Patent Description:
It is desirable for hydraulic fluids to exhibit good power transmission, but it is also desirable for them to exhibit other important characteristics such as thermal stability, rust inhibition, and anti-wear performance. Additives may thus be added to hydraulic fluids in order to help achieve satisfactory performance in various different respects.

However, there can be a trade off when it comes to the achievement of multiple different desirable properties. For instance, anti-wear additives may be added to improve pump performance in some situations, but not all anti-wear additives are thermally stable, so at higher concentrations they may contribute to the formation of sludge or varnish, and/or may break down to form acidic species that can lead to the blockage of filters.

Meanwhile, the goals of improving the reliability of machinery and minimising maintenance requirements mean it is desirable for hydraulic fluids to remain functional for longer and longer time periods. It is advantageous not only for hydraulic fluids to be able to function effectively for extended periods, but also for them to have good compatibility with the materials they contact.

For instance, compatibility is desired between a hydraulic fluid and any metal surfaces it may contact, including surfaces containing so called yellow metals, such as copper. In particular, it is desirable to avoid or minimise the corrosion/dissolution of such metals. One past approach to tackling this has been to employ <NUM>-<NUM> wt% of a corrosion inhibiting additive with a typical chemical structure selected from carboxylic acids, benzotriazole, metal sulphonates and alkylated carboxylic acids (Hydraulic Fluids, <NUM>, P. For instance, carboxylic acids described for this purpose include both aryl and aliphatic carboxylic acids - see e.g. <CIT>, while <CIT> describes the use of benzotriazole, preferably in an amount of <NUM> % by weight. Derivatives of benzotriazole have also been suggested, though, such as the product sold under the trade name Irgamet® <NUM>, and also tolyltriazole (see e.g. <CIT>). The Irgamet® <NUM> corrosion inhibitor has the structure set out below.

Compounds with this dialkylaminomethyl aromatic triazole structure have been reported as providing excellent corrosion inhibiting properties even in acidic environments (see e.g. <CIT>). They also have the benefit of being a liquid at room temperature, in contrast to e.g. tolyltriazole which is a solid at room temperature.

<NUM>-<NUM>,<NUM>,<NUM>-triazole has been reported as being preferred to benzotriazole compounds on the basis that it offers comparable corrosion inhibition but provides a coating-free metal surface and reduced sediment formation (CA2442697). Combinations of <NUM>-<NUM>,<NUM>,<NUM>-triazole with benzotriazole derivatives have also been described (<CIT>), as have various triazole derivatives and also imidazole derivatives (see e.g. <CIT>), and the use of benzotriazole compounds and/or thiadiazole compounds in amounts of <NUM> to <NUM> wt% (see e.g. <CIT>).

Other more recently described corrosion inhibiting substances in relation more generally to lubricants and hydraulic fluids include (i) P- and S-free organotungstates; (ii) oil soluble <NUM>,<NUM>-dimercapto-<NUM>,<NUM>,<NUM>-thiadiazole or hydrocarbyl-substituted <NUM>,<NUM>-dimercapto-<NUM>,<NUM>,<NUM>-thiadiazole derivatives; (iii) Na or Ca salts of dinonylnaphthalene-sulfonic acid; (iv) a hydrocarbyl-substituted <NUM>,<NUM>,<NUM>-triazole; and (v) a combination of lanthanum oxide, triglycerides of higher carboxylic acids, alkylbenzenesulfonic acid, alkanolamine, lanthanum nitrate and organic solvent (see e.g. "<NPL>).

Another consideration in relation to the compatibility of a hydraulic fluid with the materials with which it comes into contact is its compatibility with the polymer materials which are used in seals, particularly in hydraulic systems. Seals have previously been made from materials such as nitrilic rubbers and their hydrogenated analogues, acrylates and vinyl-modified acrylic polymers, with contacting fluids being provided with seal swelling agents such as phthalate esters, sulfolane derivatives and naphthenic oils to swell and soften the seals to facilitate effective operation. However, more recently some systems have moved to using seals manufactured from materials such as fluoropolymers, including the subset of fluoropolymers that may be designated "FKM". Such fluoropolymer seals can offer advantages but may also be vulnerable to degradation, e.g. via de-polymerisation or cross-linking reactions. In particular, there is the potential for some of the different types of additive that may be included in hydraulic fluids to cause or encourage such degradative reactions. For instance, FKM fluoropolymers do not always show good resistance to ethers, ketones, esters, and amines, or to hydraulic fluids based on phosphate esters. Thus, there can be a trade-off between the potentially competing aims of providing good functionality and good seal compatibility. Achieving good seal compatibility without compromising on functionality can therefore be difficult.

Some ways of improving fluoropolymer seal compatibility have been described in the context of other fluids. For instance, one approach described in <CIT> in connection with lubricant compositions involves adding epoxide compounds such as the one depicted below in combination with an amine compound having a total base number of at least <NUM> KOH/g (when tested according to ASTM D4739).

However, introducing extra agents in order to improve seal compatibility is not an ideal solution, not least because it can give rise to complications. For example, in <CIT> it is noted that epoxide compounds such as the one depicted above have the potential to react with other additives such as acids, amines, anyhydrides, triazoles, and/or oxides.

More recently, <CIT> has reported that the seal compatibility of power transmitting fluids containing a dispersant, an anti-wear agent and an antioxidant together with either of two different common commercial friction modifiers (one made by reacting tetraethylene pentamine with iso-stearic acid, the other made by reacting tetraethylene pentamine with iso-octadecenylsuccinic anhydride) may be improved by replacing the commercial friction modifier with an alternative friction modifier that is made by reacting (a) iso-stearic acid or oleic acid, with (b) <NUM> molecular weight polyethylene glycol or ETHOMEEN® C-<NUM> (said to comprise polyalkoxylated alkyl amine compounds), in the presence of an esterification catalyst. <CIT> is concerned with hydraulic systems with good seal compatibility comprising corrosion inhibitors. there remains a need for improving the seal compatibility of other types of fluid.

The present invention is based on the surprising finding that the use of a small amount of a certain type of corrosion inhibiting agent can enable the provision of an unexpectedly advantageous balance of properties, in particular in relation to the potentially competing goals of good functionality (such as good corrosion inhibition) and good fluoropolymer seal compatibility. Thus, the corrosion inhibiting agent defined herein has been found to provide robust corrosion inhibition at very low concentrations, in particular when also combined with certain other additives. Among the benefits of this are that it enables any potential negative impact the corrosion inhibiting agent may have on fluoropolymer seals to be minimised. Further, the minimal effect that the corrosion inhibiting agent has on the seals (i.e. its good seal compatibility) makes it possible to raise the levels of other additives that might otherwise have been avoided or used relatively sparingly due to concern that they may have a degradative effect on fluoropolymer seals, thus enabling the achievement of new and improved levels of functionality for hydraulic fluids with good fluoropolymer seal compatibility.

The corrosion inhibiting agent for use according to the invention is one or more compounds of formula (I):
<CHM>
and/or tribologically acceptable salts thereof, wherein in formula (I):.

The finding that using very low quantities of the above corrosion inhibiting agent can enable the achievement of excellent performance in terms of both fluoropolymer seal compatibility and the various other functional requirements of a hydraulic fluid is particularly striking when compared to the balance of properties that can be achieved using the known corrosion inhibitor Irgamet® <NUM> (the structure of which is set out above in the Background section).

The present invention provides a hydraulic system comprising at least one fluoropolymer seal and a hydraulic fluid as defined herein which comes into contact with the seal, the hydraulic fluid comprising:.

The hydraulic fluid in the hydraulic system of the present invention comprises <NUM> ppm to <NUM> ppm by weight in terms of nitrogen (based on the total weight of the hydraulic fluid) of a corrosion inhibiting agent which is one or more compounds of formula (I) as defined above and/or tribologically acceptable salts thereof.

In this regard, for the avoidance of doubt, the hydraulic fluid may comprise more than one different type of compound of formula (I) and/or salt thereof, provided that the total amount of said compounds/salts does not exceed the upper limit of <NUM> ppm by weight in terms of nitrogen content. In other words, component (a) may be one or more compounds of formula (I) and/or tribologically acceptable salts thereof (wherein <NUM> to <NUM> ppm refers to the total concentration of all such compounds and/or salts in terms of their nitrogen content). In this regard, the term "one or more" preferably means one, two, or three, and more preferably it means one or two. Typically, though, it is only necessary to include one compound of formula (I) and/or tribologically acceptable salt thereof.

Preferably in formula (I), each R<NUM> is independently a straight or branched alkyl group or an aryl group such as phenyl. More preferably each R<NUM> is independently a straight or branched alkyl group.

Preferably, each R<NUM> independently comprises <NUM> to <NUM> carbon atoms, more preferably <NUM> to <NUM> carbon atoms, and yet more preferably <NUM> to <NUM> carbon atoms. Preferred examples for R<NUM> are alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, and t-butyl. Methyl and ethyl are particularly preferred, and methyl most preferred.

The upper limit for the moiety x is preferably <NUM>, more preferably <NUM>. The lower limit for x is preferably <NUM>. It is particularly preferred for x to be <NUM> or <NUM>. Most preferably, x is <NUM>.

R<NUM> is preferably hydrogen or a straight or branched alkyl group or an aryl group such as phenyl. More preferably R<NUM> is hydrogen or a straight or branched alkyl group. Most preferably R<NUM> is hydrogen.

When R<NUM> is a hydrocarbyl group containing <NUM> to <NUM> carbon atoms, R<NUM> preferably comprises <NUM> to <NUM> carbon atoms, more preferably <NUM> to <NUM> carbon atoms, and yet more preferably <NUM> to <NUM> carbon atoms. Preferred examples for R<NUM> in this regard are alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, and t-butyl, with methyl and ethyl being particularly preferred, and methyl most preferred.

When R<NUM> is a hydrocarbyl group containing <NUM> to <NUM> carbon atoms, it preferably comprises <NUM> to <NUM> carbon atoms, more preferably <NUM> to <NUM> carbon atoms, and yet more preferably <NUM> to <NUM> carbon atoms. Preferred examples for R<NUM> in this regard are alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, and t-butyl, with methyl and ethyl being particularly preferred, and methyl most preferred.

Preferably, each of R<NUM> and R<NUM> is independently an aryl group substituted with one or more hydrocarbyl groups. More preferably, the aryl group of each of R<NUM> and R<NUM> independently is substituted with one, two or three hydrocarbyl groups, yet more preferably one or two hydrocarbyl groups, and most preferably one hydrocarbyl group.

Preferably the aryl group of each of R<NUM> and R<NUM> independently comprises <NUM> to <NUM> carbon atoms, and most preferably <NUM> carbon atoms. When the aryl group of each of R<NUM> and R<NUM> independently is substituted with one or more hydrocarbyl groups, each hydrocarbyl group independently preferably comprises <NUM> to <NUM> carbon atoms, more preferably <NUM> to <NUM> carbon atoms, and yet more preferably <NUM> to <NUM> carbon atoms. Preferred examples for the hydrocarbyl groups in this regard are alkyl groups such as the straight and branched forms of hexyl, heptyl, octyl, nonyl and decyl, with n-octyl most preferred.

Preferably, each of R<NUM> and R<NUM> is independently a phenyl group substituted with one or more hydrocarbyl groups (typically alkyl groups), said hydrocarbyl groups containing <NUM> to <NUM> carbon atoms. Preferably the hydrocarbyl groups (which typically are alkyl groups) are located in the para position.

In a particularly preferred embodiment, x is <NUM> or <NUM>, R<NUM> is a straight or branched alkyl group comprising <NUM> to <NUM> carbon atoms such as methyl or ethyl (typically methyl), R<NUM> is hydrogen or a straight or branched alkyl group comprising <NUM> to <NUM> carbon atoms such as methyl or ethyl (typically R<NUM> is hydrogen), R<NUM> is hydrogen or a straight or branched alkyl group comprising <NUM> to <NUM> carbon atoms such as methyl or ethyl (typically R<NUM> is hydrogen), R<NUM> is -NR<NUM>R<NUM>, R<NUM> is a phenyl group substituted with a hydrocarbyl group comprising <NUM> to <NUM> carbon atoms (typically n-octyl), and R<NUM> is a phenyl group substituted with a hydrocarbyl group comprising <NUM> to <NUM> carbon atoms (typically n-octyl). More preferably in this regard, x is <NUM>. It is also preferred for the hydrocarbyl group comprising <NUM> to <NUM> carbon atoms to be in the para position.

An example of a preferred compound of formula (I) is Compound <NUM>.

Some compounds and salts suitable for use as component (a) are known and are generally available commercially and/or can be prepared by well-known methods. For instance, compound <NUM> is available in diluted form as the commercial product Vanlube® <NUM>.

The concentration of the corrosion inhibitor in the hydraulic fluid is from <NUM> ppm to <NUM> ppm by weight in terms of nitrogen content (in the overall hydraulic fluid). The amount in terms of nitrogen content is preferably at least <NUM> ppm, such as at least <NUM> ppm, at least <NUM> ppm, at least <NUM> ppm, at least <NUM> ppm, at least <NUM> ppm, at least 75ppm or at least <NUM> ppm. The upper limit for the amount in terms of nitrogen content is preferably at most <NUM> ppm, such as at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, or at most <NUM> ppm. In some embodiments, the amount is preferably at most <NUM> ppm, such as at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, or at most <NUM> ppm. Examples of preferred ranges are <NUM> to <NUM> ppm, <NUM> to <NUM> ppm and <NUM> to <NUM> ppm.

The amount of the corrosion inhibitor in the hydraulic fluid (i.e. not in terms of nitrogen content) may vary depending on the identity of x, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM> and R<NUM>. Typically the amount is at least <NUM> ppm, such as at least <NUM> ppm, at least <NUM> ppm, at least <NUM> ppm, , or at least <NUM> ppm. The upper limit for the amount may be (e.g.) up to <NUM> ppm, up to <NUM> ppm, up to <NUM> ppm, up to <NUM> ppm, up to <NUM> ppm, up to <NUM> ppm, up to <NUM> ppm, up to <NUM> ppm, or up to <NUM> ppm. In some embodiments the amount is preferably up to <NUM> ppm, up to <NUM> ppm, up to <NUM> ppm, up to <NUM> ppm or up to <NUM> ppm. Examples of preferred ranges are <NUM> to <NUM> ppm, <NUM> to <NUM> ppm and <NUM> to <NUM> ppm. The lower values for the possible upper limits are particularly relevant for embodiments when x is lower and/or when R<NUM> and R<NUM> are smaller groups, such as in (a) the embodiment wherein x is <NUM> or <NUM>, R<NUM> is a straight or branched alkyl group comprising <NUM> to <NUM> carbon atoms such as methyl or ethyl (typically methyl), R<NUM> is hydrogen or a straight or branched alkyl group comprising <NUM> to <NUM> carbon atoms such as methyl or ethyl (typically R<NUM> is hydrogen), R<NUM> is hydrogen or a straight or branched alkyl group comprising <NUM> to <NUM> carbon atoms such as methyl or ethyl (typically R<NUM> is hydrogen), R<NUM> is -NR<NUM>R<NUM>, R<NUM> is a phenyl group substituted with a hydrocarbyl group comprising <NUM> to <NUM> carbon atoms (typically n-octyl), and R<NUM> is a phenyl group substituted with a hydrocarbyl group comprising <NUM> to <NUM> carbon atoms (typically n-octyl) and (b) the embodiment wherein the compound of formula (I) is Compound <NUM>.

In the hydraulic fluid in the hydraulic system of the present invention, preferably, the total content of substituted or unsubstituted benzotriazole compounds (of any kind, i.e. including compounds not embraced by formula (I)) and, if present, preferably also any substituted or unsubstituted triazole compounds is at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm or at most <NUM> ppm. In terms of nitrogen content (in the overall fluid), the total content is preferably at most <NUM> ppm, such as at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, or at most <NUM> ppm. The use of such concentration levels is useful for helping balance fluoropolymer compatibility and corrosion inhibition. Typically the total nitrogen content of substituted or unsubstituted benzotriazole compounds (and, if present, preferably also any substituted or unsubstituted triazole compounds) corresponds essentially to the concentration of compounds of formula (I).

The hydraulic fluid is preferably substantially free of any substituted or unsubstituted benzotriazole compounds other than component (a). More preferably, the hydraulic fluid is substantially free of any substituted or unsubstituted benzotriazole or triazole compounds other than component (a). Yet more preferably, the hydraulic fluid is substantially free of any corrosion inhibitors other than component (a).

The hydraulic fluid in the hydraulic system of the present invention comprises <NUM> to <NUM> % by weight of an ashless nitrogen-containing dispersant.

In this regard, for the avoidance of doubt, the hydraulic fluid may comprise more than one different type of ashless nitrogen-containing dispersant, provided that the total amount of said dispersants does not exceed the upper limit of <NUM> % by weight. In other words, component (b) may be one or more nitrogen-containing dispersants (wherein <NUM> to <NUM> % refers to the total concentration of all such dispersants). In this regard, the term "one or more" preferably means one, two, or three, and more preferably it means one or two. Typically, though, it is only necessary to include one dispersant (although as is usual in this field, such a single dispersant will generally not be a single compound but rather a mixture of compounds).

A preferred option for the ashless nitrogen-containing dispersant is a product obtainable from the reaction of (a) an amino compound, with (b) succinic acid and/or succinic anhydride (preferably succinic anhydride) substituted by a hydrocarbyl group having a number average molecular weight of at least <NUM>, wherein said reaction involves the formation of at least one imido, amido, amidine, and/or acyloxy ammonium linkage, and wherein the product is substituted by a hydrocarbyl group having a number average molecular weight of at least <NUM>.

More preferably, the ashless nitrogen-containing dispersant is a product obtainable from the reaction of (a) an amino compound, with (b) succinic acid and/or succinic anhydride (preferably succinic anhydride) substituted by a hydrocarbyl group having a number average molecular weight of <NUM> to <NUM>, wherein said reaction involves the formation of at least one imido, amido, amidine, and/or acyloxy ammonium linkage, and wherein the product is substituted by a hydrocarbyl group having a number average molecular weight of <NUM> to <NUM>.

Typically the dispersant is a hydrocarbyl substituted succinimide, wherein the hydrocarbyl group has a number average molecular weight of at least <NUM>, preferably <NUM> to <NUM>.

The hydrocarbyl group in the above embodiments for the dispersant component is preferably PIB group.

The number average molecular weight of the hydrocarbyl group (preferably a PIB group) is preferably at least <NUM>, such as at least <NUM>, at least <NUM>, or at least <NUM>. The number average molecular weight is preferably at most <NUM>, such as at most <NUM>, at most <NUM>, at most <NUM>, at most <NUM> or at most <NUM>. Examples of preferred ranges are <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, and <NUM> to <NUM>.

The amino compound for use in making the ashless nitrogen-containing dispersant may be a polyamine, for example a polyamine which is a polyalkylene polyamine, and/or which is a polyamine substituted by a hydroxyalkyl, heterocyclic and/or aromatic group.

Suitable polyalkylene polyamines which may also be substituted by hydroxyalkyl include compounds of formula (R<NUM>)<NUM>N-(Z-N(R<NUM>))nR<NUM>, wherein each R<NUM> is independently selected from hydrogen, a hydrocarbyl group comprising <NUM> to <NUM> carbon atoms and a hydroxy-substituted hydrocarbyl group containing <NUM> to <NUM> carbon atoms, provided that at least one R<NUM> is hydrogen; n is from <NUM> to <NUM>; and each Z is independently an alkylene group comprising <NUM> to <NUM> carbon atoms. Preferably each R<NUM> is independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, n-butyl, i-butyl and t-butyl. Most preferably each R<NUM> is hydrogen. Z is preferably an alkylene group comprising <NUM> to <NUM> carbon atoms, more preferably ethylene - i.e. more preferably the polyalkylene polyamine is a polyethylene polyamine. The moiety n is preferably from <NUM> to <NUM>, such as from <NUM> to <NUM> or from <NUM> to <NUM>.

Examples of polyalkylene polyamines include ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, tri-(trimethylene)tetramine, <NUM>,<NUM>-propylene diamine, and mixtures thereof. Mixtures of such polyamines also optionally including one or more further higher boiling fractions containing <NUM> or more nitrogen atoms may conveniently be used.

Examples of polyalkylene polyamines substituted by hydroxyalkyl include N-(<NUM>-hydroxyethyl) ethylene diamine, N,N'-bis(<NUM>-hydroxyethyl) ethylene diamine, N-(<NUM>-hydroxybutyl) tetramethylene diamine and mixtures thereof.

Heterocyclic-substituted polyamines include hydroxyalkyl-substituted polyamines wherein the polyamines are polyalkylene polyamines as described above and the heterocyclic substituent is selected from nitrogen-containing aliphatic and aromatic heterocycles, for example piperazines, imidazolines, pyrimidines, and/or morpholines.

Examples of the heterocyclic-substituted polyamines are N-<NUM>-aminoethyl piperazine, N-<NUM> and N-<NUM> amino propyl morpholine, N-<NUM>(dimethyl amino) propyl piperazine, <NUM>-heptyl-<NUM>-(<NUM>-aminopropyl) imidazoline, <NUM>,<NUM>-bis (<NUM>-aminoethyl) piperazine, <NUM>- (<NUM>-hydroxyethyl) piperazine, and <NUM>-heptadecyl-<NUM>-(<NUM>-hydroxyethyl)-imidazoline.

Aromatic polyamines include phenylene diamines and naphthalene diamines.

Examples of aromatic polyamines include compounds of formula Ar(N(R<NUM>)<NUM>)y, wherein Ar is an aromatic moiety comprising <NUM> to <NUM> carbon atoms, each R<NUM> is independently as defined above, and y is from <NUM> to <NUM>.

Preferably the polyamine is selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, dimethylaminopropylamine, aminoethylethanolamine, and mixtures thereof.

The ashless nitrogen-containing dispersant may be made by reacting (a) the amino compound, with (b) succinic acid and/or succinic anhydride (preferably succinic anhydride) substituted by a hydrocarbyl group having a number average molecular weight of at least <NUM>, at a molar ratio of (a):(b) of from <NUM>:<NUM> to <NUM>:<NUM>, preferably from <NUM>:<NUM> to <NUM>:<NUM>, more preferably from <NUM>:<NUM> to <NUM>:<NUM> and most preferably from <NUM>:<NUM> to <NUM>:<NUM>. This type of acylation reaction is well known to those skilled in the art.

Preferably, the ashless nitrogen-containing dispersant is present in an amount of <NUM> to <NUM> ppm, more preferably <NUM> to <NUM> ppm, yet more preferably <NUM> to <NUM> ppm, and more preferably still <NUM> to <NUM> ppm by weight.

The amount of ashless nitrogen-containing dispersant is preferably at least <NUM> ppm, such as at least <NUM> ppm, or at least <NUM> ppm by weight. The amount of ashless nitrogen-containing dispersant is preferably <NUM> ppm or less, <NUM> ppm by weight or less, <NUM> ppm by weight or less, or <NUM> ppm by weight or less. Examples of preferred ranges for the amount include <NUM> to <NUM> ppm, <NUM> to <NUM> ppm, <NUM> to <NUM> ppm and <NUM> to <NUM> ppm by weight.

In a preferred embodiment, the hydraulic fluid in the hydraulic system of the present invention may further comprise up to <NUM> ppm of metal detergent. More preferably, the hydraulic fluid comprises <NUM> to <NUM> ppm by weight of a metal detergent.

In this regard, for the avoidance of doubt, the metal detergent may comprise more than one different type of metal detergent, provided that the total amount of metal detergent (if present) does not exceed the upper limit of <NUM> ppm by weight. In other words, the hydraulic fluid may further comprise one or more metal detergents. In this regard, the term "one or more" preferably means one, two, or three, and more preferably it means one or two. Typically, though, it is only necessary to include one metal detergent.

The metal detergent is preferably an alkaline earth metal detergent. More preferably, the hydraulic fluid comprises one or more alkaline earth metal detergents selected from phenate detergents, substituted benzene sulfonate detergents, and salicylate detergents, wherein the total amount of said one or more alkaline earth metal detergents is <NUM> to <NUM> ppm by weight (based on the total weight of the hydraulic fluid).

The term substituted benzene sulfonate detergents refers to detergent compounds having a benzene sulfonate moiety wherein the benzene substituents include one or more (e.g. one, two or three, but typically one) hydrophobic groups. Preferably said hydrophobic groups are selected from hydrocarbyl groups, and more preferably they are selected from alkyl groups. Typically the substituted benzene sulfonate detergents are alkylbenzene sulfonate detergents.

Preferably the alkaline earth metal is calcium or magnesium, more preferably calcium. Thus, preferably said metal detergent is (i) a calcium detergent, (ii) a magnesium detergent, or (iii) a calcium detergent and a magnesium detergent. More preferably said metal detergent is one or more calcium detergents, such as one calcium detergent.

Preferably said metal detergent comprises an alkaline earth metal phenate (e.g. a calcium phenate). More preferably said metal detergent is a calcium phenate.

Preferably the calcium phenate is a calcium phenate having a total base number (TBN) of at least <NUM> KOH/g, such as at least <NUM> KOH/g, e.g. <NUM> to <NUM> KOH/g. TBN may preferably be measured by ASTM D2896.

Preferably the calcium phenate has a calcium content of <NUM> to <NUM> % by weight, such as <NUM> to <NUM> % by weight. Typically it is around <NUM> % by weight.

The lower limit for the total amount of said metal detergent is typically <NUM> ppm, but preferably may be higher, e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, or <NUM> ppm. The upper limit for the total amount of said one or more alkaline earth metal detergents is <NUM> ppm, but preferably may be lower, e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. Typical preferred concentration ranges are e.g. <NUM> to <NUM> ppm, <NUM> to <NUM> ppm, <NUM> to <NUM> ppm, or <NUM> to <NUM> ppm.

The lower limit for the total amount of said metal detergent may typically be <NUM> ppm in terms of metal content (based on the total weight of the hydraulic fluid), but preferably may be higher, e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. The upper limit for the total amount of said metal detergent in terms of metal content may typically be <NUM> ppm, but preferably may be lower, e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. Typical preferred concentration ranges are e.g. <NUM> to <NUM> ppm, or <NUM> to <NUM> ppm. The content of metal may preferably be measured by ASTM D4951.

Preferably the total content of alkaline earth metal detergents, if present, is at most <NUM> ppm, such as at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, or at most <NUM> ppm.

Preferably the hydraulic fluid in the hydraulic system of the present invention comprises <NUM> to <NUM> ppm by weight of one or more alkaline earth metal (preferably calcium) phenates, such as <NUM> to <NUM> ppm or <NUM> to <NUM> ppm by weight thereof.

The hydraulic fluid in the hydraulic system of the present invention preferably comprises a phosphorus-containing anti-wear agent, wherein the total amount of said phosphorus-containing anti-wear agent is <NUM> to <NUM> ppm by weight (based on the total weight of the hydraulic fluid). The phosphorus-containing anti-wear agent may comprise (and preferably is) an ashless phosphate and/or an ashless phosphite.

Preferably the phosphorus-containing anti-wear agent is a phosphate. Thus, the hydraulic fluid in the hydraulic system of the present invention preferably comprises one or more phosphate anti-wear agents, wherein the total amount of said one or more phosphate anti-wear agents is <NUM> to <NUM> ppm by weight (based on the total weight of the hydraulic fluid).

In this regard, the term "one or more" preferably means one, two, or three phosphate anti-wear agent(s), more preferably one or two phosphate anti-wear agent(s), and most preferably two phosphate anti-wear agents.

Preferably said one or more phosphate anti-wear agents is one or more dithiophosphate anti-wear agents.

Preferably the phosphate anti-wear agents are free of zinc, and more preferably they are ashless. Thus, preferably said one or more phosphate anti-wear agents is one or more ashless phosphate anti-wear agents. Typically said one or more ashless phosphate anti-wear agents is one or more organic phosphate anti-wear agents, and preferably it is one or more ashless organic dithiophosphate anti-wear agents.

Preferably said one or more phosphate anti-wear agents is one or more phosphate compounds of formula (III):
<CHM>
and/or tribologically acceptable salts thereof, wherein:.

Preferably, each RA and RB is independently a straight or branched alkyl group or an aryl group such as phenyl. More preferably each RA and RB is independently a straight or branched alkyl group.

Preferably, each RA and RB independently comprises <NUM> to <NUM> carbon atoms, more preferably <NUM> to <NUM> carbon atoms, and yet more preferably <NUM> to <NUM> carbon atoms. Preferred examples for RA and RB are alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, and t-butyl. The groups i-propyl and i-butyl are particularly preferred.

Preferably, RC is a straight or branched alkylene group or an arylene (i.e. divalent aryl) group such as phenylene. More preferably RC is a straight or branched alkylene group.

Preferably, RC comprises <NUM> to <NUM> carbon atoms, more preferably <NUM> to <NUM> carbon atoms, and yet more preferably <NUM> to <NUM> carbon atoms. Preferred examples for RC are alkylene groups such as -CH<NUM>-, -CH<NUM>-CH<NUM>-,-CH<NUM>-CH<NUM>-CH<NUM>-, -CH(CH<NUM>)-CH<NUM>-, -CH<NUM>-CH(CH<NUM>)-, -CH<NUM>-CH<NUM>-CH<NUM>-CH<NUM>-, -CH(CH<NUM>)-CH<NUM>-CH<NUM>-, -CH<NUM>-CH(CH<NUM>)-CH<NUM>-, -CH<NUM>-CH<NUM>-CH(CH<NUM>)-, -CH(CH<NUM>)-CH(CH<NUM>)-, -C(CH<NUM>)<NUM>-CH<NUM>-, and -CH<NUM>-C(CH<NUM>)<NUM>-. Of these, groups containing <NUM> or <NUM> carbon atoms are preferred, in particular -CH<NUM>-CH<NUM>- and -CH<NUM>-CH(CH<NUM>)-.

In a particularly preferred embodiment, X<NUM> and X<NUM> are S, and X<NUM> and X<NUM> are O.

When RD is a hydrocarbyl group containing <NUM> to <NUM> carbon atoms, it preferably comprises <NUM> to <NUM> carbon atoms, more preferably <NUM> to <NUM> carbon atoms, and yet more preferably <NUM> to <NUM> carbon atoms.

Preferably, RD is hydrogen, a straight or branched alkyl group, or an aryl group such as phenyl. More preferably RD is hydrogen or a straight or branched alkyl group.

When RD is a straight or branched alkyl group, preferred examples for RD are methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, and t-butyl. Ethyl, n-propyl, and i-propyl are particularly preferred, and i-propyl most preferred.

In an even more preferred embodiment, said one or more phosphate compounds of formula (III) is one or more (preferably both) of the following two compounds
<CHM>.

The lower limit for the total amount of said phosphorus-containing anti-wear agent (which typically is one or more phosphate anti-wear agents) is <NUM> ppm, but preferably may be higher, e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. The upper limit for the total amount of said phosphorus-containing anti-wear agent (which typically is one or more phosphate anti-wear agents) is <NUM> ppm, but in some (low phosphorus) embodiments may be lower, e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. Preferred concentration ranges are e.g. <NUM> to <NUM> ppm, or <NUM> to <NUM> ppm, or <NUM> to <NUM> ppm.

The lower limit for the total amount of said phosphorus-containing anti-wear agent (which typically is one or more phosphate anti-wear agents) in terms of phosphorus content (based on the total weight of the hydraulic fluid) is typically <NUM> ppm, but preferably may be higher, e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. The upper limit for the total amount of said phosphorus-containing anti-wear agent (which typically is one or more phosphate anti-wear agents) in terms of phosphorus content (based on the total weight of the hydraulic fluid) is typically <NUM> ppm, but in some (low phosphorus) embodiments may be lower, e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. Preferred concentration ranges are e.g. <NUM> to <NUM> ppm, or <NUM> to <NUM> ppm, or <NUM> to <NUM> ppm.

In a particularly preferred embodiment, said phosphorus-containing anti-wear agent (which typically is one or more phosphate anti-wear agents) is a combination of (i) a compound of formula (III) or a tribologically acceptable salt thereof, wherein each RA and RB is independently an alkyl group comprising <NUM> to <NUM> carbon atoms (typically <NUM> carbon atoms, such as isobutyl); X<NUM> and X<NUM> are S; X<NUM> and X<NUM> are O; RC is a divalent alkyl group comprising <NUM> to <NUM> carbon atoms (typically -CH<NUM>-CH(CH<NUM>)-); X<NUM> is -C(O)O-; and RD is hydrogen; and (ii) a compound of formula (II) or a tribologically acceptable salt thereof, wherein each RA and RB is independently an alkyl group comprising <NUM> to <NUM> carbon atoms (typically <NUM> carbon atoms, such as isopropyl); X<NUM> and X<NUM> are S; X<NUM> and X<NUM> are O; RC is a divalent alkyl group comprising <NUM> to <NUM> carbon atoms (typically ethylene); X<NUM> is -C(O)O-; and RD is an alkyl group comprising <NUM> to <NUM> carbon atoms. In this regard, it is preferred that agent (i) is used in an amount of <NUM> to <NUM> ppm, preferably <NUM> to <NUM> ppm, more preferably <NUM> to <NUM> ppm, and/or (preferably and) that agent (ii) is used in an amount of <NUM> to <NUM> ppm, preferably <NUM> to <NUM> ppm, more preferably <NUM> to <NUM> ppm, more preferably still <NUM> to <NUM> ppm.

Preferably the hydraulic fluid is substantially free of anti-wear agents other than the above described phosphorus-containing anti-wear agent.

Preferably the hydraulic fluid is substantially free of phosphorous-containing compounds other than the above described phosphorus-containing anti-wear agent.

Preferably the hydraulic fluid is substantially free of anti-wear agents and phosphorous-containing compounds other than the above described phosphorus-containing anti-wear agent.

For instance, in preferred aspects of the invention wherein the above described phosphorus-containing anti-wear agent is a particular subset/type of phosphate anti-wear agent or a combination thereof, the hydraulic fluid is preferably substantially free of any other phosphate anti-wear agent.

Preferably the total content of phosphorus containing compounds (of any kind) in the hydraulic fluid is <NUM> to <NUM> ppm by weight. More preferably, the total content of phosphorus containing compounds is at most <NUM> ppm, such as at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, or at most <NUM> ppm. Typically the total content of phosphorus containing compounds (when present) corresponds essentially to the concentration of the above phosphorus-containing anti-wear agent.

Preferably the total phosphorus content of the hydraulic fluid is at most <NUM> ppm, such as at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm or at most <NUM> ppm. The present invention also enables the formulation of low phosphorus content fluids. Thus, in a further preferred embodiment the total phosphorus content of the hydraulic fluid is at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm or at most <NUM> ppm. Typically the total phosphorus content of the hydraulic fluid is at least <NUM> ppm, such as at least <NUM> ppm, at least <NUM> ppm, at least <NUM> ppm, at least <NUM> ppm or at least <NUM> ppm. In particular preferred aspects the total phosphorus content of the hydraulic fluid is <NUM> to <NUM> ppm, <NUM> to <NUM> ppm, or <NUM> to <NUM> ppm. Phosphorus content may preferably be measured by ASTM D4951.

As mentioned above the phosphorus-containing anti-wear agent is preferably ashless. Moreover, preferably the total zinc content of the hydraulic fluid is at most <NUM> ppm, more preferably at most <NUM> ppm, more preferably still at most <NUM> ppm, such as at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm or at most <NUM> ppm. In a particularly preferred embodiment the hydraulic fluid is essentially free of zinc. Zinc content may preferably be measured by ASTM D4951.

The hydraulic fluid in the hydraulic system of the present invention preferably further comprises one or more rust inhibitors. Preferably said one or more rust inhibitors comprise at least one sulfonate rust inhibitor, and more preferably at least one derivative of an optionally substituted naphthalenesulfonic acid, which derivative is selected from the group consisting of:.

wherein the naphthalenesulfonic acid is preferably a compound of the following formula:
<CHM>
wherein each R<NUM> and each R<NUM> is independently a hydrocarbyl group comprising <NUM> to <NUM> carbon atoms, x is <NUM> to <NUM>, and y is <NUM> to <NUM>. Preferably x+y ≥ <NUM>. Preferably the hydrocarbyl groups are alkyl groups. Thus, preferably the optionally substituted naphthalenesulfonic acid is a mono-, di, or poly-alkylated naphthalenesulfonic acid. Suitable derivatives are described in <CIT>. Such agents can be particularly useful in enhancing the corrosion inhibiting properties of the fluids in the hydraulic system of the invention. Preferably in this regard, said hydrocarbyl group has at least <NUM> carbon atoms, more preferably at least <NUM> carbon atoms. Preferably said hydrocarbyl group has up to <NUM> carbon atoms, more preferably up to <NUM> carbon atoms. Preferably said hydrocarbyl group is a straight or branched alkyl group, more preferably a straight alkyl group.

Preferably the derivative is a Ca alkylnaphthalenesulfonate/carboxylate complex. The Ca content of the complex is preferably <NUM> to <NUM> % by weight, such as <NUM> to <NUM> % by weight. Typically it is around <NUM> % by weight.

The lower limit for the total amount of said one or more rust inhibitors, when present, is preferably <NUM> ppm, but more preferably is higher, e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. The upper limit for the total amount is preferably <NUM> ppm, but more preferably may be lower, e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. Typical preferred concentration ranges are e.g. <NUM> to <NUM> ppm, or <NUM> to <NUM> ppm.

The hydraulic fluid in the hydraulic system of the present invention preferably further comprises one or more antioxidants.

In this regard, the term "one or more antioxidants" preferably means one, two, or three antioxidant(s), more preferably one or two antioxidant(s), and most preferably two antioxidants. For the avoidance of doubt, though, in situations where the term "one or more" is defined as a particular number, e.g. two, this does not preclude the presence of further antioxidants.

Preferably said one or more antioxidants are selected from phenolic antioxidants (typically hindered phenol antioxidants) and/or amine antioxidants (typically aromatic amine antioxidants). In a particularly preferred embodiment, said one or more antioxidants is a phenolic antioxidant and an amine antioxidant.

Preferred phenolic antioxidants are alkylated monophenols. Examples of alkylated monophenol antioxidants include <NUM>,<NUM>-di-tert-butyl-phenol, <NUM>,<NUM>-di-tert-butyl-<NUM>-methylphenol, <NUM>-tert-butyl-<NUM>,<NUM>-dimethylphenol, <NUM>,<NUM>-di-tert-butyl-<NUM>-ethylphenol, <NUM>,<NUM>-di-tert-butyl-<NUM>-n-butylphenol, <NUM>,<NUM>-di-tert-butyl-<NUM>-isobutylphenol, <NUM>,<NUM>-dicyclopentyl-<NUM>-methylphenol, <NUM>-(α-methylcyclohexyl)-<NUM>,<NUM>-dimethylphenol, <NUM>,<NUM>-dioctadecyl-<NUM>-methylphenol, <NUM>,<NUM>,<NUM>-tricyclohexylphenol, <NUM>,<NUM>-di-tert-butyl-<NUM>-methoxymethylphenol, <NUM>,<NUM>-di-nonyl-<NUM>-methylphenol, and combinations thereof.

Examples of amine antioxidants include N,N'-dinonyl-p-phenylenediamine, N,N'-dioctyl-p-phenylenediamine, N,N'-didecyl-p-phenylenediamine, N,N'-diisopropyl-p-phenylenediamine, N,N'-di-sec-butyl-p-phenylenediamine, N,N'-bis(<NUM>,<NUM>- dimethylpentyl)-p-phenylenediamine, N,N'-bis(l-ethyl-<NUM>-methylpentyl)-p-phenylenediamine, N,N'-bis(l-methylheptyl)-p-phenylenediamine, N,N'- dicyclohexyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-bis(<NUM>- naphthyl)-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N-(<NUM>,<NUM>-dimethyl-butyl)-N'-phenyl-p-phenylenediamine, N-(l-methylheptyl)-N'-phenyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, <NUM>-(p-toluenesulfamoyl)diphenylamine, N,N'-dimethyl-N,N'-di-sec-butyl-p-phenylenediamine, diphenylamine, N-allyldiphenylamine, <NUM>-isopropoxydiphenylamine, N-phenyl-<NUM>-naphthylamine, N-phenyl-<NUM>-naphthylamine, octylated diphenylamine - for example p,p'-di-tert-octyldiphenylamine, <NUM>-N- butylaminophenol, <NUM>-butyrylaminophenol, <NUM>-nonanoylaminophenol, <NUM>-dodecanoylaminophenol, <NUM>-octadecanoylaminophenol, bis(<NUM>-methoxyphenyl)amine, <NUM>,<NUM>-di-tert-butyl-<NUM>-dimethylamino methylphenol, <NUM>,<NUM>'-diaminodiphenylmethane, <NUM>,<NUM>'-diaminodiphenylmethane, N,N,N',N'-tetramethyl-<NUM>,<NUM>'-diaminodiphenylmethane, <NUM>,<NUM>- bis[(<NUM>-methyl-phenyl)amino]ethane, <NUM>,<NUM>-bis(phenylamino)propane, (o-tolyl)biguanide, bis[<NUM>-(l',<NUM>'-dimethylbutyl)phenyl]amine, tert-octylated N-phenyl-<NUM>-naphthylamine, a mixture of mono- and dialkylated tert-butyl/tert-octyldiphenylamines, a mixture of mono- and dialkylated isopropyl/isohexyldiphenylamines, mixtures of mono- and dialkylated tert-butyldiphenylamines, <NUM>,<NUM>-dihydro-<NUM>,<NUM>-dimethyl-<NUM>-l,<NUM>-benzothiazine, phenothiazine, N-allylphenothiazine, N,N,N',N'-tetraphenyl-l,<NUM>-diaminobut-<NUM>-ene, and combinations thereof.

Preferred amine antioxidants are aromatic amine antioxidants, and in particular dialkylated or diarylated diarylamine antioxidants, such as dialkylated / diarylated diphenylamine antioxidants. Thus, preferably the amine antioxidant is N,N'-dialkyl-p-phenylenediamine or N,N'-diaryl-p-phenylenediamine. More preferably in this regard the aryl moieties are unsubstituted or substituted phenyl and the alkyl moieties contain <NUM> to <NUM> carbon atoms, such as <NUM> to <NUM> carbon atoms, or <NUM> to <NUM> carbon atoms. More preferably still, the amine antioxidant is an N,N'-dialkyl-p-phenylenediamine wherein the alkyl moieties contain <NUM> to <NUM> carbon atoms, such as <NUM> to <NUM> carbon atoms, or <NUM> to <NUM> carbon atoms.

The total amount of said one or more antioxidants (preferably a phenolic antioxidant and an amine antioxidant), when present, is preferably from <NUM> ppm to <NUM> ppm. The lower limit may preferably be e.g. <NUM> ppm, 700ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. The upper limit may preferably be e.g. <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. Typical preferred concentration ranges are e.g. <NUM> to <NUM> ppm, or <NUM> to <NUM> ppm.

In a particularly preferred embodiment, said one or more antioxidants is a phenolic antioxidant and an amine antioxidant, wherein the phenolic antioxidant is an alkylated monophenol (preferably <NUM>,<NUM>-di-tert-butyl-phenol) and the amine antioxidant is an N,N'-dialkyl-p-phenylenediamine wherein the alkyl moieties contain <NUM> to <NUM> carbon atoms (preferably N,N'-dinonyl-p-phenylenediamine).

In preferred aspects wherein said one or more antioxidants is a phenolic antioxidant and an amine antioxidant, the amount of the phenolic antioxidant is preferably from <NUM> to <NUM> ppm, and the amount of the amine antioxidant is preferably from <NUM> to <NUM> ppm. The lower limit for the amount of the phenolic antioxidant is preferably <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, or <NUM> ppm. In some cases it may be higher still, such as <NUM> ppm or <NUM> ppm. The upper limit for the amount of the phenolic antioxidant is preferably <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. The lower limit for the amount of the amine antioxidant is preferably <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm, <NUM> ppm or <NUM> ppm. In some cases it may be higher still, such as <NUM> ppm, <NUM> ppm, or <NUM> ppm. The upper limit for the amount of the amine antioxidant is preferably <NUM> ppm, such as <NUM> ppm, <NUM> ppm, <NUM> ppm. In some cases it may be lower still, such as <NUM> ppm, <NUM> ppm, or <NUM> ppm.

The hydraulic fluid in the hydraulic system of the present invention comprises a major amount of a base oil. The term "major amount" means that the base oil accounts for the majority of the hydraulic fluid in terms of weight, i.e. it accounts for at least <NUM> % by weight. Typically the base oil accounts for at least <NUM> %, such as at least <NUM> %, at least <NUM> %, at least <NUM> %, at least <NUM> %, at least <NUM>%, or at least <NUM>%. The base oil may account for the vast majority of the hydraulic fluid, such as up to <NUM> %, up to <NUM> %, up to <NUM> %, up to <NUM> % or up to <NUM> %. Typically the base oil accounts for <NUM> to <NUM> %, such as <NUM> to <NUM> % or <NUM> to <NUM> % by weight of the hydraulic fluid.

The base oil may be a natural oil, a synthetic oil, or mixture of one or more natural oils and/or one or more synthetic oils.

The base oil, particularly when it is a mineral oil, may have a kinematic viscosity of <NUM><NUM>/s (cSt) to <NUM><NUM>/s (cSt) at <NUM>° C. The hydraulic fluid may though also comprise certain amounts of oils with other viscosities, e.g. oils derived from the carrier fluids used to deliver some of the additives. Thus, the hydraulic fluid may comprise delivering fluids with kinematic viscosity between <NUM> and <NUM>.

Suitable natural oils are an animal oil, a vegetable oil (e.g., castor oil and lard oil), a petroleum oil, a mineral oil, or an oil derived from coal or shale. Preferably the natural oil is mineral oil.

In a preferred embodiment the base oil is a mineral oil. Suitable mineral oils include all common mineral oil basestocks.

The mineral oil preferably has a sulfur content of no more than <NUM> ppm, preferably no more than <NUM> ppm, and more preferably no more than <NUM> ppm. In some embodiments the sulfur content may be lower still, such no more than <NUM> ppm, no more than <NUM> ppm, no more than <NUM> ppm, no more than <NUM> ppm, or no more than <NUM> ppm.

The mineral oil preferably has a saturates content of at least <NUM>%, more preferably at least <NUM>%, at least <NUM>%, or at least <NUM>%.

The mineral oil is preferably a Group I, Group II or Group III base oil, or a mixture of two or more base oils selected from Group I, Group II and Group III base oils.

The mineral oil may be naphthenic or paraffinic. The mineral oil may be refined by conventional methodology using acid, alkali, and clay or other agents such as aluminum chloride, or may be an extracted oil produced, e.g. by solvent extraction with solvents such as phenol, sulfur dioxide, furfural or dichlorodiethyl ether. The mineral oil may be hydrotreated or hydrofined, dewaxed by chilling or catalytic dewaxing processes, or hydrocracked, such as the Yubase ® family of hydrockracked base oils from SK Innovation Co. (Seoul, Korea). The mineral oil may be produced from natural crude sources or be composed of isomerized wax materials or residues of other refining processes.

Possible options for the synthetic oil include hydrocarbon oils and halo-substituted hydrocarbon oils such as oligomerized, polymerized, and interpolymerized olefins (e.g. polybutylenes, polypropylenes, propylene, isobutylene copolymers, chlorinated polylactenes, poly(<NUM>-hexenes), poly(<NUM>-octenes), poly-(<NUM>-decenes), and mixtures thereof); alkylbenzenes (e.g. dodecyl-benzenes, tetradecylbenzenes, dinonyl-benzenes, and di(<NUM>-ethylhexyl)benzene); polyphenyls (e.g. biphenyls, terphenyls, and alkylated polyphenyls); alkylated diphenyl ethers; and alkylated diphenyl sulfides. Preferred synthetic oils are oligomers of α-olefins, particularly oligomers of <NUM>-decene.

Other possible options for the synthetic oil include alkylene oxide polymers, interpolymers, copolymers, and derivatives thereof where the terminal hydroxyl groups have been modified by e.g. esterification or etherification. Examples include: polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide; the alkyl and aryl ethers of these polyoxyalkylene polymers (e.g., methyl-polyisopropylene glycol ether having an average molecular weight of e.g. around <NUM>, and diphenyl ether of polypropylene glycol having a molecular weight of e.g. <NUM>-<NUM>); and mono- and poly-carboxylic esters thereof (e.g. the acetic acid esters, mixed C<NUM>-C<NUM> fatty acid esters, and the C<NUM> oxo-acid diester of tetraethylene glycol).

Other possible options for the synthetic oil include the esters of dicarboxylic acids (e.g. phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebasic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkylmalonic acids, or alkenyl malonic acids) with a variety of alcohols (e.g. butyl alcohol, hexyl alcohol, dodecyl alcohol, <NUM>-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoethers, or propylene glycol). Examples of these esters include dibutyl adipate, di(<NUM>-ethylhexyl) sebacate, din-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the <NUM>-ethylhexyl diester of linoleic acid dimer, and the complex ester formed by reacting one mole of sebasic acid with two moles of tetraethylene glycol and two moles of <NUM>-ethyl-hexanoic acid. Preferred in this class of synthetic oils are adipates of C<NUM> to C<NUM> alcohols.

Esters useful as synthetic base oils also include those made from C<NUM> to C<NUM> monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylolpropane pentaerythritol, dipentaerythritol, and tripentaerythritol.

Other possible options for the synthetic oil include silicon-based oils, such as the polyalkyl-, polyaryl-, polyalkoxy-, or polyaryloxy-siloxane oils and silicate oils. Examples include tetra-ethyl silicate, tetraisopropyl silicate, tetra-(<NUM>-ethylhexyl)silicate, tetra-(<NUM>-methyl-<NUM>-ethylhexyl)silicate, tetra-(p-tert-butylphenyl)silicate, hexa-(<NUM>-methyl-<NUM>-pentoxy)-disiloxane, poly(methyl)-siloxanes and poly(methylphenyl)siloxanes.

Other synthetic oils include liquid esters of phosphorus-containing acids (e.g., tricresyl phosphate, trioctyl phosphate, and diethyl ester of decylphosphonic acid), polymeric tetrahydrofurans, and poly-α-olefins. Naturally, though, liquid esters of phosphorus-containing acids will not be an appropriate choice of base oil for the preferred embodiments of the invention noted above wherein the hydraulic fluid contains relatively low levels of phosphorus.

Oils may be unrefined, refined, re-refined, or may contain a mixture of unrefined / refined / re-refined oils. Unrefined oils are obtained directly from a natural source or a synthetic source (e.g., coal, shale, or tar sands bitumen) without further purification or treatment. Examples of unrefined oils include a shale oil obtained directly from a retorting operation, a petroleum oil obtained directly from distillation, or an ester oil obtained directly from an esterification process, each of which is then used without further treatment. Refined oils are similar to the unrefined oils except that refined oils have been treated in one or more purification steps to improve one or more properties. Suitable purification techniques include distillation, hydro treating, dewaxing, solvent extraction, acid or base extraction, filtration, and percolation, all of which are known to those skilled in the art. Re-refined oils are obtained by treating used oils in processes similar to those used to obtain the refined oils. These re-refined oils are also known as reclaimed or reprocessed oils and are often additionally processed to remove spent additives and oil breakdown products. Base oils for use in the present invention are preferably refined or re-refined oils, and more preferably they are refined oils.

Other possible options for the base oil include oils derived from natural gas by a process such as the Fischer-Tropsch reaction, sometimes referred to as Gas-to-Liquid (GTL) basestocks.

In embodiments where the base oil is a mixture of one or more natural oils with one or more synthetic oils, the natural oil is preferably a mineral oil and/or (typically and) the synthetic oil is preferably an oil based on poly-α-olefins (PAO), for example oligomers of <NUM>-decene.

The hydraulic fluid in the hydraulic system of the present invention preferably comprises a demulsifier. Preferably the demulsifier is a non-ionic surfactant. More preferably it is a block copolymer terminating in hydroxyl groups.

The concentration of the demulsifier in the hydraulic fluid is preferably from <NUM> ppm to <NUM> ppm by weight. The amount is preferably at least <NUM> ppm, such as at least <NUM> ppm, at least <NUM> ppm, or at least <NUM> ppm. The upper limit for the amount is preferably <NUM> ppm, such as at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm, at most <NUM> ppm or at most <NUM> ppm.

The hydraulic fluid in the hydraulic system of the present invention may comprise a viscosity modifier (VM), which may also be referred to as a viscosity index improver (VII). Examples of VIIs include polyacrylates, polymethacrylates, vinylpyrrolidone/methacrylate copolymers, polyvinylpyrrolidones, polybutenes, olefin copolymers, styrene/acrylate copolymers, polyethers, and combinations thereof. If present, the VII can be used in an amount to deliver a viscosity index (VI) of between <NUM> and <NUM>. More preferably, the VII can be used in an amount to deliver a VI of between <NUM> and <NUM> for improved low temperature properties and/or system operating efficiency.

The hydraulic fluid in the hydraulic system of the present invention may have a kinematic viscosity of <NUM><NUM>/s (cSt) to <NUM><NUM>/s (cSt) at <NUM>° C.

The hydraulic fluid in the hydraulic system of the present invention may comprise a pour point depressant (PPD). Examples of PPDs include polymethacrylate and alkylated naphthalene derivatives, and combinations thereof. If present, the PPD can be used in an amount of <NUM> to <NUM> % by weight of the hydraulic fluid, for improved low temperature properties.

The hydraulic fluid in the hydraulic system of the present invention may comprise a carrier or solvent for (among others) the corrosion inhibiting agent. The corrosion inhibiting agent for use according to the invention may be in solid form, in which case it is preferable to dissolve it in a carrier or solvent before contacting it with the other components of the hydraulic fluid. Thus, the hydraulic fluid in the hydraulic system of the present invention typically comprises <NUM> to <NUM> ppm of a carrier or solvent that is suitable for dissolving the corrosion inhibiting agent (i.e. component (a)). The amount of the carrier (or solvent), if present, may be at least <NUM> ppm, such as at least <NUM> ppm or at least <NUM> ppm. The amount of the carrier (or solvent), if present, is preferably at most <NUM> ppm, such as at most <NUM> ppm, at most <NUM> ppm or at most <NUM> ppm. Preferably the carrier/solvent is an alcohol, typically an alkanol (i.e. a non-aromatic alcohol). Preferably the carrier/solvent is a primary alcohol. Preferred examples for the alcohol are straight or branched alkyl alcohols, having <NUM> to <NUM> carbon atoms. Suitable examples include <NUM>-hexanol, <NUM>-ethylhexanol, <NUM>-octanol and <NUM>-decanol.

Unless indicated otherwise (e.g. in relation to embodiments which introduce upper limits for the amount of certain types of compound), as a general rule the hydraulic fluid in the hydraulic system of the invention may optionally comprise one or more further additives that are known in the art, such as antioxidants (e.g. metal dithiophosphates and/or sulfurized olefins), which may be used in an amount of <NUM>-<NUM> %; corrosion inhibitors (e.g. carboxylic acids, metal sulphonates and/or alkylated carboxylic acids), which may be used in an amount of <NUM>-<NUM> %; defoamants (e.g. polysiloxanes and/or organic esters), which may be used in an amount of <NUM>-<NUM> ppm; anti-wear agents (e.g. aryl phosphates, zinc dialkyldithiophosphates and/or organic sulphur/phosphorus compounds), which may be used in an amount of <NUM>-<NUM> %; viscosity index improvers (e.g. polymethacrylate esters, styrene isoprene copolymers and/or polyolefins), which may be used in an amount of <NUM>-<NUM> %; pour point depressants (e.g. polymethacrylate esters and/or naphthalene wax condensation products), which may be used in an amount of <NUM>-<NUM> %; friction modifiers (e.g. fatty acids and/or esters of fatty acids), which may be used in an amount of <NUM>-<NUM> %; detergents (e.g. metal salicylates and/or metal sulphonates), which may be used in an amount of <NUM>-<NUM> %; and/or (preferably and) seal swell agents (e.g. organic esters and/or aromatics), which may be used in an amount of <NUM>-<NUM>%.

While the hydraulic fluid in the hydraulic system of the present invention may comprise various optional additives, it is preferred to avoid the unnecessary use of additives that will detract from the beneficial effects of the invention as described herein. Thus, it is preferred to avoid or minimise the use of additives which are harmful to seals and/or yellow metals (e.g. it is preferred to avoid the use of fatty imidazolines which can negatively affect seals). In line with this, it is preferred that the fluid may enjoy performance levels such as those noted below.

The hydraulic fluid in the hydraulic system of the present invention preferably provides passing scores, i.e. scores within the tolerance limits (more preferably within the ideal limits) in terms of one or more (preferably all) of the following properties determinable according to RFT-EC-Rexroth-Fluid-Test-Elastomer-Compatibility HLP/HVLP/HEPR: change in volume, change in weight, change in hardness, change in tensile strength and/or change in elongation at break. Preferably in this regard the seal used is an FKM fluoropolymer (or FKM fluoroelastomer) such as <NUM> FKM <NUM>.

The hydraulic fluid in the hydraulic system of the present invention preferably scores a rating of at least 1B, and more preferably 1A, when tested according to the ASTM D130 Copper Strip Test, with the test being run for a time period of <NUM> hours and at a temperature of <NUM>.

The hydraulic fluid in the hydraulic system of the present invention preferably scores a rating of at least 1B, and more preferably at least 1A, when tested according to the ASTM D130 Copper Strip Test, with the test being run for a time period of <NUM> hours and at a temperature of <NUM>.

The hydraulic fluid in the hydraulic system of the present invention preferably provides (i) a copper weight loss of less than <NUM>, more preferably less than <NUM>; and/or (ii) a copper rating of at least 2B, more preferably at least 1B, when tested according to the ASTM D2619.

The hydraulic fluid in the hydraulic system of the present invention preferably provides a H2O TAN score of zero, when tested according to the ASTM D664.

The hydraulic fluid in the hydraulic system of the present invention preferably provides an RPVOT score of at least <NUM> minutes, more preferably at least <NUM> minutes, when tested according to the ASTM D2272 Standard Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel.

The hydraulic fluid in the hydraulic system of the present invention preferably achieves a pass in the ASTM D665 Standard Test Method for Rust-Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water.

The hydraulic fluid in the hydraulic system of the present invention, when tested according to the ASTM D4310 Standard Test Method for Determination of Sludging and Corrosion Tendencies of Inhibited Mineral Oils, preferably achieves (i) a copper weight of <NUM> or less and preferably <NUM> or less; and/or (ii) an iron weight of <NUM> or less and preferably <NUM> or less.

Lubricating oil compositions such as hydraulic fluids are routinely prepared by formulators by combining a base oil with an additive concentrate which contains multiple additives in a relatively high concentration. The present disclosure provides an additive concentrate comprising:.

Preferably the corrosion inhibiting agent is present in an amount of at least <NUM> %, more preferably at least <NUM> %, more preferably still at least <NUM> %, and typically at least <NUM> % by weight. The upper limit for the amount of the corrosion inhibiting agent is preferably <NUM> %, more preferably <NUM> %, more preferably still <NUM> %, and typically <NUM> % by weight. Typically the corrosion inhibiting agent is present in an amount of <NUM> to <NUM> % by weight, more typically <NUM> to <NUM> %.

The corrosion inhibiting agent is preferably present in an amount of at least <NUM> %, more preferably at least <NUM> %, more preferably still at least <NUM> %, and typically at least <NUM> % by weight. The upper limit for the amount of the corrosion inhibiting agent is preferably <NUM> %, more preferably <NUM> %, more preferably still <NUM> %, and typically <NUM> % by weight. The corrosion inhibiting agent is typically present in an amount of <NUM> to <NUM> % by weight.

Preferably the dispersant is present in an amount of at least <NUM> %, more preferably at least <NUM> %, and typically at least <NUM> % by weight. The upper limit for the amount of the dispersant is preferably <NUM> %, more preferably <NUM> %, and typically <NUM> % by weight. Typically the dispersant is present in an amount of <NUM> to <NUM> % by weight.

Preferably the corrosion inhibiting agent is present in an amount of <NUM> to <NUM> % by weight and the dispersant is present in an amount of <NUM> to <NUM> % by weight.

Preferably the additive concentrate further comprises one or more metal detergents. Said one or more metal detergents are preferably present in an amount of at least <NUM> %, more preferably at least <NUM> %, more preferably still at least <NUM> % and typically at least <NUM> % by weight. The upper limit for the amount of said one or more metal detergents is preferably <NUM> %, more preferably <NUM> %, more preferably still <NUM> %, and typically <NUM> % by weight. Typically said one or more metal detergents are present in an amount of <NUM> to <NUM> % by weight.

Preferably the additive concentrate further comprises a phosphorus-containing anti-wear agent. More preferably the phosphorus-containing anti-wear agent is one or more phosphate anti-wear agents. Said phosphorus-containing anti-wear agent (which preferably is one or more phosphate anti-wear agents) is preferably present in an amount of at least <NUM> %, more preferably at least <NUM> %, more preferably still at least <NUM> % and typically at least <NUM> % by weight. The upper limit for the amount of said phosphorus-containing anti-wear agent (which preferably is one or more phosphate anti-wear agents) is preferably <NUM> %, more preferably <NUM> %, more preferably still <NUM> % by weight. Typically said phosphorus-containing anti-wear agent (which preferably is one or more phosphate anti-wear agents) is present in an amount of <NUM> to <NUM> % by weight.

Preferably the additive concentrate further comprises one or more antioxidants. Said one or more antioxidants are preferably present in an amount of at least <NUM> %, more preferably at least <NUM> %, and typically at least <NUM> % by weight. The upper limit for the amount of said one or more antioxidants is preferably <NUM> %, more preferably <NUM> %, and typically <NUM> % by weight. Typically said one or more antioxidants are present in an amount of <NUM> to <NUM> % by weight.

Preferably the additive concentrate further comprises one or more rust inhibitors. Said one or more rust inhibitors are preferably present in an amount of at least <NUM> %, more preferably at least <NUM> %, and typically at least <NUM> % by weight. The upper limit for the amount of said one or more rust inhibitors is preferably <NUM> %, more preferably <NUM> %, and typically <NUM> % by weight. Typically said one or more rust inhibitors are present in an amount of <NUM> to <NUM> % by weight.

Preferably the additive concentrate further comprises a demulsifier. Said demulsifier is preferably present in an amount of at least <NUM> %, more preferably at least <NUM> %, and typically at least <NUM> % by weight. The upper limit for the amount of said one or more demulsifier is preferably <NUM> %, more preferably <NUM> %, and typically <NUM> % by weight. Typically said one or more demulsifiers are present in an amount of <NUM> to <NUM> % by weight.

In a typical embodiment, the additive concentrate (further) comprises:.

The features set out above/herein relating to the nature of the additives that may be present in the hydraulic fluid in the hydraulic system of the invention (i.e. the corrosion inhibiting, dispersant, detergent, anti-wear, antioxidant, rust inhibitor, and demsulfier components) also apply (independently) to the additives for use in the additive concentrate.

The additive concentrate preferably comprises a diluent.

When a diluent is present, the identity of any substances making up the diluent is not particularly limited. Any substances which are suitable for serving as a carrier for one or more of the additive components present may be used. Typically the diluent is a base oil. The features set out above/herein relating to the nature of the base oil that is present in the hydraulic fluid in the hydraulic system of the invention also apply (independently) to the base oil for possible use as a diluent in the additive concentrate.

The additive concentrate is suitable for use in preparing a hydraulic fluid for use in the hydraulic system of the present invention as defined herein (e.g. by combining an appropriate amount of the additive concentrate with a base oil).

Unless indicated otherwise, all references herein to ppm or % are intended to refer to ppm or % in terms of weight. Also, unless indicated otherwise, all such references are intended to refer to the amount of the given substance relative to the total weight of the hydraulic fluid.

As used herein, the term "hydrocarbyl" refers to a group having a carbon atom directly attached to the rest of the molecule and having a hydrocarbyl or predominantly hydrocarbyl character. Non-hydrocarbon (hetero) atoms, groups or substituents may be present provided their presence does not alter the predominantly hydrocarbyl nature of the group - e.g. preferably there should be at least <NUM>, more preferably at least <NUM>, yet more preferably at least <NUM>, and more preferably still at least <NUM> carbon atoms for every heteroatom, heteroatom-containing group or heteroatom-containing substituent (preferably for every heteroatom). Preferred heteroatoms are O, S, N and halo, and more preferred are O, S and N. Preferred heteroatom-containing groups or substituents are amine, keto, halo, hydroxy, nitro, cyano, alkoxy and acyl. Preferred are hydrocarbyl groups which contain at most one or two heteroatoms, heteroatom-containing groups or heteroatom-containing substituents. More preferred are hydrocarbyl groups based only on carbon and hydrogen atoms, and most preferred are aliphatic groups, in particular alkyl groups.

As used herein, the phrase "tribologically acceptable salt(s)", unless otherwise indicated, includes salts of acidic and/or basic groups. Thus, base addition salts and acid addition salts may be contemplated. As will be recognized by a skilled artisan, tribology is a term defining a study that deals with the interaction of surfaces in relative motion, in particular in terms of friction, lubrication and wear. Tribologically acceptable salts are salts that do not negate or interfere with the tribological activity of the compounds.

Bases that may be used to prepare base addition salts contemplated for compounds herein that are acidic in nature are those that form tribologically acceptable base addition salts with such compounds (i.e. salts containing tribologically acceptable cations). Such cations/base salts may include, but are not limited to, cations such as alkali metal cations (e.g. potassium and sodium) and alkaline earth metal cations (e.g. calcium and magnesium), ammonium or amine addition salts such as N-methylglucamine-(meglumine), and alkanolammonium and other base salts of tribologically acceptable organic amines, including but not limited to alkylamines such as octylamine and oleylamine, and also alkanolamines. In certain embodiments, however, the base addition salts of the compounds (in particular for compounds of formula (I)) are not amine salts. In this regard, it can also be preferred to minimize the content of amine salts generally in the hydraulic fluid in the hydraulic system of the invention. Thus, any other components (in particular antiwear agent(s)) present in the form of amine salts are preferably present in the hydraulic fluid in the hydraulic system of the invention in an amount less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, or less than or equal to about <NUM> wt%.

Acids that may be used to prepare acid addition salts contemplated for compounds herein that are basic in nature are those that form tribologically acceptable acid addition salts with such compounds (i.e. salts containing tribologically acceptable anions). Such acid salts may include, but are not limited to, hydrochloride, hydrobromide, hydroiodide, nitrate, sulfate, bisulfate, phosphate, acid phosphate, isonicotinate, acetate, lactate, salicylate, citrate, acid citrate, tartrate, pantothenate, bitartrate, ascorbate, succinate, maleate, fumarate, gluconate, glucuronate, saccharate, formate, benzoate, glutamate, methanesulfonate, ethanesulfonate, benzenesulfonate, p-toluenesulfonate and pamoate [i.e., <NUM>,<NUM>'-methylene-bis-(<NUM>-hydroxy-<NUM>-naphthoate)] salts. Compounds of the present disclosure that include a basic moiety, such as an amino group, may form tribologically acceptable salts with various amines, in addition to the acids mentioned above.

Some of the compounds described herein and/or salts thereof may be able to exist in different tautomeric forms, as illustrated below for the compounds of formula (I). All such tautomeric forms are included within the scope of the present disclosure. In formula (I) this is reflected by the dotted lines between the adjacent nitrogen atoms in the triazole ring and the fact that the position of the -CR<NUM>R<NUM>R<NUM> group on this ring is left open. As a general rule, at any instances herein where just one tautomer may be described, alternative possible tautomeric forms are also envisaged.

In instances where a compound described herein may exist in more than one different stereoisomeric form, all such stereoisomeric forms (e.g. optical isomers, i.e. R and S enantiomeric configurations), positional isomers, as well as racemic, diastereomeric and other mixtures of such isomers are envisaged and included within the scope of the present invention.

The present invention provides a hydraulic system comprising at least one fluoropolymer seal and a hydraulic fluid as defined herein which comes into contact with the seal.

The hydraulic system preferably also comprises one or more components comprising a yellow metal such as copper, brass or bronze, wherein said fluid comes into contact with the yellow metal. In particular, it is preferred for the hydraulic system to comprise one or more components comprising copper, wherein said fluid comes into contact with the copper. The yellow metal (typically copper) may be present, for instance, in one or more valves in the hydraulic system.

As used herein, the term fluoropolymer is intended to mean fluorine-containing elastomer, and may also be referred to as a fluoroelastomer. Preferably the fluoropolymer is one that is categorised as FKM, FFKM or FEPM according to ASTM D1418, and more preferably the fluoropolymer is one that is categorised as FKM according to ASTM D1418, i.e. more preferably the fluoropolymer is an FKM fluoropolymer (or FKM fluoroelastomer) such as <NUM> FKM <NUM>.

In one embodiment the fluoropolymer is a copolymer of hexafluoropropylene (HFP) and vinylidene fluoride (VF2/VDF). In this regard, the fluoropolymer preferably has a fluorine content which (a) is at least <NUM> wt%, at least <NUM> wt%, or at least <NUM> wt%, and/or (b) is at most <NUM> wt%, at most <NUM> wt%, at most <NUM> wt%, or at most <NUM> wt%. Typically the fluorine content is around <NUM> wt%. Thus, the fluoropolymer may be a Type <NUM> FKM fluoropolymer. Type <NUM> FKM fluoropolymers may show good overall performance.

In another embodiment the fluoropolymer is a terpolymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP) and vinylidene fluoride (VF2/VDF). In this regard, the fluoropolymer preferably has a fluorine content which (a) is at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, or at least <NUM> wt%, and/or (b) is at most <NUM> wt%, at most <NUM> wt%, at most <NUM> wt%, or at most <NUM> wt%. Typically the fluorine content is around <NUM>-<NUM> weight %. Thus, the fluoropolymer may be a Type <NUM> FKM fluoropolymer. Type <NUM> FKM fluoropolymers may enable relatively good performance in terms of chemical and heat resistance, but a weaker compression set and low temperature flexibility.

In another embodiment the fluoropolymer is a terpolymer of tetrafluoroethylene (TFE), a fluorinated vinyl ether (PMVE), and vinylidene fluoride (VF2/VDF). In this regard, the fluoropolymer preferably has a fluorine content which (a) is at least <NUM> wt%, or at least <NUM> wt%, and/or (b) is at most <NUM> wt%, at most <NUM> wt%, at most <NUM> wt%, or at most <NUM> wt%. Typically the fluorine content is around <NUM>-<NUM> wt %. Thus, the fluoropolymer may be a Type <NUM> FKM fluoropolymer. Type <NUM> FKM fluoropolymers may provide relatively good performance in terms of low temperature flexibility.

In another embodiment the fluoropolymer is a terpolymer of tetrafluoroethylene (TFE), propylene (P) and vinylidene fluoride (VF2/VDF). In this regard, the fluoropolymer preferably has a fluorine content which (a) is at least <NUM> wt%, at least <NUM> wt%, or at least <NUM> wt%, and/or (b) is at most <NUM> wt%, at most <NUM> wt%, at most <NUM> wt%, or at most <NUM> wt%. Typically the fluorine content is around <NUM> wt%. Thus, the fluoropolymer may be a Type <NUM> FKM fluoropolymer. Type <NUM> FKM fluoropolymers may provide increased base resistance, but less desirable performance in terms of swelling properties, especially in hydrocarbons.

In another embodiment the fluoropolymer is a pentapolymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), ethylene (E), a fluorinated vinyl ether (PMVE) and vinylidene fluoride (VF2/VDF). Thus, the fluoropolymer may be a Type <NUM> FKM fluoropolymer. Type <NUM> FKM fluoropolymers may enable good performance in terms of base resistance and high temperature hydrogen sulfide resistance.

In another embodiment the fluoropolymer is a perfluoroelastomer, wherein the polymer backbone is (substantially) fully fluorinated. In particular, the fluoropolymer may be a copolymer of tetrafluoroethylene (TFE) and perfluoromethylvinyl ether (MVE). (In this regard, the copolymer may also contain a unit derived from a cure-site monomer (CSM), i.e. a monomer that contains a site reactive towards free radicals - an example of such cure-site monomer is <NUM>-bromo-<NUM>,<NUM>,<NUM>,<NUM>-tetrafluorobutene (BTFB)). Thus, all substituents on the polymer backbone in the perfluoroelastomer are preferably fluoro, perfluoroalkyl, or perfluoroalkoxy, and the fluoropolymer may be of the polymethacrylate type. In a particular aspect of this embodiment, the fluoropolymer may be an FFKM fluoropolymer.

In another embodiment the fluoropolymer is a copolymer of tetrafluoroethylene (TFE) and propylene (P). Thus, the fluoropolymer may be an FEPM fluoropolymer.

As explained above and demonstrated below in the Examples, the present invention is based on the finding that a certain type of corrosion inhibiting agent can provide robust corrosion inhibition at very low concentrations, particularly when combined with certain other additives, and that the benefits of this include improved fluoropolymer seal compatibility and improvements in the functional characteristics of fluoropolymer seal compatible fluids.

In one aspect, in the hydraulic system of the present invention, <NUM> to <NUM> ppm by weight in terms of nitrogen content of a corrosion inhibiting agent as defined herein is used, in the hydraulic fluid, to improve fluoropolymer seal compatibility.

In one aspect, in the hydraulic system of the present invention, <NUM> to <NUM> ppm by weight in terms of nitrogen content of a corrosion inhibiting agent as defined herein is used, in the hydraulic fluid, to preserve the integrity of one or more fluoropolymer seals which come into contact with said hydraulic fluid.

In one aspect, in the hydraulic system of the present invention, <NUM> to <NUM> ppm by weight in terms of nitrogen content of a compound of formula (I) or a tribologically acceptable salt thereof is used, in the hydraulic fluid, to inhibit corrosion while also improving fluoropolymer seal compatibility.

In one aspect, in the hydraulic system of the present invention, <NUM> to <NUM> ppm by weight in terms of nitrogen content of a compound of formula (I) or a tribologically acceptable salt thereof is used, in the hydraulic fluid, to inhibit corrosion while also preserving the integrity of one or more fluoropolymer seals which come into contact with said hydraulic fluid.

In the uses noted above, the hydraulic fluid is preferably as defined generally herein, i.e. the preferred aspects of the hydraulic fluid and the components thereof as set out above apply.

As will be readily apparent to the skilled person, references above to the improvement of fluoropolymer compatibility or the preservation of the integrity of one or more fluoropolymer seals refer to the fact that <NUM> to <NUM> ppm by weight in terms of nitrogen content of the specified agent degrades the fluoropolymer seal(s) at a lower rate than other corrosion inhibitors (such as Irgamet® <NUM>) that might otherwise be employed at their usual treat rates.

Methods for determining such effects are known to the skilled person. For example, samples of the fluoropolymer material can be immersed in the hydraulic fluid comprising the specified component(s) for extended periods and at elevated temperatures, to mimic in-use conditions. The samples are then subjected to mechanical testing and/or physical measurement and compared to samples which have been exposed to one or more other fluid(s) and/or no fluid (as a control). A relevant technical effect may be an increase in tensile strength, an increase in elongation at break or a reduction in the change in volume, weight and/or hardness as compared to the other fluid(s).

Thus, in the context of the present invention, use to improve fluoropolymer seal compatibility or to preserve the integrity of a fluoropolymer seal, may preferably mean use (i) to reduce the rate of loss of the tensile strength of the fluoropolymer, (ii) to reduce the rate of decrease in elongation at break of the fluoropolymer, (iii) to reduce the rate of change in volume of the fluoropolymer, (iv) to reduce the rate of change in weight of the fluoropolymer, and/or (v) to reduce the rate of change in hardness of the fluoropolymer.

Fluoropolymer seal compatibility, and in particular any or all of the specific properties noted above (i.e. tensile strength, elongation at break, and change in volume, weight and/or hardness) may be determinable according to RFT-EC-Rexroth-Fluid-Test-Elastomer-Compatibility HLP/HVLP/HEPR: change in volume, change in weight, change in hardness, change in tensile strength and/or change in elongation at break. Preferably in this regard the seal is an FKM fluoropolymer (or FKM fluoroelastomer) such as <NUM> FKM <NUM>.

In relation to the above uses, references to the inhibition of corrosion preferably refer to the corrosion of yellow metals, and more preferably copper.

For instance, references to the inhibition of corrosion may preferably refer to the inhibition of corrosion as determinable according to any of the standard tests discussed above, e.g. ASTM D130, ASTM D2619, ASTM D664, ASTM D2272, ASTM D4310 and/or ASTM D665.

Thus, references to the inhibition of corrosion may refer to the provision of any of the preferred performance characteristics for the hydraulic fluid (in terms of corrosion inhibition) that are noted above. For example, they may refer to the provision of (i) a rating of at least 1B and more preferably 1A, determinable according to ASTM D130 with the test being run for a time period of <NUM> hours at a temperature of <NUM>, (ii) a rating of at least 1B and more preferably at least 1A, determinable according to ASTM D130 with the test being run for a time period of <NUM> hours at a temperature of <NUM>; (iii) a copper weight loss of less than <NUM>, more preferably less than <NUM>, determinable according to ASTM D2619; (iv) a copper rating of at least 2B, more preferably at least 1B, determinable according to ASTM D2619; (v) a H2O TAN score of zero, determinable according to ASTM D664; (vi) an RPVOT score of at least <NUM> minutes, more preferably at least <NUM>, determinable according to ASTM D2272; (vii) a pass in the ASTM D665 test; and/or (viii) as determinable according to ASTM D4310, a copper weight of <NUM> or less and preferably <NUM> or less, and/or an iron weight of <NUM> or less and preferably <NUM> or less.

In relation to the above uses, references to the improvement of fluoropolymer seal compatibility or preservation of the integrity of a fluoropolymer seal preferably refer to one or more properties determinable according to RFT-EC-Rexroth-Fluid-Test-Elastomer-Compatibility HLPIHVLP/HEPR, such as one or more of the change in volume, change in weight, change in hardness, change in tensile strength and/or change in elongation at break. Preferably in this regard the seal used is an FKM fluoropolymer (or FKM fluoroelastomer) such as <NUM> FKM <NUM>.

In preferred aspects, in the hydraulic system of the present invention the compound of formula (I) or a tribologically acceptable salt thereof is used to inhibit corrosion in any one of the different respects noted above, while (also) degrading one or more fluoropolymer seals which come into contact with the fluid at a rate such that the hydraulic fluid provides passing scores, i.e. scores within the tolerance limits (more preferably within the ideal limits) in terms of one or more (preferably all) of the following properties determinable according to RFT-EC-Rexroth-Fluid-Test-Elastomer-Compatibility HLP/HVLP/HEPR: change in volume, change in weight, change in hardness, change in tensile strength and/or change in elongation at break. Preferably in this regard the seal used is an FKM fluoropolymer (or FKM fluoroelastomer) such as <NUM> FKM <NUM>.

All of the above aspects of the hydraulic fluid for use in the hydraulic system of the present invention described herein apply to the context of the above uses. Thus, in the context of the above uses, the hydraulic fluid is preferably a hydraulic fluid as defined herein. Also, the hydraulic fluid and fluoropolymer seals are comprised in a hydraulic system of the present invention as defined herein.

Some compounds of formula (I) are known and available commercially. In any case, the compounds may generally be prepared by known methods, such as by a Mannich reaction between (i) benzotriazole carrying one or more substituents on the benzene ring thereof (corresponding to the R<NUM> groups), (ii) R<NUM>C(=O)R<NUM>, and (iii) R<NUM>-H which is an amine of formula HNR<NUM>R<NUM>.

For instance, it is known that the preferred compound of formula (I) wherein R<NUM> is methyl, x is <NUM>, R<NUM> and R<NUM> are hydrogen, R<NUM> is -NR<NUM>R<NUM>, and R<NUM> and R<NUM> are both <NUM>-octylphenyl (i.e. the compound <NUM>-[di(<NUM>-octylphenyl)aminomethyl]toluyltriazole) can be made by reacting toluyltriazole, formaldehyde and di(<NUM>-octylphenyl)amine (see e.g. <CIT>), and for reference purposes a compound wherein R<NUM> is methyl, x is <NUM>, R<NUM> is hydrogen, R<NUM> is octyl, R<NUM> is OR<NUM>, and R<NUM> is butyl can be prepared by reacting toluyltriazole, nonanal and butanol (see Example <NUM> below).

To <NUM> grams (<NUM> moles) of toluyltriazole (mixture of isomers), <NUM> mLs (<NUM> moles, excess) of n-butanol was added as both solvent and reagent. The toluyltriazole did not dissolve to any significant extent. To this reaction mixture, <NUM> grams (<NUM> mLs, <NUM> moles) of nonanal was poured in one portion. An immediate exotherm was noted, from <NUM> to <NUM>. Solution was heated to reflux and water was collected from azeotrope with n-butanol in Dean-Stark trap (<NUM> mLs theoretical, actual not recorded). Excess n-butanol was removed by rotary evaporation followed by full pump vacuum. Crude yield was <NUM>. %N Found <NUM>, Calc. The reaction product was then characterized by GC-MS (Table <NUM>, <FIG>) and FT-IR (<FIG>).

Compound <NUM> (<NUM>-[<NUM>-(butyloxy)octyl]toluyltriazole) and Irgamet <NUM> (which contains the above depicted compound without any diluent) were compared in the absence of other additives.

Thus, a first sample solution of single component system Compound <NUM> (<NUM> wt%) in base oil was prepared, and then a second solution was also then prepared which differed from the first solution only in that it contained Irgamet® <NUM> (<NUM> wt%) instead of Compound <NUM> (the use of relatively high concentrations of each of the additives meant that their negative impact on the seals was exaggerated, which allowed their respective effects to be more clearly distinguished from each other). Each solution was subjected to fluoropolymer seal compatibility testing performed against SAE J2643 FKM-<NUM>, which is bisphenol AF cured type II elastomer (samples of FKM fluoropolymer material were immersed in the solutions for a defined period of time and at a specific temperature). The seals from each sample were then analysed and their properties compared. In particular, the change in hardness, elongation and tensile stress of the samples were measured after <NUM>, <NUM> and <NUM> days. Fluoropolymer seal compatibility test results are set out below in Table <NUM>.

<FIG> show the effect of <NUM> wt% of Irgamet® <NUM> and <NUM> wt% of Compound <NUM>, respectively (c. the <NUM> day stress-strain curves in <FIG> (provided here for reference purposes) which demonstrate different types of failure relative to a new elastomer). With Irgamet® <NUM> it can be seen that within <NUM> days significant loss of tensile properties, both tensile strength and elongation, was seen, as well as a significant increase in hardness. The significant increase in hardness indicates a crosslinking mechanism. However, with Compound <NUM> it can be seen that almost no loss of elongation occurred within <NUM> days, and only minor loss of elongation occurred at <NUM> days. Hardness does not increase to any significant amount indicating that the crosslinking mechanism has been shut down.

Compound <NUM> (<NUM>-[<NUM>-(butyloxy)octyl]toluyltriazole) and Irgamet® <NUM> were compared in the presence of other additives to simulate a fully formulated hydraulic fluid (see Fluids <NUM>-<NUM>).

Thus, three hydraulic fluids referred to below as Fluids <NUM> to <NUM> with the compositions given in Table <NUM> were prepared. Fluids <NUM> and <NUM> contained Compound <NUM> as the sole corrosion inhibitor (in differing amounts), whereas Fluid <NUM> contained Irgamet® <NUM> as the sole corrosion inhibitor (whose % N is equivalent to the triazole compound in Fluid <NUM>). Each of Fluids <NUM> to <NUM> also included (in addition to the components that are identified below in Table <NUM>) <NUM> % of a viscosity modifier; <NUM> % of a pour point depressant; <NUM> % of a combination of phenolic and aminic antioxidants; minor amounts (≤<NUM> % each) of a sulfonate rust inhibitor, a solubilizer, a Ca phenate detergent, a demulsifier, some C<NUM>-alcohol solvent, and a defoamant (with the same additives being used in each case); with the balance being base oil.

Each of Fluids <NUM> to <NUM> was subjected to fluoropolymer seal compatibility testing. Samples of FKM fluoropolymer material were immersed in the hydraulic fluid for a defined period of time and at a specific temperature. The samples were then analysed. An improvement in fluoropolymer seal compatibility may be evidenced by one or more of, an increase in tensile strength, an increase in elongation at break, or a reduction in the change in hardness. The results are set out below in Table <NUM>.

Fluid <NUM>, which contained Irgamet® <NUM> in a relatively low amount, failed the FKM seal compatibility test (see the elongation at break and tensile strength results for Fluid <NUM>). These results reflect the aggressive nature of the test (<NUM> at <NUM>), which in turn reflects the increasingly high standards required in modern hydraulic systems in terms of seal compatibility. The Fluids containing Compound <NUM> in varying amounts met the criteria to meet the FKM seal compatibility test (one failing parameter is acceptable). Both passed the FKM seal compatibility test, even including the one with an equivalent wt.

Compound <NUM> (<NUM>-[di(<NUM>-octylphenyl)aminomethyl]toluyltriazole) and Irgamet® <NUM> were compared in the presence of other additives to simulate a fully formulated hydraulic fluid (see Fluids <NUM>-<NUM>) and also in the absence of other additives (see Fluids <NUM>-<NUM>).

Thus, firstly, four hydraulic fluids referred to below as Fluids <NUM> to <NUM> with the compositions given in Table <NUM> were prepared. Fluids <NUM> to <NUM> contained Compound <NUM> as the sole corrosion inhibitor (in differing amounts), whereas Fluid <NUM> contained Irgamet® <NUM> as the sole corrosion inhibitor (in a molar amount which lies between the molar amount of the triazole compound in Fluids <NUM> and <NUM>). Each of Fluids <NUM> to <NUM> also included (in addition to the components that are identified below in Table <NUM>) <NUM> % of a viscosity modifier; <NUM> % of a pour point depressant; <NUM> % of a combination of phenolic and aminic antioxidants; minor amounts (≤<NUM> % each) of a sulfonate rust inhibitor, a solubilizer, a Ca phenate detergent, a demulsifier, some C<NUM>-alcohol solvent, and a defoamant (with the same additives being used in each case); with the balance being base oil.

And then secondly, six further fluids (labelled Fluids <NUM> to <NUM>) were prepared as solutions of single component systems of Compound <NUM> or Irgamet® <NUM> in base oil. The compositions are set out in Table <NUM> below.

Each of Fluids <NUM> to <NUM> was subjected to fluoropolymer seal compatibility testing. Samples of FKM fluoropolymer material were immersed in the hydraulic fluid for a defined period of time and at a specific temperature. The samples were then analysed. An increase in fluoropolymer seal compatibility may be evidenced by one or more of, an increase in tensile strength, an increase in elongation at break or a reduction in the change in hardness. The results are set out below in Tables <NUM> and <NUM>.

Fluids <NUM> and <NUM>, which contained Irgamet® <NUM> in a relatively low amount, failed the FKM seal compatibility test (see the elongation at break result for Fluid <NUM> and the tensile strength result for Fluid <NUM>). These results reflect the aggressive nature of the test (<NUM> at <NUM>), which in turn reflects the increasingly high standards required in modern hydraulic systems in terms of seal compatibility. The Fluids containing Compound <NUM> in varying amounts all passed the FKM seal compatibility test, even including those which had a greater molar amount of the triazole compound.

Fluids <NUM> to <NUM> as described in Table <NUM> above were tested according to the standard tests set out below. The copper corrosion test results are set out beneath that in Table <NUM>.

Although the scores vary for Fluids <NUM>-<NUM>, all scores are passing in the copper corrosion tests. Fluid <NUM> which contains Irgamet® <NUM> in a relatively low amount is able to provide satisfactory corrosion inhibition but (as noted above in Example <NUM>) failed the FKM seal compatibility test. Fluids <NUM> and <NUM> contain varying amounts of Compound <NUM> as the sole corrosion inhibitor. Each of Fluids <NUM> and <NUM> provided robust performance in terms of both corrosion inhibition (e.g. compare the ASTM D2619 copper weight loss of just <NUM>, <NUM>, and <NUM> respectively, as compared to <NUM> for Fluid <NUM> which contains Irgamet® <NUM>) and seal compatibility (see Example <NUM> above).

It is noteworthy that Fluid <NUM> is able to achieve both strong corrosion inhibition and good seal compatibility in the context of fluids containing a series of further additives-including, among others, detergent, dispersant, phosphate anti-wear and antioxidant additives (which will impart further properties to the fluid). This illustrates how the surprising effectiveness of the corrosion inhibiting agent of the present invention allows the formulation of fluoropolymer seal compatible fluids offering an advantageous balance of desirable properties.

Fluids <NUM>-<NUM> as described above in Table <NUM> were tested according to the standard tests set out below. The copper corrosion test results are set out beneath that in Table <NUM>.

Fluids <NUM>-<NUM> all pass the Copper corrosion tests. Fluid <NUM> which contains Irgamet® <NUM> in a relatively low amount is able to provide satisfactory corrosion inhibition but (as noted above in Example <NUM>) failed the FKM seal compatibility test. Fluids <NUM>-<NUM> contain varying amounts of Compound <NUM> as the sole corrosion inhibitor. Each of Fluids <NUM>-<NUM> provided robust performance in terms of both corrosion inhibition (e.g. compare the ASTM D2619 copper weight loss of just <NUM>, <NUM>, and <NUM> respectively, as compared to <NUM> for Fluid <NUM> which contains Irgamet® <NUM>) and seal compatibility (see Example <NUM> above).

It is noteworthy that Fluid <NUM> is able to achieve both strong corrosion inhibition and good seal compatibility in the context of fluids containing a series of further additives - including, among others, detergent, dispersant, phosphate anti-wear and antioxidant additives (which will impart further properties to the fluid). This illustrates how the surprising effectiveness of the corrosion inhibiting agent of the present invention allows the formulation of fluoropolymer seal compatible fluids offering an advantageous balance of desirable properties.

It can be seen from the above results that using Compound <NUM> or Compound <NUM> affords a surprisingly improved balance of properties when it comes to the potentially competing goals of good functionality (such as good corrosion inhibition) and good fluoropolymer seal compatibility.

Claim 1:
A hydraulic system comprising at least one fluoropolymer seal and a hydraulic fluid which comes into contact with the seal, wherein the hydraulic fluid comprises:
(a) <NUM> to <NUM> ppm by weight in terms of nitrogen content of a corrosion inhibiting agent which is one or more compounds of formula (I):
<CHM>
and/or tribologically acceptable salts thereof, wherein in formula (I):
- each R<NUM> is independently a straight or branched alkyl group comprising <NUM> to <NUM> carbon atoms,
- x is <NUM> or <NUM>,
- each of R<NUM> and R<NUM> is independently hydrogen or a straight or branched alkyl group comprising <NUM> to <NUM> carbon atoms,
- R<NUM> is -NR<NUM>R<NUM>,
- each of R<NUM> and R<NUM> is independently a phenyl group substituted with a hydrocarbyl group comprising <NUM> to <NUM> carbon atoms, and
- in each of said hydrocarbyl groups containing <NUM> or more carbon atoms, the carbon chain may, independently, optionally be interrupted by one or more ether groups;
(b) <NUM> to <NUM> % by weight of an ashless nitrogen-containing dispersant; and
(c) a major amount of a base oil.