Lubricating composition

Abstract

A substantially zinc-free hydraulic fluid is provided. The substantially zinc-free hydraulic fluid contains a calcium detergent, an ashless antioxidant, and a metal-free phosphorus-containing antiwear agent. In one embodiment, the fluid comprises at least 90 weight percent base oil having less than 500 ppm sulfur, a calcium detergent in an amount to deliver 5 ppm to 200 ppm calcium to the fluid, at least one metal-free phosphorus-containing antiwear agent to provide 10 ppm to 150 ppm phosphorus, and one or more ashless antioxidants. A method of lubricating a hydraulic system with a substantially zinc-free fluid is also provided.

Description

Technical Field

[0001] The present invention relates to a low - zinc hydraulic fluid composition capable of providing wear protection in a hydraulic system.

Background Art

[0002] Hydraulic systems rely on hydraulic fluid under pressure to cause movement in mechanical components. A pump is used to create a combination of flow rate and pressure in a hydraulic system. Hydraulic fluid is useful in such systems to provide pressurized fluid. The main purpose of hydraulic fluid is to transmit energy (power) from a source (pump) to a final use (motor, cylinder, etc.). However, hydraulic fluid also serves to provide lubrication, minimize wear, reduce friction, provide cooling, inhibit corrosion, and minimize deposits, thereby extending the life and efficiency of the system.

[0003] Due to environmental concerns and potential toxicity issues, there is increasing interest in lubricating compositions containing ashless additives. Depending on the application, the use of anti - wear additives such as ZDDP is reduced, and other ashless additives are preferred. As a result, in hydraulic systems, it is necessary to provide a hydraulic fluid composition containing ashless additives while providing wear performance at least equal to or better than that of zinc - containing additives. The present 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, and 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 500 ppm sulfur, (b) an amount of a calcium detergent sufficient to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm of calcium to the fluid, (c) at least one metal-free phosphorus-containing antiwear agent, and (d) one or more ashless antioxidants, the hydraulic fluid has 10 ppm to 150 ppm of phosphorus, and the hydraulic fluid is substantially free of zinc.

[0006] The present invention also includes a method of lubricating a hydraulic system, the method comprising supplying a hydraulic fluid composition to the hydraulic system, the hydraulic fluid composition comprising (a) at least 90 weight percent of a base oil having less than 500 ppm sulfur, (b) an amount of a calcium detergent sufficient to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm of calcium to the fluid, (c) at least one metal-free phosphorus-containing antiwear agent, and (d) one or more ashless antioxidants, the hydraulic fluid has 10 ppm to 150 ppm of phosphorus, and the hydraulic fluid is substantially free of zinc.

[0007] The present invention also includes the use of a hydraulic fluid, the hydraulic fluid comprising, for lubricating a hydraulic system, (a) at least 90 weight percent of a base oil having less than 500 ppm sulfur, (b) an amount of a calcium detergent sufficient to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm of calcium to the fluid, (c) at least one metal-free phosphorus-containing antiwear agent, and (d) one or more ashless antioxidants, the hydraulic fluid has 10 ppm to 150 ppm of phosphorus, and the hydraulic fluid is substantially free of zinc.

[0008] The components and uses of the present invention are described in more detail in the detailed description of the invention.

Embodiments for Carrying Out the Invention

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

[0010] Oil of lubricating viscosity One component of the disclosed invention is a base oil. The base oil may be selected from any of Group I-V base oils of the American Petroleum Institute (API) Base Oil Interchangeability Guidelines, i.e., as follows. [Table 2] Groups I, II, and III are mineral oil base stocks. Oils of lubricating viscosity may include natural or synthetic oils and mixtures thereof. Mixtures of mineral and synthetic oils, such as polyalphaolefin oils and / or polyester oils, may be used.

[0011] Natural oils include animal and vegetable oils (e.g., vegetable acid esters), and mineral lubricating oils such as liquid petroleum, and paraffinic, naphthenic, or mixed paraffin-naphthenic solvent-treated or acid-treated mineral lubricating oils. 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 halo-substituted hydrocarbon oils, such as polymerized and copolymerized olefins, and mixtures thereof, alkylbenzenes, polyphenyls, alkylated diphenyl ethers, and alkylated diphenyl sulfides, and their derivatives, analogs, and homologs. Alkylene oxide polymers and interpolymers, and their derivatives, and those modified by terminal hydroxyl groups, for example, by esterification or etherification, are other classes of synthetic lubricating oils. Other suitable synthetic lubricating oils include esters of dicarboxylic acids, and those made from C5-C12 monocarboxylic acids and polyols or polyol ethers. Other synthetic oils include liquid esters of phosphorus-containing acids, high molecular weight tetrahydrofuran, silicone-based oils, such as polyalkyl oils, polyaryl oils, polyalkoxy oils, or polyaryloxysiloxane oils, and silicate oils.

[0013] Other synthetic oils include those produced by the Fischer-Tropsch reaction, typically hydroisomerized Fischer-Tropsch hydrocarbons or waxes. In one embodiment, the oil can be prepared by a Fischer-Tropsch gas liquefaction synthesis procedure, as well as other gas liquefied oils.

[0014] Natural or synthetic unrefined, refined, and re-refined oils (and mixtures thereof) of the types disclosed above can be used. Unrefined oils are those obtained directly from natural or synthetic sources without further refining treatment. Refined oils are similar to unrefined oils except that they have been further processed in one or more refining steps to improve one or more properties. Re-refined oils are obtained by a process similar to the process used to obtain refined oils applied to previously used refined oils. Re-refined oils are often further processed to remove used additives and oil degradation products.

[0015] In some embodiments, the industrial lubricating composition may contain a small 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 oil of lubricating viscosity that is present is typically the remainder left after subtracting the total amount of the compounds of the present invention and other performance additives from 100 weight percent. The oil of lubricating viscosity can be present in a major amount in the case of a lubricating composition or in a concentrate-forming amount in the case of a concentrate and / or additive composition. The industrial lubricating composition of the present invention can be either a lubricating composition or a concentrate and / or additive composition.

[0017] In a fully formulated lubricating oil composition according to the present invention, the oil of lubricating viscosity is generally present in a large amount (i.e., an amount in excess of 50 weight percent). Typically, the oil of lubricating viscosity is present in an amount of 75 to 98 weight percent, often 80 weight percent, or even in excess of 90 weight percent of the total composition.

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

[0019] In a concentrate composition, typically the amounts of additives and other components remain the same, but the amount of oil of lubricating viscosity is decreased to make the composition more concentrated and more efficient to store and / or transport. One skilled in the art will be able to readily adjust the amount of oil of lubricating viscosity present 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 contains sulfur in an amount less than 1000 weight ppm, or further less than 750 weight ppm, or further less than 500 weight ppm.

[0021] Calcium detergent Moreover, the hydraulic fluid of the present invention 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 be a neutral or overbased detergent. The overbased detergent may have a total base number (TBN) of 80 mg KOH / g to 300 mg KOH / g. The neutral detergent has a total base number (TBN) of 10 mg KOH / g or less, or further 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 selected from sulfur-free phenates, sulfur-containing phenates, sulfonates, salicylates, and mixtures thereof. In one embodiment, the metal-containing detergent is a calcium detergent selected from calcium phenates, calcium sulfonates, calcium salicylates, calcium salicylates, and mixtures thereof.

[0023] In one embodiment, the metal-containing detergent used in the hydraulic fluid of the present invention comprises an alkylated aromatic sulfonate. The sulfonate detergent may be prepared from monohydrocarbyl-substituted benzene or dihydrocarbyl-substituted benzene (or toluene, naphthalene, indenyl, indanyl, or bicyclopentadienyl) sulfonic acid, where 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 suitable alkyl groups include branched and / or linear decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, octadecenyl, nonadecyl, eicosyl, un-icosyl, do-icosyl, tri-icosyl, tetra-icosyl, penta-icosyl, hexa-icosyl, or mixtures thereof. In one embodiment, the hydraulic fluid of the present invention contains a neutral calcium salt of alkylated benzene sulfonic acid. In another embodiment, the detergent comprises a neutral calcium salt of alkylated naphthalene sulfonic acid. In another embodiment, the detergent comprises a neutral calcium salt of alkylated toluene sulfonic acid. In another embodiment, the alkyl group of the alkylated sulfonate detergent contains 6 to 20 carbon atoms.

[0024] In one embodiment, the hydraulic fluid of the present invention contains the calcium detergent described herein in an amount sufficient to deliver 5 weight ppm to 200 weight ppm, or even 10 weight ppm to 150 weight ppm, or even 20 weight ppm to 100 weight ppm of calcium to the hydraulic fluid. Phosphorus antiwear agent

[0025] In one embodiment, the hydraulic fluid of the present invention contains at least one metal-free phosphorus-containing anti-wear agent. Examples of suitable anti-wear agents include tartrates, tartramides, oil-soluble amine salts of phosphorus compounds, sulfurized olefins, phosphites (such as dibutyl or dioleyl phosphite), phosphonates, thiocarbamate-containing compounds, such as thiocarbamate esters, thiocarbamate amides, thiocarbamate ethers, alkylene-bonded thiocarbamates, bis(S-alkyldithiocarbamyl) disulfide, 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] Examples of phosphorus compounds used in the present invention may include triaryl phosphates or triaryl thiophosphates represented by the following formula (1).

Chemical formula

[0027] In formula (1), R is a hydrogen atom or an alkyl group having 3 to 9 carbon atoms, for example, having 3, 4, 5, 6, 7, 8, 9 carbon atoms, or a combination of those numbers, and X is an oxygen atom or a sulfur atom. In formula (1), the three R groups may be the same as or different from each other. Examples of alkyl groups having 4 or fewer carbon atoms include 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 formula (1) include triphenyl phosphate, tricresyl phosphate, triphenyl thiophosphate, tricresyl thiophosphate, and butylated triphenyl phosphorothionate.

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

[0030] In 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 a 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 even more preferably a branched alkylene group. Specifically, R1 is preferably, for example, -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, more preferably a linear or branched alkyl group having 4 to 6 carbon atoms. Specifically, R2 to R3 are 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 an oxygen atom. In another embodiment, both X 2 and X 3 represent a sulfur atom. 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 that may be useful in the present invention includes a thiophosphate compound represented by the following formula (3). [Chemical formula]

[0035] In formula (3), R 4 , R 5 , and R 7 are each independently a straight-chain 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 straight-chain or branched alkylene group having 1 to 8 carbon atoms, and X 4 and X 5 are each independently an oxygen atom or a sulfur atom. In one embodiment of formula (3), at least one sulfur atom is present.

[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 antiwear agent of the present invention may be selected from methyl 3-((dialkoxyphosphorothioyl)thio)propanoate having a mixed C4 / C5 alkoxy group, 3-((diisobutoxyphosphorothioyl)thio)-2-methylpropanoic acid, and mixtures thereof.

[0038] The hydraulic fluid of the present invention contains 10 to 200 weight ppm of phosphorus, or even 20 to 150 weight ppm of phosphorus. When the anti-wear agent is the only phosphorus-containing compound present in the hydraulic fluid, such a compound is present in an amount 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 contains at least one ashless antioxidant selected from a hindered phenolic ester antioxidant, an alkylated diarylamine antioxidant, or a mixture thereof. The antioxidant may be present in the lubricant in an amount of 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%.

[0040] In some embodiments, the lubricating composition may further contain at least one ashless antioxidant, and suitable antioxidants may include phenolic antioxidants that can be represented by the general formula (IV):

Chemical formula

Chemical formula

Chemical formula

[0041] In some embodiments, the antioxidant may include a sterically hindered phenol. Examples of suitable hydrocarbyl groups for sterically hindered phenols include, but are not limited to, 2-ethylhexyl or n-butyl esters, 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-tert-butylphenol), or mixtures thereof.

[0042] The antioxidant also includes aromatic amines such as those of formula (VII),

Chemical formula

Chemical formula

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

[0044] In addition to the above specific additives, the hydraulic fluid composition may also contain one or more additional other additives. In some embodiments, the additional additives can 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 surfactants can include substituted polyisobutenyl compounds. For example, useful surfactants can include (i) polyetheramines, (ii) succinimide dispersants, (iii) Mannich reaction products of dialkylamines, aldehydes, and hydrocarbyl-substituted phenols, 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 total composition. In an exemplary embodiment, the hydraulic fluid contains 0.025 wt% to 0.075 wt% of a surfactant.

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

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

[0048] Defoamers, also known as antifoaming agents, are known in the art and include organic silicones and non-silicone defoamers. Examples of organic silicones include dimethyl silicone and polysiloxane. Examples of non-silicone defoamers include copolymers of ethyl acrylate and 2-ethylhexyl acrylate, copolymers of ethyl acrylate, 2-ethylhexyl acrylate and vinyl acetate, polyethers, polyacrylates, and mixtures thereof. In some embodiments, the defoamer is a polyacrylate. The defoamer may be present in the composition at 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, alkylamines, amino alcohols, diamines, polyamines reacted sequentially with ethylene oxide or substituted ethylene oxide, or mixtures thereof. Examples of demulsifiers include polyethylene glycol, polyethylene oxide, polypropylene oxide, (ethylene oxide - propylene oxide) polymers, and mixtures thereof. In some embodiments, the demulsifier is a polyether. In one embodiment, the demulsifier may be an oxyalkylated phenol resin blend. Such blends may include formaldehyde polymers having 4 - nonylphenol, ethylene oxide, and propylene oxide, as well as formaldehyde polymers having 4 - nonylphenol ethylene oxide. The demulsifier may be present in the composition at 0.002 wt% to 0.012 wt%.

[0050] Pour point depressants are known in the art and include esters of maleic anhydride - styrene 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, alkylphenol formaldehyde condensation resins, alkyl vinyl ethers, and mixtures thereof, but are not limited thereto.

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

[0052] Suitable hydrocarbylamine salts of alkyl phosphates can be represented by the following formula,

Chemical formula

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

[0054] In one embodiment, the hydrocarbylamine salt of alkyl phosphate is C 11 ~C 14The C of Primene® 81R, a mixture of tertiary alkyl primary amines (produced and sold by Rohm & Haas). 14 ~C 18 is a reaction product of an alkylated phosphoric acid.

[0055] Hydrocarbylamine salts of dialkyldithiophosphoric acids can include rust inhibitors such as hydrocarbylamine salts of dialkyldithiophosphoric acids. These can be reaction products of heptyl or octyl or nonyldithiophosphoric acid with ethylenediamine, morpholine, or Primene® 81R, or mixtures thereof.

[0056] Hydrocarbylamine salts of hydrocarbylarylsulfonic acids may include ethylenediamine salts of dinonylnaphthalenesulfonic acid.

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

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

[0059] The hydraulic fluid may also contain a metal deactivator. The metal deactivator may be selected from derivatives of benzotriazole, 1,2,4-triazole, benzimidazole, 2-alkyldithiobenzimidazole, 2-alkyldithiobenzothiazole, or dimercaptothiadiazole. Examples of such derivatives include 2,5-dimercapto-1,3,4-thiadiazole, or its oligomers, hydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole, hydrocarbylthio-substituted 2,5-dimercapto-1,3,4-thiadiazole, or its oligomers. The oligomers of hydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole are typically formed by forming sulfur-sulfur bonds between 2,5-dimercapto-1,3,4-thiadiazole units to form two or more oligomers of the thiadiazole units. Examples of suitable thiadiazole compounds include at least one of dimercaptothiadiazole, 2,5-dimercapto-[1,3,4]-thiadiazole, 3,5-dimercapto-[1,2,4]-thiadiazole, 3,4-dimercapto-[1,2,5]-thiadiazole, or 4-5-dimercapto-[1,2,3]-thiadiazole. Typically, readily available materials such as 2,5-dimercapto-1,3,4-thiadiazole or hydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole or hydrocarbylthio-substituted 2,5-dimercapto-1,3,4-thiadiazole are commonly used. In different embodiments, the number of carbon atoms in the hydrocarbyl substituent includes 1 to 30, 2 to 25, 4 to 20, 6 to 16, or 8 to 10. 2,5-Dimercapto-1,3,4-thiadiazole may be 2,5-dioctyldithio-1,3,4-thiadiazole or 2,5-dinonyldithio-1,3,4-thiadiazole. The metal deactivator may also be described as a corrosion inhibitor.

[0060] The metal deactivator may be present in the lubricating oil composition in the range of 0 or 0.001 wt% to 0.1 wt%, 0.01 wt% to 0.04 wt%, or 0.015 wt% to 0.03 wt%. The metal deactivator may also be present in the composition at 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 in the lubricating composition at 0 wt% to 3 wt%, or 0.02 wt% to 2 wt%, or 0.05 wt% to 1 wt%.

[0062] As used herein, the terms "fatty alkyl" or "fatty" with respect to a friction modifier mean a carbon chain having 8 to 22 carbon atoms, typically a straight-chain carbon chain. Alternatively, the fatty alkyl may typically be a monobranched alkyl group branched at the β-position. Examples of monobranched alkyl groups include 2-ethylhexyl, 2-propylheptyl, or 2-octyldodecyl.

[0063] Examples of suitable friction modifiers include amines, fatty esters, or long-chain fatty acid derivatives of fatty epoxides; fatty imidazolines, such as condensation products of carboxylic acids and polyalkylene-polyamines; amine salts of alkyl phosphates; 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 polyhydroxyl fatty amines; hydroxyalkylamides; metal salts of fatty acids; metal salts of alkyl salicylates; fatty oxazolines; aliphatic ethoxylated alcohols; condensation products of carboxylic acids and polyalkylene polyamines; or reaction products of fatty carboxylic acids with guanidine, aminoguanidine, urea or thiourea, and salts thereof.

[0064] The hydraulic fluid may also include one or more viscosity modifiers. Any known viscosity modifier may be used. In one embodiment, the lubricating composition of the present invention substantially does not contain or completely does not contain poly(meth)acrylate as a viscosity modifier. Viscosity modifiers suitable for use in the present invention (often also referred to as viscosity index improvers) include polymer materials containing styrene-butadiene rubber, olefin copolymers, hydrogenated styrene-isoprene polymers, hydrogenated radical isoprene polymers, poly(meth)acrylic acid esters, polyalkylstyrenes, hydrogenated alkenylaryl conjugated diene copolymers, esters of maleic anhydride styrene copolymers, or mixtures thereof. In some embodiments, the viscosity modifier is a poly(meth)acrylic acid ester, an olefin copolymer, or a mixture thereof. The viscosity modifier may be present in the lubricant at 0 wt% to 10 wt%, 0.5 wt% to 8 wt%, 1 wt% to 6 wt%.

[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 containing transition metals. In yet another embodiment, the lubricating composition may include an additive in which calcium is the only metal. Industrial applications

[0066] According to one aspect of the exemplary embodiment, the hydraulic fluid is for use in a hydraulic system, a turbine system, or other circulating oil systems. A hydraulic system may be a device or apparatus in which the hydraulic fluid transfers energy to different parts of the system by hydraulic pressure. Turbine lubricating oil 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. Circulating oil is typically used to distribute heat to the device or apparatus through which it circulates or via them.

[0067] Viscosity grades generally suitable for hydraulic oil 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% measured by ASTM D445 or ISO 3104. Thus, ISO 46, which is 46 cSt at 40 °C, can 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 following table.

Table 3

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

[0069] The present invention has 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 500 ppm of sulfur, (b) a calcium detergent in an amount sufficient to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm of calcium to the fluid, the calcium detergent comprising or consisting of a neutral or overbased alkylated aromatic sulfonate containing a linear or branched alkyl group containing 6 to 20 carbon atoms and having a TBN of less than 10 mg KOH / g, (c) at least one metal-free phosphorus-containing antiwear 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, and contains 10 ppm to 150 ppm of phosphorus and contains less than 10 ppm or even less than 5 ppm of zinc, and includes a hydraulic fluid. In one embodiment, the calcium detergent further comprises an alkylated naphthalene sulfonic acid, a calcium phenate detergent, a calcium salicylate detergent, or a calcium salixarate detergent. The hydraulic fluid described in this paragraph also includes 0.025 wt% to 0.75 wt% of an ashless surfactant, which comprises or consists of an ashless polyisobutenyl surfactant, for example, a polyisobutenyl succinimide derived from an aromatic polyamine.

[0070] The present invention also relates to a hydraulic fluid having an ISO viscosity grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt, comprising: (a) at least 90 weight percent of a base oil having less than 500 ppm of sulfur; (b) a calcium detergent in an amount sufficient to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm of calcium to the fluid, the calcium detergent comprising or consisting of a neutral salt of an alkylated naphthalene sulfonic acid and having a TBN of less than 10 mg KOH / g; (c) at least one metal-free phosphorus-containing antiwear agent comprising or consisting of a (thio)phosphate ester; and (d) one or more ashless antioxidants in an amount of 0.02 wt% to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt%, the hydraulic fluid containing 10 ppm to 150 ppm of phosphorus and containing less than 10 ppm or even less than 5 ppm of zinc. In one embodiment, the calcium detergent further comprises a neutral or overbased alkylated aromatic sulfonate containing a straight-chain or branched alkyl group having 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 0.025 wt% to 0.75 wt% of an ashless surfactant, which comprises or consists of an ashless polyisobutenyl surfactant, for example, a polyisobutenyl succinimide derived from an aromatic polyamine.

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

[0072] In one embodiment, the present invention is a method for lubricating a hydraulic system, having an ISO viscosity grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt, comprising (a) at least 90 weight percent of a base oil having less than 500 ppm of sulfur, and (b) a calcium detergent in an amount sufficient to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm of calcium to the fluid, the calcium detergent comprising or consisting of a neutral or overbased alkylated aromatic sulfonate containing a linear or branched alkyl group containing 6 to 20 carbon atoms and having a TBN of less than 10 mg KOH / g, (c) at least one metal-free phosphorus-containing antiwear agent comprising or consisting of a (thio)phosphate ester, (d) one or more ashless antioxidants in an amount of 0.02 wt% to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt%, the hydraulic fluid containing 10 ppm to 150 ppm of phosphorus and the hydraulic fluid containing less than 10 ppm or even less than 5 ppm of zinc, and (e) 0.025 wt% to 0.75 wt% of an ashless surfactant comprising or consisting of an ashless polyisobutenyl surfactant such as a polyisobutenyl succinimide derived from an aromatic polyamine, the method comprising supplying the hydraulic fluid composition to the hydraulic system.

[0073] In another embodiment, the present invention is a method of lubricating a hydraulic system, having an ISO viscosity grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt, comprising (a) at least 90 weight percent base oil having less than 500 ppm sulfur, and (b) a calcium detergent in an amount sufficient to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm calcium to the fluid, the calcium detergent comprising or consisting of a neutral salt of alkylated naphthalene sulfonic acid and having a TBN of less than 10 mg KOH / g, (c) at least one metal-free phosphorus-containing antiwear agent comprising or consisting of a (thio)phosphate ester, (d) one or more ashless antioxidants in an amount of 0.02 wt% to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt%, and (e) an ashless surfactant in an amount of 0.025 wt% to 0.75 wt% comprising or consisting of an ashless polyisobutenyl surfactant such as a polyisobutenyl succinimide derived from an aromatic polyamine, the hydraulic fluid containing 10 ppm to 150 ppm phosphorus and the hydraulic fluid containing less than 10 ppm or even less than 5 ppm zinc, the method comprising supplying the hydraulic system.

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

[0075] The present invention also includes the use of the hydraulic fluid described herein for lubricating hydraulic system components and protecting them from wear.

[0076] In one embodiment, the present invention relates to a hydraulic fluid for lubricating a hydraulic system, having an ISO viscosity grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt, comprising (a) at least 90 weight percent of a base oil having less than 500 ppm of sulfur, and (b) a calcium detergent in an amount sufficient to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm of calcium to the fluid, the calcium detergent comprising or consisting of a neutral or overbased alkylated aromatic sulfonate containing a linear or branched alkyl group containing 6 to 20 carbon atoms, the calcium detergent having a TBN of less than 10 mg KOH / g, (c) at least one metal-free phosphorus-containing antiwear agent comprising or consisting of a (thio)phosphate ester, (d) one or more ashless antioxidants in an amount of 0.02 wt% to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt%, the hydraulic fluid containing 10 ppm to 150 ppm of phosphorus and the hydraulic fluid containing less than 10 ppm or even less than 5 ppm of zinc, and (e) 0.025 wt% to 0.75 wt% of an ashless surfactant comprising or consisting of an ashless polyisobutenyl surfactant such as a polyisobutenyl succinimide derived from an aromatic polyamine.

[0077] In another embodiment, the present invention also provides a hydraulic fluid for lubricating a hydraulic system, having an ISO viscosity grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt, comprising: (a) at least 90 wt% base oil having less than 500 ppm sulfur; (b) a calcium detergent in an amount sufficient to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm calcium to the fluid, said calcium detergent comprising or consisting of a neutral salt of alkylated naphthalene sulfonic acid and having a TBN of less than 10 mg KOH / g; (c) at least one metal-free phosphorus-containing antiwear agent comprising or consisting of a (thio)phosphate ester; (d) one or more ashless antioxidants in an amount of 0.02 wt% to 3.0 wt% or 0.03 wt% to 1.5 wt% or 0.05 wt% to 0.5 wt%, said hydraulic fluid containing 10 ppm to 150 ppm phosphorus and said hydraulic fluid containing less than 10 ppm or even less than 5 ppm zinc; and (e) 0.025 wt% to 0.75 wt% ashless surfactant comprising or consisting of an ashless polyisobutenyl surfactant such as polyisobutenyl succinimide derived from aromatic polyamine.

[0078] A series of exemplary hydraulic lubricant compositions were prepared and evaluated as summarized in Table 1. Unless otherwise specified, all treatment rates are oil-free (i.e., active). The fluids of the examples were evaluated using a Mini-Traction Machine (MTM test) and a Bosch-Rexroth pump test as described below. [Table 1] 1. Nonylated naphthalene sulfonic acid, Ca salt, TBN 1.0, 50% diluted oil 2. Methyl 3-((dialkoxyphosphorothioyl)thio)propanoate having a mixed C4 / C5 alkoxy group 3. 3-((Diisobutoxyphosphorothioyl)thio)-2-methylpropanoic acid 4. 4,4'-Methylenebis(dibutyldithiocarbamate) 5. Succinimide derived from aromatic polyamine (PIB Mn 2300Da; TBN 0.1mg KOH / g) (containing 50 wt% oil) 6. Other additives include corrosion inhibitors, demulsifiers, defoaming additives, diluent oils, and pour point depressants. 7. The compositions of the examples were evaluated for coefficient of friction using a Mini Traction Machine (MTM) available from PCS Instruments. The test configuration consisted of a bearing steel ball approximately 19.05 mm (3 / 4 inch) in diameter contacting an highly polished surface on a bearing steel disk 46 mm in diameter. The ball contacted the disk and spin at the contact was eliminated. The rolling speed, slide / roll ratio, temperature, and load were parameters that could be varied during each test. The specimen speed was independently controlled using a servo motor to generate the desired slide / roll motion at contact. The specimen was contained in a sealed temperature-controlled reservoir that held approximately 35 mL of the fluid sample. The test temperature was controlled by an electric heater and the fluid temperature was monitored. The contact was automatically loaded to the desired Hertz pressure and the ball and disk speeds were controlled by electric motors. A series of tests performed for this study were conducted at a Hertz pressure of approximately 1.00 GPa, a temperature of approximately 100 °C, a rolling speed of approximately 100 mm / s, and a fixed slide-to-roll ratio of approximately 100%. The tests were conducted in 10-minute steps and the total time was approximately 120 minutes. After each 10-minute step, the rolling / sliding motion at the contact between the ball and the disk was stopped. The portion of the ball contacting the disk was pressed against a glass window. Images of the contact area on the ball were recorded using a microscope and a camera. The test was then continued for the next 10-minute segment. At the end of the 120-minute test, the recorded images were visually examined and then analyzed to examine the formation of the reacted film (friction film) and the change in its thickness over each 10-minute test sequence. A record of the film formation and change in film thickness was then created over the 120-minute test time. 8. "Rexroth Fluid Test Axial Piston Units Closed Loop Applications (RFT-APU-CL)", Bosch procedure number RE 96270, which is available upon request on 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 would measurably affect the relevant properties of the fluid. "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 substances as contaminants. "Substantially free" may also mean that the material in question may be present in an amount lower than the detection limit of standard test methods currently known to those skilled in the art or developed in the future. In some embodiments, "substantially free" may mean less than 10 weight ppm, or even less than 5 weight ppm.

[0080] Since some of the materials described above may interact in the final formulation, it is known that the components of the final formulation may be different from those initially added. The products formed herein, including the products formed when using the lubricant compositions of the present invention in their intended use, may not be easily described. Nevertheless, all such modifications and reaction products are included within the scope of the present invention. The present invention encompasses lubricant compositions prepared by mixing the above components.

[0081] Each of the documents referred to above is incorporated herein by reference. Except for examples, or unless otherwise explicitly indicated, all quantities in this description specifying amounts of materials, reaction conditions, molecular weights, numbers of carbon atoms, etc. are to be understood as being modified by the term "about". Unless otherwise indicated, each chemical substance or composition referred to in this specification is to be construed as a commercial grade substance that may contain isomers, by-products, derivatives, and other such materials that are normally understood to be present in commercial grades. However, the amounts of each chemical component are presented excluding any solvent or diluent oil that may typically be present in a commercial material, unless otherwise indicated. It should be understood that the upper and lower limits of the amounts, ranges, and ratios described herein may be combined independently. Similarly, the ranges and amounts of each element of this specification may be used with any range or amount of other elements.

[0082] Although the invention has been described in connection with its preferred embodiments, it should be understood that various modifications will be apparent to those skilled in the art upon reading this specification. Accordingly, 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.

Claims

1. A hydraulic fluid comprising: (a) at least 90 weight percent of a base oil having less than 500 ppm of sulfur; (b) a calcium detergent in an amount to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm of calcium to the fluid; (c) at least one metal-free phosphorus-containing antiwear agent; and (d) one or more ashless antioxidants, the hydraulic fluid having 10 ppm to 150 ppm of phosphorus and being substantially free of zinc.

2. The hydraulic fluid according to claim 1, wherein the calcium detergent comprises an alkylated aromatic sulfonate.

3. The hydraulic fluid according to claim 2, wherein the calcium detergent comprises a neutral or overbased salt of an alkylated aromatic sulfonic acid.

4. The hydraulic fluid according to claim 3, wherein the calcium detergent comprises or consists of a neutral salt of an alkylated aromatic sulfonic acid.

5. The hydraulic fluid according to any one of claims 1 to 4, wherein the alkylated aromatic sulfonic acid comprises an alkyl group containing 6 to 20 carbon atoms.

6. The hydraulic fluid according to claim 5, wherein the alkyl group is branched.

7. The hydraulic fluid according to claim 5, wherein the alkyl group is linear.

8. The hydraulic fluid according to any one of claims 1 to 7, wherein the calcium detergent comprises or consists of a neutral salt of an alkylated naphthalene sulfonic acid.

9. The hydraulic fluid according to any one of claims 1 to 8, wherein the calcium detergent further comprises a calcium phenate detergent, a calcium salicylate detergent, or a calcium salixarate detergent.

10. The hydraulic fluid according to any one of claims 1 to 9, wherein the total base number of the calcium detergent is less than 10 mg KOH / g according to ASTM D4739.

11. The hydraulic fluid according to any one of claims 1 to 10, wherein the metal-free phosphorus-containing antiwear agent comprises or consists of a (thio)phosphate ester.

12. The hydraulic fluid according to any one of claims 1 to 11, wherein the fluid comprises 0.02 weight percent to 3.0 weight percent, or 0.03 weight percent to 1.5 weight percent, or 0.05 weight percent to 0.5 weight percent of the antioxidant.

13. The hydraulic fluid according to any one of claims 1 to 12, further comprising an ashless surfactant.

14. The hydraulic fluid according to claim 13, wherein the ashless surfactant comprises or consists of an ashless polyisobutenyl surfactant.

15. The hydraulic fluid according to claim 14, wherein the ashless polyisobutenyl surfactant comprises or consists of a substituted polyisobutenyl compound.

16. The hydraulic fluid according to claim 15, wherein the substituted polyisobutenyl compound comprises or consists of a polyisobutenyl succinimide derived from an aromatic polyamine.

17. The hydraulic fluid according to any one of claims 13 to 16, wherein the fluid comprises 0.025 to 0.75 weight percent of the ashless surfactant.

18. The hydraulic fluid according to any one of claims 1 to 17, wherein the fluid has an ISO viscosity grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt.

19. The hydraulic fluid according to any one of claims 1 to 18, wherein the fluid contains less than 10 ppm or even less than 5 ppm of zinc.

20. A method of lubricating a hydraulic system, the method comprising supplying to the hydraulic system a hydraulic fluid composition according to any one of claims 1 to 19.

21. The method according to claim 20, wherein the hydraulic system is operated at a pressure of 300 bar or more.

22. The method according to claim 20 or 21, wherein the hydraulic system comprises a pump operating at a speed of 2500 revolutions per minute or more.

23. Use of a composition according to any one of claims 1 to 19 for lubricating a hydraulic system.

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