular
weight of 1000, diphenyl ether of polypropylene glycol having a molecular
weight of
100-1500); and mono- and poly-carboxylic esters thereof (e.g., the acetic acid
esters,
mixed C3-C8 fatty acid esters, and C,z oxo acid diester of tetraethylene
glycol).
Another suitable class of synthetic lubricating oils comprises the esters of
dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids
and alkenyl
succinic acids, malefic acid, azelaic acid, suberic acid, sebacic acid,
fumaric acid,
adipic acid, linoleic acid dimer, malonic acid, alkylmalonic acids and alkenyl
malonic acids) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol,
dodecyl
alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoethers
and
propylene glycol). Specific examples of these esters include dibutyl adipate,
di(2-
ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl
azelate,
diisodecyl azelate, dioctyl isophthalate, didecyl phthalate, dieicosyl
sebacate, the 2-
CA 02287726 1999-10-28
-l0-
ethylhexyl diester of linoleic acid dimer, and the complex ester formed by
reacting
one mole of sebacic acid with two moles of tetraethylene glycol and two moles
of 2-
ethyl-hexanoic acid. A preferred type of oil from this class of synthetic oils
are
adipates of Ca to C, Z alcohols.
Esters useful as synthetic lubricating oils also include those made from CS to
C,2 monocarboxylic acids and polyols and polyol ethers such as neopentyl
glycol,
trimethylolpropane pentaerythritol, dipentaerythritol and tripentaerythritol.
Silicon-based oils (such as the polyalkyl-, polyaryl-, polyalkoxy-, or
polyaryloxy-siloxane oils and silicate oils) comprise another useful class of
synthetic
lubricating oils. These oils include tetra-ethyl silicate, tetraisopropyl
silicate, tetra-
(2-ethylhexyl) silicate, tetra-(4-methyl-2-ethylhexyl) silicate, tetra-(p-tert-
butylphenyl) silicate, hexa-(4-methyl-2-pentoxy)-disiloxane, poly(dimethyl)-
siloxanes and poly (methylphenyl) siloxanes. Other synthetic lubricating oils
include
liquid esters of phosphorus containing acids (e.g., tricresyl phosphate,
trioctylphosphate, and diethyl ester of decylphosphonic acid), polymeric tetra-
hydrofurans and poly-a-olefins.
The lubricating base oils may be derived from refined, re-refined oils, or
mixtures thereof. Unrefined oils are obtained directly from a natural source
or
synthetic source (e.g., coal, shale, or tar sands bitumen) without further
purification
or treatment. Examples of unrefined oils include a shale oil obtained directly
from a
retorting operation, a petroleum oil obtained directly from distillation, or
an ester oil
obtained directly from an esterification process, each of which is then used
without
further treatment. Refined oils are similar to the unrefined oils except that
refined
oils have been treated in one or more purification steps to improve one or
more
properties. Suitable purification techniques include distillation,
hydrotreating,
dewaxing, solvent extraction, acid or base extraction, filtration, and
percolation, all
of which are known to those skilled in the art. Re-refined oils are obtained
by
treating used oils in processes similar to those used to obtain the refined
oils. These
re-refined oils are also known as reclaimed or reprocessed oils and are often
additionally processed by techniques for removal of spent additives and oils
breakdown products. White oils, as taught in U.S. 5,736,490 may also be used
as the
CA 02287726 1999-10-28
base oil, especially for turbine applications.
In an embodiment of the invention the base oil is a Group I, Group II or
Group III base oil. The use of Group II or Group III base oils is preferred.
The American Petroleum Institute has categorized these different basestock
j types as follows: Group I, >0.03 wt% sulphur, and/or <90 vol% saturates,
viscosity
index between 80 and 120; Group II, <_0.03 wt% sulphur, and >_ 90 vol%
saturates,
viscosity index between 80 and I20; Group III, <_ 0.03 wt% sulphur, and >_ 90
vol%
saturates, viscosity index > 120; Group IV, all polyalphaolefins. Hydrotreated
basestocks and catalytically dewaxed basestocks, because of their low sulphur
and
aromatics content, generally fall into the Group II and Group III categories.
Polyalphaolefins (Group IV basestocks) are synthetic base oils prepared from
various
a-olefins and are substantially free of sulphur and aromatics.
The lubricant composition of the present invention may be prepared by
simple blending of the various components with a suitable base oil.
For the sake of convenience, and in another embodiment of the present
invention, the additive components used in practice of this invention may be
provided as a concentrate for formulation into a lubricant composition ready
for use.
The concentrate may comprise, in addition to the fluid components, a solvent
or diluent for the fluid components. The solvent or diluent should be miscible
with
and/or capable of dissolving in the base oil to which the concentrate is to be
added.
Suitable solvents and diluents are well known. The solvent or diluent may be
the
base oil of the lubricating oil composition itself. The concentrate may
suitably
include any of the conventional additives used in lubricating oils
compositions. The
proportions of each component in the concentrate are controlled by the
intended
degree of dilution, though top treatment of the formulated fluid is possible.
Other additives commonly used in lubricants/fluids for turbine, antiwear
hydraulic and industrial applications may be included in the compositions or
concentrates of the present invention. These include demulsifiers, corrosion
inhibitors, dispersants, sulphur- and/or phosphorus-containing antiwear agents
and
rust inhibitors. These additives, when present, are used in amounts
conventionally
used in such applications. Some additives may be included in the concentrate
and
CA 02287726 1999-10-28
-12-
some added to the fully formulated lubricant/fluid as a top-treat.
The invention will now be illustrated by the following Examples that are not
intended to limit the scope of the invention in any way.
EXAMPLES
A lubricant composition was prepared by blending components in the
proportions specified in the following table.
Component % by weight
Corrosion inhibitor0.0085
Detergent 0.050
Rust inhibitor 0.051
Phenolic antioxidant0.013
Demulsifier 0.0064
Process oil 0.0111
*ZDDP 0.510
Base oil Balance to 100%
The ZDDP was zinc di(2-ethylhexyl)dithiophosphate.
The base oil used was either a Group I or Group II base oil. Further details
of
this are given in the following table.
To this lubricant composition was blended various additional components at
the concentrations) listed in the following table. The resulting lubricant
compositions were then tested in the CCM "A", NOC and RBOT tests. The results
are also shown in the following table.
CA 02287726 1999-10-28
-l3-
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O
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O
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y1 i O n i n , ~, .-~N ~!1
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CA 02287726 1999-10-28
-14-
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CA 02287726 1999-10-28
-1S-
NOTES
The Group I base oil was Texaco ISO 46. The Group II base oil was RLOP
ISO 46. In Runs 8-l 1 the sulphurised phenolic compound was thioethylene-
bis(3,5-
S di-t-butyl-4-hydroxyhydro cinnamate). In Runs 12-1S a different sulphurised
phenolic compound was used. The sulphurised olefin was a commercially
available
one derived from a mixture of C,b_,8 isomerised a-olefins. The ashless
dithiocarbamate was methylene-bis(dibutyldithiocarbamate).
The NOC test was carried out as follows. To each of four SO ml beakers
added 4S g of test oil and an eighth length of a Copper/Iron coil used for
ASTM
D943. The beakers were stored in an oven at 140°C and after 4, 6, 8 and
10 days, the
beaker removed from the oven and the test oil analysed [for colour (ASTM D 1
S00)]
and sludge content (0.8mm filter). The 10 day sludge results are given as mg
sludge
per 100 ml oil.
1S Thermal stability was also assessed using the Cincinnati Milacron Thermal
Stability test, procedure A (CCM "A") which runs for 168 hours at
13S°C with
copper and iron rods.
The RBOT was performed in accordance with ASTM D2272. The test
measures oxidation life in minutes and can be used as an indicator of
oxidation
performance in the ASTM D943 (TOST) test.
In the table low sludge in the NOC test after 10 days using a Group I
basestock and a high RBOT result (greater than S00 minutes) using a Group II
basestock are illustrative of antioxidants which impart the desired
combination of
thermal stability and oxidation stability.
2S In Run 1 the additive pack is used in a Group I basestock. A significant
amount of sludge is formed resulting in filter blocking in the NOC test. In
Runs 2-1S
various antioxidants and combinations of antioxidants are employed. However,
in
these Runs either filter blocking occurs when a Group I basestock is used
and/or the
RBOT results are insufficiently low (less than S00 minutes) when a Group II
basestock is used. The antioxidants) used in Runs 2-1S do not provide the
desired
combination of thermal stability (in a Group I basestock) and oxidative
stability (in a
CA 02287726 1999-10-28
-16-
Group II basestock).
In contrast, Runs 16-23 are illustrative of the present invention. In these
Runs
antioxidant combinations are employed which give extended oxidation stability
in
the Group II basestock without excessive sludge formation when a Group I
basestock
is used. The results for Runs 16-19 show that addition of an ashless
dithiocarbamate
can extend the oxidative stability of the combination diphenylamine and phenyl-
a-
napthylamine without excessive sludge formation. The same is true for the use
of
2,6-di-t-butyl phenol (Runs 20 and 21) and sulphurised olefin (Runs 22 and
23). The
results for these Runs suggest that there is some kind of synergy between the
individual antioxidants used.
These results confirm that the selection of antioxidants in accordance with
the
present invention provides antioxidant system that allows extended oxidation
stability in Group II basestocks without excessive sludge formation when a
Group I
or II basestock is used.
