[00011 The present invention relates to a low zinc hydraulic fluid composition capable of providing wear protection in a hydraulic system.

Background

[0002] Hydraulic systems rely on a hydraulic fluid under pressure to create motion in machine components. Pumps are used to create the combination of flow and pressure in hydraulic systems. Hydraulic fluids are useful in such systems to provide the pressurized fluid. While the primary purpose of a hydraulic fluid is to transmit energy (power) from the source (pump) to the end use (motor, cylinder, etc.), the hydraulic fluid provides lubrication, helping to minimize wear, reduce friction, provide cooling, inhibit corrosion, and minimize deposits, thereby extending the lifetime and efficiency of the system.

[0003] There is increasing interest in lubricating compositions that contain ashless additives due to environmental concerns and potential toxicity issues. In some applications, the use of antiwear additives such as ZDDP is being reduced in favor of other ashless additives. As a result, for hydraulic systems, there is a need to provide hydraulic fluid compositions that contain ashless additives while still providing wear performance at least as good as, or even better than, zinc- containing additives. The invention may also be useful for reducing leakage in high pressure hydraulic systems.

Summary of the Invention

[0004] The present invention provides a hydraulic fluid. The hydraulic fluid of the present invention comprises a base oil, a calcium detergent, a metal-free phosphorus containing anti-wear agent, and an ashless antioxidant, where the composition is substantially free of zinc.

[0005] In one embodiment, the hydraulic fluid comprises (a) at least 90 weight percent of a base oil having less than 500ppm sulfur, (b) a calcium detergent in an amount sufficient to deliver 5ppm to 200ppm or 5ppm to 150ppm or 5ppm to lOOppm calcium to the fluid, (c) at least one metal-free phosphorus containing anti-wear agent, and (d) one or more ashless antioxidants, wherein the hydraulic fluid as lOppm to 150 ppm phosphorus and wherein the hydraulic fluid is substantially free of zinc.

[0006] The present invention also includes a method of lubricating a hydraulic system, comprising supplying to said hydraulic system a hydraulic fluid composition comprising (a) at least 90 weight percent of a base oil having less than 500ppm sulfur, (b) a calcium detergent in an amount sufficient to deliver 5ppm to 200ppm or 5ppm to 150ppm or 5ppm to lOOppm calcium to the fluid, (c) at least one metal-free phosphorus containing anti-wear agent, and (d) one or more ashless antioxidants, wherein the hydraulic fluid as lOppm to 150 ppm phosphorus and wherein the hydraulic fluid is substantially free of zinc.

[0007] The present invention also includes the use of a hydraulic fluid comprising (a) at least 90 weight percent of a base oil having less than 500ppm sulfur, (b) a calcium detergent in an amount sufficient to deliver 5ppm to 200ppm or 5ppm to 150ppm or 5ppm to lOOppm calcium to the fluid, (c) at least one metal-free phosphorus containing anti-wear agent, and (d) one or more ashless antioxidants, wherein the hydraulic fluid as lOppm to 150 ppm phosphorus and wherein the hydraulic fluid is substantially free of zinc to lubricate a hydraulic system.

[0008] The components and application for the present invention will be described in more detail in the Detailed Description of the Invention.

Detailed Description of the Invention

[0009] The present invention provides a hydraulic fluid composition which comprises a base oil, a calcium detergent, at least one metal-free phosphorus containing anti-wear agent, and one or more ashless antioxidants as described herein. Preferably, the hydraulic fluid is substantially free of zinc.

Oils of Lubricating Viscosity

[0010] One component of the disclosed invention is a base oil. The base oil may be selected from any of the base oils in Groups I-V of the American Petroleum Institute (API) Base Oil

Interchangeability Guidelines, namely

Base Oil Category Sulfur (%) Saturates (%) Viscosity Index

Group I >0.03 and/or <90 80 to 120

Group II <0.03 and >90 80 to 120

Group III <0.03 and >90 >120

Group IV All polyalphaolefins (PAOs)

Group V All others not included in Groups I, II, III or IV Groups I, II and III are mineral oil base stocks. The oil of lubricating viscosity can include natural or synthetic oils and mixtures thereof. Mixture of mineral oil and synthetic oils, e.g., polyalphaolefin oils and/or polyester oils, may be used.

[0011] Natural oils include animal oils and vegetable oils (e.g. vegetable acid esters) as well as mineral lubricating oils such as liquid petroleum oils and solvent-treated or acid treated mineral lubricating oils of the paraffinic, naphthenic, or mixed paraffinic-naphthenic types. Hydrotreated or hydrocracked oils are also useful oils of lubricating viscosity. Oils of lubricating viscosity derived from coal or shale are also useful.

[0012] Synthetic oils include hydrocarbon oils and halosub stituted hydrocarbon oils such as polymerized and interpolymerized olefins and mixtures thereof, alkylbenzenes, polyphenyl, alkylated diphenyl ethers, and alkylated diphenyl sulfides and their derivatives, analogs and homologues thereof. Alkylene oxide polymers and interpolymers and derivatives thereof, and those where terminal hydroxyl groups have been modified by, e.g., esterification or etherification, are other classes of synthetic lubricating oils. Other suitable synthetic lubricating oils comprise esters of dicarboxylic acids and those made from C5 to C12 monocarboxylic acids and polyols or polyol ethers. Other synthetic lubricating oils include liquid esters of phosphorus -containing acids, polymeric tetrahydrofurans, silicon-based oils such as polyalkyl-, polyaryl-, polyalkoxy-, or polyaryloxy-siloxane oils, and silicate oils.

[0013] Other synthetic oils include those produced by Fischer-Tropsch reactions, typically hydroisomerized Fischer-Tropsch hydrocarbons or waxes. In one embodiment oils may be prepared by a Fischer-Tropsch gas-to-liquid synthetic procedure as well as other gas-to-liquid oils. [0014] Unrefined, refined and rerefined oils, either natural or synthetic (as well as mixtures thereof) of the types disclosed hereinabove can be used. Unrefined oils are those obtained directly from a natural or synthetic source without further purification treatment. Refined oils are similar to the unrefined oils except they have been further treated in one or more purification steps to improve one or more properties. Rerefined oils are obtained by processes similar to those used to obtain refined oils applied to refined oils which have been already used in service. Rerefined oils often are additionally processed to remove spent additives and oil breakdown products. [0015] In some embodiments the industrial lubricant composition may also include a minor amount of one or more non-synthetic base oils. Examples of these non-synthetic base oils include any of those described herein, including API Group I, Group II, or Group III base oils.

[0016] The amount of the oil of lubricating viscosity present is typically the balance remaining after subtracting from 100 wt % the sum of the amount of the compounds of the invention and the other performance additives. The oil of lubricating viscosity can be present in a major amount, for a lubricant composition, or in a concentrate forming amount, for a concentrate and/or additive composition. The industrial lubricant composition of the invention may be either lubricant compositions or concentrate and/or additive compositions.

[0017] In a fully formulated lubricating oil composition in accordance with the present invention, the oil of lubricating viscosity is generally present in a major amount (i.e. an amount greater than 50 percent by weight). Typically, the oil of lubricating viscosity is present in an amount of 75 to 98 percent by weight, and often greater than 80 percent or even 90 percent by weight of the overall composition.

[0018] The various described oils of lubricating viscosity may be used alone or in combinations. The oil of lubricating viscosity (considering all oil present) may be used in the described industrial lubricant compositions in the range of about 40 or 50 percent by weight to about 99 percent by weight, or from a minimum of 50, 70, 80, 90, or even 97 up to a maximum of 98, 98.5, 99 or even 99.8 percent by weight.

[0019] In concentrate compositions, typically the amount of additives and other components remains the same, but the amount of oil of lubricating viscosity is reduced, in order to make the composition more concentrated and more efficient to store and/or transport. A person skilled in the art would be able to easily adjust the amount of oil of lubricating viscosity present in order to provide a concentrate and/or additive composition.

[0020] In one embodiment of the present invention, the base oil used in the hydraulic fluid of the present invention will contain less than lOOOppm by weight, or even less than 750ppm by weight, or even less than 500ppm by weight sulfur.

Calcium Detergent

[0021] The hydraulic fluid of the present invention also contains a metal-containing detergent. In some embodiments, the metal -containing detergent may be a calcium or magnesium detergent. In one embodiment, the metal containing detergent comprises or consists of a calcium detergent. In one embodiment, the metal-containing detergent may also be a neutral or overbased detergent. Overbased detergents may have a total base number (TBN) of 80 mg KOH/g to 300 mg KOH/g. A neutral detergent has a total base number (TBN) of 10 mg KOH/g or less or even 5 mg KOH/g or less, for example, 0 mg KOH/g, 1 mg KOH/g, 2 mg KOH/g, 3 mg KOH/g, or 4 mg KOH/g. In another embodiment, the metal containing detergent comprises or consists of a neutral calcium detergent.

[0022] The metal-containing detergent may be chosen from non-sulfur containing phenates, sulfur containing phenates, sulfonates, salixarates, salicylates, and mixtures thereof. In one embodiment, the metal-containing detergent is a calcium detergent selected from calcium phenates, calcium sulfonates, calcium salixarates, calcium salicylates, and mixtures thereof.

[0023] In one embodiment, metal-containing detergent used in the hydraulic fluid of the present invention comprises an alkylated aromatic sulfonate salt. The sulfonate detergent may be prepared from a mono- or di- hydrocarbyl-substituted benzene (or toluene, naphthalene, indenyl, indanyl, or bicyclopentadienyl) sulfonic acid, wherein the hydrocarbyl group may contain 6 to 40, or 8 to 35 or 9 to 20 carbon atoms. The hydrocarbyl group may be derived from polypropylene or a linear or branched alkyl group containing at least 10 carbon atoms. Examples of a suitable alkyl group include branched and/or linear decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, octadecenyl, nonodecyl, eicosyl, un-eicosyl, do-eicosyl, tri-eicosyl, tetra-eicosyl, penta-eicosyl, hexa-eicosyl or mixtures thereof. In one embodiment, the hydraulic fluid of the present invention contains a neutral calcium salt of an alkylated benzene sulfonic acid. In another embodiment, the detergent comprises a neutral calcium salt of an alkylated naphthalene sulfonic acid. In another embodiment, the detergent comprises a neutral calcium salt of an alkylated toluene sulfonic acid. In another embodiment, the alkyl group of the alkylated sulfonic acid detergent contains 6 to 20 carbon atoms. [0024] In one embodiment, the hydraulic fluid of the present invention contains a calcium detergent as described herein in an amount sufficient to deliver 5 ppm to 200 ppm, or even 10 ppm to 150 ppm, or even 20 ppm to 100 ppm by weight calcium to the hydraulic fluid. Phosphorus Anti-wear Agent

[0025] In one embodiment, the hydraulic fluid of the present invention comprises at least one metal-free phosphorus containing anti-wear agent. Examples of suitable anti-wear agents include tartrates, tartrimides, oil soluble amine salts of phosphorus compounds, sulfurized olefins, phosphites (such as dibutyl or dioleyl phosphite), phosphonates, thiocarb amate- containing compounds, such as thiocarbamate esters, thiocarbamate amides, thiocarbamic ethers, alkylene-coupled thiocarbamates, bis(S-alkyldithiocarbamyl) disulfides, and oil soluble phosphorus amine salts. In one embodiment, the metal-free phosphorus anti-wear agent comprises or consists of a (thio)phosphate ester. As used herein, the term (thio)phosphate ester should be understood to include phosphate esters, thiophosphate esters or mixtures thereof.

[0026] Phosphorus compounds usable in the present invention may include triaryl phosphate or triaryl thiophosphate represented by a formula (1) below:

[0027] In the formula (1), R is a hydrogen atom or an alkyl group having 3 to 9 carbon atoms, for example 3, 4, 5, 6, 7, 8, 9, or combinations thereof of carbon atoms and X is an oxygen atom or a sulfur atom. In the formula (1), the three R groups may be mutually the same or different. Examples of the alkyl group having 4 or less carbon atoms include a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group and tertiary butyl group.

[0028] Examples of the phosphorus compound represented by the formula (1) include triphenyl phosphate, tricresyl phosphate, triphenyl thiophosphate, tricresyl thiophosphate, and butylated triphenyl phosphorothi onate.

[0029] Another example of a phosphorus compound useful in the present invention is represented by a formula (2) below.

[0030] In the formula (2), R1 represents a linear or branched alkylene group having 1 to 8 carbon atoms, R2 and R3 each represent a hydrocarbon group having 3 to 20 carbon atoms, and X ² and X ³ each, independently, represent an oxygen atom or sulfur atom.

[0031] In one embodiment, R1 may be a linear or branched alkylene group having 1 to 8 carbon atoms, more preferably a linear or branched alkylene group having 2 to 4 carbon atoms, and further preferably a branched alkylene group. Specifically, R1 is preferably, for instance, — CH2CH2— , — CH2CH(CH3)— , — CH2CH(CH2CH3)— or — CH2CH(CH2CH2CH3)— , and more preferably — CH2CH(CH3)— or — CH2CH(CH3)CH2— .

[0032] In one embodiment, R2 to R3 each preferably represent a linear or branched alkyl group having 3 to 8 carbon atoms, and more preferably a linear or branched alkyl group having 4 to 6 carbon atoms. Specifically, R2 to R3 is each preferably selected from the group consisting of propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl, hexyl, 2-ethylbutyl, 1 -methylpentyl, 1,3- dimethylbutyl and 2-ethylhexyl groups.

[0033] In one embodiment, both X ² and X ³ represent oxygen atoms. In another embodiment, both X ² and X ³ represent sulfur atoms. In another embodiment, X ² is oxygen and X ³ is sulfur, and in another embodiment, X ² is sulfur and X ³ is oxygen.

[0034] Another phosphorus compound which may be useful in the present invention comprises a thiophosphate compound represented by a formula (3) below.

[0035] In the formula (3), R ⁴ , R ⁵ and R ⁷ are each independently a linear or branched saturated or unsaturated aliphatic hydrocarbon group having 1 to 18 carbon atoms or a branched or unbranched saturated or unsaturated cyclic hydrocarbon group having 5 to 18 carbon atoms. R ⁶ is a linear or branched alkylene group having 1 to 8 carbon atoms, X ⁴ and X ³ are each independently an oxygen atom or sulfur atom. In one embodiment of formula (3), at least one sulfur atom exists. [0036] In one embodiment, both X ⁴ and X ⁵ represent oxygen atoms. In another embodiment, both X ⁴ and X ⁵ represent sulfur atoms. In another embodiment, X ⁴ is oxygen and X ⁵ is sulfur, and in another embodiment, X ⁴ is sulfur and X ⁵ is oxygen.

[0037] In one embodiment, the metal-free anti-wear agent of the present invention may be selected from Methyl 3-((dialkoxyphosphorothioyl)thio)propanoate with mixed C4/C5 alkoxy groups, 3-((diisobutoxyphosphorothioyl)thio)-2-methylpropanoic acid, and mixtures thereof.

[0038] The hydraulic fluid of the present invention will contain 10 ppm to 200 ppm by weight phosphorus or even 20 ppm to 150ppm by weight phosphorus. If the anti -wear agents are the only phosphorous containing compound present in the hydraulic fluid, such compounds will be present in amounts sufficient to deliver the required amount of phosphorus.

Antioxidant

[0039] The hydraulic fluid of the present invention also contains at least one ashless antioxidant. In some embodiments, the hydraulic fluid comprises at least one ashless antioxidant selected from a hindered phenol ester antioxidant, alkylated diarylamine antioxidant, or mixtures thereof. The anti-oxidant may be present at 0 wt % to 4.0 wt %, or 0.02 wt % to 3.0 wt %, or 0.03 wt % to 1.5 wt % or 0.05 wt % to 0.5 wt % of the lubricant.

[0040] In some embodiments, the lubricant compositions may further comprise at least one ashless antioxidant, suitable antioxidants include phenolic antioxidants, which may be represented by the general formula wherein R ⁵ is an alkyl group containing 1 to 24, or 4 to 18, carbon atoms and a is an integer of 1 to 5 or 1 to 3, or 2. The phenol may be a butyl substituted phenol containing 2 or 3 t- butyl groups, such as in formula (V):

The para position may also be occupied by a hydrocarbyl group or a group bridging two aromatic rings. In certain embodiments the para position is occupied by an ester-containing group, such as, for example, an antioxidant of the formula (VI): wherein R ⁶ is a hydrocarbyl group such as an alkyl group containing, e.g., 1 to 18 or 2 to 12 or 2 to 8 or 2 to 6 carbon atoms; and t-alkyl can be t-butyl. Such antioxidants are described in greater detail in U.S. Patent 6,559, 105.

[0041] In some embodiments, the antioxidant may include sterically hindered phenols. Examples of suitable hydrocarbyl groups for the sterically hindered phenols include but are not limited to 2-ethylhexyl or n-butyl ester, dodecyl or mixtures thereof. Examples of methylene- bridged sterically hindered phenols include but are not limited to 4,4’-methylene-bis(6-tert-butyl o-cresol), 4,4’-methylene-bis(2-tert-amyl-o-cresol), 2,2’-methylene-bis(4-methyl-6-tert- butylphenol), 4,4’ -methylene-bis(2,6-di -tertbutylphenol) or mixtures thereof.

[0042] Antioxidants also include aromatic amines, such as those of formula (VII): wherein R ⁷ can be an aromatic group such as a phenyl group, a naphthyl group, or a phenyl group substituted by R ⁹ , and R ⁸ and R ⁹ can be independently a hydrogen or an alkyl group containing 1 to 24 or 4 to 20 or 6 to 12 carbon atoms. In one embodiment, an aromatic amine antioxidant can comprise an alkylated diphenylamine such as nonylated diphenylamine of formula (VIII): or a mixture of a di-nonylated diphenylamine and a mono-nonylated diphenylamine.

Other Additives

[0043] The hydraulic fluid composition of the present invention may be in the form of a concentrate and/or a fully formulated lubricant. If the hydraulic fluid of the invention (comprising the additives disclosed herein) is in the form of a concentrate (which may be combined with additional oil to form, in whole or in part, a finished lubricant), the ratio of the of these additives to the oil of lubricating viscosity and/or to diluent oil include the ranges of 1 :99 to 99: 1 by weight, or 80:20 to 10:90 by weight.

[0044] In addition to the specific additives described above, the hydraulic fluid compositions may also contain one or more additional other additives. In some embodiments the additional additives may include corrosion inhibitors, rust inhibitors, foam inhibitors, surfactants, dispersants, demulsifiers, metal deactivators, friction modifiers, emulsifiers, extreme pressure agents, pour point depressants, viscosity modifiers, or any combination thereof.

[0045] In one embodiment, the fluid of the present invention contains a surfactant. In one embodiment, the surfactant is an ashless surfactant. Suitable surfactant may include substituted polyisobutenyl compounds. For examples, useful surfactants may include (i) polyetheramines; (ii) succinimide dispersants; (iii) Mannich reaction products of a dialkylamine, an aldehyde and a hydrocarbyl substituted phenol; or any combination thereof. In some embodiments the surfactant may be present at 0 wt % or 0.01 wt % to 2.0 wt%, 0.025 wt% to 1.5 wt %, or 0.05 wt % to 1 wt %, or 0.05 wt % to 0.5 wt % of the overall composition. In one exemplary embodiment, the hydraulic fluid contains 0.025wt % to 0.075 wt% of the surfactant.

[0046] The surfactant used in the present invention may also comprise one or more dispersants. Dispersants which may be included in the composition include those with an oil soluble polymeric hydrocarbon backbone and having functional groups that are capable of associating with particles to be dispersed. The polymeric hydrocarbon backbone may have a weight average molecular weight ranging from 750 to 1500 Daltons. Exemplary functional groups include amines, alcohols, amides, and ester polar moieties which are attached to the polymer backbone, often via a bridging group. Example dispersants include Mannich dispersants, described in U.S. Patent Nos. 3,697,574 and 3,736,357; ashless succinimide dispersants described in U.S. Patent Nos. 4,234,435 and 4,636,322; amine dispersants described in U.S. Patent Nos. 3,219,666, 3,565,804, and 5,633,326; Koch dispersants, described in U.S. Patent Nos. 5,936,041, 5,643,859, and 5,627,259, and polyalkylene succinimide dispersants, described in U.S. Patent Nos. 5,851,965, 5,853,434, and 5,792,729.

[0047J In one embodiment, the surfactant comprises a polyisobutenyl succinimide, a polyisobutenyl succinimide derived from aromatic polyamine, or mixtures thereof.

[0048] Anti-foam agents, also known as foam inhibitors, are known in the art and include organic silicones and non-silicon foam inhibitors. Examples of organic silicones include dimethyl silicone and polysiloxanes. Examples of non-silicone foam inhibitors include copolymers of ethyl acrylate and 2-ethylhexylacrylate, copolymers of ethyl acrylate, 2 -ethylhexyl acrylate and vinyl acetate, polyethers, polyacrylates and mixtures thereof. In some embodiments the anti-foam is a polyacrylate. Antifoams may be present in the composition from 0.001 wt % to 0.012 wt % or 0.004 wt % or even 0.001 wt % to 0.003 wt %.

[0049] Demulsifiers are known in the art and include derivatives of propylene oxide, ethylene oxide, polyoxyalkylene alcohols, alkyl amines, amino alcohols, diamines or polyamines reacted sequentially with ethylene oxide or substituted ethylene oxides or mixtures thereof. Examples of demulsifiers include polyethylene glycols, polyethylene oxides, polypropylene oxides, (ethylene oxi de-propylene oxide) polymers and mixtures thereof. In some embodiments the demulsifiers is a polyether. In one embodiment, the demulsifier may be an oxyalkylated phenolic resin blend. Such a blend may comprise formaldehyde polymers with 4-nonylphenol, ethylene oxide and propylene oxide and formaldehyde polymers with 4-nonylphenol ethylene oxide. Demulsifier may be present in the composition from 0.002 wt % to 0.012 wt %.

[0050] Pour point depressants are known in the art and include esters of maleic anhydridestyrene copolymers, polymethacrylates; polyacrylates; polyacrylamides; condensation products of haloparaffin waxes and aromatic compounds; vinyl carboxylate polymers; and terpolymers of dialkyl fumarates, vinyl esters of fatty acids, ethylene-vinyl acetate copolymers, alkyl phenol formaldehyde condensation resins, alkyl vinyl ethers and mixtures thereof.

[0051] The hydraulic fluid composition may also include a rust inhibitor. Suitable rust inhibitors include hydrocarbyl amine salts of alkylphosphoric acid, hydrocarbyl amine salts of dialkyldithiophosphoric acid, hydrocarbyl amine salts of hydrocarbyl aryl sulfonic acid, fatty carboxylic acids or esters thereof, an ester of a nitrogen-containing carboxylic acid, an ammonium sulfonate, an imidazoline, alkylated succinic acid derivatives reacted with alcohols or ethers, or any combination thereof, or mixtures thereof.

[0052] Suitable hydrocarbyl amine salts of alkylphosphoric acid may be represented by the following formula: wherein R ²⁶ and R ²⁷ are independently hydrogen, alkyl chains or hydrocarbyl, typically at least one of R ²⁶ and R ²⁷ are hydrocarbyl. R ²⁶ and R ²⁷ contain 4 to 30, or 8 to 25, or 10 to 20, or 13 to 19 carbon atoms. R ²⁸ , R ²⁹ and R ³⁰ are independently hydrogen, alkyl branched or linear alkyl chains with 1 to 30, or 4 to 24, or 6 to 20, or 10 to 16 carbon atoms. R ²⁸ , R ²⁹ and R ³⁰ are independently hydrogen, alkyl branched or linear alkyl chains, or at least one, or two of R ²⁸ , R ²⁹ and R ³⁰ are hydrogen.

[0053] Examples of alkyl groups suitable for R ²⁸ , R ²⁹ and R ³⁰ include butyl, sec butyl, isobutyl, tert-butyl, pentyl, n-hexyl, sec hexyl, n-octyl, 2-ethyl, hexyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, octadecenyl, nonadecyl, eicosyl or mixtures thereof.

[0054] In one embodiment, the hydrocarbyl amine salt of an alkylphosphoric acid is the reaction product of a Ci4 to Cis alkylated phosphoric acid with Primene® 81R (produced and sold by Rohm & Haas) which is a mixture of CH to C tertiary alkyl primary amines. [0055] Hydrocarbyl amine salts of dialkyldithiophosphoric acid may include a rust inhibitor such as a hydrocarbyl amine salt of dialkyldithiophosphoric acid. These may be a reaction product of heptyl or octyl or nonyl dithiophosphoric acids with ethylene diamine, morpholine or Primene® 81R or mixtures thereof.

[0056] The hydrocarbyl amine salts of hydrocarbyl aryl sulfonic acid may include ethylene diamine salt of dinonyl naphthalene sulfonic acid.

[0057] Examples of suitable fatty carboxylic acids or esters thereof include glycerol monooleate and oleic acid.

[0058] The rust inhibitors may be present in the range from 0 or 0.02 wt % to 0.2 wt %, from 0.03 wt % to 0.15 wt % , from 0.04 wt % to 0.12 wt %, or from 0.05 wt % to 0.1 wt % of the lubricating oil composition. The rust inhibitors may be used alone or in mixtures thereof.

[0059] The hydraulic fluid may also contain a metal deactivator. Metal deactivators may be chosen from derivatives of benzotriazole, 1,2,4-triazole, benzimidazole, 2- alkyldithiobenzimidazole, 2-alkyldithiobenzothiazole, or dimercaptothiadiazole. Examples of such derivatives include 2,5-dimercapto-l,3,4-thiadiazole, or oligomers thereof, a hydrocarbyl- substituted 2,5-dimercapto-l,3,4-thiadiazole, a hydrocarbylthio-substituted 2,5-dimercapto-l,3,4- thiadiazole, or oligomers thereof. The oligomers of hydrocarbyl-substituted 2,5-dimercapto-l,3,4- thiadiazole typically form by forming a sulfur-sulfur bond between 2,5-dimercapto-l,3,4- thiadiazole units to form oligomers of two or more of said thiadiazole units. Examples of a suitable thiadiazole compound include at least one of a dimercaptothiadiazole, 2,5-dimercapto-[l,3,4]- thiadiazole, 3,5-dimercapto-[l,2,4]-thiadiazole, 3,4-dimercapto-[l,2,5]-thiadiazole, or 4-5- dimercapto-[l,2,3]-thiadiazole. Typically, readily available materials such as 2,5-dimercapto-l,3,4-thiadiazole or a hydrocarbyl-substituted 2,5-dimercapto-l,3,4-thiadiazole or a hydrocarbylthio-substituted 2,5-dimercapto-l,3,4-thiadiazole are commonly utilized. In different embodiments the number of carbon atoms on the hydrocarbyl -substituent group includes 1 to 30, 2 to 25, 4 to 20, 6 to 16, or 8 to 10. The 2,5-dimercapto-l,3,4-thiadiazole may be 2,5- dioctyl dithio- 1, 3, 4-thiadiazole, or 2,5-dinonyl dithio-l,3,4-thiadiazole. The metal deactivators may also be described as corrosion inhibitors.

[0060] The metal deactivators may be present in the range from 0 or 0.001 wt % to 0.1 wt %, from 0.01 wt % to 0.04 wt % or from 0.015 wt % to 0.03 wt % of the lubricating oil composition. Metal deactivators may also be present in the composition from 0.002 wt % or 0.004 wt % to 0.02 wt %.

[0061] In one embodiment, the hydraulic fluid disclosed herein may contain at least one friction modifier. The friction modifier may be present at 0 wt % to 3 wt %, or 0.02 wt % to 2 wt %, or 0.05 wt % to 1 wt %, of the lubricant composition.

[0062] As used herein the term “fatty alkyl” or “fatty” in relation to friction modifiers means a carbon chain having 8 to 22 carbon atoms, typically a straight carbon chain. Alternatively, the fatty alkyl may be a mono branched alkyl group, with branching typically at the P-position. Examples of mono branched alkyl groups include 2-ethylhexyl, 2-propylheptyl or 2-octyldodecyl. [0063] Examples of suitable friction modifiers include long chain fatty acid derivatives of amines, fatty esters, or fatty epoxides; fatty imidazolines such as condensation products of carboxylic acids and polyalkylene-polyamines; amine salts of alkylphosphoric acids; fatty phosphonates; fatty phosphites; borated phospholipids, borated fatty epoxides; glycerol esters; borated glycerol esters; fatty amines; alkoxylated fatty amines; borated alkoxylated fatty amines; hydroxyl and polyhydroxy fatty amines; hydroxy alkyl amides; metal salts of fatty acids; metal salts of alkyl salicylates; fatty oxazolines; fatty ethoxylated alcohols; condensation products of carboxylic acids and polyalkylene polyamines; or reaction products from fatty carboxylic acids with guanidine, aminoguanidine, urea, or thiourea and salts thereof.

[0064] The hydraulic fluid may also contain one or more viscosity modifiers. Any known viscosity modifier may be used. In one embodiment, the lubricating composition of the present invention is substantially free of or totally free of poly(meth)acrylates as viscosity modifiers. Viscosity modifiers (often referred to as viscosity index improvers) suitable for use in the invention include polymeric materials including a styrene-butadiene rubber, an olefin copolymer, a hydrogenated styrene-isoprene polymer, a hydrogenated radical isoprene polymer, a poly(meth)acrylic acid ester, a poly alkyl styrene, an hydrogenated alkenylaryl conjugated-diene copolymer, an ester of maleic anhydride-styrene copolymer or mixtures thereof. In some embodiments the viscosity modifier is a poly(meth)acrylic acid ester, an olefin copolymer or mixtures thereof. The viscosity modifiers may be present at 0 wt % to 10 wt %, 0.5 wt % to 8 wt %, 1 wt % to 6 wt % of the lubricant. [0065] In one embodiment, all of the additives used in the lubricating composition may be ashless. In another embodiment, the lubricating composition may be free of additives that contain transition metals. In still another embodiment, the lubricating composition may contain additives where calcium is the only metal.

Industrial Application

[0066] In accordance with one aspect of the exemplary embodiment, the hydraulic fluid is for use in a hydraulic system, turbine system or other circulating oil system. The hydraulic system may be a device or apparatus in which the hydraulic fluid transmits energy to different parts of the system by hydraulic force. A turbine lubricant is typically used to lubricate the gears or other moving parts of a turbine (or turbine system), such as a steam turbine or a gas turbine. A circulating oil is typically used to distribute heat to or through a device or apparatus through which it is circulated.

[0067] Viscosity grades generally suitable for hydraulic oils are ISO 10, 15, 22, 32, 46, 68, 100 and 150 (cSt). The viscosity of each grade is the kinematic viscosity at 40 °C +/-10% as measured by ASTM D445 or ISO 3104. As such, an ISO 46 is 46cSt at 40 °C may have a kinematic viscosity of 41.4 - 50.6 cSt at 40 °C. The ISO viscosity classification system is defined in ISO 3448. Exemplary viscosity grades are listed in the table below:

[0068] Accordingly, in some embodiments, the lubricating composition may have an ISO viscosity grade (VG) of 10, 15, 22, 32, 46, 68, 100 or 150 (cSt) grade lubricant. In yet other embodiments, the lubricating composition may have an ISO VG of 22 cSt, 32 cSt, 46 cSt, or 68 cSt. In accordance with one aspect of the exemplary embodiment, a method for providing reduced sludge formation in a hydraulic system may include supplying the exemplary hydraulic fluid to the hydraulic system.

[0069] The present invention includes a hydraulic fluid having an ISO Viscosity Grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt and comprises (a) at least 90 weight percent of a base oil having less than 500ppm sulfur, (b) a calcium detergent in an amount sufficient to deliver 5ppm to 200ppm or 5ppm to 150ppm or 5ppm to lOOppm calcium to the fluid, wherein the calcium detergent comprises or consists of a neutral or overbased alkylated aromatic sulfonate salt comprising a linear or branched alkyl group containing 6 to 20 carbon atoms and a TBN of less than 10 mg KOH/g (c) at least one metal-free phosphorus containing anti-wear agent comprising or consisting of a (thio)phosphate ester, and (d) 0.02 wt % to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt% of one or more ashless antioxidants, wherein the hydraulic fluid as lOppm to 150 ppm phosphorus and wherein the hydraulic fluid contains less than lOppm or even less than 5ppm zinc. In one embodiment, the calcium detergent further comprises an alkylated naphthalene sufonic acid, a calcium phenate detergent, a calcium salicylate detergent, or a calcium salixarate detergent. The hydraulic fluid described in this paragraph also comprises an 0.025 wt % to 0.75 wt% of an ashless surfactant, which comprises or consists of an ashless polyisobutenyl surfactant, such as a polyisobutenyl succinimide derived from an aromatic polyamine.

[0070J The present invention also includes a hydraulic fluid having an ISO Viscosity Grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt and comprises (a) at least 90 weight percent of a base oil having less than 500ppm sulfur, (b) a calcium detergent in an amount sufficient to deliver 5ppm to 200ppm or 5ppm to 150ppm or 5ppm to lOOppm calcium to the fluid, wherein the calcium detergent comprises or consists of a neutral salt of an alkylated naphthalene sulfonic acid and a TBN of less than 10 mg KOH/g (c) at least one metal-free phosphorus containing anti-wear agent comprising or consisting of a (thio)phosphate ester, and (d) 0.02 wt % to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt% of one or more ashless antioxidants, wherein the hydraulic fluid as lOppm to 150 ppm phosphorus and wherein the hydraulic fluid contains less than lOppm or even less than 5ppm zinc. In one embodiment, the calcium detergent further comprises a neutral or overbased alkylated aromatic sulfonate salt comprising a linear or branched alkyl group containing 6 to 20 carbon atoms, a calcium phenate detergent, a calcium salicylate detergent, or a calcium salixarate detergent. The hydraulic fluid described in this paragraph also comprises an 0.025 wt % to 0.75 wt% of an ashless surfactant, which comprises or consists of an ashless polyisobutenyl surfactant, such as a polyisobutenyl succinimide derived from an aromatic polyamine.

[0071] The present invention also provides a method of lubricating a hydraulic system, wherein the method comprises supplying to a hydraulic system the hydraulic fluid as described herein.

[0072] In one embodiment, the invention provides a method of lubricating a hydraulic system, comprising supplying to said hydraulic system a hydraulic fluid composition having an ISO Viscosity Grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt and comprising (a) at least 90 weight percent of a base oil having less than 500ppm sulfur, (b) a calcium detergent in an amount sufficient to deliver 5ppm to 200ppm or 5ppm to 150ppm or 5ppm to 1 OOppm calcium to the fluid, wherein the calcium detergent comprises or consists of a neutral or overbased alkylated aromatic sulfonate salt comprising a linear or branched alkyl group containing 6 to 20 carbon atoms and a TBN of less than 10 mg KOH/g (c) at least one metal -free phosphorous containing anti -wear agent comprising or consisting of a (thio)phosphate ester, and (d) 0.02 wt % to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt% of one or more ashless antioxidants, wherein the hydraulic fluid as lOppm to 150 ppm phosphorus and wherein the hydraulic fluid contains less than lOppm or even less than 5ppm zinc, and (e) 0.025 wt % to 0.75 wt% of an ashless surfactant, which comprises or consists of an ashless polyisobutenyl surfactant, such as a polyisobutenyl succinimide derived from an aromatic polyamine.

[0073] In another embodiment, the present invention provides a method of lubricating a hydraulic system comprising supplying to said hydraulic system a having an ISO Viscosity Grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt and comprising (a) at least 90 weight percent of a base oil having less than 500ppm sulfur, (b) a calcium detergent in an amount sufficient to deliver 5ppm to 200ppm or 5ppm to 150ppm or 5ppm to 1 OOppm calcium to the fluid, wherein the calcium detergent comprises or consists of a neutral salt of an alkylated naphthalene sulfonic acid and a TBN of less than 10 mg KOH/g (c) at least one metal -free phosphorous containing anti -wear agent comprising or consisting of a (thio)phosphate ester, and (d) 0.02 wt % to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt% of one or more ashless antioxidants, wherein the hydraulic fluid as lOppm to 150 ppm phosphorus and wherein the hydraulic fluid contains less than lOppm or even less than 5ppm zinc and (e) 0.025 wt % to 0.75 wt% of an ashless surfactant, which comprises or consists of an ashless polyisobutenyl surfactant, such as a polyisobutenyl succinimide derived from an aromatic polyamine.

[0074] The method of the present invention includes operating the hydraulic system at pressures at or above 300 bar. The method provided herein also includes operating a pump at a speed at or above 2500 revolutions per minute.

[0075] The present invention also includes the use of the hydraulic fluid as described herein to lubricate and protect hydraulic system components from wear. [0076] In one embodiment, the present invention includes the use of a hydraulic fluid having an ISO Viscosity Grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt and comprising (a) at least 90 weight percent of a base oil having less than 500ppm sulfur, (b) a calcium detergent in an amount sufficient to deliver 5ppm to 200ppm or 5ppm to 150ppm or 5ppm to lOOppm calcium to the fluid, wherein the calcium detergent comprises or consists of a neutral or overbased alkylated aromatic sulfonate salt comprising a linear or branched alkyl group containing 6 to 20 carbon atoms and a TBN of less than 10 mg KOH/g (c) at least one metal -free phosphorous containing anti -wear agent comprising or consisting of a (thio)phosphate ester, and (d) 0.02 wt % to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt% of one or more ashless antioxidants, wherein the hydraulic fluid as lOppm to 150 ppm phosphorus and wherein the hydraulic fluid contains less than lOppm or even less than 5ppm zinc, and (e) 0.025 wt % to 0.75 wt% of an ashless surfactant, which comprises or consists of an ashless polyisobutenyl surfactant, such as a polyisobutenyl succinimide derived from an aromatic polyamine to lubricate a hydraulic system.

[0077] In another embodiment, the present invention also includes the use of a hydraulic fluid having an ISO Viscosity Grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt and comprising (a) at least 90 weight percent of a base oil having less than 500ppm sulfur, (b) a calcium detergent in an amount sufficient to deliver 5ppm to 200ppm or 5ppm to 150ppm or 5ppm to lOOppm calcium to the fluid, wherein the calcium detergent comprises or consists of a neutral salt of an alkylated naphthalene sulfonic acid and a TBN of less than 10 mg KOH/g (c) at least one metal-free phosphorous containing anti-wear agent comprising or consisting of a (thio)phosphate ester, and (d) 0.02 wt % to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt% of one or more ashless antioxidants, wherein the hydraulic fluid as lOppm to 150 ppm phosphorus and wherein the hydraulic fluid contains less than lOppm or even less than 5ppm zinc and (e) 0.025 wt % to 0.75 wt% of an ashless surfactant, which comprises or consists of an ashless polyisobutenyl surfactant, such as a polyisobutenyl succinimide derived from an aromatic polyamine to lubricate a hydraulic system.

[0078] A set of exemplary hydraulic lubricating compositions was prepared and evaluated as summarized in Table 1. All treat rates are oil free (i.e., active) unless otherwise indicated. The example fluids were evaluated using a Mini -Traction Machine (MTM test) and the Bosch-Rexroth Pump test as described below.

1. Nonylated naphthalenesulfonic acid, Ca Salt, TBN 1.0, 50% diluent oil

2. Methyl 3-((dialkoxyphosphorothioyl)thio)propanoate with mixed C4/C5 alkoxy groups

3. 3-((diisobutoxyphosphorothioyl)thio)-2 -methylpropanoic acid

4. 4,4'-methylene bis(dibutyldithiocarbamatc)

5. Succinimide derived from aromatic polyamine (PIB Mn 2300 Da; TBN 0.1 mg KOH/g) (includes 50% oil by weight)

6. Other additives include corrosion inhibitors, demulsifiers, anti-foam additives, diluent oil and pourpoint depressant)

7. Example compositions were evaluated for coefficient of friction using a Mini Traction Machine (MTM) available from PCS Instruments. The test configuration is that of about 19.05 mm ( ³ /4 inch) diameter bearing steel ball making a contact on a highly polished surface on a 46 mm diameter bearing steel disk. The ball makes contact with the disc such that spin in the contact is eliminated. Rolling velocity, slide/roll ratio, temperature and load, were the parameters that could be varied during each test. The specimen speeds are independently controlled using servo-motors to produce desired slide/roll motion at the contact. The specimens arc contained in a scaled temperature controlled reservoir that contains an approximately 35 ml fluid sample. The test temperature is controlled by electric heaters and the fluid temperature is monitored. The contact is automatically loaded to the desired Hertz pressure, ball and disc speeds are controlled by electric motors. The series of tests that were run for this study were carried out at a Hertz pressure of about 1.00 GPa, temperature of about 100° C, rolling velocity of about 100 mm/s and a fixed slide-to-roll ratio of about 100%. Test was conducted in 10 min steps, and total duration was about 120 min. After each 10 min step, the rolling/sliding motion at the ball and disc contact was stopped. The portion of the ball in contact with disc was pressed against a glass window. Using a microscope and camera, an image of the contact region on the ball was recorded. The test then continued for next 10 minutes segment. At the conclusion of test after 120 minutes, the recorded images were visually examined, and then analyzed to study the formation of reacted film (tribo film) and the change in its thickness over each 10 minutes test sequence. A record of film formation and change in film thickness was then prepared for the duration of 120 min. test time.

8. “Rexroth Fluid Test Axial Piston Units Closed Loop Applications (RFT-APU-CL),” Bosch procedure number is RE 96270 which is available by request at the Bosch Rexroth website.

[0079] As used herein, “substantially free” means that the amount of the material in question is less than an amount that will affect the relevant performance of the fluid in a measurable way.

“Substantially free” may also mean that the material in question is not intentionally added to the composition but does not exclude the presence of such material as contaminants. “Substantially free” may also mean that the material in question may be present in amounts lower than the detection limit of standard test methods now known to those skilled in the art or hereafter developed. In some embodiments, “substantially free” may mean less than 10 ppm by weight or even less than 5 ppm by weight.

[0080] It is known that some of the materials described above may interact in the final formulation, so that the components of the final formulation may be different from those that are initially added. The products formed thereby, including the products formed upon employing lubricant composition of the present invention in its intended use, may not be susceptible of easy description. Nevertheless, all such modifications and reaction products are included within the scope of the present invention; the present invention encompasses lubricant composition prepared by admixing the components described above

[0081] Each of the documents referred to above is incorporated herein by reference. Except in the Examples, or where otherwise explicitly indicated, all numerical quantities in this description specifying amounts of materials, reaction conditions, molecular weights, number of carbon atoms, and the like, are to be understood as modified by the word “about.” Unless otherwise indicated, each chemical or composition referred to herein should be interpreted as being a commercial grade material which may contain the isomers, by-products, derivatives, and other such materials which are normally understood to be present in the commercial grade. However, the amount of each chemical component is presented exclusive of any solvent or diluent oil, which may be customarily present in the commercial material, unless otherwise indicated. It is to be understood that the upper and lower amount, range, and ratio limits set forth herein may be independently combined. Similarly, the ranges and amounts for each element of the invention may be used together with ranges or amounts for any of the other elements.

[0082] While the invention has been explained in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.