Note: Descriptions are shown in the official language in which they were submitted.
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LUBRICATING COMPOSITIONS
This invention relates to compositions such as lubricating oil compositions,
more especially to compositions suitable for use in piston engines, especially
gasoline (spark-ignited) and diesel (compression-ignited), crankcase
lubrication, such
compositions being referred to as crankcase lubricants; to additive
concentrates
therefor; and to use of additives in friction modification.
A crankcase lubricating oil composition, or lubricant, is an oil used for
general
lubrication in an engine where there is an oil sump below the crankshaft of
the engine
and to which circulated oil returns. It is well-known to include additives in
crankcase
lubricants for several purposes.
The invention concerns use of organic friction modifiers in crankcase
lubrication. Friction modifiers, also referred to as friction-reducing agents,
may be
boundary additives that operate by lowering friction coefficient and hence
improve
fuel economy.
The use of glycerol monoesters as friction modifiers has been described in the
art, for example in US-A-4,495,088; US-A-4,683,069; EP-A-0 092 946; and WO-A-
01/72933. One or more of these documents indicate that what is often referred
to as
glycerol mono-oleate, in its commercially available form, is a mixture that
includes the
diester and that, when glycerol is esterified with a fatty acid, mono-, di-
and triesters
form. Also, certain of the above listed documents teach that the proportion of
monoester in the mixture is high and EP-A-0 092 946 teaches the use of
essentially
all monoester in an ester component.
WO-A-01/72933 (referred to above) and US-B-6,723,685 each describe the
use of a glycerol ester additive in combination with a molybdenum compound in
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lubricating oil compositions. But WO-A-01/72933 repuires the monoester content
of
the ester additive to be at least 75 mole percent and, in a comparative
example,
refers to use of 68 mole percent of monoester in combination with a molybdenum
compound and US-B-6,723,685 makes no reference to the monoester content.
EP-A-0 743 354 discloses a lubricating oil providing improved wear protection
comprising an alkylamine phosphate and at least one additive selected from the
group comprising oxymolybdenum sulphide dithiocarbamate, oxymolybdenum
sulphide organophosphorosithioate, fatty ester and organic amides. The
examples of
EP-A-0 743 354 include use of a fatty ester comprising 50% monoester. WO-A-
96/37581 discloses a lubricating oil composition comprising a metal
dithiocarbamate
extreme pressure agent of specific formula, wherein the metal may be
molybdenum
or tungsten, which is said to exhibit excellent wear resistance, extreme-
pressure
lubricity and low coefficient of friction. The lubricating oil composition may
additionally comprise a fatty acid ester, and example 2 uses a fatty acid
ester
comprising 50% monoester.
A problem faced by formulators of lubricants is to reduce the amount of fuel
consumed in operation of piston engines. The present invention provides,
surprisingly, as evidenced by the data in this specification, an improvement
in friction
modification at higher temperatures by employing, in combination with
molybdenum
compounds, glycerol ester additives in which the proportions of monoester
thereof is
controlled.
Thus, in a first aspect, this invention provides a composition comprising:
(A) an oil of lubricating viscosity;
(B) as an ester additive component, one or more esters of glycerol and a
carboxylic acid containing 12 to 30 carbon atoms and 0 to 3 carbon-
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carbon double bonds wherein less than 50% by mass of the component
is one or more monoesters; and
(C) as a further additive component, an oil-soluble molybdenum compound.
In a second aspect, this invention provides a method for improving the
friction
modification of an internal combustion engine at high temperature comprising
operating the engine and lubricating the engine with a composition according
to the
first aspect of the invention.
In a third aspect, this invention provides the use of an additive (B) in
combination
with an additive (C), as defined in the first aspect of the invention, for
enhancing the
high-temperature friction-modification properties of a lubricating oil
composition in the
lubrication of an internal combustion engine.
In a fourth aspect, this invention provides a composition comprising:
(A) an oil of lubricating viscosity;
(B) as an ester additive component, one or more esters of glycerol and a
carboxylic acid containing 12 to 30 carbon atoms and 0 to 3 carbon-
carbon double bonds wherein less than 55% by mass of the component
is one or more monoesters; and
(C) as a further additive component, an oil-soluble tri-nuclear molybdenum
compound.
In a fifth aspect, this invention provides a method for improving the friction
modification of an internal combustion engine at high temperature comprising
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operating the engine and lubricating the engine with a composition according
to the
fourth aspect of the invention.
In a sixth aspect, this invention provides the use of an additive (B) in
combination
with an additive (C), as defined in the fourth aspect of the invention, for
enhancing
the high-temperature friction-modification properties of a lubricating oil
composition in
the lubrication of an internal combustion engine.
In this specification, the following words and expressions shall 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 in excess of 50 mass % of a composition;
"minor amount" means less than 50 mass % of a composition.
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.
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Further, it is to be understood that any upper and lower quantity, range and
ratio limits set forth herein may be independently combined.
The features of the invention relating, unless otherwise specified, to each
and
all aspects of the invention, will now be described in more detail as follows:
Additive Component (B)
The carboxylic acid is preferably a saturated or unsaturated C16 to C18 fatty
acid, such as oleic acid.
Preferably, in respect of the first aspect of the invention the component
contains, as lower limits, 1, 5 or 10, and, as upper limits, 30, 40 or 45,
mass % of one
or more monoesters, which upper and lower limits may be independently
combined.
Preferably, in respect of the fourth aspect of the invention the component
contains,
as lower limits, 1, 5 or 10, and, as upper limits, 30, 40, 45 or 50, mass % of
one or
more monoesters, which upper and lower limits may be independently combined.
In one embodiment of either the first aspect of the invention or the fourth
aspect of the invention, the component consists of partial esters only, ie of
mono- and
diesters; this embodiment contains less than 40, such as 5 to less than 40, %
by
mass of one or more monoesters, ie 60 or more, such as 60 to 95, % by mass of
one
or more diesters.
In either the first or the fourth embodiment, where one or more triesters are
present in the component, they may constitute 60 or more, such as 60 to 95, %
by
mass of the component.
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In another embodiment, monoesters may be absent from the component,
when the component consists wholly of diester(s) or wholly of triester(s) or
wholly of
mixtures thereof.
The esters may be borated, for example as described in above-mentioned
WO-A-01 /72933.
Oil of Lubricating Viscosity (A)
The oil of lubricating viscosity (sometimes referred to as "base stock" or
"base
oil") is the primary liquid constituent of a lubricant, into which additives
and possibly
other oils are blended, for example to produce a final lubricant (or lubricant
composition).
A base oil is useful for making concentrates as well as for making lubricating
oil compositions therefrom, and may be selected from natural (vegetable,
animal or
mineral) and synthetic lubricating oils and mixtures thereof. It may range in
viscosity
from light distillate mineral oils to heavy lubricating oils such as gas
engine oil,
mineral lubricating oil, motor vehicle oil and heavy duty diesel oil.
Generally the
viscosity of the oil ranges from 2 to 30, especially 5 to 20, mm2s' at
100°C.
Natural oils include animal and vegetable oils (e.g. castor and lard oil)
liquid
petroleum oils and hydrorefined, solvent-treated mineral lubricating oils of
the
paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of
lubricating
viscosity derived from coal or shale are also useful base oils.
Synthetic lubricating oils include 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-
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decenes)); alkylbenzenes (e.g. dodecylbenzenes, tetradecylbenzenes,
dinonylbenzenes, di(2-ethylhexyl)benzenes); polyphenols (e.g. biphenyls,
terphenyls,
alkylated polyphenols); and alkylated diphenyl ethers and alkylated diphenyl
sulfides
and the derivatives; analogs and homologs thereof.
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, sebasic 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 these esters include 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.
Esters useful as synthetic oils also include those made from C5 to C~2
monocarboxylic acids and polyols, and polyol ethers such as neopentyl glycol,
trimethylolpropane, pentaerythritol, dipentaerythritol and tripentaerythritol.
Unrefined, refined and re-refined oils can be used in the 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, a petroleum oil obtained directly
from
distillation or ester oil obtained directly from an esterification process and
used
without further treatment would be unrefined oil. Refined oils are similar to
the
unrefined oils except they have been further treated in one or more
purification steps
to improve one or more properties. Many such purification techniques, such as
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distillation, solvent extraction, acid or base extraction, filtration and
percolation are
known to those skilled in the art. Re-refined oils are obtained by processes
similar to
those used to obtain refined oils applied to refined oils which have been
already used
in service. Such re-refined oils are also known as reclaimed or reprocessed
oils and
often are additional processed by techniques for approval of spent additive
and oil
breakdown products.
Other examples of base oil are gas-to-liquid ("GTL") base oils, ie the base
oil
may be an oil derived from Fischer-Tropsch synthesised hydrocarbons made from
synthesis gas containing H2 and CO 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.
Base oil may be categorised in Groups I to V according to the API EOLCS
1509 definition.
The oil may be present in a concentrate-forming amount (e.g., from 30 to 70,
such as 40 to 60, mass %) so that the composition is in the form of a
concentrate
containing for example 1 to 90, such as 10 to 80, preferably 20 to 80, more
preferably
20 to 70, mass % active ingredient of an additive or additives, being
components (B)
and (C) above, or a combination of components (B) and (C) and one or more co-
additives.
The oil of lubricating viscosity used in a concentrate is a suitable
oleaginous,
typically hydrocarbon, carrier fluid, e.g. mineral lubricating oil, or other
suitable
solvent. Oils of lubricating viscosity such as described herein, as well as
aliphatic,
naphthenic, and aromatic hydrocarbons are examples of suitable carrier fluids
for
concentrates.
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Concentrates constitute a convenient means of handling additives before their
use, as well as facilitating solution or dispersion of additive in lubricating
oil
compositions. When preparing a lubricating oil composition that contains more
than
one type of additive (sometime referred to as "additive components"), each
additive
may be incorporated separately - each in the form of a concentrate. In many
instances, however, it is convenient to provide a so-called additive "package"
(also
referred to as an "adpack") comprising two or more additives in a single
concentrate.
The oil of lubricating viscosity may be provided in a major amount, in
combination with a minor amount of component (B) and component (C) and, if
necessary, a minor amount of one or more co-additives such as described
hereinafter, constituting a lubricating oil composition. This preparation may
be
accomplished by adding the additive directly to the oil or by adding it in the
form of a
concentrate thereof to disperse or dissolve the additive. Additives may be
added to
the oil by any method known to those skilled in the art, either prior to,
contemporaneously with, or subsequent to addition of other additives.
Additive Component ~C)
In respect of the first aspect of the invention, any suitable oil-soluble
organo-
molybdenum compound having friction modifying and/or anti-wear properties in
lubricating oil compositions may be employed. As an example of such oil-
soluble
organo-molybdenum compounds, there may be mentioned the dithiocarbamates,
dithiophosphates, dithiophosphinates, xanthates, thioxanthates, sulfides, and
the like,
and mixtures thereof. Particularly preferred are molybdenum dithiocarbamates,
dialkyldithiophosphates, alkyl xanthates and alkylthioxanthates.
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The molybdenum compound may be mono, di-, tri- or tetra-nuclear. binuclear
and trinuclear molybdenum compounds are preferred.
Additionally, the molybdenum compound may be an acidic molybdenum
compound. These compounds will react with a basic nitrogen compound as
measured by ASTM test D-664 or D-2896 titration procedure and are typically
hexavalent. Included are molybdic acid, ammonium molybdate, sodium molybdate,
potassium molybdate, and other alkaline metal molybdates and other molybdenum
salts, eg, hydrogen sodium molybdates, MoOCl4, Mo02Br2, Mo203C16, molybdenum
trioxide or similar acidic molybdenum compounds. Alternatively, the
compositions of
the present invention can be provided with molybdenum by molybdenum/sulfur
complexes of basic nitrogen compounds as describes, for example, in US Patent
Nos.
4,263,152; 4,285,822; 4,283,295; 4,272,387; 4,265,773; 4,261,843; 4,259,195
and
4,259,194; and WO 94/06897.
Among the molybdenum compounds useful in the compositions of this
invention are organo-molybdenum compounds of the formulae.
Mo(ROCS2)4 and
Mo(RSCS2)4
wherein R is an organo group selected from the group consisting of alkyl,
aryl, aralkyl
and alkoxyalkyl, generally of from 1 to 30 carbon atoms, and preferably 2 to
12
carbon atoms and most preferably alkyl of 2 to 12 carbon atoms. Especially
preferred are the dialkyldithiocarbamates of molybdenum.
In respect of the fourth aspect of the invention, any suitable tri-nuclear oil-
soluble organo-molybdenum compound having friction modifying and/or anti-wear
properties in lubricating oil compositions may be employed. As an example of
such
oil-soluble organo-molybdenum compounds, there may be mentioned the
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dithiocarbamates, dithiophosphates, dithiophosphinates, xanthates,
thioxanthates,
sulfides, and the like, and mixtures thereof. Particularly preferred are
molybdenum
dithiocarbamates, dialkyldithiophosphates, alkyl xanthates and
alkylthioxanthates.
The tri-nuclear molybdenum compound of the fourth aspect of the invention
may comprise tetra-nuclear molybdenum compound. Preferably, the tri-nuclear
molybdenum compound comprises at least 90%, preferably at least 95% and more
preferably substantially 100% tri-nuclear molybdenum compound.
One class of preferred organo-molybdenum compounds useful in all aspects
of the present invention are tri-nuclear molybdenum compounds of the formula
Mo3SkLnQZ and mixtures thereof wherein L are independently selected ligands
having
organo groups with a sufficient number of carbon atoms to render the compounds
soluble or dispersible in the oil, n is from 1 to 4, k varies from 4 through
to 7, Q is
selected from the group of neutral electron donating compounds such as water,
amines, alcohols, phosphines, and ethers, and z ranges from 0 to 5 and
includes
non-stoichiometric values. At least 21 total carbon atoms should be present
among
all the ligands' organo groups, such as at least 25, at least 30, or at least
35 carbon
atoms.
The terms "oil-soluble" or "dispersible", or cognate terms, used herein do not
necessarily indicate that the compounds or additives are soluble, dissolvable,
miscible, or are 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 lubricating oil compositions may be used to lubricate mechanical engine
components, particularly in internal combustion engines, e.g. spark-ignited,
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compression-ignited two or four stroke reciprocating engines, by adding the
composition thereto.
The lubricating oil compositions and concentrates comprise defined
components that may or may not remain the same chemically before and after
mixing
with an oleaginous carrier. This invention encompasses compositions and
concentrates which comprise the defined components before mixing, or after
mixing,
or both before and after mixing.
When concentrates are used to make the lubricating oil compositions, they
may for example be diluted with 3 to 100, e.g. 5 to 40, parts by weight of oil
of
lubricating viscosity per part of the concentrate.
In lubricating oil compositions of this invention, representative effective
amounts of additive component (B), as an organic friction modifier, are from
0.05 to 5,
such as 0.05 to 0.3 or to 0.6 or to 1.5, mass %.
The lubricating oil compositions of the present invention may contain the
molybdenum compound, (C), in an amount providing the composition with at least
10,
such as 50 to 2000 ppm of molybdenum. Preferably, the molybdenum from the
molybdenum compound is present in an amount of from 10 ppm to 1500 ppm, such
as 20 ppm to 1000 ppm, more preferably from 30 ppm to 750 ppm, based on the
total
weight of the lubricating oil composition. For some applications, the
molybdenum is
present in an amount of greater than 500 ppm.
Other co-additives, with representative effective amounts in lubricating oil
compositions are listed below. All the values listed are stated as mass
percent active
ingredient.
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ADDITIVE MASS % MASS
(Broad) (Preferred)
Ashless Dispersant 0.1 - 20 1 - 8
Metal Detergents 0.1 - 6 0.2 - 4
Corrosion Inhibitor 0 - 5 0 - 1.5
Metal Dihydrocarbyl Dithiophosphate0.1 - 10 0.2 - 4
Anti-Oxidants 0 - 5 0.01 - 1.5
Pour Point Depressant 0.01 - 5 0.01 - 1.5
Anti-Foaming Agent 0 - 5 0.001 - 0.15
Supplemental Anti-Wear Agents 0 - 0.5 0 - 0.2
Viscosity Modifier (1 ) 0.01 - 6 0 - 4
Mineral or Synthetic Base Oil Balance Balance
(1) Viscosity modifiers are used only in multi-graded oils.
The final lubricating oil composition, typically made by blending the or each
additive into the base oil, may contain from 5 to 25, preferably 5 to 18,
typically 7 to
15, mass % of the concentrate, the remainder being oil of lubricating
viscosity.
Co-Additives
The above mentioned co-additives are discussed in further detail as follows;
as is known in the art, some additives can provide a multiplicity of effects -
for
example, a single additive may act as a dispersant and as an oxidation
inhibitor.
A dispersant is an additive whose primary function is to hold solid and liquid
contaminations in suspension, thereby passivating them and reducing engine
deposits at the same time as reducing sludge depositions. Thus, for example, a
dispersant maintains in suspension oil-insoluble substances that result from
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oxidation during use of the lubricant, thus preventing sludge flocculation and
precipitation or deposition on metal parts of the engine.
Dispersants are usually "ashless", as mentioned above, being non-metallic
organic materials that form substantially no ash on combustion, in contrast to
metal-
containing, and hence ash-forming materials. They comprise a long chain of
hydrocarbon with a polar head, the polarity being derived from inclusion of
e.g. an O,
P, or N atom. The hydrocarbon is an oleophilic group that confers oil-
solubility,
having, for example 40 to 500 carbon atoms. Thus, ashless dispersants may
comprise an oil-soluble polymeric backbone.
A preferred class of olefin polymers is polybutenes, specifically
polyisobutenes
(PIB) or poly-n-butenes, such as may be prepared by polymerization of a C4
refinery
stream.
Dispersants include, for example, derivatives of long chain hydrocarbon-
substituted carboxylic acids, examples being derivatives of high molecular
weight
hydrocarbyl-substituted succinic acid. A noteworthy group of dispersants are
hydrocarbon-substituted succinimides, made, for example, by reacting the above
acids (or derivatives) with a nitrogen-containing compound, advantageous a
polyalkylene polyamine, such as a polyethylene polyamine. Particularly
preferred are
the reaction products of polyalkylene polyamines with alkenyl succinic
anhydrides,
such as described in US-A-3,202,678; -3,154,560; -3,172,892; -3,024,195; -
3,024,237, -3,219,666; and -3,216,936; and BE-A-66,875 that may be post-
treated to
improve their properties, such as borated (as described in US-A-3,087,936 and -
3,254,025) fluorinated and oxylated. For example, boration may be accomplished
by
treating an acyl nitrogen-containing dispersant with a boron compound selected
from
boron oxide, boron halides, boron acids and esters of boron acids.
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A detergent is an additive that reduces formation of piston deposits, for
example high-temperature varnish and lacquer deposits, in engines; it normally
has
acid-neutralising properties and is capable of keeping finely divided solids
in
suspension. Most detergents are based on metal "soaps", that is metal salts of
acidic
organic compounds.
Detergents generally comprise a polar head with a long hydrophobic tail, the
polar head comprising a metal salt of an acidic organic compound. The salts
may
contain a substantially stoichiometric amount of the metal in which case they
are
usually described as normal or neutral salts, and would typically have a total
base
number or TBN (as may be measured by ASTM D2896) of from 0 to 80. Large
amounts of a metal base can be included by reacting an excess of a metal
compound, such as an oxide or hydroxide, with an acidic gas such as carbon
dioxide.
The resulting overbased detergent comprises neutralised detergent as an outer
layer
of a metal base (e.g. carbonate) micelle. Such overbased detergents may have a
TBN of 150 or greater, and typically of from 250 to 500 or more.
Detergents that may be used include oil-soluble neutral and overbased
sulfonates, phenates, sulfurized phenates, thiophosphonates, salicylates, and
naphthenates and other oil-soluble carboxylates of a metal, particularly the
alkali or
alkaline earth metals, e.g. sodium, potassium, lithium, calcium and magnesium.
The
most commonly used metals are calcium and magnesium, which may both be
present in detergents used in a lubricant, and mixtures of calcium and/or
magnesium
with sodium. Particularly convenient metal detergents are neutral and
overbased
calcium sulfonates and sulfurized phenates having a TBN of from 50 to 450.
Anti-oxidants are sometimes referred to as oxidation inhibitors; they increase
the resistance of the composition to oxidation and may work by combining with
and
modifying peroxides to render them harmless, by decomposing peroxides, or by
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rendering an oxidation catalyst inert. Oxidative deterioration can be widened
by
sludge in the lubricant, varnish-like deposits on the metal surfaces, and by
viscosity
g rowth .
They may be classified as radical scavengers (e.g. sterically hindered
phenols,
secondary aromatic amines, and organo-copper salts); hydroperoxide decomposers
(e,g, organo sulphur and organophosphorus additives); and multifunctionals
(e.g.
zinc dihydrocarbyl dithiophosphates, which may also function as anti-wear
additives,
and organo-molybdenum compounds, which may also function as friction modifiers
and anti-wear additives).
Examples of suitable antioxidants are selected from copper-containing
antioxidants, sulphur-containing antioxidants, aromatic amine-containing
antioxidants,
hindered phenolic antioxidants, dithiophosphates derivatives, metal
thiocarbamates,
and molybdenum-containing compounds.
Dihydrocarbyl dithiophosphate metals salts are frequently used as antiwear
and antioxidant agents. The metal may be an alkali or alkaline earth metal, or
aluminium, lead, tin, molybdenum, manganese, nickel or copper. The zinc salts
are
most commonly used in lubricating oil in amounts of 0.1 to 10, preferably 0.2
to 2
wt %, based upon the total weight of the lubricating oil compositions. They
may be
prepared in accordance with known techniques by first forming a dihydrocarbyl
dithiophosphoric acid (DDPA), usually by reaction of one or more alcohols or a
phenol with P2S5 and then neutralising the formed DDPA with a zinc compound.
For
example, a dithiophosphoric acid may be made by reacting mixtures of primary
and
secondary alcohols. Alternatively, multiple dithiophosphoric acids can be
prepared
where the hydrocarbyl groups on one are entirely secondary in character and
the
hydrocarbyl groups on the others are entirely primary in character. To make
the zinc
salt, any basic or neutral zinc compound could be used but the oxides,
hydroxides
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and carbonates are most generally employed. Commercial additives frequently
contain an excess of zinc due to use of an excess of the basic zinc compound
in the
neutralisation reaction.
Anti-wear agents reduce friction and excessive wear and are usually based on
compounds containing sulphur or phosphorous or both, for example that are
capable
of depositing polysulfide films on the surfaces involved. Noteworthy are the
dihydrocarbyl dithiophosphates, such as the zinc dialkyl dithiophosphates
(ZDDP's)
discussed herein as anti-oxidants.
Examples of ashless anti-wear agents include 1,2,3-triazoles, benzotriazoles,
thiadiazoles, sulfurised fatty acid esters, and dithiocarbamate derivatives.
Rust and corrosion inhibitors serve to protect surfaces against rust and/or
corrosion.
As rust inhibitors there may be mentioned non-ionic polyoxyalkylene polyols
and esters thereof, polyoxyalkylene phenols, and anionic alkyl sulfonic acids.
Pour point depressants, otherwise known as tube oil flow improvers, lower the
minimum temperature at which the fluid will flow or can be poured. Such
additives
are well known. Typical of those additive which improve the low temperature
fluidity
of the fluid are C8 to C~$ dialkyl fumerate/vinyl acetate copolymers and
polyalkylmethacrylates.
Additives of the polysiloxane type, for example silicone oil or polydimethyl
siloxane can provide foam control.
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A small amount of a demulsifying component may be used. A preferred
demulsifying component is described in EP-A-330,522. It is obtained by
reacting an
alkylene oxide with an adduct obtained by reacting a bis-epoxide with
polyhydric
alcohol. The demulsifier should be used at a level not exceeding 0.1 mass %
active
ingredient. A treat rate of 0.001 to 0.05 mass % active ingredient is
convenient.
Viscosity modifiers (or viscosity index improvers) impart high and low
temperature operability to a lubricating oil. Viscosity modifiers that also
function as
dispersants are also known and may be prepared as described above for ashless
dispersants. In general, these dispersant viscosity modifiers are
functionalised
polymers (e.g. interpolymers of ethylene-propylene post grafted with an active
monomer such as malefic anhydride) which are then derivatised with, for
example, an
alcohol or amine.
1 S The lubricant may be formulated with or without a conventional viscosity
modifier and with or without a dispersant viscosity modifier. Suitable
compounds for
use as viscosity modifiers are generally high molecular weight hydrocarbon
polymers,
including polyesters. Oil-soluble viscosity modifying polymers generally have
weight
average molecular weights of from 10,000 to 1,000,000, preferably 20,000 to
500,000, which may be determined by gel permeation chromatography or by light
scattering.
EXAMPLES
The invention will now be particularly described in the following non-limiting
examples.
Example 1
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Four additive components were prepared consisting of various proportions of a
monoester (glycerol mono-oleate) and a diester (glycerol dioleate). The
proportions,
by mass %, of the mono and diester are indicated in Table 1 below for each
additive
component.
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Table 1
Additive
Component
1 2 A B
Monoester 0 33 67 100
Diester 100 67 33 0
Components 1 and 2 were for use in examples of the invention and
components A and B were for reference purposes.
Each component was blended into a lubricating oil composition, by methods
known in the art, to provide a fully formulated oil composition containing 0.3
mass
of the component as active ingredient and a molybdenum additive providing 200
ppm
by mass of molybdenum, and identical customary amounts of an ashless
dispersant,
a metal detergent, an anti-oxidant, a zinc dihydrocarbyl dithiophosphate, and
an
antifoam.
A high frequency reciprocating rig (HFRR) was used to evaluate the coefficient
of friction characteristics of oils 1, 2, A and B. The instrument is called
the
AUTOHRF and is manufactured by PCS Instruments. The test protocol is shown in
Table 2 below. A stepped ramp temperature profile was followed, whereby each
300
seconds the temperature was raised by a step of 20 °C and held constant
for 300
seconds until the next successive 20 °C ramp.
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Table 2 - HFRR Protocol
Contact 6 mm. Ball on 10 mm Disc
Load, N 3.9
Stroke Length, mm 1
Frequency, Hz. 20
Temperature range, C 40-140
Temperature step, C 20
Time between temperature steps,300
seconds
Results are expressed as average friction coefficient as a function of
S temperature and are summarised in Table 3 below, where the compositions
tested
are referred to as 1, 2, A and B in accordance with which additive component
they
contain.
Table 3 Composition
Temperature
Stage (C) 1 2 A B
40 0.124 0.127 0.124 0.125
60 0.121 0.122 0.113 0.110
80 0.111 0.110 0.106 0.103
100 0.083 0.099 0.098 0.095
120 0.065 0.073 0.075 0.089
140 0.056 0.065 0.060 0.078
Table 3 shows that at lower temperature, Reference Examples A and B, are
generally superior to Examples 1 and 2 in that they exhibit lower friction
coefficients.
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At higher temperatures, between 80 °C and 100 °C, they become
comparable. As
temperature increases further, between 120 °C and 140 °C the
results for Examples
1 and 2 are generally superior to those of Reference Examples A and B.
Example 2
Six additive components were prepared consisting of various proportions of a
monoester (glycerol mono-oleate) and a diester (glycerol dioleate). The
proportions,
by mass %, of the mono and diester are indicated in Table 4 below for each
additive
component.
Table 4
Additive
Component
3 4 5 6 7 C
Monoester 0 10 20 30 45 50
Diester 100 90 80 70 55 50
Each component was blended into a lubricating oil composition, by methods
known in the art, to provide a fully formulated oil composition containing 0.3
mass
of the component as active ingredient and a molybdenum additive providing 200
ppm
by mass of molybdenum, and identical customary amounts of an ashless
dispersant,
a metal detergent, an anti-oxidant, a zinc dihydrocarbyl dithiophosphate, and
an
antifoam.
The high frequency reciprocating rig (HFRR) used in Example 1 was used to
evaluate the coefficient of friction characteristics of Oils 3, 4, 5, 6, 7 and
C. The test
protocol used differed from that of Example 1, and is shown in Table 5 below.
In
Example 2, a stepped ramp temperature profile was followed, whereby each 600
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seconds the temperature was raised by a step of 20 °C and held constant
for 600
seconds until the next successive 20 °C ramp.
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Table 5- HFRR Protocol
Contact 6 mm. Ball on 10 mm Disc
Load, N 3.9
Stroke Length, mm 1
Frequency, Hz. 20
Temperature range, C 40-140
Temperature step, C 20
Time between temperature steps,600
seconds
Results are expressed as average friction coefficient as a function of
temperature and are summarised in Table 6 below, where the compositions tested
are referred to as 3, 4, 5, 6, 7 and C in accordance with which additive
component
they contain. Each value is the average of two repeat tests.
Table 6
TemperatureComposition
Stage (C) 3 4 5 6 7 C
40 0.129 0.127 0.129 0.129 0.128 0.127
60 0.127 0.125 0.126 0.126 0.123 0.121
80 0.123 0.120 0.121 0.120 0.116 0.116
100 0.109 0.112 0.108 0.114 0.110 0.109
120 0.077 0.084 0.084 0.092 0.097 0.099
140 0.065 0.063 0.067 0.070 0.085 0.086
Table 6 shows that at lower temperature the friction coefficient decreases as
the proportion of mono ester increases. Whereas, at higher temperatures,
around 80
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°C to 100 °C the Compositions 3 to 7 become comparable to
Composition C. As
temperature increases further, between 120 °C and 140 °C the
results for
Compositions 3 to 7 are superior to those of Reference Composition C.
Example 3
Additive component 8 was prepared comprising 53 mass% mono ester and 47
mass% diester. Component 8 was blended into a lubricating oil composition, by
methods known in the art, to provide Composition 8 and Reference composition
D.
Compositions 8 and D each contained 0.3 mass % of Component 8 as active
ingredient and identical customary amounts of an ashless dispersant, a metal
detergent, an anti-oxidant, a zinc dihydrocarbyl dithiophosphate, and an
antifoam.
Composition 8 and Composition D differed in that Composition 8 comprised a tri-
nuclear molybdenum additive providing 200 ppm by mass of molybdenum and
Composition D comprised a di-nuclear molybdenum additive providing 200 ppm by
mass of molybdenum
The high frequency reciprocating rig (HFRR) used in Example 1 was used to
evaluate the coefficient of friction characteristics of Oils 8 and D. The test
protocol
used was the same as that used in Example 2, and as set out in Table 5 above.
Results are expressed as average friction coefficient as a function of
temperature and are summarised in Table 7 below. Each value is the average of
two
repeat tests.
Table 7 Composition
Temperature
Stage (C) 8 D
40 0.127 0.130
60 0.121 0.126
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80 0.116 0.119
100 0.108 0.112
120 0.101 0.105
140 0.080 0.100
It can be seen from Table 7 that at equivalent molybdenum content, the use of
a tri-nuclear molybdenum source significantly reduces the friction coefficient
compared to an equivalent composition comprising a di-nuclear molybdenum
source.
Example 4
Two additive components were prepared consisting of various proportions of a
monoester (glycerol mono-oleate), a diester (glycerol dioleate) and a triester
(glycerol
trioleate). The proportions, by mass %, of the mono, diester and triester are
indicated in Table 8 below for each additive component.
Table 8
Additive Component
9 10
Monoester 0 0
Diester 50 0
Triester 50 100
Each component was blended into a lubricating oil composition, by methods
known in the art, to provide a fully formulated oil composition containing 0.3
mass °lo
of the component as active ingredient and a molybdenum additive providing 200
ppm
by mass of molybdenum, and identical customary amounts of an ashless
dispersant,
a metal detergent, an anti-oxidant, a zinc dihydrocarbyl dithiophosphate, and
an
antifoam.
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The high frequency reciprocating rig (HFRR) of Example 1 was used to
evaluate the coefficient of friction characteristics of Oils 9 and 10. The
test protocol is
the same as that used in Examples 2 and 3 and as shown in Table 5 above.
Results are expressed as average friction coefficient as a function of
temperature and are summarised in Table 9 below, where the compositions tested
are referred to as 9 and 10 in accordance with which additive component they
contain.
Table 9 Composition
Temperature
Stage (C) 9 10
40 0.127 0.133
60 0.127 0.141
80 0.123 0.134
100 0.101 0.074
120 0.072 0.070
Table 9 shows that at higher temperatures, the composition comprising a
greater proportion of triester is generally superior to the composition
comprising a
lower proportion of triester.
