EP0028789A1 - 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) formals.

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

The values required for these properties. 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 loss of evaporation 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 ether) formals (compare German patent specification 939 045, German interpretations 17 68 933 and 24 57 097, German Offenlegungsschriften 21 41 441, 22 57 546, 24 37 936, 24 38 038, 25 25 403, 25 32 228, 27 24 193 and 28 04 535).

However, these known brake fluids still leave something to be desired. The main reason for this is that the requirements that a brake fluid is supposed to 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 conforms 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 paid for 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 for longer ones To achieve usage times. 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 evaporation test mentioned above.

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), Diethylenglykol (HOCH₂CH₂OCH₂CH₂OH) und einen Ethylenglykolmonoalkylether der Formel I
  
  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 Ethylenglykolmonoalkylether der Formel I, worin R und x die ge- . nannte Bedeutung haben;
• C) 10 bis 40 Gew.-%, bezogen auf das Gewicht der gesamten Flüssigkeit, von mindestens einem Bis-(ethylenglykolmonoalkylether)-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;
  • _R ⁵ 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 wt .-%, based on the weight of the total liquid, of a boric acid ester, which is obtained when orthoboric acid (H ₃ B0 ₃ ), diethylene glycol (HOCH ₂ CH ₂ OCH ₂ CH ₂ OH) and one Ethylene glycol monoalkyl ether of the formula I.
  
  where 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 wt .-%, based on the weight of the total liquid, of at least one ethylene glycol monoalkyl ether of the formula I, wherein R and x are the total. have named meaning;
• C) 10 to 40 wt .-%, based on the weight of the total liquid, of at least one bis (ethylene glycol monoalkyl ether) formal 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 - is carried out according to known procedures. The reaction components mentioned are reacted in a reaction vessel equipped with a stirrer and, if appropriate, 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 (that is to say 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.degree .

The product obtained in this way represents component A) 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 carbon atoms, preferably Is CH ₃ or C ₂ H _s 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 I 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 accepted, 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 monalkyl ethers of the formula I 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 is 3.

Methyltriethylene glycol is particularly preferred

Preferred components 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 III. Examples of the radicals R ³ and R ⁵ (which may 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 C atoms of R ³ and R ⁵ 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 ^{5 are} hydrogen or - (CH ₂ CH ₂ O) _y H, where y is an integer from 1 to 5, 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 ^{S 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).

• anorganischen Alkalisalze, vorzugsweise die Natriumsalze der Kohlensäure, der phosphorigen Säure oder der Phosphorsäure;
• Alkalisalze von Fettsäuren, vorzugsweise das Natriumsalz der Laurinsäure, Palmitinsäure, Stearinsäure oder Ölsäure; Trialkanolamine, vorzugsweise Triethanolamin; und Trialkylamine (tert.-Amine), beispielsweise Dimethylcaprylamin und Diethylcaprylamin.

Among the suitable pH stabilizers, preference is given to 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;
• Ester der phosphorigen Säure oder der Phosphorsäure mit aliphatischen Alkoholen mit 1 bis 6 C-Atomen, vorzugsweise Ethylphosphat, Dimethylphosphat, Isopropylphosphat, Diisopropylphosphat, Butylphosphit und Dimethylphosphit; und/oder
• Triazole, vorzugsweise Benztriazol.

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-α-naphthylamin, Diphenylamin und Derivate hiervon;
• substituierte Phenole, vorzugsweise Dibutylkresol, 2,6-Di-butyl-p-kresol, 2,6-Di-tert.-butyl-p-kresol und 2,4 Dimethyl-6-tert.-butylphenol;
• Brenzkatechin und Hydrochinon, gegebenenfalls kernsubstituiert;
• Chinone, vorzugsweise Antrachinon; und
• Phenothiazine, die auch kernsubstituiert sein können.

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

• aromatic amines, preferably phenyl-α-naphthylamine, diphenylamine and derivatives thereof;
• substituted phenols, preferably dibutyl cresol, 2,6-di-butyl-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.

• A) 25 bis 35 Gew.-%;
• B) 35 bis 58 Gew.-%;
• C) 15 bis 32 Gew.-%;
• D) 0.2 bis 4 Gew.-%; und
• E) 0.2 bis 4 Gew.-%, Gewichtsprozente jeweils bezogen auf das Gewicht der gesamten Flüssigkeit.

The hydraulic fluid according to the invention preferably consists essentially of

• A) 25 to 35% by weight;
• B) 35 to 58% by weight;
• C) 15 to 32% by weight;
• D) 0.2 to 4% by weight; and
• E) 0.2 to 4% by weight, percentages by weight in each case based on the weight of the entire liquid.

The hydraulic fluid according to the invention is produced by mixing the components together, for example in a container with 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, it can optionally also be carried out at a higher temperature (30 to 50 ° C.), it being advisable 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 A, ist ein Umsetzungsprodukt von Orthoborsäure, Diethylenglykol und Triethylenglykolmonomethylether (Methyltriethylenglykol);
• Borsäureester A₂ ist ein Umsetzungsprodukt von Orthoborsäure, Diethylenglykol und Diethylenglykolmonomethylether;
• Borsäureester A₃ ist ein Umsetzungsprodukt von Orthoborsäure, Diethylenglykol und Triethylenglykolmonoethylether;
• Bosäureester A₄ ist ein Umsetzungsprodukt von Orthoborsäure, Diethylenglykol und Diethylenglykolmonobutylether.

The following boric acid esters (A, to A ₄ ) to be used according to the invention are produced 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 to A ₄ :

• Boric acid ester A, 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;
• Bosic 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 liquids 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 differentiate.

Claims (3)

1. Hydraulic fluid consisting essentially of A) 20 to 40 wt .-%, based on the weight of the total liquid, of a boric acid ester, which is obtained when orthoboric acid, diethylene glycol and an ethylene glycol monoalkyl ether of the formula I

where 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 the formula I, in which 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) formal of the formula II

wherein R ¹ and R ^{2 are} an alkyl group having 1 to 4 carbon atoms and n, and n _{2 is} 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 hydrogen,

where y is an integer from 1 to 5; R ^{5 is} hydrogen,

in which. 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 Is 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. 2. Hydraulic liquid according to claim 1, characterized in that the components A) bi.s E) are present in the following amounts: A) 25 to 35% by weight; B) 35 to 58% by weight; C) 15 to 32% by weight; D) 0.2 to 4% by weight; E) 0.2 to 4% by weight. 3. Hydraulic fluid according to claim 1, characterized in that the component A) is a reaction product of orthoboric acid, diethylene glycol and methyl or ethyltriethylene glycol in a molar ratio of 1: 1: 1; the component B) methyl or ethyltri.ethylene glycol; the component C) a bis (di or triethylene glycol monomethyl or ethyl ether) formal; the component D) an alkylamine of the formula III, in which R ^{3 is} an alkyl group having 1 to 9 C atoms and R ⁴ and R ^{5 is} hydrogen or - (CH ₂ CH ₂ O) _y H, where y is an integer from 1 to 5 is; and the component E) an inhibitor is selected from the group consisting of benzotriazole, phenyl-α-naphthylamine, diphenylamine, 2,6-dibutyl cresol, phenothiazine and isopropyl phosphate.