Aqueous Lubricant

1. Field of the Invention

This invention relates to water-content hydraulic fluids and more particularly a concentrate for addition to water for the preparation of water-content hydraulic fluids. The invention further relates to a method of lubricating with water-content hydraulic fluids which may contain up to 95% or more water.

2. Description of the Prior Art

Heretofore, the technology of lubrication generally centered about the development of petroleum oils for lubricants or greases and the application of the lubricant so prepared to the point of wear or friction. Innumerable and complex lubricating compositions have been proposed comprising, generally, a hydrocarbon oil, a bodying or thickening ingredient and various additive agents designed to enhance the lubricant with respect to viscosity, foam stability, antiwear, and corrosion prevention properties. More recently, current interest has been directed to the preparation of aqueous lubricants, particularly water-content hydraulic fluids, due to the increasing cost of petroleum oils, the problem of flammability and the ever increasing problem of suitable disposal of contaminated or spent petroleum-based fluids. Water-content hydraulic fluids containing up to 95 percent or more water offer an obvious cost advantage over petroleum-based hydraulic fluids but because of their viscosity suffer the disadvantage of being susceptible to leakage, thereby resulting in loss of volumetric efficiency and markedly reducing the service life of hydraulic pumps. Although primarily used for transmitting forces, water-content hydraulic fluids must provide lubrication for impellers, support bearings, rings, gears, pistons, and the like, with a minimum of internal leakage in order to prevent excessive wear and failure of such parts.

It is known from U.S. Pat. No. 4,215,002 to prepare water-content hydraulic fluids by adding to water 0.5 to 4 wt.% of a blend of C.sub.6-18 alkylphosphonate or an amine adduct thereof and an ethoxylate of an acid or an alcohol containing from 3 to 20 ethoxy groups wherein the acid or alcohol is derived from fatty or synthetic sources.

U.S. Pat. No. 4,225,447 discloses an emulsifiable concentrate for use in water-in-oil fire-resistant hydraulic fluids comprising a lubricant and an alkenylsuccinic anhydride or a salt thereof.

U.S. Pat. No. 4,253,975 discloses an aqueous hydraulic fluid containing a metal dithiophosphate and a system of solubilizers therefor.

It is also known from U.S. Pat. No. 4,289,636 to provide aqueous lubricating compositions comprising water and a minor amount of a water-soluble amide derived from primary and secondary alkyl amines and succinic, tetrahydrophthalic or tetrahydrofuran tetracarboxylic acids. The amide is effective as a corrosion or antirust inhibitor. Aqueous lubricant formulations containing the amide in combination with other known special purpose additives provide a blend having good hard water stability characteristics.

U.S. Pat. Nos. 3,826,745 and 3,838,049 disclose the use of polyisobutylene polymers in lubricating compositions for internal combustion engines.

U.S. Pat. No. 4,212,750 discloses a water-based metal working lubricant which may contain at least about 2 parts by weight polyisobutylene.

The prior art does not disclose the use of polyisobutylene in high water-content hydraulic fluids in combination with the emulsifier/dispersant and antiwear/antirust inhibitor systems described herein.

In accordance with the present invention, an improved water-content hydraulic fluid having a reduced tendency to leak is prepared by admixing a small amount of polyisobutylene polymer with a soluble oil concentrate comprising an appropriate base oil blended with certain emulsifier/dispersant and antiwear/antirust inhibitor systems. Such concentrates, when mixed with a sufficient quantity of water, are capable of forming stable, translucent oil-in-water emulsions in which the oil is present as the continuous phase. When used as high water-content hydraulic fluids, significant improvement is obtained whereby the tendency of the fluids to internally leak in hydraulic systems is minimized, thereby reducing the loss of volumetric efficiency in hydraulic pumps conventionally used for industrial applications. Additionally, the water-content hydraulic fluids are excellent lubricants which are characterized by improved wear-preventing characteristics and antirust performance.

The polyisobutylene polymers used for purposes of the invention are known materials having a mean molecular weight between about 500 and 2000 and preferably between 1000 and 1500. These polymers are generally obtained by polymerizing C.sub.4 mono-olefins in the presence of a Friedel-Crafts catalyst to obtain polymer mixtures containing primarily polyisobutylene and polybutylene in varying proportions. Typical polymer mixtures will contain about 10 to 80% polyisobutylene and 80 to 20% of polybutylene. It is to be understood that either of these polymers may be used since such polymers are similar with regard to performance. Further, since the polymers contain a terminal group which is unsaturated they may be saturated by hydrogenation.

The polyisobutylene polymer may be added to the concentrate before dilution with water. Based on the soluble oil concentrate, the amount of polymer employed ranges from 0.001 to 3.0 percent by weight.

In addition to the polyisobutylene polymer, the soluble oil concentrate contains from about 25 to 60 percent by weight of an emulsifier/dispersant and about 10 to 20 percent by weight of an antiwear/antirust inhibitor system. The balance of the concentrate comprises the base oil and, possibly, minor amounts of other additives conventionally employed to impart certain properties. Among such additives are defoamers, metal deactivators, antibacterial agents, and the like. In practicing the invention, the concentrate is simply diluted with distilled or deionized water to provide hydraulic fluids consisting of about 80 to 99 weight percent water and 0.005 to 20.0 percent concentrate. On the basis of results obtained, improvement in flow rates and volumetric efficiency losses are achieved when the amount of the total concentrate used is less than 5.0% based on the weight of the aqueous hydraulic fluid composition.

The emulsifier/dispersant systems used for purposes of the invention include a wide variety of anionic, cationic and nonionic compounds which are well known in the art and have been employed for this purpose. Any compatible combination of emulsifying or dispersing agent can be employed. Likewise, compounds which possess both emulsifying and dispersing properties may be employed alone or in combination with other emulsifiers and/or dispersants. The emulsifier/dispersant systems serve to disperse the antirust and antiwear additives in the aqueous phase of the water-content fluids and hence various combinations are thus possible for this purpose.

Typical anionic emulsifiers suitable for the present invention are amine soaps, and the like. Such soaps are prepared by the reaction of an amine with a fatty acid such as palmitic acid, lauric acid, oleic acid, myristic acid, tall oil acids, palm oil acids, or the like, in about stoichiometric amounts at room temperature or slightly elevated temperatures. Examples of amine soaps include triethanolamine stearate, triethanolamine oleate, triethanolamine coconut oil soap, isopropanolamine oleate, N,N-oleate, and the like.

The cationic emulsifiers contemplated herein are the combination of an organic acid, such as cyclic imidazoline, tertiary ethyloxylated soya amine, tallow polyethoxylated amine having two ethoxy units in the polyethoxylated position of the molecule, oleyl polyethoxylated amines having two to five ethoxy units in the polyethoxylated portion of the molecule, soya polyethoxylated amine having five ethoxy units in the polyethoxylated portion of the molecule, and the like.

Other emulsifiers include the alkali and alkaline earth metal salts of fatty acids, rosin acids and naphthenic acids. Preferred fatty acids are the wood, gum and rosin acids derived from crude tall oil and various distilled products of tall oil. Tall oil is a byproduct of the sulfate industry where it is found in the sulfide liquor that has been used to digest wood. The oil is a crude product containing various unsaturated fatty acids, chiefly oleic and linoleic, rosin acids and some unsaponifiable materials. The crude tall oil can be employed as such in the invention, however, more suitably, the metal salts or soaps of various refined of distilled products of the crude oil are employed. Examples of these are the tall oil distillate that contains only slight amounts of rosin acids and from about 75-90% unsaturated fatty acids. Other products are distilled tall oil having 25-35% rosin acids and 60-75% fatty acids. The tall oil pitch from the distillation has from about 20-25% rosin acids and 30-40% unsaturated fatty acids, the balance being unsaponifiable material.

The alkali and alkaline salts of rosin acids are water insoluble and are highly useful emulsifiers for purposes of the invention. Additionally, they also aid in sealing the tolerances between the moving surfaces of hydaulic pumps.

Other emulsifiers which can be employed are nonionic and include the polyalkylene glycol ethers containing from about 4 to about 80 mols of alkylene oxide. Illustrative non-ionic emulsifiers are the nonylphenyl polyethylene glycol ethers containing about 4 moles of ethylene oxide, the trimethylnonyl polyethylene glycol ethers containing about 6 moles ethylene oxide, the nonylphenyl polyethylene glycol ethers containing about 7 moles of ethylene oxide, mixed polyalkylene glycol ethers containing about 60 moles of a mixture of ethylene oxide and 1,2-propylene oxide in a mole ratio of about 2:1. The nonionic emulsifiers are well known in the art and may be prepared by condensing a 1,2 alkylene oxide, preferably ethylene oxide, with an organic compound containing at least 6 carbon atoms and a reactive hydrogen atom such as alcohols, phenols, thiols, primary and secondary amines and carboxylic and sulfonic acids and their amides. The amount of alkylene oxide or equivalent condensed with a reactive chain will generally depend upon the particular compound employed. About 20 and 85 percent by weight of combined alkylene oxide is generally obtained in a condensation product, however, the optimum amount of alkylene oxide or equivalent utilized will depend upon the desired hydro-phobiclipophilic balance desired.

The preferred dispersant used herein is the reaction product of amine with an alkyl or alkenyl succinic acid anhydride. Any alkyl or alkenyl succinic acid anhydride or the corresponding acid is utilizable in the present invention. The general structural formulae of these compounds are: ##STR1## wherein R is an alkyl or alkenyl radical. When R is alkenyl, the alkenyl radical can be straight-chain or branched-chain; and it can be saturated at the point of unsaturation by the addition of a substance which adds to olefinic double bonds, such as hydrogen, sulfur, bromine, chlorine, or iodine. It is obvious, of course, that there must be at least two carbon atoms in the alkenyl radical, but there is no real upper limit to the number of carbon atoms therein. The alkyl and alkenyl succinic acid anhydrides and succinic acids are interchangeable for the purposes of the present invention.

The methods of preparing the alkenyl succinic acid anhydrides are well known to those familiar with the art. The most feasible method is by the reaction of an olefin with maleic acid anhydride.

A more detailed description of the alkenyl succinic anhydrides suitable for use in the above formulations and their preparation is disclosed in U.S. Pat. No. 2,638,450, issued May 12, 1953.

Any alkyl or alkenyl succinic acid, the alkyl or alkenyl substituent of which contains from about 6 to about 22 carbon atoms may be employed for reaction with the amine. Typically representative of such alkyl or alkenyl succinic acids, are tetrapropenyl-succinic, octenylsuccinic, dodecenylsuccinic, polybutenylsuccinic, hexadecenylsuccinic, triacontenylsuccinic and isooctadecylsuccinic acids. Especially preferred materals are alkenylsuccinic anhydrides wherein the alkenyl radical is derived from an olefin containing 2 to 10 carbon atoms and has an average molecular weight of from about 300 to 3000, preferably about 900 to about 1300.

The alkyl or alkenyl succinic acid anhydrides are reacted with an amine such as the aforementioned amines listed for preparation of the cationic emulsifiers. The reaction is carried out at temperatures of about 150.degree. C. to 250.degree. C. and the exact composition of the resulting product mixture is extremely complex depending upon whether primary amines or tertiary hydroxy amines enter into the reaction. This may be illustrated as follows: ##STR2##

The neat concentrate will contain about 25 to 60 percent by weight of the emulsifier/dispersant system in which the emulsifier is present in an amount ranging from 20 to 50 percent by weight or more.

The antiwear/antirust inhibitor system is present in amounts ranging from about 10 to 20 percent by weight based on the weight of the neat concentrate. It is contemplated that a wide variety of additives conventionally employed to impart antiwear and antirust properties may be used. Specifically useful antiwear inhibitors are zinc dialkyl dithiophosphates such as zinc di (iso-octyl primary) dithiophosphate, zinc di (n-octyl primary) dithiophosphate, zinc butyl hexyl dithiophosphate, zinc butyl, 1,2-di methylpropyl dithiophosphate and zinc di (4 methyl-2-pentyl) dithiophosphate.

Although the zinc dialkyl dithiophosphates provide antiwear and some antirust properties, it has been found desirable to add an additional antirust inhibitor to the concentrate such as a metal dialkylnaphthalene sulfonate. The metal dialkylnaphthalene sulfonate has a sulfonate group attached to one ring of the naphthalene nucleus and an alkyl group attached to each ring. Each alkyl group can independently contain from about six to about twenty carbon atoms, but it is preferred that they contain from about eight to twelve carbon atoms. The dialkylnaphthalene sulfonate group is attached to the metal through the sulfonate group. In the case of monovalent metals, one dialkylnaphthalene sulfonate group is attached to each metal atom while there are two groups attached to each atom of a divalent metal. Calcium, barium, sodium, magnesium and lithium can be used as the metal, but it is preferred to use calcium as the metal in the sulfonate. The metal dialkylnaphthalene sulfonate is used in amounts of 30 to 60 percent by weight based on the weight of the combined antiwear/antirust inhibitor system.

The oil vehicles employed in the composition of the present invention may comprise mineral oils, synthetic oils, especially synthetic hydrocarbon oils, or combinations of mineral oils with synthetic oils of lubricating viscosity. When high temperature stability is not a requirement, mineral oils having a viscosity of at least 40 SSU at 100.degree. F., and particularly those falling within the range from about 60 SSU to about 6,000 SSU at 100.degree. F. may be employed. In instances where synthetic vehicles are employed, either alone or in addition to mineral oils, as the lubricating vehicle, various compounds of this type may be successfully utilized. Typical synthetic vehicles include polypropylene glycol, trimethylopropane esters, neopentyl and pentaerythritol esters, di-(2-ethyl hexyl-sebacate, di-(2-ethyl hexyl) adipate, dibutyl phthalate, fluorocarbons, silicate esters, silanes, esters of phosphorus-containing acids, liquid ureas, ferrocene derivatives, hydrogenated mineral oils, chain-type polyphenols, siloxanes and silicones (poly-siloxanes), alkyl-substituted diphenyl ethers typified by a butyl-substituted bis-(p-phenoxy phenyl)ether, phenoxy phenyl ethers, and the like.

The synthetic hydrocarbons which may be used are of the type normally made by polymerizing monoolefins in the presence of a suitable catalyst, such as BF.sub.3 or AlCl.sub.3. The lower olefins may be employed for the purpose provided the degree of polymerization is sufficient. The lower olefins include, for example, ethylene, propylene, butylene and the like. Those useful in the practice of this invention preferably contain at least 30 carbon atoms. One such member is made by trimerizing decene. The synthetic hydrocarbon, or polyolefin, suitable for use in this invention may have an upper limit of about 75 carbon atoms. Such hydrocarbon fluids retain their fluidity at the lower temperatures and have enhanced resistance to flame and explosion hazards.

In combination with the aforementioned emulsifier/dispersant and antiwear/antirust systems, other additives may be employed to impart certain desired properties. An alkali metal nitrite may also be employed in the formulation in order to impart increased antirust properties to the lubricant composition. In this respect, more specific increased resistance to copper corrosion may be obtained by the use of the sodium salt of mercaptobenzothioazole. In addition, the overall performance properties of the lubricant composition may be enchanced by the addition of germicidal agents, particularly phenolic materials such as phenol, sodium salts of orthophenylphenol, chlorinated phenols, such as hexachlorophene, tetrachlorophenol and p-chloro-m-xylenol, and also boric acid or oxides of boron. In order to obtain fungus protection, improve the rust protection properties, and also to function as a load-support agent, an alkali metal hydroxide, serving to raise the pH of the system, may be employed. These may include, for example, sodium, lithium or potassium hydroxide. Furthermore, if desired, various water-soluble chelating agents may be employed to soften the water vehicle. Thus, for example, the sodium salt of diethylene triamine pentaacetic acid or salts of ethylenediamine tetraacetic acid or nitrilotriacetic acid can be used.

The alkali metal nitrite, when included in the final formulation is generally employed in an amount from about 0.1 to about 10 percent, and preferably from about 0.1 to about 5 percent, by weight. When the sodium salt of mercaptobenzothiazole is included in the formulation, this material is generally present in an amount from about 0.1 to about 6 percent, preferably from about 0.1 to about 3 percent, by weight. The germicidal agents disclosed above, when present, are generally employed in amount from about 0.05 to about 3 percent, and preferably from about 0.05 to about 1.5 percent, by weight. The water-soluble boron additive, e.g., boric acid, when present, is generally employed in an amount from about 0.1 to about 5 percent, and preferably from about 0.1 to about 3 percent, by weight. The alkali metal hydroxide, e.g., sodium hydroxide, is employed in an amount from about 0.1 to about 1.5 percent, by weight when present. When any of the aforementioned chelating agents or additive agents are employed, these are generally present in an amount from about 0.1 to about 5 percent, by weight.

The following examples illustrate the best mode now contemplated for carrying out the invention.

A concentrate which can be added to water to provide high water based fluids was prepared according to the following recipe:

Two parts by weight of a polyisobutylene polymer having an average molecular weight of about 2000 (Lubrizol 3174) were mixed with 98 parts by weight of the concentrate of Example 1.

Two parts by weight of a polyisobutylene polymer having an average molecular weight of about 1500 (Lubrizol 5183) were mixed with 98 parts by weight of the concentrate of Example 1.

One part by weight of a polyisobutylene polymer having an average molecular weight of about 1,000,000 was mixed with 99 parts by weight of the concentrate of Example 1.

The compositions of Examples 1 to 4 were admixed with water to provide high water base fluids and then evaluated for volumetric efficiency by the Vickers V-104C Vane Pump Test (Modified ASTM D-2882). In this test, hydraulic fluid is drawn from a closed sump to the intake side of a Vickers V-104C vane-type pump. The pump is driven by, and directly coupled to, a twenty-five horsepower, 1250 rpm electric motor. The fluid is discharged from the pump through a pressure regulating valve. From there it passes through a calibrated venturi (used to measure flow rate) and back to the sump. Cooling of the fluid is accomplished by a heat exchanger through which cold water is circulated. No external heat is required, the fluid temperature being raised by the frictional heat resulting from the pump's work on the fluid. Excess heat is removed by passing the fluid through the heat exchanger prior to return to the sump. The Vickers V-104C vane-type pump comprises a cylindrical enclosure (the pump body) in which there is housed a so-called "pump cartridge". The "pump cartridge" assembly consists of front and rear circular, bronze bushings, a rotor, a cam-ring and rectangular vanes. The bushings and cam-ring are supported by the body of the pump and the rotor is connected to a shaft which is turned by an electric motor. A plurality of removable vanes are inserted into slots in the periphery of the rotor. The cam-ring encircles the rotor and the rotor and vanes are enclosed by the cam-ring and bushings. The inner surface of the cam-ring is cam-shaped. Turning the rotor results in a change in displacement of each cavity enclosed by the rotor, the cam-ring, two adjacent vanes and the bushings. The body is ported to allow fluid to enter and leave the cavity as rotation occurs.

The test procedure used herein involves circulating 5 gallons of the water based fluid through the pump apparatus at a temperature of 120.+-.3.degree. F. for 100 hours. The pump is run at 1200.+-.60 rpm at a pump discharge pressure (load) of 800.+-.15 psi. Flow rate in gallon per minute is measured and recorded every four hours. The flow rates reported in Table I are averaged over the 100 hours operation. Leakage flow is calculated by subtracting average flow rate from a rated flow rate of 7.2 gpm for this type of pump. Volumetric efficiency loss is defined as: ##EQU1##

As shown below in Table I, the use of polyisobutylene polymers provides unexpected results in reducing internal leakage in hydraulic pumps, thereby increasing flow rate and volumetric pump efficiency.