Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
TWO- OR FOUR-STROKE MARINE ENGINE LUBRICATING OIL COMPOSITION
COMPRISING STAR POLYMER OR OLEFIN COPOLYMER VISCOSITY MODIFIER
DISPERSED IN A HEAVY BASESTOCK DILUENT OIL
FIELD OF THE INVENTION
This invention relates to the lubrication of two-stroke and four-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
with 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, mm2s-I, such as a solvent-extracted,
de-asphalted
product from vacuum residuum generally having a kinematic viscosity at 100 C
of 28-36
MM2S-1.
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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. Both use liquid, oil-
miscible
polyisobutylene (` PIB ' ).
A problem with brightstock-free MDCL's and TPEO's is that they give rise to
evaporation debits (i.e. lubricating oil evaporation and consumption). As
discussed in US
2008/0287329, the degradation of polyisobutylene leads to the formation of
volative
products that escape from the engine, which results in lube oil consumption.
The aim of the invention is to overcome the problems of the prior art. In
particular, an aim of the present invention is to reduce lubricating oil
consumption.
SUMMARY OF THE INVENTION
It is now found that the use of star polymers (such as an amorphous styrene-
diene
copolymer) or olefin copolymers (such as an ethylene-propylene copolymer)
dispersed in
a heavy diluent oil 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 blended with
(A) one of more additives, in respective minor amounts; and
(B) a viscosity modifier in the form of either (i) a polymer comprising a
core
and a plurality of polymeric arms extending therefrom, or (ii) an olefin
copolymer, the viscosity modifier being dispersed in a heavy diluent oil of
kinematic viscosity at 100 C in the range of 6-15, such as 7-14, mm2 s-I
2
wherein the two-stoke marine engine lubricating oil composition has a TBN of
10 to 100
such as 40 to 100 using ASTM D2896 and the four-stroke marine engine
lubricating oil
composition has a TBN of 25 to 60 using ASTM D2896.
The composition contains less than 0.5, preferably less than 0.1, mass %
brightstock, and even more preferably is completely or substantially free of
brightstock.
In further aspects the present invention comprises:-
a method of making a two-stroke or four-stroke marine engine lubricating oil
composition comprising blending an oil of lubricating viscosity in a major
amount with:
(A) one or more additives, in respective minor amounts; and
(B) a viscosity modifier in the form of either (i) a polymer comprising a
core
and a plurality of polymeric arms extending therefrom, or (ii) an olefin
copolymer, the viscosity modifier being dispersed in a heavy diluent oil of
kinematic viscosity at 100 C in the range of 6-15, such as 7-14, mm2 s-1,
wherein the two-stoke marine engine lubricating oil composition has a
TBN of 10 to 100 such as 40 to 100 using ASTM D2896 and the four-
stroke marine engine lubricating oil composition has a TBN of 25 to 60
using ASTM D2896;
a two-stroke or four-stroke marine engine lubricating oil composition
obtainable
by the above method of this invention.
a method of lubricating a cross-head marine diesel engine comprising supplying
the composition of the invention 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
the use of a viscosity modifier (B) as defined in the first aspect of the
invention to
improve the carbon deposition properties of a marine diesel cylinder lubricant
of TBN
10-100 such as 40 to 100 using ASTM D2896 or a trunk piston engine oil having
a TBN
of 25-60 using ASTM
D2896.
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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;
"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, preferably 60
mas % or more, even more preferably 70 mass% or more;
"minor amount" means less than 50 mass % of a composition, preferably less
than
40 mass %, even more preferably less than 30 mass %;
"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;
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"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.
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.
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Synthetic lubricating oils include hydrocarbon oils and halo-substituted
hydrocarbon oils such as polymerized and interpolymerized olefins (e.g.,
polybutylenes,
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, etherification,
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 Cl2
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)silic ate, 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.
The American Petroleum Institute (API) publication "Engine Oil Licensing and
Certification System", Industry Services Department, Fourteenth Edition,
December
1996, Addendum 1, December 1998 categorizes base stocks as follows:
a) Group I base stocks contain less than 90 percent saturates and/or greater
than
0.03 percent sulphur and have a viscosity index greater than or equal to 80
and less
than 120 using the test methods specified in Table E-1.
b) Group II base stocks contain greater than or equal to 90 percent saturates
and
less than or equal to 0.03 percent sulphur and have a viscosity index greater
than or
equal to 80 and less than 120 using the test methods specified in Table E-1.
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c) Group III base stocks contain greater than or equal to 90 percent saturates
and
less than or equal to 0.03 percent sulphur and have a viscosity index greater
than or
equal to 120 using the test methods specified in Table E-1.
d) Group IV base stocks are polyalphaolefins (PAO).
e) Group V base stocks include all other base stocks not included in Group I,
II, III,
or IV.
Analytical Methods for Base Stock are tabulated below:
PROPERTY TEST METHOD
Saturates ASTM D 2007
Viscosity Index ASTM D 2270
Sulphur ASTM D 2622
ASTM D 4294
ASTM D 4927
ASTM D 3120
The present invention preferably embraces those of the above oils containing
greater than or equal to 90% saturates and less than or equal to 0.03% sulphur
as the oil
of lubricating viscosity, eg Group II, III, IV or V. They also include
basestocks derived
from hydrocarbons synthesised by the Fischer-Tropsch process. In the Fischer-
Tropsch
process, synthesis gas containing carbon monoxide and hydrogen (or syngas') is
first
generated and then converted to hydrocarbons using a Fischer-Tropsch catalyst.
These
hydrocarbons typically require further processing in order to be useful as a
base oil. For
example, they may, by methods known in the art, be hydroisomerized;
hydrocracked and
hydroisomerized; dewaxed; or hydroisomerized and dewaxed. The syngas may, for
example, be made from gas such as natural gas or other gaseous hydrocarbons by
steam
reforming, when the basestock may be referred to as gas-to-liquid ("GTL") base
oil; or
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from gasification of biomass, when the basestock may be referred to as biomass-
to-liquid
("BTL" or "BMTL") base oil; or from gasification of coal, when the basestock
may be
referred to as coal-to-liquid ("CTL") base oil.
Preferably, the oil of lubricating viscosity in this invention contains 50
mass % or
more said basestocks. It may contain 60, such as 70, 80 or 90, mass % or more
of said
basestock or a mixture thereof. The oil of lubricating viscosity may be
substantially all of
said basestock or a mixture thereof.
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 10-100, such as 40-100,
preferably
60-90, more preferably 70-80.
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
base stock balance balance
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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 'Yo 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
ADDITIVES (A)
More detailed description of additive components is given below.
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.
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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.
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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.
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
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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 (B)
In this invention, as stated above, a viscosity modifier (B) is additionally
provided
in the form of (i) a so-called star polymer, or (ii) an olefin copolymer. Its
concentration in
the composition may, for example, be in the range of 0.01 to 40 mass %.
(1) Star Polymers
These are 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
hereinbefore, 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.
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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:
A,(B-A)y-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;
x and z are, independently, a number equal to 0 or 1; and
y is a whole number ranging from 1 to about 15.
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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
AJB 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
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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.
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
copolymers, 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
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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 allyl 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 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.
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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.
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-(CH=CH7)x 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.
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=
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 A 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
crosslinked poly(polyalkenyl coupling agent) and a number of arms of
substantially
linear 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
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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
Raney nickel and nickel on kieselguhr. Particularly suitable hydrogenation
catalysts are
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
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.
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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 Vo
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 SV2SOTM,
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 1 to 15, mass % based on the mass of the lubricating oil
composition.
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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
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 J Polymer
Science, Part
A: Polymer Chemistry, Vol. 26, 1189-1198 (1988); J Polymer Science, Polymer
Letters,
Vol. 20, 481-486 (1982) and]. 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; I Applied
Polymer Science, Vol. 33, 2549-2558 (1987) to Gaylord, Mehta and Mehta.
(ii) Olefin Copolymers
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In this invention olefin copolymers (OCP's) may be used. Examples of ranges in
the composition include 0.1-6, 0.1-5, 0.1-4, mass % and lower limits of 1 or 2
mass %.
These may be copolymers of two or more monomers of C2 to C30, e.g. C2 to C8)
olefins, including both alpha-olefins and internal olefins, which may be
straight or
branched, aliphatic, aromatic, alkyl-aromatic, or cycloaliphatic. Frequently,
they are of
ethylene with C3 to C30 olefins, particularly preferred being copolymers of
ethylene and
propylene. They may also be copolymers of C6 and higher alpha olefins and
terpolymers
of styrene, e.g. with isoprene and/or butadiene and hydrogenated derivatives
thereof
Preferred OCP's are ethylene copolymers containing 15 to 90, preferably 30 to
80,
mass % of ethylene and 10 to 85, preferably 20 to 70, mass % of one or more C3
to C283
preferably C3 to C18, more preferably C3 to C8, alpha-olefins. Such OCP's may
have a
degree of crystallinity of less than 25 mass %, as determined by x-ray and
differential
scanning calorimetry. As indicated above, copolymers of ethylene and propylene
are
most preferred. Other alpha-olefins suitable in place of propylene, or in
combination
with ethylene and propylene to form a terpolymer or tetrapolymer, for example,
include:
1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene; and
branched
chain alpha-olefins such as 4-methyl-1-pentene, 4-methyl-1-hexene, 4-methyl
pentene-1,
4, 4-dimethyl- 1 -pentene, 6-methylheptene-1, and mixtures thereof
There may also be included terpolymers and tetrapolymers of ethylene, said C3
to
C28 alpha-olefin, and a non-conjugated diolefin or mixtures of such diolefins.
The non-
conjugated diolefm is generally present as 0.5 to 20, preferably 1 to 7, mole
percent of
the total moles of ethylene and alpha-olefin.
Diluent Oil
The viscosity modifier is dispersed (e.g. dissolved) in a heavy basestock
diluent
oil. As stated, the latter has a kinematic viscosity at 100 C in the range of
6-15,
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preferably 7-14, mm2s-1. As examples of concentrations of the viscosity
modifier in the
heavy basestock diluent oil, the following ranges, in mass %, may be
mentioned; 0.05 to
5, such as to 4, 3 or 2; 0.01 to 5, 4, 3 or 2, preferably 0.01 to 2; more
preferably 1 to 2
such as 1 to 1.5. The main consideration is that the resulting dispersion
should have the
same or similar kinematic viscosity to that of a brightstock oil.
EXAMPLES
The present invention is illustrated by, but not limited to, the following
examples.
FORMULATIONS
Marine diesel cylinder lubricants (MDCL's)
Each MDCL comprised a calcium alkylsalicylate detergent package of basicity
index 18 and containing 12.4 mass% Ca; 23 mass% of a viscosity modifier or, as
a
comparison, of a brightstock or polyisobutylene; and 55.6 mass% of an oil of
lubricating
viscosity (a Group I oil (X0M600)). All MDCL's had a TBN of about 70. The
detailed
formulations are given in TABLE 1 below.
The viscosity modifiers used were:
= a star polymer in the form of an amorphous styrene-diene copolymer
dispersed
either in a heavy oil diluent or a light oil diluent ("star"); and
= an olefin copolymer in the form of an amorphous ethylene-propylene
copolymer
dispersed either in a heavy oil diluent or a light oil diluent ("OCP")
The brightstock used was a Group I brightstock with a kinematic viscosity at
100 C
of greater than 20mm2s-1.
Trunk piston engine oils (TPEO's)
24
Each TPEO comprised a calcium alkylsalicylate detergent package of basicity
index 5.8 and containing 8.9 mass% Ca; 7 mass% of a viscosity modifier or, as
a
comparison, of a brightstock or polyisobutylene; and 77.1 mass% of an oil of
lubricating
viscosity (a Group II oil (ChevronTM 600)). All TPEO's had a TBN of 40. The
detailed
formulations are given in TABLE 2 below. The viscosity modifiers, the
brightstock and
the polyisobutylene were the same as those in the MDCL's.
TESTING & RESULTS
Samples of the above formulations were tested for carbon deposition properties
using the Panel Coker Test and for evaporation loss using the NOACK volatility
tests.
The tests are described as follows:
Panel Coker Test
Lubricating oils may degrade on hot engine surfaces and leave deposits which
will affect engine performance; the panel coker test simulates typical
conditions and
measures the tendency of oils to form such deposits. The oil under test is
splashed onto a
heated metal plate by spinning a metal comb-like splasher device within a sump
containing the oil. At the end of the test period, deposits are measured.
An overview of the test method is as follows:
= 225 ml of the oil is heated in an oil bath to 100 C.
= A heated aluminium panel is located above the oil bath at an incline,
maintained
at a temperature of 320 C.
= The oil is splashed for 15 seconds against this panel, followed by no
splashing for
45 seconds.
= This cycle of intermittent splashing is continued for 1 hour.
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=
= The panel is weighed and the deposits are calculated in grams (g).
NOACK Volatility Test determines the evaporation loss of lubricants in high
temperature service. It is otherwise known as ASTM D-5800.
TABLE 1- An MDCL including a major amount of a Group I oil (X0M600)
Ex Star Star OCP OCP Brightstock Polyisobutylene Panel NOACK
(L3%) (1.3%) (1.4%) (1.4%) 950 Mol. Wt. Coker D5800
in in in in (g) Evap.
Diluent Diluent Diluent Diluent Loss
having having having having (mass%)
a a a a
Kv100 Kv100 Kv100 Kv100
11.21 5.21 11.21 5.21
mm2 S-1 MM2 S-1 MM2 S-1 MM2 S-1
1 I 0.0426 3.8
A 0.0736 6.6
2 0.0755 4.0
0.0509 6.7
0.0988 3.9
0.0452 4.4
Table 1 shows that replacing brightstock with either star polymer or an olefin
copolymer reduces the amount of deposits in the Panel Coker Test. Table 1 also
shows
that the use of higher viscosity diluent for the star polymer and the olefin
copolymer
reduces the evaporation loss (i.e. the lube oil consumption) compared to the
use of a
lighter viscosity diluent.
In the Tables, a tick indicates presence of a particular component and a blank
space indicates absence.
TABLE 2- TPEO including a major amount of a Group II oil (Chevron 600)
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Ex Star Star OCP OCP
Brightstock Polyisobutylene Panel NOACK
(1.3%) in (1.3%) (1.4%) (1.4%) (Mol. Weight Coker D5800
Diluent in in in 950) (g) Evap.
having a Diluent Diluent Diluent Loss
Kv100 having a having having (mass%)
12.16 Kv100 a a
mm251 5.21 Kv100 Kv100
mm2s1 12.16 5.21
mm2 S-1 MM2 S-1
3 4 0.0191 3.7
0.0188 4.1
4 0.0187 3.2
X 0.0166 3.9
0.0310 3.1
0.0193 3.4
Table 2 shows that replacing brightstock with either star polymer or an olefin
copolymer reduces the amount of deposits in the Panel Coker Test. Table 2 also
shows
that the use of a higher viscosity diluent for the star polymer and the olefin
copolymer
reduces the evaporation loss (i.e. the lube oil consumption) compared to the
use of a
lighter viscosity diluent.
Examples 1-4 fall within the invention. Examples A-D and W-Z are comparative
examples.
27
