Note: Descriptions are shown in the official language in which they were submitted.
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AS ORIGINALLY FILED
DOT 4 brake fluids
P.F. 0000054341/Ab
The present invention relates to novel DOT 4 brake fluids, in which the
addition of borates
(boric acid esters) is not necessary. The brake fluids comprise
(a) from 10 to 50% by weight of diethylene glycol and/or dipropylene glycol
and
(b) from 50 to 90% by weight of (poly)ethylene glycol monoalkyl ether
and/or (poly)propylene glycol monoalkyl ether
and are preferably free of polyglycol dialkyl diethers.
Hydraulic fluids and in particular brake fluids for motor vehicles are subject
to very high
requirements with respect to their chemical and physical properties. According
to the
existing standards and specifications for brake fluids of the US Department of
2o Transportation (DOT) in the Federal Motor Vehicle Safety Standard FMVSS No.
116 and
the standard SAE J 1704 published by the Society of Automotive Engineers,
modern brake
fluids should on the one hand have a high equilibrium reflux boiling point
(ERBP) and
high wet ERBP, but on the other hand should also have a viscosity which
changes only
slightly within a wide temperature range.
Accordingly, for a DOT 4 brake fluid according to FMVSS No. 116, the
specification
values shown below must be complied with:
ERBP: > 230°C
Wet ERBP: >_ 155°C
Viscosity at -40°C: <_ 1 800 mm2/s
There are moreover more stringent requirements for sufficiently good
protection of metals
and nonferrous metals from corrosion by brake fluids, which can be achieved by
corrosion
inhibitor additives contained therein.
Commercial DOT 4 brake fluids always contain boric acid esters, for example
methyltriglycol borate, which can chemically eliminate certain amounts of
penetrating
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water from the brake fluid by hydrolysis. A disadvantage is that boric acid
esters are
themselves hygroscopic, with the result that such DOT 4 brake fluids,
particularly in
regions of high relative humidity, for example in tropical and subtropical
regions, can very
rapidly absorb so much moisture that, in spite of the trapping function of the
boric acid
esters, the operability of a brake system filled therewith can be adversely
affected.
US 3,625,899 describes DOT 4 brake fluids which contain from 54.5 to 92% of at
least one
boric acid ester, up to 20% of polyalkylene glycols and from 3 to 43% of
polyglycol
monoalkyl or dialkyl ethers, in addition to further additives.
to
US 3,972,822 describes DOT 4 brake fluids which contain from 40 to 65% of
polyglycol
monoalkyl ethers, from 16 to 45% of polyglycols and from 10 to 19% of boric
acid esters
plus corrosion inhibitors.
WO 00/46325 describes DOT 4 brake fluids which contain methyltriglycol borate,
glycol
ethers and glycols in different amounts and an additive system.
WO 02/38711, too, discloses corresponding DOT 4 brake fluids which contain
different
methylpolyglycol borates, polyglycol monoalkyl ethers and corrosion
inhibitors.
DE 36 27 432 C2 describes borate-free brake fluids comprising from 30 to 80%
of a glycol
component and up to 70% of polyglycol alkyl ether. The glycol component in
turn contains
from 0 to 80, preferably from 55 to 80, % by weight of diethylene glycol
andlor
dipropylene glycol. The polyglycol alkyl ether component contains from 0 to
90,
preferably from 0 to 50, % by weight of at least one polyglycol monoalkyl
ether. In
selected mixing ratios, these fluids fulfill the DOT 4 specification. A
disadvantage in the
case of these formulations is in particular the ERBP only just above the
specification limit
and moreover the use of polyglycol dialkyl ethers which are more expensive to
synthesize
and often also lead to incompatibility reactions of rubber and sealing
materials.
There is furthermore a need for low viscosity brake fluids which fulfill the
DOT 4
specification.
It is an object of the present invention to provide such a brake fluid.
Preferably, this brake
fluid should not be very hygroscopic and should be capable of being used in
regions of
high relative humidity. In particular, it should be necessary to use only
small amounts of
boric acid esters or ideally the use of such esters should even be completely
superfluous.
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We have found that this object is achieved by a brake fluid comprising
P.F. 0000054341/Ab
a) from 10 to 50% by weight of diethylene glycol and/or dipropylene glycol
and
b) from 50 to 90% by weight of one or more monoalkyl ethers of
(poly)ethylene glycol or (poly)propylene glycol.
In particular, the novel fluids are free of boric acid esters.
1o Diethylene glycol or dipropylene glycol or a mixture of diethylene glycol
and dipropylene
glycol in any desired ratio may be used. Diethylene glycol is preferred.
Diethylene glycol and/or dipropylene glycol are present in the novel brake
fluids in an
amount of from 10 to 50, preferably from 20 to 40, % by weight.
A further component of the novel brake fluid comprises one or more monoalkyl
ethers of
(poly)ethylene glycols and/or (poly)propylene glycols, which are present in
the novel
fluids in an amount of from 50 to 90, preferably from 60 to 80, % by weight.
2o Examples of suitable (poly)ethylene glycols are monoethylene glycol,
diethylene glycol,
triethylene glycol, tetraethylene glycol, pentaethylene glycol and
hexaethylene glycol.
Examples of suitable (poly)propylene glycols are monopropylene glycol,
dipropylene
glycol, tripropylene glycol, tetrapropylene glycol, pentapropylene glycol and
hexapropylene glycol.
Diethylene glycol, triethylene glycol and/or tetraethylene glycol are
preferred.
The alkyl radical in the monoalkyl ethers of (poly)ethylene glycol and
(poly)propylene
3o glycol used according to the invention is preferably a linear or branched
C1-C6-alkyl
radical. It is more preferable to use a linear or branched C1-C4-alkyl
radical, for example
methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl or tert-
butyl.
The alkyl radicals are in particular methyl, ethyl, isopropyl or n-butyl.
In the present invention, the use of methyldiethylene glycol,
methyltriethylene glycol,
methyltetraethylene glycol and/or butyltriethylene glycol is preferred.
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The novel brake fluids have wet ERBPs and in particular ERBPs which are close
to those
which have been achieved to date with borate-free brake fluids. They are
comparable with
those achieved today only with borate-containing fluids. Owing to the absence
of borate,
however, the novel fluids are substantially less hygroscopic than borate-
containing ones.
This is advantageous in particular during use in tropical and subtropical
regions, since,
although a part of the water is bound by the addition of borate, water is also
relatively
rapidly absorbed. This results in each case in a deterioration in the quality
of the brake
fluid. In particular, this loss of quality occurs frequently in the brake
system of motor
vehicles but also during storage and transport of the fluids. The novel brake
fluids do not
to have said disadvantages.
It is true that the novel brake fluids may contain different amounts of boric
acid esters.
However, the advantages according to the invention of low hygroscopicity are
generally
not achieved thereby. This is the case in particular when boric acid esters
are added in the
amounts customary according to the prior art.
Furthermore, the novel fluids are in particular free of polyalkylene glycol
dialkyl ethers.
Although these too may be present in different amounts, in general the
advantages of the
novel brake fluids, in particular the compatibility with rubber and sealing
materials, are
2o then not achieved, this too of course being dependent on the amount of any
polyalkylene
glycol dialkyl ethers present.
Further polyglycols may be present as an optional component in the novel
formulations.
Relatively high-boiling reaction products of ethylene oxide and/or propylene
oxide and/or
butylene oxide with water or diol are preferably used. In particular, reaction
products of
mixtures of ethylene oxide and propylene oxide with water are used. The number
of
alkylene oxide units in said polyglycols is usually from 2 to 10, preferably 2
or 3, and in an
amount of up to 5%.
3o The effect of these high-boiling polyglycols is that of a lubricant, which
is due
substantially to an improvement in the temperature-viscosity behavior. The
polyglycols
impart sufficient viscosity to the polyglycol monoalkyl ethers, which often
have low
viscosity at high temperatures, and thus ensure sufficient lubrication.
Sufficient lubrication
is desired since, in the components of the motor vehicle brake system, rubber
or elastomers
have to slide on metal with very little wear.
In a further embodiment, the novel DOT 4 brake fluids for motor vehicles
furthermore
contain from 0.001 to 10, preferably from 0.005 to 4, in particular from 0.005
to 1, % by
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P.F. 0000054341/Ab
weight of one or more corrosion inhibitors, for example 1H-1,2,3-
benzotriazole, 1H-1,2,3-
tolutriazole, hydrogenated 1H-1,2,3-tolutriazole, benzimidazole and/or
derivatives thereof,
alkali metal salts of phosphoric acid and phosphorous acid, fatty acids,
preferably caprylic,
lauric, palmitic, stearic or oleic acid, and alkali metal salts thereof,
esters of phosphoric
acid and of phosphorous acid, preferably ethyl phosphate, dimethyl phosphate,
isopropyl
phosphate, diisopropyl phosphate, butyl phosphite or dimethyl phosphite, mono-
and
dialkylamines which may be ethoxylated and salts thereof with mineral and
fatty acids,
preferably butylamine, hexylamine, octylamine, isononylamine, oleylamine,
dipropylamine, diisopropylamine or dibutylamine, alkanolamines which may be
to ethoxylated, preferably mono-, di- or triethanolamine, N,N'-di-n-
butylaminoethanol or
1,1'-iminodipropan-2-ol, cyclohexylamine, and/or vitro aromatics, preferably 3-
nitrobenzaldehyde.
The novel brake fluids may also contain one or more of the heterocyclic
compounds which
are described in WO 01/90281 and are of the following formula
Xi N
(R~)n~ ~ ~z (I)
N
H
where
(i) XisN,YisCRandZisNor
(ii) X is N, Y is N and Z is N or CR or
(iii) X is CR, Y is N and Z is N,
R, in each case independently of further radicals R present, being a hydrogen
atom or a
radical R1,
R', in each case independently of further radicals R1 present, being alkyl,
aryl, aralkyl,
halogen, haloalkyl, unsubstituted or alkyl-, aryl- or aralkyl-substituted
amino, a
heterocyclic radical, cyano, carboxyl, alkoxycarbonyl, hydroxyl or alkoxy,
said organic
radicals R' each being of 1 to 30 carbon atoms, and
n being 0, 1 or 2. Examples of preferred compounds of this type include
purine, adeinine,
6-chloropurine, 2,6-dichloropurine, 6-methoxypurine, 1H-1,2,3-
triazolo[4,Sb]pyridine, 6-
histaminopurine and 6-furfurylaminopurine.
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The novel borate-free DOT 4 brake fluids may furthermore contain the
formulations
described in WO 02/081604 and comprising 1H-1,2,4-triazole.
The novel brake fluids may additionally contain the cyclic carboxylic acid
derivatives
which are mentioned in WO 00/65001 and are of the formula I
X
/C"0
~A~n
where
to
X is an oxygen atom or a group of the formula N-R',
R1 being hydrogen or a linear or branched C1- to C2o-alkyl group which
additionally
may be interrupted by up to 9 nonneighboring oxygen atoms and/or may carry up
to
6 hydroxyl groups, or a cycloalkyl group or an unsubstituted or substituted
phenyl
group,
A is a group of the formula -CR2R3-,
2o R2 and R3 each being hydrogen or C1- to C8-alkyl groups which additionally
may be
interrupted by up to 4 nonneighboring oxygen atoms and/or may carry up to 3
hydroxyl groups, and
n is from 2 to 7.
These are suitable as components for reducing the low-temperature viscosity in
the
presence of water.
Further components and assistants in the novel brake fluids for motor vehicles
are
3o conventional antioxidants, e.g. phenothiazine and/or those based on phenol,
and
conventional antifoams and markers.
All percentages by weight stated above and below are based in each case on the
total
amount of the hydraulic fluid or of the brake fluid.
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The novel borate-free DOT 4 brake fluids meet the requirements stated at the
outset in an
outstanding manner and moreover have generally good corrosion behavior
compared with
the prior art, i.e. very good corrosion prevention is ensured in the case of
metals such as
iron, steel, tin plate, cast iron (gray cast iron), lead, tin, chromium, zinc,
aluminum,
magnesium and alloys thereof and in the case of solder metals, for example tin
solder, and
in the case of nonferrous metals such as copper and alloys thereof, for
example brass.
In addition to the hygroscopic properties substantially reduced owing to the
freedom from
borate, further advantages of the novel DOT 4 brake fluids for motor vehicles
which may
be singled out are their advantageous low-temperature viscosity, good water
compatibility,
a mild pH, good low temperature, high temperature and oxidation stability and
good
chemical stability, advantageous behavior toward (i.e. good compatibility
with) materials
such as rubbers, plastics, glue joints, fiber, elastomer and rubber seals and
similar materials
and good lubricating behavior.
The examples which follow illustrate the invention without restricting it.
Use examples:
2o The novel borate-free DOT 4 brake fluid BF1 used had the following
composition:
Novel example BF 1:
31.0% of diethylene glycol
67.7% of a mixture of methyldiglycol, butyldiglycol, butyltriglycol and
methyltetraglycol
1.3% of a mixture of 1,1'-iminodipropan-2-ol, bisphenol A, tolutriazole and 3-
nitrobenzaldehyde
3o Comparative example BF 2
(corresponds to example 5 from DE 36 27 432 C2)
39% of diethylene glycol
26% of triethylene glycol
24% of triethylene glycol dimethyl ether
10% of methyltriglycol
1% of corrosion inhibitor (1,1'-iminodipropan-2-of used)
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Physical data:
BF 1 BF 2 (comparison)
ERBP [°C]: 251 234
wet ERBP [°C]: 159 153
(Water absorption: (Water absorption:
P.F. 0000054341/Ab
3.27%; reference RM 71 3.73%) 3.93%; reference RM 71 3.70%)
Viscosity -40°C: 1393
[mm2/s] 1277
Compared with the prior art according to DE 3627432 C2, the novel borate-free
DOT 4
brake fluids have in particular a substantially higher ERBP which, in the case
of BF 1,
easily exceeds the minimum requirement according to FMVSS No. 116 by
20°C, and a
lower water absorption and, associated therewith, a higher wet ERBP.
The novel brake fluids moreover lead to very good corrosion prevention, as
shown by the
results below for BF 1:
Corrosion test according to SAE J 1704, test duration 120 h/100°C:
Metal Weight change Appearance
[mg/cmz]
Tin plate 0.00 unchanged
Steel + 0.01 unchanged
Aluminum 0.00 unchanged
Gray cast iron + 0.04 unchanged
Brass - 0.05 slightly tarnished
Copper - 0.05 slightly tarnished
Zinc + 0.03 tarnished
pH before/after test: 9.9/9.6
