IE65470B1 - Brake fluid based on glycol compounds and inhibited against metallic corrosion - Google Patents

Abstract

The brake fluid described consists essentially of A) at least one glycol compound as the main component, B) at least one inhibitor for fluids based on glycol compounds and C) an effective quantity of a mixture of acidic phosphate esters which essentially consists of monophosphate esters and diphosphate esters and has been obtained by reacting a phosphorus-containing compound with a monohydric alcohol and a polyol. The novel brake fluid shows high corrosion inhibition, in particular towards the metal tin.

Description

Description The invention relates to a brake fluid which is inhibited against metallic corrosion and essentially comprises at » least one glycol compound as main component and at least one inhibitor for fluids based on glycol compounds.

The brake fluids currently in use belong, as is known, to the types DOT 3, DOT 4 and DOT 5 (DOT = Department of Transportation, USA). The required properties for these fluids are listed in U.S. Federal Motor Vehicle Safety Standard 116 (FMVSS No. 116) and in U.S. Society of Automotive Engineers J 1703 (SAE J 1703). As is known, the most important properties of a brake fluid include dry boiling point (also called reflux boiling point-dry or simply boiling point), the wet boiling point (also called reflux boiling point-wet) and the viscosity at -40°C. The appropriate required values are summarized below: COP 3 EOT 4 EOT 5 Railing paint W&: bailing point Viaoosity at -40°C min. 2Q5°C min. 140°C max. 1500 mrf/s mill. 230°C min. 155°C max. 1800 mrf/s min. 260°C min. 180°C max. 900 mrf/s A number of brake fluids have already been described, for example in British Patent 850,990 and in US Patents 3,711,411, 3,972,822, 4,088,590 and 4,371,448, which essentially comprise at least one glycol compound as the main component and at least one corrosion inhibitor for fluids based on glycol compounds. These brake fluids meet the requirements mentioned with respect to boiling point, wet boiling point and viscosity at -40°C more or less satisfactorily. They also show corrosion inhibition against a number of metals/construction materials, but their corrosion behavior toward the metal tin leaves something to be desired. The lack of corrosion protection of this type is also a problem simply because brake fluids are often dispensed and stored in tin-plated containers. For this reason, it is desired to also have a brake fluid available which is particularly effective against tin corrosion.

Accordingly, the object of the invention is to create a brake fluid which not only has the normal properties mentioned but also good corrosion inhibition against the usual metals and simultaneously against tin. Thus, the new brake fluid should correspond to the types DOT 3, DOT 4 and DOT 5 with respect to dry boiling point, wet boiling point and viscosity at -40°C and should have been made highly anticorrosive especially with respect to the metal tin.

The brake fluid according to the invention essentially comprises A) at least one glycol compound as main component, B) at least one inhibitor for fluids based on glycol compounds and C) 0.005 to 0.5% by weight, preferably 0.01 to 0.1% by weight, percent by weight being based on the weight of the (ready-to-use) brake fluid, of a mixture of acid phosphoric esters (as additional inhibitor) essentially comprising mono- and diphosphoric esters and obtained by reacting a phosphorus-containing compound with a monohydric alcohol and a polyol.

The present invention is based on the surprising finding that the incorporation of the specific phosphoric ester product according to component C) in known brake fluids based on glycol compounds achieves an unexpectedly high corrosion inhibition especially with the metal tin, which is independent of the type of basis compound, which may belong to the group of glycols, mono- and diethers thereof, glycol formals, glycol boric esters and the like. The addition of component C) obviously results in a specific synergism which is probably due to the combination of component C) and the inhibitors already present in the fluid. This combination surprisingly achieves excellent corrosion protection, especially for the metal tin, and its inhibition against the usual metals, such as cast iron and steel, copper, aluminum, zinc and the like, meets the current requirements. Brake fluids based on glycol compounds together with phosphoric esters of different types in combination with conventional corrosion inhibitors, such as alkylamines, alkanolamines, alkali metal salts of inorganic or organic acids, triazoles and the like have already been known for a long time (see the publications mentioned at the beginning). Although these brake fluids of the types DOT 3, DOT 4 and DOT 5 have relatively good corrosion protection against the usual metals, they leave something to be desired with respect to tin. It is therefore indeed surprising that a highly anticorrosive behavior especially towards tin is obtained by means of the phosphoric ester product according to component C).

Component A) of the brake fluid according to the invention comprises one or more glycol compounds and forms the main component of the fluid. The glycol compounds which can be used are all those which usually form the basis for the brake fluids in question (see the publications mentioned at the beginning). As a rule, they are the known glycol compounds from the group of glycols, glycol monoalkyl ethers, glycol dialkyl ethers, glycol formals, glycol boric esters and glycol monoalkyl boric esters. Preferred glycols are those of the formula 1 below Rl (1) HO-(CH2CHO)X-H in which R1 is H or CB3 and is also H and CH3 within the polyalkoxylene chain (this is understood to mean that R1 can also have both meanings mentioned within the chain of the polyalkoxylene radical), preferably H, and x is 1 to 8, preferably 2 to 5. Examples of glycols are monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and further polyoxyethylene glycols having a molecular weight of up to 400 and the corresponding propylene glycols and mixed alkoxylates, the ethylene glycols being preferred.

Preferred glycol monoalkyl ethers are those of the formula 2 below R2 I (2) R3O-(CH2CHO,y-H in which R2 is H or CH3 and is also H and CH3 within the polyalkoxylene chain, preferably H, R2 is Cj- to C4-alkyl and y is 1 to 6, preferably 2 to 4. Examples of glycol monoethers are diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monoethyl ether and the corresponding propylene glycol ethers and mixed alkoxylate derivatives, the ethylene glycol ethers being preferred.

Preferred glycol dialkyl ethers are those of the formula 3 below R4 I (3) R5O-(CH2CHO)Z-R6 in which R4 is H or CH3 and is also H and CH3 within the polyalkoxylene chain, preferably H, R5 is C3- to C4-alkyl, Re is C3- to C4-alkyl and z is 1 to 6, preferably 2 to 4. Examples of glycol diethers are diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, triethylene glycol diisopropyl ether, triethylene glycol methyl isopropyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diisopropyl ether and tetraethylene glycol dibutyl ether and the corresponding propylene glycol ethers and mixed alkoxylate derivatives, ethylene glycol ethers being preferred.

Preferred glycol formals are those of the formula 4 below R70- { CHjCHjO ) b-CHj- (OCH2CH2) n-0R8 (4) in which R7 is C3- to C4-alkyl, R8 is Ci- to C4-alkyl, m is to 4 and n is 1 to 4. Particularly preferred bis(ethylene glycol monoalkyl ether) formals of the formula 4 are those where R7 and R8 are CH3 and m is in each case or 3, m being equal to n.

Preferred glycol boric esters and glycol monoalkyl ether boric esters are those of the formulae 5 and 6 below [R’O-(CH2CH2O)a]3-B (5) in which R’ is Cx- to C4-alkyl and a is 1 to 6, preferably 2 to 4, OCH2CH2OCH2CH2O ,rt / \ Rl0o-(CH2CH2O)b-B B-(OCH2CH2)c'OR11 \ / OCH2CH2OCH2CH2O (6) in which R10 and Ru are Cx- to C4-alkyl and b and c are each 1 to 6, preferably 1 to 4. Particularly preferred boric esters of the formulae 5 and 6 are those where R’ is CH3 and a is 2, 3 or 4; R10 and R11 are CH3 and b and c are each 2, 3 or 4.

Component B) of the brake fluid according to the invention comprises one or more compounds which are usually used as inhibitors in fluids based on glycols and/or glycol derivatives (see the publications mentioned at the beginning). As a rule, they are the known inhibitor compounds from the group comprising alkylamines, cycloalky lamines, alkanolamines, monocarboxylic acids and alkali metal salts thereof, dicarboxylic acids and alkali metal salts thereof, alkali metal salts of carbonic acid, phosphoric acid and molybdic acid, triazoles, imidazoles and antioxidant aromatic compounds. Preferred alkylamines are mono-, di- and trialkylamines having 1 to 18 carbon atoms, preferably 3 to 8 carbon atoms, in each alkyl group, such as butylamine, hexylamine, octylamine, isononylamine, isotridecylamine, oleylamine, diisopropylamine, dioctylamine, tributylamine, trihexylamine and dimethyloctylamine. The preferred cycloalkylamine is cyclohexylamine.

Preferred alkanolamines are those of the formula 7 below Rl2 I CH2CH-(CH2)4-OH r13-N^ in which R12 is H or CH3, d is 0, 1 or 2, preferably 0, R13 is H, C3- to C18-alkyl, preferably C3- to C8-alkyl or a radical of the formula Rl2 I -CH2CH-(CH2)d-OH in which R12 and d have the meanings given, and R14 has one of the meanings of R13, such as ethanolamine, methyldiethanolamine, isopropanolamine, diethanolamine, diisopropanolamine, butyldiethanolamine, octyldiethanolamine, triethanolamine and triisopropanolamine.

Preferred monocarboxylic acids and alkali metal salts thereof are C5- to C18-monocarboxylic acids (fatty acids) and sodium salts thereof, such as caprylic acid, lauric acid, stearic acid and oleic acid.

Preferred dicarboxylic acids and alkali metal salts thereof are those of the formula HOOC- (CH2) 4_10- - 7 ~ Preferred alkali metal salts of carbonic acid, phosphoric acid and molybdic acid are sodium carbonate, sodium phosphate and sodium molybdate (Na2Mo04).

Preferred triazoles and imidazoles are benzotriazole (also termed ΙΗ-benzotriazole or 1,2,3-benzotriazole), tolyltriazole (usually a mixture of isomers) and benzimidazole.

Preferred antioxidant aromatic compounds are those from the group comprising phenols, bisphenols, cresols, quinolines and naphthylamines, such as phenol, bisphenol A, 2,4-dimethyl-6-tert.-butylphenol, styrenemodified phenol, 2,6-dimethyl-p-cresol, diphenylamine, phenyl-a-naphthylamine, styrenated diphenylamine, 4,4'dioctyldiphenylamine hnd polymeric 2,2,4-trimethyl1,2-dihydroquinoline.

Component B) is in general present in an amount of 0.1 to 10% by weight, preferably in an amount of 0.5 to 8% by weight, the percent by weight being based on the weight of the (ready-to-use) brake fluid. Component B) usually comprises one or more of the abovementioned inhibitors. It preferably comprises one of the alkylamines or alkanolamines mentioned or an alkylamine and an alkanolamine and one of the triazole compounds mentioned, the alkylamine and/or the alkanolamine representing the major amount, while the triazole is present in a relatively small amount. Accordingly, component B) preferably comprises 0.5 to 8% by weight, preferably 0.5 to 6% by weight, of one of the alkylamines and/or alkanolamines mentioned, the alkanolamines being preferred, and 0.01 to 0.5% by weight, preferably 0.05 to 0.3% by weight, of one of the triazole compounds mentioned, the percent by weight being based on the weight of the brake fluid.

Component C) of the brake fluid according to the invention is a mixture of acid phosphoric esters. Thus, it essentially comprises phosphoric monoesters and phosphoric diesters. Phosphoric triesters are present if at all only in a very small amount. A further feature of the phosphoric ester product is that not only a monohydric alcohol but also a polyol can be used for esterification with the starting phosphorus compound. In order to maintain the acid character of the phosphoric ester product, the three reaction components of course used in such a molar ratio that essentially only primary and secondary phosphoric esters are formed. The acid number of the phosphoric ester mixture is in general 300 to 700, preferably 350 to 600 (the acid number is determined by the known method, i.e. by titration using NaOH solution up to the second point of inflection of the titration curve and conversion of NaOH consumption into mg of KOH per g of product).

Examples of suitable phosphorus compounds are phosphoric acid (H3PO4), phosphorus trichloride (PC13), phosphorus pentachloride (PC15) and phosphorus pentoxide (P«O10) . Of the possible phosphorus compounds, phosphorus pentoxide is preferred because the use of this compound avoids the relatively time-consuming removal of the water of reaction or HC1 formed in the esterification.

Suitable monohydric alcohols are those from the group comprising alkanols and alkoxylated alkanols. The monohydric alcohols which are preferably used are C3- to C12alkanols, preferably C3- to Ce-alkanols (straight-chain or branched), or their ethoxylates and propoxylates, preferably ethoxylates, having 1 to 15 alkoxylene units, preferably 1 to 8 alkoxylene units. Thus, preferred monohydric alcohols are those of the formula 8 below Rl* k I (8) R16O-(CH2CHO)e-H in which R15 is H or CH3, preferably H, R18 is a preferably straight-chain alkyl radical having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, and e is 0 to 15, preferably 0 to 8. Individual representatives of monohydric alcohols are methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, n-amyl alcohol, isoamyl alcohol, n-hexanol, isononyl alcohol, n-decanol, lauryl alcohol and isotridecyl alcohol and propoxylates thereof, preferably ethoxylates, having 1 to 15 alkoxylene units, preferably 1 to 8 alkoxylene units.

Suitable polyols are those from the group comprising alkanediols, alkanetriols, alkanetetrols, pentitols and hexitols, such as ethanediol (ethylene glycol), 1,2propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, pentanediol and hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol and pentaethylene glycol and the corresponding propylene glycols, glycerol, trimethylolpropane, trimethylolethane, erythritol and pentaerythritol, diols and triols being preferred. Particularly preferred polyols are the alkanediols of the formula 9 below HO-(CH2)f-OH (9) in which f is 2 to 8, preferably 2 to 5 (i.e. alkylene glycols), and the formula 10 below Rl7 HO-(CH2CHO)g-H (10) in which R17 is H or CH3, preferably H, and g is 1 to 10, preferably 1 to 5 (i.e. alkoxylene glycols).

Component C) of the brake fluid according to the invention is preferably a phosphoric ester product according to US Patent 4,141,938 and according to European Patent 28,674-Bl, incorporated herein by reference. Accordingly, a preferred acid phosphoric ester mixture is one obtained by reacting phosphorus(V) oxide with a mixture comprising a monohydric alcohol and an alkane-polyol having 2 to 12 carbon atoms and 2 to 6 hydroxyl groups, preferably while maintaining a molar ratio of phosphorus(V) oxide : monohydric alcohol : alkanepolyol of 1 : 2 : 4/n', in which n' is the number of hydroxyl groups in the alkanepolyol molecule, or a stoichiometric excess of the alcoholic components, in which the reactants are stirred or kneaded at a temperature of about 0 to 120°C with the exclusion of moisture and in the presence of an inert gas for about 1 to 6 hours. Thus, in the case of a monohydric alcohol and an alkanediol the molar ratio of phosphorus(V) oxide : monohydric alcohol : alkanediol is 1 : 2 : 2 and in the case of an alkanetetrol as the alkanepolyol it is 1 : 2 : 1. It has proven advantageous to carry out the reaction of the phosphorus(V) oxide with the monohydric alcohol and the alkanepolyol in the exothermic phase of the reaction - by cooling the reaction mixture - at a temperature of 0 to 70**C, preferably 20 to 60°C, and in the final phase of the reaction - by heating the reaction mixture - at a temperature of 80 to 100°C. During this reaction, it is recommended to use an inert gas, such as, for example, nitrogen. In general, the reaction is completed within 1 to 3 hours, which is indicated by the absence of the heat of reaction formed in the initially exothermic reaction. After the reaction is completed and the reaction mixture has been cooled, the desired mixture of acid phosphoric esters is present. As already mentioned above, the monohydric alcohols of the formula 8 and the alkanediols of the formulae 9 and 10 represent the preferred reactants for preparing component C) apart from phosphorus pentoxide.

As shown by the above description, the characteristic features of the brake fluid according to the invention are its inhibitory system according to components B) and C) and the independence of the inhibitory system of component A), i.e. the detailed type of component A) is not critical for the effect of the inhibitory system. As is known, component A) determines the type of brake fluid, i.e., it is virtually only up to component A,, whether a brake fluid belongs to the currently customary types DOT 3, DOT 4 and/or DOT 5 with respect to the properties mentioned at the beginning, i.e. dry boiling point, wet boiling point and viscosity. Thus, the effect of the inhibitory system according to components B) and C) is displayed in all these types of brake fluids known per se. As for the details of component A), preference is given, as is known, to two variations. In one variation, component A) essentially comprises the glycol compounds mentioned from the group comprising glycols, glycol monoalkyl ethers and glycol dialkyl ethers, which are used in such a ratio that the desired type of brake fluid is obtained. According to the second variation, component A) essentially comprises the glycol compounds mentioned from the group comprising glycol boric esters and glycol monoalkyl boric esters, glycol monoalkyl ethers, glycol dialkyl ethers, glycols and glycol formals, which are again used in such a ratio that the desired type of brake fluid is obtained. A few typical compositions of component A) such as described by the prior art and present in the types of brake fluids mentioned are listed below, in which the individual components are designated A3, A2 and A3 and the percentages by weight given are based on the weight sum of Ax, A2 and A3.

Composition 1: AJ 30 to 80 % of A2) 20 to 70 % of Composition 2: AJ 40 to 50 % of A2) 50 to 60 % of glycols of molecular weight of up to 300, the amount of glycol of molecular weight of more than 150 being at least 20% by weight, and glycol monoalkyl ether and/or glycol dialkyl ether glycols of molecular weight of up to 200 and glycol monoalkyl ether Composition 3: Ax) 50 to 70 % of glycol of molecular weight of up to 200 and A2) 30 to 50 % of glycol dialkyl ether Composition 4: Ax) 30 to 50 % of glycols of molecular weight 150 to 300, A2) 20 to 50 % of A3) 10 to 20 % of glycol monoalkyl ether and glycol dialkyl ether Composition 5: Ax) 40 to 95 % of boric ester of glycols and/or glycol monoalkyl ethers and A2) 5 to 60 % of glycol monoalkyl ether, and/or glycol dialkyl ether Composition 6: Ax) 40 to 90 % of boric ester of glycols and/or glycol monoalkyl ethers A2) 5 to 50 % of glycol monoalkyl ether and/or glycol dialkyl ether and A3) 2 to 10 % of glycols of molecular weight 150 to 300 Composition 7: Ax) 10 to 50 % of boric ester of glycols and/or glycol monoalkyl ethers and A2) 50 to 90 % of glycol monoalkyl ether Composition 8: Ax) 10 to 20 % of boric ester of glycol mono- A2) 40 to 60 % of A3) 15 to 45 % of alkyl ethers glycol monoalkyl ether and glycols of molecular weight 150 to 300 Composition 9: Αχ) 20 to 40 % of boric ester of glycols and glycol monoalkyl ethers ». a2) 30 to 60 % of glycol monoalkyl ether and ( A,) 10 to 40 % of bis(ethylene glycol mono- alkyl ether) formals The preparation of the brake fluids according to the invention takes place by mixing the components, for example in a vessel containing a stirrer, as a result of which a homogeneous mixture is obtained in a simple manner. As a rule, the mixing is carried out at atmospheric pressure and at room temperature, during which it is advantageous to keep away moisture. The mixing can also be carried out at higher temperature, for example at 30 to 50°C.

The brake fluids according to the invention are suitable in particular for hydraulic brake systems, preferably those in motor vehicles.

The invention is illustrated in more detail by way of examples and comparative examples.

The percentages given in the examples and comparative examples are by weight, and the individual brake fluids were prepared by mixing the components listed at room temperature. The brake fluids from the examples and comparative examples were tested with respect to boiling point (dry boiling point), wet boiling point, viscosity at -40’C and tin corrosion. The boiling point, wet boiling point and viscosity at -40eC were determined exactly according to FMVSS No. 116. The tin corrosion was likewise determined according to FMVSS No. 116, but in addition a more severe form of the test was selected by not carrying out the addition of 5% by volume of water to the brake fluid sample, which is part of the test; thus, the brake fluid was used as such, as is the case in technical application. As is known, a water content of up to 5% by volume is often only reached after several years of use of the brake fluid.

Example 1 A) 42.00 % of 22.10 % of 35.00 % of B) 0.80 % of 0.05 % of C) 0.05 % of triethylene glycol diethylene glycol monomethyl ether triethylene glycol mono-n-butyl ether diisopropanolamine tolyltriazole an acid phosphoric ester mixture prepared as described below.

Boiling point 235°C Wet boiling point 147°C Viscosity 1,284 mm2/§ Tin corrosion ± 0 mg/cm2 Preparation of the acid phosphoric ester mixture: 33.3 g (0.45 mol) n-butanol and 27.9 g (0.45 mol) of ethylene glycol were mixed in a 250-ml glass vessel equipped with a stirrer under a nitrogen atmosphere. 63.9 g (0.225 mol) of P4O10 were stirred into the mixture over a period of 30 minutes, during which the mixture was cooled with a water/ice mixture. During the addition, the temperature of the reaction mixture increased from 22 to 55®C. After the exothermic reaction had subsided, the mixture was heated to 80®C within an hour and maintained at 80 to 85°C for 1 hour. After cooling, 125 g of a colorless, viscous liquid having an acid number of 564 mg of KOH/g up to the second point of inflection and a pH of 9.5 were obtained.

Example 2 A) 42.07 % of 6.60 % of 35.00 % of triethylene glycol triethylene glycol monomethyl ether triethylene glycol mono-n-butyl ether B) C) 15.00 % of 1.10 % of 0.20 % of 0.03 % of triethylene glycol dimethyl ether tributylamine benzotriazole the acid phosphoric ester mixture according to Example 1 Boiling point 257°C Wet boiling point 146°C Viscosity 1,090 mm2/s Tin corrosion -0.01 mg/cm2 Example 3 A) 34.59 % of 61.40 % of B) 3.90 % of 0.10 % of C) 0.01 % of tetraethylene glycol monomethyl ether boric ester of the formula [CHjO- (CHjCHjO) 3 ]3B butyldiethanolamine benzotriazole the acid phosphoric ester mixture according to Example 1 Boiling point 282°C Wet boiling point 187®C Viscosity 1,264 mm2/s Tin corrosion -0.01 mg/cm2 Example 4 A) 61.40 % of 35.50 % of tetraethylene glycol monomethyl ether boric ester of the formula OCH2CH2OCH2CH2O / \ CH3O-(CH2CH2O)3-B B-(OCH2CH2)3-OCH3 \ / OCH2CH2OCH2CH2O B) 3.00 0.05 C) 0.05 % of diisopropanolamine % of tolyltriazole % of the acid phosphoric ester mixture according to Example 1 Boiling point 270°C Wet boiling point 174°C Viscosity 1,768 mm2/s Tin corrosion ± 0 mg/cm2 Example 5 A) B) C) 15 .30 % of 61.40 % of 3.20 % of 0.05 % of 0.05 % of tetraethylene glycol monomethyl ether boric ester as in Example 3 diisopropanolamine tolyltriazole an acid phosphoric ester mixture prepared as described below.

Boiling point 284 °C Wet boiling point 186°C Viscosity 1,250 mm2/s Tin corrosion ± 0 mg/cm2 Preparation of the acid phosphoric ester mixture: g (0.5 mol) of triethylene glycol and 30 g (0.5 mol) of isopropanol are mixed in a 250-ml glass vessel equipped with a stirrer under a nitrogen atmosphere. 71 g (0.25 mol) of P«O10 were then stirred into the mixture over a period of 30 minutes, during which the mixture was cooled with a water/ice mixture. During the addition, the temperature of the reaction mixture increased from 22 to 60°C. The reaction mixture was then maintained at 80**C for 2 hours. The product cooled to room temperature was a slightly brown-colored viscous liquid. The acid number of the product up to the second point of inflection was 482 mg of KOH/g.

Example 6 A) 59.00 % of tetraethylene glycol monomethyl ether 35.50 % of boric ester as in Example 4 B) 5.40 % of octyldiethanolamine 0.10 % of benzotriazole C) 0.03 % of an acid phosphoric ester mixture prepared as described below Boiling point 270°C Wet boiling point 173 °C Viscosity 1,760 mm2/s Tin corrosion ± 0 mg/cm2 Preparation of the acid phosphoric ester mixture: The procedure of Example 5 was repeated, except that 38 g (0.5 mol) of 1,3-propanediol and 23 g (0.5 mol) of ethanol were reacted with 71 g (0.25 mol) of P4O10. A slightly brown-colored viscous liquid having an acid number up to the second point of inflection of 589 mg of KOH/g was obtained.

Example 7 A) 17.99% of triethylene glycol monomethyl ether .00% of tetraethylene glycol dimethyl ether 74.80% of boric ester as in Example 3 B) 2.10% of diisopropanolamine 0.10% of tolyltriazole C) 0.01% of the acid phosphoric ester mixture according to Example 1 Boiling point 275°C Wet boiling point 195 **C Viscosity 880 mm2/s Tin corrosion ±0 mg/cm2 Comparative Examples 1 to 7 Examples 1 to 7 according to the invention were repeated, except that component C) was not used [the brake fluid mixture was supplemented with the first representative from component A) to give 100% by weight].

These brake fluids had virtually the same values as the brake fluids according to the invention with respect to boiling point, wet boiling point and viscosity at -40°C but were considerably worse with respect to tin corrosion; the tin corrosion values were in the range from -0.12 to -0.16 mg/cm2.

Comparative Example 8 A) 35.30% of tetraethylene glycol monomethyl ether 61.40% of boric ester as in Example 3 B) 3.20% of diisopropanolamine 0.05% of tolyltriazole C) 0.05% of an acid phosphoric ester mixture prepared as described below.

Boiling point 285®C Wet boiling point 185eC Viscosity 1,285 mm2/s Tin corrosion -0.10 mg/cm2 Preparation of the acid phosphoric ester mixture: g (1.5 mol) of isopropanol were immediately introduced into a 250 ml glass vessel equipped with stirrer under a nitrogen atmosphere. 71 g (0.25 mol) of P4O10 were then stirred in in portions, during which the mixture was maintained at 22 to 40®C by cooling with a water/ice mixture. The reaction mixture was then maintained at 80®C for 1 hour. A water-clear, viscous liquid having an acid number up to the second point of inflection of 490 mg of KOH/g was obtained.

Claims (7)

1. Patent claims

1. A brake fluid inhibited against metallic corrosion, essentially comprising A) at least one glycol compound as main component, B) at least one inhibitor for fluids based on glycol compounds and C) 0.005 to 0.5% by weight, percent by weight being based on the weight of the brake fluid, of a mixture of acid phosphoric esters, essentially comprising monophosphoric esters and diphosphoric esters and obtained by reacting a phosphoruscontaining compound with a monohydric alcohol and a polyol.

2. A brake fluid as claimed in claim 1, in which the amount of component C) is 0.01 to 0.1% by weight.

3. A brake fluid as claimed in claim 1 or 2, in which component C) is a mixture of acid phosphoric esters obtained by reacting phosphorus(V) oxide with a mixture comprising a monohydric alcohol and an alkanepolyol having 2 to 12 carbon atoms and 2 to 6 hydroxyl groups, while maintaining a molar ratio of phosphorus(V) oxide : monohydric alcohol : alkanepolyol of 1 ϊ 2 : 4/n', in which n' is the number of hydroxyl groups in the alkanepolyol molecule, or a stoichiometric excess of the alcoholic components, with mixing or kneading of the reactants at a temperature of about 0 to 120°C with the exclusion of moisture and in the presence of an inert gas for about 1 to 6 hours.

4. A brake fluid as claimed in claim 1 or 2 in which component C) is a mixture of acid phosphoric esters obtained by reacting phosphorus (V) oxide with a mixture comprising a monohydric alcohol of the formula 8 below (8) RlS R 16 O-(CH 2 CHO) e -H in which R 1S is H or CH 3 , R 1S is an alkyl radical having 1 to 12 carbon atoms and e is 0 to 15, and an alkanepolyol of the formula 9 below HO-(CH 2 ) f -OH (9) in which f is 2 to 8, or of the formula 10 below Rl7 I HO-(CH 2 CHO) g -H (10) in which R 17 is H or CH 3 and g is 1 to 10 while maintaining a molar ratio of phosphorus(V) oxide : monohydric alcohol : alkanepolyol of 1 : 2 ϊ 4/n z , in which n' is the number of hydroxyl groups in the alkanepolyol molecule, or a stoichiometric excess of the alcoholic components, with mixing or kneading of the reactants at a temperature of about 0 to 120 e C with the exclusion of moisture and in the presence of an inert gas for about 1 to 6 hours. A brake fluid as claimed in one or more of claims 1 to 4, in which component A) comprises glycol compounds selected from the group comprising glycols, glycol monoalkyl ethers, glycol dialkyl ethers, glycol formals, glycol boric esters and glycol monoalkyl ether boric esters, and component B) comprising inhibitors selected from the group comprising alkylamines, cycloalkylamines, alkanolamines, monocarboxylic acids and alkali metal salts thereof, dicarboxylic acids and alkali metal salts thereof, alkali . metal salts of carbonic acid, phosphoric acid and molybdic acid, triazoles, imidazoles and antioxidant aromatic compounds.

5. 6. A brake fluid as claimed in one or more of claims 1 to 4, in which component A) comprises glycol compounds selected from the group comprising glycols of the formula 1 below Rl I (1) HO-(CH 2 CHO) x -H in which R 1 is H or CH 3 and is also H and CH 3 within the polyalkoxylene chain and x is 1 to 8, glycol monoalkyl ethers of the formula 2 below * 2 (2) R 3 o-(ca 2 cao) y -H in which R 2 is H or CH3 and is also H and 'CH3 within the polyalkoxylene chain, R 3 is C3- to C 4 -alkyl and y is 1 to 6, glycol dialkyl ethers of the formula 3 below I (3) R 5 O-(CH 2 CHO) z -R 6 in which R 4 is H or CH3 and is also H and CH3 within the polyalkoxylene chain, R 5 is C3- to C 4 -alkyl, R* is C 3 - to C 4 -alkyl and z is 1 to 6, glycol formals of the formula 4 below R 7 0- (CH 2 CH 3 O) b -CH 3 - (OCHjCHj) b -0R 8 (4) in which R 7 is Cx- to C4-alkyl, R 8 is C3- to C 4 -alkyl, m is 1 to 4 and n is 1 to 4, and glycol boric esters of formulae 5 below [R’O- (CH 2 CH 2 O) J 3 -B (5) in which R* is C x - to C 4 -alkyl and a is 1 to 6, and glycol monoalkyl ether boric esters of formula 6 below OCH2CH2OCH2CH2O Rl0o-(CH2CH2O)b“B B-{OCH2CH2)c’OR 11 ( 6 ) \ / OCH 2 CH 2 OCH 2 CH 2 O in which R 7 * * 10 is C3- to C4-alkyl, R u is Cx- to C 4 -alkyl and b is 1 to 6 and c is 1 to 6, and component B) comprises inhibitors selected from the group comprising mono-, di- and trialkylamines having 1 to 18 carbon atoms in each alkyl group, alkanolamines of formula 7 below Rl2 CH2CH-(CH2)d*OH R13-N (7) in which R 12 is H or CH3, d is 0, 1 or 2, R 1J is H, Ci to C18 -alkyl or a radical of the formula below Rl2 -CH 2 CH-(CH 2 ) d -OH in which R 12 and d have the meanings given, and R 14 has one of the meanings of R 13 , C 5 - to C 18 -monocarboxylic acids and alkali metal salts thereof, dicarboxylic acids of the formula HOOC-(CH 2 ) k -COOH, in which k is 4 to 10, alkali metal salts of carbonic acid, phosphoric acid and molybdic acid, and triazoles, imidazoles and antioxidant aromatic compounds of the group comprising phenols, bisphenols, cresols, quinolines and naphthylamines.

6. 7. A brake fluid as claimed in one or more of claims 1 to 6, in which component B) comprises inhibitors selected from the group comprising mono-, di- and trialkylamines having 1 to 18 carbon atoms in each alkyl group, alkanolamines of formula 7 below Rl2 R13-N CH2CH-(CH2) d-θΗ Rl* (7) i in which R 22 is H or CH3, d is 0, 1 or 2, R 23 is H, C3- to C 1B -alkyl or a radical of the formula below Rl2 I -CH 2 CH-(CH 2 )d- OH in which R 12 and d have the meanings given, and R 24 has one of the meanings of R 13 , and triazoles. A brake fluid as claimed in one or more of claims 1 to 7, in whi£h component B) is present in an amount of 0.1 to 10% by weight, the percent by weight being based on the weight of the brake fluid. A brake fluid as claimed in one or more of claims 1 to 8, in which component B) comprises inhibitors selected from the group comprising mono-, di- and trialkylamines having 1 to 18 carbon atoms in each alkyl group, alkanolamines of formula 7 below Rl2 R13-N CH 2 CH-(CH2)d“<3H (7) in which R 22 is H or CH3, d is 0, 1 or 2, R 23 is H, C3- to C 18 -alkyl or a radical of the formula below Rl2 I -CH 2 CH-(CH 2 )d“°H in which R 22 and d have the meanings given, and R 24 has one of the meanings of R 23 , in an amount of 0.5 to 8% by weight, and triazoles in an amount of 0.01 to 0.5% by weight, the percent by weight being based on the weight of the brake fluid.

7. 10. A brake fluid according to claim 1, substantially as hereinbefore described and exemplified.