GB2108147A - Anti-wear additives - Google Patents

Abstract

The use of oil soluble salts of phosphate esters of formula <IMAGE> where R is C1-12 alkyl or alkoxy and R' is H or RO, as antiwear additives in lubricant formulations containing overbased sodium additives has been found preferable to the use of the conventional ZDDP's. In a preferred embodiment the salts of the phosphate esters are used together with sulphur donors such as phosphosulphurised polybutene.

Description

SPECIFICATION Improved antiwear additives The present invention relates to lubricating oil formulations, especially crankcase lubricants for automobiles. Such lubricants contain combinations of various additives to give the desired properties for the lubricant. Typical additives include compounds to control the viscosity/temperature relationship of the oil, dispersants to help retain particulate material suspended in the oil, antioxidants to retard oxidation and thickening of the oil, antiwear additives to inhibit wear of the engine through contact between moving metal parts and organo metallic compounds frequently highly basic compounds which act both as dispersants and to neutralise acids that may form in the oil during operation of the engine.

Examples of typical antioxidant and antiwear additives are the zinc dialkyldithiophosphates which are frequently used in combination with the organo calcium and magnesium compounds such as calcium and magnesium phenates or sulphonates. These calcium and magnesium compounds are often present as their basic phenates or sulphonates which consist of dispersions of colloidal metal carbonate held in oil by the sulphonate or phenate radical. Whilst these combinations have given adequate lubricants with the current trend towards oils having longer operating times and to oils operating under more stringent engine running conditions some or all of the calcium and magnesium organo compounds are being replaced by the more basic sodium containing compounds.

We find, however, that lubricants containing basic sodium compounds together with zinc dialkyldithiophosphate impart inferior antiwear properties during operation of the engine than is achieved using lubricants containing the traditional calcium and/or magnesium additives and the zinc dialkyldithiophosphate. We have found that the antiwear properties of lubricants containing basic sodium additives may be improved by the incorporation of certain oil soluble salts of phosphate esters in the lubricant. In a preferred embodiment the antiwear properties are further improved by the incorporation of a sulphur donor compound.

The present invention, therefore, provides a lubricating oil containing from 0.05% to 20% by weight of an overbased sodium compound and from 0.05% to 5% by weight of an oil soluble salt of a mono- or di-alkyl phosphate of the general formula

where R is alkyl or alkoxy containing from 1 to 12 carbon atoms and R' is hydrogen or RO where R is as defined above, where R' is RO the two R groups may be the same or different.

The present invention further provides the use as a lubricant additive the combination of an overbased sodium compound and an oil soluble salt of a phosphate ester of the general formula

where R is alkyl or alkoxy containing 1 to 12 carbon atoms and R' is hydrogen or RO where R is as defined above and where R' is RO the two R groups may be the same or different.

An overbased sodium compound within the terms of this agreement is an oil soluble organo sodium compound having a Total Base Number (TBN) greater than 20 Examples of suitable overbased sodium compounds include the carbonated derivatives of the reaction product of sodium with phosphosulphurised polyisobutylene such as those described in United Kingdom patent specification 921124. Alternatively overbased sodium sulphonates such as those prepared by carbonating oil solutions of sulphonic acids reacted with a stoichiometric excess of a sodium compounds may be used.

The salts of the phosphate esters used in the present invention should be salts of mono- or di-alkyl phosphates the alkyl group or groups imparting oil solubility. The phosphate esters are of the general formula:

where R is alkyl or alkoxy containing from 1 to 12 carbon atoms where R' may be hydrogen or RO.

Examples of preferred phosphate esters from which the salts may be made include the butyl phosphates such as di-n-butyl phosphate and di-iso-butyi phosphate although other suitable phosphate esters include dipropyl phosphate, dioctyl phosphate and phosphate mono- and di-ester containing alkoxy groups. The preferred salts are the amine salts obtained by reacting the phosphate esters of the type described above with a stoichiometric amount of an alkyl amine especially are containing from 4 to 12 carbon atoms such as Primene 81 R.

We have found that the antiwear properties of the lubricant may be further improved by the incorporation of oil soluble sulphur containing compounds which act as sulphur donors. Suitable compounds include the alkyl sulphides which may be mono- or poly-sulphides and/or mixtures thereof.

An example of a suitable sulphide is sulphurised butene. We prefer to use an amount of the sulphide that results in contributing from 0.1% to 2.0% by weight of sulphur to the lubricating oil. Other suitable sulphur compounds include sulphurised polybutenes.

The lubricating compositions of the present invention may and usually will contain other traditional lubricant additives such as rust inhibitors such as lecithin, sorbitan mono-oleate, dodecyl succinic anhydride or ethoxylated alkyl phenols; pour point depressants such as copolymers of vinyl acetate with fumaric acid esters of coconut oil alcohols; viscosity index improvers such as olefin copolymers, polymethacrylates; etc.

Dispersancy can be provided by a traditional lubricating oil ashless dispersant compounds such as derivatives of long chain hydrocarbon substituted carboxylic acids in which the hydrocarbon groups contains 50 to 400 carbon atoms. These will generally be a nitrogen containing ashless dispersant having a relatively high molecular weight aliphatic hydrocarbon oil solubilising group attached thereto or an ester of a succinic acid/anhydride with a high molecular weight aliphatic hydrocarbon attached thereto and derived from monohydric and polyhydric alcohols, phenols and naphthols.

The nitrogen containing dispersant additives are those known in the art as sludge dispersants for crankcase motor oils. These dispersants include material oil-soluble salts, amides, imides, oxazolines and esters of mono- and di-carboxylic acids (and where they exist the corresponding acid anhydrides) of various amines and nitrogen containing materials having amino nitrogen or hetercyclic nitrogen and at least one amido or hydroxy group capable of salt, amide, imide, oxazoline or ester formation. Other nitrogen containing dispersants which may be used in this invention include those wherein a nitrogen containing polyamine is attached directly to the long chain aliphatic hydrocarbon as shown in U.S.

Patents 3,275,554 and 3,565,804 where the halogen group on the halogenated hydrocarbon is displaced with various alkylene polyamines.

Another class of nitrogen containing dispersants which may be used are those containing Mannich base or Mannich condensation products as they are known in the art. Such Mannich condensation products generally are prepared by condensing about 1 mole of an alkyl substituted phenol with about 1 to 2.5 moles of formaldehyde and about 0.5 to 2 moles polyalkylene polyamine as disclosed, e.g. in U.S.

Patent 3,442,808. Such Mannich condensation products may include a long chain, high molecular weight hydrocarbon on the phenol group or may be reacted with a compound containing such a hydrocarbon, e.g., alkenyl succinic anhydride as shown in said aforementioned 3,442,808 patent.

Monocarboxylic acid dispersants have been described in U.K. Patent Specification 983,040. Here, the high molecular weight monocarboxylic acid can be derived from a polyolefin, such as polyisobutylene, by oxidation with nitric acid or oxygen; or by addition of halogen to the polyolefin followed by hydrolyzing and oxidation. Another method is taught in Belgian Patent 658,236 where polyolefins, such as polymers of C2 to C5 monoolefin, e.g. polypropylene or polyisobutylene, are halogenated, e.g. chlorinated, and then condensed with an alpha-beta-unsaturated, monocarboxylic acid of from 3 to 8, preferably 3 to 4, carbon atoms, e.g. acrylic acid, alpha-methyl-acrylic acid, etc.

Esters of such acids, e.g. ethyl methacrylate, may be employed if desired in place of the free acid.

The most commonly used dicarboxylic acid is alkenyl succinic anhydride wherein the alkenyl group contains about 50 to about 400 carbon atoms.

Primarily because of its ready availability and low cost, the hydrocarbon portion of the mono- or di-carboxylic acid or other substituted group is preferably derived from a polymer of a C2 to C5 monoolefin, said polymer generally having a molecular weight of about 700 to about 5000. Particularly preferred is polyisobutylene.

Polyalkyleneamines are usually the amines used to make the dispersant. These polyalkyleneamines include those represented by the general formula: H2N(CH2)n- ~- [ NH(cH2)n ] m---NH(cH2)nNH2 wherein n is 2 or 3, and m is O to 10. Examples of such polyalkyleneamines include diethylene triamine, tetraethylene pentamine, octaethylene nonamine, tetrapropylene pentamine, as well as various cyclic polyalkyleneamines.

Dispersants formed by reacting alkenyl succinic anhydride, e.g. polyisobutenyl succinic anhydride and an amine are described in U.S. Patents 3,202,678,3,154,560, 3,172,892,3,024,195, 3,024,237, 3,219,666,3,216,936 and Belgium Patent 662,875.

Alternatively, the ashless dispersants may be esters derived from any of the aforesaid long chain hydrocarbon substituted carboxylic acids and from hydroxy compounds such as monohydric and polyhydric alcohols or aromatic compounds such as phenols and naphthols, etc. The polyhydric alcohols are the most preferred hydroxy compound and preferably contain from 2 to about 10 hydroxy radicals, for example, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and other alkylene glycols in which the alkylene radical contains from 2 to about 8 carbon atoms.

Other useful polyhydric alcohols include glycerol, monooleate of glycerol, monstearate of glycerol, monomethyl ether of glycerol, pentaerythritol.

The ester dispersant 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. Mixtures of the above illustrated esters likewise are contemplated within the scope of this invention.

The alkenyl succinic polyamine type dispersants can be further modified with a boron compound such as boron oxide, boron halides, boron acids and ester of boron acids in an amount to provide about 0.1 to about 10 atomic proportions of boron per mole of the acylated nitrogen compound as generally taught in U.S. Patents 3,087,936 and 3,254,025. Mixtures of dispersants can also be used such as those described in United States Patent 4,113,639.

The oils may contain from 1.0 to 10 wt % preferably 2.0 to 7.0 wt % of these dispersants.

Alternatively the dispersancy may be provided by 0.3 to 10% of a polymeric Viscosity Index improver dispersant.

Examples of suitable Viscosity Index improvers dispersants include: (a) polymers comprised of C4 to C24 unsaturated esters of vinyl alcohol or C3 to C,O unsaturated mono- or di-carboxylic acid with unsaturated nitrogen containing monomers having 4 to 20 carbons; (b) polymers of C2 to C20 olefin with unsaturated C3 to C10 mono- or di-carboxylic acid neutralised with amine, hydroxy amine or alcohols; (c) polymers of ethylene with a C3 to C20 olefin further reacted either by grafting C4 to C20 unsaturated nitrogen containing monomers thereon or by grafting an unsaturated acid onto the polymer backbone and then reacting said carboxylic acid groups with amine, hydroxy amine or alcohol.

In these polymers the amine, hydroxy amine or alcohol "mono- or poly-hyddc" may be as described above in relation to the ashless dispersants compounds.

Magnesium and calcium containing additives may also be included in lubricating compositions.

These may be present for example as the metal salts of sulphonic acids, alkyl phenols, sulphurised alkyl phenols, alkyl salicylates, naphthenates, and other oil soluble mono- and di-carboxylic acids.

The highly basic alkaline earth metal sulfonates are usually produced by heating a mixture comprising an oil-soluble alkaryl sulfonic acid with an excess of alkaline earth metal compound above that required for complete neutralization of the sulfonic and thereafter forming a dispersed carbonate complex by reacting the excess metal with carbon dioxide to provide the desired overbasing. The sulfonic acids are typically obtained by the sulfonation of alkyl substituted aromatic hydrocarbons such as those obtained from the fractionation of petroleum by distillation and/or extraction or by the alkylation of aromatic hydrocarbons as for example those obtained by alkylating benzene, toluene, xylene, naphthalene, diphenyl and the halogen derivatives such as chlorobenzene, chlorotoluene and chloronaphthalene.The alkylation may be carried out in the presence of a catalyst with alkylation agents having from about 3 to more than 30 carbon atoms such as for example haloparaffins, olefins that may be obtained be dehydrogenation of paraffins, polyolefins as for example polymers from ethylene, propylene, etc. The alkaryl sulfonates usually contain from about 9 to about 70 or more carbon atoms, preferably from about 16 to about 50 carbon atoms per alkyl substituted aromatic moiety.

The alkaline earth metal compounds which may be used in neutralizing these alkaryl sulfonic acids to provide the sulfonates includes the oxides and hydroxides, alkoxides, carbonates, carboxylate, sulfide, hydrosulfide, nitrate, borates and ethers of magnesium, calcium, and barium. Examples are calcium oxide, calcium hydroxide, magnesium acetate and magnesium borate. As noted, the alkaline earth metal compound is used in excess of that required to complete neutralization of the alkaryl sulfonic acids.

Generally, the amount ranges from about 100 to 220%, although it is preferred to use at least 125%, of the stoichiometric amount of metal required for complete neutralization.

Polyvalent metal alkyl salicylate and naphthenate materials are known additives for lubricating oil compositions to improve their high temperature performance and the counteract depositions of carbonaceous matter on pistons (U.S. Patent 2,744,069). An increase in reserve basicity of the polyvalent metal alkyl salicylates and naphthenates can be realized by utilizing alkaline earth metal, e.g.

calcium, salts of mixtures of C8-C26 alkyl salicylates and phenates (see U.S. Patent 2,744,069) or polyvalent metal salts of alkyl salicyclic acids, said acids obtained from the alkylation of phenols followed by phenation, carboxylation and hydrolysis (U.S. Patent 3,704,315) which could then be converted into highly basic salts by techniques generally known and used for such conversion. The reserve basicity of these metal-containing rust inhibitors is usefully at TBN levels of between about 60 and 150. Included with the useful polyvalent metal salicylate and naphthenate materials are the methylene and sulfur bridged materials which are readily derived from alkyl substituted salicyclic or naphthenic acids or mixtures of either or both with alkyl substituted phenols. Basic sulfurized salicylates and a method for their preparation is shown in U.S.Patent 3,595,791.

The present invention is illustrated but in no way limited by reference to the following examples in which the antiwear performance of a lubricating oil containing 1.0 wt % of a 400 TBN sodium sulphonate and various antiwear additives was compared with that of the oil containing 1.0 wt % of a 400 TBN magnesium sulphonate and the antiwear additives in the 4 Bail test. A series of tests were carried out using different loads and the initial seizure load of the formulation was obtained by plotting the wear scar diameter against the load.

As well as the 1 wt % of the basic additive the lubricant contained 5 wt % of a dispersant blend and the amounts of the salt of the phosphate ester specified in the following Table. The remainder was a neutral mineral lubricating oil of Initial Seizure Load Basic Additive Antiwear Additive Sodium Magnesium 2.4 wt % of the salt of di-n-butyl phosphate + 0.7 wt % 105 110 of sulphurized polybutene 2.1 wt % of the salt of di-iso-butyl phosphate and 106 108 "Primene 81 R" + 1.0 wt % of sulphurized polybutene ZDDP 110 155 2.1 wt % of salt of polyoxyalkyl diphosphate (Briphos L2D) 110 110 and "Primene 81 R" 2.1 wt % of salt of polyoxyalkyl diphosphate (Briphos L2D) 110 150 and "Primene 81 R" + 0.7 wt % of sulphurised polybutene

Claims (2)

1. A lubricating oil containing from 0.05% to 20% by weight of an overbased sodium compound and from 0.05% to 5% by weight of an oil soluble salt of a mono- or di-alkyl phosphate of the general formula

where R is alkyl or alkoxy containing from 1 to 12 carbon atoms and R' is hydrogen or RO where R is as defined above, where R' is RO the two R groups may be the same or different.

2. The use as a lubricant additive the combination of an overbased sodium compound and an oil soluble salt of a phosphate ester of the general formula

where R is alkyl or alkoxy containing 1 to 12 carbon atoms and R' is hydrogen or RO where R is as defined above and where R' is RO the two R groups may be the same or different.