Note: Descriptions are shown in the official language in which they were submitted.
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Hydraulic fluids having improved corrosion protection
The present invention relates to hydraulic fluids, in particular
brake fluids for motor vehicles, having improved corrosion
protection which comprise
(a) from 0.005 to 0.125% by weight of 1H-1,2,4-triazole, and
(b) from 0 to 10% by weight of one or more further corrosion
inhibitors, where, on concomitant use of 1H-1,2,3-
benzotriazole and/or 1H-1,2,3-tolutriazole and/or derivatives
thereof, the weight ratio between 1H-1,2,4-triazole and said
1H-1,2,3-triazoles must be greater than 4:1.
Hydraulic fluids and in particular brake fluids for motor
vehicles are subject to very high requirements with respect to
their chemical and physical properties. In accordance with the
existing standards and specifications for brake fluids from the
US Department of Transportation in Federal Motor Vehicle Safety
Standard FMVSS-No. 116 and the SAE J 1704 standard published by
the Society of Automotive Engineers, modern brake fluids should
on the one hand have high dry boiling points (equilibrium ref lux
boiling points "ERBP") and high wet boiling points ("wet
ERBP"), but on the other hand should also have a viscosity which
changes only slightly within a broad temperature range.
In addition, there are more exacting requirements from the
automobile industry for improved corrosion protection in the case
of metals and nonferrous metals. Corrosion inhibitors in brake
fluids have the job of preventing destruction of metallic
materials caused by corrosion.
The use of 1H-1,2,3-triazoles, such as 1H-1,2,3-benzotriazole or
1H-1,2,3-tolutriazole, as corrosion inhibitors in hydraulic
fluids or brake fluids has been known for some time, for example
from EP-A 028 789 (1) and EP-A 454 110 (2).
WO 00/46325 (3) recommends hydraulic fluids which comprise a
combination of 1H-1,2,3-benzotriazole or derivatives thereof,
such as 1H-1,2,3-tolutriazole, and 1H-1,2,4-triazole or
derivatives thereof in a weight ratio of from 1:4 to 4:1 as
corrosion inhibitor system. WO 00/46325 defines the benzotriazole
and its derivatives useful in the 1325 invention as represented by
the formula
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R'
C
C
\ /N
R~ II "N
i
i
C\C/C\ N
wherein R and R' are the same or different and can be hydrogen,
an alkyl group containing from 1 to 8 carbon atoms, an amino
group such as-NH,-NHR or-NRR', an acyl group such as -COR, or an
aryl group such as benzene or toluene.
For comparative purposes, Tables 1 to 4 in (3) also indicate
hydraulic fluids which comprise 1H-1,2,4-driazole alone in
concentrations of 0.15% by weight; however, its corrosion-
inhibiting action is acceptable only in the case of
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copper.
The hydraulic fluids and brake fluids for motor vehicles which
are known in the prior art are, however, still unsatisfactory
with respect to their properties and in particular their
corrosion protection. It was therefore an object of the present
invention to provide hydraulic fluids which, in particular,
satisfy the abovementioned requirements for improved corrosion
protection in the case of metals and nonferrous metals.
We have found that this object is achieved by the hydraulic or
power-transmission fluids defined at the outset.
The hydraulic fluids, in particular motor vehicle brake fluids,
according to the invention preferably comprise from 0.005 to
0.10% by weight, preferably from 0.005 to 0.08% by weight, in
particular from 0.005 to 0.06% by weight, of component (a).
In a preferred embodiment, the hydraulic fluids, in particular
motor vehicle brake fluids, according to the invention comprise
component (a) as the only triazole-based corrosion inhibitor.
This is intended to mean that triazoles, such as 1H-1,2,3-
benzotriazole, 1H-1,2,3-tolutriazole or hydrogenated 1H-1,2,3-
tolutriazole, are excluded here, but inorganic and/or organic
corrosion inhibitors having a different structure may be present.
In another preferred embodiment, the hydraulic fluids, in
particular motor vehicle brake fluids, according to the invention
also comprise up to 10% by weight, in particular up to 5% by
weight, of one or more further corrosion inhibitors (b), where,
in the case of the concomitant use of 1H-1,2,3-benzotriazole
and/or 1H-1,2,3-tolutriazole and/or derivatives thereof, the
weight ratio between 1H-1,2,4-triazole and said 1H-1,2,3-
triazoles must be greater than 4:1.
Suitable further corrosion inhibitors (b) here are, in
particular, alkali metal salts of phosphoric acid and phosphorous
acid, fatty acids, such as caprylic, lauric, palmitic, stearic or
oleic acid and alkali metal salts thereof, esters of phosphoric
acid and phosphorous acid, such as ethyl phosphate, dimethyl
phosphate, isopropyl phosphate, diisopropyl phosphate, butyl
phosphite or dimethyl phosphite, substituted or unsubstituted
ethoxylated mono- and dialkylamines and salts thereof with
mineral acids and fatty acids, for example butylamine,
hexylamine, octylamine, isononylamine, oleylamine, dipropylamine,
diisopropylamine or dibutylamine, substituted or unsubstituted
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ethoxylated alkanolamines, for example mono-, di- or
triethanolamine, N,N'-di-n-butylaminoethanol or 1,1'-
iminodipropan-2-ol, cyclohexylamine, benzimidazole and
hydrogenated tolutriazole, and nitroaromatic compounds, for
example 3-nit robenzaldehyde.
Said corrosion inhibitors (b) are preferably present in the
hydraulic fluids, in particular motor vehicle brake fluids,
according to the invention in amounts of from 0.001 to 10% by
weight, in particular from 0.001 to 5% by weight.
In a particularly preferred embodiment, the hydraulic fluids, in
particular motor vehicle brake fluids, according to the invention
comprise, besides 1H-1,2,4-triazole (a), from 0.001 to 5% by
weight, in particular from 0.001 to 0.5% by weight, of one or
more compounds from the group consisting of benzimidazole,
hydrogenated 1H-1,2,3-tolutriazole, purine, adenine, 6-
chloropurine, 2,6-dichloropurine, 6-methoxypurine, 1H-1,2,3-
triazolo(4,5-b)pyridine, 6-histaminopurine and 6-
furfurylaminopurine and, if desired, further corrosion inhibitors
other than (a) as additional corrosion inhibitors (b). Said
purine derivatives are described in German Patent Publication
DE A 100 26 010 as non-ferrous metal corrosion inhibitors for
hydraulic fluids or brake fluids.
All the percent by weight data given above and below in each case
relate to the total amount of the hydraulic fluid or brake fluid,
unless stated otherwise. The sum of all components listed above
and below for the hydraulic fluids or brake fluids according to
the invention in each case adds up to 100% by weight.
The present invention relates, in particular, to brake fluids for
motor vehicles which comprise, as corrosion inhibitors, said
components (a) and, if desired, (b).
In a preferred embodiment, the motor vehicle brake fluids
according to the invention furthermore comprise, in addition to
components (a) and, if desired, (b), from 0.1 to 97% by weight,
in particular from 30 to 97% by weight, especially from 50 to 97%
by weight, of one or more polyglycol ethers and/or borates
thereof.
Suitable polyglycol ethers here are, in particular, ethylene
glycol monoalkyl ethers having up to 6 ethylene oxide units and
having up to 4 carbon atoms in the alkyl radical, for example
diethylene glycol monomethyl ether, triethylene glycol monomethyl
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ether, triethylene glycol monobutyl ether or tetraethylene glycol
monomethyl ether. Also suitable are ethylene glycol dialkyl
ethers and propylene glycol dialkyl ethers having up to 6
alkylene oxide units and having up to 4 carbon atoms in each of
the alkyl radicals, for example triethylene glycol dimethyl
ether, tetraethylene glycol dimethyl ether, diethylene glycol di-
tert-butyl ether, diethylene glycol dibutyl ether, diethylene
glycol di-tert-butyl ether or dipropylene glycol dimethyl ether.
Suitable boric acid esters of said or other polyglycol ethers are
described, in particular, in the specifications EP-B 013 925
(cyclic bisboric acid esters), DE-C 28 04 535 (nitrogen-
containing boric acid esters), DE-A 24 38 038 (boric acid
alkylene glycol monoalkyl ether esters) and DE-B 17 68 933 (boric
acid trisalkoxyalkyl esters).
Instead of said polyglycol ethers and/or boric acid esters
thereof, the motor vehicle brake fluids according to the
invention may also comprise, as principal component, those based
on carboxylic acid esters, mineral oils or silicone oils.
In a further preferred embodiment, the motor vehicle brake fluids
according to the invention furthermore comprise, besides
components (a) and, if desired, (b), from 0.1 to 50% by weight,
in particular from 1 to 40% by weight, especially from 5 to 30%
by weight, of one or more polyglycols.
Suitable polyglycols here are, in particular, relatively high-
boiling products of the reaction of ethylene oxide and/or
propylene oxide and/or butylene oxide with water or diols, in
particular corresponding products of the mixtures of ethylene
oxide and propylene oxide with water. The number of alkylene
oxide units in polyglycols of this type is normally from 2 to 10.
The action of these high-boiling polyglycols is that of a
lubricant, which is attributable essentially to an improvement in
the temperature/viscosity behavior. The polyglycols give the low-
viscosity polyglycol ethers sufficient viscosity at high
temperatures and thus ensure adequate lubrication. Adequate
lubrication is necessary in the components of the motor vehicle
braking system since rubber or elastomers have to slide on metal
with very low wear in these systems.
Further components and assistants in the motor vehicle brake
fluids according to the invention can be conventional
antioxidants, for example phenothiazine and/or those based on
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phenol, and conventional antifoams.
In addition, the brake fluids according to the invention may
comprise the cyclic carboxylic acid derivatives mentioned in
WO 00/65001, which are suitable as components for reducing the
low-temperature viscosity in the presence of water.
The presence of said small amount of 1H-1,2,4-triazole ensures,
in an excellent manner, that the hydraulic fluids or motor
vehicle brake fluids according to the invention meet the
requirements mentioned at the outset and that, in particular, a
corrosion behavior which is generally good compared with the
prior art, i.e. improved corrosion protection in the case of
metals, such as iron, steel, tinplate, cast iron (gray iron),
lead, tin, chromium, zinc, aluminum, magnesium and alloys
thereof, and in the case of solder metals, for example solder
tin, and in the case of non-ferrous metals, such as copper and
alloys thereof, for example brass, is effected.
Further advantages of the hydraulic fluids or motor vehicle brake
fluids according to the invention are their favorable low-
temperature viscosity, good water compatibility, a mild pH, good
low-temperature, high-temperature and oxidation stability and
good chemical stability, a favorable behavior (i.e. good
compatibility) with materials such as rubbers, plastics, glue
lines, fiber, elastomer and rubber seals and similar materials,
as well as good lubricating behavior.
Not least, the use of only a small amount of 1H-1,2,4-triazole in
the hydraulic fluids or motor vehicle brake fluids according to
the invention is advantageous both in economic and in ecological
terms.
The examples below are intended to explain the present invention
without representing a restriction.
Applicational examples
Based on the commercially available DOT 4 or DOT 5.1 brake fluids
BF 1 (ERBP: 267_C, wet ERBP: 173_C, kinematic viscosity at -40_C:
676 cSt) and BF 2 (ERBP: 263_C, wet ERBP: 181_C, kinematic
viscosity at -40_C: 850 cSt) each with 0.05% by weight of 1H-
1,2,3-tolutriazole as non-ferrous metal corrosion inhibitor, the
brake fluids BF la, BF lb, BF lc and BF 2a according to the
invention were tested in comparison thereto.
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The motor vehicle brake fluids used had the following
compositions:
BF 1:
55.00% by weight of triethylene glycol methyl ether borate,
43.44% by weight of a mixture of triethylene glycol monomethyl
ether, tetraethylene glycol monomethyl ether,
triethylene glycol monobutyl ether and
diethylene glycol monomethyl ether,
1.51% by weight of a mixture of 1,1'-iminodipropan-2-ol,
phenothiazine and a phosphoric acid ester
0.05% by weight of 1H-1,2,3-tolutriazole
BF 2:
68.00% by weight of triethylene glycol methyl ether borate,
28.84% by weight of a mixture of triethylene glycol monomethyl
ether, diethylene glycol monomethyl ether,
diethylene glycol monobutyl ether and diethylene
glycol,
3.11% by weight of a mixture of 1,1'-iminodipropan-2-ol,
phenothiazine and a phosphonic acid derivative
0.05% by weight of 1H-1,2,3-tolutriazole.
Brake fluids BF la and BF 2a according to the invention differ
from BF 1 and BF 2 only in that the 0.05% by weight of 1H-1,2,3-
tolutriazole has been replaced by the same amount of 1H-1,2,4-
triazole; brake fluid BF lb comprises 0.04% by weight of 1H-
1,2,4-triazole and 0.01% by weight of adenine instead of 0.05% by
weight of 1H-1,2,3-tolutriazole; brake fluid BF lc according to
the invention comprises 0.07% by weight of 1H-1,2,4-triazole (but
only 54.98% by weight of triethylene glycol monomethyl ether
borate) instead of 0.05% by weight of 1H-1,2,3-tolutriazole.
The applicational studies were carried out in accordance with the
PSA Peugeot-Citroen D 53 5387 copper corrosion test in the 2000
version. In this test, firstly a copper sheet which has
previously been cleaned in acetone, with a total surface area of
1000 cm2 (dimensions: 71.4 cm x 7 cm x 0.05 cm) is coiled up in
the form of a round cylinder in such a way that the metal surface
in the interior is not in contact with itself. The copper sheet
is placed in a mixture of 294 ml of brake fluid containing 6 ml
of distilled water and heated at 100_C for 100 hours; 10 liters
per hour of air which had previously been passed through
distilled water cooled to 2_C are passed through the fluid. After
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the test, the appearance of the unrolled copper sheet and the
appearance of the fluid are assessed visually, and the copper
content of the fluid is determined.
The results from the test described are shown in Table 1 below.
Table 1:
Cu Cu sheet, Fluid, appearance pH
content appearance
[mg/kg]
BF 1 24 Thick coating Cloudy, 7.4
(Comp.): precipitations
BF la: 29 Bright, no Amber-colored, 7.6
coating clear
BF lb: 34 Bright, no Amber-colored, 7.6
coating clear
BF lc: 18 Bright, no Amber-colored, 7.5
coating clear
BF 2 10 Thick coating Cloudy, 7.6
(Comp.): precipitations
BF 2a: 30 Bright, no Amber-colored, 7.7
coating clear
It can be seen that the formulations according to the invention,
in contrast to conventional brake fluids, such as BF 1 and BF 2,
not only offer very good copper corrosion protection with a low
Cu content in the test fluid, but in addition also produce a
coating-free metal surface and no sediment formation in the brake
fluid.
The results shown below for the corrosion test in accordance with
SAE J 1704 (Jan. 97) also confirm that brake fluids according to
the invention, such as BF 2a, having a low 1H-1,2,4-triazole
content offer advantages over formulations not in accordance with
the invention, such as BF ld, having a high 1H-1,2,4-triazole
content, since they exhibit a better corrosion result in the case
of copper (BF id corresponded to BF 1, but comprised 0.20% by
weight of 1H-1,2,4-triazole instead of 1H-1,2,3-tolutriazole and
comprised only 54.85% by weight of triethylene glycol monomethyl
ether borate):
The results from the corrosion test in accordance with SAE J 1704
(Jan. 97) are shown in Table 2 below.
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Table 2:
Metal BF 2a BF id (comparison)
Weight change [mg/cm2] Weight change [mg/cmz]
Tinplate 0.00 -0.01
Steel +0.03 0.00
Aluminum 0.00 0.00
Cast iron +0.05 +0.02
Brass 0.00 0.00
Copper -0.05 -0.11
Zinc +0.05 +0.04
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