WO2009074664A1

WO2009074664A1 - Lubricating oil composition

Info

Publication number: WO2009074664A1
Application number: PCT/EP2008/067362
Authority: WO
Inventors: Akimitsu Fujiwara; Mitsuhiro Nagakari; Norimitsu Tanaka
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2007-12-12
Filing date: 2008-12-11
Publication date: 2009-06-18

Abstract

The present invention provides a lubricating composition comprising a base oil, an aspartic acid derivative and a succinic acid derivative. In another aspect the present invention provides the use of the lubricating composition for improving low- friction and/or rust-preventing properties.

Description

LUBRICATING OIL COMPOSITION

This invention relates to lubricating compositions and among them to the generality of industrial lubricating oils using refined base oils, and in particular relates to lubricating compositions used as machine oils, hydraulic oils, turbine oils, compressor oils, gear oils, sliding friction oils, bearing oils and calibration oils.

Corrosion resistance is required as a fundamental property of lubricating oils in machinery installations so as to maintain performance. This is because the lubricating oil temperature within tanks in mechanical apparatus rises and falls in accordance with conditions of use, and therefore the lubricating oil within the tanks may be subject to admixture with condensed water, or to admixture with moisture because of leaks from cooling water pipes.

Also, in recent years, good friction properties have been required of industrial lubricating oil compositions. This is in order to be able to efficiently reduce friction losses in mechanical apparatus and to achieve large energy economies through having a low friction coefficient (μ) , that is by imparting low friction properties to the lubricating oil. Also, hydraulic apparatus is widely used in construction machinery and so on, and if the friction coefficient of the lubricating oils used for the hydraulic oil actuating the machinery is high, the phenomenon of minute stick-slip may occur in the sliding friction parts of the packing owing to the reciprocating movement of the hydraulic cylinders, and chatter, vibration, squealing and other abnormal sounds — ? —

may occur in the cylinders, so that it becomes impossible to control the hydraulic plant with satisfactory precision. In consequence it is necessary to reduce the friction coefficient of the lubricating oil so that the hydraulic cylinders move smoothly and accurately.

In order to obtain the rust™preventing effect as mentioned above, it is known that an N-acyl-N-hydrocarbon oxyalkyl aspartic acid ester can be blended in the lubricating oil composition. See Japanese Laid-open Patent H6-200268 (1994) .

This invention is intended to obtain an industrial lubricating oil which not only has excellent rust- preventing properties but also imparts low friction properties to the lubricating oil and has high energy- saving properties.

This invention is based on the discovery that, if an aspartic acid derivative and a succinic acid derivative are used as additives in a mineral oil or synthetic oil type base oil, not only are rust-preventing properties obtained by the synergy of these compounds, but excellent low friction properties are also obtained, and a lubricating oil composition suitable for use as industrial lubricating oils such as hydraulic oils can be obtained on the basis of this discovery. Also, by further adding at least one compound selected from amine compounds, amide compounds, alcohol compounds, carboxylic acid compounds, and ester compounds, a lubricating oil composition with even more excellent low friction properties is obtained. According to this invention, it is possible to obtain a superior lubricating oil composition in which the generation of rust is inhibited and the friction coefficient is low. By reducing the friction coefficient it is possible to reduce effectively the friction losses generated in various kinds of industrial machinery, and it is possible to bring about energy savings. Also, in the case of use as a hydraulic oil, it is possible to control the hydraulic apparatus with precision by reducing the friction coefficient and so not giving rise to phenomena in the hydraulic apparatus such as chatter, vibrations, squeaking or generation of abnormal sounds. This lubricating oil composition can be widely used for the generality of industrial lubricating oils, and in particular can be used effectively in machine oils, hydraulic oils, turbine oils, compressor oils, gear oils, sliding friction oils, bearing oils and calibration oils. For the base oil of the present lubricating oil composition it is possible to use mineral oils describable as highly refined base oils, and synthetic oils, and in particular it is possible to use, singly or as mixtures, base oils which belong to Group I, Group II, Group III, Group IV and so on of the API (American Petroleum Institute) base oil categories. The base oils used here have an elemental sulphur content of less than 700 ppm and preferably less than 500 ppm. The density is preferably 0.8 to 0.9. The aromatic content is preferably more than 5% and preferably not more than 3%. Group I base oils include, for example, paraffinic mineral oils obtained by appropriate use of a suitable combination of refining processes such as solvent refining, hydrorefining, and dewaxing in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil. The viscosity index (ASTM

D2270) is typically from 80 to 120 and preferably from 95 to 110. The kinematic viscosity at 40⁰C (ASTM D445) is from 2 to 680 mmVs and even more preferably from 8 to 220 mmVs. Also, the total sulphur content Is typically less than 700 ppm and preferably less than 500 ppm. The total nitrogen content is typically less than 50 ppm and preferably less than 25 ppm. In addition, oils with an aniline point of from 80 to 150⁰C and preferably from 90 to 12O⁰C are typically used.

Group II base oils include, for example, paraffinic mineral oils obtained by appropriate use of a suitable combination of refining processes such as hydrorefinlng and dewaxing In respect of lubricating oil fractions obtained by atmospheric distillation of crude oil. Group II base oils refined by hydrorefining methods such as the Gulf Company method have a total sulphur content of less than 10 ppm and an aromatic content of not more than 5% and so are suitable for this invention. The viscosity of these base oils is not specially limited, but the viscosity index (ASTM D2270) is typically from 80 to 120 and preferably from 100 to 120. The kinematic viscosity at 40⁰C (ASTM D445) is typically from 2 to 680 mm²/s and even more preferably from 8 to 220 mmVs. Also, the total sulphur content is typically less than 300 ppm, preferably less than 200 ppm and even more preferably less than 10 ppm. The total nitrogen content is typically less than 10 ppm and preferably less than 1 ppm. In addition, oils with an aniline point of from 80 to 150⁰C and preferably from 100 to 135^αC are typically used.

Suitable Group III base oils and Group 11+ base oils include paraffinic mineral oils manufactured by a high degree of hydrorefining in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil, base oils refined by the Isodewax process which dewaxes and substitutes the wax produced by the dewaxing process with isoparaffins, and base oils refined by the Mobil wax isomerisation process. They include those that may be designated as "synthetic oils" according to the rulings of the NAD {National Advertising Division) which is responsible for advertising adjudications in America. The viscosity of these base oils is not specially limited, but the viscosity index (ASTM D2270) is typically from 95 to 145 and preferably from 100 to 140. The kinematic viscosity at 40⁰C (ASTM D445) is typically from 2 to 680 mm²/s and preferably from 8 to 220 mmVs. Also, the total sulphur content is typically from 0 to 100 ppm and preferably less than 10 ppm. The total nitrogen content is typically less than 10 ppm and preferably less than 1 ppm. In addition, oils with an aniline point of from 80 to 150⁰C and preferably from 110 to 135°C are preferred.

GTLs {gas to liquid; or "GTL derived base oils") synthesised by the Fischer-Tropsch method of converting natural gas to liquid fuel have a very low sulphur content and aromatic content compared with mineral oil base oils refined from crude oil and have a very high paraffin constituent ratio, and so have excellent oxidative stability, and because they also have extremely small evaporation losses, they are suitable as base oils for this invention. The viscosity of GTL base oils is not specially limited, but the viscosity index (ASTM D2270) is typically from 130 to 180 and preferably from 140 to 175. Also, the kinematic viscosity at 40⁰C (ASTM D445) is typically from 2 to 680 mm²/s and preferably from 5 to 120 mmVs. Normally the total sulphur content is also less than 10 ppm and the total nitrogen content less than 1 ppm. A commercial example of such a GTL base oil is Shell XHVI (registered trademark) . As examples of synthetic oils mention may be made of polyolefins, alkylbenzenes, alkylnaphthalenes, esters, polyoxyalkylene glycols, polyphenyl ethers, dialkyldiphenyl ethers, fluorine-containing compounds (perfluoropolyethers, fluorinated polyolefins) and silicone oils.

The aforementioned polyolefins include polymers of various olefins or hydrides thereof. Any olefin may be used, and as examples mention may be made of ethylene, propylene, butene and α-olefins with five or more carbons. In the manufacture of polyolefins, one kind of the aforementioned olefins may be used singly or two or more kinds may be used in combination. Particularly suitable are the polyolefins called poly-α-olefins (PAO) . These are base oils of Group IV. The viscosity of these synthetic oils is not specially limited, but the kinematic viscosity at 40⁰C (ASTM D445) is preferably from 2 to 680 roiαVs and more preferably from 8 to 220 rninVs. The amount of the aforementioned base oil to be incorporated in the lubricating oil composition of this invention is not specially limited, but, taking as a basis the total amount of the lubricating oil composition, is typically at least 60% by mass, preferably at least 80% by mass, more preferably at least 90% by mass, and yet more preferably at least 95% by mass .

The aspartic acid derivatives are shown by General Formula 1.

{ Formula 1 )

In the aforementioned General Formula 1, Xl and X2 are each hydrogen or alkyl groups, alkenyl groups or hydroxyalkyl groups with 3 - 6 carbons which may be the same or different, and are preferably respectively a 2- methylpropyl group and a tertiary butyl group, X3 has 1 - 30 carbons and is an alkyl group or an alkenyl group, or an alkyl group having ether bonds, or a hydroxyalkyl group. For example , an octadecyl group, an alkoxypropyl group, a 3- (C6-C18 ) hydrocarbonoxy (C3-C6) alkyl group, and more preferably a cyclohexyloxypropyl group, a 3- octyloxypropyl group, a 3-isooctyloxypropyl group, a 3- decyloxypropyl group, a 3-isodecyloxypropyl group and a 3- (C12-C16) alkoxypropyl group are suitable. X4 is a saturated or unsaturated carboxylic acid group comprising 1 - 30 carbons, or an alkyl group, alkenyl group or hydroxyalkyl group comprising 1 - 30 carbons. For example, a propionic acid group or a propionyl acid group is suitable.

The aforementioned aspartic acid derivatives typically have an acid number as determined by JIS K2501 of 10 - 200 rαgKOH/g and preferably 50 - 150 mgKOH/g. The amount of aspartic acid derivatives used in the lubricating oil composition is typically approximately 0.001 - 0.5% by mass, preferably approximately 0.001 - 0.1% by mass and more preferably approximately 0.005 - 0.05% by mass. One kind or a mixture of these aspartic acid derivatives may be used.

The succinic acid derivatives are shown by General Formula 2.

COOX_fi

K GOOXe

( Formula 2 ) In the aforementioned General Formula 2, X5 and X6 are each hydrogen or alkyl groups, alkenyl groups or hydroxyalkyl groups with 3 - 6 carbons which may be the same or different, and preferably are hydrogen atoms, 1- hydroxypropyl groups, 2-hydroxypropyl groups, 2- methylpropyl groups or tertiary butyl groups. X7 has 1 - 30 carbons and is an alkyl group or an alkenyl group, or an alkyl group having ether bonds, or a hydroxyalkyl group. For example, a methyl group, an ethyl group, a propyl group, a butyl group, pentyl group, a hexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a dodecylene group, a tridecyl group, a tetradecyl group, a tetradecylene group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, an octadecylene group, an eicosyl group, a docosyl group, an alkoxypropyl group, a 3- (C6-C18) hydrocarbonoxy (C3-C6) alkyl group, and more preferably a tetraisopropyl group, an oleyl group, a cyclohexyloxypropyl group, a 3- octyloxypropyl group, a 3-isooctyloxypropyl group, a 3- decyloxypropyl group, a 3-isodecyloxypropyl group and a 3- (C12-C16) alkoxypropyl group are suitable. Aminated forms of these compounds are also suitable. _ Q _

The aforementioned succinic acid derivatives typically have an acid number as determined by JIS K2501 of 10 - 300 mgKOH/g and preferably 30 - 200 mgKOH/g. The amount of succinic acid derivatives used in the lubricating oil composition is approximately 0.001 - 0.5% by mass, preferably approximately 0.001 - 0.1% by mass and more preferably approximately 0.005 - 0.05% by mass. One kind or a mixture of these succinic acid derivatives may be used. Amine compounds can be blended into this lubricating oil composition. Aliphatic amine compounds can be used for these amine compounds, and as examples mention may be made of the primary amines shown by General Formula 3, the secondary amines shown by General Formula 4, the tertiary amines shown by General Formula 5 and the diamines amines shown by General Formula 6.

( Formula 3 )

In the aforementioned General Formula 3, X8 is an alkyl group or alkenyl group of 1 - 30 carbons. As examples of such compounds, mention may be made of laurylamine, coconut amine, n-tridecylamine, myristylamine, n-pentadecylamine, n-palmitylamine, n~ heptadecylamine, n-stearylamine, isostearylaraine, n- nonadecylamine, n-eiσosylamine, n-heneicosylamine, n- docosylamine, n-tricosylamine, n-pentacosylamine, oleylamine, beef tallow amine, hydrogenated beef tallow amine and soybean amine. The number of carbons in X8 is preferably 8 - 24, and more preferably 12 - 18. Also, X8 may be a straight-chain aliphatic, a branched-chain aliphatic or a tertiary alkyl group. X₉-NH-X₁₀ (Formula 4)

In the aforementioned General Formula 4, X9 and XlO are alkyl groups or alkenyl groups of 1 - 30 carbons. As examples of such compounds, mention may be made of dilaurylamine, dicoconut amine, di-n-tridecylam±ne, di~n- myristylamine, di-n-pentadecylamine, di-n-palmitylamine, di~n™heptadecylamine, di™n~stearylamine, diisostearylamine, di-n-nonadecylamine, di-n- eicosylamine, di-n-heneicosylamine, di-n-docosylamine, di-n-tricosylamine, di-n-pentacosylamine, dioleylamine, di-beef tallow amine, di-hydrogenated beef tallow amine and di-soybean amine. The number of carbons in X9 and XlO is preferably 8 - 24, and more preferably 12 - 18. X9 and XlO may be the same or different.

(Formula 5) In the aforementioned General Formula 5, X21 is an alkyl group or alkenyl group of 1 - 30 carbons. The number of carbons in X21 is preferably 1 - 20. X22, X23 independently is an alkyl group, an alkenyl group or a hydroxyalkyl group of 1 - 20 carbons. The number of carbons in X22, X23 is preferably 1 - 18. Assuming X21 is a methyl group, examples of dialkylmethylamines include dioctylmethylamine, dinonylmethylamine, didecylmethylamine, diundecylmethylamine, dilaurylmethylamine, ditridecylmethylamine, dimyristylmethylamine, ditetradecylmethylamine, dipentadecylmethylamine, dipalmitylmethylamine, diheptadecylmethylamine, dioleylmethylamine, distearylmethylamine, diisostearylmethylamine, dinonadecylmethylamine, dieicosylmethylamine, di-coconut methylamine, di-beef tallow methylamine, di-hydrogenated beef tallow methylamine and di-soybean methylamine. Assuming X22, X23 is a methyl group, examples of alkyldimethylamines include octyldimethylamine, nonyldimethylamine , decyldimethylamine, undecyldimethylamine , lauryldimethylamine , tridecyldimethylamine, myristyldimethylamine, tetradecyldimethylaruine, pentadecyldimethylamine, palmityldimethylamine, heptadecyldimethylamine, oleyldirnethylamine, stearyldimethylamine, isostearyldimethylamine, nonadecyldimethylamine, eicosyldimethylamine, coconut dimethylamine, beef tallow dimethylamine, hydrogenated beef tallow dimethylamine and soybean dimethylamine.

Assuming X22, X23 is a hydroxyalkyl group, examples of N-alkyldiethanolamines include K-octyldiethanolamine, N-nonyldiethanolamine, N-decyldiethanolamine, N- undecyldiethanolamine, N-lauryldiethanolamine, N- tridecyldiethanolamine, N-myristyldiethanolamine, N- tetradecyldiethanolamine, N-pentadecyldiethanolamine, N- palmityldiethanolamine, N-heptadecyldiethanolamine, N- oleyldiethanolamine, N-stearyldiethanolamine, N- isostearyldiethanolamine, N-nonadecyldiethanolamine, N- eicosyldiethanolamine, N-coconut diethanolamine, N-beef tallow diethanolamine, N-hydrogenated beef tallow diethanolamine and N-soybean diethanolamine, and examples of N-alkyldipropanolaπdnes include N- octyldipropanolamine, N-nonyldipropanolamine, N- decyldipropanolamine, N-undecyldipropanolamine, N- lauryldipropanolamine, N-tridecyldipropanolamine, N- myristyldipropanolamine, ISS-tetradecyldipropanolamine, N- pentadecyldipropanolamine, N-palmityldipropanolamine, N- heptadecyldipropanolamine, N-oleyldipropanolamine, N- stearyldipropanolamine, N-isostearyldipropanolamine, N- nonadecyldipropanolamine, N-eicosyldipropanolamine, N- coconut dipropanolamine, N-beef tallow dipropanolamine, N-hydrogenated beef tallow dipropanolamine and N-soybean dipropanolamine .

{Formula 6)

In the aforementioned General Formula 6, X13 is an alkyl group or alkenyl group of 1 - 30 carbons. The number of carbons in X13 is preferably 8 - 24 and more preferably 12 - 18. X14 is an alkylene group of 1 - 12 carbons. The number of carbons in X14 is preferably 1 - 8 and more preferably 2 - 4.

Examples of ethylenediamines include N-octyl-1, 2- ethylenediamine, N-nonyl-1, 2-ethylenediamine, N-decyl- 1,2-ethylenediamine, N-undecyl-1, 2-ethylenediamine, N- lauryl-1, 2™ethylenediamine, N-tridecyl-1, 2- ethylenediamine, N-myristyl-1, 2-ethylenediamine, N- tetradecyl-1, 2-ethylenediamine, N-pentadecyl-1, 2- ethylenediainine, N-palmityl-1, 2-ethylenediamine, N- heptadecyl-1, 2-ethylenediamine, N-oleyl-1, 2- ethylenediamine, N-stearyl-1, 2-ethylenediamine, N- isostearyl-1, 2-ethylenediamine, N-nonadecyl-1, 2- ethylenediamine, N-eicosyl-1, 2-ethylenediamine, N- coconut-1, 2-ethylenediamine, N-beef tallow-1,2- ethylenediamine, N-hydrogenated beef tallow-1,2- ethylenediamine and N-soybean-1, 2-ethylenediamine. Examples of propylenediamines include N-octyl-1, 3- propylenediamine, N-nonyl-1, 3-propylenediamine, N-decyl- 1, 3-propylenediamine, N-undecyl-1, 3-propylenediamine, N- lauryl-1, 3-propylenediamine, N-tridecyl-1, 3- propylenediamine, N-myristyl-1, 3-propylenedIamIne, N- tetradecyl~l_r 3-propylenediamine, N-pentadecyl-1, 3- propylenediamine, N-palmityl-1, 3-propylenediamine, N- heptadecyl-1, 3-ρropylenediamine, M-oleyl-1, 3- propylenediamine, N-stearyl-~l, 3-propylenediamine, N- isostearyl-1, 3-propylenediamine, N-nonadecyl-1, 3- propylenediamine, N-eicosyl-1, 3-propylenediamine, N- coconut-1, 3-propylenediamine, N-beef tallow-1,3- propylenediamine, N-hydrogenated beef tallow-1,3- propylenediamine and N-soybean-1, 3-propylenediamine.

Examples of butylenediamines include N-octyl-1,4- butylenediamine, N-nonyl-1, 4-butylenediamine, N-decyl- 1, 4-butylenediamine, N-undecyl~l, 4-butylenediamine, N- lauryl-1, 4-butylenediamine, N-tridecyl-1, A- butylenediamine, N-myristyl-1, 4-butylenediamine, N- tetradecyl~l_f 4-butylenediamine, N-pentadecyl-1, 4- butylenediamine, N~palmityl-1, 4-butylenediamine, N- heptadecyl-1, 4-butylenediamine, N-oleyl-1, 4- butylenediamine, N-stearyl-1, 4-butylenediamine, N- isostearyl-l,4~butylenediamine, N-nonadecyl-1, 4- butylenediamine, N-eicosyl-1, 4-butylenediamine, N- coconut-1, 4-butylenediamine, N-beef tallow-1,4- butylenediamine, N~hydrogenated beef tallow-1,4- butylenediamine and N-soybean-1, 4-butylenediamine. The aforementioned amine compounds typically has a base number as determined by JIS K2501 of 10 - 800 mgKOH/g and preferably 100 ~ 500 mgKOH/g. Approximately 0.005 - 5% by mass, and preferably approximately 0.01 - 1% by mass, of at least one kind of these amine compounds selected from the aforementioned groups may be used in the lubricating oil composition, singly or in suitable mixtures . As examples of amide compounds in this invention, mention may be made of amide compounds which are products based on fatty acids and monoamines or polyamines.

X₁ *₆«CONH₂*^■ (Formula 7)

Assuming the amide compound is based on a fatty acid and a monoamine, in the aforementioned General Formula 7, X15 is an alkyl group or alkenyl group of 1 - 30 carbons. For example, mention may be made of laurylamide, coconut amide, n-tridecylamide, myristylamide, n-pentadecylamide, n-palmitylamide, n-heptadecylamide, n-stearylamide, isostearylamide, nononadecylamide, n-eicosylamide, n- heneicosylamide, n-docosylamide, n-tricosylamide, n- pentacosylamide, oleylamide, beef tallow amide, hydrogenated beef tallow amide and soybean amide. The number of carbons in X15 is 6 to 30, preferably 8 - 24 and more preferably 12 - 18. X15 may also be a straight- chain aliphatic, a branched-chain aliphatic or a tertiary alkyl group.

Assuming the amide compound is based on a polyamine and a fatty acid, mention be made for example of polyalkylene polyamides of saturated or unsaturated fatty acids having 1 - 24 carbons and aliphatic amines, such as isostearic acid triethylene tetramide, isostearic acid tetraethylene pentamide, oleic acid diethylene triamide and oleic acid diethanol amide. It is possible to incorporate fatty acid esters of polyhydric alcohols in the lubricating oil composition of this invention. For example, it is possible to use partial or complete esters of saturated or unsaturated fatty acids having 6 to 30 carbons, preferably 8 to 24 carbons, more preferably 8 to 18 carbons, and polyols ™ X 5 -^~ such as glycerine, sorbitan, alkylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol and xylitol. As examples of esters of glycerin, mention may be made of glycerin monolaurate, glycerin monostearate, glycerin monopalmitate, glycerin monooleate, glycerin dilaurate, glycerin distearate, glycerin dipalmitate, glycerin dioleate.

As examples of esters of sorbitan, mention may be made of sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan dilaurate, sorbitan dipalmitate, sorbitan distearate, sorbitan dioleate, sorbitan tristearate, sorbitan dilaurate, sorbitan trioleate, sorbitan tetraoleate, sorbitan sesquioleate . As examples of esters of alkylene glycol, mention may be made of ethylene glycol monolaurate, ethylene glycol monostearate, ethylene glycol monooleate, ethylene glycol dilaurate, ethylene glycol distearate, ethylene glycol dioleate, propylene glycol monolaurate, propylene glycol monostearate, propylene glycol monooleate, propylene glycol dilaurate, propylene glycol distearate, propylene glycol dioleate.

As examples of esters of neopentyl glycol, mention may be made of neopentyl glycol monolaurate, neopentyl glycol monostearate, neopentyl glycol monooleate, neopentyl glycol dilaurate, neopentyl glycol distearate, neopentyl glycol dioleate.

As examples of esters of trimethylolpropane, mention may be made of trimethylolpropane monolaurate, trimethylolpropane monostearate, trimethylolpropane monooleate, trimethylolpropane dilaurate, trimethylolpropane distearate, trimethylolpropane dioleate . As examples of esters of pentaerythritol, mention may be made of pentaerythritol monolaurate, pentaerythritol monostearate, pentaerythritol monooleate, pentaerythritol dilaurate, pentaerythritol distearate, pentaerythritol dioleate.

As examples of esters of xylitol, mention may be made of xylitol monolaurate, xylitol monostearate, xylitol monooleate, xylitol dilaurate, xylitol distearate, xylitol dioleate, xylitol trioleate. Polyol esters such as carboxylic acid ester, preferably partial esters (reactant) of unsaturated fatty {carboxylic) acids and polyol are good.

It is possible to incorporate epoxidised ester compounds in the lubricating oil composition of this invention. Epoxidised ester compounds are manufactured by epoxidising esters of rapeseed oil, soybean oil, linseed oil, castor oil, coconut oil, palm oil palm kernel oil, sunflower oil, rice bran oil, safflower oil, beef tallow, pork tallow and so on. For example, mention may be made of epoxidised rapeseed oil esters, epoxidised soybean oil esters, epoxidised linseed oil esters, epoxidised castor oil esters and epoxidised safflower oil esters, and those manufactured by epoxidising oleic acid esters such as methyl epoxystearate, butyl epoxystearate and octyl epoxystearate. Also, the alcohol residues of the esters are alkyl groups, or alkyl groups having ether bonds, or hydroxyalkyl groups, and more preferably are butyl groups, isobutyl groups and 2-ethylhexyl groups. As examples, mention may be made of epoxidised rapeseed oil fatty acid isobutyl ester, epoxidised rapeseed oil fatty acid 2-ethylhexyl ester and epoxidised linseed oil fatty acid butyl ester. The essential constituents of ordinary rapeseed oil fatty acids are fatty acids having 18 carbons with oleic acid 63%, linolic acid 20% and linolenic acid 8%. The essential constituents of linseed fatty acids are fatty acids having 18 carbons with oleic acid 21%, linolic acid 13% and linolenic acid 57%. It is possible to incorporate mono-alcohol compounds of 6 to 30 carbons in the lubricating oil composition of this invention. These mono-alcohols are consisting of an alkyl group or alkenyl group of 6 to 30 carbons, linear or branched, saturated or unsaturated, preferably 8 to 24 carbons more preferably 10 to 22, moreover preferably 12 to 22 carbons.

As examples of mono-alkylalcohol, mention may be made of octanol, nonanol, decanol, undeσanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol (stearyl alcohol), nonadecanol, icosanol, henicosanol, docosanol (behenyl alcohol}, tricosanol, tetracosanol .

As examples of mono-alkenyl-alcohol, mention may be made of octenol, nonenol, decenol, undecenol, dodecenol, tridecenol, tetradecenol, pentadecenol, hexadecenol, heptadecenol, octadecenol (oleyl alcohol), nonadecenol, icosenol, henicosenol, docosenol, tricosenol, tetracosenol .

Mixtures of these two or more compounds are also good. In case of less than 6 carbons or more than 30 carbons of alcohol, lubricating oil composition have poor solubility against base oil or poor heat stability in this invention.

It is possible to incorporate carboxylic acids of monocarboxylic acids (monocarboxylates) , polycarboxylic acids (polycarboxylates) , cyclic carboxylic acids (cyclic carboxylates) , heterocyclic carboxylic acids (heterocyclic carboxylates) in the lubricating oil composition of this invention.

Aforementioned monocarboxylic acids have carboxylic group comprising of 6 to 30 carbons preferably 8 to 24. As examples of saturated fatty acids, mention may be made of mono-carboxylic acids with carbon number 8 to 24, linear or branched aliphatic group, octanoic acid (caprylic acid) , nonanoic acid (pelargonic acid) , decanoic acid {capric acid) , undecanioc acid, dodecanoic acid (lauric acid) , tridecanoic acid, tetradecanoic acid (myristic acid) , pentadecanoic acid, hexadecanoic acid (palmitic acid) , heptadecanoic acid, octadecanoic acid {stearic acid) , nonadecanoic acid, icosanoic acid, henicosanoic acid, docosanoic acid, tricosanoic acid, tetracosanoic acid.

As examples of unsaturated fatty acids, mention may be made of mono-carboxylic acids with carbon number 8 to 24, octenoic acid, nonenoic acid, decenoic acid, undecenioc acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, pentadecenoic acid, hexadecenoic acid, heptadecenoic acid, octadecenoic acid (oleic acid) , nonadecenoic acid, icosenoic acid, henicosenoic acid, docosenoic acid, tricosenoic acid, tetracosenoic acid.

As examples of other monocarboxylic acids, saturated or unsaturated, linear or branched, mention may be made of N-methyl-N- (1-oxodecyl) glycine, N-methyl-ISH (1- oxoundecyl) glycine, N-methyl-N-- (1-oxododecyl) glycine, N-methyl-N- { 1-oxotridecyl ) glycine , N-methyl-N- { 1- oxotetradecyl) glycine, N-methyl-N- ( 1- oxopentadecyl) glycine, N-methyl-N- (1- oxohexadecyl) glycine, N-methyl-N- (1- oxoheptadecyl) glycine, N-methyl-N- (1- oxooctadecyl) glycine, N-methyl-N- (l-oxo-9- _ i n __

octadecenyl) glycine, N-methyl-N- { 1-oxononadecyl) glycine, N-rnethyl-N- (l~-oxoicosyl) glycine.

As examples of di-carboxylic acids, mention may be made of saturated or unsaturated, linear or branched, 1, 6-hexanedioic acid (adipic acid), 1, 7-heptanedioic acid (pimelic acid}, 1, 8~octanedioic acid (suberic acid), 1,9- nonanedioic acid (azelaic acid), 1, 10-decanedioic acidl (sebacic acid), 1, 6-hexenedioic acid, 1, 7-heptenedioic acid, 1, 8-octenedioic acid, 1, 9-nonenedioic acid, 1,10- decenedioic acid.

As examples of tri-carboxylic acids, mention may be made of hexane-tricarboxylic acid, heptane-tricarboxylic acid, octane-tricarboxylic acid, nonane-tricarboxylic acid, decane-tricarboxylic acid, also tetracarboxylic acids, mention may be made of saturated or unsaturated, linear or branched acids.

As examples of cyclic carboxylic acids (cyclic carboxylates) having one or more carboxylic groups, for instance, mention may be made of cyclohexane- monocarboxylic acid, methylcyclohexane-rnonocarboxylic acid, ethylcyclohexane-monocarboxylic acid, propylcyclohexane-monocarboxylic acid, butylcyclohexane- monocarboxylic acid, pentylcyclohexane-monocarboxylic acid, hexylcyclohexane-monocarboxylic acid, heptylcyclohexane-monocarboxylic acid, octylσyclohexane- monocarboxylic acid, cycloheptane-monocarboxylic acid, cyclooctane-monocarboxylic acid, trimethylcyclopentane- dicarboxylic acid (camphoric acid: cis-1,2,2- trimethylcyclopentane-1, 3-dicarboxylic acid), may be able to having 3 to 40 carbons, benzenecarboxylic acid (benzoic acid) , methylbenzoic acids (toluic acid) , dimethylbenzoic acids (xylic acid) , ethylbenzoic acid, propylbenzoic acid, benzene-dicarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid) , benzene- tricarboxylic acids (hemimellitic acid, trimellitic acid, trimesic acid) , benzene-tetracarboxylic, acids (mellophanic acid, prehnitic acid, pyromellitic acid) , riaphthalenecarboxylic acids (1- or 2-naphthoic acid} , 2- phenylpropionic acid (hydroatropic acid) , 3- phenylpropionic acid (hydrocinnamic acid) , phenylpropenoic acid (atropic acid, σinnaraic acid) , 2- phenyl-2-propenoic acid {atropic acid) , 3-phenyl-2- propenoic acid (cinnamic acid) , methylphenoxyacetic acid, ethylphenoxyacetic acid, butylphenoxyacetic acid, hexylphenoxylacetic acid, heptylphenoxylacetic acid, octylphenoxyacetic acid, nonylphenoxyacetic acid, decylphenoxyacetic acid, alkylphenoxyacetic acids, salicylic acid, alkylsalicylic acids.

As examples of the aforementioned heterocycliccarboxylic acids, mention may be made of tributyl phosphate, for example, furancarboxylic acids, thiophenecarboxylic acids, pyridinecarboxylic acids (nicotinic acid, isonicotinic acid) etc., and those are having 5 to 40 carbons.

It is possible to incorporate thiophosphate ester compounds in the composition according to the invention. As examples of thiophosphate ester compounds, mention may be made of the thiophosphate esters shown in the undermentioned General Formulas (8) and (9) .

X₁₆O -X ^ ^S

XoO 3 """ Xiβ LfOuX₁₉

( Formula 8 ) In the aforementioned General Formula (8) , X16 and X17 may be the same or different and each denotes a hydrogen atom or a hydrocarbon group of 1 - 30 carbons. Mention may be made, for example, of alkyl groups, alkenyl groups, aryl groups, alkylaryl groups and arylalkyl groups. X18 denotes an alkylene group of 1 - 20 carbons and X19 denotes a hydrogen atom or a hydrocarbon group of 1 - 30 carbons. Among the aforementioned phosphorylated carboxylic acids, assuming β™ dithiophosphorylated carboxylic acid where X19 is a hydrogen atom, mention may be made specifically of, for example, 3- (di-isobutoxy^thiophosphoryl sulphenyl) -2- methyl-propionic acid.

X19 is an ethyl group, mention may be made specifically of, as β-dithiophosphorylated carboxylic ester, for example, ethly-3- ( (bis (1-methyletoxy) phosphinochioyl) thio) propionate.

(Formula 9)

In the aforementioned General Formula (9) , X20 denotes a hydrogen atom or a hydrocarbon group of 1 - 30 carbons. Mention may be made specifically of, for example, triphenyl phosphorothionate or nonylphenyl phosphorothionate .

The content of the thiophosphate ester compounds in the lubricating oil composition of this invention is not specially limited, but is preferably 0.001 - 1% by mass, and more preferably 0.002 - 0.5% by mass, in respect of 100% by mass of base oil. If the amount of thiophosphate ester compound is less than the above-mentioned lower limit, there will be a tendency for sufficient lubricating properties not to be obtained. On the other hand, if the above-mentioned upper limit is exceeded, there will be a tendency for the effect of improvement in lubrication matching the extra amount added not to be achieved, and furthermore there is a risk that thermal and oxidative stability or hydrolytic stability may decrease. These thiophosphate ester compounds may be used singly or in mixtures of more than one kind. It is possible to add phosphorus compounds other than thiophosphate esters to the lubricating oil of this invention, and it is possible thereby to impart further anti-wear properties and extreme-pressure properties. As examples of phosphorus compounds suitable for this invention, mention may be made of phosphate esters, acidic phosphate esters, amine salts of acidic phosphate esters, phosphite esters, phosphorothionates, zinc dithiophosphates, phosphorus-containing carboxylic acids and phosphorus-containing carboxylic acid esters. These phosphorus compounds may be used singly or in plural combinations within the range of 0.01 - 2% by mass relative to 100% by mass of base oil.

As examples of the aforementioned phosphate esters, mention may be made of tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, triundecyl phosphate, tridodecyl phosphate, tritridecyl phosphate, tritetradecyl phosphate, tripentadecyl phosphate, trihexadecyl phosphate, triheptadecyl phosphate, trioctadecyl phosphate, trioleyl phosphate, triphenyl phosphate, tris(iso- propylphenyl) phosphate, triallyl phosphate, tricresyl phosphpate, trixylenyl phosphate, cresyldiphenyl phosphate and xylenyldiphenyl phosphate.

As specific examples of the aforementioned acidic phosphate esters, mention may be made of monobutyl acid phosphate, monopentyl acid phosphate, monohexyl acid phosphate, monoheptyl acid phosphate, monooctyl acid phosphate, monononyl acid phosphate, monodecyl acid phosphate, monoundecyl acid phosphate, monododecyl acid phosphate, monotridecyl acid phosphate, monotetradecyl acid phosphate, monopentadecyl acid phosphate, monohexadecyl acid phosphate, monoheptadecyl acid phosphate, monooctadecyl acid phosphate, monooleyl acid phosphate, dibutyl acid phosphate, dipentyl acid phosphate, dihexyl acid phosphate, diheptyl acid phosphate, dioctyl acid phosphate, dinonyl acid phosphate, didecyl acid phosphate, diundecyl acid phosphate, didodecyl acid phosphate, ditridecyl acid phosphate, ditetradecyl acid phosphate, dipentadecyl acid phosphate, dihexadecyl acid phosphate, diheptadecyl acid phosphate, dioctadecyl acid phosphate and dioleyl acid phosphate.

As examples of the aforementioned amine salts of acidic phosphate esters, mention may be made of the methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylarnine, octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine and trioctylamine salts of the previously mentioned acidic phosphate esters.

As examples of the aforementioned phosphite esters, mention may be made of dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, didoecyl phosphite, dioleyl phosphite, diphenyl phosphite, dicresyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite, trioctyl phosphite, trinonyl phosphite, tridecyl phosphite, triundecyl phosphite, tridodecyl phosphite, trioleyl phosphite, triphenyl phosphite and tricresyl phosphite. As examples of the aforementioned zinc dithiophosphates, mention may be made in general of zinc dialkyl dithiophosphates, zinc diaryl dithiophosphates and zinc arylalkyl dithiophosphates. For example, zinc dialkyl dithiophosphates where the alkyl groups of the zinc dialkyl dithiophosphates have primary or secondary alkyl groups of 3 - 22 carbons or alkylaryl groups substituted with alkyl groups of 3 - 18 carbons may be used. As specific examples of zinc dialkyl dithiophosphates, mention may be made of zinc dipropyl dithiophosphate, zinc dibutyl dithiophosphate, zinc dipentyl dithiophosphate, zinc dihexyl dithiophosphate, zinc diisopentyl dithiophosphate, zinc diethylhexyl dithiophosphate, zinc dioctyl dithiophosphate, zinc dinonyl dithiophosphate, zinc didecyl dithiophosphate, zinc didoecyl dithiophosphate, zinc dipropylphenyl dithiophosphate, zinc dipentylphenyl dithiophosphate, zinc dipropylmethylphenyl dithiophosphate, zinc dinonylphenyl dithiophosphate and zinc didodecylphenyl dithiophosphate . In order to improve oiliness, it is possible to incorporate fatty acid esters of polyhydric alcohols in the lubricating oil composition of this invention. For example, it is possible to use partial or complete esters of saturated or unsaturated fatty acids having 1 - 24 carbons and polyhydric alcohols such as glycerol, sorbitol, alkylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol and xylidol. As examples of glycerol esters, mention may be made of glycerol monolaurylate, glycerol monostearate, glycerol monopalmitate, glycerol monooleate, glycerol dilaurylate, glycerol distearate, glycerol dipalmitate and glycerol dioleate. For sorbitol esters mention may be made of sorbitol monolaurylate, sorbitol monopalmitate, sorbitol monostearate, sorbitol monooleate, sorbitol dilaurylate, sorbitol dipalmitate, sorbitol distearate, sorbitol dioleate, sorbitol tristearate, sorbitol trilaurylate, sorbitol trioleate and sorbitol tetraoleate.

Alkylene glycol esters include ethylene glycol monolaurylate, ethylene glycol monostearate, ethylene glycol monooleate, ethylene glycol dilaurylate, ethylene glycol distearate, ethylene glycol dioleate, propylene glycol monolaurylate, propylene glycol monostearate, propylene glycol monooleate, propylene glycol dilaurylate, propylene glycol distearate and propylene glycol dioleate.

For neopentyl glycol esters mention may be made of neopentyl glycol monolaurylate, neopentyl glycol monostearate, neopentyl glycol monooleate, neopentyl glycol dilaurylate, neopentyl glycol distearate and neopentyl glycol dioleate.

Trimethylolpropane esters include trimethylolpropane monolaurylate, trimethylolpropane monostearate, trimethylolpropane monooleate, trimethylolpropane dilaurylate, trimethylolpropane distearate, trimethylolpropane dioleate and pentaerythritol trimethylolpropane monolaurylate .

Pentaerythritol esters include pentaerythritol monostearate, pentaerythritol monooleate, pentaerythritol dilaurylate, pentaerythritol distearate, pentaerythritol dioleate and dipentaerythritol monooleate. For such fatty acid esters of polyhydric alcohols it is preferable to use partial esters of polyhydric alcohols and unsaturated fatty acids. In order to enhance oxidative stability, it is possible to incorporate anti-oxidants in this invention. For the anti-oxidants, those used in lubricating oils are preferred for practical use, and mention may be made of phenolic anti-oxidants, aromatic amine-based anti- oxidants, sulphur-based anti-oxidants and phosphorus- based anti-oxidants, and so on. These anti-oxidants may be used singly or in plural combinations within the range of 0.01 - 5% by mass relative to 100% by mass of base oil. As examples of the aforementioned aromatic amine- based anti-oxidants, mention may be made of dialkyl- diphenylamines such as p, p' -dioctyl-diphenylamine (Nonflex OD-3, made by Seiko Chemical Ltd), p,p'-di-α- methylbenzyl-diphenylamine and N-p-butylphenyl-N-p¹ - octylphenylamine, monoalkyldiphenylamines such as mono-t- butyldiphenylamine and monooctyldiphenylamine, bis (dialkylphenyl) amines such as di{2,4- diethylphenyl) amine and di (2-ethyl-4-nonylphenyl) amine, alkylphenyl-1-naphthylamines such as octyl-phenyl-1- naphthylamine and N-t-dodecylphenyl-1-naphthylamine, 1- naphthylamine, aryl-naphthylamines such as phenyl-1- naphthylamine, phenyl-2-naphthylamine, N-hexylphenyl-2- naphthylamine and N-octylphenyl-2-naphthylamine, phenylenediamines such as N, N' -diisopropyl-p- phenylenediamine and N, N ' -diphenyl-p-phenylenediamine, and phenothiazin.es such as Phenothiazine (made by Hodogaya Chemical Ltd.) and 3, 7~dioctylphenothiazine. Phenolic anti-oxidants include 2-t-butylphenol, 2-t- butyl-4-methylphenol, 2~t-butyl-5-methylphenol, 2,4-di-t- butylphenol, 2, 4-dimethyl-6-t~butylphenol, 2-t-butyl-4- methoxyphenol, 3-t~-butyl-4-methoxyphenol, 2,5-di-t- butylhydroquinone (Antage DBH, made by Kawaguchi Chemical Industry Co. Ltd.), 2, β-di-t-butylphenol, 2, 6-di-t-butyl- 4-alkylphenols such as 2, 6-di-t-butyl-4~methylphenol and 2, 6-di-t-butyl-4-ethylphenol, and 2, 6-di-t-butyl-4- alkoxyphenols such as 2, S-di-t-butyl~4-methoxyphenol and 2, 6™di-t-butyl-4-ethoxyphenol. Also, there are 3, 5-di-t-butyl-4- hydroxybenzylmercapto-octylacetate, alklyl-3- (3, 5-di-t- butyl-4-hydroxyρhenyl) propionates such as n-octadecyl-3- (3, 5-di-t-butyl-4-hydroxyphenyl) propionate {Yoshinox SS, made by Yoshitomi Fine Chemicals Ltd.}, n-dodecyl™3~ {3, 5- di~t-butyl-4-hydroxyphenyl) propionate and 2 ' -ethylhexyl- 3- (3, 5-di-t-butyl~4-hydroxyphenyl) propionate, benzenepropanoic acid 3, 5-bis (1, 1-dimethyl-ethyl) -4- hydroxy-C7-C9 side-chain alkyl esters (Irganox L135, made by Ciba Specialty Chemicals Ltd.), 2, 6-di-t-butyl-α- dimethylamino-p-cresol, and 2, 2 ' -methylenebis (4-alkyl-β- t-butylphenol} s such as 2, 2 ' -methylenebis {4~methyl-6-t- butylphenol) (Antage W-400, made by Kawaguchi Chemical Industry Ltd.) and 2, 2 ' -methylenebis (4-ethyl-6-t- butylphenol) (Antage W-500, made by Kawaguchi Chemical Industry Ltd} .

Furthermore, there are bisphenols such as 4,4'- butylidenebis (3-methyl-6-t-butylphenol) (Antage W-300, made by Kawaguchi Chemical Industry Ltd.), 4,4'- methylenebis {2, 6-di-t-butylphenol) (Ionox 220AH, made by Shell Japan Ltd.), 4, 4 ' -bis (2, 6-di~t-butylphenol) , 2,2- (di-ρ-hydroxyphenyl) propane (Bisphenol A, made by Shell Japan Ltd.), 2, 2-bis (3, 5-di-t-butyl-4- hydroxyphenyl) propane, 4, 4 ' -cyclohexylidenebis {2, 6-t- butylphenol) , hexamethylene glycol bis [3- (3, 5-di-t-butyl- 4~hydroxyρhenyl) propionate] {Irganox L109, made by Ciba Specialty Chemicals Ltd.}, triethylene glycol bis [3™ (3-t- butyl-4-hydroxy-5-methylphenyl) propionate] (Tominox 917, made by Yoshitomi Fine Chemicals Ltd.), 2,2'-thio-

[diethyl-3- { 3 , 5-di-t-butyl-4-hydroxyphenyl ) propionate (Irganox L115, made by Ciba Specialty Chemicals Ltd.}, 3, 9-bis{ 1, l-dimethyl-2- [3- {3-t-butyl-4-hydroxy-5- methylphenyl ) propionyloxy] ethyl } 2 , 4 , 8 , 10- tetraoxaspiro [5, 5] undecane (Sumilizer GA80, made by Sumitomo Chemicals), 4, 4 ' -thiobis (3-methyl-6-t- butylphenol) {Antage RC, made by Kawaguchi Chemical Industry Ltd.} and 2, 2 ' -thiobis (4, 6-di-t-butyl- resorcinol) . Mention may also be made of polyphenols such as tetrakis [methylene-3- (3, 5-di-t-butyl-4-hydroxyphenyl) propionate] methane (Irganox LlOl, made by Ciba Specialty Chemicals Ltd.), 1, 1, 3-tris (2-methyl-4-hydroxy-5-t- butylphenyl) butane (Yoshinox 930, made by Yoshitomi Fine Chemicals Ltd.), 1, 3, 5-trimethyl-2, 4, 6-tris (3, 5-di~t~ butyl-4-hydroxybenzyl) benzene {Ionox 330, made by Shell Japan Ltd.), bis- [3, 3 ' -bis- (4 ' -hydroxy-3 ' -t-butylphenyl) butyric acid] glycol ester, 2~ (3 ' , 5 ' -di-t-butyl-4- hydroxyphenyl) methyl-4- {2¹ ' ,4' ' -di-t-butyl-3¹ '- hydroxyphenyl) methyl-6-t-butylphenol and 2, 6, -bis (2 '- hydroxy-3 ' -t-butyl-5 ' -methyl-benzyl) -4~methylphenol, and phenol-aldehyde condensates such as condensates of p-t- butylphenol and formaldehyde and condensates of p-t- butylphenol and acetaldehyde.

As examples of sulphur-based anti-oxidants, mention may be made of dialkyl sulphides such as didodecyl sulphide and dioctadecyl sulphide, thiodipropionate esters such as didodecyl thiodipropionate, dioctadecyl thiodipropionate, dimyristyl thiodipropionate and dodecyloctadecyl thiodipropionate, and 2- mercaptobenzoimidazole . As examples of phosphorus-based anti-oxidants mention may be made of triarylphosphites such as triphenylphosphite and tricresylphosphite, trialkylphosphites such as trioctadecylphosphite and tridecylphosphite, and tridodecyltrithiophosphite. Additives to prevent metallic corrosion can be incorporated in this invention with a view to reinforcing compatibility with metallic materials. Metal deactivators that can be used together with the composition of this invention include benzotriazole and benzotriazole derivatives which are 4-alkyl-benzotriazoles such as 4- methyl-benzotriazole and 4-ethyl~benzotriazole, 5-alkyl- benzotriazoles such as 5-methyl-benzotriazole and 5- ethyl-benzotriazole, 1-alkyl-benzotriazoles such as 1- dioctylaminomethyl-2, 3-benzotriazole and 1-alkyl- tolutriazoles such as l-dioctylaminomethyl-2, 3- tolutriazole, and benzoimidazole and benzoimidazole derivatives which are 2- {alkyldithio) -benzoimidazoles such as 2- (octyldithio) -benzoimidazole, 2~ (decyldithio) - benzoimidazole and 2- (dodecyldithio) -benzoimidazole and 2- (alkyldithio) toluimidazoles such as 2- (octyldithio) - toluimidazole, 2- (decyldithio) -toluimidazole and 2~ (dodecyldithio) toluimidazole . Also, mention may be made of indazole, indazole derivatives which are toluindazoles [sic] such as 4- alkyl-indazoles and 5-alkyl-indazoles, benzothiazole, and benzothiazole derivatives which are 2- mercaptobenzothiazole derivatives (Thiolite B-3100, made by Chiyoda Chemical Industries Ltd.)_/- 2- (alkykldithio) benzothiazoles such as 2- (hexyldithio) benzothiazole and 2- (octyldithio) benzothiazole, 2- (alkyldithio} toluthiazoles such as 2~ (hexyldithio) toluthiazole and 2- (octyldithio) toluthiazole, 2- (N, N- dialkylydithiocarbamyl) -benzothiazoles such as 2- (N, N- diethyldithiocarbamyl) -benzothiazole, 2- (N, N- dibutyldithiocarbamyl} -benzothiazole and 2- (N, N- dihexyldithiocarbamyl) -benzothiazole, and 2- (N, N- dialkylydithiocarbarαyl) -toluzothiazoles [sic] such as 2- (N, N-diethyldithiocarbamyl) -toluthiazole, 2™ (N, N- dibutyldithiocarbamyl) -toluthiazole and 2- (N, N- dihexyldithiocarbamyl ) -toluthiazole . Further, mention may be made of benzooxazole derivates which are 2- (alkyldithio) benzooxazoles such as 2- (octyldithio) benzooxazole, 2- (decyldithio) benzooxazole and 2- (dodecyldithio)benzooxazole or which are 2- (alkyldithio) toluoxazoles such as 2- (octyldithio) toluoxazole, 2- (decyldithio) toluoxazole and 2- (dodecyldithio) toluoxazole, thiadiazole derivatives which are 2, 5-bis (alkyldithio) -1, 3, 4-thiadiazoles such as 2, 5-bis (heptyldithio) -1,3, 4~thiadiazole, 2, 5- bis (nonyldithio) -1,3, 4-thiadiazole, 2, 5- bis (dodecyldithio) -1, 3, 4-thiadiazole and 2,5- bis (octadecyldithio) -1,3, 4-thiadiazole, 2, 5-bis (N, N- dialkyldithiocarbamyl) -1, 3, 4-thiadiazoles such as 2,5- bis (N, N~diethyldithiocarbamyl} -1,3, 4-thiadiazole, 2 , 5- bis (N, N-dibutyldithlocarbamyl) -1, 3, 4-thiadiazole and 2,5- bis (N,N~~dioctyldithiocarbamyl) -1, 3, 4™thiadiazole and 2- N,N-dialkyldithiocarbamyl-~5-mercapto-l, 3, 4-thiadiazoles such as 2-N, N-dibutyldithiocarbamyl-5-mercapto-l, 3, 4- thiadiazole and 2-N,N-dioctyldithiocarbamyl-5-mercapto- 1, 3, 4-thiadiazole, and triazole derivates which are, for example, l-alkyl-2, 4-triazoles such as 1-di- octylaminomethyl-2, 4-triazole.

These metal deactivators may be used singly or in plural combinations within the range 0.01 - 0.5% by mass relative to 100% by mass of base oil.

In order to improve performance further, it is possible where necessary to make appropriate use of various additives other than those aforementioned. As examples of these, mention may be made of defoaming agents, viscosity index improvers, pour-point depressants, detergent dispersants, rust preventatives, demulsifying agents, and other known lubricating oil additives . In order to improve the low-temperature flow characteristics and viscosity characteristics, pour-point depressants and viscosity-index improvers may also be added to the lubricating oil composition of this invention. As examples of viscosity-index improvers mention may be made of non-dispersant type viscosity- index improvers such as polymethacrylates and olefin polymers such as ethylene-propylene copolymers, styrene- diene copolymers, polyisobutylene and polystyrene, and dispersant type viscosity-index improvers where nitrogen- containing monomers have been copolymerised with these. As regards the amount to be added, they may be used within the range 0.05 - 20% by mass relative to 100% by mass of base oil. As examples of pour-point depressants mention may be made of polymethacrylate-based polymers. As regards the amount to be added, they may be used within the range 0.01 - 5% by mass relative to 100% by mass of base oil. Defoaming agents may also be added in order to impart defoaming characteristics to the lubricating oil composition of this invention. As examples of such defoaming agents, mention may be made of organosilicates such as dimethylpolysiloxane, diethylsilicate and fluorosilicone, and non-silicone type defoaming agents such as polyalkylacrylates. As regards the amount to be added, they may be used singly or in plural combinations within the range of 0.0001 to 0.1% by mass relative to 100% by mass of base oil. As examples of demulsifiers suitable for this invention, there are those in the known art normally used as additives for lubricating oils. As regards the amount to be added, they may be used within the range of 0.0005 to 0.5% by mass relative to 100% by mass of base oil. Examples

The invention is explained in specific detail below by means of Examples and Comparative Examples, but the invention is not limited to only these forms of embodiment . For preparation of the Examples and Comparative

Examples, the compositions and materials mentioned below were used.

1. Base Oils

{1-1) Base Oil 1: A paraffinic mineral oil obtained by appropriate use of a suitable combination of refining processes such as hydrocracking and dewaxing in respect of a lubricating oil fraction obtained by atmospheric distillation of crude oil, and classified as Group II according to the API (American Petroleum Institute) base oil classification. {Characteristics: kinematic viscosity at 100⁰C (ASTM D445), 5.35 mni²/s; kinematic viscosity at 40⁰C (ASTM D445), 31.4 rranVs; viscosity index (ASTM D2270), 103; 15°C density, 0.864; sulphur content (as converted to elemental sulphur) , less than 10 ppm; nitrogen content (as converted to elemental nitrogen) , less than 1 ppm; aniline point, 110⁰C; ring-analysis paraffin content according to the method of ASTM D3238, 62%; naphthene content ditto, 38%; aromatic content ditto, less than 1%; initial boiling point temperature according to gas chromatography distillation by the method of ASTM D5480, 312°C)

(1-2) Base Oil 2: A paraffinic mineral oil obtained by appropriate use of a suitable combination of refining processes such as hydrocracking and dewaxing in respect of a lubricating oil fraction obtained by atmospheric distillation of crude oil, and classified as Group III according to the API (American Petroleum Institute) base oil classification. (Characteristics: kinematic viscosity at 100⁰C (ASTM D445) , 6.57 mmVs; kinematic viscosity at 40^QC (ASTM D445), 37.5 mmVs; viscosity index (ASTM D2270), 130; 15°C density, 0.823; sulphur content (as converted to elemental sulphur) , less than 10 ppm; nitrogen content (as converted to elemental nitrogen) , less than 1 ppm; aniline point, 13O⁰C; ring-analysis paraffin content according to the method of ASTM D3238, 78%; naphthene content ditto, 22%; aromatic content ditto, less than 1%; polynuclear aromatic content according to the method of IP 346, 0.2%)

(1-3) Base Oil 3: A GTL base oil synthesised by the Fischer-Tropsch method, and classified as Group III according to the API (American Petroleum Institute) base oil classification. (Characteristics: kinematic viscosity at 100⁰C (ASTM D455) , 5.10 mm²/s; kinematic viscosity at 40⁰C (ASTM D445), 23.5 mmVs; viscosity index (ASTM D2270), 153; 15⁰C density, 0.821; sulphur content {as converted to elemental sulphur} , less than 10 ppm; nitrogen content (as converted to elemental nitrogen) , less than 1 ppm; ring-analysis aromatic content according to the method of ASTM D3238, less than 1%)

(1-4) Base Oil 4: A synthetic oil being a poly-α™ olefin (PAO) with the general name PAO6, and classified as Group IV according to the API (American Petroleum Institute) base oil classification. (Characteristics: kinematic viscosity at 100°C (ASTM D445) , 5.89 mm^z/s; kinematic viscosity at 40⁰C (ASTM D445) , 31.2 mm²/s; viscosity index (ASTM D2270) , 135; 15°C density, 0.827; sulphur content (as converted to elemental sulphur) , less than 10 ppm; nitrogen content (as converted to elemental nitrogen), less than 1 ppm; aniline point, 128⁰C; ring- analysis aromatic content according to the method of ASTM D3238, less than 1%; initial boiling point temperature according to gas chromatography distillation by the method of ASTM D5480, 403⁰C)

(1-5) Base Oil 5: A paraffinic mineral oil obtained by appropriate use of a suitable combination of refining processes such as dewaxing in respect of a lubricating oil fraction obtained by atmospheric distillation of crude oil, and classified as Group I according to the API (American Petroleum Institute) base oil classification. (Characteristics: kinematic viscosity at 100°C (ASTM D445), 4.60 mm²/s; kinematic viscosity at 40⁰C

(ASTM D445), 24.6 ramVs; viscosity index (ASTM D2270), 101; 15°C density, 0.866; sulphur content (as converted to elemental sulphur) , 460 ppm; nitrogen content (as converted to elemental nitrogen) , 20 ppm; ring-analysis paraffin content according to the method of ASTM D3238, 66%; naphthene content ditto, 31%; aromatic content ditto, 3%; aniline point , 99°C; polynuclear aromatic content according to the method of IP 346, 0.8%; initial boiling point temperature according to gas chromatography distillation by the method of ASTM D5480, 331°C) 2. Additives

{2-1) Additive A: Aspartic acid derivative: a mixture of N-l-oxo-3-carbonyloxypropyl-N~3- octyloxypropyl-diisobutyl aspartate ester, N-l-oxo-3- carbonyloxypropyl-N-3-decyloxypropyl-diisobutyl aspartate ester, N-l~oxo-3-carbonyloxypropyl-N-3-dodecyloxypropyl- diisobutyl aspartate ester and N-l~oxo-3- carbonyloxypropyl-N-S-tetradecyloxypropyl-diisobutyl aspartate ester (acid number by the method of JIS K2501: 100 mgKOH/g)

(2-2) Additive B: Succinic acid derivative: tetrapropenyl succinic acid, 1, 3-propanediol half ester (acid number by the method of JIS K2501: 160 mgKOH/g)

(2-3) Additive Cl: Coconut amine (the main constituent being dodecylamine; primary amine compound of primary alkyl (base number by the method of JIS K2501: 390 mgKOH/g) (2-4) Additive C2 : Coconut diamine (the main constituent being N-dodecyl-1, 3-propylenediamine) (base number by the method of JIS K250X: 440 mgKOH/g)

(2-5) Additive C3: Primary amine compound with C18 tertiary alkyl group (Primary amine compound having 16 to 22 carbons, mainly 1,1,3,3,5,5,7,7,9,9- decamethyldodecylamine, ) (base number by the method of JIS K2501: 155 mgKOH/g) (2-6) Additive C4 : N-alkyl diethanolamine (the main constituent being N-oleyl diethanolamine) ; tertiary amine compound (base number by the method of JIS K2501: 160 mgKOH/g) {2-1) Additive C5 : isostearic acid triethylene tetramide (base number by the method of JIS K2501: 7.2 mgKOH/g)

(2-8) Additive C6: behenyl alcohol

(2-9) Additive C7 : ester of 2-ethylhexyl alcohol and epoxylated Rapeseed-oil carboxylic acid

(2-10) Additive C8 : sorbitan sesquioleate (hydroxyl number by the method of JIS K0070: 200 mgKOH/g)

(2-11) Additive C9: oleic acid (acid number by the method of JIS K2501: 197 mgKOH/g) (2-12) Additive ClO: N-methyl~-N- (l-oxo-9- octadecenyl) glycine (acid number by the method of JIS K2501: 157 mgKOH/g)

(2-13) Additive CIl: p-nonylphenoxyacetic acid (acid number by the method of JIS K2501: 190 mgKOH/g) Examples 1 - 17, Comparative Examples 1 - 3

Using the aforementioned compositions and materials _r the lubricating oil compositions of Examples 1 to 11 and Comparative Examples 1 to 3 were prepared with the constitutions shown in Tables 1 to 4. Tests

The following tests were carried out on the lubricating oil compositions of the aforementioned Examples 1 to 17 and Comparative Examples 1 to 3 in order to observe their performance. Rust Prevention Tests

Following JIS K2510, 300 ml of test oil was taken and put in a container installed in a constant- temperature bath. It was agitated at a speed of 1000 turns per minute. When the temperature reached 60⁰C, an iron test specimen was inserted into the oil and 30 ml of artificial sea water was also added. Keeping the temperature at 60⁰C, agitation was continued for 24 hours. Then the specimen was removed and assessed visually for occurrence of any rust. If no rust appeared, a pass was awarded. Friction Coefficient

The friction coefficient was measured by means of a Masuda pendulum-type oiliness test rig made by Shinko Engineering Co. Ltd. In this test, the test oil is supplied to the frictional part of the point of support of the pendulum, the pendulum is oscillated and the friction coefficient is obtained from the attenuation of the oscillations.

Evaluation of the tests was carried out using the following criteria:

Friction coefficient is not more than 0.135: 0 (Excellent) Friction coefficient is from 0.136 to under 0.150: O (Good)

Friction coefficient is 0.150 or more: X (Not acceptable) Test Results

The results of the tests are shown in Tables 1 to 3. Discussion

As is clear from the test results shown in Table 1 and Table 3, in the cases of Examples 1 and 2 where an aspartic acid derivative (Additive A) and a succinic acid derivative (Additive B) are together added to a base oil, no evidence of rust was seen, and the friction coefficient decreased substantially. It was clear that the synergistic effect of the two additives was creating even more improvement in the low-friction properties. Also, in the cases of Examples 3 - 6 the base oil was varied, but both when using a highly refined base oil such as Base Oil 2 as in Example 3 or Base Oil 5 as in Example 6, and when using a synthetic base oil such as Base Oil 3 in Example 4 or Base Oil 4 as in Example 5, no evidence of rust was seen, and the friction coefficient decreased substantially. It was clear that the combination of aspartic acid derivative and succinic acid derivative had a synergistic effect. In Examples 7 - 17, in addition to the combination of aspartic acid derivative and succinic acid derivative, by further addition of the amine compounds of Additives Cl ~ C4, and by further addition of the amide compound of Additive C5 instead of an amine compound in the case of Example 11, and by further addition of the alcohol compound of Additive C6 instead of an amine compound in the case of Example 12, and by further addition of the ester compound of Additive C7 to C8 instead of an amine compound in the case of Example 13 to 14, and by further addition of the carboxylic acid compound of Additive C9 to CIl instead of an amine compound in the case of Example 15 to 17, good rust-preventing properties as compared with Example 1 were maintained in each case, and at the same time the friction coefficient was further reduced. It was clear that the addition of an amine compound or an amide compound effected even further improvement of the low-friction properties.

In contrast, in the case of Comparative Example 1 which used only Base Oil 1, rust appeared and the friction coefficient was high. Also, in the case of

Comparative Example 2 where the aspartic acid derivative (Additive A) , was added to Base Oil, or in the case of Comparative Example 3 where the succinic acid derivative (Additive B) was added, rust prevention was obtained but the friction coefficient was high and it was clear that they did not have adequate friction performance.

Table 1

Table 2

Table 3

4- K)

Table 4

4-

Claims

C L A I M S

1. A lubricating composition comprising a base oil, an aspartic acid derivative and a succinic acid derivative.

2. A lubricating composition according to Claim 1 further containing at least one compound selected from amine compounds, amide compounds, alcohol compounds, carboxylic acid compounds, and ester compounds.

3. A lubricating composition according to Claim 1 or 2, wherein the acid number of the aspartic acid derivative is from 10 to 200 mgKOH/g.

4. A lubricating composition according to any of Claims

1 to 3, wherein the acid number of the succinic acid derivative is from 10 to 300 mgKOH/g.

5. A lubricating composition according to any of Claims

2 to 4, wherein the compound selected from amine compound, amide compound, alcohol compound, carboxylic acid compound, and ester compound, as the additive is an aliphatic amine compound and/or amide compound, and the aliphatic carbon number is 1 to 30, or alcohol compound and/or carboxylic acid compound and/or ester compound and the aliphatic carbon number is 6 to 30.

6. A lubricating composition according to any of Claims 1 to 5, wherein the base oil comprises a synthetic oil.

7. A lubricating composition according to Claim 6, wherein the synthetic oil comprises a poly~α~olefin.

8. A lubricating composition according Claim 6, wherein the aforementioned synthetic oil comprises a GTL-derived base oil.

9. Use of the lubricating composition according to any of Claims 1 to 8 for improving one or more of low- friction and rust-preventing properties.