Description

The present invention relates to a low viscosity functional fluid composition comprising a mixture of methyl polyglycols, polyglycols and additives, the fluid having a low content in boric acid esters of glycols or alkylpolyglycols. The fluid exhibits a low temperature kinematic viscosity of less than 700 centistokes, determined at -40°C and exhibits an equilibrium reflux boiling point (ERBP) of at least 250°C and a wet equilibrium reflux boiling point (WERBP) of at least 155 °C, according to the FMVSS no. 116.

The low viscosity functional fluid composition according to the present invention is useful in a variety of applications and in particular as a brake fluid, especially for new electronic or automated anti-lock brake systems which require lower viscosity fluids for satisfactory operation at low temperatures.

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, corrosion protection and rubber swelling.

While borate esters are advantageous to meet the DOT 4 and DOT 5.1 criteria according to Federal Motor Vehicle Safety Standards (FMVSS) No 116, especially a very high wet boiling point (wERBP), borate containing brake fluids are associated with two problems. Federal Motor Vehicle Safety Standards (FMVSS) No 116 refers to 49 CFR § 571 .116 in the 10-1 -2016 edition and will be referred to as FMVSS in this specification. 1 .) Boric acid is known to be a CMR-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 handling/filling of the brake fluid.

2.) The content of boron in the brake fluids is associated with a certain risk of gel formation or precipitation due to salt formation of 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.

WO-00/65001 describes hydraulic fluids comprising alkoxy glycol borate esters, alkoxy glycols and corrosion inhibitors, additionally containing cyclic carboxylic acid derivatives.

WO-02/38711 describes low viscosity functional fluid compositions comprising alkoxy glycol borate esters, alkoxy glycol components and additives such as corrosion inhibitors, wherein the alkoxylation degrees of the alkoxy glycol borate esters and the alkoxy glycols are restricted to a certain narrow pattern.

US-4371448A teaches a hydraulic fluid which formally fulfils the specification DOT 5. 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.

EP-0750033A1 teaches a hydraulic fluid composition, especially a brake fluid composition, based on a boric ester of a glycol ether and comprising a corrosion- inhibiting system which includes: (1 ) at least one constituent (A) chosen from fatty amines or the salts of one or more carboxylic acids with the said amines, and (2) at least one constituent (B) chosen from the products resulting from the reaction of one or more carboxylic fatty acids with a polyoxyalkylene glycol, or from the transesterification reaction of one or more esters of carboxylic fatty acids with a polyoxyalkylene glycol.

EP-0617116A1 teaches a hydraulic fluid composition having a high boiling point, in particular a high equilibrium reflux boiling point and a low viscosity. The composition contains, as additive, at least one ether amine having a molecular weight between 120 and 300 and having the formula in which

R3 is linear or branched radical having at least one ether functional group and no alcohol functional group,

R is a methyl radical or a hydrogen atom, p is an integer from 1 to 3 and q is an integer from 0 to 2.

WO-2012/003117A1 discloses a functional fluid composition comprising

(i) an alkoxy glycol mixture in an amount of about 38% to 47% by weight of the functional fluid composition, where the alkoxy glycol mixture is comprised alkoxy glycols having the formula

R ₂ R ₄

R _lO - (C - C - O) _n H

R ₃ ^R 5 with repeat unit:

R ₂ R4

(C - C - O)

R ₃ R ₅ wherein each of R1 , R2, R3, R4, Rs is either hydrogen (H) or an alkyl group containing 1 to 8 or more carbon atoms or mixtures thereof, wherein said mixture has a first alkoxy glycol component in an amount of about 36% to about 73% by weight of said mixture where n = 3, a second alkoxy glycol component from 17% to about 43% by weight of said mixture where n = 4, and a third alkoxy glycol component in an amount from about 2% to about 10% by weight of said mixture where n is greater than or equal to 5 and

(ii) a glycol borate ester in an amount of about 53% to 62% by weight of the functional fluid composition.

EP-A-0129240 teaches hydraulic fluids with a boron content of from 0 to 1 % by weight, and consisting essentially of a) 2 - 40% by weight, of an alkylenglycol of general formula (I):

HO - (R _a O)x - H (I) wherein

R _a is an alkylene radical having from 2 to 3 carbon atoms, and x is an integer between 1 and 3; b) 15 - 65% by weight, referred to the total weight of the fluid, of an alkylenglycol monoalkylether of general formula (II); R - (RaO) _x - OH (II) wherein

R _a and x have the above indicated meanings, and R is a Ci -C4 alkyl; c) 15 - 55% by weight, referred to the total weight of the fluid, of at least one polyalkyleglycol monoalkylether of general formula (III)

R - (OCHR'CH ₂ )n - OH (III) wherein

R is a Ci -C4 alkyl; R' is H or CH3 and n is an integer whereby the molecular weight of the compound will be between 208 and 1000; d) 0 - 54% by weight, referred to the total weight of the fluid, of the reaction product of H3 BO3 with the alkylenglycols of formula (I), in a molar ratio of 1 : 1.5 - 3; e) 0 - 10% by weight, referred to the total weight of the fluid, of at least one inhibitor.

DE3627432 teaches a brake fluid based on glycols and glycol ethers, consisting essentially of A) 30 to 80% by weight, based on the total weight of the brake fluid, of a glycol component, consisting of a) 0 to 80% by weight diethylene glycol and I or dipropylene glycol and b) 20 to 100% by weight of triethylene glycol, tripropylene glycol, tetraethylene glycol and I or tetrapropylene glycol, percent by weight based on the mixture of these glycols, B) 20 to 70% by weight, based on the total weight of the brake fluid, of a glycol ether component, consisting of a) 10 to 100% by weight. -% of at least one glycol dialkyl ether of the following formula R- (OAlkl ) x-0R1 , in which R and R1 are an alkyl group with 1 to 4 C atoms, Alk1 is the ethylene or a propylene group and x is an integer from 3 to 6, and b) 0 to 90 wt. -% of at least one glycol monoalkyl ether of the following formula

R2- (OAIk2) y-OH, in which R2 is an alkyl group with 1 to 4 carbon atoms, Alk2 is the ethylene or a propylene group and y is an integer from 2 to 4, percent by weight based on the mixture of these glycol ethers, and C) 0 to 5% by weight, based on the total weight of the brake fluid, of at least one inhibitor for fluids based on glycol and glycol ethers, with the proviso that at least 14% by weight in the brake fluid of the glycol component b) are contained, weight percent based on the total weight of the brake fluid.

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 WERBP temperature requirements, as fulfilled by the hydraulic fluid compositions and brake fluids commonly used.

Examples of borate-free brake fluids are described in the literature

1 .) DOT3/class 3 fluids, which are in general of a lower ERBP, lower wERBP and higher viscosity at -40°C), according to FMVSS.

2.) DE-3627432C2 (Hoechst) and US2006/0264337 (BASF) disclose diethylene/triethylene glycol and dipropylene glycol based brake fluids, fulfilling just the minimum requirement of DOT 4 and ISO 4925 class 4 norm.

3.) WO-2007/005593A2 (DOW) describes compositions of brake fluids containing 0-10 wt.-% of borate ester and the use of larger quantities of butoxy-glycols, mainly butoxy-triglycol.

4.) EP-0129240A1 (Montedison S.p.A.) discloses borate-free brake fluid formulations consisting of min. 30 wt.-% diethylene glycol or higher glycols but suffering from elevated viscosity at -40 °C.

These developments allow for high ERBP but suffer from a still too high viscosity at -40°C and from a low wERBP. Especially the use of higher quantities of alkoxy glycols, such as butoxy glycols can limit the performance by elevated viscosity. In addition, relatively pure butoxy glycols are require for brake fluids to avoid hazard labelling by butyl glycol and butyl diglycol. The problem to be solved by the instant invention is to provide a hydraulic fluid having the properties mentioned below, and being essentially or entirely free of borate and butoxy glycols.

Yet, a borate-free composition, fulfilling these criteria is not known.

According to the present invention, a functional fluid composition being essentially free from borates and butoxy glycols 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.

In a first aspect, this invention relates to a functional fluid, comprising

(A) at least 75wt.-% of alkoxy glycol according to formula (I)

CH ₃ - 0 - (CH ₂ - CH ₂ - O)n - H (I) wherein n is a number from 2 to 5, with the proviso that in at least 50 wt.-% of all compounds according to formula (I) n is 3, and with 8 - 40 wt.-% of all compounds according to formula (I) n is 4 or 5, (B) 0 wt% to 10 wt% of alkoxy glycol according to formula (II)

Ri - O - (CH ₂ - CH ₂ - O) _m - H (II) wherein

Ri is a C ₂ to Cs alkyl residue, m is a number from 2 to 6,

(C) from 6 to 22, preferably 8 - 18 wt.-% of at least one compound according to formula (III)

H -O- (CH ₂ - CH ₂ - O) _k - H (III) wherein k is a number of 2 or higher, with the proviso that in at least 80 wt.-% of all compounds according to formula (III) k is 2 or 3,

(D) from 0.4 to 6 wt.-% of at least one additive, selected from the group consisting of corrosion inhibitor, alkalinity agents, aging protection agents, defoamers and lubricants, the fluid comprising 0 wt% to at most 3 wt.-% of an ester between boric acid and a glycol or polyglycol compound.

In a second aspect, this invention provides the use of the functional fluid of the first aspect as a brake fluid for vehicular brakes.

In a third aspect, this invention provides for a method of operating a vehicular brake that transmits braking force through a hydraulic system, the method comprising filling the hydraulic system with a functional fluid according to the first aspect.

The functional fluid will be referred to as fluid in the following.

Component (A) of the functional fluid according to this invention is a methyl- terminated polyglycol according to formula (I). Suitable compounds according to formula (I) comprise 2, 3, 4 or 5 ethoxy units. Compounds with a higher number of ethoxy units than 5, i.e. 6 ethoxy units or more, may be present but should preferably be restricted to a content of 3 wt.-% at most, relative to the total weight of all compounds according to formula (I).

The total amount of all compounds according to formula (I) in the fluid is at least 75 wt.-%, relative to the weight of the fluid. The relative amount of any formula (I) component with n = 2 preferably is not more than 2.5 wt.-%. The relative amount of any formula (I) component with n = 3 is at least 50 wt.-%. The relative amount of any formula (I) component with n = 4 and 5 is between 8.0 and 40.0 wt.-%. In component (A), species with n = 1 are preferably not present. In component (A), species with n = 6 or higher are preferably not present in quantities higher than 3 wt.-%. All such relative amounts are relative to the total amount of formula (I) compounds, such total amount being 100 wt.-%.

An increased amount of formula (I) components with n = 4 or higher may rise the viscosity of the fluid.

The functional fluid contains at most 10 wt% of component (B) according to formula (II). The content of the fluid in content (B) may be zero, i.e. the fluid may be free of component (B). Component (B) comprises species of ethoxylation degrees of from m = 2 to m = 6, preferably of from m = 2 to m = 4. Component (B) may be a single species or a mixture of different species with regard to the ethoxylation degree and/or to radical Ri. Radical Ri is preferably a C2- to C4-alkyl radical. Ri for example may be ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secbutyl, tert-butyl. Ethyl, and especially butyl, are most preferred.

Examples of alkoxy glycols making up component (B) of the present invention include ethyldiglycol, ethyltriglycol, ethyltetraglycol, ethylpentaglycol, ethylhexaglycol, n-propyldiglycol, n-propyltriglycol, n-propyltetraglycol, n-propylpentaglycol, n-propylhexaglycol, n-butyldiglycol, n-butyltriglycol, n-butyltetraglycol, n-butylpentaglycol, n-butylhexaglycol and mixtures thereof. For the avoidance of doubt, "glycol" always means "ethylene glycol". Most important are butyltriglycol and butyltetraglycol. The component (B) may comprise a mixture of alkoxy glycols of general formula

(II) comprising solely or predominantly species with m = 3. Predominantly means that at least 65 % by weight, more preferably at least 75 % by weight, of component (B) comprises species with m = 3. Species with m = 4 are in one embodiment present in an amount of 10 wt.-% or more. Also, alkoxy glycol species with m = 2 and/or m = 5 and/or m = 6 may be present in minor amounts. Species with m = 2 are usually present in an amount not exceeding 3 wt.-%. Species with m = 5, 6 or higher are usually present in an amount of less than 5 wt.-% in total. Weight percentages of species of component (B) are given in wt.-% with the total amount of component (B) being 100 wt.-%.

Component (C) is a polyethylene glycol according to formula (III). In formula (III), k is a number of 2, or higher. It is preferred, that k is a number from 2 - 4. More preferably, k is 2 or 3. The total amount of component (C) in the fluid is from 6 to 22 wt.-%, preferably 8 - 18 wt.-% of the weight of the fluid, i.e. the total weight of the fluid being 100 wt.-%. In one other preferred embodiment, the amount of species of formula (III) wherein k = 2 is 4 - 10 wt.-%. In one other preferred embodiment, the amount of species of formula (III) wherein k = 3 is 4 - 13 wt.-%. In one other preferred embodiment, the total amount of species according to formula (III) wherein k is 4 or higher than 4 is at most 10 wt.-%, more preferably at most 6 wt.-%. Said weight percentages provided for species according to formula

(III) are provided as weight percentages of the fluid, i.e. the total weight of the fluid is 100 wt.-%. They are not provided as weight percentages of the total weight of component (C).

Component (D) is an additive that is required to impart particular properties to the functional fluid for performing on specifications to be fulfilled for brake fluids according to the current norms and standards FMVSS, SAE J 1703 and ISO 4925. The total amount of all components (D) in the fluid is preferably from 0.4 to 6 wt.-%, more preferably from 0.5 to 5 wt.-%. Component (D) comprises one or more additives selected from the group consisting of corrosion inhibitors, amines as reserve alkalinity agents, stabilizing antioxidants, defoamers, lubricants and dyes.

Component (D) may comprise an amine. Amines are preferably alkyl or cycloalkyl amines, alkanol amines, alkyl amine ethoxylates and their mixtures. Preferred alkyl amines are mono- and di-(C4- to C2o-alkyl)amines. Examples of suitable alkyl or cycloalkyl amines are n-butylamine, n-hexylamine, n-octylamine, 2-ethylhexylamine, isononylamine, n-decylamine, n-dodecylamine, oleylamine, d-n-propylamine, di-isopropylamine, di-n-butylamine, tri-n-butylamine, di-n-amylamine, cyclohexylamine, and salts of such amines. Examples of suitable alkanolamines are mono-, di- and trimethanolamine, mono-, di- and triethanolamine, mono-, di- and tri-n-propanolamine and mono-, di- and tri-isopropanolamine. Examples of suitable alkyl amine ethoxylates are such linear or branched alkylamine ethoxylates carrying 1.5 to 20 EO moieties and an alkyl chain having 8 to 18 carbon atoms.

Component (D) of the present functional fluid composition may comprise, besides the Amine, at least one additive with corrosion inhibition action, although the alkylamine ethoxylates exhibit corrosion inhibition properties themselves. 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 or aliphatic alcohol ethoxylates; 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, tolyltriazole, 1 ,2,4-triazole, benzoimidazole, purine, adenine and derivatives of such heterocyclic organic compounds. Of course, mixtures of the above additives with corrosion inhibition action can be used.

Defoamers may be selected from groups of oil based defoamers, such as natural oils, glycerides, waxes, fine powdered silica, alkoxylates such es EO/PO block copolymers, silicone based defoamers, preferably polyether modified or silicone derivatives and mixtures thereof.

The fluid may include from 0 to 5% by weight, based on the total weight of the fluid, of a lubricant. Suitable lubricants are for example, propylene oxide containing alkylene oxide polymers that are optionally substituted with a Ci to C4 alkyl group, triglycerides, castor oil, ricinoleic acid, and ethoxylates of castor oil or ricinoleic acid and mixtures thereof. In a preferred embodiment, the lubricants are homopolymers of propylene oxide, copolymers of propylene oxide with ethylene oxide and/or butylene oxide, mono Ci to C4 alkyl substituted homopolymers of propylene oxide, mono Ci to C4 alkyl substituted copolymers of propylene oxide with ethylene oxide and/or butylene oxide, triglycerides, castor oil, ricinoleic acid, and ethoxylates of castor oil or ricinoleic acid and mixtures thereof. In case of such ethoxylates, 1 to 50 ethoxy units are preferred. In another preferred embodiment, the propylene oxide containing alkylene oxide polymers that are optionally substituted with a Ci to C4 alkyl group have a number average molecular weight in the range of 150 to 3000 g/mol.

Suitable stabilizers or antioxidants are phenolic stabilizers like Bisphenols (e,g. Bisphenol A or Bisphenol M), butyl hydroxytoluene, methoxy phenols, butylated hydroxy anisole, hydroquinone derivatives; sterically hindered amines such as benzylated, alkylated or styrenated diphenylamine, styrenated phenylamine, substituted piperidine derivatives, phenothiazine derivatives or quinoline derivatives and mixtures thereof. In general, any literature known glycol stabilizing agents could be used herein.

In one preferred embodiment, the % values (A) - (D) add up to 100% by weight.

The fluid should have a low content in boric acid esters, particularly esters between boric acid and glycol or alkyl polyglycol compounds. The fluid's content in boric acid esters, particularly esters between boric acid and glycol or alkyl polyglycol compounds, is less than 3 wt.-%, preferably less than 0.3 wt.-%, the fluid being most preferably essentially free of such boric acid ester. The content of the fluid in said boric acid esters may be zero.

In one preferred embodiment, the weight ratio between component (A) and component (C) is (A):(C) = 3:1 to 12:1 .

The functional fluid composition of the present invention exhibits superior behavior in ERBP and WERBP temperature and simultaneously in low temperature viscosity performance. It exhibits an ERBP of at least 250 °C, more preferably of at least 255 °C and a WERBP of at least 155 °C, more preferably at least 158 °C. The functional fluid composition of the present invention exhibits a low temperature kinematic viscosity of less than 700 centistokes ("cSt") (= mm ² /s), more preferably of less than 670 cSt, each determined at a temperature of -40 °C. All analytical methods are described in FMVSS to which reference is made. For the purpose of this specification, ERBP and WERBP are to be determined according to FMVSS.

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.

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, a good lubrication performance and good foaming behavior. Examples

Table 1 shows functional fluid compositions and their performance. Numbers are provided in wt.-%, unless noted otherwise. Table 1

(♦) = according to the present invention, or according to the required specification (■) = not according to the invention, or not according to the required specification