Note: Descriptions are shown in the official language in which they were submitted.
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WO 00/63325 PCT/EPOO/03258
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HYDRAULIC FLUID
The present invention relates to a hydraulic fluid.
Background of the Invention
WO 93/03121 relates to hydraulic fluids having
improved wet filterability and having increased
resistance to loss of zinc when the oil is exposed to
water. These compositions comprise (A) a combination of
a metal salt selected from the group consisting of
sulfonates, phenates, carboxylates and mixtures thereof,
(B) an aliphatic carboxylic acid or anhydride, or
carboxylic acid group containing derivative thereof,
wherein the aliphatic group contains at least 20 carbon
atoms, and optionally (C) a metal salt of (C)(I) at
least one organic phosphorus acid or mixture of (C)(I)
at least one organic phosphorus acid and (C)(II) at
least one carboxylic acid group, and optionally (D)
triazole. In one embodiment, the carboxylic acids of (A)
are aromatic carboxylic acids. Zinc, calcium and
magnesium salts of these aromatic carboxylic acids, and
especially salicylic acids, are preferred. Although
magnesium salicylate and zinc dithiophosphate are both
mentioned per se, there is no teaching to use the
combination of these compounds.
WO 89/04358 relates to compositions comprising (A) a
neutral or basic metal salt of an acidic organic
compound, (B) a metal deactivator, preferably an
optionally substituted benzotriazole, and (C) a sulfur
and/or phosphorus-containing compound selected from the
group consisting of (C-1) phosphorus-containing amide,
(C-2) phosphorus-containing ester, (C-3) sulfur-coupled
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dithiocarbamate, (C-4) sulfur-containing compound
according to formula (I). Particularly preferred metals
for the salts (A) are sodium, magnesium, calcium or
mixtures of two or more thereof. In the extensive list
of additional compounds which can be present, zinc
dialkyl dithiophosphate is mentioned. Although magnesium
salicylate and zinc dithiophosphate are both mentioned
per se, there is no teaching to use the combination of
these compounds.
EP-A-604 218 describes functional fluids comprising
a major amount of an oil of lubricating viscosity, at
least one metal salt of thiophosphoric acid, a zinc salt
of salicylic acid, and a rust inhibitor, which fluid
contains less than about 1 %wt of dispersant and less
than about 1 %wt of basic sulfonate salt. The
thiophosphoric acid is most commonly a dihydrocarbyl
dithiophosphoric acid; the metal is most preferably
zinc. The teaching of the document is restricted to the
use of zinc salicylate.
In US-A-4,627,928, a process has been described for
preparing basic magnesium salicylates which can be
characterised as having a magnesium content of at least
150% up to 500%, of the stoichiometrically equivalent
amount of magnesium based on the amount of total acid
present. The magnesium salts obtained are described to
be suitable for use as additives in general, more
specifically as additives for a variety of lubricating
oils and fuels, e.g. gasoline and diesel fuels. It is
mentioned that these specific magnesium salicylates can
be used in combination with a wide range of other
compounds. There is no disclosure or teaching to apply
a combination of zinc dithiophosphate and magnesium
salicylate in a hydraulic fluid.
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Hydraulic fluids need to meet special requirements
as they both lubricate and transmit pressure. In order
to meet these requirements, hydraulic fluids contain
additives. Generally, hydraulic fluide contain
antiwear/extreme pressure additives. The conditions for
a hydraulic fluid are especially difficult in vane pumps
where the vane tips slide against the casing at high
speed under heavy load and at high temperature. Further,
the increasingly high operating temperatures of modern
hydraulic equipment requires the fluid to be thermally
stable to avoid the formation of deposits and$ludge and
to resist the corrosion of both ferrous and non-ferrous
metals. The requirement of good thermal stability in
hydraulic fluids containing an anti-wear additive, means
that these additives are often used in combination with
detergents. However, the calcium salts of alkylbenzene
sulphonates, alkyl-naphthalene sulphonates, petroleum
suiphonates, alkylphenates, alkyl suiphurized phenates
or alkylsalicylates which are usually applied, give.
increased wear. The increased wear is especially marked
in vane pumps, more specifically under low load
conditions. Low load coziditions occur in practice when
the pump.is idle.
= WO-A-97/10318 describes lubricants with improved
acid neutralisation properties and excellent sludge' and
wear performance in the Seq. 5E test. said lubricants
are formed using a detergent system comprising one or
more alkali or alkaline earth metal salts of an oil
soluble organic acid selected from the group consisting
of sulfonic acids, phenols, sulfurised phenols and
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carboxylic acids (including salicylate acids) wherein at
least one metal salt,is overbased and the ratio of
inorganic to organic salt present in the detergent
system expressed as TBN from inorganic salts (the
overbasing) to the total moles of organic salt is at
least 2S00.
US-A-5 558 802 describes multigrade crankcase
lubricants that have.good low temperature pumpability
and low volatility.
US-A-5 558 802 states that neutral and overbased
calcium'salts of organic acids have been found to
increase low-temperature high shear viscosity when
measured in a cold cranking simulator (CCS).
In order to produce lubricants with low CCS
viscosities under high shear rates (i.e- to allow the
engine to crank more easily at lower temperatures and
thus improve engine startability at those ambient
temperatures), it is said in US-A-5 558 802 that these
salts should be avoided altogether or used at a level
not exceeding 0.0007 moles of calcium salt per 100 grams
of lubricant.
WO-A-96/37582 describes lubricating oil compositions
for internal-combustion engines, automatic transmission
gearboxes, dampers, power steering units and the like.
Lubricating oils of described in WO-A-96/37582
comprise sulfoxymolybdenum dithiocarbamate having a
specific alkyl group, zinc dialkyl dithiophosphate
having a specific alkyl group, specific
alkylsalicylate(s), and, if desired, succinimide
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containing boron, each in a predetermined amount intra
lubricating oil base stock.
US-A-446291s describes a lubricating oil composition
comprising a major proportion of a lubricating oil and a
minor proportion of each of a Group II metal
dithiophosphate and a composition having the formula:
R1O.CO.CR2(NR3R4).CR6R7.CO.OR5, where R1, R2, R3, R4,
R5, R6 and R7 are hydrogen or a hydrocarbon radical
containing 1-30 carbon atoms, and wherein R3 or R4 are
independently selected from hydrogen, hydrocaxbon
containing from 1 to 30 carbon atoms, and acyl
containing from 1 to 30 carbon.
summary of the Ipvention
it has now aurprisingly been found that hydraulic
fluid containing a combination of magnesium salicylate
and zinc dithiophosphate, gives improved performance at
low load compared with a combination containing calcium
salicylate. Additionally, it was found that this
combiiiation also provides greater thermal stability.
Less sludge and deposits are formed when subjecting the
hydraulic fluid of the present invention to the
Cincinnati Milacron Thermal stability Test.
The present invention provides a hydraulic flu3.d
comprising a lubricant base oil in combination with (a)
from 0.001 to 5twt of magnesium aalicylate, (b) from
0.01 to 8twt of zinc dithiophosphate, which amounts are
based on total weight of hydraulic fluid.
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In one aspect of the invention, there is provided use of a composition
comprising
a lubricant base oil in combination with (a) from 0.001 to 5 %wt of magnesium
salicylate, (b) from 0.01 to 8 %wt of zinc dithiophosphate to give improved
wear
performance at low load in a hydraulic fluid, the composition being free of
calcium
salicylate.
In another aspect of the invention, there is provided use of an additive
package
comprising magnesium salicylate, zinc dithiophosphate and optionally a
dicarboxylic
acid or its mono- or di-ester or its monoamide or di-amide or imide containing
in total
between 4 and 70 carbon atoms, wherein the weight ratio of said magnesium
salicylate
to said zinc dithiophosphate is from 1:5 to 1:100 and the weight ratio of
magnesium
salicylate to said dicarboxylic acid or its mono- or di-ester or its monoamide
or di-amide
or imide is from 1:0 to 1:50, the package being free of calcium salicylate, to
prepare a
hydraulic fluid with improved wear performance at low load.
In a further aspect of the invention, there is provided a hydraulic fluid
comprising a composition comprising a lubricant base oil in combination with
(a) from
0.001 to 5 %wt of magnesium salicylate, (b) from 0.01 to 8 %wt of zinc
dithiophosphate, and (c) from 0.001 to 5 %wt of a compound according to the
following
formula I:
R3R4C-COOR,
1 (I)
R6R7X-CR5-COOR2
in which R, and R2 are each hydrogen or alkyl or hydroxyalkyl of 1 to 30
carbon atoms;
R3, R4 and R5 are each hydrogen or alkyl or hydroxyalkyl of 1 to 4 carbon
atoms: X is
CH or N and R6 and R7 are each hydrogen, alkyl or alkenyl of I to 30 carbon
atoms, or
an acyl group derived from a saturated or unsaturated carboxylic acid of up to
30 carbon
atoms.
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In a still further aspect of the invention, there is provided an additive
package for
preparing a hydraulic fluid, which additive package comprises: magnesium
salicylate,
zinc dithiophosphate and a compound according to the following fonnula I:
R3R4C-COOR,
I (I)
R6R7X-CR5-COOR2
in which R, and R2 are each hydrogen or alkyl or hydroxyalkyl of I to 30
carbon atoms;
R3, R4 and R5 are each hydrogen or alkyl or hydroxyalkyl of 1 to 4 carbon
atoms; X is
CH or N and R6 and R7 are each hydrogen, alkyl or alkenyl of 1 to 30 carbon
atoms, or
an acyl group derived from a saturated or unsaturated carboxylic acid of up to
30 carbon
atoms, wherein the weight ratio of magnesium salicylate to zinc
dithiophosphate is from
1:5 to 1:100 and the weight ratio of magnesium salicylate to said compound of
formula
Iisfroml:>Oto1:50.
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tZnt3ilesi DPa -=; ation of the Inyg i nn
The magnesium salicylate for use in the present
invention can be either neutral or overbased. The
expression "overbased" is equivalent to "basic",
"superbased", "hyperbased" and "high-metal containing
salts". These magnesium salicylates contain an excess
metal content compared to the amount of metal which
would be present accbrding to the stoichiometry of the
metal and the salicylie acid reacted with the metal.
Processes for making such neutral and basic metal salts
are well known in the art. Neutral salte can be made by
heating a mineral oil solution of an acidic organic
compound with a stoichiometric equivalent amount of a
metal neutralizing agent such as the metal oxide,
hydroxide, carbonate, bicarbonate, or sulfide at a
temperature above 50 C and filtering the resulting
mass. Basic salts are made similarly with the exception
that a stoichiometric excess of the metal is used.
Preferably, overbased magnesium salicylate is used.
20= These compositions can be characterized by their total
base number (TBN). The total base number is preferably
at least 100 mg KOH/g, more preferably at least 200 mg
KOH/g, most preferably at least 300 mg KOH/g. The total
= base number is preferably at most 600 mg KOH/g. Another
method of characterising overbased magnesium salicylates
is by the magnesium content relative to the
stoichiometrically equivalent amount of magnesium based
on the amount of total acid present. Overbased
magnesium salicyclates for use in the present invention
preferably have a magnesium content of more than 500% of
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the stoichiometrically equivalent amount of magnesium
based on the amount of total acid present, more
preferably at least 550%.
The salicylate can be either substituted or
unsubstituted. Suitable substituents include aliphatic
groups containing from 1 to 40 carbon atoms and
optionally containing one or more oxygen and/or nitrogen
atoms, and hydroxy groups. Preferred substituents are
alkyl= groups containing from 6 to 30 carbon atoms,
preferably from 12 to 20 carbon atoms. Preferably, the
substituents are linear. The salicylate can contain from
1 to 4 substituents, preferably from 1 to 3, most
preferably 1 or 2 subatituents. Most preferably, the
salicylate is substituted by 1 linear alkyl group
containing from 14 to 18 carbon atoms.
Generally, mono-alkyl salycylic acids are prepared
by alkylation of phenol and subsequent carboxylation.
Therefore, a small amount (generally at most 20 Wmol) of
dialkyl salicylate and unsubstituted salicylate can be
present in the mono-alkyl salicylate.
Magnesium salicylate which can be used in the
present invention, is commercially available. A suitable
commercial product is SAP 007 (ex Infineum). The
magnesium salicylate will usually be supplied in
combination with mineral oil. The amounts referred to in
this document, relate to the compound per se without
mineral oil.
A process by which suitable magnesium salicylate can
be prepared, has been described in US-A-4,627,928.
~
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Zinc dithiophosphate ie well known in the art.
Preferred dithiophosphate for use in the present
invention.are represented by the following formula
O-R'
1
R8 - O- P - S (formula II)
S"
in which R and R8 can be either hydrogen or an
aliphatic group. The aliphatic group is preferably a
hydrocarbyl group. The hydrocarbyl group optionally
contains an acid, a hydroxyand/or ari ester group. The
hydrocarbyl group is preferably an alkyl containing up
to 12 carbon atoms optionally further containing an
acid, a hydroxy and/or an ester group. The hydrocarbyl
substituted dithiophosphate can contain 1 or 2 aliphatic
groups, or it can be a mixture of dithiophosphates
having 1 aliphatic group and dithiophosphates having 2
aliphatic groups. Preferably, the zinc dithiophosphate
is a zinc dialkyl dithiophosphate.
Substituted dithiophosphates can contain primary,
secondary and/or tertiary aliphatic substituents, i.e.
substituents which are attached to the oxygen atom via a
carbon atom attached to one, two or three further carbon
= 25 atoms, respectively. In the present invention, it is
preferred that at least 60 twt of the aliphatic,
preferably alkyl, substituents of the zinc
dithiophosphate, are primary aliphatic substituents.
More preferably at least 80 %wt of the aliphatic
substituents are primary aliphatic substituents.
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suitable zinc dithiophosphates which are
commercially available include Elco 108 (ex Elco
Corporation), Lz 1375 (ex Lubrizol), OLOA 4269Q (ex
Oronite) and HITEC 680 (ex Ethyl).
The amount of magnesium salicylate which is present
is preferably at most 1twt, based on total composition,
more preferably at most 0.5 twt, most preferably at most
0.3 %wt. The amount of magnesium salicylate which is
present is preferably at least 0.001 %wt, more
preferably -at least 0.005 %wt more preferably at least
0.01 %wt, most preferably at least 0.015 twt. The
amount of zinc dithiophosphate which-is present is
preferably at most 5 %wt, based on total composition,
more preferably at most 3 %wt, moet preferably at most 1
%wt: The amount of zinc dithiophosphate which is present
is preferably at least 0.05 %wt, more preferably at
least 0.7 &wt, most preferably at least 0.1 %wt.
The hydraulic fluid can further comprise (c) from
0.001 to 5 %wt of a rust inhibitor based on total.
composition, preferably a carboxylic acid or ester or
amide or imide containing compound, more preferably a
dicarboxylic acid or its mono- or di-eater or its mono-
amide or di-amide or imide, more preferably a
= dicarboxylic acid or its ester, amide or imide
containing a total number of between 4 and 70 carbon
atoms. More preferably, the number of carbon atoms of
the compound is between 20 and 40. A preferred compound
is an aliphatic succinimide or succinic diamide. Such
compounds have been described in EP-A-776964.
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Most preferably, (c) is from 0.001 to 5 %wt of a compound according to the
following formula I
R3R4C-COORI
I (1)
R6R7X-CR5-COOR2
in which Rl and R2 are each hydrogen or alkyl or hydroxyalkyl of 1 to 30
carbon atoms;
R3, R4 and R5 are each hydrogen or alkyl or hydroxyalkyl of 1 to 4 carbon
atoms; X is
CH or N and R6 and R7 are each hydrogen, alkyl or alkenyl of 1 to 30 carbon
atoms, or
an acyl group derived from a saturated or unsaturated carboxylic acid of up to
30 carbon
atoms. Preferably, RI and R2 are each an alkyl of from 3 to 6 carbon atoms,
R3, R4 and
R5 are each hydrogen, X is N and R6 and R7 are each an alkyl of 15 to 20
carbon atoms
or an acyl group derived from a saturated or unsaturated dicarboxylic acid
containing 4
to 10 carbon atoms, at least one of R6 and R7 being an acyl group. Especially
preferred
is aspartic acid, N-(3-carboxy-l-oxo-2-propenyl)-octadecyl-bis(2-methylpropyl)
ester.
Such aspartic acid esters are commercially available; processes for preparing
such
compounds having been described in EP-A-434 464.
The weight ratio in which the compounds of the present invention are present
can
differ within wide ranges. Preferably, the hydraulic fluid comprises magnesium
salicylate,
zinc dithiophosphate and optionally a rust inhibitor in such quantities that
the weight ratio
of magnesium salicylate to zinc dithiophosphate is from 1:5 to 1:100 and the
weight
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ratio of magnesium salicylate to rust inhibitor is from
1:0 to 1:50.
The lubricant base oils present in the hydraulic
fluid of the present invention, can be any base fluid
which is suitable for use in hydraulic fluids. The base
oil can be a natural or a synthetic lubricant base oil,
or a mixture thereof. The natural oil can be an animal
oil or vegetable oil, such as.lard oil or castor oil, or
a mineral oil such as liquid petroleum oils and solvent
treated or acid treated mineral lubricating oil of the
paraffinic, naphthenic, or mixed paraffinic/naphthenic
type which may be further refined by hydrocracking and
hydrofinishing processes and/or dewaxing. Synthetic
lubricating oils include hydrocarbon oils and halo-
substituted hydrocarbon oils such as polymerised and
interpolymerised olefins. A suitable base oil contains
poly-alpha-olefins, such as polydecene. Preferably, the
base oil is a hydrocarbon base oil. More preferably, the
base fluid is a mineral oil which contains less than 10
t by weight of aromatic compounds, preferably less than
5t by weight, most preferably less than 3.0 $ by
weight, measured according to DIN 51378. It is further
preferred that the base oil contains less than 1.0 twt
of sulphur, calculated as elemental sulphur, preferably
less than 0.1 kwt, more preferably less than 0.05 twt,
measured according to ASTM D 4045. Such mineral oils can
be prepared by severe hydroprocessing. Preferably, the
lubricating oil has a kinematic viscosity in the range
of from 5 to 220 cSt at 40 C, more preferably of from
10 to 200 cSt, most preferably of from 20 to 100 cst.
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The hydraulic fluid according to the present
invention can contain further additives usually present
in hydraulic fluids, such as pour point depressants,
anti-foam agents and demulsifier. Pour point depressants
generally are high molecular weight polymers such as
alkylaromatic polymers and polymethacrylates. As anti-
foam agents, silicone polymers and/or polymethacrylates
are generally ueed. Demulsifiers which are generally
applied are polyalkylene glycol ethers. Furthermore,
further detergents such as sulphonates and phenates,
metal deactivators, antioxidants such as phenolic
compounds, diphenyl amines and phenyl naphthyl amines,
ashless anti-wear agents and/or ashless dispersants,
such as succinimides, can be present.
The hydraulic fluids of the present invention
contain magnesium salicylate. For specific applications,
it can be advantageous that the fluids contain a
combination of magnesium and calcium salicylate.
The components of the present invention can be added
per se to a lubricating oil, or they can be mixed into
an additive package before being added to the
lubricating oil. The.additive package for preparing the
hydraulic fluid preferably contains magnesium
salicylate, zinc dithiophosphate and optionally a
dicarboxylic acid or its mono- or di-ester or its mono-
amide or di-amide or imide containing in total between 4
and 70 carbon atoms,.wherein the weight ratio of
magnesium salicylate to zinc dithiophosphate is from 1:5
to 1:100 and the weight ratio of magnesium salicylate to
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dicarboxylic acid or its mono- or di-ester or its mono-
amide or di-amide or'imide is from 1:0 to 1:50.
E;XAI~PLES
Formulations were prepared containing the following
additives:
Magnesium salicylate: highly overbased magnesium
alkylealicylate having a total base number of 337 mg
KOH/g (SAP 007 ex INFINEUM) and a magnesium content of
about 7504 of the stoichiometrically equivalent amount
of magnesium based on the amount of total aci4,
containing 40 %wt of mineral oil
Calcium salicylate: overbased calcium alkylsalicylate
having a total base number of 168 mg KOH/g (SAP 001 ex
INFINEUM), containing 40 -1wt of mineral oil.
The amounts of metal salicylate mentioned in Table
1, are the amounts of metal salicylate per se, without
mineral oil.
Zinc dithiophosphate: zinc di(ethyl-
hexyl)dithiophosphate (Elco 108 ex Elco corporation)
Compound according to formula I: aspartic acid, N-(3-
carboxy-l-oxo-2-propenyl)-N-octadecyl , bis(2-
rnethylpropyl)ester.
These compounds were added to a lubricant base oil
= containing less than 1.0 & by weight of aromatic
compounds, legs than 0.05 %wt of sulphur, calculated as
elemental sulphur and having a kinematic viscosity in
the range of 32 cSt (at 40 ) (ISO viscosity grade 32).
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The compositions obtained are described in Table 1.
The amounts are of the compounds per se, excluding the
mineral oil.
Compositions 1 and 2 were used in Vickers V104C vane
pump tests. A new pump cartridge was used for each test.
The test duration was 250 hours, performed at a fluid
temperature of about 66 C, at a fluid outlet pressure
of 35 bar (3.5 MPa) and at a pump speed of 1450
revolutions per minute. The results are described in
Table 1.
T b~1 ~1
Composition 1 Composition 2
magnesium salicylate 0.06 twt -
calcium salicylate - 0.06 twt
zinc dithiophosphate 0.37 twt 0.37 twt
compound of formula I 0.10 %wt 0.10 $wt
lubricant base oil balance balance
Low load test
ring weight loss (mg) 13 96
vane weight loss (mg) 2 1
total weight loss (mg) 15 97
From Table 1 it is clear that better protection against
wear is provided by a composition containing magnesium
salicylate (1), than by a composition containing calcium
salicylate (2). The ring weight loss and total.weight
loss incurred when using composition 1 is significantly
less than that incurred when composition 2 is employed-
The vane weight loss is similar for both compositions.
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