Note: Descriptions are shown in the official language in which they were submitted.
MARINE ENGINE LUBRICATING OIL COMPRISING A POLYMER
COMPRISING A CORE AND A PLURALITY OF POLYMERIC ARMS
EXTENDING THEREFROM
FIELD OF THE INVENTION
This invention relates to the lubrication of 2-stroke and 4-stroke marine
diesel
internal combustion engines, the former usually being referred to as cross-
head engines
and the latter as trunk piston engines. Respective lubricants therefor are
usually known as
marine diesel cylinder lubricants ("MDCL's") and trunk piston engine oils
("TPEO's").
BACKGROUND OF THE INVENTION
Cross-head engines are slow engines with a high to very high power range. They
include two separately-lubricated parts: the piston/cylinder assembly
lubricated with total-
loss lubrication by a highly viscous oil (an MDCL); and the crankshaft
lubricated by a less
viscous lubricant, usually referred to as a system oil.
Trunk piston engines may be used in marine, power-generation and rail traction
applications and have a higher speed than cross-head engines. A single
lubricant (TPEO)
is used for crankcase and cylinder lubrication. All major moving parts of the
engine, i.e.
the main and big end bearings, camshaft and valve gear, are lubricated by
means of a
pumped circulation system. The cylinder liners are lubricated partially by
splash
lubrication and partially by oil from the circulation systems that finds its
way to the
cylinder wall through holes in the piston skirt via the connecting rod and
gudgeon pin.
It is known in the art to include brightstock in MDCL's and TPEO's,
brightstock
being a high viscosity oil that is highly refined and dewaxed and that is
produced from
residual stocks or bottoms. It may, for example, have a kinematic viscosity at
100 C of
greater than 25, usually greater than 30, mm2s1, such as a solvent-extracted,
de-asphalted
product from vacuum residuum generally having a kinematic viscosity at 100 C
of 28-36
MM2S-1.
Brightstock is however expensive and art describes ways of replacing it. WO
99/64543 describes MDCL's formulated without brightstock and US 2008/0287329
describes a TPEO containing little or no brightstock.
A problem in the art is to formulate brightstock-free MDCL's and TPEO's at
reduced cost. A further problem in the art is to formulate brightstock-free
MDCL's and
TPEO's at reduced cost and at the same time provide improved antiwear
properties.
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SUMMARY OF THE INVENTION
It is now found that the use of star polymers such as amorphous styrene-diene
copolymer in an MDCL or a TPEO enables the above problem to be overcome.
Thus, the present invention provides a two-stroke or four-stroke marine engine
lubricating oil composition comprising an oil of lubricating viscosity in a
major amount
and
(A) additives, in respective minor amounts; and
(B) a viscosity modifier in the form of a polymer comprising a core and a
plurality of polymeric arms extending therefrom, in an amount in the range of
0.05 -6
mass%,
wherein the composition includes less than 0.5 mass%, preferably less than 0.1
mass%, of
brightstock; preferably brightstock is completely or substantially absent from
the
composition.
In further aspects the present invention comprises:-
the use of a viscosity modifier (B) to improve the anti-wear properties of a
marine
diesel cylinder lubricant or a trunk piston engine oil which includes less
than 0.5 mass%,
preferably less than 0.1 mass%, of brightstock; preferably brightstock is
absent or is
substantially absent from the marine diesel cylinder lubricant or the trunk
piston engine
oil;
a method of lubricating a cross-head marine diesel engine comprising supplying
the composition to the piston/cylinder assembly of the engine;
a method of lubricating a trunk piston marine diesel engine comprising
supplying
the composition to the engine; and
a method of, or for, reducing the amount of brightstock in a two-stroke or
four-
stroke marine engine lubricating oil composition comprising an oil of
lubricating viscosity
in a major amount and (A) additives, in respective minor amounts; the method
comprising
the step of replacing, in part or in full, the brightstock with (B) a
viscosity modifier in the
form of a polymer comprising a core and a plurality of polymeric arms
extending
therefrom, in an amount in the range of 0.05 to 6 mass %.
In this specification, the following words and expressions, if and when used,
have
the meanings ascribed below:
"active ingredients" or "(a.i.)" refers to additive material that is not
diluent or
solvent;
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"comprising" or any cognate word specifies the presence of stated features,
steps,
or integers or components, but does not preclude the presence or addition of
one or more
other features, steps, integers, components or groups thereof; the expressions
"consists of"
or "consists essentially of' or cognates may be embraced within "comprises" or
cognates,
wherein "consists essentially of" permits inclusion of substances not
materially affecting
the characteristics of the composition to which it applies;
"major amount" means 40 or 50 mass % or more of a composition;
"minor amount" means less than 50 mass % of a composition;
"TBN" means total base number as measured by ASTM D2896.
Furthermore in this specification, if and when used:
"calcium content" is as measured by ASTM 4951;
"phosphorus content" is as measured by ASTM D5185;
"sulphated ash content" is as measured by ASTM D874;
"sulphur content" is as measured by ASTM D2622;
"KV100" means kinematic viscosity at 100 C as measured by ASTM D445.
Also, it will be understood that various components used, essential as well as
optimal and customary, may react under conditions of formulation, storage or
use and that
the invention also provides the product obtainable or obtained as a result of
any such
reaction.
Further, it is understood that any upper and lower quantity, range and ratio
limits
set forth herein may be independently combined.
DETAILED DESCRIPTION OF THE INVENTION
The features of the invention will now be discussed in more detail below.
OIL OF LUBRICATING VISCOSITY
The lubricant composition contains a major proportion of an oil of lubricating
viscosity. Such lubricating oils may range in viscosity from light distillate
mineral oils to
heavy lubricating oils. Generally, the viscosity of the oil ranges from 2 to
40, such as 3 to
15, mm2/sec, as measured at 100 C, and a viscosity index of 80 to 100, such as
90 to 95.
The lubricating oil may comprise greater than 60, typically greater than 70.
mass % of the
composition.
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Natural oils include animal oils and vegetable oils (e.g., castor oil, lard
oil); liquid
petroleum oils and hydrorefined, solvent-treated or acid-treated mineral oils
of the
paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of
lubricating viscosity
derived from coal or shale also serve as useful base oils.
Synthetic lubricating oils include hydrocarbon oils and halo-substituted
hydrocarbon oils such as polymerized and interpolymerized olefins (e.g.,
polybutylencs,
polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes,
poly(1-
hexenes), poly(1-octenes), poly(1-decenes)); alkybenzenes (e.g.,
dodecylbenzenes,
tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes); polyphenyls
(e.g.,
biphenyls, terphenyls, alkylated polyphenols); and alkylated diphenyl ethers
and alkylated
diphenyl sulphides and derivative, analogues and homologues thereof.
Alkylene oxide polymers and interpolymers and derivatives thereof where the
terminal hydroxyl groups have been modified by esterification, etherifieation,
etc.,
constitute another class of known synthetic lubricating oils. These are
exemplified by
polyoxyalkylene polymers prepared by polymerization of ethylene oxide or
propylene
oxide, and the alkyl and aryl ethers of polyoxyalkylene polymers (e.g., methyl-
polyiso-
propylene glycol ether having a molecular weight of 1000 or diphenyl ether of
poly-
ethylene glycol having a molecular weight of 1000 to 1500); and mono- and
polycarboxylic esters thereof, for example, the acetic acid esters, mixed C3-
C8 fatty acid
esters and C13 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, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric
acid, adipic
acid, linoleic acid dimer, malonic acid, alkylmalonic acids, alkenyl malonic
acids) with a
variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-
ethylhexyl
alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol).
Specific
examples of such esters includes dibutyl adipate, di(2-ethylhexyl) sebacate,
di-n-hexyl
fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl
phthalate, didecyl
phthalate, dieicosyl sebacate, the 2-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-ethylhexanoic acid.
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Esters useful as synthetic oils also include those made from C5 to C12
monocarboxylic acids and polyols and polyol esters such as neopentyl glycol,
trimethylolpropane, pentaerythritol, dipentaerythritol and tripentaerythritol.
Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- or
polyaryloxysilicone oils and silicate oils comprise another useful class of
synthetic
lubricants; such oils include tetraethyl silicate, tetraisopropyl silicate,
tetra-(2-
ethylhexyl)silicate, tetra-(4-methyl-2-ethylhexyl)silicate, tetra-(p-tert-
butyl-phenyl)
silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl)siloxanes and
poly(methylphenyl)siloxanes. Other synthetic lubricating oils include liquid
esters of
phosphorus-containing acids (e.g., tricresyl phosphate, trioctyl phosphate,
diethyl ester of
decylphosphonic acid) and polymeric tetrahydrofurans.
Unrefined, refined and re-refined oils can be used in lubricants of the
present
invention. Unrefined oils are those obtained directly from a natural or
synthetic source
without further purification treatment. For example, a shale oil obtained
directly from
retorting operations; petroleum oil obtained directly from distillation; or
ester oil obtained
directly from esterification and used without further treatment are unrefined
oils.
Marine Diesel Cylinder Lubricant ("MDCL")
An MDCL may employ 10-35, preferably 13-30, most preferably 16-24, mass % of
a concentrate or additive package, the remainder being base stock. It
preferably includes
at least 50, more preferably at least 60, even more preferably at least 70,
mass % of oil of
lubricating viscosity based on the total mass of MDCL. Preferably, the MDCL
has a
compositional TBN (using ASTM D2896) of 40-100, such as 50-60.
The following may be mentioned as examples of typical proportions of additives
in
an MDCL.
Additive Mass% a.i. Mass % a.i.
(Broad) (Preferred)
detergent(s) 1-20 3-15
dispersant(s) 0.5-5 1-3
anti-wear agent(s) 0.1-1.5 0.5-1.3
pour point dispersant 0.03-1.15 0.05-0.1
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base stock balance balance
Trunk Piston Engine Oil ("TPEO")
A TPEO may employ 7-35, preferably 10-28, more preferably 12-24, mass % of a
concentrate or additives package, the remainder being base stock. Preferably,
the TPEO
has a compositional TBN (using D2896) of 25-60, such as 25-55.
The following may be mentioned as typical proportions of additives in a TPEO.
Additive Mass% a.i. Mass % a.i.
(Broad) (Preferred)
detergent(s) 0.5-12 2-8
dispersant(s) 0.5-5 1-3
anti-wear agent(s) 0.1-1.5 0.5-1.3
oxidation inhibitor 0.2-2 0.5-1.5
rust inhibitor 0.03-0.15 0.05-0.1
pour point dispersant 0.03-1.15 0.05-0.1
base stock balance balance
When a plurality of additives is employed it may be desirable, although not
essential, to prepare one or more additive packages comprising the additives,
whereby
several additives can be added simultaneously to the base oil to form the
lubricating oil
composition. Dissolution of the additive package(s) into the lubricating oil
may be
facilitated by solvents and by mixing accompanied with mild heating, but this
is not
essential. The additive package(s) will typically be formulated to contain the
additive(s)
in proper amounts to provide the desired concentration, and/or to carry out
the intended
function, in the final formulation when the additive package(s) is/are
combined with a
predetermined amount of base lubricant. Thus, compounds in accordance with the
present
invention may be admixed with small amounts of base oil or other compatible
solvents
together with other desirable additives to form additive packages containing
active
ingredients.
More detailed description of additive components is given below.
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Detergents
A detergent is an additive that reduces formation of deposits, for example,
high-
temperature varnish and lacquer deposits, in engines; it has acid-neutralising
properties
and is capable of keeping finely divided solids in suspension. It is based on
metal "soaps",
that is metal salts of acidic organic compounds, sometimes referred to as
surfactants.
A detergent comprises a polar head with a long hydrophobic tail. Large amounts
of a metal base are included by reacting an excess of a metal compound, such
as an oxide
or hydroxide, with an acidic gas such as carbon dioxide to give an overbased
detergent
which comprises neutralised detergent as the outer layer of a metal base (e.g.
carbonate)
micelle.
The detergent is preferably an alkali metal or alkaline earth metal additive
such as
an overbased oil-soluble or oil-dispersible calcium, magnesium, sodium or
barium salt of a
surfactant selected from phenol, sulphonic acid, carboxylic acid, salicylic
acid and
naphthenic acid, wherein the overbasing is provided by an oil-insoluble salt
of the metal,
e.g. carbonate, basic carbonate, acetate, formate, hydroxide or oxalate, which
is stabilised
by the oil-soluble salt of the surfactant. The metal of the oil-soluble
surfactant salt may be
the same or different from that of the metal of the oil-insoluble salt.
Preferably the metal,
whether the metal of the oil-soluble or oil-insoluble salt, is calcium.
The TBN of the detergent may be low, i.e. less than 50 mg KOH/g, medium, i.e.
50-150 mg KOH/g, or high, i.e. over 150 mg KOH/g, as determined by ASTM D2896.
Preferably the TBN is medium or high, i.e. more than 50 TBN. More preferably,
the TBN
is at least 60, more preferably at least 100, more preferably at least 150,
and up to 500,
such as up to 350 mg KOH/g, as determined by ASTM D2896.
Anti-oxidants
The trunk piston diesel engine lubricant composition may include at least one
anti-
oxidant. The anti-oxidant may be aminic or phenolic. As examples of amines
there may
be mentioned secondary aromatic amines such as diarylamines, for example
diphenylamines wherein each phenyl group is alkyl-substituted with an alkyl
group having
4 to 9 carbon atoms. As examples of anti-oxidants there may be mentioned
hindered
phenols, including mono-phenols and bis-phenols.
Preferably, the anti-oxidant, if present, is provided in the composition in an
amount
of up to 3 mass %, based on the total amount of the lubricant composition.
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Other additives such as pour point depressants, anti-foamants, metal rust
inhibitors,
pour point depressants and/or demulsifiers may be provided, if necessary.
The terms 'oil-soluble' or 'oil-dispersable' as used herein do not necessarily
indicate that the compounds or additives are soluble, dissolvable, miscible or
capable of
being suspended in the oil in all proportions. These do mean, however, that
they are, for
instance, soluble or stably dispersible in oil to an extent sufficient to
exert their intended
effect in the environment in which the oil is employed. Moreover, the
additional
incorporation of other additives may also permit incorporation of higher
levels of a
particular additive, if desired.
The lubricant compositions of this invention comprise defined individual (i.e.
separate) components that may or may not remain the same chemically before and
after
mixing.
It may be desirable, although not essential, to prepare one or more additive
packages or concentrates comprising the additives, whereby the additives can
be added
simultaneously to the oil of lubricating viscosity to form the lubricating oil
composition.
Dissolution of the additive package(s) into the lubricating oil may be
facilitated by
solvents and by mixing accompanied with mild heating, but this is not
essential. The
additive package(s) will typically be formulated to contain the additive(s) in
proper
amounts to provide the desired concentration, and/or to carry out the intended
function in
the final formulation when the additive package(s) is/are combined with a
predetermined
amount of base lubricant.
Thus, the additives may be admixed with small amounts of base oil or other
compatible solvents together with other desirable additives to form additive
packages
containing active ingredients in an amount, based on the additive package, of,
for example,
from 2.5 to 90, preferably from 5 to 75, most preferably from 8 to 60, mass %
of additives
in the appropriate proportions, the remainder being base oil.
The final formulations may typically contain about 5 to 40 mass % of the
additive
packages(s), the remainder being base oil.
VISCOSITY MODIFIER
In this invention, as stated above, a viscosity modifier (B) is additionally
provided.
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This invention employs polymers comprising a core and a plurality of polymeric
arms extending from the core. Such polymers are known as star-shaped polymers
(or star
or radial polymers). Examples of ranges of (B) in the composition include 0.1
¨6, 0.1 ¨ 5,
0.1 ¨4,0.1-3, mass % and a lower limit of 1 mass %.
The viscosity modifier may comprise at least one star-shaped, at least
partially
hydrogenated, polymer derivable, at least in part, from the polymerisation of
one or more
conjugated diene monomers as defined hereinbefore. Suitably, the star-shaped
polymer
includes multiple arms extending from a central core; the arms being derived
from the
polymerisation of one or more conjugated diene monomers as defined
hereinbeforc, and
optionally a vinyl aromatic hydrocarbon monomer as defined hereinbefore.
The arms of the star polymer may be a homopolymer derived essentially from the
polymerisation of a single conjugated diene monomer as defined herein, such as
isoprene
or 1,3-butadiene, particularly isoprene.
Alternatively, the arms of the star polymer may be a copolymer derived
essentially
from the polymerisation of two or more conjugated diene monomers as defined
herein,
such as an isoprene and 1,3-butadiene copolymer, or a copolymer derived
essentially from
the polymerisation of one or more conjugated diene monomers as defined herein
and a
vinyl aromatic hydrocarbon monomer as defined herein, such as an isoprene-
styrene
copolymer, a butadiene-styrene copolymer or an isoprene-butadiene-styrene
copolymer.
As used herein in connection with polymer composition, "derived essentially"
permits the inclusion of other substances not materially affecting the
characteristics of the
polymer to which it applies. Preferably, "derived essentially" means the
specified
monomer and comonomers, in the case of a copolymer, are present in an amount
of at
least 90 %, more preferably 95 %, even more preferably greater than 99 % by
mass of the
polymer.
The arms of the star polymer may also be a block copolymer, preferably a
linear
block copolymer, more preferably a linear diblock copolymer, such as one
represented by
the following general formula:
Az-(B-A)y-Bõ
wherein:
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A is a polymeric block derived predominantly from vinyl aromatic hydrocarbon
monomer;
B is a polymeric block derived predominantly from conjugated diene monomer;
x and z are, independently, a number equal to 0 or 1; and
y is a whole number ranging from 1 to about 15.
The arms of the star polymer may also be a tapered linear block copolymer such
as
one represented by the following general formula:
A-A/B-B
wherein:
A is a polymeric block derived predominantly from vinyl aromatic hydrocarbon
monomer;
B is a polymeric block derived predominantly from conjugated diene monomer;
and
A/B is a tapered segment derived from both vinyl aromatic hydrocarbon monomer
and conjugated diolefin monomer.
Preferably, the arms of the star polymer comprise a hydrogenated isoprene-
butadiene copolymer, a hydrogenated styrene-isoprene-butadiene copolymer, a
hydrogenated isoprene-styrene copolymer or a hydrogenated butadiene-styrene
copolymer.
Most preferably, the arms of the star polymer comprise a linear diblock
copolymer
as defined herein. Preferably, the linear diblock copolymer comprises at least
one block
derivable predominantly from a vinyl aromatic hydrocarbon monomer as defined
herein
and at least one block derivable predominantly from one or more conjugated
diene
monomers as defined herein. Preferably, the vinyl aromatic hydrocarbon monomer
comprises styrene. Preferably, the one or more conjugated diene monomers
comprise
isoprene, butadiene or a mixture thereof. Most preferably, the linear diblock
copolymer is
at least partially hydrogenated.
Preferably, the at least one block derivable predominantly from a vinyl
aromatic
hydrocarbon monomer (e.g. styrene) in the linear diblock copolymer is present
in an
amount of up to 35 %, even more preferably up to 25 %, most preferably 5 to 25
%, by
mass based on the total mass of the linear diblock copolymer.
CA 02799597 2012-12-21
Preferably, the at least one block derivable from predominantly from one or
more
conjugated diene monomers is present in an amount of greater than 65 %, even
more
preferably greater than or equal to 75 %, most preferably 75 to 95 %, by mass
based on the
total mass of the linear diblock copolymer.
Preferably, the linear diblock copolymer comprises at least one polystyrene
block
and a block derived from isoprene, butadiene, or a mixture thereof. Highly
preferred
linear diblock copolymers comprise linear diblock copolymers including at
least one linear
diblock copolymer selected from hydrogenated styrene/isoprene diblock
copolyrners,
hydrogenated styrene/butadiene diblock copolymers and hydrogenated
styrene/isoprene-
butadiene diblock copolymers.
Preferably, when the linear diblock copolymer comprises at least one isoprene-
butadiene block the block is derived predominantly from 70 to 90 mass %
isoprene
monomers and 30 to 10 mass % 1,3-butadiene monomers.
The arms of the star polymer typically comprise a copolymer derived from 70 to
90 mass % isoprene monomers and 30 to 10 mass % 1,3-butadiene monomers. More
preferably, the arms of the star polymer further include a vinyl aromatic
hydrocarbon
monomer as defined herein, particularly styrene. A highly preferred copolymer
is derived
from isoprene monomers, 1,3-butadiene monomers and a vinyl aromatic
hydrocarbon
monomer, especially styrene. The vinyl aromatic hydrocarbon monomer may be
present
in an amount of up to 35 mass %, preferably up to 25 mass %, based on the
total mass of
the copolymer.
Preferably, the arms of the star polymer are formed via anionic polymerization
to
form a living polymer. Anionic polymerization has been found to provide
copolymers
having a narrow molecular weight distribution (Mw/Mn), such as a molecular
weight
distribution of less than about 1.2
As is well known, and disclosed, for example, in U.S. Patent No. 4,116,917,
living
polymers may be prepared by anionic solution polymerization of a mixture of
the
conjugated diene monomers in the presence of an alkali metal or an alkali
metal
hydrocarbon, e.g., sodium naphthalene, as anionic initiator. The preferred
initiator is
lithium or a monolithium hydrocarbon. Suitable lithium hydrocarbons include
unsaturated
compounds such as ally! lithium, methallyl lithium; aromatic compounds such as
phenyl
lithium, the tolyl lithiums, the xylyl lithiums and the naphthyl lithiums, and
in particular,
the alkyl lithiums such as methyl lithium, ethyl lithium, propyl lithium,
butyl lithium. amyl
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lithium, hexyl lithium, 2-ethylhexyl lithium and n-hexadecyl lithium.
Secondary-butyl
lithium is the preferred initiator. The initiator(s) may be added to the
polymerization
mixture in two or more stages, optionally together with additional monomer.
The living
polymers are olefinically unsaturated.
The solvents in which the living polymers are formed are inert liquid
solvents,
such as hydrocarbons e.g., aliphatic hydrocarbons such as pentane, hexane,
heptane,
octane, 2-ethylhexane, nonane, decane, cyclohexane, methylcyclohexane, or
aromatic
hydrocarbons e.g., benzene, toluene, ethylbenzene, the xylenes,
diethylbenzenes,
propylbenzenes. Cyclohexane is preferred. Mixtures of hydrocarbons e.g.,
lubricating
oils, may also be used.
The temperature at which the polymerization is conducted may be varied within
a
wide range, such as from about -50 C to about 150 C, preferably from about 20
C to
about 80 C. The reaction is suitably carried out in an inert atmosphere, such
as nitrogen,
and may optionally be carried out under pressure e.g., a pressure of from
about 0.5 to
about 10 bars.
The concentration of the initiator used to prepare the living polymer may also
vary
within a wide range and is determined by the desired molecular weight of the
living
polymer.
To form the star polymer, the living polymers formed via the foregoing process
are
reacted in an additional reaction step, with a polyalkenyl coupling agent.
Polyalkenyl
coupling agents capable of forming star polymers have been known for a number
of years
and are described, for example, in U.S. Patent No. 3,985,830. Polyalkenyl
coupling agents
are conventionally compounds having at least two non-conjugated alkenyl
groups. Such
groups are usually attached to the same or different electron-withdrawing
moiety e.g. an
aromatic nucleus. Such compounds have the property that at least of the
alkenyl groups
are capable of independent reaction with different living polymers and in this
respect are
different from conventional conjugated diene polymerizable monomers such as
butadiene,
isoprene, etc. Pure or technical grade polyalkenyl coupling agents may be
used. Such
compounds may be aliphatic, aromatic or heterocyclic. Examples of aliphatic
compounds
include the polyvinyl and polyallyl acetylene, diacetylenes, phosphates and
phosphates as
well as dimethacrylates, e.g. ethylene dimethylacrylate. Examples of suitable
heterocyclic
compounds include divinyl pyridine and divinyl thiophene.
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The preferred coupling agents are polyalkenyl aromatic compounds and most
preferred are the polyvinyl aromatic compounds. Examples of such compounds
include
those aromatic compounds, e.g. benzene, toluene, xylene, anthracene,
naphthalene and
durene, which are substituted with at least two alkenyl groups, preferably
attached directly
thereto. Specific examples include the polyvinyl benzenes e.g. divinyl,
trivinyl and
tetravinyl benzenes; divinyl, trivinyl and tetravinyl ortho-, meta- and para-
xylenes, divinyl
naphthalene, divinyl ethyl benzene, divinyl biphenyl, diisobutenyl benzene,
diisopropenyl
benzene, and diisopropenyl biphenyl. The preferred aromatic compounds are
those
represented by the formula A-(CII¨C112)õ wherein A is an optionally
substituted aromatic
nucleus and x is an integer of at least 2. Divinyl benzene, in particular meta-
divinyl
benzene, is the most preferred aromatic compound. Pure or technical grade
divinyl
benzene (containing other monomers e.g. styrene and ethyl styrene) may be
used. The
coupling agents may be used in admixture with small amounts of added monomers
which
increase the size of the nucleus, e.g. styrene or alkyl styrene. In such a
case, the nucleus
can be described as a poly(dialkenyl coupling agent/monoalkenyl aromatic
compound)
nucleus, e.g. a poly(divinylbenzene/monoalkenyl aromatic compound) nucleus.
The polyalkenyl coupling agent should be added to the living polymer after the
polymerization of the monomers is substantially complete, i.e. the agent
should be added
only after substantially all the monomer has been converted to the living
polymers.
The amount of polyalkenyl coupling agent added may vary within a wide range,
but preferably, at least 0.5 mole of the coupling agent is used per mole of
unsaturated
living polymer. Amounts of from about 1 to about 15 moles, preferably from
about 1.5 to
about 5 moles per mole of living polymer are preferred. The amount, which can
be added
in two or more stages, is usually an amount sufficient to convert at least
about 80 mass %
to 85 mass % of the living polymer into star-shaped polymer.
The coupling reaction can be carried out in the same solvent as the living
polymerization reaction. The coupling reaction can be carried out at
temperatures within a
broad range, such as from 0 C to 150 C, preferably from about 20 C to about
120 C. The
reaction may be conducted in an inert atmosphere, e.g. nitrogen, and under
pressure of
from about 0.5 bar to about 10 bars.
The star polymers thus formed are characterized by a dense centre or nucleus
of
erosslinked poly(polyalkenyl coupling agent) and a number of arms of
substantially linear
13
=
unsaturated polymers extending outwardly from the nucleus. The number of arms
may
vary considerably, but is typically between about 4 and 25.
The resulting star polymers can then be hydrogenated using any suitable means.
A
hydrogenation catalyst may be used e.g. a copper or molybdenum compound.
Catalysts
containing noble metals, or noble metal-containing compounds, can also be
used.
Preferred hydrogenation catalysts contain a non-noble metal or a non-noble
metal-
containing compound of Group VIII of the periodic Table i.e., iron, cobalt,
and
particularly, nickel. Specific examples of preferred hydrogenation catalysts
include
RaneyTM nickel and nickel on kieselguhr. Particularly suitable hydrogenation
catalysts arc
those obtained by causing metal hydrocarbyl compounds to react with organic
compounds
of any one of the group VIII metals iron, cobalt or nickel, the latter
compounds containing
at least one organic compound that is attached to the metal atom via an oxygen
atom as
described, for example, in U.K. Patent No. 1,030,306. Preference is given to
hydrogenation catalysts obtained by causing an aluminium trialkyl (e.g.
aluminium diethyl
(Al(Et3)) or aluminium triisobutyl) to react with a nickel salt of an organic
acid (e.g. nickel
diisopropyl salicylate, nickel naphthenate, nickel 2-ethyl hexanoate, nickel
di-tert-butyl
benzoate, nickel salts of saturated monocarboxylic acids obtained by reaction
of olefins
having from 4 to 20 carbon atoms in the molecule with carbon monoxide and
water in the
presence of acid catalysts) or with nickel enolates or phenolates (e.g.,
nickel
acetonylacetonate, the nickel salt of butylacetophenone). Suitable
hydrogenation catalysts
will be well known to those skilled in the art and the foregoing list is by no
means
intended to be exhaustive.
The hydrogenation of the star polymer is suitably conducted in solution, in a
solvent which is inert during the hydrogenation reaction. Saturated
hydrocarbons and
mixtures of saturated hydrocarbons are suitable. Advantageously, the
hydrogenation
solvent is the same as the solvent in which polymerization is conducted.
Suitably, at least
50%, preferably at least 70%, more preferably at least 90%, most preferably at
least 95%
by mass of the original olefinic unsaturation is hydrogenated.
The hydrogenated star polymer may then be recovered in solid form from the
solvent in which it is hydrogenated by any convenient means, such as by
evaporating the
solvent. Alternatively, oil e.g. lubricating oil, may be added to the
solution, and the
solvent stripped off from the mixture so formed to provide a concentrate.
Suitable
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CA 02799597 2012-12-21
=
concentrates contain from about 3 mass % to about 25 mass %, preferably from
about 5
mass % to about 15 mass % of the hydrogenated star polymer VI improver.
The star polymers useful in the practice of the present invention can have a
number
average molecular weight of from about 10,000 to 700,000, preferably from
about 30,000
to 500,000. The term "number average molecular weight", as used herein, refers
to the
number average weight as measured by Gel Permeation Chromatography ("GPC")
with a
polystyrene standard, subsequent to hydrogenation. It is important to note
that, when
determining the number average molecular weight of a star polymer using this
method. the
calculated number average molecular weight will be less than the actual
molecular weight
due to the three dimensional structure of the star polymer.
In one preferred embodiment, the star polymer of the present invention is
derived
from about 75 % to about 90 % by mass isoprene and about 10 % to about 25 % by
mass
butadiene, and greater than 80 % by mass of the butadiene units are
incorporated 1,4-
addition product. In another preferred embodiment, the star polymer of the
present
invention comprises amorphous butadiene units derived from about 30 to about
80 % by
mass 1,2-, and from about 20 to about 70 % by mass 1,4-incorporation of
butadiene. In
another preferred embodiment, the star polymer is derived from isoprene,
butadiene, or a
mixture thereof, and further contains from about 5 to about 35 % by mass
styrene units.
Typically, the star polymer has a Shear Stability Index (SSI) of from about 1
% to
35 % (30 cycle). An example of a commercially available star polymer VI
improver
having an SSI equal to or less than 35 is Infineum SV200TM, available from
Infineum USA
L.P. and Infineum UK Ltd. Other examples of commercially available star
polymer VI
improver having an SSI equal to or less than 35 include Infineum SV25OTM,
Infineum
SV261TM and Infineum SV27OTM, also available from Infineum USA L.P. and
Infineum
UK Ltd.
Typically, the viscosity modifier may be provided in an amount of from 0.01 to
20,
preferably Ito 15, mass % based on the mass of the lubricating oil
composition.
Optionally, one or both types of viscosity modifiers used in the practice of
the
invention can be provided with nitrogen-containing functional groups that
impart
dispersant capabilities to the VI improver. One trend in the industry has been
to use such
"multifunctional" VI improvers in lubricants to replace some or all of the
dispersant.
Nitrogen-containing functional groups can be added to a polymeric VI improver
by
grafting a nitrogen- or hydroxyl- containing moiety, preferably a nitrogen-
containing
CA 02799597 2012-12-21
moiety, onto the polymeric backbone of the VI improver (functionalizing).
Processes for
the grafting of a nitrogen-containing moiety onto a polymer are known in the
art and
include, for example, contacting the polymer and nitrogen-containing moiety in
the
presence of a free radical initiator, either neat, or in the presence of a
solvent. The free
radical initiator may be generated by shearing (as in an extruder) or heating
a free radical
initiator precursor, such as hydrogen peroxide.
The amount of nitrogen-containing grafting monomer will depend, to some
extent,
on the nature of the substrate polymer and the level of dispersancy required
of the grafted
polymer. To impart dispersancy characteristics to both star and linear
copolymers, the
amount of grafted nitrogen-containing monomer is suitably between about 0.4
and about
2.2 mass %, preferably from about 0.5 to about 1.8 mass %, most preferably
from about
0.6 to about 1.2 mass %, based on the total weight of grafted polymer.
Methods for grafting nitrogen-containing monomer onto polymer backbones, and
suitable nitrogen-containing grafting monomers are known and described, for
example, in
U.S. Patent No. 5,141,996, WO 98/13443, WO 99/21902, U.S. Patent No.
4,146,489, U.S.
Patent No. 4,292,414, and U.S. Patent No. 4,506,056. (See also JPolymer
Science, Part
A: Polymer Chemistry, Vol. 26, 1189-1198 (1988); 1 Polymer Science, Polymer
Letters,
Vol. 20, 481-486 (1982) and I Polymer Science, Polymer Letters, Vol. 21, 23-30
(1983),
all to Gaylord and Mehta and Degradation and Cross-linking of Ethylene-
Propylene
Copolymer Rubber on Reaction with Maleic Anhydride and/or Peroxides; J.
Applied
Polymer Science, Vol. 33, 2549-2558 (1987) to Gaylord, Mehta and Mehta.
EXAMPLES
The present invention is illustrated by, but in no way limited to, the
following
examples.
MDCL's
A set of MDCL's was formulated, each containing 20.89 mass % of the same
additives in the proportions and having a TBN of about 70. The set comprised a
control
consisting of additive and base oil; a reference consisting of additives, base
oil and
brightstock; and an inventive MDCL consisting of additives, base oil and
viscosity
modifier. The additives were additives known in the art and used in
proportions known in
the art for conferring MDCL properties. The viscosity modifier was a star
polymer in the
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form of amorphous styrene-diene copolymer. The brightstock was a Group I
bright stock
with a kinematic viscosity of >20cSt at 100 C. The base oil was a Group 1 base
oil.
TPEO's
A set of TPEO's was formulated, each containing 16 mass % of the same
additives
in the same proportions and having a TBN of about 40. The set comprised a
control
consisting of additives and base oil; a reference consisting of additives,
base oil and bright
stock; and an inventive TPEO consisting of additives, base oil and viscosity
modifier. The
additives were additives known in the art and used in proportions known in the
art for
conferring TPEO properties. The viscosity modifier, brightstock and base oil
were as used
in the MDCL's.
TESTING & RESULTS
Samples of the above formulations were tested using a PCS Instruments high
frequency reciprocating rig (HFRR) on a standard protocol comprising the
following
conditions:
= 120 minutes
= 20 Hz reciprocation of lmm stroke length
= 200g load using standard equipment manufacturer supplied steel
substrates.
Each test was repeated two further times and the recorded wear measurement was
the average of these values.
The HFRR data for the compositions are summarized in the table below.
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. ,
Table 1
TPEO Additive Base oil Brightstock Star Polymer Result
(wear vol m3)
Control 16 84 - - 5,584
Reference 16 75.5 8.5 - 8,279
1 16 82.98 - 1.02 2,170
MDCL
Control 20.89 79.11 - - 33,960
Reference 20.89 58.89 20.22 - 3,940
2 20.89 76.68 - 2.43 13,291
The above results show amorphous styrene-diene isoprene star polymer
advantageously
reduces the wear scar volume as compared with the control and reference for
TPEO oils.
For MDCL it is clearly advantageous to include the star polymer versus using
no
brightstock at all.
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