WO2008031808A2

WO2008031808A2 - Lubricating oil composition an aspartic acid derivative and a fatty ester of a polyhydric alcohol

Info

Publication number: WO2008031808A2
Application number: PCT/EP2007/059498
Authority: WO
Inventors: Hiroshi Kaneko; Yoshiharu Baba; Mitsuhiro Nagakari; Hirohiko Otsu; Masayoshi Osawa
Original assignee: Showa Shell Sekiyu KK; Shell Internationale Research Maatschappij BV
Current assignee: Showa Shell Sekiyu KK; Shell Internationale Research Maatschappij BV
Priority date: 2006-09-11
Filing date: 2007-09-11
Publication date: 2008-03-20
Anticipated expiration: 2009-03-11
Also published as: EP2074202A2; US20090318320A1; CN101511984A; WO2008031808A3

Abstract

The present invention aims to obtain a lubricating oil composition which has good rust-preventing properties in lubricating oil compositions, among them the generality of industrial lubricating oils using highly refined base oils, and in particular machine oils, hydraulic oils, turbine oils, compressor oils, gear oils and bearing oils, and which also has excellent energy-saving characteristics through having a low friction coefficient. To this end an aspartic acid derivative and a fatty acid ester of a polyhydric alcohol are incorporated as additives in a base oil of e.g. mineral oil or synthetic oil type. By this means, a lubricating oil composition having excellent rust-preventing properties, reduced friction coefficient and excellent energy-saving properties and so being suitable for industrial lubricating oils can be obtained. Also, by further adding an epoxy compound and by adding also a fatty acid amine, it is possible to obtain a lubricating oil composition even more endowed with rust-preventing properties and energy-saving properties.

Description

LUBRICATING OIL COMPOSITION

This invention provides a lubricating oil compositions, among them to the generality of industrial lubricating oils using highly refined base oils, and in particular provides lubricating oil compositions used as machine oils, hydraulic oils, turbine oils, compressor oils, gear oils and bearing oils.

In the case of lubricating oil compositions, and, among these, industrial lubricating oil compositions, good rust preventing properties and friction characteristics are required. What is required is, by having a low friction coefficient (μ) , to reduce friction losses efficiently in machinery and apparatus and to achieve high energy-saving properties.

For example, hydraulic systems are often used in construction machinery and the like, but if the friction coefficient of the lubricating oil used as the hydraulic oil is high, a minute stick-slip phenomenon occurs in the sliding parts of the reciprocating motion packing of the hydraulic cylinders, then phenomena such as chatter, vibration, squeaking and generation of abnormal sounds occur and precise control of the hydraulic equipment becomes impossible. See e.g. Japanese Laid-open Patent 9- 111277 (1997) . Therefore, in order to ensure that the hydraulic cylinders operate accurately and smoothly, it is desired to reduce the friction coefficient of the lubricating oil.

In the case of lubricating oils used in machinery and equipment, to maintain performance thereof, rust preventing properties are fundamentally essential. Furthermore, it has been pointed out that in such hydraulic apparatus and control apparatus, accompanying the realisation of higher performance or higher oil pressures of the apparatus, formic acid or acetic acid is generated by ultrasonic waves generated by extremely minute vibrations of the spools in valves or by allowing the lubricating oil to be exposed to high pressures or high shear conditions . The acid accumulates in the lubricating oil of the closed hydraulic circuit and possibly corrodes the metallic material. See Japanese Laid-open Patent 2005-60526.

This invention aims to obtain an industrial lubricating oil which reduces the friction coefficient exhibited by the lubricating oil and which has high energy-saving properties. Also, when such a lubricating oil composition is used as a hydraulic oil in hydraulic apparatus, it will not only ensure that it is possible to control the hydraulic apparatus with good precision without giving rise to phenomena in the hydraulic cylinders such as chatter, vibration, squeaking and generation of abnormal sounds, but will also ensure that generation of rust is inhibited and so will impart good rust-preventing properties. Thus, the invention aims to obtain a lubricating oil composition of high functional efficiency which has good rust-preventing properties and is well endowed with energy-saving properties.

Furthermore, it is aimed to obtain a lubricating oil composition even more endowed with rust-preventing properties and energy-saving properties in that it has the resistance to ensure no rust is generated even when lower fatty acids such as formic acid or acetic acid, which are possibly generated within the hydraulic apparatus , are present . This invention is capable of obtaining a lubricating oil composition suitable as an industrial lubricating oil composition, such as in hydraulic oils, by incorporating in mineral or synthetic base oils, as additives, aspartic acid derivatives and fatty acid esters of polyhydric alcohols .

It is also possible to obtain a lubricating oil composition even more endowed with rust-preventing properties and with superior energy-saving properties by adding, as further additives, epoxidised compounds or by adding aliphatic amines.

According to this invention, 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 precisely 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. Furthermore, it is possible to obtain a lubricating oil composition well endowed with rust-preventing properties by inhibiting the generation of rust. Also, it is possible to produce a lubricating oil composition even more endowed with rust-preventing properties by not giving rise to generation of rust even if lower fatty acids such as formic acid or acetic acid are generated within the hydraulic apparatus and accumulate in the oil.

For the base oil of the present lubricating oil composition it is possible to use mineral oils and synthetic oils as normally used for lubricating 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.

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 may be from 80 to 120 and preferably from 95 to 110. The kinetic viscosity at 40⁰C is preferably from 2 to 680 mm²/s and even more preferably from 8 to 220 mm²/s. Also, the total sulphur content may be less than 700 ppm and preferably less than 500 ppm. The total nitrogen content may be less than 50 ppm and preferably less than 25 ppm. In addition, oils with an aniline point from 80 to 150⁰C and preferably from 90 to 120⁰C may be used.

Group II base oils include, for example, paraffinic mineral oils obtained by appropriate use of a suitable combination of refining processes such as hydrorefining 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 under 5% and so are suitable for this invention. The viscosity of these base oils is not specially limited, but the viscosity index may be from 90 to 125 and preferably from 100 to 120. The kinetic viscosity at 4O⁰C may preferably be from 2 to 680 mm²/s and even more preferably from 8 to 220 mm²/s. Also, the total sulphur content may be less than 700 ppm, preferably less than 500 ppm and even more preferably less than 10 ppm. The total nitrogen content may be less than 10 ppm and preferably less than 1 ppm. In addition, oils with an aniline point from 80 to 15O⁰C and preferably from 100 to 135⁰C may be used.

Among Group III base oils and Group 11+ base oils, 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 are suitable, for example. The viscosity of these base oils is not specially limited, but the viscosity index may be from 95 to 145 and preferably from 100 to 140. The kinetic viscosity at 40⁰C may preferably be from 2 to 680 mm²/s and even more preferably from 8 to 220 mm²/s. Also, the total sulphur content may be from 0 to 100 ppm and preferably less than 10 ppm. The total nitrogen content may be less than 10 ppm and preferably less than 1 ppm. In addition, oils with an aniline point from 80 to 150⁰C and preferably from 110 to 135⁰C may be used.

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 above-mentioned 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 above-mentioned 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 kinetic viscosity at 40⁰C is preferably from 2 to 680 mm²/s and even more preferably from 8 to 220 mm²/s.

GTLs (gas to liquid 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 derived base oils is not specially limited, but normally the viscosity index is from 130 to 180 and preferably from 140 to 175. Also, the kinetic viscosity at 4O⁰C may be from 2 to 680 mm²/s and even more preferably from 5 to 120 mm²/s. 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) .

The amount of the above-mentioned 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 preferably be at least 60% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, and yet more preferably at least 95% by weight.

Preferred embodiments of the aspartic acid derivatives are shown by General Formula 1.

(Formula I)

In the above-mentioned General Formula 1, Xl and X2 are each hydrogen or from 3 to 6 carbon alkyl groups which may be the same or different, or hydroxyalkyl groups, and are preferably respectively a 2-methylpropyl group and a tertiary-butyl group.

X3 is an alkyl group comprising from 1 to 30 carbon atoms, or an alkyl group having ether bonds, or a hydroxyalkyl group. For example, an octadecyl group, an alkoxypropyl group, a 3- (C6-C18) hydrocarbon oxy(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 from 1 to 30 carbon atoms, or an alkyl group comprising from 1 to 30 carbon atoms, or an alkenyl group, or a hydroxyalkyl group. For example, a propionic acid group or a propionyl acid group is suitable. The above-mentioned aspartic acid derivatives may have an acid number as determined by JIS-K2501 of from 10 to 200 mgKOH/g and preferaby from 50 to 150 mgKOH/g. The amount of aspartic acid derivatives used in the lubricating oil composition is preferably from 0.01 to 5% by weight and preferably from 0.05 to 2% by weight. For the above-mentioned fatty acid ester of a polyhydric alcohol it is possible to use those used in the prior art as oiliness agents, for example partial or complete esters of saturated or unsaturated fatty acids having from 1 to 24 carbons and polyhydric alcohols such as glycerol, sorbitol, alkylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol and xylidol.

Specific examples of such include, as glycerol esters, 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 glycoldioleate .

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 raonolaurylate, trimethylolpropane monostearate, trimethylolpropane monooleate, trimethylolpropane dilaurylate, trimethylolpropane distearate, trimethylolpropane dioleate and trimethylolpropane monolaurylate .

Pentaerythritol esters include pentaerythritol monostearate, pentaerythritol monolaurylate, 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. These fatty acid esters of polyhydric alcohols are preferably used in the lubricating oil composition to the amount of approximately from 0.01 to 5% by weight and more preferably to the amount of approximately from 0.05 to 2% by weight. If the amount used is outside the above- mentioned range, the effect of reducing the friction coefficient may be diminished.

The above-mentioned epoxy compounds may be manufactured by epoxidising, for example, rapeseed oil, soybean oil, linseed oil, castor oil, coconut oil, palm oil, palm kernel oil, sunflower oil, rice bran oil, safflower oil, beef tallow and pork tallow, and mention may be made of epoxidised fatty acid glycerides such as epoxidised rapeseed oil, epoxidised soybean oil, epoxidised linseed oil, epoxidised castor oil and epoxidised safflower oil.

Epoxidised fatty acid esters are also suitable as epoxy compounds. For example, mention may be made of those manufactured by epoxidising oleic acid esters such as methyl epoxystearate, butyl epoxystearate and octyl epoxystearate .

Epoxidised forms of 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 fatty acids derived from plant oils with Cl ~ C8 alcohols are also suitable.

As an example mention may be made of epoxidised rapeseed oil fatty acid isobutyl ester. In general, the essential constituents of rapeseed oil fatty acids are fatty acids having 18 carbons with oleic acid 63%, linolic acid 20% and linolenic acid 8%.

These epoxy compounds are known as plasticisers and stabilisers for rubbers and plastics, and the amount of epoxy compound to be incorporated in the lubricating oil may be from 0.01 to 5% by weight, more preferably from 0.01 to 2% by weight, and yet more preferably from 0.01 to 1% by weight.

For the aliphatic amines there are alkyl amines as shown by General Formula 2 below: (Formula 2)

(R¹J_nNH_3-11 (2)

(in Formula 2, R¹ denotes a straight-chain saturated or unsaturated alkyl group with from 6 to 30 carbons, and n is an integer 1 or 2) .

The alkyl amines shown by the above-mentioned General Formula (2) include, as primary amines, those shown by General Formula (3) below. (Formula 3)

H₂N - X₅ (3) In the above-mentioned General Formula 3, X5 denotes an alkyl group or an alkenyl group with from 1 to 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, isostearylamine, n- nonadecylamine, n-eicosylamine, n-heneicosylamine, n- docosylamine, n-tricosylamine, n-pentacosylamine, oleylamine, beef tallow amine, hydrogenated beef tallow amine and soybean amine. The number of carbons in X5 are preferably from 8 to 24, and more preferably from 12 to 18. Also, X5 may be a straight-chain aliphatic, a branched-chain aliphatic or a tertiary alkyl group. Further, as examples of secondary amines mention may be made of dilaurylamine, dicoconut amine, di-n- tridecylamine, 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 aliphatic amines may also be the amines shown by General Formula (4) below. (Formula 4)

X₆ - HN - X₇ - NH₂ (4)

In the above-mentioned General Formula 4, X6 denotes an alkyl group or an alkenyl group with from 1 to 30 carbons . The number of carbons in X6 are preferably from 8 to 24, and more preferably from 12 to 18. X7 denotes an alkylene group with from 1 to 12 carbons . The number of carbons in X7 are preferably from 1 to 8 , and more preferably from 2 to 4.

As examples of such diamine compounds of General Formula 4, mention may be made of 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- ethylenediamine, 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 .

Further, there are propylenediamines such as 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-1, 3-propylenediamine, N- pentadecyl-1, 3-propylenediamine, N-palmityl-1, 3- propylenediamine, N-heptadecyl-1, 3-propylenediamine, N- oleyl-1,3 -propylenediamine , N-stearyl-1,3- 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 . There are also butylenediamines such as N-octyl-1,4- butylenediamine, N-nonyl-1, 4-butylenediamine, N-decyl- 1, 4-butylenediamine, N-undecyl-1, 4-butylenediamine, N- lauryl-1, 4-butylenediamine, N-tridecyl-1, 4- butylenediamine, N-myristyl-1, 4-butylenediamine, N- tetradecyl-1, 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-1 , 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 . In addition, for the aliphatic amines mention may be made of the amines shown by General Formula (5) below. (Formula 5)

X₈ - N - (X₉)₂ (5)

In the above-mentioned General Formula 5, X8 denotes an alkyl group or an alkenyl group with from 1 to 30 carbons . The number of carbons in X8 are preferably from 1 to 20, and more preferably from 1 to 8 or from 12 to 18. X9 denotes an alkyl group, an alkylene group or a hydroxyalkyl group with from 1 to 20 carbons. The number of carbons in X9 are preferably from 1 to 8 or from 12 to 18.

Examples of cases where X8 is a methyl group include dialkyl methylamines such as dioctyl methylamine, dinonyl methylamine, didecyl methylamine, diundecyl methylamine, dilauryl methylamine, ditridecyl methylamine, dimyristyl methylamine, ditetradecyl methylamine, dipentadecyl methylamine, dipalmityl methylamine, diheptadecyl methylamine, dioleyl methylamine, distearyl methylamine, diisostearyl methylamine, dinonadecyl methylamine, dieicosyl methylamine, di-coconut methylamine, di-beef tallow methylamine, di-hydrogenated beef tallow methylamine and di-soybean methylamine.

Also, examples of cases where X9 is a methyl group include alkyl dimethylamines such as octyl dimethylamine, nonyl dimethylamine, decyl dimethylamine, undecyl dimethylamine, lauryl dimethylamine, tridecyl dimethylamine, myristyl dimethylamine, tetradecyl dimethylamine, pentadecyl dimethylamine, palmityl dimethylamine, heptadecyl dimethylamine, oleyl dimethylamine, stearyl dimethylamine, isostearyl dimethylamine, nonadecyl dimethylamine, eicosyl dimethylamine, coconut dimethylamine, beef tallow dimethylamine, hydrogenated beef tallow dimethylamine and soybean dimethylamine .

Further, examples of cases where X9 is a hydroxyalkyl group include N-alkyl diethanolamines such as N-octyl diethanolamine, N-nonyl diethanolamine, N- decyl diethanolamine, N-undecyl diethanolamine, N- lauryl diethanolamine, N-tridecyl diethanolamine, N-myristyl diethanolamine, N-tetradecyl diethanolamine, N-pentadecyl diethanolamine, N-palmityl diethanolamine, N-heptadecyl diethanolamine, N-oleyl diethanolamine, N-stearyl diethanolamine, N- isostearyl diethanolamine, N-nonadecyl diethanolamine, N-eicosyl diethanolamine, N-coconut diethanolamine, N-beef tallow diethanolamine, N- hydrogenated beef tallow diethanolamine and N-soybean diethanolamine, and also N-alkyl dipropanolamines such as N-octyl dipropanolamine, N-nonyl dipropanolamine, N-decyl dipropanolamine, N-undecyl dipropanolamine, N-lauryl dipropanolamine, N-tridecyl dipropanolamine, N-myristyl dipropanolamine, N-tetradecyl dipropanolamine, N- pentadecyl dipropanolamine, N-palmityl dipropanolamine, N-heptadecyl dipropanolamine, N-oleyl dipropanolamine, N- stearyl dipropanolamine, N-isostearyl dipropanolamine, N- nonadecyl dipropanolamine, N-eicosyl dipropanolamine, N- coconut dipropanolamine, N-beef tallow dipropanolamine, N-hydrogenated beef tallow dipropanolamine and N- soybean dipropanolamine . At least one of these aliphatic amines selected from the above-mentioned groups may be used in the lubricating oil composition in the amount of approximately from 0.005 to 5% by weight and preferably in the amount of approximately from 0.01 to 1% by weight. Apart from the above-mentioned constituents, it is possible, in order to improve performance further, to make appropriate use, as required, of various additives. Mention may be made of anti-oxidants , metal deactivators, extreme-pressure additives, oiliness improvers, defoaming agents, viscosity index improvers, pour-point depressants, detergent dispersants, rust-preventatives, demulsifiers and so on, as well as other known lubricating oil additives.

For the anti-oxidants used in this invention, those used in lubricating oils are preferred for practical use, and mention may be made of phenolic anti-oxidants, phosphorus-type anti-oxidants, amine-type anti-oxidants and sulphur-type anti-oxidants. These anti-oxidants may be used singly or in combinations of several within the range of from 0.01 to 5.0 parts by weight in respect of 100 parts by weight of the base oil.

As examples of the above-mentioned amine-type antioxidants, 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-naphthylamines, aryl-naphthylamines such as phenyl-1-naphthylamine, phenyl-2-naphthylamine, N- hexylphenyl-2-naphthylamine and N-octylphenyl-2- naphthylamine , phenylenediamines such as N, N¹- diisopropyl-p-phenylenediamine and N, N¹ -diphenyl-p- phenylenediamine , and phenothiazines such as Phenothiazine (made by Hodogaya Chemical Ltd.) and 3,7- dioctylphenothiazine .

As examples of sulphur-type 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 .

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- butylhydroxon (Antage DBH, made by Kawaguchi Chemical Industry Co. Ltd.), 2 , 6-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, 6-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-hydroxyphenyl) 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-6- 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 Kagaku 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-p- hydroxyphenyl) propane (Bisphenol A, made by Shell Japan Ltd.) , 2, 2-bis (3 , 5-di-t-butyl-4-hydroxyphenyl) propane, 4,4 ' -eyelohexylidenebis (2, 6-t-butylphenol) , hexamethylene glycol bis [3- (3 , 5-di-t-butyl-4-hydroxyphenyl) 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 -1-butyl-4 -hydroxy- 5 -methylpheny1) 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 Kagaku) 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-5-5- 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-(2' ',4' ' -di-t-buty-3 ' '- 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 phosphorus -type anti-oxidants mention may be made of triarylphosphites such as triphenylphosphite and tricresylphosphite, trialkylphosphites such as trioctadecylphosphite and tridecylphosphite, and tridodecyltrithiophosphite . 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 l-dioctylaminomethyl-2, 3- benzotriazole and 1-alkyl-tolutriazoles such as 1- dioctylaminomethyl-2 , 3-tolutriazole, and benzoimidazole and benzoimidazole derivatives which are 2-

(alkyldiothio) -benzoimidazoles such as 2- (octyldithio) - benzoimidazole, 2- (decyldithio) -benzoimidazole and 2-

(dodecyldithio) -benzoimidizole and 2- (alkyldiothio) 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 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-(N₇N- dibutyldithiocarbamyl) -benzothiazole and 2- (N, N- dihexyldithiocarbamyl) -benzothiazole, and 2- (N, N- dialkylydithiocarbamyl) -toluzothiazoles such as (N, N- diethyldithiocarbamyl) -toluzothiazole, 2- (N, N- dibutyldithiocarbamyl) -toluzothiazole and 2- (N, N- dihexyldithiocarbamyl) -toluzothiazole .

Further, mention may be made of benzooxazole derivates which are 2- (alkyldithio) benzooxazoles such as

2- (octyldithio) benzooxazole, 2- (decyldithio) benzooxazole and 2- (dodecyl) benzooxazole or which are 2-

(alkyldithio) toluoxazoles such as 2-

(octyldithio) toluoxazole, 2- (decyldithio) toluoxazole and

2- (dodecyl) 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-dibutyldithiocarbamyl) -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, in respect of 100 parts by weight of the base oil, singly or in combinations of several, within the range of from 0.01 to 0.5 parts by weight. In order to impart anti-wear properties and extreme- pressure properties to the lubricating oil composition of this invention, it is possible to add phosphorus compounds . 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, chlorinated phosphate esters, phosphite esters, phosphorothionates, zinc dithiophosphates, esters of dithiophosphates and alkanols or polyether-type alcohols or derivatives thereof, phosphorus-containing carboxylic acids and phosphorus-containing carboxylic acid esters.

These phosphorus compounds may be used, in respect of 100 parts by weight of the base oil, singly or in combinations of several, within the range of from 0.01 to 2 parts by weight.

As examples of the above-mentioned 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, tri(iso- propylphenyl) phosphate, triallyl phosphate, tricresyl phosphpate, trixylenyl phosphate, cresyldiphenyl phosphate and xylenyldiphenyl phosphate . As specific examples of the above-mentioned acidic phosphate esters, mention may be made of monobutyl acid phosphate, monopentyl acid phosphate, monohexyl acid phosphate, monoheptyl 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 above-mentioned amine salts of acidic phosphate esters, mention may be made of the methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine and trioctylamine salts of the previously mentioned acid phosphate esters.

As examples of the above-mentioned phosphite esters, mention may be made of dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, dioleyl phosphite, diphenyl phosphite, dicresyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite, trioctyl phosphite, trinonyl phosphite, tridecyl phosphite, triundecyl phosphite, trioleyl phosphite, triphenyl phosphite and tricresyl phosphite.

As examples of the above-mentioned phosphorothionates , mention may be made specifically of tributyl phosphorothionate, tripentyl phosphorothionate, trihexyl phosphorothionate, triheptyl phosphorothionate, trioctyl phosphorothionate, trinonyl phosphorothionate, tridecyl phosphorothionate, triundecyl phosphorothionate, tridodecyl phosphorothionate, tritridecyl phosphorothionate, tritetradecyl phosphorothionate, tripentadecyl phosphorothionate, trihexadecyl phosphorothionate, triheptadecyl phosphorothionate, trioctadecyl phosphorothionate, trioleyl phosphorothionate, triphenyl phosphorothionate, tricresyl phosphorothionate, trixylenyl phosphorothionate, cresyldiphenyl phosphorothionate, xylenyldiphenyl phosphorothionate, tris (n-propylphenyl) phosphorothionate, tris (isopropylphenyl) phosphorothionate, tris (n-butylphenyl) phosphorothionate, tris (isobutylphenyl) phosphorothionate, tris(s- butylphenyl) phosphorothionate and tris (t-butylphenyl) phosphorothionate .

As examples of the above-mentioned zinc dithiophosphates, mention may be made in general of zinc dialkyly dithiophosphates, zinc diaryl dithiophosphates and zinc arylaklyl dithiophosphates. For example, zinc dialkyl dithiophosphates where the alkyl groups of the zinc dialkyl dithiophosphates have primary or secondary alkyl groups of from 3 to 22 carbons or alkylaryl groups substituted with alkyl groups of from 3 to 18 carbons may be used.

As specific examples of 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 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 in the range of from 0.05 to 20 parts by weight in respect of 100 parts by weight of the base oil.

As examples of pour-point depressants mention may be made of polymethacrylate-type polymers. As regards the amount to be added, they may be used in the range of from 0.01 to 5 parts by weight in respect of 100 parts by weight of the base oil.

In order to impart defoaming characteristics to the lubricating oil composition of this invention, defoaming agents may also be added. As examples of defoaming agents suitable for this invention, 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 combinations of several, in the range of from 0.0001 to 0.1 parts by weight in respect of 100 parts by weight of the base oil.

As examples of demulsifiers suitable for this invention, mention may be made of those in the known art normally used as additives for lubricating oils. As regards the amount to be added, they may be used in the range of from 0.0005 to 0.5 parts by weight in respect of 100 parts by weight of the 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 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: kinetic viscosity at 100⁰C, 5.35 mm²/s; kinetic viscosity at 4O⁰C, 31.4 mm²/s; viscosity index, 103; sulphur content (as converted to elemental sulphur), less than 10 ppm by mass,- nitrogen content (as converted to elemental nitrogen) , less than 1 ppm by mass,- 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, 312⁰C)

(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: kinetic viscosity at 100⁰C, 6.57 mm²/s; kinetic viscosity at 40⁰C, 37.5 mm²/s; viscosity index, 130; sulphur content (as converted to elemental sulphur), less than 10 ppm by mass; nitrogen content (as converted to elemental nitrogen) , less than 1 ppm by mass,- 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: kinetic viscosity at 100⁰C, 5.10 mm²/s; kinetic viscosity at 40⁰C, 23.5 mm²/s ; viscosity index, 153; 15⁰C density, 0.821; sulphur content (as converted to elemental sulphur) , less than 10 ppm by mass,- nitrogen content (as converted to elemental nitrogen) , less than 1 ppm by mass; ring-analysis aromatic content according to the method of ASTM D3238, less than 1%)

(1-4) Base Oil 4: A synthetic oil/poly-α-olefin with the general name PAO6 , and classified as Group IV according to the API (American Petroleum Institute) base oil classification. (Characteristics: kinetic viscosity at 100⁰C, 5.89 mm²/s,- kinetic viscosity at 4O⁰C, 31.2 mm²/s ; viscosity index, 135; 15⁰C density, 0.827; sulphur content (as converted to elemental sulphur) , less than 10 ppm by mass; nitrogen content (as converted to elemental nitrogen), less than 1 ppm by mass; 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: kinetic viscosity at 100⁰C, 4.60 mm²/s; kinetic viscosity at 40⁰C, 24.6 mm²/s; viscosity index, 101; 15°C density, 0.866; sulphur content (as converted to elemental sulphur) , 450 ppm by mass; nitrogen content (as converted to elemental nitrogen) , 20 ppm by mass; 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 Al: Aspartic acid derivative (K-CORR 100 made by King Industries Ltd. , acid number by the method of JIS K2501 being 100 mgKOH/g)

(2-2) Additive A2 : Aspartic acid derivative (MONACOR 39 made by Unichema Ltd. , acid number by the method of JIS K2501 being 60 mgKOH/g)

(2-3) Additive Bl: Pentaerythritol monooleate (2-4) Additive B2 : Glycerol monooleate

(2-5) Additive C: Epoxidised rapeseed oil fatty acid isobutyl ester (2-6) Additive Dl: Coconut amine (the main constituent being dodecylamine)

(2-7) Additive D2 : Oleylamine Examples 1 ~ 16, Comparative Examples 1 - 3 Using the above-mentioned compositions and materials, the lubricating oil compositions of Examples 1 to 16 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 Examples 1 to 16 and Comparative Examples 1 to 3 in order to observe their performance . 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 0.145:

O (Good) Friction coefficient is 0.146 or more:

X (Not acceptable) 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 6O⁰C, agitation was continued for 48 hours . Then the specimen was removed and assessed visually for occurrence of any rust. Rust prevention tests with inclusion of formic acid

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 6O⁰C, an iron test specimen was inserted into the oil and 30 ml of artificial sea water plus 0.1 ml of formic acid were 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.

This rust prevention test with inclusion of formic acid had more severe conditions than the above-mentioned rust prevention test using artificial sea water alone, and was carried out in respect of Examples 11 to 16. Test results

The results of the tests are shown in Tables 1 to 4. As is clear from the test results shown in Table 1 and Table 2, the lubricating oil compositions shown for Examples 1 to 8 , which used an aspartic acid derivative (Additive A) and a polyhydric alcohol ester (Additive B) together added to highly refined base oils Base Oils 1 to 5, all had an excellent (0) friction coefficient, this being low, and they scored a pass in the rust-prevention tests, no rust occurring in artificial sea water. Also, as seen in the case of Examples 9 and 10, the lubricating oil compositions which used an aspartic acid derivative (Additive A) and a polyhydric alcohol ester (Additive B) together and further had a fatty acid amine (Additive D) added also had an excellent (0) friction coefficient, this being low, and they scored a pass in the rust- prevention tests, no rust occurring in artificial sea water. The lubricating oil compositions of Examples 1 to 10 could thus be confirmed as having brought about a reduction in the friction coefficient and an improvement in rust-preventing properties.

As is clear from the test results shown in Table 3, the lubricating oil composition shown for Example 11, which used an aspartic acid derivative (Additive A) , a polyhydric alcohol ester (Additive B) and an epoxy compound (Additive C) together, had an excellent (0) friction coefficient, this being low, and it scored a pass in both the rust-prevention tests, no rust occurring in artificial sea water or in the more severe case of artificial sea water with inclusion of formic acid, so that excellent results had evidently been obtained. Also, the lubricating oil compositions of Examples 12 to 16, which used an aspartic acid derivative (Additive A) , a polyhydric alcohol ester (Additive B) , an epoxy compound (Additive C) and a fatty acid amine (Additive D) together added to Base Oils 1 to 4 , also had an excellent (0) friction coefficient, this being low, and scored a pass in both the rust-prevention tests, no rust occurring in artificial sea water or in the more severe case of artificial sea water with inclusion of formic acid, so that excellent friction-coefficient reducing effects and rust-preventing properties had evidently been obtained. On the other hand, as can be seen from the test results of Table 4, in the case of Comparative Example 1 with only Base Oil 1 the friction coefficient was unacceptably high (X) and rust occurred in artificial sea water in the rust-prevention test and the rust-prevention test with inclusion of formic acid. In the case of Comparative Example 2, where an aspartic acid derivative (Additive A) had been added to Base Oil 1, the friction coefficient was unacceptably high (X) and, although it passed the rust-prevention test, it did not pass the rust-prevention test with inclusion of formic acid, rust occurring. Also, in the case of Comparative Example 3, where a polyhydric alcohol ester (Additive B) had been added to Base Oil 1, the friction coefficient did at least pass as good (0) , but in both the rust-prevention test and rust-prevention test with inclusion of formic acid rust occurred. In the case of Comparative Examples 1 to 3, therefore, no improvement in friction characteristics or rust-preventing properties was observed in their use as lubricating oil compositions.

Table 1

K*

Table 2

Table 3

OJ

Table 4

Ul

Claims

C L A I M S

1. A lubricating oil composition comprising a base oil and as additives an aspartic acid derivative and a fatty acid ester of a polyhydric alcohol.

2. A lubricating oil composition according to Claim 1, wherein the aspartic acid derivative has the Formula 1 below,

[Formula 1]

( Formula I )

wherein Xl and X2 are each hydrogen or C3-6 alkyl groups, which may be the same or different, or hydroalkyl groups; X3 is a Cl-30 alkyl group, or an alkyl group having ether bonds or a hydroalkyl group,- and

X4 is a saturated or unsaturated Cl-30 carboxylic acid group, or an Cl-30 alkyl group; or an Cl-30 alkenyl group, or a hydroxyalkyl group.

3. A lubricating oil composition according to Claim 1 or 2, further comprising an epoxy compound.

4. A lubricating oil composition according to any of Claims 1 or 3 , further comprising an aliphatic amine.

5. A lubricating oil composition according to any of Claims 1 to 4 , wherein the acid number of the above- mentioned aspartic acid derivative is from 10 to 200 mgKOH/g.

6. A lubricating oil composition according to any of Claims 1 to 5, wherein the fatty acid of the above- mentioned fatty acid ester of a polyhydric alcohol is an alkyl or alkenyl group which has from 8 to 24 carbons and which may have a hydroxyl group.

7. A lubricating oil composition according to any of Claims 3 to 6 , wherein the above-mentioned epoxy compound is an epoxidised fatty acid ester derived from an animal oil or fat or vegetable oil or fat.

8. A lubricating oil composition according to any of

Claims 4 to 7, wherein the aliphatic moiety of the above- mentioned aliphatic amine has from 6 to 30 carbons.

9. A lubricating oil composition according to any of Claims 1 to 8 , wherein the above-mentioned base oil is a synthetic oil, preferably selected from a poly-α-olefin and a GTL-derived base oil.

10. Use of the lubricating oil composition according to any one of Claims 1 to 9, as an industrial lubricating

011. such as a machine oil, hydraulic oil, turbine oil, compressor oil, gear oil, bearing oil, preferably as an hydraulic oil.

11. Method for improving the lubrication of an apparatus by lubricating the apparatus with the lubricating oil composition according to any one of Claims 1 to 9.