WO2011126736A1 - Zinc salicylates for rust inhibition in lubricants - Google Patents

Abstract

A useful lubricant is prepared from (a) an oil of lubricating viscosity; (b) a zinc salt of a hydrocarbyl-substituted salicylic acid; (c) a propylene glycol polymer having a number average molecular weight of about 400 to about 10,000 and having terminal OH groups; and (d) at least about 0.02 percent by weight of a metal dihydrocarbyldithiophosphate.

Description

TITLE

Zinc Salicylates for Rust Inhibition in Lubricants

BACKGROUND OF THE INVENTION

[0001] The disclosed technology relates to lubricants for internal combustion engines, which lubricants exhibit good resistance to rust and corrosion.

[0002] The lubricants used for internal combustion engines must perform many functions. Besides reducing the friction between metal parts of the engine, they also must provide protection against wear, aid in removal or distribution of heat (while themselves being resistant to oxidative and thermal degradation), neutralize acidic combustion products, disperse soot and other contaminants that may appear in oil in a lubricant sump, promote engine cleanliness, and many others. They should also impart corrosion resistance and rust resistance.

[0003] Certain lubricating oils seek to preserve and protect both spark -ignition and compression ignition engines used in harsh service environments such as found in certain military engine applications. Such oils are sometimes also used as power transmission fluids in certain military vehicles. Other vehicle components that may be found, and which typically require lubrication, include power take-offs, wet brakes, hydraulic devices, and manual transmissions. One important criterion for such fluids is that they perform well in the Acid Neutralization Test (4.3.3.9.3 of United States MIL-PRF-21260E Specifications), in this test, the oil must neutralize a hydrobromic acid solution while assuring that rusting does not occur over time on steel parts, in particular, steel panels that are used for this test.

[0004] Many lubricants have been proposed as lubricants for Internal combustion engines. For instance, U.S. Patent Application Publication 2008/ 01 1 9377, Devlin et al., May 22, 2008, discloses a lubricant composition comprising a base oil and an additive composition comprising, for example a detergent and an additive chosen from various enumerated classes (mentioning, La., dispersants and corrosion inhibitors). Examples of suitable metal-containing detergents include, among others, a zinc salicylate. Also disclosed is a method of lubricating a machine such as an engine.

[0005] U.S. Patent Application Publication 2009/001 1963, Anderson et al., January 8, 2009, discloses a lubricant system for a truck fleet comprising an engine oil, a transmission fluid, and a gear oil. The engine oil comprises at least one additive chosen from a viscosity index improver, a dispersant, a detergent, an anti-oxidant, and an antiwear compound. A suitable detergent can include an oil-soluble neutral or overbased salt of alkali or alkaline earth metal with an acidic substance from, among others listed, a salicylic acid. Examples include, among others, a zinc salicylate.

[0006] U.S. Patent. Application Publication 2009/0156446, McAtee et al, June 18, 2009, discloses a lubricating composition containing, among other materials, a corrosion inhibitor comprising monomeric units of oxyalkylene groups.

[0007] U.S. Patent Application Publication 2004/0242441 , Chiu, December 2, 2004, discloses a continuously variable transmission fluid comprising a hydrogenated cyclic dirner and a low temperature viscosity control agent. The low temperature viscosity control agent may be, among other materials, poly- ether oils. Polyether oils include polya!kylene oxides, and in particular, polyethylene oxides, polypropylene oxides, polybutylene oxides, and mixtures thereof. The polyether oil typically has a molecular weight in the ranges suitable for maintaining an appropriate viscosity and non-volatility. The low temperature viscosity control agent may have a viscosity of less than 2.5x 10^-6 m²/s at 100°C. Its amount should preferably be about 1 to 20 percent by weight. Another component of the lubricant formulation may be an oil soluble zinc salt. Suitable zinc salts include zinc phosphates, phosphites, phosphonates, sulfonates, carboxylates, phenates, and salicylates. The CVT fluids should be substantially free from any thiophosphate derivatives.

[0008] U.S. Patent 6,482,778, Tersigni et al., November 19, 2002, discloses transmission fluid composition comprising a zinc detergent and at least one phosphorus-containing additive. Neutral zinc detergents include, among others, zinc salicylates. The transmission fluids may also contain a metal dihydrocarbyl dithiophosphate; the metal may be zinc.

[0009] U.S. Patent 6,2 1 4,778, Todd, April 10, 2001 , discloses a grease composition comprising a major amount of an oil of lubricating viscosity; a thickener, and an oil soluble neutral or overbased salt of a carboxylic acid such as, among others, the zinc salts of hydrocarbyl-substituted salicylic acids.

[0010] European Patent Application EP 0 604 21 8, Konzman, June 29, 1994, discloses a functional fluid which includes an oil and an additive composition of a metal salt of a thiophosphorus acid and a salt of a salicylic acid, which is said to exhibit improved thermal and hydroiytic stability, even in the presence of acid rust inhibitors. The salicylic acid is in the form of a zinc salt. Miscellane- ous additives include, among others, corrosion inhibitors.

[0011] The disclosed technology solves the problem of providing an engine lubricant with one or more of good acid neutralization, anti-rust, and anticorro-

? sion properties, by including in said lubricant a zinc salt of a hydrocarbyl salicylate and a polypropylene oxide. This may be particularly advantageous for equipment that is not in use for an extended period of time.

SUMMARY OF THE INVENTION

[0012] The disclosed technology provides a lubricant composition comprising: (a) an oil of lubricating viscosity; (b) a zinc salt of a hydrocarbyl- substituted salicylic acid; and (c) a polypropylene glycol having a number average molecular weight of 400 to 10,000 and having terminal OH groups, and at least 0.02 percent by weight of a metal dihydrocarbyldithiophosphate.

[0013] The disclosed technology further provides a method for lubricating an internal combustion engine, comprising supplying thereto the lubricant composition disclosed herein,

[0014] In other embodiments, the disclosed technology provides a method for lubricating an internal combustion engine, or for lubricating a metal-working operation, comprising supplying thereto a lubricant composition comprising: (a) an oil of lubricating viscosity; (b) a zinc salt of a hydrocarbyl-substituted salicylic acid; and (c) a polypropylene glycol having a number average molecular weight of 400 to 10,000 and having terminal OH groups.

[0015] In yet another embodiment, the disclosed technology provides a method for protecting a metal surface, comprising applying to said surface a lubricant composition comprising: (a) an oil of lubricating viscosity; (b) a zinc salt of a hydrocarbyl-substituted salicylic acid; and (c) a propylene glycol polymer having a number average molecular weight of 400 to 1 0,000 and having terminal OH groups.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Various preferred features and embodiments will be described below by way of non-limiting illustration.

[0017] The amount of each chemical component described is presented exclusive of any solvent or diluent oil, which may be customarily present in the commercial material, that is, on an active chemical basis, unless otherwise indicated. However, 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.

[0018] As used herein, the term "hydrocarbyl substituent" or "hydrocarbyl group" is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the molecule and having predominantly hydrocarbon character. Examples of hydrocarbyl groups include: hydrocarbon substituents, including aliphatic, alicyclic, and aromatic substituents; substituted hydrocarbon substituents, that is, substituents containing non-hydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbon nature of the substituent; and hetero substituents, that is, substituents which similarly have a predominantly hydrocarbon character but contain other than carbon in a ring or chain. A more detailed definition of the term "hydrocarbyl substituent" or "hydrocarbyl group" is found in paragraphs [01 18] to [01 19] of international Publication WO2008147704 and paragraphs [0137] to [0141 ] of published application US 2010-0197536.

[0019] One component of the present technology is an oil of lubricating viscosity. The base oil used in the inventive lubricating oil composition may be selected from any of the base oils in Groups I-V as specified in the American Petroleum Institute (API) Base Oil Interchangeability Guidelines. The five base oil groups are as follows:

Base Oil Category Sulfur (%) Saturates(%) Vise. Index

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

Group 11 <0.03 and >90 80 to 120

Group 111 <0.03 and >90 >I 20

Group IV All poiyaiphaolefins (PAOs)

Group V All others not included in Groups I, II. Ill or IV

[0020] Groups I, II and III are mineral oil base stocks. The oil of lubricating viscosity, then, can include natural or synthetic lubricating oils and mixtures thereof. Mixture of mineral oil and synthetic oils, particularly polya!phaolefm oils and polyester oils, are often used.

[0021 ] Natural oils include animal oils and vegetable oils (e.g. castor oil, lard oil and other 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. Hy- drotreated or hvdrocracked oils are included within the scope of useful oils of lubricating viscosity.

[0022] Oils of lubricating viscosity derived from coal or shale are also useful. Synthetic lubricating oils include hydrocarbon oils and halosubstituted hydrocarbon oils such as polymerized and interpolymerized olefins and mixtures thereof, alkylbenzenes, polypheny!, (e.g., biphenyls, terphenyls, and alkylated polyphenyls), alkylated diphenyl ethers and alkylated diphenyl sulfides and their derivatives, analogs and homologues thereof. Alkylene oxide polymers and iiiterpolymers and derivatives thereof, and those where terminal hydroxyl groups have been modified by, for example, esterification or etherifi cation, constitute other classes of known synthetic lubricating oils that can be used. Another suitable class of synthetic lubricating oils that can be used comprises the esters of dicarboxylic acids and those made from C5 to C 12 monocarboxylic acids and polyols or polyol ethers.

[0023] Other synthetic lubricating oils include liquid esters of phosphorus- containing acids, polymeric tetrahydrofurans, silicon-based oils such as the poly- alkyl-, polyaryl-, polyalkoxy-, or polyaryloxy-siloxane oils, and silicate oils.

[0024] Hydrotreated naphthenic oils are also known and can be used. Synthetic oils may be used, such as those produced by Fischer-Tropsch reactions and typically may be hydroisomerised Fischer-Tropsch hydrocarbons or waxes, in one embodiment oils may be prepared by a Fischer-Tropsch gas-to-iiquid synthetic procedure as well as other gas-to-liquid oils.

[0025] Unrefined, refined and rerefined oils, either natural or synthetic (as well as mixtures of two or more of any of these) of the type disclosed hereinabove can used in the compositions of the present invention. Unrefined oils are those obtained directly from a natural or synthetic source without further purifi- cation treatment. Refined oils are similar to the unrefined oils except they have been further treated in one or more puriiication steps to improve one or more properties. Rerefined oils are obtained by processes simi lar to those used to obtain refined oils applied to refined oils which have been already used in service. Such rerefined oils often are additionally processed by techniques directed to removal of spent additives and oil breakdown products.

[0026] The amount of oil in a fully formulated lubricant will typically be the amount remaining to equal 100. percent after the remaining additives are accounted for. Typically this may be 60 to 99 percent by weight, or 70 to 97 percent, or 80 to 95 percent, or 85 to 93 percent. The disclosed technology may also be delivered as a concentrate, in which case the amount of oil is typically reduced and the concentrations of the other components are correspondingly increased, in such cases the amount of oil may be 30 to 70 percent by weight or 40 to 60 percent.

[0027] Another component of the disclosed technology is a zinc salt of a hydrocarbyl-substituted salicylic acid. The zinc hydrocarbyl salicylate may be symbolized by the following formula:

wherein R may be a hydrocarbyi group containing 7 to 40 carbon atoms. The R group may be any hydrocarbyi group; alkyl groups containing from 7 to 40 carbon atoms are suitable, as are alkyl groups containing 7 to 30 carbon atoms or 1 1 to 30 or 12 to 1 8 carbon atoms. The zinc salts may be neutral or substantially neutral. The expression "substantially neutral" means that the carboxy functionality is reacted with a metal ion and there is little or no excess basic metal present, that is, it is not an overbased material. Thus, 95- 105% or 98- 102% or 99- 101 % or 100% of a stoichiometric amount of metal ion may be present. That is, there will be nominally one zinc ion for two salicylate moieties. Also, the term "substantially neutral" takes into account that the OH functionality of the salicylic acid is not normally neutralized but may be reactive to a suitably strong base. Also, since salicylic acid is a comparatively weak acid, a substantially neutral zinc salt thereof may typically indicate some basicity as measured by Total Base Number (ASTM D 2.896 or 4739). In one embodiment, a neutral or substantially neutral zinc salicylate may exhibit a TBN of about 95 and a Total Acid Number of about 65 (measured on conventional oil-containing materials).

[0028] A neutral or substantially neutral zinc salicylate may be prepared from a neutral sodium hydrocarbyi salicylate by metal exchange. In this method of preparation, the sodium salicylate is treated with a substantial ly equivalent amount of a zinc salt, such as zinc chloride, to give the desired zinc salt, with a sodium salt such as NaCl being eliminated. A substantially neutral zinc hydro- carbyl salicylate may be produced in mineral oil as a solvent. One such material may contain 67% oil and have a zinc content of 3.15%, which corresponds to a zinc content of 9.3% for the neat (oil-free) material.

[0029] In another method of preparation, an alkali metal phenate along with an excess of an alkali metal hydroxide is treated with carbon dioxide. The product is an overbased salicylate of up to 200 conversion (that is, 100% stoichiometric excess of basic metal). When this salt is treated with a zinc salt or acidified and then reacted with more zinc base such as zinc oxide, a basic zinc salicylate is produced. [0030] The amount of the zinc hydrocarbyi salicylate in a fully formulated lubricant may be 0.04 to 2 percent by weight, or alternatively 0.1 to 1 .5, or 0.2 to 1 .2, or 0.3 to 1.0, or 0.5 to 0.9, or 0.15 to 0.7 or 0.15 to 0.8 weight percent. In a concentrate, the amount of zinc hydrocarbyi salicylate will be correspondingly higher, such as up to 40 or 50 percent, e.g., 1 to 50 or 2 to 45 or 5 to 40 or 10 to 30 percent.

[0031] Preparative example - Zinc salicylate. 40 to 80 parts (by weight) of mineral oil is charged to a stirred vessel under nitrogen. To this is added 1 7 parts zinc chloride along with about 20 parts water, and the mixture is heated to 90-95°C. To the heated, stirred mixture is gradually added 100 parts of sodium alkyl-substituted salicylate (the alkyl group having predominantly 1 6 to 20 carbon atoms) plus solvent commercially supplied along with the salicylate. After stirring at temperature for multiple hours, water and other volatile materials are removed by stripping under nitrogen flow at about 1 60°C. Thereafter, additional diluent oil is added, if desired, and the resulting mixture is filtered. The filtrate is the product, in diluent oil. Various processing aids, such as cellulosic filter aid or commercial antifoam agent, may be employed if desired.

[0032] Another component of the disclosed technology is a propylene glycol polymer having a number average molecular weight of 400 to 10,000 and having terminal OH groups, in certain embodiment there may be at least two or exactly two terminal OH groups per polymer molecule for the majority of the polymer molecules. A propylene glycol polymer may also be referred to as a poly(propylene glycol) or a poly(propylene oxide), although it need not be a homopolymer of propylene oxide. For example, it may contain a portion of monomer units from other alkylene oxides such as ethylene oxide or butylene oxide. However, the polymer will typically contain a majority of monomer units of propylene oxide, for example, 50 mole percent or greater, or 70 or 80 or 90 or 95 mole percent or greater propylene oxide units. Such a material may be expressed by the general formula ΗΟ-^Η_ό-Ο^,-Η, when written as the ho- mopolymer. In another expression it may be represented as

although no assertion is intended that the pendant methyl group is necessarily attached to one rather than the other of the two carbon atoms shown. For materials of the disclosed technology, having a molecular weight of 400 to 1 0,000, the corresponding value of n in the above formulas will typically be 7 to 169. Other suitable molecular weight ranges may be 1000 to 8000, or 2000 to 6000, or 3000 to 5000, or about 4000, which would correspond approximately to values of n of 17 to 135, or 34 to 101 , or 51 to 84, or about 67.

[0033] Propylene oxide polymer of the present type are typically prepared by ionic polymerization of propylene oxide. If the initiator molecule is a monool, the resulting polymer will typically be a monool, having on OH group at the terminal end and the alkyl or R group from the initiating alcohol at the other end. When a polymer is desired having terminal OH group, that is, an OH group at each end, the polymerization may be initiated with a diol such as, for instance, ethylene glycol or 1 ,2-propylene glycol. Propylene oxide polymers are available commercially under such trade names as Pluriol* P4000, from BASF, and Synaolox^® 100-D280 from Dow.

[0034 j The amount of the propylene glycol polymer used in the materials of the disclosed technology is typically 0.01 to 1 .0 weight percent, or 0.05 to 0.9 weight percent, or 0.1 to 0.8 weight percent, or 0.2 to 0.6 weight percent, in a concentrate, the amount of propylene glycol polymer will be correspondingly higher, such as 1 to 10 percent or 10 to 20 percent or 2 to 5 percent.

[0035] The lubricants of the disclosed technology may contain other additives that are typically used for lubricants (for example, for lubricants for internal combustion engines). One such additive may be a metal dihydrocarbyl- dithiophosphate. Metal salts of the formula

S 9

wherein R^l and R are independently hydrocarbyl groups containing 3 to 30 or to 20, to 16, or to 14 carbon atoms are readily obtainable by the reaction of phosphorus pentasulfide (P₂.S5) and an alcohol or phenol to form an Ο,Ο- dihydrocarbyl phosphorodithioic acid corresponding to the formula

The reaction involves mixing, at a temperature of 20°C to 200°C, four moles of an alcohol or a phenol with one mole of phosphorus pentasulfide. Hydrogen sulfide is liberated in this reaction. The acid is then reacted with a basic metal compound to form the salt. The metal M, having a valence n, generally is aluminum, lead, tin, manganese, cobalt, nickel, zinc, or copper, and in certain embodiments is zinc. The basic metal compound may thus be zinc oxide, and the resulting metal compound is represented by the formula

The R and R⁹ groups are independently hydrocarbyl groups that are typically free from acetylenic and usually also from ethyl enic unsaturation. They are typically alkyl, cycloalkyl, aralkyl or alkaryl group and have 3 to 20 carbon atoms, such as 3 to 16 carbon atoms or up to 13 carbon atoms, e.g., 3 to 12 carbon atoms. The alcohol which reacts to provide the R^¾ and R^¾ groups can be a mixture of a secondary alcohol and a primary alcohol, for instance, a mixture of 2-ethylhexanol and 2-propanol or, alternatively, a mixture of secondary alcohols such as 2-propanol and 4~methyl-2-pentanol. Such materials are often referred to as zinc dialkyldithiophosphates or simply zinc dithiophosphates. They are well known and readily available to those skilled in the art of lubricant formulation.

[0036] In certain embodiments, the zinc diaikyldithiophosphate may have R^s and R⁹ groups selected to reduce phosphorus volatility from the lubricant, that is, to increase retention of phosphorus in the lubricant. Suitable formulations to provide good phosphorus retention in an engine are disclosed, for instance, in US published application 2008-0015 129, see, e.g., claims. Thus, in certain embodiments the zinc diaikyldithiophosphate may a zinc salt prepared of a material or mixture of materials represented by the formula

wherein R and R are independently hydrocarbyl groups (or alkyl groups), the average total number of carbon atoms per phosphorus-containing moiety being at least 10.4, wherein at least one of the R⁸ and R⁹ hydrocarbyl groups in the overall mixture of zinc diaikyldithiophosphate compounds contains 4 or fewer carbon atoms and up to 40 mole percent of all the R and R hydrocarbyl groups supplied by the phosphorus-containing zinc salt contain 4 or fewer carbon atoms. In certain further embodiments, in less than 8 mole percent of the molecules of the above formula in the mixture of phosphorus-containing compounds, each of R⁸ and R⁹ contain 2 to 4 carbon atoms and in greater than 1 1 mole percent of the molecules of the above formula in said mixture, R⁸ has 2 to 4 carbon atoms and R⁹ has 5 to 12 carbon atoms; and within the formula, the average total number of hydrogen atoms in R and R on carbon atoms located beta to the O atoms is at least 7.25.

[0037] The amount of the metal salt of a phosphorus acid in a completely formulated lubricant, if present, will typically be at least 0.02 percent by weight, for instance, at least 0.08 or 0. 1 or 0. 15 or 0.2 or 0.5 percent by weight. An upper limit may be appropriate if it is desired to restrict the amount of sulfur or metals in the composition, and may be appropriately selected at 5 or 3 or 1 percent by weight. Thus, suitable ranges may include 0.02 to 5 percent, or 0.2 to 3 percent, or 0.5 to 1 percent by weight, as well as other combinations of the upper and lower amounts. Its concentration in a concentrate will be correspondingly increased, to, e.g., 1 to 20 weight percent. When the disclosed technology is used in a lubricant for an internal combustion engine, it typically will contain a metal dihydrocarbyldithiophosphate, although in some embodiments it will not. When used in other applications, such as metal working lubrication, it typically will not contain a metal dihydrocarbyldithiophosphate, although it may do so.

[0038] The lubricant may also contain additional additives. Among these are detergents other than the above-described zinc salt of a hydrocarbyl-substituted salicylic acid. Detergents are often in the form of overbased materials, other- wise referred to as overbased or superbased salts, which are generally single phase, homogeneous Newtonian systems characterized by a metal content in excess of that which would be present for neutralization according to the stoichiometry of the metal and the particular acidic organic compound reacted with the metal. The overbased materials are prepared by reacting an acidic material (typically an inorganic acid or lower carboxylic acid, such as carbon dioxide) with a mixture comprising an acidic organic compound, a reaction medium comprising at least one inert, organic solvent (e.g., mineral oil, naphtha, toluene, or xylene) for said acidic organic material, a stoichiometric excess of a metal base (e.g., Li, Na, K, Mg, Ca, or Ba oxides or hydroxides), and a promoter such as a phenol or alcohol.

[0039] The acidic organic material will normally have a sufficient number of carbon atoms to provide a degree of solubility in oil. The amount of excess metal is commonly expressed in terms of metal ratio. The term "metal ratio" is the ratio of the total equivalents of the metal to the equivalents of the acidic organic compound. A neutral metal salt has a metal ratio of one. A salt having 4.5 times as much metal as present in a normal salt will have metal excess of 3.5 equivalents, or a ratio of 4.5.

[0040] Such overbased materials are well known to those skilled in the art. Patents describing techniques for making basic salts of sulfonic acids, carbox- ylic acids, phenols, phosphonic acids, and mixtures of any two or more of these include U.S. Patents 2,501 ,731 ; 2,61 6,905; 2,616,91 1 ; 2,61 6,925; 2,777,874; 3,256, 186; 3 ,384,585; 3 ,365,396; 3 ,320, 162; 3 ,3 18,809; 3,488,284; and 3,629, 109. Yet another type of detergent is a salixarate detergent. These include overbased materials prepared from the product of salicylic acid (which may be unsubstituted) with a hydroearbyl-substituted phenol, such entities being- linked through -CH2- or other alkylene bridges. It is believed that the salixarate derivatives have a predominantly linear, rather than macrocyclic, structure, although both structures are intended to be encompassed by the term "salixarate." Salixarate derivatives and methods of their preparation are described in greater detail in U.S. patent number 6,200,936 and PCT Publication WO 01 /56968.

[0041 ] In certain embodiments, the additional detergent may comprise one or more calcium detergents. The detergents may be, among others, a phenate or a sulfonate or mixtures thereof. The amount of detergent (other than zinc salicylate), if present, may be 0.1 to 5 percent or 0.5 to 4, or 1 to 3 percent, by weight.

[0042] Another material that may be present is a dispersant, which may be a nitrogen-containing dispersant. Dispersants are well known in the field of lubricants and include primarily what is known as ashless dispersants and polymeric dispersants. Ashless dispersants are so-called because, as supplied, they do not contain metal and thus do not normally contribute to sulfated ash when added to a lubricant. However they may, of course, interact with ambient metals once they are added to a lubricant which includes metal-containing species. Ashless dispersants are characterized by a polar group attached to a relatively high molecular weight hydrocarbon chain. Typical ashless dispersants include N-substituted long chain alkenyl succinimides, having a variety of chemical structures including typically

where each R¹ is independently an alkyl group, frequently a polyisobutylene group with a molecular weight (M_n) of 500-5000 based on the polyisobutylene precursor, and R² are alkylene groups, commonly ethylene (C₂H₄) groups. Such molecules are commonly derived from reaction of an alkenyl acyiating agent with a polyamine, and a wide variety of linkages between the two moieties is possible beside the simple imide structure shown above, including a variety of amides and quaternary ammonium salts. Also, a variety of modes of linkage of the R¹ groups onto the imide structure are possible, including various cyclic linkages. The ratio of the carbonyl groups of the acyiating agent to the nitrogen atoms of the amine may be 1 :0.5 to 1 :3, and in other instances 1 : 1 to 1 :2.75 or 1 : 1 .5 to 1 :2.5. Succinimide dispersants are more fully described in U.S. Patents 4,234,435 and 3, 172,892 and in EP 0355895.

[0043] Another class of ashless dispersant is high molecular weight esters. These materials are similar to the above-described succinimicles except that they may be seen as having been prepared by reaction of a hydrocarbyl acyiating agent and a polyhydric aliphatic alcohol such as glycerol, pentaerythritol, or sorbitol. Such materials are described in more detail in U.S. Patent 3,38 1 ,022.

[0044] Another class of ashless dispersant is Mannich bases. These are materials which are formed by the condensation of a higher molecular weight, alkyl substituted phenol, an alkylene polyamine, and an aldehyde such as formaldehyd

(including a variety of isomers and the like) and are described in more detail in U.S. Patent 3,634,515.

[0045] Other dispersants include polymeric dispersant additives, which are generally hydrocarbon-based polymers which contain polar functionality to impart dispersancy characteristics to the polymer. [0046] Dispersants can also be post-treated by reaction with any of a variety of agents. Among these are urea, thiourea, dimercaptothiadiazoles, carbon disulfide, aldehydes, ketones, carboxylic acids, hydrocarbon-substituted succinic anhydrides, nitriles, epoxides, boron compounds, and phosphorus com- pounds. References detailing such treatment are listed in U.S. Patent 4,654,403.

[0047] Another component is an antioxidant. Antioxidants encompass phenolic antioxidants, which may comprise a butyl substituted phenol containing 2 or 3 t-butyl groups. The para position may also be occupied by a hydro- carbyl group or a group bridging two aromatic rings. The latter antioxidants are described in greater detail in U.S. Patent 6,559, 105. Antioxidants also include aromatic amine, such as nonylated diphenylamines. Other antioxidants include sulfurized olefins, titanium compounds, and molybdenum compounds. U.S. Pat. No. 4,285,822, for instance, discloses lubricating oil compositions containing a molybdenum and sulfur containing composition. Typical amounts of antioxi- dants will, of course, depend on the specific antioxidant and its individual effectiveness, but illustrative total amounts can be 0.01 to 5 percent by weight or 0.15 to 4.5 percent or 0,2 to 4 percent. Additionally, more than one antioxidant may be present, and certain combinations of these can be synergistic in their combined overall effect.

[0048] Viscosity improvers (also sometimes referred to as viscosity index improvers or viscosity modifiers) may be included in the compositions of this invention. Viscosity improvers are usually polymers, including polyisobutenes, polymethacrylic acid esters, diene polymers, polyalkylstyrenes, esterified styrene- maleic anhydride copolymers, alkenylarene-conjugated diene copolymers and polyolefins. Polymers prepared from diene monomers are often hydrogenated. Multifunctional viscosity improvers, which also have dispersant and/or anti- oxidancy properties are known and may optionally be used.

[0049] Another additive is an antiwear agent. Examples of anti-wear agents include phosphorus-containing antiwear/extreme pressure agents such as metal thiophosphates, phosphoric acid esters and salts thereof, phosphorus-containing carboxylic acids, esters, ethers, and amides; and phosphites. In certain embodiments a phosphorus antiwear agent may be present in an amount to deliver 0.01 to 0.2 or 0.015 to 0.15 or 0.02 to 0.1 or 0.025 to 0.08 percent phosphorus. Often the antiwear agent is a zinc dialkyldithiophosphate (ZDP), as has been described above. Non-phosphorus-containing anti-wear agents include borate esters (including borated epoxides), dithiocarbamate compounds, molybdenum- containing compounds, and sulfurized olefins. [0050] Other types of antiwear agents include tartrate esters, tartramides, and tartrimides, such as oleyl tartrirnide, as well as esters, amides, and imides of hydroxy-polycarboxylic acids in general. These materials may also impart additional functionality to a lubricant beyond antiwear performance. These materials are described in greater detail in US Publication 2006-007941 3 and US Provisional Application 61/120932, filed 9 December 2008.

[0051] Other additives that may optionally be used in lubricating oils include pour point depressing agents, extreme pressure agents, anti-wear agents, color stabilizers and anti-foam agents.

[0052] in certain embodiments, the lubricant of the disclosed technology may have a phosphorus content (as supplied by all of the phosphorus-containing additives) of less than 3000 or less than 1500 or less than 1 100 parts per million by weight, for instance, 250 or 300 or 400 to 1500 or to 3000 parts per million by weight. Alternative amounts are 450 to 1 100 ppm, 500 to 1000 ppm, or 600 to 800 ppm.

[0053] The presently disclosed lubricant may be used for lubricating any of a variety of devices. Among the internal combustion engines that may be lubricated - by supplying thereto the presently disclosed lubricant - are sump- lubricated spark-ignited (e.g., gasoline) engines and sump-lubricated compres- sion-ignited (e.g., diesel) engines, including heavy-duty diesel engines, and also engines fueled by bio-diesel fuels, alcohols, or hydrogen, it may also be used for "dry-sump" lubricated engines, that is engines employing an externally supplied lubricant, it may also be used for lubrication of power transmission devices such as automatic transmissions (in particular, stepped gear (non- continuously variable) transmissions), gears in manual gearboxes, continuously variable transmissions, traction drives, differentials, power take-offs, wet brakes, and hydraulic systems, it may also be used for lubrication of metal- working applications, which may include cutting and forming operations.

[0054] 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. For instance, metal ions (of, e.g., a detergent) can migrate to other acidic or anionic sites of other molecules. The products formed thereby, including the products formed upon employing the 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 the composition prepared by admixing the components described above,

EXAMPLES

[0055] Lubricant formulations are prepared as shown in the Table below. All amounts are presented on an oil-free/solvent-free basis. Amounts enclosed in brackets [ ] represent the TBN contributed to the formulation by the particular component. The lubricant formulations are subjected to one or more of the ASTM D6594 High Temperature Cummins Bench Corrosion Test and the 4.3.3.9.3 Acid Neutralization test.

[0056] In the Acid Neutralization test, in summary, three steel test panels are cleaned and sand-blasted, then immersed for not more than 1 second in a 0. 1 % aqueous solution of hydrobromic acid. Within 1 second after removal from the acid solution, the panels are immersed completely, with agitation, into a sample of the test oil at 25 °C. The panel is immersed in and removed from the oil 12 times in 60 seconds. The panels are then allowed to stand in air at 25 °C for 4 hours. Thereafter, the remaining oil film is removed from the panel with naphtha and the panel is observed for the extent of corrosion.

- : not measured

[0057] Each of the documents referred to above is incorporated herein by reference. The mention of any document is not an admission that such document qualifies as prior art or constitutes the general knowledge of the skilled person in any jurisdiction. 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." 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 can be used together with ranges or amounts for any of the other elements. As used herein,, the expression "consisting essentially of permits the inclusion of substances that do not materially affect the basic and novel characteristics of the composition under consideration.

Claims

What is claimed is:

1 . A lubricant composition comprising;

(a) an oil of lubricating viscosity;

(b) a zinc salt of a hydrocarbyi-substituted salicylic acid;

(c) a propylene glycol polymer having a number average molecular weight of about 400 to about 10,000 and having terminal OH groups; and

(d) at ieast about 0.02 percent by weight of a metal dihydrocarbyldithio- phosphate.

2. The lubricant of claim 1 wherein the zinc salt of the hydrocarbyi- substituted salicylic acid is a substantially neutral salt.

3. The lubricant of claim 1 or claim 2 wherein the hydrocarbyl substitu- ent on the salicylic acid has about 7 to about 40 carbon atoms.

4. The lubricant of any of claims 1 through 3 wherein the amount of the zinc salt of the hydrocarbyi-substituted salicylic acid is about 0.04 to about 2 weight percent and the amount of the propylene glycol polymer is about 0.1 to about 1 weight percent.

5. The lubricant of any of claims 1 through 4 wherein the metal dihydro- carbyidithiophosphate is a zinc dialkyldithiophosphate.

6. The lubricant of any of claims 1 through 5 wherein the metal dihydro- carbyldithiophosphate is a zinc dialkyldithiophosphate characterized by the average total number of carbon atoms per phosphorus-containing moiety being at least 10.4, wherein at least one of alkyl groups in the overall mixture of zinc dialkyldithiophosphate compounds contains 4 or fewer carbon atoms and up to 40 mole percent of all the alkyl groups supplied by the phosphorus-containing zinc salt contain 4 or fewer carbon atoms.

7. The lubricant of any of claims 1 through 6 further comprising at least one metal-containing detergent other than a zinc salt of a hydrocarbyi- substituted salicylic acid, and nitrogen-containing dispersant.

8. The lubricant of any of claim 1 through 7 wherein the phosphorus content of the lubricant is about 250 ppm to about 3000 ppm by weight.

9. A composition prepared by admixing the components of any of claims 1 through 8.

10, A method for lubricating an internal combustion engine, comprising supplying thereto the lubricant of any of claims 1 through 9.

1 1 . The method of claim 10 wherein the internal combustion engine is a sump-lubricated compression-ignited engine.

12. The method of claim 1 0 wherein the internal combustion engine is a sump-lubricated spark-ignited engine.

13. A method for lubricating an internal combustion engine, comprising supplying thereto a lubricant composition comprising:

(a) an oil of lubricating viscosity;

(b) a zinc salt of a hydrocarbyl-substituted salicylic acid; and

(c) a propylene glycol polymer having a number average molecular weight of about 400 to about 1 0,000 and having terminal OH groups.

14. A method for lubricating a stepped gear transmission, comprising supplying to said transmission a lubricant composition comprising:

(a) an oil of lubricating viscosity;

(b) a zinc salt of a hydrocarbyl-substituted salicylic acid; and

(c) a propylene glycol polymer having a number average molecular weight of about 400 to about 10,000 and having terminal OH groups.

15. A method for lubricating a metal-working operation, comprising supplying thereto a lubricant composition comprising:

(a) an oil of lubricating viscosity;

(b) a zinc salt of a hydrocarbyl-substituted salicylic acid; and

(c) a propylene glycol polymer having a number average molecular weight of about 400 to about 10,000 and having terminal OH groups.

16. A method for protecting a metal surface, comprising applying to said surface a lubricant composition comprising:

(a) an oil of lubricating viscosity;

(b) a zinc salt of a hydrocarbyl-substituted salicylic acid; and

(c) a propylene glycol polymer having a number average molecular weight of about 400 to about 10,000 and having terminal OH groups.