EP0768367A1

EP0768367A1 - Lubricating composition

Info

Publication number: EP0768367A1
Application number: EP96307408A
Authority: EP
Inventors: Noriyoshi Asahi Denka Kogyo K.K. Tanaka
Original assignee: Adeka Corp; Asahi Denka Kogyo KK
Current assignee: Adeka Corp
Priority date: 1995-10-12
Filing date: 1996-10-11
Publication date: 1997-04-16
Anticipated expiration: 2016-10-11
Also published as: CA2187474C; CA2187474F; ES2390958T3; EP0768367B1; CA2187474A1

Abstract

A lubricating composition contains a base oil and an organomolybdenum compound and has a sodium content of not greater than 200 ppm. The limited content of a sodium metal allows the organomolybdenum compound to fully exhibit its peculiar physical performance in that composition. Sufficient friction reduction can be achieved when the lubricating composition is applied as a lubricant composition. Excellent frictional and wearing properties are attainable when the lubricating composition is used as a grease composition.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to lubricating compositions and has particular reference to a lubricant composition containing a base lubricating oil and one or more molybdenum compounds and having a sodium content of not greater than 200 ppm, and also to a grease composition containing a base lubricating grease and one or more molybdenum compounds and having a sodium content of not greater than 200 ppm. In particular, the grease composition is excellent in its frictional and wearing characteristics and hence is suitably applicable to universal joints inclusive of constant velocity joints (CVJ) for automotive use, constant velocity gears and variable speed gears.

Description of the Related Art

In the present situation surrounding automotive vehicles, controls regarding fuel economy, exhaust gas emissions and the like have become stricter. Behind these controls lie concerns about the environmental protection from global warming, air pollution, acid rain and the like as well as the protection of natural resources, especially out of concern about the exhaustion of limited petroleum deposits. In coping with the above trend, automotive fuel economy is most effective means available at present. To this end, it is of importance that the automobile itself be enhanced in respect to body weight, engine performance and the like, whereas improvements in engine oil in regards to lowered viscosity, the addition of suitable friction regulating additives, etc. is also very important.
Automotive engine oils, however, must now be used under more severe conditions than in the past. This is partly due to the impaired or adverse frictional conditions between engine oil and the engine, and elevated oil temperatures of accompanying increases in engine performance output. Another cause is seen in reduced quantities of engine oil used in order to reduce automobile weight. Thus, reductions in viscosity are a cause of engine wear or seizing.
A keen demand, therefore, has been voiced for the development of an additive that can overcome those problems stemming from engine oils that have reduced viscosities. An engine oil generally contains, to maintain desired performance, various additives such as friction regulating additives, antioxidants, cleaning agents, dispersants, extreme pressure agents, viscosity index improvers, pour point depressants, antiwear agents and the like. For instance, Japanese Patent Laid-Open No. 5-508188 discloses a lubricating composition in which an overbasified alkali metal salt such as of a sodium, potassium, lithium or like metal of an acidic organic compound, a dispersant, dihydrocarbyl dithiophosphate and an antioxidant are incorporated to reduce deterioration and prevent wear of the engine, and to present sludge formation. However, in order to solve the problems of wear and seizing noted above, organomolybdenum compounds are now being seen as essential additives.
Also, Japanese Patent Laid-Open No. 5-279686 suggests that the friction characteristics of an engine oil can be improved, without wear resistance and other important qualities impaired, by formulation of an organomolybdenum compound, a fatty ester, a metallic cleaning agent (calcium sulfonate, magnesium sulfonate, calcium phenate and magnesium phenate), an ashless cleaning dispersant (benzylamine, its boron derivative, an imide of alkenyl succinate and its boron derivative) and an antiwear agent [zinc dithiophosphate (ZDTP) and zinc dithiocarbamate (ZDTC)].
Constant velocity joints (CVJ) are being widely used for the rapidly growing numbers of FF and 4WD vehicles or FR vihicles with indepedent suspension. Although CVJ's are used to transmit engine-power to the wheels, smooth power transmission is also required even in when the steering wheel has been turned left or right. To this end, CVJ's are generally a plunger type joint that is axially slidable on the engine side and a fixed type joint that is fixed axially on the wheel side. The plunger joint involves sliding resistance arising in the axial direction from its rolling and sliding movements as it reciprocates, thus leading to undesirable noise and vibration in an automatic transmission car, namely vibration during idling, rolling during startup and acceleration of the car, and beat frequency and entrapped noises from the car at certain speeds. Vibration damping is now a significant problem in keeping with the demand for more comfortable quiter, automotive vehicles. Consequently, focus has been centered not only on improving the joints themselves, but also on improving the grease compositions to be filled therein.
In view of the fact that the damped vibration of an automobile is correlated to the friction coefficient and hence conducive to saved fuel, a grease composition has been sought which could hold vibration to an absolute minimum.
Molybdenum disulfide, a sulfur-phosphorus type additive, a lead type additive or the like has heretofore been employed as an additive to be incorporated in a grease composition for use with constant velocity joints. In recent years, however, organomolybdenum compounds have been put to use in the production of a grease exhibiting damped vibration that is a key quality in the art, i.e., a grease with low friction performance.
Japanese Patent Laid-Open No. 6-184583, for example, discloses a grease for use with constant velocity joints and also a grease composition for such joints wherein a urea grease is formulated with molybdenum dithiophosphate, molybdenum dithiocarbamate and ZDTC.
Engine oils, however, are usually composed of a wide variety of additives as already discussed. In such oils, the additives tend to interact in some cases with each other and thus fail to impart their respective inherent properties.
Furthermore, when the prevailing trend toward improved mileage fuel savings are taken into account, it becomes important to bring out the physical performance of a given organomolybdenum compound and retain it. Here, investigation is needed to see which of vrious selected additives would need to be formulated in such a way that the organomolybdenum compound could fully give rise to its performance.
In the case of the grease of Japanese Patent Laid-Open No. 6-184583 cited above, it has been found that good friction reduction performance is not necessarily attainable.
Generally, greases contain additives including oiliness improvers, antiwear agents, extreme pressure agents, solid lubricants, pour point depressants, viscosity index improvers, tackifiers, structural stabilizers and the like as well as special additives including cleaning dispersants, defoamesr, antiseptics, dyes, antistatic agents, emulsifiers, demulsifiers and the like. These additives would in some instances interact with each other, and the same thing can be said of organomolybdenum compounds.
In order to meet the requirements for greases recently developed, it is import for organomolybdenum compound to exhibit its full physical performance. Accordingly, a formulation is required that eliminates the causes of bars to such performance.

SUMMARY OF THE INVENTION

Accordingly, the present invention seeks to provide a lubricating composition suitable for use as a lubricant composition or as a grease composition.
As a result of extensive research made in an effort to overcome the foregoing deficiencies of the prior art, the present inventors have now found that friction reduction can be enhanced with good friction coefficient by lowering the content of alkali metal, particularly of sodium metal, in a lubricating composition. The present invention is based on such finding.
More specifically, the present invention in a first aspect provides a lubricating composition comprising a base oil and an organomolybdenum compound, characterized in that the composition has a sodium content of not greater than 200 ppm.
In a second aspect, the invention provides a lubricating composition comprising a base oil and one or more organomolybdenum compounds selected from the group consisting of sulfurized oxymolybdenum dithiocarbamates (MoDTC) represented by Formula (1)
wherein R¹ to R⁴ are each a hydrocarbyl group, and X¹ is an oxygen or sulfur atom; and sulfurized oxymolybdenum dithiophosphates (MoDTP) represented by Formula (2)
wherein R⁵ to R⁸ are each a hydrocarbyl group, and X² is an oxygen or sulfur atom, characterized in that the composition has a sodium content of not greater than 200 ppm.
In a third aspect, the invention provides a lubricating composition comprising a base oil; one or more organomolybdenum compounds selected from the group consisting of MoDTC represented by Formula (1)
wherein R¹ to R⁴ and X¹ are as defined above;
and MoDTP represented by Formula (2)
wherein R⁵ to R⁸ and X² are as defined above;
and one or more organozinc compounds selected from the group consisting of ZDTP represented by Formula (3)
wherein a is 0 or 1/3, and R⁹ and R¹⁰ are each a hydrocarbyl group;
and ZDTC represented by Formula (4)
wherein R¹¹ and R¹² are each a hydrocarbyl group,
characterized in that the composition has a sodium content of not greater than 200 ppm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The lubricating composition according to the present invention contains said organomolybdenum compound as an essential component. In order to ensure that such compound be able to exhibit its peculiar physical characteristics, the sodium content in the present composition should be not greater than 200 ppm, preferably below 100 ppm based on total amount of the composition. Also, the total content of an alkali metal including sodium in the composition should be set to be not beyond 200 ppm, preferably below 100 ppm, more preferably less than 50 ppm. Further, alkali metals mentioned herein are those classed among Group I of the Periodic Table in which lithium, sodium, potassium, rubidium, cesium and francium are included.
In general, an alkali metal such as sodium becomes introduced into the resultant lubricating composition in cases where such alkali metal has not been completely removed after it was employed as a catalyst or starting material in separating and purifying or synthesizing the desired base lubricating oil. Another such case is found with respect to alkali metals or their salts not being completely eliminated subsequent to their use as a catalyst or starting material in the syntheses of various additives as commonly practiced frequently. Alkali metal compounds for use as starting materials and catalysts are exemplified by basic reagents such as alkali hydroxides, alkali sulfides, alkali hydrosulfides, alkali oxides, alkali alcoholates and the like, and reducing reagents such as alkali metals, alkali metal halides, alkali aluminum halides, alkali boron halides and the like.
In the case where the lubricating composition of the present invention is applied as a lubricating oil composition, additives such as for example an alkali metal type cleaning agent might often be added. However, the use of such particular additive is not preferable in the practice of the present invention. When the lubricating composition is applied as a grease composition, there are instances wherein a base lubricating oil is incorporated with an alkali metal-containing thickener such as for example sodium soap, lithium soap, sodium terephthalamate or the like, instances wherein sodium nitrite or sodium sulfonate is added as a rust preventive, and instances wherein, though rarely, a cleaning dispersant is added. Thus, some alkali metal compounds are present in the resultant grease composition.
The organomolybdenum compounds that can be used in the present invention include, in addition to MoDTC and MoDTP, reaction products of molybdic acid with amines, oxymolybdenum organophosphates, (sulfurized) oxymolybdenum xanthate, reaction products of molybdenum with basic nitrogens, molybdenum-containing dispersants and the like. MoDTC and MoDTP among these compounds are noticeably affected by the sodium content in the lubricating composition.
According to the lubricating composition of the present invention, MoDTC is represented by the compounds of Formula (1) indicated above, whereas MoDTP is represented by the compounds of Formula (2) shown above. In both formulae, R¹ to R⁴ and R⁵ to R⁸ are all hydrocarbyl groups that may be by nature saturated, unsaturated, chained, branched-chain or straight-chain. Such hydrocarbyl groups may be of an aliphatic, alicyclic or aromatic nature in which alkyl, alkenyl, alkylaryl, cycloalkyl, cycloalkenyl groups and the like are included.
Suitable alkyl groups are chosen from among methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertiary butyl, pentyl, isopentyl, neopentyl, tertiary pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tridecyl, isotridecyl, myristyl, palmityl, stearyl, eicosyl, docosyl, tetracosyl, triacontyl, 2-octyl-dodecyl, 2-dodecylhexadecyl, 2-tetradecyloctadecyl, branched monomethyl-isostearyl groups and the like.
Suitable alkenyl groups are chosen from among vinyl, ally, propenyl, isopropenyl, butenyl, isobutenyl, pentenyl, isopentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tetradecenyl, oleyl groups and the like.
Suitable alkylaryl groups are chosen from among phenyl, tolyl, xylyl, cumenyl, mesithyl, benzyl, phenethyl, styryl, cinnamyl, benzhydryl, trityl, ethylpheny, propylphenyl, butylphenyl, pentylphenyl, hexylphenyl, heptylphenyl, octylphenyl, nonylphenyl, alpha-naphthyl, beta-naphthyl groups and the like.
Suitable cycloalkyl and cycloalkenyl groups are chosen from among cyclopentyl, cyclohexyl, cycloheptyl, methylcyclopentyl, methylcyclohexyl, methylcycloheptyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, methyl-cyclopentenyl, methylcyclohexenyl, methylcycloheptenyl groups and the like.
The substituent groups, R¹ to R⁸, may be the same or different; that is, R¹ to R⁴ may be identical to, or different from R⁵ to R⁸. Where the base oil is a base oil for lubricating oil, i.e., where the lubricating composition is a lubricating oil composition, an alkyl group of 8 to 13 carbon atoms is preferred as R¹ to R⁴ that are in MoDTC and an alkyl group of 6 to 13 carbon atoms as R⁵ to R⁸ that are in MoDTP. The case where R¹ to R⁴ are different from each other, is preferable when the resultant lubricating oil composition is to have long drain or long service life..
When the base oil is a base grease, i.e., when the lubricating composition is a grease composition, an alkyl group with a carbon number of 1 to 15, preferably of 2 to 13, more preferably of 2 to 8, is preferred as R¹ to R⁴ that are related to MoDTC, while an alkyl group with a carbon number of 1 to 15, preferably of 2 to 15, more preferably of 2 to 8, is preferred as R⁵ to R⁸ that are related to MoDTP.
Each of the X¹ in Formula (1) and X² in Formula (2) is an oxygen or sulfur atom and may be identical or different. Too small a number of oxygen atoms invites insufficient lubricity, and too large a number of sulfur atoms makes the finished lubricating composition highly corrosive. Where severer lubricating conditions in particular are to be met, the atomic ratio of oxygen to sulfur is preferably from 1 : 3 to 3 : 1.
In the lubricating composition according to the present invention, the organomolybdenum compounds specified above can be used singly or in combination. Though not particularly restricted, the amount of such compound added is of itself limited to gain adequate lubricity and to prevent adverse sludge. For example, when the lubricating composition is a lubricating oil composition, the organomolybdenum compound may be used in an amount of 0.005 to 0.2 percent by weight in terms of molybdenum, preferably of 0.01 to 0.1 percent by weight, based on a selected base oil.
One or more members of the above organomolybdenum compounds can also be used when the lubricating composition is a grease composition. Such a compound if added in too small an amount is ineffective for achieving sufficient friction regulation, and the compound if added in too large an amount produces no better results with uneconomical burdens. Thus, the organomolybdenum compound is added in an amount of 0.01 to 10 percent by weight, preferably of 0.05 to 5 percent by weight, based on the weight of the base grease.
MoDTC and MoDTP tend to contain a greater content of alkali metals, particularly of sodium metals since they are synthesized usually with the use of an alkali metal compound, especially of sodium hydrosulfide. Thus, it is preferred that MoDTC and MoDTP for use in the lubricating composition of the present invention be derived for example by the production methods stated below.
MoDTC can preferably be produced by the method disclosed for instance in Japanese Patent Laid-Open No. 56-12638. In this known method, molybdenum trioxide or molybdate salt is reacted with an alkali sulfide or alkali hydrosulfide, followed by addition of carbon disulfide and a secondary amine, and the reaction is continued at an appropriate temperature.
MoDTP can preferably be produced by the methods taught for instance in Japanese Patent Laid-Open Nos. 61-87690 and 61-106587. Both methods are contrived to react an alkali sulfide or alkali hydrosulfide, followed by addition of P₂S₅ and a secondary amine, and the reaction is continued at an appropriate temperature.
The lubricating composition of the present invention may be incorporated further with either one or both of ZDTP and ZDTC as organozinc compounds. ZDTP is represented by the compounds of Formula (3) as previously shown, and R⁹ and R¹⁰ in that formula are each hydrocarbyl groups similar to R¹ to R⁸. ZDTC is represented by the compounds of Formula (4) also indicated above, and R¹¹ and R¹² are each hydrocarbyl groups similar to R¹ to R⁸.
In the ZDTP of Formula (3), R⁹ and R¹⁰ are each hydrocarbyl groups and may be the same or different. Both of the substituent groups may be selected, like R¹ to R⁸, from alkyl, alkenyl, alkylaryl groups and the like, among which an alkyl group of 3 to 14 carbon atoms is particularly preferred.
In addition, among the R⁹ and R¹⁰ of one or more ZDTP compounds to be used more than 60% are preferably occupied by a primary alkyl group. The remaining quantity of less than 40% may be a secondary alkyl and/or a tertiary alkyl group.
In Formula (3), a is 0 or 1/3, and the resulting compound is termed a "neutral ZnDTP" when a is zero and a "basic ZnDTP" when a is 1/3.
ZDTP to be used in the present invention can be obtained by the method disclosed for instance in Japanese Patent Laid-Open No. 48-37251. That is, P₂S₅ is reacted with a given alcohol to form an alkyl-substituted dithio-phosphoric acid which is then neutralized or basified with zinc oxide, whereby a zinc salt is prepared.
In the ZDTC of Formula (4), R¹¹ and R¹² are each hydrocarbyl groups and may be the same or different. The two substituent groups are selected, like R¹ to R⁸, from alkyl, alkenyl, alkylaryl groups and the like, among which an alkyl group of 3 to 14 carbon atoms is particularly preferred.
One or more members of the above organozinc compounds can be used in the lubricating composition of the present invention. When this composition is applied as a lubricating oil composition, no particular restriction is placed on the amount of the organozinc compound to be added. Too small an amount of such compound, however, results in an insufficient level of extreme pressure performance. Conversely, too large an amount of the compound is responsible for impaired properties of extreme pressure performance and oxidation resistance. In regards to ZDTP, as it contains phosphorus it tends to contaminate catalysts employed inexhaust gas-treating systems. The organozinc compound is therefore added in an amount of 0.005 to 2% by weight, preferably of 0.01 to 1% by weight, based on the weight of the base lubricating oil selected. The organozinc compound contributes to improvements in extreme pressure performance and oxidation resistance of the lubricant composition.
Also, when the lubricating composition is applied as a grease composition, the amount of the organozinc compound to be used is not particularly restricted. Needless to say, if too little of such compound is added a sufficient level of extreme pressure performance cannot be effectively gain and if too much is added it will be prone to poor lubricity. The amount of the organozinc compound, therefore, is added in an amount of 0.01 to 10% by weight, preferably of 1 to 5% by weight, based on the weight of the base lubricating grease selected. Further, the organozinc compound plays a role in improving the friction reduction perfomance of the grease composition.
The lubricating composition of the present invention is comprised of a base oil, one or more organomolybdenum compounds as specified above and, if desired, one or more organozinc compounds as previously stated. Here, the base oil may be a base oil for lubricating oil or a base grease.
The base oil for lubricating oil that can be used as the base oil may be mineral or synthetic oils. By the term mineral oil is meant such derived from cracking of crude oil and from subsequent distillation and refining. Included in the term mineral oil is paraffinic oils, naphthenic oils and oils made available from hydrogenation and solvent refining thereof. The term synthetic oil denotes a chemically synthesized lubricating oil and includes poly-alpha-olefins, polyisobutylene (polybutenes), diesters, polyol esters, phosphate esters, silicate esters, polyalkylene glycols, polyphenylethers, silicones, fluorine compounds, alkyl benzenes and the like.
When the lubricating composition of the present invention is used as an engine oil composition, it is preferred to select as the base, a mineral oil such as hydrogenated oils and hydrogenation refined oils, synthetic oils such as poly-alpha-olefins, diesters, polyol esters and the like.
The base greases that can be used as the base oil are composed of a base lubricating oil and a thickener. Suitable examples of the thickener are soap thickners such as of aluminum, barium, calcium and the like, complex soap thickners such as of complex calcium, complex aluminum and the like, urea compounds such as aromatic diureas, aliphatic diureas, alicyclic diureas, triureas, tetraureas and the like, organic non-soap thickners such as terephthalates and the like, inorganic non-soap thickeners such as bentonites, silca aerogels and the like. Amongst the above exemplified compounds, ureas are particulary preferred, diureas more preferred and aromatic diureas most preferred. The thickeners are usually used alone, but two or more members may be used in combination if desired. Though not restricted, the thickener is added usually in an amount of 3 to 40 percent by weight, preferably of 5 to 20 percent by weight, based on the weight of the base grease.
The base lubricating oils that can be used in the base grease may be selected from various base lubricating oils such as those of a mineral class, those of a synthetic class and blends thereof which have been commonly employed for greases. The mineral oil type base lubricating oils may include those resulting from refining of crude oil by means of solvent refining, hydrogenation refining or the like, or combinations thereof. The synthetic oil type base lubricating oils may include alpha-olefin polymers such as alpha-olefin oligomers of 3 to 12 carbon atoms, sebacates such as 2-ethylhexyl sebacates and dioctyl sebacates, dialkyl diesters of 4 to 12 carbon atoms such as azelates and adipates, polyol esters such as trimethylolpropane, esters resulting from reaction of pentaerythritol and monobasic acids of 3 to 12 carbon atoms, alkyl benzenes having an alkyl group of 9 to 40 carbon atoms, polyglycols such as polyglycols derived from condensation of butyl alcohol with propylene oxides, phenylethers having about 2 to 5 ether chains and about 3 to 6 phenyl groups, synthetic oils of a silicone class and synthetic oils of a fluorine class such as perfluoroalkyl polyethers. These mineral and synthetic oil type base lubricating oils may be used singly or in combination. Though selectively determinable with a view to meeting any prescribed properties, the amount of the base lubricating oil to be added is usually in the range of 60 to 97 percent by weight, preferably of 80 to 95 percent by weight, based on the weight of the base grease.
It is preferable that said base grease containing the base lubricating oil and thickener in the above stated proportion have a worked consistency of 175 to 400 at 25□C, preferably of 205 to 310.
If the lubricating composition of the present invention is used as a lubricating oil composition, numerous known additives may be incorporated which are chosen from friction relaxants such as higher fatty acids, higher alcohols, amines, esters and the like, extreme pressure agents such as of a sulfur, chlorine, phosphorus or organometallic type or the like, antioxidants such as phenols, amines and the like, cleaning agents such as sulfonates, phenates, carboxylates and the like of neutral or highly basic alkaline earth metals, dispersants such as imide succinates, benzyl-amines and the like, viscosity index improvers such as high-molecular poly(meth)acrylates, polyisobutylenes, polystyrenes, ethylene-propylene copolymers, styrene-isobutylene copolymers and the like, defoamers such as esters, silicones and the like, rust preventives, pour point depressants and molybdic acid amines. The amount of each of such additive to be added is within the range commonly accepted in the art.
Advantageously, the lubricating oil composition having the formulation as stated above, can be used as a lubricant for internal combustion engines such as engines for vehicles inclusive of automobiles, 2-cycle engines, aircraft engines, marine engines, locomotive engines (irrespective of whether the combustion system is gasoline, diesel, gas or turbine), as an automatic transmission fluid, as a trans axle lubricant, as a gear lubricant and as a metal working lubricant.
If the lubricating composition of the present invention is used as a grease composition, various known additives may be incorporated which are chosen from friction relaxants such as higher fatty acids, higher alcohols, amines, esters and the like, extreme pressure agents such as of a sulfur, halogen, phosphorus or lead type or the like, antioxidants such as phenols, amines, sulfurs, seleniums and the like, rust preventives such as long-chain carboxylic acids and their derivatives, sulfonate salts, amines, phosphate esters and their salts and the like, solid lubricants such as graphites, molybdenum disulfides, polyethylenes, polytetrafluoroethylenes (PTFE), boron nitrides and the like, pour point depressants, viscosity index improvers, tackifiers, structural stabilizers, cleaning dispersants, antiseptics, defoamers, colorants, cleaning agents such as of neutral or highly basic alkaline earth metals, antistatic agents, emulsifiers, demulsifiers and the like.
Also advantageously, the grease composition having the formulation as stated above according to the present invention is suited for universal joints inclusive of constant velocity joints for automotive use, constant velocity gears and variable speed gears for automotive use as well as for various other fields of application.
In accordance with the invention, a novel lubricating oil composition is provided which exhibits good performance of friction reduction.
In accordance with the invention, a novel grease composition is further provided which excels in frictional and wear characteristics.

EXAMPLES

The present invention is further described hereunder with reference to the following examples.
The details of the components used in the inventive and comparative lubricating compositions are given below.

Base Oils

Base oil for lubricating oil:

A high VI oil of a mineral class derived by subjecting a crude oil-induced mineral oil to a hydrocracking process; kinematic viscosity: 4.1 cSt at 100□C; VI: 126; sodium content: below 10 ppm.

Base grease 1:

A base grease obtained by mixing a refined mineral oil of 15 cSt at 100□C with an aliphatic amine-based urea compound (a thickener), followed by uniform dispersion of the mixture for a worked consistency to reach 287 at 25□C; sodium content: below 10 ppm.

Base grease 2:

A base grease obtained by mixing a low-refined mineral oil of 16.7 cSt at 100□C with a sodium soap (a thickener), followed by uniform dispersion of the mixture for a worked consistency to reach 271 at 25□C.

Organomolybdenum Compounds

Mo compound 1:

MoDTC of R¹ to R⁴ = 2-ethylhexyl group, X¹ = S/O = 2.2 in Formula (1); sodium content: below 10 ppm.

Mo compound 2:

MoDTC of R¹ to R⁴ = 2-ethylhexyl group : isotridecyl group = 1 : 1, X¹ = S/O = 2.2 in Formula (1); sodium content: below 10 ppm.

Mo compound 3:

MoDTP of R⁵ to R⁸ = 2-ethylhexyl group, X² = S/O = 2.2 in Formula (2); sodium content: below 10 ppm.

Mo compound 4:

MoDTC of R¹ to R⁴ = n-butyl group, X¹ = S/O = 2.2 in Formula (1); sodium content: below 10 ppm.

Cleaning agent 1:

Calcium sulfonate; sodium content: below 10 ppm.

Cleaning agent 2:

Magnesium sulfonate; sodium content: below 10 ppm.

Cleaning agent 3:

Calcium salicylate; sodium content: below 10 ppm.

Cleaning agent 4:

Sodium phenate; sodium content: 10.5 percent by weight.

Organozinc Compounds

ZDTP:

R⁹ to R¹⁰ = 2-ethylhexyl group (primary alkyl group), neutral salt : basic salt = 55 : 45 (in molar ratio) in Formula (3); sodium content: below 10 ppm.

ZDTC:

R¹¹ to R¹² = 2-ethylhexyl group in Formula (4); sodium content: below 10 ppm. Na Compound:
Sodium sulfite (rust preventive) (sodium content: 36.5%)
The sodium content of each of the above components was measured by an ICP process after incineration. No alkali metals other than a sodium metal were detected in the base oil for lubricating oil, base grease 1, Mo compounds 1 to 4, ZDTP, ZDTC or cleaning agents 1 to 3.

Example 1

The above prepared components were formulated in the proportions shown in Tables 1 and 2 below, whereby inventive and comparative lubricant compositions were provided. In these tables, the numerical figures related to the Mo compounds are expressed by percent by weight in terms of molybdenum, and other figures are expressed by percent by weight.
The resulting lubricant compositions were examined for their coefficients of friction.

Friction Coefficient Measurement Test:

Friction coefficient measurements were carried out with an SRV measuring apparatus and under the set of conditions indicated below.

Measurement Conditions:

Line Contact:

Testing was done in accordance with a cylinder-on-plate line contact test. Namely, an upper cylinder (□ 15 x 22 mm) was set to vertically positioned in the reciprocating direction on a plate (□ 24 x 6.85 mm) and then allowed to reciprocally vibrate. After a lapse of 7 minutes, measurement was made of the friction coefficient. Both the cylinder and the plate were made of SUJ-2.

loading: 200 N
temperature: 80□C
measuring time: 15 minutes
vibrational amplitude: 1 mm
cycle: 50 Hz

Table 2

Comparative Product	1	2	3	4	5	6
Mo compound 1	0.07					0.07
Mo compound 2		0.07			0.15
Mo compound 3			0.07
Cleaning agent 4	1.0	1.0	1.0	1.0	1.0	1.0
ZDTP						1.0
Na content (ppm)	1,000	1,010	1,010	1,010	1,010	1,010
Friction coefficient	0.12	0.12	0.12	0.15	0.13	0.12

Example 2

The foregoing components were formulated in the proportions enumerated in Tables 3 and 4 below, whereby inventive and comparative grease compositions were obtained. In these tables, all the numerical figures are expressed by percent by weight relative to the weight of a given base grease.
The resulting grease compositions were tested in respect of their frictional properties under the set of conditions indicated below.

Friction Test:

Point Contact:

Testing was done in accordance with cylinder-on-plate point contact test. Namely, an upper ball (□ 10 mm) was disposed on a plate (□ 24 x 7.85 mm) and then allowed to reciprocally vibrate. After a lapse of 2 hours, measurement was made of the friction coefficient. Both the ball and the plate were made of SUJ-2.

loading: 200 N
temperature: 50□C
measuring time: 2 hours
vibrational amplitude: 1 mm
cycle: 50 Hz

The coefficient of friction and the diameter of wear scar were measured with a high-speed four-ball testing apparatus under the set of conditions indicated below.

revolution: 1,800 rpm
loading: 40 kg
temperature: 40□C
time: 60 minutes

The compositons of tested grease and test results are shown in Tables 3 and 4 wherein all the numerical figures are expressed by percent by weight.

Table 4

Comparative Product	7	8	9	10	11	12	13
Base grease No.	1	1	1	1	1	2	2
Mo compound 4	3.0				3.0	3.0	3.0
Mo compound 1		3.0
Mo compound 2			3.0
Mo compound 3				3.0
ZDTP	3.0	3.0	3.0	3.0		3.0	3.0
ZDTC					3.0
Na compound	1.0	1.0	1.0	1.0	1.0	1.0
Na content (ppm)	3,500	3,600	3,500	3,700	3,700	21,000	17,000
SRV/friction coefficient	0.06	0.070	0.064	0.07	0.064	0.07	0.07
High-speed four-ball test wear scar dia (mm)	0.63	0.75	0.65	0.73	0.65	0.74	0.75

Claims

A lubricating composition comprising a base oil and organomolybdenum compound, characterized in that said composition has a sodium content of not greater than 200 ppm.
A lubricating composition comprising a base oil and one or more organomolybdenum compounds selected from the group consisting of sulfurized oxymolybdenum dithiocarbamates represented by Formula (1)
wherein R¹ to R⁴ are each a hydrocarbyl group, and X¹ is an oxygen or sulfur atom; and sulfurized oxymolybdenum dithiophosphates represented by Formula (2)
wherein R⁵ to R⁸ are each a hydrocarbon group, and X² is an oxygen or sulfur atom; characterized in that said composition has a sodium content of not greater than 200 ppm.
The lubricating composition according to claim 2, wherein the base oil is a base oil for lubricating oil.
The lubricating composition according to claim 3, wherein an amount of the organomolybdenum compound added ranges from 0.005 to 0.2 percent by weight in terms of molybdenum based on the weight of the base oil for lubricating oil.
The lubricating composition according to claim 2, wherein the base oil is a base grease comprising a base lubricating oil and a thickener.
The lubricating composition according to claim 5, wherein an amount of the organomolybdenum compound added ranges from 0.01 to 10 percent by weight based on the weight of the base grease.
The lubricating composition according to claim 2, wherein the composition has a total content of alkali metals including a sodium metal of not greater than 200 ppm.
A lubricating composition comprising a base oil; one or more organomolybdenum compounds selected from the group consisting of sulfurized oxymolybdenum dithiocarbamates represented by Formula (1)
wherein R¹ to R⁴ are each a hydrocarbyl group, and X¹ is an oxygen or sulfur atom; and sulfurized oxymolybdenum dithiophosphates represented by Formula (2)
wherein R⁵ to R⁸ are each a hydrocarbyl group, and X² is an oxygen or sulfur atom; and one or more organozinc compounds selected from the group consisting of zinc dithiophosphates represented by Formula (3)
wherein a is 0 or 1/3, and R⁹ and R¹⁰ are each a hydrocarbyl group;
and zinc dithiocarbamates represented by Formula (4)
wherein R¹¹ and R¹² are each a hydrocarbyl group;
characterized in that said composition has a sodium content of not greater than 200 ppm.
The lubricating composition according to claim 8, wherein the base oil is a base oil for lubricating oil.
The lubricating composition according to claim 9, wherein an amount of the organomolybdenum compound added ranges from 0.005 to 2 percent by weight in terms of molybdenum based on the weight of the base oil for lubricating oil, and an amount added of the organozinc compound ranges from 0.005 to 2 percent by weight based on the weight of the base oil for lubricating oil.
The lubricating composition according to claim 8, wherein the base oil is a base grease comprising a base lubricating oil and a thickener.
The lubricating composition according to claim 11, wherein an amount of the organomolybdenum compound added ranges from 0.01 to 10 percent by weight based on the weight of the base grease, and an amount of the organozinc compound added ranges from 0.01 to 10 percent by weight based on the weight of the base grease.
The lubricating composition according to claim 8, wherein the composition has a total content of alkali metals including a sodium metal of not greater than 200 ppm.