Solid Particles Containing Lubricating Oil Composition and Method for Using Same

This invention relates to improved lubricating oil compositions. More particularly, this invention relates to lubricating oil compositions which include solid materials to enhance the properties of such compositions.

Oil compositions are conventionally used to lubricate internal combustion engines, for example, such engines which power motor vehicles. Previous studies have indicated that the inclusion of certain solid materials, e.g., graphite, in these oil compositions improves the engine's fuel efficiency. For example, studies reported in "Stable Colloid Additives for Engine Oils -- Potential Improvement in Fuel Economy", James E. Bennington et al, Society of Automotive Engineers, Fuels and Lubricants Meeting, Houston, Texas, June 3-5, 1975, indicate that a gasoline mileage improvement of between 3 to 5 percent is obtained by adding one percent graphite to a conventional lubricating oil composition. Such improvement in fuel economy is particularly valuable in view of, for example, the short supply of such fuels.

However, other criteria must be met by lubricating oil compositions in order to be effective in modern internal combustion engines. For example, such compositions are required to meet certain specifications with regard to tendency to form deposits, e.g., varnish, sludge and the like, on engine components. The presence of the solid lubricants in these compositions tends to increase these deposit forming tendencies. A lubricating oil composition containing at least one of certain solid lubricants and having acceptable deposit forming characteristics is clearly desirable.

Therefore, one object of the present invention is to provide an improved lubricating oil composition.

Another object of this invention is to provide a solid particles-containing lubricating oil composition having reduced deposit forming tendency.

A still further object of the invention is to provide an improved method of lubricating an internal combustion engine. Other objects and advantages of the present invention will become apparent hereinafter.

An improved lubricating oil composition has now been developed. This composition comprises a major amount by weight of oil of lubricating viscosity; a minor amount by weight of solid particles effective to improve the lubricating properties of the composition; and a minor amount by weight of at least one of certain specific nitrogen-containing polymers.

One preferred nitrogen-containing polymer is a graft polymer having an dialkylaminoalkyl-methacrylate, or mixtures thereof, grafted to the polymer backbone.

A second preferred nitrogen-containing polymer is an oil soluble interpolymer prepared from a long chain n-alkyl methacrylate and a dialkylaminoalkylmethacrylate or a N(alkanone) acrylamide.

Preferred nitrogen-containing graft polymers employed in the invention comprise an oil soluble substantially linear terpolymer backbone of ethylene, preferably in an amount of about 15% to about 75% by weight of the polymer, at least one terminally unsaturated straight chain alkene containing from 3 to about 12 carbon atoms, preferably in an amount of about 25% to about 85% of the polymer, and at least one terminally unsaturated non-conjugated diolefin containing 5 to about 8 carbon atoms, preferably in an amount of about 0.10% to about 15% by weight of the polymer; said backbone having an average chain length of about 700 to about 7,000 carbon atoms and having recurringly grafted thereon a polymerized monomer of a dialkylaminoalkyl methacrylate of the formula: ##STR1## where R.sup.'1 and R.sup.'2 are alkyl of 1 to 2 carbon atoms and A is a divalent alkylene radical of from 2 to about 4 carbon atoms and (3) mixtures thereof. Preferably, the graft polymer has an inherent viscosity of between about 0.6 and 1.9 as a 0.10 wt.% solution in tetrachloroethylene at 30.degree. C and has a weight ratio of backbone component to said graft component of between about 1000:1 and about 1:10 Preferred nitrogen-containing interpolymers employed in the invention comprise interpolymers prepared from monomers selected from the group consisting of (1) a C.sub.4 -C.sub.22 n-alkylmethacrylate, mixtures thereof, and (2) a dialkylaminoalkylmethacrylate or a N(alkanone) acrylamide, said interpolymer having a number average molecular weight of about 30,000 to 120,000.

The incorporation of minor amounts of these nitrogen-containing polymers into the present solid particles-containing compositions has been found to provide a surprising degree of reduction in detrimental deposit formation, e.g., on internal combustion engine components lubricated by the present compositions.

The oils used in the compositions of the present invention are those conventionally used in lubricant manufacture. The suitable lubricating oils include those having a viscosity within the range of about 50 SUS to about 2000 SUS at 100.degree. F. These oils may be refined or otherwise processed to produce an oil having the desired quality. Although mineral oils are preferred, the oil may be synthetic in nature. The oil used in the present invention is preferably a mineral oil having a viscosity of about 100 SUS to about 1000 SUS at 100.degree. F. Combinations of two or more different oils in a single lubricating composition are within the scope of the present invention. The lubricating oil comprises a major proportion, preferably at least about 60 percent still more preferably at least about 70 percent, by weight of the total composition.

The present compositions include a minor amount by weight of solid particles effective to improve the lubricating properties of the compositions. Preferably, a major portion, by weight, and more preferably substantially all, of such solid particles, have a maximum transverse dimension in the range of about 1 miilimicron to about 2 microns, and most preferably in the range of about 1 millimicron to about 1 micron. Suitable solid particles for use in the present invention include those materials known to provide improved lubricating properties to lubricating oil compositions. Such solid particles include, for example, graphite, molybdenum disulfide, zinc oxide, tungsten disulfide, mica, boron nitrate, borax silver sulfate, cadmium iodide, lead iodide, barium fluoride, tin sulfide mixtures thereof and the like. The solid particles useful in the present compositions are preferably selected from the group consisting of graphite, molybdenum disulfide, zinc oxide, and mixtures thereof; more preferably from the group consisting of graphite, molybdenum disulfide and mixtures thereof; and most preferably, graphite.

The solid particles are preferably present in the present compositions in an amont of about 0.05% to about 5%, more preferably about 0.1% to about 2%, by weight of the total composition. The solid particles component of the present invention is preferably prepared as a colloidal suspension, in, for example, a conventional lubricating oil and/or at least one conventional lubricating oil detergent. For example, such colloidal suspensions or concentrates may contain about 2% to about 25% or more, by weight of such solid particles.

Any conventional lubricating oil detergent may be used to aid in stabilizing these colloidal suspensions of the presently useful solid particles. Such detergents are often characterized as comprising at least one surface active compound which, when included in a lubricating oil composition tends to inhibit solid contaminants, e.g., combustion by-product present in the engine's lubricating oil, from adhering to metallic surfaces of engine components. Although both ash-containing, metal-based detergents and ashless detergents are useful as such solid particles-containing suspension, the ashless detergents are preferred.

There are many examples of ash-containing, metal-based detergents which are suitable in such solid particles-containing suspension. The ashless detergents preferred for use are compounds which comprise an oil-solubilizing tail and a polar detergent head. Many ashless detergents fitting this general description are known to the art and are commercially available.

Specific examples of this type of ashless detergent include the polyamino-polyalkylene alkenyl succinimides. Amine salts of alkyl phosphoric acids, are also suitable. Polyamine derivatives of long chained hydrocarbons may also be used. Reaction products of alkylene polyamines with long chained alkenyl succinic anhydrides and long chained esters of Mannich bases are suitable detergents. As can be seen, the required polarity may be supplied by groups containing, for example, oxygen, sulfur, phosphorous, nitrogen and mixtures thereof. All of these suitable ashless detergents may be generally characterized as compounds comprising at least one substantially hydrocarbon portion of sufficient size to render the compound oil-soluble and at least one non-metallic polar portion which when attached to the hydrocarbon portion provides a substantial part, often essentially all, of the detergent action.

To illustrate, specific examples of ashless detergents suitable for use as solid particles stabilizers include polyamineopolyalkylene alkenyl succinimines, long chain polyamines, dihydrocarbon substituted polyamines, substituted-phenol substituted polyamine products and mixtures thereof. These compounds may be represented by the following structures:

It is preferred that R and R.sub.3 be alkenyl, preferably selected from the group consisting of polypropenyl and polyisobutenyl. It is preferred that each R.sub.1 be an independently selected alkylene radical containing from 1 to about 8, more preferably from 2 to about 6, carbon atoms. Suitable alkylene radicals from which each R.sub.1 may be independently selected include methylene, ethylene, propylene, butylene, hexylene, octylene and the like. Although each R.sub.1 may be independently selected, it is preferred that for any given ashless detergent all the R.sub.1 's contained therein are the same radicals.

The substantially hydrocarbon monovalent radicals from which each R.sub.2 may be independently selected each contain from 1 to about 8, preferably from 1 to about 4, carbon atoms. These substantially hydrocarbon radicals include alkyl, such as methyl, ethyl, propyl, butyl, hexyl, oxtyl and the like, alkenyl, such as ethenyl, propenyl, butenyl, hexenyl, octenyl and the like; aryl, alkaryl, aralkyl, alkenaryl and aralkenyl, such as phenyl, methyl phenyl, phenyl ethyl, ethenyl phenyl, phenyl ethenyl and the like.

The substantially hydrocarbon radicals from which R.sub.4 is selected contain from 2 to about 30, preferably from about 4 to about 24, carbon atoms. These radicals may be straight chain or branched, saturated or unsaturated, aliphatic (including cycloaliphatic), aromatic or combinations thereof. Examples of suitable radicals s include alkyl such as butyl, octyl, decyl, dodecyl, octadecyl, C.sub.24 alkyl and the like; alkenyl such as butenyl, octenyl, dodecenyl, octydecenyl, C.sub.24 alkenyl and the like; and aryl, alkaryl, aralkyl, alkenaryl, aralkenyl such as phenyl, benzyl, naphthyl, ethyl phenyl, decyl phenyl, octadecyl phenyl, phenyl butyl, phenyl decyl, phenyl octadecyl, butenyl phenyl, decenyl phenyl, octadecenyl phenyl, phenyl butenyl, phenyl decenyl, phenyl octadecenyl and the like. More preferably, R.sub.4 is selected from the group consisting of alkyl and alkenyl containing from about 10 to about 24 carbon atoms. pg,12

Each R.sub.5 is preferably independently selected from alkyl radicals containing from 4 to about 30, preferably from about 8 to about 20, carbon atoms. Examples of radicals from which each R.sub.5 may be independently selected include amyl, octyl, decyl, octadecyl and the like. The ##STR6## portion of the substituted phenol substituted polyamine acid salts may be replaced by, for example, alkylnaphthols and similar derivatives of biphenyl, terphenyl, phenanthrene, anthracene and the like.

The term "substantially" hydrocarbon radicals referred to herein includes those radicals which are composed primarily of carbon and hydrogen and also includes radicals which contain, in addition, minor amounts of substituents, such as oxygen, halide, sulfur, nitrogen and the like which do not substantially affect the hydrocarbon character of the radicals.

The specific ashless detergents noted above, as well as other of the many suitable ashless detergent materials and methods for preparing these materials are described in the following U.S. Pat. Nos.: 3,237,614; 3,018,247; 3,513,093; 3,753,670; 3,008,993; 3,275,554; 3,473,011; 3,574,576; 3,576,743; 3,578,422; 3,597,174; 3,369,110; 3,652,240; 3,655,351; 3,658,494; 3,658,495; 3,676,089; 3,701,640; 3,711,255; 3,717,447; 3,728,091; 3,746,520; 3,751,255; 3,756,793; 3,762,889; 3,764,281; 3,765,850; 3,773,479; 3,752,657; 3,753,670; 3,779,724 and 3,782,912.

The nitrogen-containing graft polymers useful in the present invention may be prepared using conventional methods well known in the art. For example, one such method involves a two stage procedure.

The first stage comprises contacting an oil soluble substantially linear terpolymer of ethylene, a terminally unsaturated straight chain alkene of 3 to about 12 carbons and a terminally unsaturated non conjugated alkadiene of 5 to about 8 carbons, the terpolymer reactant having an average carbon chain length of about 700 to about 7000 and an inherent viscosity of about 0.6 to about 1.9 at 0.10 wt.% solution in tetrachloroethylene at 30.degree. C with an alkyl lithium of 3 to about 10 carbon atoms in the presence of a liquid alkane, as solvent, of about 5 to about 10 carbon atoms and N,N,N',N' tetralkylalkylene diamine promoter wherein the alkyl and alkylene moieties in the diamine are from 1 to about 4 carbons to form a lithiated terpolymer intermediate. The first stage contacting is preferably conducted under anhydrous conditions (less than 0.01 wt.% water) and in an inert atmosphere, e.g., nitrogen and at a temperature between about 20.degree. and 100.degree. C for a period of between 1 and 25 hours. The first stage contacting preferably involves about 10 to about 200 moles alkyl lithium/100 g. of terpolymer and a mole ratio of alkyl lithium to diamine promoter of about 0.40 to about 2.0.

In the second stage the lithiated hydrocarbon terpolymer intermediate is contacted with a aminoalkyl methacrylate monomer of the formula: ##STR7## where R.sup.1 ' and R.sup.2 ' are alkyl of 1 or 2 carbons and A is a divalent alkylene radical of 2 to about 4 carbons, preferably at a temperature between about 100.degree. C. and -100.degree. C under anhydrous conditions and in an inert atmosphere utilizing a weight ratio of lithiated intermediate to total monomer reactant of about 0.2:1 to about 1000:1. The reaction period in the second stage is preferably between about 0.5 and 24 hours.

The graft polymer products is recovered from final reaction mixture by standard means, e.g., adding a lower alkanol having from 1 to 4 carbon atoms in quantities of between about 0.1 and 10 wt.% of the reaction mixture to destroy the alkyl lithium and diamine promoter followed by washing the solution with dilute aqueous mineral acid, (e.g., 5 10 wt.% aq. HCl) and then with water followed, if desired, by further standard purification techniques such as precipitation.

In the first stage of the reaction lithium moieties are randomly placed along the terpolymer chain, the lithiated locations being where the polymethacrylate graft component attaches via replacement of the lithium moieties.

Examples of the alkene component in the terpolymer reactant include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, and 1-dodecene. Suitable alkadiene components in said terpolymer reactant include 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 2-methyl,1, 5 hexadiene, 1,6-heptadiene and 1,7-octadiene. More preferably, the terpolymer is derived of about 40 to 55 wt.% ethylene, about 40 to 60 wt.% propylene and about 1 to 5 wt.% 1,4-hexadiene and has a carbon atom chain length of about 800 and about 5000. Excellent results are obtained wherein the terpolymer reactant contains 50.5 wt.% ethylene, 46 wt.% propylene and 3.5 wt.% 1,4-hexadiene and has a carbon atom chain length of between about 900 and 2600.

Examples of suitable dialkylaminoalkyl methacrylate monomers, are the N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, N,N-diemethylaminopropyl methacrylate and N,N-diethylaminophopyl methacrylate.

Examples of suitable alkyl lithium are butyl lithium, hexyl lithium, octyl lithium and decyl lithium.

Examples of suitable, N,N,N',N',-tetraalkylalkylenediamines are N,N,N',N',-tetramethylethylene diamine, N,N,N',N'-tetramethylpropylene diamine, N,N,N',N'-tetramethylbutylene diamine, and N,N,N',N'-terrabuthlmethylene diamine.

Examples of suitable inert reaction solvents are hexane, cyclohexane and heptane.

The nitrogen-containing interpolymers suitable for use in the composition of the present invention is an oil soluble interpolymer prepared from a long chain n-alkyl-methacrylate and a dialkylaminoalkylmethacrylate or a N(alkanone) acrylamide. Preferably the interpolymer has a number average molecular weight below about 120,000. These interpolymers are prepared by the complete polymerization of the monomer or mixtures thereof by conventional bulk, solution, or dispersion polymerization methods involving known polymerization catalysts, e.g., azo catalysts, such as azobisisobutronitrile of U.S. Pat. No. 2,471,959 or the well known peroxide catalysts such as benzoyl peroxide and lauryl peroxide, utilized in catalyst quantities of between about 0.1 and 5 wt. percent. Polymerization is normally conducted at a temperature between about 50.degree. and 150.degree. C. preferably at 80.degree.-100.degree. C., and usually carried out in an inert atmosphere such as nitrogen or carbon dioxide to prevent undesirable oxidation. During polymerization, samples are taken periodically for refractive index determination. The polymerization reaction is continued until the refractive index remains relatively steady with the normal reaction time taken between 1 and 10 hours.

The monomers utilized to prepare the useful nitrogen-containing interpolymers include n-alkylmethacrylates and a dialkylaminoalkylmethacrylate or a N(alkanone) acrylamide. The n-alkylmethacrylate monomers are generally selected from those which contain from about 4 to about 22, preferably about 12 to about 18, carbon atoms in the aliphatic hydrocarbon chain. These methacrylates are prepared by standard esterification techniques through the reaction of methacrylic acid with technical grades of long chain primary alcohols. These commercially available alcohols are mixtures of n-alkanols of various chain lengths containing between about 4 and 22 carbons in the alkyl group. Several suitable sources of these alcohols mixtures and the technical grade alcohols sold under the tradename "Neodols" by Shell Chemical Corporation and under the tradename "Alfols" by Continental Oil Company. Typical analysis of two useful alcohols are set forth below:

One of the nitrogen-containing monomers which can be employed to a suitable nitrogen-containing interpolymer used in this invention is a dialkylaminoalkylmethacrylate. A preferred dialkylaminoalkylmethacrylate is a diC.sub.1 -C.sub.6 alkylamino C.sub.1 -C.sub.6 alkylmethacrylate. Specific examples of these useful methacrylate monomers are diethylaminopropylmethacrylate, dimethylaminoethylmethacrylate, the propylaminoethacrylates and the butylaminobutylmethacrylates. We find that dimethylaminoethymethacrylate is particularly useful.

Another suitable nitrogen-containing monomer is an acrylamide. Preferred acrylamides are N(1,1-dimethylbutan-3-one) acrylamide and N(1,2-dimethyl-1-ethyl-butan-3-one) acrylamide.

The compositions of the present invention preferably contain about 0.1% to about 12% by weight (based on the total composition) of at least one of the above-described nitrogen-containing polymers, more preferably, about 3% to about 10% by weight of the total composition. Preferably, the amount by weight of such nitrogen-containing polymers in the composition of this invention is at least equal to the amount of solid particles, e.g., graphite, molybdenum disulfide and the like, present. More preferably, the amount of polymer is at least about 2 times and most preferably at least about 3 times, the amount of solid particles.

The compositions of the present invention possess the advantageous combination of a high degree of effectiveness with respect to lubricity, dispersant-detergent properties, pour-point depressing action and viscosity index improvements. Further, the present compositions provide for improved fuel economy and reduced tendency to form deposits.

In addition to the components already described herein, lubricating compositions contemplated herein can advantageously contain other conventional adjuvants, such as, for example, anti-oxidants, metal deactivators, pour point depressants, oiliness agents, blooming agents, peptizing agents, and the like.

The lubricating compositions of the present invention may be prepared in any conventional manner. For example, the various components may be brought together and blended at a slightly elevated temperature, i.e., about 100.degree. to 130.degree. F., to insure a uniform composition.

In many instances, the additives incorporated into the present lubricating compositions are available as a mixture in a mineral oil or other solvent carrier. Unless otherwise noted, the weight proportions given above refer to the amount of additive material on a carrier or solvent free basis.

The lubricating compositions of the present invention can be used to lubricate internal combustion engines. Maintaining (or causing to be maintained) a lubricating amount of the lubricating compositions of the present invention on the components of such internal combustion engine requiring lubrication, results in obtaining substantial benefits from the present invention.

The following examples illustrate clearly the present invention. However, these examples are not to be interpreted as specific limitations on the invention.

The following examples illustrate certain of the outstanding benefits of the present invention.

A series of four lubricating oil compositions were prepared by blending together individual components, noted below, at a slightly elevated temperature, i.e., about 100.degree. F. to about 130.degree. F., to insure proper mixing. The final compositions were as follows:

The Sequence V C Test described in Examples 1 and 2 illustrate the problems in formulating a suitable solids particles-containing lubricating composition. Examples 3 and 4 are lubricating oil composition in accordance with the invention. These lubricating compositions containing graphite and nitrogen-containing graph polymer and nitrogen-containing interpolymers of the invention provide reduced sludge and varnish deposition relative to lubricating compositions not containing these nitrogen-containing polymers, and are illustrative of the improved solids containing lubricating compositions of the invention.

While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.

Each of the lubricating oil compositions identified in Examples 1 and 2 was used to lubricate an internal combustion engine which, in turn, was operated through a Reference Sequence V C Test. This test, in which the engine is operated for 192 hours, is described in "Multicylinder Test Sequences for Evaluating Automotive Engine Oils--ASTM Special Technical Publication 315F", American Society for Testing and Materials (1973). This procedure is known to produce data which can be used to make valid comparisons of the effects various lubricating oil compositions have on engine sludge and varnish ratings under normal operating conditions.

Sludge and varnish ratings in the Reference Sequence V C Test are based upon visual inspection of various engine components and comparison with a series of CRC reference standards.

Results of this test using each of the above-described lubricating compositions are summarized below. For comparison purposes, minimum SE standard lubricating oil qualification ratings are also presented.

The above data indicate that compositions which include solid particles cause a substantial decrease in sludge and varnish ratings (increase in sludge and varnish formation). This conclusion is apparent by comparing the results from Composition 2 with those from the non-graphite containing Composition 1. Thus, the inclusion of the conventional viscosity index improver, which provides adequate sludge and varnish formation protection (see Example 1) when included in a composition without solid particles, fails to meet the SE qualification standards when such solid particles are added.