Note: Descriptions are shown in the official language in which they were submitted.
CA 02723531 2016-11-29
1
LUBRICATING COMPOSITIONS COMPRISING
ORGANIC ANHYDRIDES
FIELD OF THE INVENTION
The present invention relates to automotive lubricating oil compositions, more
especially to automotive lubricating oil compositions for use in piston
engines, especially
gasoline (spark-ignited) and diesel (compression-ignited) crankcase
lubrication, such
compositions being referred to as crankcase lubricants. In
particular, although not
exclusively, the present invention relates to use of additives with friction
modification
properties in automotive lubricating oil compositions.
BACKGROUND OF THE INVENTION
A crankcase lubricant is an oil used for general lubrication in an internal
combustion
engine where an oil sump is situated generally 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.
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
art describes use of glycerol monoesters as friction modifiers, for example in
US-A-
4,495,088; US-A-4,683,069; EP-A-0 092 946; and WO-A-01/72933. Glycerol
monoester
friction modifiers have been and are used commercially.
Lubricant specifications are becoming more exacting. For example, passenger
car
motor oil (PCMO) specifications have or will require more stringent fuel
economy
performance, such as in respect of improved fuel economy retention. Known
friction
modifiers such as glycerol monoesters may not be able to meet those
requirements at
moderate treat rates.
CA 02723531 2010-11-30
2
The art describes chemistries other than glycerol monoesters as having
friction
modification properties. For example, US-A-5,840,662 ('662) describes, as a
friction
modifier, a succinic anhydride that is mono-substituted with a depicted C6 to
C30 isomerized
alkenyl group, or its fully saturated alkyl analog. '662 is mainly concerned
with power
transmitting fluids but briefly alludes to applicability to "a wide variety of
lubricating oils
(e.g. , crankcase engine oils, etc.)". '662 makes no mention of fuel economy
retention.
SUMMARY OF THE INVENTION
The present invention meets the above problem by providing, as crankcase
lubricant
friction modifiers, certain organic acid anhydrides carrying aliphatic
hydrocarbyl groups. In
contrast to the anhydrides of '662, the hydrocarbyl groups are linear (i.e.
unbranched). The
data in this specification demonstrate solution of the technical problem in
the prior art and
enhanced performance of compounds with linear substituent groups as opposed to
branched
substituent groups.
In accordance with a first aspect, the present invention provides a crankcase
lubricating oil composition comprising or made by admixing
(A) an oil of lubricating viscosity; and
(B) as an additive component, one or more oil-soluble organic acid
anhydrides, the
or each anhydride carrying at least one linear unbranched aliphatic
hydrocarbyl
group having 12 to 36, such as 12 to 24, carbon atoms.
According to a second aspect, the present invention provides a method of
enabling a
passenger car motor oil composition to achieve a reduced boundary friction
coefficient when
the oil is fresh and to retain that boundary friction performance under
oxidative conditions,
which method comprises providing the composition with minor amounts of one or
more
additives (B) as defined in the first aspect of the invention. The oil may
meet the viscosity-
dependent fuel economy specifications of GF-4 as measured on the sequence VIB
engine test.
According to a third aspect, the present invention provides a method of
lubricating
surfaces of an internal combustion engine during its operation comprising:
CA 02723531 2010-11-30
3
(i) providing, in a minor amount, one or more additives (B) as defined in
the first
aspect of the invention in a major amount of an oil of lubricating viscosity
to
make a lubricant, to improve the friction modifying properties of the
lubricant;
(ii) providing the lubricant to the crankcase of the internal combustion
engine;
(iii) providing a hydrocarbon fuel in the combustion chamber of the engine;
and
(iv) combusting the fuel in the combustion chamber.
In this specification, the following words and expressions, if and when used,
have the
meanings ascribed below:
"active ingredient" 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;
-hydrocarbyl" means a chemical group of a compound that contains only hydrogen
and carbon atoms and that is bonded to the remainder of the compound directly
via a
carbon atom;
"oil-soluble" or "oil-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 example, 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
CA 02723531 2010-11-30
4
additional incorporation of other additives may also permit incorporation of
higher
levels of a particular additive, if desired;
"major amount" means in excess of 50 mass % of a composition;
-minor amount" means less than 50 mass % of a composition;
-TBN- means total base number as measured by ASTM D2896;
-phosphorus content" is measured by ASTM D5185;
-sulfur content" is measured by ASTM D2622; and
"sulfated ash content" is measured by ASTM D874.
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.
Furthermore, the constituents of this invention may be isolated or be present
within a
mixture and remain within the scope of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The features of the invention relating, where appropriate, to each and all
aspects of the
invention, will now be described in more detail as follows:
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
CA 02723531 2010-11-30
blended, for example to produce a final lubricant (or lubricant composition).
Also, a base oil
is useful for making concentrates as well as for making lubricants therefrom.
A base oil 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-1 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-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,
analogues and
homologues 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, maleic
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.
CA 02723531 2010-11-30
6
Esters useful as synthetic oils also include those made from C5 to Cp
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 compositions 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 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 additionally processed by techniques for removing spent additive and
oil breakdown
products.
Other examples of base oil are gas-to-liquid ("GTL") base oils, i.e. the base
oil may be
an oil derived from Fischer-Tropsch synthesised hydrocarbons made from
synthesis gas
containing FL 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 American
Petroleum
Institute (API) publication "Engine Oil Licensing and Certification System-,
Industry
Services Department, Fourtenth Edition, December 1996, Addendum 1, December
1998;
1509 definition.
When the oil of lubricating viscosity is used to make a concentrate, it is
present in a
concentrate-forming amount (e.g., from 30 to 70, such as 40 to 60, mass %) to
give 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 component
CA 02723531 2010-11-30
7
(B) above, optionally with 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.
Concentrates constitute a convenient means of handling additives before their
use, as
well as facilitating solution or dispersion of additives in lubricants. When
preparing a
lubricant 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 one or more co-
additives, such as
described hereinafter, in a single concentrate.
To obtain a crankcase lubricant, the oil of lubricating viscosity may be
provided in a
major amount, in combination with a minor amount of additive component (B) as
defined
herein and, if necessary, one or more co-additives, such as described
hereinafter. This may be
done 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 before, at the same time as, or
after addition of other
additives.
Preferably, the oil of lubricating viscosity is present in the lubricant in an
amount of
greater than 55 mass %, more preferably greater than 60 mass %, even more
preferably
greater than 65 mass %, based on the total mass of the lubricant. Preferably,
the oil of
lubricating viscosity is present in an amount of less than 98 mass %, more
preferably less than
95 mass %, even more preferably less than 90 mass %, based on the total mass
of the
lubricant.
The terms "oil-soluble" or "oil-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 example, 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
CA 02723531 2010-11-30
8
incorporation of other additives may also permit incorporation of higher
levels of a particular
additive, if desired.
The lubricants of the invention may be used to lubricate mechanical engine
components, particularly in internal combustion engines, e.g. spark-ignited or
compression-
ignited two- or four-stroke reciprocating engines, by adding the lubricant
thereto.
The lubricating oil compositions of the invention comprise defined components
that
may or may not remain the same chemically before and after mixing with an
oleaginous
carrier. This invention encompasses compositions which comprise the defined
components
before mixing, or after mixing, or both before and after mixing.
When concentrates are used to make the lubricants, they may for example be
diluted
with 3 to 100, e.g. 5 to 40, parts by mass of oil of lubricating viscosity per
part by mass of the
concentrate.
The lubricants of the present invention may contain low levels of phosphorus,
namely
not greater than 0.09 mass %, preferably up to 0.08 mass %, more preferably up
to 0.06 mass
% of phosphorus, expressed as atoms of phosphorus, based on the total mass of
the lubricant.
Typically, the lubricants may contain low levels of sulfur. Preferably, the
lubricant
contains up to 0.4, more preferably up to 0.3, most preferably up to 0.2, mass
% sulfur,
expressed as atoms of sulfur, based on the total mass of the lubricant.
Typically, the lubricant may contain low levels of sulfated ash. Preferably,
the
lubricant contains up to 1.0, preferably up to 0.8, mass % sulfated ash, based
on the total mass
of the lubricant.
Suitably, the lubricant may have a total base number (TBN) of between 4 to 15,
preferably 5 to 11.
ADDITIVE COMPONENT (B)
CA 02723531 2010-11-30
=
9
In (B), the organic acid anhydrides are anhydrides of carboxylic acids and may
be
cyclic or linear. The cyclic anhydrides may be aliphatic such as anhydrides of
dicarboxylic
acids, for example having a two-carbon atom chain separating the carboxyl
groups, particular
examples of the anhydrides being succinic anhydride and maleic anhydride; or
the cyclic
anhydrides may be aromatic for example phthalic anhydride. The linear
anhydrides may be
symmetrical anhydrides of monocarboxylic acids or mixed anhydrides of
different
monocarboxylic acids.
Without wishing to be bound by any theory, it is believed that the anhydrides,
in
operation in lubricants and to achieve the performance benefits described
herein, are
convertible to carboxylic acids carrying at least one said aliphatic
hydrocarbyl substituent
group.
Each anhydride, as stated, carries at least one linear (unbranched) aliphatic
hydrocarbyl group having 12 to 36, such as 12 to 24, carbon atoms. For
example, the
hydrocarbyl group may be saturated, i.e. be an alkyl group, or be a double-
bond unsaturated
hydrocarbyl group having one or more sources of unsaturation, preferably an
alkenyl group.
Preferably, the or each anhydride is mono-substituted with an aliphatic
hydrocarbyl group.
When di-substituted, the substituent groups are independent.
Preferably, (B) is a succinic anhydride, and as an example of (B), there may
be
mentioned a substituted succinic anhydride of the formula:
0
r0
0
where R is a linear (unbranched) aliphatic hydrocarbyl group having 12 to 36
carbon atoms.
In a preferred example, the hydrocarbyl substituent or R is n-octadecyl.
Acid anhydrides useful in the present invention may be commercially available
or may
be made by methods known to those skilled in the art.
CA 02723531 2010-11-30
=
Suitably, the additive component (B) is present in an amount of 0.1 to 10,
preferably
0.1 to 5, more preferably 0.1 to 2, mass % of the lubricant, based on the
total mass of the
lubricant.
CO-ADDITIVES
Co-additives, with representative effective amounts in lubricants, that may
also be
present, different from additive component (B), are listed below. All the
values listed are
stated as mass percent active ingredient.
Additive Mass % Mass %
(Broad) (Preferred)
Ashless Dispersant 0.1 ¨ 20 1 ¨ 8
Metal Detergents 0.1 ¨ 15 0.2 ¨ 9
Friction modifier 0 ¨ 5 0 ¨ 1.5
Corrosion Inhibitor 0 ¨ 5 0 ¨ 1.5
Metal Dihydrocarbyl Dithiophosphate 0 ¨ 10 0 ¨ 4
Anti-Oxidants 0 ¨ 5 0.01 ¨ 3
Pour Point Depressant 0.01 ¨ 5 0.01 ¨ 1.5
Anti-Foaming Agent 0 ¨ 5 0.001 ¨0.15
Supplement Anti-Wear Agents 0 ¨ 5 0 ¨ 2
Viscosity Modifier (1) 0 ¨ 6 0.01 ¨ 4
Mineral or Synthetic Base Oil Balance Balance
(1) Viscosity modifiers are used only in multi-graded oils.
The final lubricant, 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
additives, i.e. (B) and
any co-additives, the remainder being oil of lubricating viscosity.
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.
CA 02723531 2010-11-30
11
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. For example, a dispersant maintains
in suspension
oil-insoluble substances that result from 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 hydrocarbon chain with a
polar head, the
polarity being derived from inclusion of e.g. an 0, 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 constituted by 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 is constituted by
hydrocarbon-
substituted succinimides, made, for example, by reacting the above acids (or
derivatives) with
a nitrogen-containing compound, advantageously 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,
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.
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.
CA 02723531 2010-11-30
12
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 when 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 reaction of
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 preferred metal detergents are neutral and overbased alkali or
alkaline earth
metal salicylates having a TBN of from 50 to 450, preferably a TBN of 50 to
250. Highly
preferred salicylate detergents include alkaline earth metal salicylates,
particularly magnesium
and calcium, especially, calcium salicylates.
Friction modifiers include glyceryl monoesters of higher fatty acids, for
example, glyceryl
mono-oleate; esters of long chain polycarboxylic acids with diols, for
example, the butane
diol ester of a dimerized unsaturated fatty acid; oxazoline compounds; and
alkoxylated alkyl-
substituted mono-amines, diamines and alkyl ether amines, for example,
ethoxylated tallow
amine and ethoxylated tallow ether amine.
Other known friction modifiers comprise oil-soluble organo-molybdenum
compounds.
Such organo-molybdenum friction modifiers also provide antioxidant and
antiwear credits to
a lubricating oil composition. Suitable oil-soluble organo-molybdenum
compounds have a
molybdenum-sulfur core. As examples there may be mentioned dithiocarbamates,
dithiophosphates, dithiophosphinates, xanthates, thioxanthates, sulfides, and
mixtures thereof.
CA 02723531 2010-11-30
13
Particularly preferred are molybdenum dithiocarbamates,
dialkyldithiophosphates, alkyl
xanthates and alkylthioxanthates. The molybdenum compound is dinuclear or
trinuclear.
One class of preferred organo-molybdenum compounds useful in all aspects of
the present
invention is tri-nuclear molybdenum compounds of the formula Mo3SkL,Q, 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 molybdenum compounds may be present in a lubricating oil composition at a
concentration in the range 0.1 to 2 mass %, or providing at least 10 such as
50 to 2,000 ppm by
mass of molybdenum atoms.
Preferably, the molybdenum from the molybdenum compound is present in an
amount of
from 10 to 1500, such as 20 to 1000, more preferably 30 to 750, ppm based on
the total weight of
the lubricant. For some applications, the molybdenum is present in an amount
of greater than
500 ppm.
Anti-oxidants are sometimes referred to as oxidation inhibitors; they increase
the
resistance of the lubricant to oxidation and may work by combining with and
modifying
peroxides to render them harmless, by decomposing peroxides, or by rendering
an oxidation
catalyst inert. Oxidative deterioration can be evidenced by sludge in the
lubricant, varnish-
like deposits on the metal surfaces, and by viscosity growth.
They may be classified as radical scavengers (e.g. sterically-hindered
phenols, secondary
aromatic amines, and organo-copper salts); hydroperoxide decomposers (e.g.,
organosulfur
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).
CA 02723531 2010-11-30
. .
14
Examples of suitable antioxidants are selected from copper-containing
antioxidants,
sulfur-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, zinc molybdenum, manganese, nickel or copper. Zinc salts are most
commonly used in
lubricants such as in amounts of 0.1 to 10, preferably 0.2 to 2, mass %, based
upon the total
mass of the lubricant. 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 reaction with
mixtures of
primary and secondary alcohols. Alternatively, multiple dithiophosphoric acids
can be
prepared where the hydrocarbyl groups on one acid are entirely secondary in
character and the
hydrocarbyl groups on the other acids are entirely primary in character. To
make the zinc
salt, any basic or neutral zinc compound could be used but the oxides,
hydroxides 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 sulfur 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.
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 lube oil flow improvers, lower the
minimum
temperature at which the oil will flow or can be poured. Such additives are
well known.
CA 02723531 2010-11-30
Typical of these additive are C8 to C18 dialkyl fumerate/vinyl acetate
copolymers and
polyalkylmethacrylates.
Additives of the polysiloxane type, for example silicone oil or polydimethyl
siloxane, can
provide foam control.
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 reaction of a bis-epoxide with a 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 lubricant. 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 maleic anhydride) which are then
derivatised with,
for example, an alcohol or amine.
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 examples
which are
not intended to limit the scope of the claims hereof.
The following friction modifiers were tested:-
n-octadecen-2-y1 succinic anhydride ("nODSA"),
CA 02723531 2010-11-30
16
n-octadecyl succinic anhydride ("2H-nODSA"),
n-iso-octadecen-2-y1 succinic anhydride ("isoODSA"),
polyisobutene succinic anhydride (C17 straight chain) ("PIBSA"),
Each of the nODSA, 2H-nODSA and isoODSA were commercially available
materials. PIBSA was made by known methods.
Each of the above friction modifiers was blended separately into a lubricating
oil
composition (Oil A) at a treat rate of 0.5 wt % to give a set of test
lubricants. Apart from the
identity of the friction modifier, each lubricant was the same and comprised
an adpack
consisting of detergents, antifoam, dispersants, antioxidant and diluent
blended with a
viscosity modifier, pour point depressant, base stock and the friction
modifier.
TESTING AND RESULTS
Fresh Oil HFRR Testing
A high frequency reciprocating rig ("HFRR") was used to evaluate the
coefficient of
friction of certain of the above lubricants. Experimentation was carried out
using a step ramp
profile: coefficient of friction was measured for 5 minutes at each
temperature as the
temperature was increased from 40 C to 140 at 20 C intervals. A 4 N load was
applied via a
400 g weight and the upper specimen reciprocated over a distance of 1 mm at a
frequency of
40 Hz.
Table 1 below sets out results of a first set of experiments. It gives a
representative
average coefficient of friction value at each temperature.
CA 02723531 2010-11-30
17
TABLE 1
Temp ( C):- 40 60 80 100 120 140
Oil A 142 144 148 159 166 163
* Oil A+
2H-nODSA 118 113 110 105 97 89
(0.5 wt %)
Oil A+
isoODSA 136 135 130 126 119 110
(0.5 wt %)
Values given are friction coefficient (x 103), lower values indicating better
performance.
The values demonstrate that the 2H-nODSA-containing lubricant (of the
invention and
indicated by an asterisk) is better than the isoODSA-containing lubricant (a
comparison,
representative of the prior art), both at the same treat rate.
Table 2 below sets out results of a second set of experiments in the same way
as in
Table 1 (treat rates are 0.5 wt %).
TABLE 2
Temp ( C):- 40 60 80 100 120 140
Oil A
142 144 145 163 173 171
* Oil A+
117 115 112 107 106 103
2H-nODSA
* Oil A+
120 125 119 113 105 95
nODSA
_
Oil A+
139 148 143 139 140 140
PIBSA
CA 02723531 2010-11-30
18
The values demonstrate that both of the 2H-nODSA- and nODSA-containing
lubricants (of the invention and indicated by asterisks) are better than Oil A
alone and Oil A
and PIBSA, thereby demonstrating the friction modifying properties of the
additives of the
invention.
Aged Oil Testing
Certain of the above lubricants were aged using the CEC L-48-B test procedure
running at 150 C for 50 hours. Aliquots were sampled from the CEC L-48-B test
apparatus
after 8, 24, 30 and 50 hours of running time, and then tested on the HFRR as
described above
for boundary friction performance. Table 3 below summarises coefficient of
friction values
thereby attained for each lubricant at 140 C over the duration of the CEC L-48-
B ageing
procedure (treat rates are 0.5 wt %).
TABLE 3
Ageing Time 0 8 24 30 50
(hours)
Oil A 171 167 157 165 159
* Oil A+
103 95 97 96 148
2H-nODSA
* Oil A+
95 131 153 154 150
nODSA
- Oil A+
140 161 157 157 155
PIBSA
The figures show that 2H-nODSA gives rise to superior boundary friction
reducing
durability in comparison with the control in the HFRR when subjected to
oxidative
conditions. Also, they show that the 2H-nODSA-containing lubricant retains
friction
modifying efficiency over the initial 30 hours of the test. This is a clear
demonstration that the
2H-nODSA-containing lubricant retains friction modifier efficiency under
oxidative
conditions.
