Novel low viscosity functional fluid composition

Abstract

The present invention relates to a low viscosity functional fluid composition with high dry and wet equilibrium reflux boiling points as well as improved lubricating properties.

Description

[0001] Novel low viscosity functional fluid composition

[0002] Description

[0003] The present invention relates to a low viscosity functional fluid composition with high dry and wet equilibrium reflux boiling points as well as improved lubricating properties.

[0004] The said functional fluid composition is useful in a variety of applications and in particular as a brake fluid. It provides for excellent lubricating action with moving parts within technical devices filled with such functional or hydraulic fluids, e.g. the brake systems of vehicles with hydraulic brake systems such as passenger cars and small trucks.

[0005] In modern vehicle brake systems, braking control is regulated by hydraulic units which contain pumps with a running time much longer than in conventional vehicle brake systems. A typical running time of such pump in such a hydraulic unit is about 1,000 hours, in contrast to about 10 hours pump running time in vehicle brake systems with conventional ABS hydraulic units. Pumps in hydraulic units comprise sealing parts made of rubber or elastomeric material which normally suffers from wear. Therefore, modern functional fluids must exhibit excellent lubricating action and reduce friction, ensuring that no or only a very low degree of wear of the parts of the hydraulic unit occurs. Especially, they must protect the rubber or elastomeric material of sealing parts from becoming deformed and leaking, thus causing misoperation and lack of safety for running the vehicle.

[0006] Functional fluid compositions based on borate esters are well known in the art. To be useful for example as DOT 4 or DOT 5.1 brake fluids, these borate ester based compositions must meet stringent physical properties and performance requirements particularly with respect to minimum dry equilibrium reflux boiling point ("ERBP"), minimum wet equilibrium reflux boiling point ("WERBP") and maximum low temperature kinematic viscosity (e.g. determined at -40°C) while maintaining adequate resistance to corrosion, stability and meeting other physical property requirements such as pH, reserve alkalinity and rubber swell. The requirements for brake fluids, especially their boiling points and viscosities and methods of measurement, are laid down in standards SAE J 1703, SAE J 1704, and ISO 4925.

[0007] There is a strong demand for improved high performance hydraulic fluid compositions and brake fluids having low temperature viscosity while meeting or exceeding at the same time the minimum ERBP and especially the mm2 / s at minus 40 °C temperature requirements as fulfilled by the hydraulic fluid compositions and brake fluids described in the art.

[0008] The present viscosity requirements are not more than 450 mm2 / s at minus 40 °C and at least 1.50 mm2 / s at 100 °C. The WERBP should be at least 165 °C, the ERBP should be higher than 250 °C according to ISO 4925, class 6.

[0009] WO 2013 / 171052 discloses functional fluids comprising from 15 to 90% of one or more alkoxy glycol borate esters, 5 to 80% of one or more alkoxy glycol components, and one or more additives with corrosion inhibition action.

[0010] The lubricating action and friction properties of the compositions disclosed in WO 2013 / 171052 do not fulfil modern standards.

[0011] WO 2015 / 052234 discloses the use of alkoxylates of ricinoleic acid, of castor oil or of any other ricinoleic acid ester as lubricants in hydraulic fluids.

[0012] It is a disadvantage that a further component needs to be added to such functional fluids which may lead to misdosing of such components and complex compositions of such functional fluids.

[0013] The explicit examples in these documents of the prior art disclose compositions with a high content of borate esters of more than 60% by weight.

[0014] Furthermore, functional fluids comprising such high amounts of alkoxy glycol borate esters exhibit a relatively high low temperature viscosity so that the above-mentioned viscosity requirement is not met.

[0015] However, boric acid is known to be a OMR-compound (repro tox category 1), therefore, also its esters are suspect to similar health threat (currently classified as repro tox category 2) and, therefore of potential danger during storage, handling and filling of the brake fluid. Furthermore, the content of boron in the brake fluids is associated with a certain risk of gel formation or precipitation due to salt formation due to the inorganic character of boron salts, especially upon ageing of the brake fluids. As a result, particles may occur in the brake fluid and limit its performance in critical situations.

[0016] Therefore, there is a demand for functional fluids which meet modern low viscosity lubrication standards without the need for additional component additives and which contain reduced levels of boric acid esters.

[0017] WO 2021 / 213693 teaches a low viscosity brake fluid composition comprising an alkoxy glycol component (B), which may be a single species or a mixture of different species with regards to the ethoxylation degree and / or the radical, an oligo ethylene glycol component (C) according to the present application, and octylamine ethoxylate (p. 1 , I. 5-12; ex.

[0018] 2; claims 1 , 28-30). A low content of boric acid esters is preferred

[0019] The problem was solved by low viscosity functional fluid composition comprising

[0020] (A) from 4 to less than 45% by weight, based on the weight of the total composition, of one or more alkoxy glycol borate esters having the general formula (I)

[0021] [R1-O-(CH2CH2-O)n]3B (I) wherein R1is a C to C4-alkyl radical or a mixture of such radicals and n has a value of from 2 to 6,

[0022] (B) from 45 to 97% by weight, based on the weight of the total composition, of at least two alkoxy glycol components (B1) and (B2), component (B1) having the general formula (Ila)

[0023] H3C-O-(CH2CH2-O)m-H (Ila) and alkoxy glycol component (B2) having the general formula (lib)

[0024] R2-O-(CH2CH2-O)m-H (lib) wherein R2is a C2- to Cs-alkyl radical or a mixture of such radicals and m has a value of from 2 to 6, R2and / or m being different or identical to R1and / or n, respectively,

[0025] (C) from 0.25 to 20% by weight, based on the weight of the total composition, of at least one oligo ethylene glycol having the general formula (III)

[0026] HO-(CH2CH2-O)k-H (III) wherein k has a value of from 2 to 6,

[0027] (D) from 0.1 to 10% by weight, based on the total weight of the composition, of an additive package comprising one or more additives with corrosion inhibition action, wherein at least one of the additives contained in the additive package of component (D) is selected from alkylamine ethoxylates, with the proviso that the amounts of all components of the composition always add up to 100% by weight.

[0028] The said low viscosity functional fluid composition is useful in a variety of applications and in particular as a brake fluid, especially for new electronic or automated anti-lock brake systems, such as improved electrohydraulic brake systems for battery electric vehicles which require lower viscosity fluids for satisfactory operation at low temperatures.

[0029] According to the present invention, the above-defined functional fluid composition has been found which exhibits superior values of ERBP and of WERBP and for low temperature kinematic viscosity while maintaining excellent resistance to corrosion, high stability and meeting other physical property requirements such as pH, reserve alkalinity and rubber swell. Especially very high WERBP values are achieved. Moreover, kinematic viscosity value at very low temperatures below -40°C, e.g. at -50°C, are superior compared to functional fluid compositions of the art.

[0030] The functional fluid composition of the present invention exhibits superior behaviour in ERBP and WERBP temperature and simultaneously in low temperature viscosity performance. Preferably, it exhibits an ERBP of at least 255°C, more preferably of at least 257°C and / or a WERBP of at least 165°C.

[0031] The functional fluid composition of the present invention exhibits a low temperature kinematic viscosity of preferably less than 450 centistokes ("cSt") (= mm2 / s), more preferably of less than 440 cSt, most preferably less than 430 cSt, each determined at a temperature of -40°C.

[0032] The functional fluid composition of the present invention exhibits a high temperature kinematic viscosity of preferably at least 1 .50 centistokes cSt, more preferably of at least 1.55 cSt, most preferably at least 1.60 cSt, each determined at a temperature of 100°C.

[0033] It is a special feature of the hydraulic fluids according to the present invention that they already fulfil the high demands which are placed on abrasion resistance and noise development of modern hydraulic fluids. Such demands are defined in DIN standards DIN 51834-5:2024-06 and DIN 51834-6 Draft V8 which are presently under discussion.

[0034] For fulfilling such demands there is no need to add alkoxylates of ricinoleic acid as disclosed in WO 2015 / 052234.

[0035] Component (A) of the functional fluid composition of general formula (I) comprises species of ethoxylation degree of from n = 2 to n = 6, preferably of from n = 2 to n = 4, more preferably of n = 3. Component (A) may be a single species or a mixture of different species with regard to the ethoxylation degree and / or to radical R1.

[0036] Radical R1is preferably a Ci- to C4-alkyl radical and may be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl and 2-ethylhexyl, ethyl and especially methyl being preferred.

[0037] The said borate esters and their methods of preparation are well known in the art. Borate esters especially useful in the functional fluid composition of the present invention may be prepared by reacting boric acid with suitable alkoxy glycol components which are different or identical to those of component (B). Typically, such alkoxy glycol components are mixtures of different species with regard to the ethoxylation degree and / or to radical R1.

[0038] Examples of useful borate esters include those containing methyl triethylene glycol borate ester which can also be named tris-[2-[2-(2-methoxyethoxy)-ethoxy]-ethyl) orthoborate, ethyl triethylene glycol borate ester, n-butyl triethylene glycol borate ester and mixtures thereof.

[0039] Further useful borate esters include those containing methyl tetraethylene glycol borate ester, methyl diethylene glycol borate ester, ethyl tetraethylene glycol borate ester, ethyl diethylene glycol borate ester, n-butyl tetraethylene glycol borate ester, n-butyl diethylene glycol borate ester and mixtures thereof.

[0040] In a preferred embodiment, component (A) comprises at least one alkoxy glycol borate ester of general formula (I) wherein the ethoxylation degree has a value of n = 3 and R1is a methyl radical.

[0041] Preferably the moiety R1-O-(CH2CH2-O)n-H of component (A) is a mixture consisting mainly of triethylene glycol monomethyl ether and tetraethylene glycol monomethyl ether and in which higher and lower alkylene glycol monomethyl ether preferably account for less than 10% by weight each, especially preferably less than 10% by weight in total. The moiety R1-O-(CH2CH2- O)n-H of component (A) is particularly preferably mainly triethylene glycol monomethyl ether, in which higher and lower alkylene glycol monomethyl ethers preferably account for less than 20% by weight each, and especially preferably less than 10% by weight.

[0042] The proportion of triethylene glycol monomethyl ether in the moiety R1-O-(CH2CH2-O)n-H of component (A) is at least 30% by weight, preferably at least 40%, preferably at least 50% and especially preferably at least 60% by weight.

[0043] In a preferred embodiment, the proportion of triethylene glycol monomethyl ether in the moiety R1-O-(CH2CH2-O)n-H of component (A) is at least 75% by weight, especially preferably at least 85%, especially preferably at least 90%, especially at least 95% by weight.

[0044] Component (B) of the functional fluid composition of the present invention is a mixture of at least two, preferably exactly two alkoxy glycol components (B1) and (B2), wherein component (B1) is a methoxy glycol component and (B2) is a C2-Cs-alkoxy glycol component. Component (B) of the functional fluid composition of general formula (II) comprises species of ethoxylation degree of from m = 2 to m = 6, preferably of from m = 2 to m = 4, more preferably of from m = 3 to m = 4, and even more preferably m = 3.

[0045] Components (B1) and (B2) may exhibit the same or a different ethoxylation degree, preferably m is the same for both (B1) and (B2). Even more preferably m is the same for both (B1) and (B2) and identical with n.

[0046] In a preferred embodiment the alkoxy glycol used in the alkoxy glycol borate esters (A) is the same as component (B1) or (B2), more preferably it is the same as component (B1).

[0047] Radical R2is a C2- to Cs-alkyl radical and may be ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl n-heptyl, n-octyl and 2-ethylhexyl. Preferably R2is a C2- to C4-alkyl radical, more preferably R2is ethyl or n-butyl, and especially n-butyl.

[0048] Examples of useful methoxy glycols for component (B1) of the present invention include methyldiglycol, methyltriglycol, methyltetraglycol, methyl pentaglycol, methylhexaglycol and mixtures thereof. Preferred components (B1) are methyltriglycol and methyltetraglycol, with methyltriglycol being especially preferred.

[0049] For the avoidance of doubt, "glycol" always means "ethylene glycol".

[0050] Preferably, component (B1) is a mixture consisting mainly of triethylene glycol monomethyl ether and tetraethylene glycol monomethyl ether and in which higher and lower alkylene glycol monomethyl ether preferably account for less than 10% by weight each, especially preferably less than 10% by weight in total. Component (B1) is particularly preferably mainly triethylene glycol monomethyl ether, in which higher and lower alkylene glycol monomethyl ethers preferably account for less than 20% by weight each, and especially preferably less than 10% by weight.

[0051] The proportion of triethylene glycol monomethyl ether in component (B1) is at least 30% by weight, preferably at least 40%, preferably at least 50% and especially preferably at least 60% by weight.

[0052] In a preferred embodiment, the proportion of triethylene glycol monomethyl ether in component (B1) is at least 75% by weight, especially preferably at least 85%, especially preferably at least 90%, especially at least 95% by weight.

[0053] Examples of useful alkoxy glycols for component (B2) of the present invention include ethyldiglycol, ethyltriglycol, ethyltetraglycol, ethylpentaglycol, ethyl hexaglycol, n-propyl-diglycol, n-propyltriglycol, n-propyltetraglycol, n-propylpentaglycol, n-propylhexaglycol, n-butyldiglycol, n- butyltriglycol, n-butyltetraglycol, n-butylpentaglycol, n-butylhexaglycol, n-pentyldiglycol, n- pentyltriglycol, n-pentyltetraglycol, n-pentylpentaglycol, n-pentyl-hexaglycol, n-hexyldiglycol, n- hexyltriglycol, n-hexyltetraglycol, n-hexylpentaglycol, n-hexylhexaglycol, 2-ethylhexyldiglycol, 2- ethylhexyltriglycol, 2-ethylhexyltetraglycol, 2-ethylhexylpentaglycol, 2-ethylhexyl hexaglycol and mixtures thereof.

[0054] Special preference is given to ethyltriglycol, ethyltetraglycol, n-butyltriglycol, and n- butyltetraglycol.

[0055] In a preferred embodiment, component (B) comprises a mixture of alkoxy glycols of general formula (II) comprising solely or predominantly species with m = 3. Predominantly shall mean that at least 60% by weight, more preferably at least 75% by weight, most preferably at least 90% by weight, of component (B) comprises species with m = 3. In the last case, alkoxy glycol species with m = 2 and / or m = 4 and / or m = 5 and / or m = 6 may be present in minor amounts.

[0056] In a preferred embodiment, component (B2) is a mixture consisting mainly of triethylene glycol mono-n-butyl ether and tetraethylene glycol mono-n-butyl ether and in which higher and lower alkylene glycol monoalkyl ethers preferably account for less than 10% by weight each, and in particular preferably less than 10% by weight in total. Component (B2) is mainly triethylene glycol mono-n-butyl ether, in which higher and lower alkylene glycol monoalkyl ethers preferably account for less than 20% by weight each, and especially preferably less than 10% by weight.

[0057] The proportion of triethylene glycol monoalkyl ether in component (B2) is at least 65% by weight, preferably at least 70%, especially preferably at least 75 and especially preferably at least 80% by weight. Typically, the weight ratio of methoxy glycol (B1) to alkoxy glycol (B2) in this mixture is from 10 : 1 to 1 : 10, preferably from 9 : 1 to 1 : 5, more preferably from 8 : 1 to 1 : 2, and especially from 7 : 1 to 1 : 1.

[0058] Component (C) is at least one oligo ethylene glycol having the general formula (III)

[0059] HO-(CH2CH2-O)k-H (III) wherein k has a value of from 2 to 6.

[0060] Preferred values for k are 2 to 5, more preferably 2 to 4, even more preferably 2 or 3 and especially 3.

[0061] Components (C) may be selected from the group consisting of diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and hexaethylene glycol, preferably selected from the group consisting of diethylene glycol, triethylene glycol, and tetraethylene glycol, even more preferably may be diethylene glycol or triethylene glycol or mixtures thereof, and especially triethylene glycol.

[0062] Preferably at least 80% by weight of all components (C) are diethylene glycol and / or triethylene glycol, especially preferably at least 85%, especially preferably at least 90 and especially at least 95% by weight. In a preferred embodiment component (C) comprises at least 60% by weight of triethylene glycol, more preferably at least 75%, and especially at least 90% by weight.

[0063] The alkylamine ethoxylates as part of component (D) and their interaction with the other components and additives of the present functional fluid composition are deemed to contribute to the corrosion inhibition, as well as the improved abrasion resistance- and noise developmentproperties of the composition.

[0064] The alkylamine residue in the said alkylamine ethoxylates may be a secondary or preferably a primary aliphatic monoamine which is capable of being ethoxylated. Usually secondary or preferably primary aliphatic monoamines are used, however, polyamines with at least one secondary and / or primary amino group which is capable of being ethoxylated may also be used. The alkyl residues to the nitrogen atom normally comprise saturated linear or branched alkyl groups, however, unsaturated linear or branched alkyl residues or saturated or unsaturated cycloalkyl residues may also be comprised by the term "alkyl".

[0065] In a preferred embodiment, the said alkylamine ethoxylates comprise at least one linear or branched C3 to C2o alkyl chain, preferably at least one linear or branched C4 to C13 alkyl chain, more preferably at least one linear or branched Ce to C12 alkyl chain, most preferably at least one linear or branched C7 to Cn alkyl chain. Preferably, the term "alkyl chain" here means saturated and non-cyclic hydrocarbon residues. The alkylamine ethoxylates may also comprise mixtures of such alkyl chains, for example a mixture of homologue alkyl residues, depending on the specific technical or natural origin of the alkylamines used.

[0066] Suitable examples for single alkylamine molecules being capable for ethoxylation and, therefore, suitable as surfactants for the instant invention are n-propylamine, isopropylamine, n- butylamine, isobutylamine, sec-butylamine, tert-butylamine, n-pentyl-amine, tert-pentylamine, n- hexylamine, n-heptylamine, n-octylamine, 2-ethylhexyl-amine, n-nonylamine, n-decylamine, 2- propylheptylamine, n-undecylamine, n-dodecyl-amine, n-tridecylamine, isotridecylamine, n- tetradecylamine, n-pentadecylamine, n-hexadecylamine, n-heptadecylamine, n-octadecylamine, n-nonadecylamine, n-eicosyl-amine, di-(n-hexyl)amine, di-(n-heptyl)amine, di-(n-octyl)amine, di- (2-ethylhexyl)amine, di-(n-nonyl)amine, di-(n-decyl)amine, di-(2-propylheptyl)amine, di-(n- undecyl)amine, di-(n-dodecyl)amine, di-(n-tridecyl)amine, di-(isotridecyl)amine, di-(n- tetradecyl)amine, di-(n-pentadecyl)amine, di-(n-hexadecyl)amine, di-(n-heptadecyl)amine, di-(n- octadecyl)-amine, di-(n-nonadecyl)amine, di-(n-eicosyl)amine, n-hexylmethylamine, n-heptyl- methylamine, n-octylmethylamine, (2-ethylhexyl)methylamine, n-nonylmethylamine, n- decylmethylamine, (2-propylheptyl)methylamine, n-undecylmethylamine, n-dodecyl- methylamine, n-tridecylmethylamine, isotridecylmethylamine, n-tetradecylmethylamine, n- pentadecylmethylamine, n-hexadecylmethylamine, n-heptadecylmethylamine, n-octa- decylmethylamine, n-nonadecylmethylamine and n-eicosylmethylamine.

[0067] Such alkyl residues may be derived entirely from petrochemical production, for example technical Cs-Cis alkyl mixtures, 2-ethylhexyl or 2-propylheptyl, or may entirely or partially be based on renewable raw materials, for example fatty amines such as stearyl amine, oleyl amine or tallow amine may be used as the basis for the alkylamine ethoxylates. The degree of ethoxylation is usually from 1 to 35 EO units per alkylamine molecule, i.e. the at least on alkylamine ethoxylate comprises from 1 to 35 EO units, preferably from 1.5 to 15 EO units, more preferable from 1.8 to 9 EO units, most preferably from 2 to 6 EO units. The said ethoxylation degree is a statistical value, i.e the alkylamine ethoxylates have normally to be regardes as mixtures of species (homologues) with different numbers of EO units.

[0068] In an especially preferred embodiment of the instant invention, the at least one alkylamine ethoxylate comprises at least on linear C3 to C20 alkyl chain and from 1 to 35 EO units; more preferably the at least one alkylamine ethoxylate comprises at least on linear C4 to C13 alkyl chain and from 1.5 to 15 EO units; most preferably the at least one alkylamine ethoxylate comprises at least one linear Ce to C12 alkyl chain and from 1 .8 to 9 EO units, especially the at least one alkylamine ethoxylate comprises at least one linear C7 to On alkyl chain and from 2 to 6 EO units.

[0069] Such alkylamine ethoxylates may be primary amines with one oxyethylene chain of general formula Alkyl-NH-(CH2CH2O)m-H or preferably primary amines with two oxyethylene chains of general formula Alkyl-N[(CH2CH2O)p-H][(CH2CH2O)q-H] or secondary amines of general formula (Alkyl)2N-(CH2CH2O)m-H or mixtures of such primary amines with one oxyethylene chain and such primary amines with two oxyethylene chains or mixtures of such primary and secondary amines, wherein m and (p+q), respectively, are the total ethoxylation degrees. 'Alkyl" in the above formulas normally means C3 to C20 alkyl, preferably C4 to C13 alkyl, more preferably Cs to C12 alkyl, most preferably C7 to Cn alkyl, as defined above. Residual alkylamine species may also be present in lower amounts, especially with low total ethoxylation degrees below 2.

[0070] A typical suitable alkylamine ethoxylate is octylamine (caprylamine) with 2 EO (ethylene oxide) units which is commercially available.

[0071] The said alkylamine ethoxylates can be prepared by usual methods such as the reaction of the alkylamine with ethylene oxide under catalysis by alkali metal hydroxides or under catalysis by double metal cyanides, as known to the skilled person in the art.

[0072] The said alkylamine ethoxylates has partly corrosion inhibition properties and partly solvent properties for the functional fluid composition or brake fluid, respectively, according to the present invention. Apparently the alkylamine ethoxylates also contribute to the abrasion resistance- and noise development-properties of the composition.

[0073] Component (D) of the present functional fluid composition may comprise, besides the alkylamine ethoxylates, at least one additive with corrosion inhibition action, although the alkylamine ethoxylates exhibit corrosion inhibition properties themselves.

[0074] Suitable customary additives with corrosion inhibition properties include fatty acids such as lauric, palmitic, stearic or oleic acid; esters of phosphorus or phosphoric acid with aliphatic alcohols; phosphites such as ethyl phosphate, dimethyl phosphate, isopropyl phosphate, n-butyl phosphate, triphenyl phosphite and diisopropyl phosphite; heterocyclic nitrogen containing organic compounds such as benzotriazole, tolutriazole, 1 ,2,4-triazole, benzoimidazole, purine, adenine and derivatives of such heterocyclic organic compounds; alkylamines such as mono- and di-(C4- to C2o-alkyl)amines, e.g. n-butyl-amine, n-hexylamine, n-octylamine, 2- ethy I hexylamine, isononylamine, n-decylamine, n-dodecylamine, oleylamine, d-n-proylamine, diisopropylamine, di-ni-butylamine, di-n-amylamine, cyclohexylamine and salts of such alkylamines; alkanolamines such as mono-, di- and trimethanolamine, mono-, di- and triethanolamine, mono-, di- and tri-n-propanolamine and mono-, di- and tri-isopropanolamine. Of course, mixtures of the above additives with corrosion inhibition action can be used.

[0075] Among these further components (D) azol derivatives are especially preferred:

[0076] Azole derivatives in the context of the present description mean five-membered heterocyclic compounds having 2 or 3 heteroatoms from the group consisting of nitrogen and sulphur and comprise no or at most one sulphur atom and can bear an aromatic or saturated six-membered fused-on ring.

[0077] These five-membered heterocyclic compounds (azole derivatives) usually contain two N atoms and no S atom, 3 N atoms and no S atom or one N atom and one S atom as heteroatoms.

[0078] Preferred groups of the specified azole derivatives are annellated imidazoles and annellated 1 ,2,3-triazoles of the general formula or (2) where the variable R is hydrogen or a Ci-Cio-alkyl radical, in particular methyl or ethyl, and the variable X is a nitrogen atom or the C-H group.

[0079] Typical and preferred examples of azole derivatives of the general formula (1) are benzimidazole (X = C-H, R = H), benzotriazoles (X = N, R = H) and tolutriazole (tolyltriazole) (X = N, R = CH3). A typical example of an azole derivative of the general formula (2) is hydrogenated 1 ,2,3-tolutriazole (tolyltriazole) (X = N, R = CH3).

[0080] A further preferred group of the specified azole derivatives is benzothiazoles of the general formula (3) where the variable R is as defined above and the variable R' is hydrogen, a Ci-C -alkyl radical, in particular methyl or ethyl, or in particular a mercapto group (-SH). A typical example of an azole derivative of the general formula (3) is 2-mercaptobenzothiazole.

[0081] Further suitable azole derivatives are non-annellated azole derivatives of the general formula (4)

[0082] (4) where the variables X and Y together are two nitrogen atoms or one nitrogen atom and a C-H group, for example 1 H-1 ,2,4-triazole (X = Y = N) or preferably imidazole (X = N, Y = C-H).

[0083] For the purposes of the present invention, benzimidazole, benzotriazole, tolutriazole, hydrogenated tolutriazole or mixtures thereof, in particular benzotriazole or tolutriazole, are very particularly preferred as azole derivatives.

[0084] Especially the above-mentioned alkanolamines are often used as an alternative to the alkylamine ethoxylates (D). However, it is a preferred embodiment of the present invention that such alkanolamines are not present in the compositions according to the invention.

[0085] Using ethoxylated alkylamines as compounds with corrosion inhibition action in the additive package of component (D) often results in a slight increase in viscosity of the present functional fluid composition. Besides the alkylamine ethoxylates and possibly the additives with corrosion inhibition action, further customary additives may be present in the additive package of component (D), for example stabilizers such as pH stabilizers, antioxidants such as phenolthiazine and phenolic compounds, e.g. hydroxyanisol and bisphenol A, defoamers and dyes.

[0086] Preferably, the additive package of component (D) which includes one or more alkylamine ethoxylates consists or consists essentially of a major portion of additives with corrosion inhibition action and a minor portion of additives with antioxidant action and possibly of defoamers and dyes.

[0087] The portion of alkylamine ethoxylate(s) in the additive package of component (D) is typically of from 1 to 100% by weight, preferably of from 10 to 99% by weight, more preferably of from 25 to 98% by weight, most preferably of from 40 to 97% by weight, each based on the weight of the additive package of component (D).

[0088] It is contemplated that also other materials than components (A), (B), (C), and (D) may be formulated into the present functional fluid composition so long as care is taken not to lower the ERBP or WERBP temperatures below the superior high levels of the instant invention or to increase the low temperature viscosity above an acceptable level.

[0089] It is an advantage of the present invention that the compositions according to the present invention fulfil the requirements of abrasion resistance and noise development of modern hydraulic fluids, defined in DIN standards DIN 51834-5:2024-06 and DIN 51834-6 Draft V8 without the necessity of adding alkoxylates of ricinoleic acid, of castor oil or of any other ricinoleic acid ester as lubricants according to WO 2015 / 052234.

[0090] Such alkoxylates of ricinoleic acid, of castor oil or of any other ricinoleic acid ester may be added to the compositions according to the present invention but are not necessary to fulfil the requirements of abrasion resistance and noise development.

[0091] In one preferred embodiment the compositions according to the present invention are essentially free of such alkoxylates of ricinoleic acid, of castor oil or of any other ricinoleic acid ester.

[0092] In another embodiment an alkoxylate of ricinoleic acid, of castor oil or of any other ricinoleic acid ester, preferably of ricinoleic acid or castor oil and very preferably of castor oil may optionally be present in the composition according to the present invention in amounts of from 0.01 to 5% by weight, preferably from 0.05 to 2% by weight, more preferably from 0.1 to 1% by weight, most preferably from 0.15 to 0.9% by weight.

[0093] This castor oil for the purposes of the present specification is an at least partly and preferably wholly esterified acyl glycerol wherein at least one, preferably at least two, of the acyl groups are ricinoleic acid or isoricinoleic acid, preferably ricinoleic acid.

[0094] For example, the mixture of fatty acids preferably comprises a mixture of two molecules of ricinoleic acid with a fatty acid which carries no hydroxyl group, preferably selected from the group consisting of oleic acid, linoleic acid, palmitic acid, and stearic acid.

[0095] In one preferred embodiment the castor oil has an OH number of 160 to 173 mg KOH / g.

[0096] The alkoxylate, especially the alkoxylate of ricinoleic acid, of castor oil or of any other ricinoleic acid ester, is preferably prepared by reaction of a saturated or unsaturated hydroxy-substituted Cs to C22 fatty acid or of an ester thereof, especially by reaction of ricinoleic acid, of castor oil or of any other ricinoleic acid ester, with at least one alkylene oxide. The alkylene oxide may be propylene oxide, butylene oxide, styrene oxide or preferably ethylene oxide. Mixtures of such alkylene oxides resulting in statistic or block structures of alkylene oxide units may also be used.

[0097] In detail, the structure of said alkoxylate preferably comprises a saturated or unsaturated Ca to C22 fatty monocarboxylic acid or at least one saturated or unsaturated Ca to C22 fatty monocarboxylic acid unit in the molecule, being esterified with one or more oxyalkylene units at the free carboxylic acid function if such free carboxylic acid function is present in the molecule and carrying a hydroxyl group located on the fatty acid side chain of said alkoxylate being etherified by one or more oxyalkylene units.

[0098] Examples of such saturated or unsaturated hydroxyl-substituated Cs to C22 fatty monocarboxylic acids or units thereof, preferably of saturated or unsaturated hydroxyl-substituted C14 to C20 fatty mono-carboxylic acids or units thereof, as the basis for the alkoxylates are 1 flhydroxy stearic acid, 12-hydroxystearic acid and especially ricinoleic acid. Such unsaturated hydroxyl-substituated Cs to C22 fatty mono-carboxylic acids may be taken as free carboxylic acids or as corresponding esters for preparing the alkoxylate. In case of ricinoleic acid, castor oils as its naturally occurring triglyceride may advantageously be reacted, as an interesterification, with an alkylene oxide resulting in the desired ricinoleic alkoxylate and glycerol. Any other ester of ricinoleic acid, e.g. the corresponding di- or monoglyceride or the corresponding methyl, ethyl, propyl or butyl ester, may be used as educt for interesterification. Depending on the conditions of the alkoxylation reaction with esters of ricinoleic acid, especially with castor oils, the ester and especially the triglyceride may also keep its carboxylic ester function, especially its glycerol triester function, and solely be alkoxylated at the hydroxyl group located on the fatty acid side chain, being etherified there by one or more oxyalkylene units.

[0099] The said alkoxylate, especially the alkoxylate of ricinoleic acid, of castor oil or of any other ricinoleic acid ester, usually comprises from 2 to 200, preferably from 4 to 100, more preferably from 6 to 80, most preferably from 10 to 50, and especially 20 to 40 alkylene oxide units which are preferably ethylene oxide units. "Number of alkylene oxide units" means mols of alkylene oxide per mole of the saturated or unsaturated hydroxyl-substituated Cs to C22 fatty monocarboxylic acid or of the units thereof, as the basis for the alkoxylate. Using castor oil which is the triglyceride of ricinoleic acid, the amount of alkylene oxide used for alkoxylation refers to 3 equivalents of ricinoleic acid or units thereof to be alkoxylated. For higher alkoxylation degrees, the number of alkylene units is a mean value as a statistical number, due to a distribution of alkoxylation homologues in the product. There may be two types of hydroxyl groups in the molecule to be alkoxylated, i.e. one to be esterified (or interesterified) and the other to be etherified, esterification may occur or may not occur, etherification will always occur.

[0100] Methods of alkoxylation, especially ethoxylation, of carboxylic acids or esters thereof, such as castor oil, are known in the art and, therefore, do not need to be further described in this application.

[0101] According to the present invention, the four components (A), (B), (C), and (D) are present in the functional fluid composition in the following amounts:

[0102] (A) from 4 to less than 45% by weight, preferably from 4 to less than 30% by weight, more preferably from 5 to 25% by weight, most preferably from 5 to 15% by weight, especially from 5 to 14% by weight;

[0103] (B) from 45 to 97% by weight of components (B1) and (B2) in sum, preferably from 50 to 95% by weight, more preferably from 55 to 90% by weight, most preferably from 60 to 85% by weight, especially more than 65 to 85 % by weight;

[0104] (C) from 0.25 to 20% by weight, preferably from 0.5 to 17.5% by weight, more preferably from 0.75 to 15% by weight, most preferably from 1 to 12.5% by weight, especially 2 to 11 % by weight;

[0105] (D) from 0.1 to 10% by weight, preferably from 0.5 to 7.5% by weight, more preferably from 1 to 5% by weight, most preferably from 1 .5 to 3.5% by weight, especially 1 .5 to 3.0 % by weight.

[0106] All % values for (A), (B), (C) and (D) above refer to the total composition of the present functional fluid composition, or - if other materials than components (A), (B), (C), and (D), e.g. the above-mentioned diluents and / or lubricants, are present - to the total weight of (A) plus (B) plus (C) plus (D). The % values for (A), (B), (C), and (D) add up in each case to 100% by weight.

[0107] The low viscosity functional fluid composition of the present invention is especially useful as a brake fluid, for example for vehicles such as passenger cars and trucks, especially for new electronic or automated anti-lock brake systems which require lower viscosity fluids for satisfactory operation at low temperatures.

[0108] Therefore, another subject matter of the present invention is a process for operating a brake system in vehicles, such as passenger cars and trucks, especially for new electronic or automated anti-lock brake systems, using a functional fluid composition according to the present invention.

[0109] Another subject matter of the present invention is a brake system in vehicles, such as passenger cars and trucks, especially for new electronic or automated anti-lock brake systems, comprising a functional fluid composition according to the present invention. Besides its superior behavior in ERBP and WERBP temperature and its low temperature viscosity performance, the functional fluid composition of the present invention exhibits a good corrosion protection, a good water compatibility, a mild pH value, a good stability with regard to low and high temperatures, a good oxidation stability, a good chemical stability, a good behavior towards rubber and elastomers and a good lubrication performance, especially concerning abrasion resistance and noise development.

[0110] The following examples are intended to demonstrate the behavior and performance of the low temperature functional fluid composition of the present invention without limiting it.

[0111] Examples

[0112] The ERBP (minimum dry equilibrium reflux boiling point) and WERBP (minimum wet equilibrium reflux boiling point) temperatures and kinematic viscosity values (according to ASTM D445) of the following function fluid compositions according to the present invention were determined according to test procedures described in Department of Transportation Standard FMVSS 116 (corresponding to SAE J 1704).

[0113] Abrasion resistance and noise development were determined in accordance with the present DIN standards DIN 51834-5:2024-06 and DIN 51834-6 Draft V8.

[0114] Abbreviations:

[0115] MTG Borate: boric acid triester of methyltriglycol

[0116] MTG: methyltriglycol (triethylene glycol mono methyl ether)

[0117] BTG: n-butyltriglycol (triethylene glycol mono n-butyl ether)

[0118] ODEA: n-octyl diethanolamine

[0119] DIPA: di isopropanolamine

[0120] DEG: diethylene glycol

[0121] TEG: triethylene glycol

[0122] TTZ: tolutriazole

[0123] COxEO35: Castor oil reacted with 35 moles of ethylene oxide, ethoxylation solely occuring at the hydroxyl group located on the fatty acid side chain and keeping the glycerol triester function CO*EO20: Castor oil reacted with 20 moles of ethylene oxide, ethoxylation solely occuring at the hydroxyl group located on the fatty acid side chain and keeping the glycerol triester function

[0124] Compositions 1 to 5 are comparative examples while Composition 6 is according to the invention.

[0125] Composition 7 is also comparative. Composition 1 is a comparative example according to FFC4 of WO 2015 / 052234.

[0126] It can easily be seen that Composition 1 exhibits a higher low temperature viscosity than required. Furthermore, main component is a borate ester (A) which should be avoided.

[0127] Although WO 2015 / 052234 discloses castor oil ethoxylates as lubricants in functional fluids, Compositions 2 to 5 do not meet the abrasion requirements.

[0128] Adding component (C) leads to a noise reduction (Components 3 to 5 vs. Component 2), however, does not yield a composition fulfilling the abrasion requirements.

[0129] Surprisingly, increasing the amount of component (C) and presence of two different components (B1) and (B2) yields Composition 6 according to the invention which is low viscous as well as fulfils both noise as well as abrasion requirements, despite the absence to castor oil ethoxylates.

[0130] Comparative Composition 7 shows the role of triethylene glycol (TEG) in the compositions: Compared with inventive Composition 6 the content of triethylene glycol is substituted by triethylene glycol mono methyl ether (MTG) in order to keep the low temperature viscosity at minus 40 °C sufficiently low.

[0131] Despite the presence of two different components (B1) and (B2) Composition 7 still leads to abrasion, however, meets the noise requirement.

[0132] Therefore, from Composition 7 it can be concluded that the presence of two different components (B1) and (B2) alone is not sufficient to fulfil both noise as well as abrasion requirements.

[0133] From Compositions 3 to 5 it can be concluded that the presence of component (C) alone is also not sufficient.

[0134] In contrast, the presence of both two different components (B1) and (B2) as well as component (C) according to the invention suppresses noise development as well as abrasion.

Claims

Claims1. Functional fluid composition comprising(A) from 4 to less than 45% by weight, based on the weight of the total composition, of one or more alkoxy glycol borate esters having the general formula (I)[R1-O-(CH2CH2-O)n]3B (I) wherein R1is a Ci- to C4-alkyl radical or a mixture of such radicals and n has a value of from 2 to 6,(B) from 45 to 97% by weight, based on the weight of the total composition, of at least two alkoxy glycol components (B1) and (B2), component (B1) having the general formula (Ila)H3C-O-(CH2CH2-O)m-H (Ila) and alkoxy glycol component (B2) having the general formula (lib)R2-O-(CH2CH2-O)m-H (lib) wherein R2is a C2- to Cs-alkyl radical or a mixture of such radicals and m has a value of from 2 to 6, R2and / or m being different or identical to R1and / or n, respectively,(C) from 0.25 to 20% by weight, based on the weight of the total composition, of at least one oligo ethylene glycol having the general formula (III)HO-(CH2CH2-O)k-H (III) wherein k has a value of from 2 to 6,(D) from 0.1 to 10% by weight, based on the total weight of the composition, of an additive package comprising one or more additives with corrosion inhibition action, wherein at least one of the additives contained in the additive package of component (D) is selected from alkylamine ethoxylates, with the proviso that the amounts of all components of the composition always add up to 100% by weight.

2. Functional fluid composition according to claim 1 , wherein in general formula (I) n is 3 andR1is a methyl radical.

3. Functional fluid composition according to claim 1 or 2, wherein m is from m = 3 to m = 4.

4. Functional fluid composition according to any one of the preceding claims, wherein m is the same for (B1) and (B2).

5. Functional fluid composition according to any one of the preceding claims, wherein R2is ethyl or n-butyl, and especially n-butyl.

6. Functional fluid composition according to any one of the preceding claims, wherein the weight ratio of methoxy glycol (B1) to alkoxy glycol (B2) in the composition is from 10 : 1 to 1 : 10, preferably from 9 : 1 to 1 : 5, more preferably from 8 : 1 to 1 : 2, and especially from 7 : 1 to 1 : 1.

7. Functional fluid composition according to any one of the preceding claims, wherein component (C) is selected from the group consisting of diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and hexaethylene glycol, preferably selected from the group consisting of diethylene glycol, triethylene glycol, and tetraethylene glycol, even more preferably may be diethylene glycol or triethylene glycol or mixtures thereof, and especially triethylene glycol.

8. Functional fluid composition according to any one of the preceding claims, wherein the alkylamine ethoxylate of component (D) comprises at least on linear C3to C2o alkyl chain and from 1 to 35 EO units; more preferably the at least one alkylamine ethoxylate comprises at least on linear C4 to Ci3alkyl chain and from 1 .5 to 15 EO units; mostpreferably the at least one alkylamine ethoxylate comprises at least one linear Ce to C12 alkyl chain and from 1 .8 to 9 EO units, especially the at least one alkylamine ethoxylate comprises at least one linear C7 to Cn alkyl chain and from 2 to 6 EO units.

9. Functional fluid composition according to any one of the preceding claims, wherein component (D) comprises octylamine (caprylamine) with 2 EO (ethylene oxide) units.

10. Functional fluid composition according to any one of the preceding claims, further comprising at least one azol derivative as component (D), wherein the azol derivative is a five-membered heterocyclic compound having 2 or 3 heteroatoms from the group consisting of nitrogen and sulphur and comprises no or at most one sulphur atom and can bear an aromatic or saturated six-membered fused-on ring.

11. Functional fluid composition according to any one of the preceding claims being essentially free of alkoxylates of ricinoleic acid, of castor oil or of any other ricinoleic acid ester.

12. Functional fluid composition according to any one of the preceding claims, wherein the four components (A), (B), (C), and (D) are present in the functional fluid composition in the following amounts:(A) from 4 to less than 45% by weight, preferably from 4 to less than 30% by weight, more preferably from 5 to 25% by weight, most preferably from 5 to 15% by weight, especially from 5 to 14% by weight;(B) from 45 to 97% by weight of components (B1) and (B2) in sum, preferably from 50 to 95% by weight, more preferably from 55 to 90% by weight, most preferably from 60 to 85% by weight, especially more than 65 to 85 % by weight;(C) from 0.25 to 20% by weight, preferably from 0.5 to 17.5% by weight, more preferably from 0.75 to 15% by weight, most preferably from 1 to 12.5% by weight, especially 2 to11 % by weight;(D) from 0.1 to 10% by weight, preferably from 0.5 to 7.5% by weight, more preferably from 1 to 5% by weight, most preferably from 1.5 to 3.5% by weight, especially 1 .5 to 3.0 % by weight.

13. Functional fluid composition according to any one of the preceding claims, wherein the kinematic viscosity is less than 450 centistokes at a temperature of -40°C according to ASTM D445.

14. Use of functional fluid composition according to any one of the preceding claims as a brake fluid for vehicles such as passenger cars and trucks, especially for electronic or automated anti-lock brake systems, such as electrohydraulic brake systems for battery electric vehicles.

15. Process for operating a brake system in vehicles, such as passenger cars and trucks, especially for electronic or automated anti-lock brake systems, such as electrohydraulic brake systems for battery electric vehicles, using a functional fluid composition according to any one of the claims 1 to 13.

16. Brake system in vehicles, such as passenger cars and trucks, especially for electronic or automated anti-lock brake systems, such as electrohydraulic brake systems for battery electric vehicles, comprising a functional fluid composition according to any one of the claims 1 to 13.

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