EP0028789B1 - Hydraulic fluid with improved properties - Google Patents

Abstract

A hydraulic fluid which substantially fulfils the specification DOT 5 is described. This hydraulic fluid essentially consists of (A) about 20 to 40% by weight of at least one boric acid ester obtained from orthoboric acid, diethylene glycol and an ethylene glycol monoalkyl ether; (B) 30 to 60% by weight of at least one ethylene glycol monoalkyl ether; (C) 10 to 40% by weight of at least one bis-(ethylene glycol monoalkyl ether)-formal; (D) 0.1 to 5% by weight of at least one alkylamine; and (E) 0.05 to 5% by weight of at least one stabilizer and/or inhibitor; the percentages by weight in each case being relative to the total weight of the fluid.

Description

The invention relates to a hydraulic fluid based on certain boric acid esters and bis (ethylene glycol monoalkyl ether) formal.

Hydraulic fluids, especially brake fluids, have to meet stringent chemical and physical properties. According to the currently existing standards (see specifications of the US Department of Transportation in _" Federal Motor Vehicle Safety Standard (FMVSS No. 116)" and specifications SAE J 1703 of Society of Automotive Engineers, New York), brake fluids should have the following basic properties in particular : A high dry boiling point (reflux boiling point dry) and wet boiling point (reflux boiling point wet) as well as a viscosity that changes only slightly within a wide temperature range.

The values required for these properties for a DOT-3 and DOT-4 brake fluid are summarized below:

In addition to these primary properties, a brake fluid should also have a number of other properties.

Among these properties, in addition to high thermal and chemical stability, the compatibility of the brake fluid with polymers, in particular with rubber and rubber, and their evaporation loss after carrying out the corresponding SAE test are important.

Hydraulic fluids, in particular brake fluids based on boric acid esters of glycols and / or glycol monoalkyl ethers, are already known which contain, as further main components, glycol monoalkyl ethers, glycol dialkyl ethers, polyglycols and / or bis (glycol ethers) formals (cf. German Patent No. 939045, the German ones Designation Nos. 1768933 and 2457097, German Offenlegungsschriften Nos. 2141441, 2257546, 2437936, 2438038, 2525403, 2532228, 2724193 and 2804535). In the hydraulic fluid known from US Pat. No. 3711411 with bis (ethylene glycol monoalkyl ether) formal as a possible mixture component, only monoethanolamine is used for pH stabilization, although relatively low values are accepted with regard to dry and wet boiling points.

The known brake fluids still leave something to be desired. The main reason for this is that the requirements that a brake fluid should meet include those that conflict due to the chemical and physical properties of the main components. For example, it is known that it is very difficult to adjust the viscosity of a brake fluid based on boric acid esters according to the DOT-4 standard and at the same time to achieve that the boiling point and / or its compatibility with rubber corresponds to the standard. When the known brake fluids are formulated on the basis of boric acid esters, a profit in one important property is often bought by a relatively high loss in another important property.

Recently, there has also been an increasing tendency to place higher demands on the performance of brake fluids than before in order to ensure even greater traffic safety and also to achieve longer service lives. This is reflected in the stricter specification DOT-5 (see summary below):

It would therefore be desirable to have a brake fluid which has particularly excellent values, in particular with the basic properties mentioned at the outset, in its behavior towards polymers and in the abovementioned evaporation test.

The object of the invention is therefore to provide a hydraulic fluid, in particular a brake fluid, which not only fully meets the property profile according to the standards currently required, but also meets the above-mentioned expanded requirements.

• A) 20 bis 40 Gew.%, bezogen auf das Gewicht der gesamten Flüssigkeit, von einem Borsäureester, der erhalten wird, wenn man Orthoborsäure (H₃B0₃), Diäthylenglykol (HOCH₂CH₂0CH₂CH_ZOH) und einen Äthylenglykolmonoalkyläther der Formel
  
  worin R eine Alkylgruppe mit 1 bis 4 C-Atomen und x eine ganze Zahl von 2 bis 4 ist, im Molverhältnis von 1:1:1 umsetzt;
• B) 30 bis 60 Gew.%, bezogen auf das Gewicht der gesamten Flüssigkeit, von mindestens einem Äthylenglykolmonoalkyläther der Formel I, worin R und x die genannte Bedeutung haben;
• C) 10 bis 40 Gew.%, bezogen auf das Gewicht der gesamten Flüssigkeit, von mindestens einem Bis(äthylenglykolmonoalkyläther)formal der Formel II
  
  worin R¹ und R² eine Alkylgruppe mit 1 bis 4 C-Atomen und n₁ und n₂ eine ganze Zahl von 1 bis 4 bedeuten;
• D) 0,1 bis 5 Gew.%, bezogen auf das Gewicht der gesamten Flüssigkeit, von mindestens einem Alkylamin der Formel III
  
  worin bedeuten:
  • R³ eine Alkyl- oder eine einfach ungesättigte Alkenylgruppe mit 1 bis 18 C-Atomen;
  • R⁴ Wasserstoff,
    
    wobei y eine ganze Zahl von 1 bis 5 ist;
  • R⁵ Wasserstoff,
    
    wobei y eine ganze Zahl von 1 bis 5 ist, oder eine Alkyl- oder eine einfach ungesättigte Alkenylgruppe mit 1 bis 18 C-Atomen, mit der Massgabe, dass die Summe der C-Atome von R³ und R⁵ in Formel III nicht höher als 18 ist;
  
  und
• E) 0,05 bis 5 Gew.%, bezogen auf das Gewicht der gesamten Flüssigkeit; von mindestens einem Stabilisator und/oder Inhibitor.

The hydraulic fluid according to the invention essentially consists of

• A) 20 to 40% by weight, based on the weight of the total liquid, of a boric acid ester which is obtained by using orthoboric acid (H ₃ B0 ₃ ), diethylene glycol (HOCH ₂ CH ₂ 0CH ₂ CH _Z OH) and an ethylene glycol monoalkyl ether of the formula
  
  wherein R is an alkyl group having 1 to 4 carbon atoms and x is an integer from 2 to 4, in a molar ratio of 1: 1: 1;
• B) 30 to 60% by weight, based on the weight of the total liquid, of at least one Ethylene glycol monoalkyl ether of formula I, wherein R and x have the meaning given;
• C) 10 to 40% by weight, based on the weight of the total liquid, of at least one bis (ethylene glycol monoalkyl ether) formally of the formula II
  
  wherein R ¹ and R ^{2 are} an alkyl group having 1 to 4 carbon atoms and n ₁ and n _{2 are} an integer from 1 to 4;
• D) 0.1 to 5% by weight, based on the weight of the total liquid, of at least one alkylamine of the formula III
  
  in which mean:
  • R ^{3 is} an alkyl or a monounsaturated alkenyl group with 1 to 18 C atoms;
  • R ^{4 is} hydrogen,
    
    where y is an integer from 1 to 5;
  • R ^{5 is} hydrogen,
    
    where y is an integer from 1 to 5, or an alkyl or a monounsaturated alkenyl group having 1 to 18 carbon atoms, with the proviso that the sum of the carbon atoms of R ³ and R ⁵ in formula III is not higher than 18;
  
  and
• E) 0.05 to 5% by weight, based on the weight of the entire liquid; of at least one stabilizer and / or inhibitor.

The preparation of the boric acid esters according to component A- a reaction product of orthoboric acid, diethylene glycol and an ethylene glycol monoalkyl ether of the formula I in a molar ratio of 1: 1: 1 1― takes place according to known procedures. The reaction components mentioned are reacted in a reaction vessel equipped with a stirrer and optionally with a reflux condenser at a temperature of about 50 to about 150 ° C., preferably about 110 to about 140 ° C., with the water of reaction formed being continuously removed. The reaction can be carried out in the presence of an inert water-azeotroping solvent such as benzene, toluene, xylene, ethylene benzene or the like. The water of reaction can also be removed by carrying out the reaction under reduced pressure, for example in a water jet vacuum (7 to 20 mbar). After the reaction has ended (i.e. after the theoretically liberated water has been discharged), the solvent which may be used is removed from the reaction product by customary distillation and, if further purification should be necessary, this is expediently vacuum-stripped at a temperature of 90 to 150 ° C.

The product obtained in this way is the component of the hydraulic fluid according to the invention. Among the ethylene glycol monoalkyl ethers of the formula I which are used for the preparation of the boric acid esters, preference is given to those in which R is a straight-chain alkyl group having 1 to 4 C atoms, preferably CH ₃ or C ₂ H is ₅ and x is 3.

worin R', R", x₁ und x₂ eine der Bedeutungen von R und x in Formel I haben (vorzugsweise ist R' = R" und x₁ = x₂).The reaction product of orthoboric acid, diethylene glycol and an ethylene glycol monoalkyl ether of the formula in a molar ratio of 1: 1: 1: presumably consists of a mixture of differently formulated boric acid esters in different proportions. It can be assumed that in this mixture the boric acid ester of the following formula represents the main part:

wherein R ', R ", x ₁ and x _{2 have} one of the meanings of R and x in formula I (preferably R' = R" and x ₁ = x ₂ ).

As component B of the hydraulic fluid according to the invention, preference is given to those ethylene glycol monoalkyl ethers according to the formula in which R is a straight-chain alkyl group having 1 to 4 carbon atoms, preferably CH ₃ or C ₂ H ₅ , and x 3.

Als Komponente C der erfindungsgemässen hydraulischen Flüssigkeit sind solche Bis(äthylenglykolmonoalkyläther)formale der Formel II bevorzugt, worin R¹ und R₂ eine geradkettige Alkylgruppe mit 1 bis 4 C-Atomen, vorzugsweise CH₃ oder C₂H₅ ist und n₁ und n₂ 2 oder 3 ist,- wobei vorzugsweise R¹ = R² und n₁ = n₂ ist.Methyltriethylene glycol is particularly preferred

Preferred component C of the hydraulic fluid according to the invention are bis (ethylene glycol monoalkyl ether) formals of the formula II in which R ¹ and R _{2 are} a straight-chain alkyl group having 1 to 4 C atoms, preferably CH ₃ or C ₂ H ₅ , and n ₁ and n _{2 is} 2 or 3, - preferably R ¹ = R ² and n ₁ = n ₂ .

Component D of the hydraulic fluid according to the invention consists of the alkylamines of the formula 111. Examples of the radicals R ³ and R ⁶ (which can be straight-chain or branched) are: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl , Octyl (capryl), nonyl, isononyl, dodecyl (lauryl), palmityl, stearyl and oleyl. The alkyl and alkenyl group (R ³ , R ⁵ ) preferably contains 1 to 9 carbon atoms. The sum of the R ³ carbon atoms and R ⁶ is preferably not higher than 10. The meaning of y in formula III is preferably an integer from 1 to 3.

Preferred alkylamines of the formula III are those in which R ^{3 is} an alkyl group having 1 to 9 C atoms and R ⁴ and R ^{6 are} hydrogen or - (CH ₂ CH ₂ O) _y H, where y is an integer from 1 to 5, is preferably 1 to 3.

Particularly preferred as component D are those alkylamines of the formula III in which R ^{3 is} propyl, butyl, hexyl, octyl or isononyl, and R ⁴ and R ^{5 are the} same and are hydrogen or CH ₂ CH ₂ OH.

Component E of the hydraulic fluid according to the invention consists of customary additives for fluids based on boric acid esters and glycol derivatives.

These additives include stabilizers, for example pH stabilizers, and inhibitors, for example inhibitors of corrosion and oxidation (antioxidants).

Among the suitable pH stabilizers are preferably those from the group of inorganic alkali salts, preferably the sodium salts of carbonic acid, phosphorous acid or phosphoric acid; Alkali salts of fatty acids, preferably the sodium salt of lauric acid, palmitic acid, stearic acid or oleic acid; Trialkanolamines, preferably triethanolamine; and trialkylamines (tertiary amines), for example dimethylcaprylamine and diethylcaprylamine.

The pH stabilizers are preferably used in an amount of 0.1 to 4% by weight, based on the weight of the entire liquid.

• Fettsäuren, vorzugsweise Caprylsäure, Laurinsäure, Palmitinsäure, Stearinsäure oder Ölsäure;

Among the suitable corrosion inhibitors, the following are preferably used:

• Fatty acids, preferably caprylic acid, lauric acid, palmitic acid, stearic acid or oleic acid;

Esters of phosphorous acid or phosphoric acid with aliphatic alcohols having 1 to 6 carbon atoms, preferably ethyl phosphate, dimethyl phosphate, isopropyl phosphate, diisopropyl phosphate, butyl phosphite and dimethyl phosphite; and / or triazoles, preferably benzotriazole.

The corrosion inhibitors are preferably used in an amount of 0.05 to 1% by weight, based on the weight of the entire liquid.

• aromatische Amine, vorzugsweise Phenyl-a-naphthylamin, Diphenylamin und Derivate hiervon;
• substituierte Phenole, vorzugsweise Dibutylkresol, 2,6-Dibutyl-p-kresol, 2,6-Ditert.-butyl-p-kresol und 2,4 Dimethyl-6-tert.-butylphenol; Brenzkatechin und Hydrochinon, gegebenenfalls kernsubstituiert;
• Chinone, vorzugsweise Antrachinon; und Phenothiazine, die auch kernsubsituiert sein können.

Among the suitable antioxidants, the following compounds are preferred individually or in a mixture with one another:

• aromatic amines, preferably phenyl-a-naphthylamine, diphenylamine and derivatives thereof;
• substituted phenols, preferably dibutyl cresol, 2,6-dibutyl-p-cresol, 2,6-di-tert-butyl-p-cresol and 2,4-dimethyl-6-tert-butylphenol; Pyrocatechol and hydroquinone, optionally nucleus-substituted;
• Quinones, preferably antrachinone; and phenothiazines, which can also be nucleus-substituted.

The antioxidants are preferably used in an amount of 0.05 to 1% by weight, based on the weight of the entire liquid.

The hydraulic fluid according to the invention preferably consists essentially of

The hydraulic fluid according to the invention is produced by mixing the components together, for example in a container with a stirring element, as a result of which a homogeneous mixture is obtained in a simple manner. The mixing is carried out on the shelf at atmospheric pressure and at room temperature; if necessary, it can also be carried out at a higher temperature (30 to 50 ° C.), it being expedient to keep moisture away.

The hydraulic fluids according to the invention are particularly suitable for hydraulic brake systems, preferably of motor vehicles, for hydraulic control systems and for hydraulic transmissions.

The invention is explained in more detail by the examples below.

Examples 1 to 4

• Borsäureester A₁ ist ein Umsetzungsprodukt von Orthoborsäure, Diäthylenglykol und Tri- äthylenglykolmonomethyläther (Methyltriäthylenglykol);
• Borsäureester A₂ ist ein Umsetzungsprodukt von Orthoborsäure, Diäthylenglykol und Di- äthylenglykolmonomethyläther;
• Borsäureester A₃ ist ein Umsetzungsprodukt von Orthoborsäure, Diäthylenglykol und Tri- äthylenglykolmonoäthyläther;
• Borsäureester A₄ ist ein Umsetzungsprodukt von Orthoborsäure, Diäthylenglykol und Di- äthylenglykolmonobutyläther.

The following boric acid esters to be used according to the invention (A ₁ to A4) are prepared by reacting orthoboric acid, diethylene glycol and an ethylene glycol monoalkyl ether of the formula I. The reaction is carried out in such a way that the three reaction components are kept in a molar ratio of 1: 1: 1 in a reaction vessel with stirring and in a water jet vacuum at a temperature of about 120 ° C. until the approximately theoretical amount of water has been discharged. The reaction product thus obtained represents the boric acid esters A ₁ to A ₄ :

• Boric acid ester A ₁ is a reaction product of orthoboric acid, diethylene glycol and triethylene glycol monomethyl ether (methyltriethylene glycol);
• Boric acid ester A ₂ is a reaction product of orthoboric acid, diethylene glycol and diethylene glycol monomethyl ether;
• Boric acid ester A ₃ is a reaction product of orthoboric acid, diethylene glycol and triethylene glycol monoethyl ether;
• Boric acid ester A ₄ is a reaction product of orthoboric acid, diethylene glycol and diethylene glycol monobutyl ether.

Example 5

A brake fluid according to the invention is produced by mixing the following components:

Example 6

A brake fluid according to the invention is produced by mixing the following components:

Example 7

A brake fluid according to the invention is produced by mixing the following components:

Example 8

A brake fluid according to the invention is produced by mixing the following components:

Example 9

A brake fluid according to the invention is produced by mixing the following components:

Example 10

A brake fluid according to the invention is produced by mixing the following components:

. The hydraulic fluids according to the invention of Examples 5 to 10 have been tested according to the methods of FMVSS No. 116 and SAE. The results are summarized in Tables 1 and 2 below.

Example 5 (see Table 1) has been tested completely according to the specifications mentioned. The brake fluids according to Examples 6 to 10 were only tested for the basic properties and for swelling behavior and evaporation loss, since the required values for the further properties (which are known to be much easier to achieve than the required values for the basic properties) differ from those of the brake fluid of Example 5 would hardly distinguish.

Claims (3)

1. Hydraulic fluid essentially consisting of

(A) 20 to 40% by weight, relative to the weight of the total fluid, of a boric acid ester which is obtained when orthoboric acid, diethyleneglycol and an ethyleneglycol monoalkyl ether of the formula (I):

in which R is an alkyl group with 1 to 4 C atoms and x is an integer from 2 to 4, are reacted in a molar ratio of 1:1:1;

(B) 30 to 60% by weight, relative to the weight of the total fluid, of at least one ethylene glycol monoalkyl ether of the formula (1) in which R and x have the meaning given;

(C) 10 to 40% by weight, relative to the weight of the total fluid, of at least one bis(ethyleneglycol. monoalkyl ether)formal of the formula (11):

wherein R¹ and R² denote an alkyl group with 1 to 4 C atoms, and n₁ and n₂ denote an integer from 1 to 4;

(D) 0.1 to 5% by weight, relative to the weight of the total fluid, of at least one alkylamine of the formula (III):

in which R³ denotes an alkyl or mono-unsaturated alkenyl group with 1 to 18 C atoms, R⁴ denotes hydrogen,

in which y is an integer from 1 to 5, and R⁶ denotes hydrogen,

in which y is an integer from 1 to 5, or an alkyl or mono-unsaturated alkenyl group with 1 to 18 C atoms, with the proviso that the sum of the C atoms in R³ and R⁶ in formula (III) is not greater than 18, and

(E) 0.05 to 5% by weight, relative to the weight of the total fluid, of at least one stabilizer and/or inhibitor.

2. Hydraulic fluid as claimed in claim 1, in which components A to E are present in the followina amounts:

3. Hydraulic fluid as claimed in claim 1, in which component A is a reaction product of orthoboric acid, diethyleneglycol and methyl- or ethyltriethyleneglycol in a molar ratio of 1 :1 :1; component B is methyl- or ethyltriethyleneglycol; component C is a bis(di- or triethyleneglycol monomethyl or monoethyl ether)formal; component D is an alkylamine of the formula (III) in which R³ is an alkyl group with 1 to 9 C atoms and R" and R⁵ are hydrogen or -(CH₂CH₂O)_yH, in which y is an integer from 1 to 5: and component E is an inhibitor from the group consisting of benztriazole, phenyl-a-naphthylamine. diphenylamine, 2,6-dibutylcresol, phenothiazme and isopropyl phosphate.