This invention relates to lubricating oils containing certain ashless dispersants in combination with overbased alkali metal additives. It particularly concerns crankcase lubricants having excellent properties of sludge and varnish control, giving good engine cleanliness and yet resistant to oxidation and/or with reduced tendency to thickening due to interactions in the package.

Lubricating oils used in gasoline and diesel crankcases comprise a natural and/or synthetic basestock containing one or more additives to impart desired characteristics to the lubricant. Such additives typically include ashless dispersant, metal detergent, antioxidant and antiwear components, which may be combined in a package, sometimes referred to as a detergent inhibitor (or Dl) package.

The ashless dispersant operates to suspend particles of dirt resulting from combustion or wear within the engine to prevent them depositing to form sludge or varnish in the engine. Detergents which are typically metal containing compounds act to keep the engine surfaces clean, while highly basic or overbased forms of these detergents also operate to neutralise acids formed during combustion which would otherwise cause corrosion within the engine. As engines in modern automobiles operate in an increasing severe environment, with smaller, more powerful engines operating at higher temperatures and with less frequent service intervals, the requirements for lubricants in turn become more severe. This has lead to increasing amounts of dispersants and detergents being introduced into lubricants to achieve the desired performance levels.

The increasing severe conditions also tend to accelerate oxidation of the oil, which leads to unacceptable oil thickening which can have catastrophic effects in an engine. Hence oils have to contain antioxidants to combat this effect. Unfortunately conventional additives including ashless dispersants such as polyisobutenyl succinimides and many widely used metal detergents, such as some sulphonates and carboxylates, are prooxidant and thus make the oxidation problem worse.

A new class of ashless dispersants comprising functionalized and/or derivatized olefin polymers based on polymers synthesized using metallocene catalyst systems are described in US-A-5128056, 5151204, 5200103, 5225092, 5266223, 5334775; WO-A- 94/19436, 94/13709; and EP-A-440506, 513157, 513211. These dispersants are described as providing enhanced lubricating oil dispersancy as exhibited by their enhanced sludge and varnish control. They are described in lubricating oil compositions in combination with conventional additives including detergents such as overbased metal salts, which are described in US-A-5266223 as particularly prone to interaction with ashless dispersants. Alkaline earth metal salts such as sulphonates are specifically described. US-A-5266223, which has a reference to other metal containing additives containing sodium but has no disclosure of overbased alkali metal detergents.

WO-A-94/13714, unpublished at the priority date of this application, describes lubricating oil compositions comprising functionalised and derivatised amorphous copolymers derived from at least one monomer having the formula:

H ₂ C=CHR

wherein R is a hydrocarbon having from 2 to 22 carbon atoms, and at least one comonomer of the formula:

R ¹ HC=CHR ² ; or H ₂ C=CR ² R ³

wherein Rl . R ² and R^are the same or different hydrocarbon groups or substituted hydrocarbon groups having from 1 to 22 carbon atoms, the copolymer comprising at least 50 mole% of repeating units derived from H2C=CHR, and up to 5 mole% of repeating units derived from being at least 95% amorphous and having a number average molecular weight of greater than 1300. The lubricating compositions are described as optionally containing other additives including overbased alkali or alkaline earth metal salts of one or more organic acids.

However it has been found that when additive packages are prepared from the new class of dispersant and some conventional overbased detergents there is a tendency for interaction giving rise to undesirable thickening of the packages.

WO-A-93/23504 and WO-A-93/23505 describe conventional polyisobutenyl succinimide dispersants in combination with overbased alkali metal carboxylates or sulfonate/carboxylates. WO-A-87/01722 describes diesel lubricants said to minimise undesirable viscosity increases which comprise conventional polyisobutenyl succinimide dispersants in combination with basic alkali metal salts of an acidic organic compound having a metal ratio of at least about 2. EP-A-89856 describes pretreatment of ashless dispersants with a basic salt of an alkali metal prior to mixing the dispersants with overbased magnesium compounds.

The problem remains to provide lubricating oil compositions capable of providing high levels of dispersancy for combatting sludge and varnish, together with good engine cleanliness particularly reduced piston deposits in the top groove and lower, cooloer areas of the piston, while having good resistance to oxidation and reduced tendency to interaction with overbased detergents. The use of additional detergents is a conventional way to control piston deposits, but this may adversely impact perfomance of the lubricant in other ways, for example by increasing the level of sulphated ash produced by the lubricant, as well as increasing the net treat cost of the final products.

This invention provides a lubricating oil composition prepared by combining in a lubricating oil, an overbased alkali metal detergent and an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer having >30% of terminal vinylidene unsaturation and an M _n of from 500 to 7000, but wherein the backbone is not an amorphous copolymer derived from at least one monomer having the formula:

H ₂ C=CHR

(wherein R is a hydrocarbon having from 2 to 22 carbon atoms), and at least one comonomer of the formula:

Rl HC=CHR ² ; or H ₂ C=CR ² R ³

(wherein R1 ■ R ² and R ³ are the same or different hydrocarbon groups or substituted hydrocarbon groups having from 1 to 22 carbon atoms), when the copolymer i) comprises at least 50 mole% of repeating units derived from H ₂ C=CHR and up to 5 mole% of repeating units derived from H ₂ C=CR ² R ³ , ii) is least 95% amorphous, and iii) has an Mn of greater than 1300.

The invention also provides for the use of an overbased alkali metal detergent in combination with an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer having >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000, to limit oxidation of a crankcase lubricating oil; and/or to reduce thickening caused by package interaction; and/or to limit the formation of deposits on the piston of a diesel engine, particularly in the top groove and on the third and fourth lands, the skirt and undercrown.

It further provides a process for limiting the oxidation in a crankcase of a crankcase lubricating oil comprising an ashless dispersant with an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer having >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000, and/or to reduce thickening of the package used to form the lubricating oil caused by interactions in that package, in which process the oil is prepared from an additive package which comprises the ashless dispersant and an overbased alkali metal detergent.

It also provides a process for limiting the formation of deposits on the piston (particularly in the top groove and on the third and fourth lands, the skirt and undercrown of the piston) of a diesel engine lubricated with a lubricating oil comprising an ashless dispersant with an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer having >30% of terminal vinylidene unsaturation, in which process the oil is prepared from an additive package which comprises the ashless dispersant and an overbased alkali metal detergent.

DETAILED DESCRIPTION

A. BASESTOCK

The basestock used in the lubricating oil may be selected from any of the synthetic or natural oils used as crankcase lubricating oils for spark-ignited and compression-ignited engines. The lubricating oil base stock conveniently has a viscosity of about 2.5 to about 12 mm ² /s and preferably about 2.5 to about 9 mm ² /s at 100°C. Mixtures of synthetic and natural base oils may be used if desired.

B. ASHLESS DISPERSANT

The ashless dispersant comprises an oil soluble polymeric hydrocarbon backbone having functional groups that are capable of associating with particles to be dispersed. Typically, the dispersants comprise amine, alcohol, amide, or ester polar moieties attached to the polymer backbone often via a bridging group. The ashless dispersant may be, for example, selected from oil soluble salts, esters, amino-esters, amides, imides, and oxazolines of long chain hydrocarbon substituted mono and dicarboxylic acids or their anhydrides; thiocarboxylate derivatives of long chain hydrocarbons; long chain aliphatic hydrocarbons having a polyamine attached directly thereto; and Mannich condensation products formed by condensing a long chain substituted phenol with formaldehyde and polyalkylene polyamine.

The oil soluble polymeric hydrocarbon backbone used in an ashless dispersants in the detergent inhibitor package is selected from ethylene alpha-olefin (EAO) copolymers and alpha-olefin homo- and copolymers such as may be prepared using the new metallocene catalyst chemistry, having in each case a high degree, >30%, of terminal vinylidene unsaturation. The term alpha-olefin is used herein to refer to an olefin of the formula:

R' I ^' H — C =CH ₂

*,' wherein R' is preferably a Cj - Cη8 alkyl group. The requirement for terminal vinylidene unsaturation refers to the presence in the polymer of the following structure:

R

I

Poly — C =CH ₂

wherein Poly is the polymer chain and R is typically a C-| - Ci8 alkyl group, typically methyl or ethyl. Preferably the polymers will have at least 50%, and most preferably at least 60%, of the polymer chains with terminal vinylidene unsaturation. As indicated in

WO-A-94/19426, ethylene/1 -butene copolymers typically have vinyl groups terminating no more than about 10 percent of the chains, and internal mono-unsaturation in the balance of the chains. The nature of the unsaturation may be determined by FTIR spectroscopic analysis, titration or C-13 NMR.

The oil soluble polymeric hydrocarbon backbone may be a homopolymer (e.g., polypropylene) or a copolymer of two or more of such olefins (e.g., copolymers of ethylene and an alpha-olefin such as propylene or butylene, or copolymers of two different alpha-olefins). Other copolymers include those in which a minor molar amount of the copolymer monomers, e.g., 1 to 10 mole %, is an α,ω-diene, such as a C3 to C ₂ non-conjugated diolefin (e.g., a copolymer of isobutylene and butadiene, or a copolymer of ethylene, propylene and 1 ,4-hexadiene or 5-ethylidene-2-norbomene). Atactic propylene oligomer typically having Mn of from 700 to 5000 may also be used, as described in EP-A-490454, as well as heteropolymers such as polyepoxides.

One preferred class of olefin polymers is polybutenes and specifically poly-n- butenes, such as may be prepared by polymerization of a C4 refinery stream. Other preferred classes of olefin polymers are EAO copolymers that preferably contain 1 to 50 mole% ethylene, and more preferably 5 to 48 mole% ethylene. Such polymers may contain more than one alpha-olefin and may contain one or more C3 to C ₂₂ diolefins. Also usable are mixtures of EAO's of varying ethylene content. Different polymer types, e.g., EAO, may also be mixed or blended, as well as polymers differing in M _n ; components derived from these also may be mixed or blended.

The olefin polymers and copolymers preferably have an Mn of from 700 to 5000, more preferably 2000 to 5000. Polymer molecular weight, specifically Mn , can be determined by various known techniques. One convenient method is gel permeation chromatography (GPC), which additionally provides molecular weight distribution information (see W. W. Yau, J. J. Kirkland and D. D. Bly, "Modern Size Exclusion Liquid Chromatography", John Wiley and Sons, New York, 1979). Another useful method, particularly for lower molecular weight polymers, is vapor pressure osmometry (see, e.g., ASTM D3592).

Particularly preferred copolymers are ethylene butene copolymers.

Suitable olefin polymers and copolymers may be prepared by various catalytic polymerization processes using metallocene catalysts which are, for example, bulky ligand transition metal compounds of the formula:

[L] _m M[A] _n

where L is a bulky ligand; A is a leaving group, M is a transition metal, and m and n are such that the total ligand valency corresponds to the transition metal valency. Preferably the catalyst is four co-ordinate such that the compound is ionizable to a 1 ⁺ valency state.

The ligands L and A may be bridged to each other, and if two ligands A and/or L are present, they may be bridged. The metallocene compound may be a full sandwich compound having two or more ligands L which may be cyclopentadienyl ligands or cyclopentadienyl derived ligands, or they may be half sandwich compounds having one such ligand L. The ligand may be mono- or polynuclear or any other ligand capable of η-5 bonding to the transition metal.

One or more of the ligands may π-bond to the transition metal atom, which may be a Group 4, 5 or 6 transition metal and/or a lanthanide or actinide transition metal, with zirconium, titanium and hafnium being particularly preferred.

The ligands may be substituted or unsubstituted, and mono-, di-, tri, tetra- and penta-substitution of the cyclopentadienyl ring is possible. Optionally the substituent(s) may act as one or more bridges between the ligands and/or leaving groups and/or transition metal. Such bridges typically comprise one or more of a carbon, germanium, silicon, phosphorus or nitrogen atom-containing radical, and preferably the bridge places a one atom link between the entities being bridged, although that atom may and often does carry other substituents.

The metallocene may also contain a further displaceable ligand, preferably displaced by a cocatalyst - a leaving group - that is usually selected from a wide variety of hydrocarbyl groups and halogens.

Such polymerizations, catalysts, and cocatalysts or activators are described, for ^• example, in US-A-4530914, 4665208, 4808561 , 4871705, 4897455, 4937299, 4952716, 5017714, 5055438, 5057475, 5064802, 5096867, 5120867, 5124418, 5153157, 5198401 , 5227440, 5241025; EP-A-129368, 277003, 277004, 420436, 520732; and WO-A-91/04257, 92/00333, 93/08199, 93/08221 , 94/07928 and 94/13715.

The oil soluble polymeric hydrocarbon backbone may be functionalized to incorporate a functional group into the backbone of the polymer, or as one or more groups pendant from the polymer backbone. The functional group typically will be polar and contain one or more hetero atoms such as P, O, S, N, halogen, or boron. It can be attached to a saturated hydrocarbon part of the oil soluble polymeric

hydrocarbon backbone via substitution reactions or to an olefinic portion via addition or cycloaddition reactions. Alternatively, the functional group can be incorporated into the polymer in conjunction with oxidation or cleavage of the polymer chain end (e.g., as in ozonolysis).

Useful functionalization reactions include: halogenation of the polymer at an olefinic bond and subsequent reaction of the halogenated polymer with an ethylenically unsaturated functional compound (e.g., maleation where the polymer is reacted with maleic acid or anhydride); reaction of the polymer with an unsaturated functional compound by the "ene" reaction absent halogenation; reaction of the polymer with at least one phenol group (this permits derivatization in a Mannich base-type condensation); reaction of the polymer at a point of unsaturation with carbon monoxide using a Koch-type reaction to introduce a carbonyl group in an iso or neo position; reaction of the polymer with the functionalizing compound by free radical addition using a free radical catalyst; reaction with a thiocarboxylic acid derivative; and reaction of the polymer by air oxidation methods, epoxidation, chloroamination, or ozonolysis.

The functionalized oil soluble polymeric hydrocarbon backbone is then further derivatized with a nucleophilic reactant such as an amine, amino-alcohol, alcohol, metal compound or mixture thereof to form a corresponding derivative. Useful amine compounds for derivatizing functionalized polymers comprise at least one amine and can comprise one or more additional amine or other reactive or polar groups. These amines may be hydrocarbyl amines or may be predominantly hydrocarbyl amines in which the hydrocarbyl group includes other groups, e.g., hydroxy groups, alkoxy groups, amide groups, nitriles, imidazoline groups, and the like. Particularly useful amine compounds include mono- and polyamines, e.g. polyalkylene and polyoxyalkylene polyamines of about 2 to 60, conveniently 2 to 40 (e.g., 3 to 20), total carbon atoms and about 1 to 12, conveniently 3 to 12, and preferably 3 to 9 nitrogen atoms in the molecule. Mixtures of amine compounds may advantageously be used such as those prepared by reaction of alkylene dihalide with ammonia. Preferred amines are aliphatic saturated amines, including, e.g., 1,2-diaminoethane; 1,3- diaminopropane; 1 ,4-diaminobutane; 1,6-diaminohexane; polyethylene amines such as diethylene triamine; triethylene tetramine; tetraethylene pentamine; and polypropyleneamines such as 1 ,2-propylene diamine; and di-(1,2-propylene)triamine.

Other useful amine compounds include: alicyclic diamines such as 1 ,4- di(aminomethyl) cyclohexane, and heterocyclic nitrogen compounds such as imidazolines. A particularly useful class of amines are the polyamido and related amido-amines as disclosed in US 4,857,217; 4,956,107; 4,963,275; and 5,229,022.

Also usable is tris(hydroxymethyl)amino methane (THAM) as described in US 4,102,798; 4,113,639; 4,116,876; and UK 989,409. Dendrimers, star-like amines, and comb-structure amines may also be used. Similarly, one may use the condensed amines disclosed in US 5,053,152. The functionalized polymer is reacted with the amine compound according to conventional techniques as described in EP-A 208,560; US 4,234,435 and US 5,229,022 .

The functionalized oil soluble polymeric hydrocarbon backbones also may be derivatized with hydroxy compounds such as monohydric and polyhydric alcohols or with aromatic compounds such as phenols and naphthols. Polyhydric alcohols are preferred, e.g., alkylene glycols in which the alkylene radical contains from 2 to 8 carbon atoms. Other useful polyhydric alcohols include glycerol, mono-oleate of glycerol, monostearate of glycerol, monomethyl ether of glycerol, pentaerythritol, dipentaerythritol, and mixtures thereof. An ester dispersant may also be derived from unsaturated alcohols such as ally! alcohol, cinnamyl alcohol, propargyl alcohol, 1- cyclohexane-3-ol, and oleyl alcohol. Still other classes of the alcohols capable of yielding ashless dispersants comprise the ether-alcohols and including, for example, the oxy-alkylene, oxy-arylene. They are exemplified by ether-alcohols having up to 150 oxy-alkylene radicals in which the alkylene radical contains from 1 to 8 carbon atoms. The ester dispersants may be di-esters of succinic acids or acidic esters, i.e., partially esterified succinic acids; as well as partially esterified polyhydric alcohols or phenols, i.e., esters having free alcohols or phenolic hydroxyl radicals. An ester dispersant may be prepared by one of several known methods as illustrated, for example, in US 3,381 ,022.

A preferred group of ashless dispersants includes those substituted with succinic anhydride groups and reacted with polyethylene amines (e.g., tetraethylene pentamine), aminoalcohols such as trismethylolaminomethane and optionally additional reactants such as alcohols and reactive metals e.g., pentaerythritol, and combinations thereof). Also useful are dispersants wherein a polyamine is attached directly to the backbone by the methods shown in US 3,275,554 and 3,565,804 where a halogen group on a halogenated hydrocarbon is displaced with various alkylene polyamines.

Another class of ashless dispersants comprises Mannich base condensation products. Generally, these are prepared by condensing about one mole of an alkyl- , substituted mono- or polyhydroxy benzene with about 1 to 2.5 moles of carbonyl compounds (e.g., formaldehyde and paraformaldehyde) and about 0.5 to 2 moles polyalkylene polyamine as disclosed, for example, in US 3,442,808. Such Mannich condensation products may include a polymer product of a metallocene cataylsed

polymerisation as a substituent on the benzene group or may be reacted with a compound containing such a polymer substituted on a succinic anhydride, in a mannersimilar to that shown in US 3,442,808.

Examples of functionalized and/or derivatized olefin polymers based on polymers synthesized using metallocene catalyst systems are described in publications identified above.

The dispersant can be further post-treated by a variety of conventional post treatments such as boration, as generally taught in US 3,087,936 and 3,254,025. This is readily accomplished by treating an acyl nitrogen-containing dispersant with a boron compound selected from the group consisting of boron oxide, boron halides, boron acids and esters of boron acids, in an amount to provide from about 0.1 atomic proportion of boron for each mole of the acylated nitrogen composition to about 20 atomic proportions of boron for each atomic proportion of nitrogen of the acylated nitrogen composition. Usefully the dispersants contain from about 0.05 to 2.0 wt. %, e.g. 0.05 to 0.7 wt. % boron based on the total weight of the borated acyl nitrogen compound. The boron, which appears be in the product as dehydrated boric acid polymers (primarily (HB0 ₂ )3), is believed to attach to the dispersant imides and diimides as amine salts e.g., the metaborate salt of the diimide. Boration is readily carried out by adding from about 0.05 to 4, e.g., 1 to 3 wt. % (based on the weight of acyl nitrogen compound) of a boron compound, preferably boric acid, usually as a slurry, to the acyl nitrogen compound and heating with stirring at from 135° to 190° C, e.g., 140°-170° C, for from 1 to 5 hours followed by nitrogen stripping. Alternatively, the boron treatment can be carried out by adding boric acid to a hot reaction mixture of the dicarboxylic acid material and amine while removing water.

C. OVERBASED ALKALI METAL DETERGENTS

Metal-containing or ash-forming detergents function both as detergents to reduce or remove deposits and as acid neutralizers or rust inhibitors, thereby reducing wear and corrosion and extending engine life. Detergents generally comprise a polar head with a long hydrophobic tail, with the polar head comprising a metal salt of an acidic organic compound, sometimes referred to as "soap". Salts containing a substantially stoichiometric amount of the metal are usually described as normal or neutral salts, and would typically have a metal ratio at or close to 1 (where metal ratio is the total equivalents of metal to equivalents of acidic organic compound). The total base number or TBN (as may be measured by ASTM D2896) of such neutral salts will depend on the specific acidic organic compound but for a sulphonate would typically be

close to zero and for a neutral phenate or sulphurised phenate the TBN would typically be less than 100.

The present invention employs overbased alkali metal salts which include large amounts of a metal base formed by reacting an excess of a metal compound such as an oxide or hydroxide with an acidic material, usually a gas such as carbon dioxide. The resulting overbased detergent comprises neutralised detergent as the outer layer of a metal base (e.g. carbonate) micelle. Such overbased detergents have a metal ratio greater than 1 , and typically from 2 to 50. It is usual to refer to the TBN of such overbased materials and they may have a TBN of 150 or greater, and typically of from 250 to 450 or more.

Overbased alkali metal salts which may be used in the invention as detergents include oil-soluble or oil-dispersable overbased sulfonates, phenates, sulfurized phenates, thiophosphonates, salicylates, and naphthenates and other oil-soluble or oil- dispersable carboxylates of an alkali metal, e.g., sodium, potassium or lithium. Mixtures of such salts may also be used. The most preferred metals are sodium and potassium with sodium being particularly preferred. The overbased alkali metal salts may be present as the only detergents used in a lubricant, or in mixtures with other detergents such as the neutral alkali metal salts or the neutral or overbased salts of alkaline earth metals such as calcium and/or magnesium. Particularly convenient metal detergents are overbased sodium sulfonates and/or carboxylates having a TBN of from 250 to 450 TBN, and overbased sodium phenates, sulfurized phenates and salicylates having TBN of from 150 to 500, used alone or in mixtures with other detergents including overbased and neutral calcium and/or magnesium detergents.

Sulfonates may be prepared from sulfonic acids which are typically obtained by the sulfonation of alkyl substituted aromatic hydrocarbons such as those obtained from the fractionation of petroleum or by the alkylation of aromatic hydrocarbons. Examples included those obtained by alkylating benzene, toluene, xylene, naphthalene, diphenyl or their halogen derivatives such as chlorobenzene, chlorotoluene and chloronaphthalene. The alkylation may be carried out in the presence of a catalyst with alkylating agents having from about 3 to more than 70 carbon atoms. The alkaryl sulfonates usually contain from about 9 to about 80 or more carbon atoms, preferably from about 16 to about 60 carbon atoms per alkyl substituted aromatic moiety.

The oil soluble sulfonates or alkaryl sulfonic acids may be neutralized with oxides, hydroxides, alkoxides, carbonates, carboxylate, sulfides, hydrosulfides,

nitrates, borates and ethers of the alkali metal. The amount of metal compound is chosen having regard to the desired TBN of the final product.

Alkali metal carboxylates may be prepared in a number of ways: for example, by adding a basic alkali metal compound to a reaction mixture comprising the carboxylic acid (which may be part of a mixture with another organic acid such as a sulfonic acid) or its alkali metal salt and promoter, and removing free water from the reaction mixture to form an alkali metal salt, then adding more basic alkali metal compound to the reaction mixture and removing free water from the reaction mixture. The carboxylate is then overbased by introducing the acidic material such as carbon dioxide to the reaction mixture while removing water. This can be repeated until a product of the desired TBN is obtained.

The carboxylic acids from which alkali metal overbased salts may be prepared include aliphatic, cycloaliphatic and aromatic mono- and polybasic carboxylic acids. The aliphatic acids generally will contain at least 8 carbon atoms, preferably from 8 to 50 carbon atoms, typically contains at least 12 carbon atoms and more preferably from 12 to 25 carbon atoms. Aliphatic carboxylic acids are preferred, which may be saturated or unsaturated, and include fatty acids such as, for example, stearic acid and polyaikene-substituted carboxylic acids prepared by reacting a polyalkene with an α, β- unsaturated acid or its anhydride such as maleic anhydride. The number average molecular weight of the polyalkenes may be from 100, those having Mn of from 250 to 5000 are most preferred. The polyalkenes may be conventional homopolymers or copolymers of polymerizable olefin monomers of from 2 to 18 carbon atoms, such as ethylene, propylene, 1-butene or isobutene. The polyalkenes may also be prepared using a metallocene catalyst as described above in relation to the ashless dispersant.

Hydrocarbyl-substituted succinic acids, and particularly polyisobutenyl succinic acids and anhydrides, are a preferred class of carboxylates which may be used to prepared the alkali metal overbased salts.

Aromatic carboxylic acids which may be employed are aliphatic subtituted aromatic groups having one or more carboxy substituents and optionally one or more hydroxy or thiol subtituents. Specific examples of aromatic carboxylic acids include substituted benzoic, phthalic and salicyclic acids.

Combinations of sulphonic acids and carboxylic acids may be employed and the preferred sulphonic acids are those described hereinbefore in connection with overbased sulfonates.

Alkali metal salts of phenols and sulfurised phenols are prepared by reaction with an appropriate metal compound such as an oxide, hydroxide or alkoxide and overbased products may be obtained by methods well known in the art. Sulfurised phenols may be prepared by reacting a phenol with sulfur or a sufur containing compound such as hydrogen sulfide, sulfur monohalide or sulfur dihalide, to form products which are generally mixtures of compounds in which 2 or more phenols are bridged by sulfur containing bridges.

The overbasing process is well known in the art and typically comprises reacting acidic material with a reaction mixture comprising the organic acid or its alkali metal salt, a alkali metal compound. That acidic material may be a gas such as carbon dioxide or sulphur dioxide, or as discussed below may be boric acid. Processes for the preparation of overbased alkali metal sulphonates and phenates are described in EP- A-266034. A process suitable for overbased sodium sulfonates is described in EP-A- 235929. Processes suitable for overbased alkali metal carboxylates are described in US 2,616,904; 2,616,905; 2,616,906; 3,242,080; 3,250,710, 3,256,186; 3,274,135; 3,492,231 ; and 4,230,586, and WO-A-93/23504 and 93/23505.

The overbased alkali metal detergents can be borated. The boron may be introduced by using boric acid as the acidic material used in the overbasing step. However a preferred alternative is to borate the overbased product after formation by reacting a boron compound with the overbased alkali metal salt. Boron compounds include boron oxide, boron oxide hydrate, boron trioxide, boron trifluoride, boron tribromide, boron trichloride, boron acid such as boronic acid, boric acid, tetraboric acid and metaboric acid, boron hydrides, boron amides and various esters of boron acids. Boric acid is preferred. Generally, the overbased metal salt may be reacted with a boron compound at from 50°C to 250°C, in the presence of a solvent such as mineral oil or xylene. The borated overbased alkali metal salt preferably comprises at least 0.5%, preferably from 1 % to 5%, by weight boron.

D. Other Components

Additional additives are typically incorporated into the compositions of the present invention. Examples of such additives are viscosity modifiers, antioxidants,

anti-wear agents, friction modifiers, rust inhibitors, anti-foaming agents, demulsifiers, and pour point depressants.

The viscosity modifier functions to impart high and low temperature operability to a lubricating oil. The VM used may have that sole function, or may be multifunctional (MFVM).

Multifunctional viscosity modifiers that also function as dispersants are also known and may be prepared as described above for ashless dispersants. The oil soluble polymeric hydrocarbon backbone will usually have a Mn of from 20,000, more typically from 20,000 up to 500,000 or greater. In general, these dispersant viscosity modifiers are functionalized polymers (e.g. inter polymers of ethylene-propylene post grafted with an active monomer such as maleic anhydride) which are then dehvatized with, for example, an alcohol or amine.

Suitable compounds for use as monofunctional viscosity modifiers are generally high molecular weight hydrocarbon polymers, including polyesters. Oil soluble viscosity modifying polymers generally have weight average molecular weights of from about 10,000 to 1 ,000,000, preferably 20,000 to 500,000, which may be determined by gel permeation chromatography (as described above) or by light scattering.

Representative examples of suitable viscosity modifiers are polyisobutylene, copolymers of ethylene and propylene and higher alpha-olefins, polymethacrylates, polyalkylmethacrylates, methacrylate copolymers, copolymers of an unsaturated dicarboxylic acid and a vinyl compound, inter polymers of styrene and acrylic esters, and partially hydrogenated copolymers of styrene/ isoprene, styrene/butadiene, and isoprene/butadiene, as well as the partially hydrogenated homopolymers of butadiene and isoprene and isoprene/divinylbenzene.

The viscosity modifier used in the invention will be used in an amount to give the required viscosity characteristics. Since they are typically used in the form of oil solutions the amount of additive employed will depend on the concentration of polymer in the oil solution comprising the additive. However by way of illustration, typical oli solutions of polymer used as VMs are used in amount of from 1 to 30% of the blended oil. The amount of VM as active ingredient of the oil is generally from 0.01 to 6 wt%, and more preferably from 0.1 to 2 wt%.

15

Dihydrocarbyl dithiophosphate metal salts are frequently used as anti-wear and antioxidant agents. The metal may be an alkali or alkaline earth metal, or aluminum, lead, tin, molybdenum, manganese, nickel or copper. The zinc salts are most commonly used in lubricating oil in amounts of 0.1 to 10, preferably 0.2 to 2 wt. %, based upon the total weight of the lubricating oil composition.. They may be prepared in accordance with known techniques by first forming a dihydrocarbyl dithiophosphoric acid (DDPA), usually by reaction of one or more alcohol or a phenol with P ₂ Ss and then neutralizing the formed DDPA with a zinc compound. For example, a dithiophosphoric acid may be made by reacting mixtures of primary and secondary alcohols. Alternatively, multiple dithiophosphoric acids can be prepared where the hydrocarbyl groups on one are entirely secondary in character and the hydrocarbyl groups on the others are entirely primary in character. To make the zinc salt any basic or neutral zinc compound could be used but the oxides, hydroxides and carbonates are most generally employed. Commercial additives frequently contain an excess of zinc due to use of an excess of the basic zinc compound in the neutralization reaction.

The preferred zinc dihydrocarbyl dithiophosphates are oil soluble salts of dihydrocarbyl dithiophosphoric acids and may be represented by the following formula:

- wherein R and R' may be the same or different hydrocarbyl radicals containing from 1 to 18, preferably 2 to 12, carbon atoms and including radicals such as alkyl, alkenyl, aryl, arylalkyl, alkaryl and cycloaliphatic radicals. Particularly preferred as R and R' groups are alkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, for example, be ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl, octadecyl, 2-ethylhexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl, propenyl, butenyl. In order to obtain oil solubility, the total number of carbon atoms (i.e. R and R') in the dithiophosphoric acid will generally be about 5 or greater. The zinc dihydrocarbyl dithiophosphate can therefore comprise zinc dialkyl dithiophosphates. Conveniently at least 50 (mole) % of the alcohols used to introduce hydrocarbyl groups into the dithiophosphoric acids are secondary alcohols.

Oxidation inhibitors or antioxidants reduce the tendency of mineral oils to deteriorate in service which deterioration can be evidenced by the products of oxidation such as sludge and varnish-like deposits on the metal surfaces and by viscosity growth. Such oxidation inhibitors include hindered phenols, alkaline earth metal salts of alkylphenolthioesters having preferably C5 to C12 alkyl side chains, calcium

16

nonylphenol sulfide, ashless oil soluble phenates and sulfurized phenates, phosphosulfurized or sulfurized hydrocarbons, phosphorous esters, metal thiocarbamates, oil soluble copper compounds as described in US 4,867,890, and molybdenum containing compounds.

Typical oil soluble aromatic amines having at least two aromatic groups attached directly to one amine nitrogen contain from 6 to 16 carbon atoms. The amines may contain more than two aromatic groups. Compounds having a total of at least three aromatic groups in which two aromatic groups are linked by a covalent bond or by an atom or group (e.g., an oxygen or sulfur atom, or a -CO-, -SO2- or alkylene group) and two are directly attached to one amine nitrogen also considered aromatic amines. The aromatic rings are typically substituted by one or more substituents selected from alkyl, cycloalkyl, alkoxy, aryloxy, acyl, acylamino, hydroxy, and nitro groups.

Friction modifiers may be included to improve fuel economy. Oil-soluble alkoxylated mono- and diamines are well known to improve boundary layer lubrication. The amines may be used as such or in the form of an adduct or reaction product with a boron compound such as a boric oxide, boron halide, metaborate, boric acid or a mono-, di- or trialkyl borate.

Other friction modifiers are known, Among these are esters formed by reacting carboxylic acids and anhydrides with alkanols. Other conventional friction modifiers generally consist of a polar terminal group (e.g. carboxyl or hydroxyl) covalently bonded to an oleophillic hydrocarbon chain. Esters of carboxylic acids and anhydrides with alkanols are described in US 4,702,850. Examples of other conventional friction modifiers are described by M. Belzer in the "Journal of Tribology" (1992), Vol. 114, pp. 675-682 and M. Belzer and S. Jahanmir in "Lubrication Science" (1988), Vol. 1 , pp. 3- 26.

Rust inhibitors selected from the group consisting of nonionic polyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, and anionic alkyl sulfonic acids may be used.

Copper and lead bearing corrosion inhibitors may be used, but are typically not required with the formulation of the present invention. Typically such compounds are the thiadiazole polysulfides containing from 5 to 50 carbon atoms, their derivatives and polymers thereof. Derivatives of 1 ,3,4 thiadiazoles such as those described in U.S. Pat. Nos. 2,719,125; 2,719,126; and 3,087,932; are typical. Other similar materials are

described in U.S. Pat. Nos. 3,821 ,236; 3,904,537; 4,097,387; 4,107,059; 4,136,043; 4,188,299; and 4,193,882. Other additives are the thio and polythio sulfenamides of thiadiazoles such as those described in UK. Patent Specification No. 1 ,560,830. Benzotriazoles derivatives also fall within this class of additives. When these compounds are included in the lubricating composition, they are preferrably present in an amount not exceding 0.2 wt % active ingredient.

A small amount of a demulsifying component may be used. A preferred demulsifying component is described in EP 330,522. It is obtained by reacting an alkylene oxide with an adduct obtained by reacting a bis-epoxide with a polyhydric alcohol. The demulsifier should be used at a level not exceeding 0.1 mass % active ingredient. A treat rate of 0.001 to 0.05 mass % active ingredient is convenient.

Pour point depressants, otherwise known as lube oil flow improvers, lower the minimum temperature at which the fluid will flow or can be poured. Such additives are well known. Typical of those additives which improve the low temperature fluidity of the fluid are Cβ to C-| s dialkyl fumarate/vinyl acetate copolymers and polyalkylmethacrylates.

Foam control can be provided by many compounds including an antifoamant of the polysiloxane type, for example, silicone oil or polydimethyl siloxane.

Some of the above-mentioned additives can provide a multiplicity of effects; thus for example, a single additive may act as a dispersant-oxidation inhibitor. This approach is well known and does not require further elaboration.

When lubricating compositions contain one or more of the above-mentioned additives, each additive is typically blended into the base oil in an amount which enables the additive to provide its desired function. Representative effective amounts of such additives, when used in crankcase lubricants, are listed below. All the values listed are stated as mass percent active ingredient.

ADDITIVE MASS % MASS % (Broad) (Preferred)

Ashless Dispersant 0.1 - 20 1 - 8

Metal detergents 0.1 - 15 0.2 - 9

Corrosion Inhibitor 0 - 5 0 - 1.5

Metal dihydrocarbyl dithiophosphate 0.1 - 6 0.1 - 4

Supplemental anti-oxidant 0 -5 0.01 - 1.5

Pour Point Depressant 0.01 - 5 0.01- 1.5

Anti-Foaming Agent 0 - 5 0.001-0.15

Supplemental Anti-wear Agents 0 - 0.5 0 - 0.2

Friction Modifier 0 - 5 0 - 1.5

Viscosity Modifier ¹ 0.01- 6 0 - 4

Mineral or Synthetic Base Oil Balance Balance

1. In a multigrade oil

The components may be incorporated into a base oil in any convenient way. Thus, each of the components can be added directly to the oil by dispersing or dissolving it in the oil at the desired level of concentration. Such blending may occur at ambient temperature or at an elevated temperature.

Preferably all the additives except for the viscosity modifier and the pour point depressant are blended into a concentrate or additive package described herein as the detergent inhibitor package, that is subsequently blended into basestock to make finished lubricant. Use of such concentrates is conventional. The concentrate will typically be formulated to contain the additive(s) in proper amounts to provide the desired concentration in the final formulation when the concentrate is combined with a predetermined amount of base lubricant.

Preferably the concentrate is made in accordance with the method described in US 4,938,880. That patent describes making a premix of ashless dispersant and metal detergents that is pre-blended at a temperature of at least about 100°C. Thereafter the pre-mix is cooled to at least 85°C and the additional components are added.

The final formulations may employ from 2 to 15 mass % and preferably 5 to 10 mass %, typically about 7 to 8 mass % of the concentrate or additive package with the remainder being base oil.

The compositions of the invention supήsingly enable the enhanced dispersancy of the ashless dispersants to be realised in an oil having excellent detergent properties which may be particularly useful in combatting piston deposits in diesel engines. They may also provide a higher resistance to oxidation and/or a decreased tendency to interaction with overbased additives in packages, than a formulation containing the ashless dispersant in combination with overbased alkaline earth metal salts as detergents.

The invention will now be described by way of illustration only with reference to the following examples. In the examples, unless otherwise noted, all treat rates of all additives are reported as mass percent active ingredient, and amounts expressed inparts are parts by weight.

EXAMPLES

Examples 1-4 and Comparative Examples A and B

The resistance of compositions of the invention to oxidation is demonstrated in the following tests where compositions of the invention are tested in a bench oxidation test against comparative formulations in which alkaline earth metal salts are used as detergents.

Oxidation test

The oxidation test employed is a bench test in which 300 ml of a sample to be tested is placed in an oxidation tube with a chloroform solution of ferric acetylacetonoate providing 40ppm of that compound as catalyst. Air is blown for about 20 minutes until the catalyst is dispersed uniformly. The tube is then held at a temperature of 165°C ± 5°C while air is blown through at 1.7 ± 0.2 litres/min for 64 hours. 5ml samples are taken and the viscosity measured in Pa.s at 40°C using a Haake viscometer.

The results are given in the table below, Table 2, expressed as the % viscosity increase of the tested compositions as measured after a number of hours, and the time for the viscosity to increase by 200%.

The compositions tested each contained 6 mass% of the ashless dispersant and the metal detergent in an amount to give each composition a TBN resulting from colloidal carbonate of 8. The ashless dispersants used are a conventional borated polyisobutenyl succinimide prepared from a polyisobutene having an of 2225 (identifed in the Table below as PIBSA/PAM); and an ashless dispersant as required by the present invention prepared from an ethylene-butene copolymer (Mn = 3250, ethylene content = 46%, terminal vinylidene = 66%) functionalised by a carbonyl group introduced by the Koch reaction, and subsequently aminated and then borated, as described in WO-A-94/13709 (referred to herein as EBCO/PAM).

The overbased alkali metal additives used were as set out in the table below, Table 1 , which indicates the soap content and type, the total TBN of the additive and the calculated TBN attributable to the carbonate of the overbasing:

Table 1

Additive Type Total TBN Calc. TBN from (mgKOH/g) carbonate

Na 1 Sodium sulfonate/ carboxylate 407 400 containing 25% of soap of which

20% is sulphonate, 5% is carboxylate

Na 2 Sodium sulfonate carboxylate 419 400 containing 25% of soap

(11.25% sulphonate, 13.75% carboxylate)

Na 3 Sodium carboxylate containing 378 354 25% of soap (all carboxylate)

Na 4 Sodium sulfurised phenate 420 402 containing 35% soap (30% sulfurised phenate, 5% carboxylate)

Mg Magnesium sulfonate containing 406 400 26% soap (all sulphonate)

The sodium additives Na 1 , Na 2, and Na 3 were prepared following the teaching of EP-A-266034, as follows. A mixture of 336 parts sodium hydroxide, 870 parts 2-ethoxyethanol and 720 parts xylene was azeotroped to remove 186 ml of water. To the mixture at 90°C was added a solution in oil of 950 Mn polyisobutenyl succinic anhydride (Na 1: 66.7 parts, Na 2: 155 parts, Na 3: 329.2 parts), and where appropriate a 60% oil solution of an poly-n-butene-substituted benzene sulphonic acid having an Mn of 682 (Na 1 : 362.9parts; Na 2: 203.1 parts; Na 3: 0 parts), and diluent oil. The reaction mixture was carbonated at about 90°C until breakthrough, then a mixture of 1 part water to 5 parts 2-ethoxyethanol was added dropwise until no carbon dioxide was evolved. The desired product was obtained after stripping under vacuum and filtering.

The sodium phenate Na 4 was prepared following the teaching of EP-A-266034, as follows. A mixture of 560 parts sodium hydroxide, 1450 parts 2-ethoxyethanol and 1200 parts xylene was azeotroped to remove 305 ml of water. At 60°C there was added 452.9 parts nonyl phenol sulphide, 80.5 parts of 950 M, polyisobutenyl succinic anhydride and diluent oil. This mixture was refluxed and a further 65 ml of distillate removed by azeotroping. The mixture was then cooled to 90°C and carbon dioxide blown through the mixture at 1000 ml/min until no further CO2 was absorbed, ie. when the exit rate was equal to the inlet rate. This took approximately 4 hours and during this time the temperature increased from 90 to 104°C. A mixture of 70 parts water and 250 parts 2-ethoxyethanol were slowly added to the reaction mixture and carbon dioxide was evolved. Under a nitrogen purge the product was then heated to 180°C to remove 2-ethoxyethanol and xylene. The product was then vacuum stripped and filtered.

The 400TBN overbased magnesium sulfonate was typical of commercially available materials of this type.

Table 2

Footnote:

= too viscous to measure

The results demonstrate the benefits of the compositions of the invention in resisting oxidation in comparison to compositions prepared from alkaline earth metal detergents either with conventional PIBSA/PAM dispersants or with the new EBCO/PAM dispersants in combination with overbased alkaline earth metal sulfonate.

Examples 5-8 and Comparative Examples Cand D

A further advantage of the compositions of the invention is demonstrated by comparing the behaviour of blends of mixtures of the same dispersant as used in Examples 1-4 above and overbased sodium detergents Na 1 to 4, with dispersant detergent blends using commercially available overbased calcium and magnesium sulphonates.

Blending test

Binary mixtures of 4 parts of the EBCO/PAM dispersant used in Examples 1-4 and 1 part overbased detergent were prepared by mixing the components at 100°C using a mechanical stirrer and the performance of the blend was observed. Where possible the kinematic viscosity of the blend was measured. The blends tested and the results obtained are set out in the table, Table 3, below:

Table 3

Footnotes:

1 = Na 1-4 and Mg are as defined in Table 1 , Ca is a commercially available 300TBN calcium sulphonate comprising 29% soap prepared from the same sulphonic acid as used in the preparation of Na 1 and Na 2.

2 = "normal" means the blend continued to behave as a liquid with measurable viscosity that could be stirred at 100°C; "thickening" means that the blend rapidly becoming a semi-solid intractable gel and exhibited the Weissenberg effect, climbing the stirrer shaft.

* = too viscous to measure; n.m. = not measured

These results show that the compositions of the invention also show a reduced interaction so enabling the dispersant benefits of the EBCO/PAM ashless dispersants

to be more readily deployed in lubricating particularly crankcases of gasoline and diesel engines.

Example 9 and Comparative Example E

The benefits of compositions of the invention in improving engine and particularly piston cleanliness, and in combatting corrosion caused by acids formed in engine operation, are demonstrated in the following comparison in which engine conditions are simulated in bench tests in which similar compositions containing overbased sodium and magnesium additives are compared.

Two fully formulated SAE 15W-40 multigrade oils are compared. The oils are blended in the same base oils (61 mass % Exxon ESN150 and15mass % Exxon ESN600) using identical viscosity modifiers (8 mass % PARATONE 8452 available from Exxon Chemical Limited), and 16 mass % of generally similar detergent inhibitor packages containing ashless dispersant, ash-containing detergent, antioxidant, anti- wear additive, demulsifier, friction modifier, and anti-foam additive. The ashless dispersant in both examples is the product prepared from an ethylene-butene copolymer (Mn = 3250, ethylene content = 46%, terminal vinylidene = 66%) functionalised by a carbonyl group introduced by the Koch reaction, and subsequently aminated and then borated, described hereinbefore as EBCO/PAM. The overbased detergent component used in the formulation of Example 9 is the 407 TBN sodium sulfonate/carboxylate additive, referred to hereinbefore as "Na 1". By way of comparison Comparative Example E replaces Na 1 by the 406 TBN magnesium sulphonate additive, described hereinbefore as "Mg".

Acid Neutralisation Test

The acid neutralisation test is carried out by placing a 20g sample of the oil under test in a stirred 50ml reaction flask closed to the atmosphere. This flask is held in an oil bath at 60°C and connected to a pressure transducer. The system is allowed to come to equilibrium, then 0.7ml 5M sulphuric acid is added and the pressure of carbon dioxide released by the acid treat is plotted against time. The results are expressed in Table 4 as the time to reach a carbon dioxide pressure of 1 , 1.5 and 2 psi (6.9, 10.3 and 13.8kPa). The more efficient the overbased additive is to neutralise acid build up, the shorter the time to reach a particular carbon dioxide pressure.

Panel Coker Test

The test was carried out usinga panel coking tester of the type available from Yoshida Kagaku Kikai Co. of Osaka, Japan as model PK-S, which corresponds to that described in Federal Test Method Standard No. 791 B. It was operated using a slightly modified procedure described below. The apparatus operates by splashing the test oil onto the underside of a heated test panel, which is sloped so that the oil either forms deposits on the panel or drains off into a sump from which it is recycled. The test panels are of aluminium alloy milled to a tolerance of 0.8μ which are prepared by washing first in acetone then in heptane, followed by drying at 60°C, before being placed in the apparatus.

225g of test oil is placed in the sump of the tester which is then set to operate for cycles of 15s on/45s off for 1 hour, at a sump temperature of 100°C and at panel temperatures of 280°C and 320°C. At the end of each test the panel is cooled, washed in heptane and dried. The panels are visually rated to give an indication of the type and density of deposits which are recorded as "merits" (the higher the better). The performance at the two panel temperatures is a measure of the tendency to form piston deposits on the lower (cooler) and upper (hotter) parts of a piston during lubrication of an engine.

The results of the tests on the two test oils is set out in Table 4 below:

Table 4

The results demonstrate the benefits of the invention in improved engine cleanliness and corrosion reduction.