Lubricating Composition

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

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.

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.

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.

In one embodiment, the hydraulic fluid comprises (a) at least 90 weight percent of a 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, (c) at least one metal-free phosphorus containing anti-wear agent, and (d) one or more ashless antioxidants, wherein the hydraulic fluid as 10 ppm to 150 ppm phosphorus and wherein the hydraulic fluid is substantially free of zinc.

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 500 ppm sulfur, (b) a calcium detergent in an amount sufficient to deliver 5 ppm to 200 ppm or 5ppm to 150 ppm or 5 ppm to 100 ppm 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 10 ppm to 150 ppm phosphorus and wherein the hydraulic fluid is substantially free of zinc.

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 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, (c) at least one metal-free phosphorus containing anti-wear agent, and (d) one or more ashless antioxidants, wherein the hydraulic fluid as 10 ppm to 150 ppm phosphorus and wherein the hydraulic fluid is substantially free of zinc to lubricate a hydraulic system.

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

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.

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

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.

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.

Synthetic oils include hydrocarbon oils and halosubstituted 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.

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.

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.

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.

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.

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.

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.

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.

In one embodiment of the present invention, the base oil used in the hydraulic fluid of the present invention will contain less than 1000 ppm by weight, or even less than 750 ppm by weight, or even less than 500 ppm by weight sulfur.

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.

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.

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.

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.

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, thiocarbamate-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.

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

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.

Examples of the phosphorus compound represented by the formula (1) include triphenyl phosphate, tricresyl phosphate, triphenyl thiophosphate, tricresyl thiophosphate, and butylated triphenyl phosphorothionate.

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

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 Xand Xeach, independently, represent an oxygen atom or sulfur atom.

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—.

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.

In one embodiment, both Xand Xrepresent oxygen atoms. In another embodiment, both Xand Xrepresent sulfur atoms. In another embodiment, Xis oxygen and Xis sulfur, and in another embodiment, Xis sulfur and Xis oxygen.

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

In the formula (3), R, Rand Rare 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. Ris a linear or branched alkylene group having 1 to 8 carbon atoms, Xand Xare each independently an oxygen atom or sulfur atom. In one embodiment of formula (3), at least one sulfur atom exists.

In one embodiment, both Xand Xrepresent oxygen atoms. In another embodiment, both Xand Xrepresent sulfur atoms. In another embodiment, Xis oxygen and Xis sulfur, and in another embodiment, Xis sulfur and Xis oxygen.

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.

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.

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.

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 (IV):

wherein Ris 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):