GREASE COMPOSITION

The present invention relates to a grease composition, in particular to a low friction grease composition whereby wear generated in lubricated parts such as bearings or gears is suppressed.

Greases having excellent frictional wear characteristics are required in, for example, bearings or gears of mechanical devices in the automobile, iron and steel, railway and other industries.

In particular, this is important for lubrication applications such as constant velocity joints of automobiles, in which both rolling friction and sliding friction are present and ball screws of driving gears in an injection moulding machine or an electric pressing machine .

Conventionally, greases having excellent lubricating properties were prepared by adding molybdenum disulphide to a lithium soap-thickened grease composition. Later in the art, greases have been prepared by simultaneously adding an organic molybdenum compound and zinc dithiophosphate to a urea-thickened grease. Such urea- thickened greases have been used with a view to reducing frictional wear characteristics. For example, laid-open Japanese Patent Application No. 62-207397 describes a grease composition which comprises a sulphur-phosphorus type extreme-pressure additive in which (a) molybdenum dialkyl dithiocarbamate sulphide and (b) at least one member selected from the group consisting of a sulfurized oil, a sulfurized olefin, tricresyl phosphate, trialkyl

dithiophosphate, and a zinc dialkyl dithiophosphate are combined with each other as essential components.

Further, laid-open Japanese Patent Application No. 63-046299 discloses a grease composition in which additives, namely, molybdenum dialkyl dithiocarbamate sulphide and molybdenum dithiophosphate and, optionally, zinc dithiophosphate are simultaneously blended in a urea-thickened grease.

However, in some jurisdictions such as Japan, common molybdenum-containing grease additives such as those described above are defined as restricted substances. These chemical substances are restricted in view of the danger of harmful effects on human health or ecological systems (e.g. Japanese PRTR Law: Pollutant Release Transfer Register; Law for promotion of Chemical

Management) and submission of an MSDS (Material Safety Data Sheet) on a product which contains a specified amount or more of any of these substances may be required by the laws of such jurisdictions. Lead compounds and antimony compounds, which are also defined as PRTR restricted substances, were used in grease compositions for many years. However, such compounds have been almost entirely replaced by sulphur type extreme-pressure additives or the like which are free of these problems.

However, the afore-mentioned molybdenum compounds, in particular, molybdenum dialkyl dithiocarbamate sulphide, have an excellent effect in reducing friction and wear and it is hard to find a replacement for molybdenum dialkyl dithiocarbamate. Furthermore, even if such a replacement is added to the grease, a considerable

amount thereof may be required in order to secure a sufficiently low coefficient of friction.

Tungsten disulphide, is known as a solid lubricant and is a substance which is not defined as a PRTR restricted substance. Laid-open Japanese Patent

Application No. 2003-301188 discloses that by adding tungsten disulphide to a lithium soap grease which contains polyoxypropylene and glyceryl ether as a base oil, a powder for density adjustment is prepared such that, when the grease that is used is liberated in water, this grease floats or sinks.

It is highly desirable to develop a grease composition imposing little environmental load which has excellent friction and wear characteristics and better safety by avoiding the use of molybdenum compounds that are the subject of the afore-mentioned PRTR restrictions and/or being able to reduce the amount thereof that is used in such a grease composition.

A grease composition has now been surprisingly developed which has low friction properties and excellent wear resistance by blending tungsten disulphide and zinc dithiophosphate and/or molybdenum dithiocarbamate with a urea-thickened grease.

Accordingly, the present invention provides a grease composition, comprising base oil, one or more urea thickeners, (A) in the range of from 0.1 to 5 weight% of tungsten disulphide and (B) in the range of from 0.1 to 5 weight% of one or more zinc dithiophosphates and/or one or more molybdenum dithiocarbamates, based on the total weight of the grease composition.

- A -

In a preferred embodiment of the present invention, the grease composition may further comprise (C) one or more molybdenum dithiophosphates .

According to the present invention, molybdenum compounds designated as PRTR restricted substances are not used, or the amount thereof which is used can be relatively reduced, and a grease composition having excellent performance in terms of friction and wear characteristics and high stability can thereby be obtained.

The base oil in the grease composition according to the present invention may be conveniently selected from mineral oils, vegetable oils and synthetic oils such as ester oil, ether oil or hydrocarbon oil, or mixtures thereof.

The one or more urea thickeners in the grease composition of the present invention may be selected from urea compounds such as monourea, diurea, triurea, tetraurea or other polyureas. Diurea compounds are easily obtained by the reaction of diisocyanate and monourea; tetraurea compounds can be obtained by reaction of diisocyanate, monourea and diamines .

Examples of diisocyanates that may be used to make said urea compounds include: diphenylmethane diisocyanate, tolylene diisocyanate, bitolylene diisocyanate and naphthylene diisocyanate.

Also, examples of monoamines that may be used to make said urea compounds include octylamine, dodecylamine, stearylamine, oleylamine, aniline, paratoluidine and cyclohexylamine . Also, examples of diamines that may be used to make said urea compounds

include ethylene diamine, propane diamine, butane diamine and phenylene diamine.

In a preferred embodiment, the grease composition of the present invention may comprise a total amount in the range of from 1 to 25 weight% of said one or more urea thickeners, based on the total weight of said grease composition.

The grease composition of the present invention may further comprise one or more additional thickeners such as metallic soaps, organic substances or inorganic substances, for example, lithium soaps, lithium complex soaps, sodium terephthalate, urea/urethane compounds and clays .

The tungsten disulphide which is employed as the afore-mentioned component (A) in the grease composition of the present is preferably a powder having an average particle size of less than 10 μm obtained by the Fisher method (Fisher Sub-sieve Sizer) . More preferably, the tungsten disulphide which is employed is a powder having an average particle size of about 0.6 μm obtained by the afore-mentioned method.

The one or more zinc dithiophosphates which may be employed as the afore-mentioned component (B) in the grease composition of the present invention may be conveniently selected from zinc dialkyl dithiophosphates and/or zinc diaryl dithiophosphates. Preferably, said one or more zinc dithiophosphates may be selected from compounds of formula (I),

R ¹ O S S OR'

V Zn V R'o' V V \)R'

wherein R' indicates primary or secondary alkyl groups or aryl groups, which may be the same or different. Preferably, primary or secondary alkyl groups are employed as R ¹ . Specific examples of the above R ¹ include a methyl group, ethyl group, propyl group, isopropyl group, butyl group, secondary butyl group, isobutyl group, pentyl group, 4-methyl pentyl group, hexyl group, 2-ethyl hexyl group, heptyl group, octyl group, nonyl group, decyl group, isodecyl group, dodecyl group, tetradecyl group, hexadecyl group, octadecyl group, eicosyl group, docosyl group, tetracosyl group, cyclopentyl group, cyclohexyl group, methyl cyclohexyl group, ethyl cyclohexyl group, dimethyl cyclohexyl group, cycloheptyl group, phenyl group, tolyl group, xylyl group, ethyl phenyl group, propyl phenyl group, butyl phenyl group, pentyl phenyl group, hexyl phenyl group, heptyl phenyl group, octyl phenyl group, nonyl phenyl group, decyl phenyl group, dodecyl phenyl group, tetradecyl phenyl group, hexadecyl phenyl group, octadecyl phenyl group, benzyl group and phenethyl group.

Specific examples of the above primary alkyl zinc dithiophosphate include zinc diisopropyl dithiophosphate and zinc diisobutyl dithiophosphate and zinc diisodecyl dithiophosphate.

Also, specific examples of the above secondary dialkyl zinc dithiophosphate include zinc mono or di-sec- butyl dithiophosphate, zinc mono or di-sec-pentyl dithiophosphate and zinc mono or di-4-methyl-2-pentyl dithiophosphate.

Specific examples of the above zinc aryl dithiophosphate include zinc di-para-dodecyl phenol dithiophosphate, zinc di-heptyl phenol dithiophosphate and zinc di-para-nonyl phenol dithiophosphate. Preferred examples of the one or more molybdenum dialkyl dithiocarbamates, which may be employed as component (B) in the grease composition of the present invention may be selected from compounds of formula (II), (R ¹ R ² N-CS-S) ₂ Mo ₂ O _1n S _n (II) wherein R ¹ and R ² respectively, may be independently selected from alkyl groups having a carbon number in the range of from 1 to 24, preferably in the range of from 3 to 18, m is an integer in the range of from 0 to 3, n is an integer in the range of from 1 to 4 and m+n=4. Specific examples of the afore-mentioned one or more molybdenum dialkyl dithiocarbamates include molybdenum diethyl dithiocarbamate sulphide, molybdenum dipropyl dithiocarbamate sulphide, molybdenum dibutyl dithiocarbamate sulphide, molybdenum dipentyl dithiocarbamate sulphide, molybdenum dihexyl dithiocarbamate sulphide, molybdenum dioctyl dithiocarbamate sulphide, molybdenum didecyl dithiocarbamate sulphide, molybdenum didodecyl dithiocarbamate sulphide, molybdenum di (butylphenyl) dithiocarbamate sulphide, molybdenum di (nonylphenyl) dithiocarbamate disulphide, oxy-molybdenum diethyl dithiocarbamate sulphide, oxy-molybdenum dipropyl dithiocarbamate sulphide, oxy-molybdenum dibutyl dithiocarbamate sulphide, oxy-molybdenum dipentyl dithiocarbamate sulphide, oxy-molybdenum dihexyl dithiocarbamate sulphide, oxy-molybdenum dioctyl dithiocarbamate sulphide, oxy-molybdenum didecyl

dithiocarbamate sulphide, oxy-molybdenum didodecyl dithiocarbamate sulphide, oxy-molybdenum (butylphenyl) dithiocarbamate sulphide, oxy-molybdenum di (nonylphenyl) dithiocarbamate sulphide, and mixtures thereof. Specific examples of the afore-mentioned one or more molybdenum dithiophosphates that may be employed as optional component (C) in the grease composition of the present invention include molybdenum diethyl dithiophosphate sulphide, molybdenum dipropyl dithiophosphate sulphide, molybdenum dibutyl dithiophosphate sulphide, molybdenum dipentyl dithiophosphate sulphide, molybdenum dihexyl dithiophosphate sulphide, molybdenum dioctyl dithiophosphate sulphide, molybdenum didecyl dithiophosphate sulphide, molybdenum didodecyl dithiophosphate sulphide, molybdenum di (butylphenyl) dithiophosphate sulphide, molybdenum di (nonylphenyl) dithiophosphate disulphide, oxy-molybdenum diethyl dithiophosphate sulphide, oxy-molybdenum dipropyl dithiophosphate sulphide, oxy-molybdenum dibutyl dithiophosphate sulphide, oxy-molybdenum dipentyl dithiophosphate sulphide, oxy-molybdenum dihexyl dithiophosphate sulphide, oxy-molybdenum dioctyl dithiophosphate sulphide, oxy-molybdenum didecyl dithiophosphate sulphide, oxy-molybdenum didodecyl dithiophosphate sulphide, oxy-molybdenum (butylphenyl) dithiophosphate sulphide and oxy-molybdenum di (nonylphenyl) dithiophosphate sulphide.

The afore-mentioned components (A) tungsten disulphide; and (B) one or more zinc dithiophosphates and/or one or more molybdenum dithiocarbamates are respectively blended in the grease composition of the

present invention in an amount in the range of from 0.1 to 5 weight%. Preferably, the afore-mentioned components

(A) and (B) are each blended in the grease composition of the present invention in an amount in the range of from 0.2 to 3 weight%, based on the total weight of the grease composition. If the afore-mentioned components (A) and

(B) are each blended in an amount of less than 0.1 weight%, based on the total weight of the grease composition, a low coefficient of friction cannot be obtained and frictional wear is insufficiently improved. Furthermore, if the afore-mentioned components (A) and (B) are blended in an amount exceeding 5 weight%, based on the total weight of the grease composition, then no further increase in beneficial effect is seen. The one or more molybdenum dithiophosphates (C) may be present in the grease composition of the present invention in an amount in the range of from 0.1 to 5 weight%, more preferably in the range of from 0.2 to 3 weight%. The grease composition of the present invention may further comprise various types of known additives such as antioxidants, for example, aminic and/or phenolic antioxidants, extreme pressure additives, for example, olefin sulphides and/or oil sulphides, viscosity increasing agents, for example, polybutenes and/or polymethacrylates, solid lubricants, for example, molybdenum disulphide and/or boron nitride, metallic salts, for example, sulfonates, salicylates and/or phenates capable of being used as antirust agents or structure stabilisers and phosphites and/or phosphates capable of being used as extreme pressure/wear reducing agents .

The present invention further provides a method of reducing friction and/or wear in the bearings, gears and/or joints of mechanical devices, wherein said method comprises lubricating said bearings, gears and/or joints with a grease composition as hereinbefore described.

In addition, the present invention also provides a bearing, gear and joint, characterised in that the grease composition as hereinbefore described is used therein as the lubricant. Furthermore, the present invention also provides the use of a grease composition as hereinbefore described to lubricate a bearing, a gear and/or a joint.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the invention in any way. EXAMPLES

The grease compositions of Examples 1 to 7 and Comparative Examples 1 to 8 were obtained by processing in a three-roll mill the base greases and additives shown below with the blending compositions shown in Table 1 to Table 4. [1] Base grease

[1-1] Diurea grease

Diphenyl methane-4 , 4 ' -diisocyanate (295.2 g) and octylamine (304.8 g) were reacted in refined mineral oil (5400 g) having a kinematic viscosity of about 15 mm ² /s at 100 ⁰ C, and the diurea compound produced was uniformly dispersed to obtain a base grease. The content of urea compound in the base grease was 10 weight%. The consistency of this diurea grease (25 ⁰ C, 60 W) according

to JS-K2220 was 283 and its dropping point was 263 ⁰ C. [1-2] Tetraurea grease

Diphenyl methane-4 , 4 ' -diisocyanate (382.7 g) , stearylamine (411.4 g) and ethylene diamine (46.0 g) were reacted in refined mineral oil (5160 g) having a kinematic viscosity of about 15 mm ² /s at 100 ⁰ C, and the urea compound produced was uniformly dispersed to obtain a base grease.

The content of the urea compound in the base grease was 14 weight% . The consistency of this tetraurea grease (25 ⁰ C, 60 W) according to JS-K2220 was 285 and its dropping point was 202 °C.

[2] Additives

[2-1] Tungsten disulphide (indicated in the Tables as WS ₂ ) : a tungsten disulphide powder having an average particle size of 0.6 μm, available under the trade designation of

"Tanmik B" from Nippon Lubricants Ltd. was employed. [2-2] Zinc dithiophosphate (indicated in the

Tables as Zn-DTP) : additive available under the trade designation "Lubrizol 1395" from

Lubrizol Inc. was employed.

[2-3] Molybdenum dithiocarbamate (indicated in the Tables as Mo-DTC) : additive available under the trade designation "Molyvan A" from Vanderbilt Inc. was employed.

[2-4] Molybdenum dithiophosphate (indicated in the Tables as Mo-DTP) : additive available under

the trade designation "Sakuralube 300" from Asahi Electrochemical Industries Ltd. was employed.

[2-5] Molybdenum disulphide (indicated in the Tables as MoS ₂ ) : Molybdenum disulphide having an average particle size of 0.7 μm as manufactured by CLIMAX MOLYBDENUM UK Ltd was employed.

[2-6] Graphite (indicated in the Tables as graphite) : graphite as manufactured under the trade name "FAHN" by Fuji Graphite Ltd was employed. Falex Wear Resistance Test

Evaluation was conducted by carrying out the Falex Wear Resistance Test for checking performance of the grease compositions obtained according to the Examples and Comparative Examples, and measuring the wear coefficient and wear resistance (surface roughness of the test sample) in respect of these grease compositions. The Falex wear resistance test is based on IP 241 (IP: Institute of Petroleum, UK); tests are carried out in accordance with the following conditions, to obtain a wear coefficient after completion of the test. Also, the Rmax (μm) (maximum surface roughness) of a reference test sample was measured. Test conditions

Rotational speed: 290±10 rpm Temperature: room temperature (about 25 ⁰ C) Load: 890N (200 lbf) Time: 15 min

Amount of grease applied: about 1 gram applied to the test sample

Test results

The results of the Falex wear resistance test are listed in Table 1 to Table 4.

Table 1

Table 2

Table 3

Table 4

As is clear from Table 1 and Table 2, Examples 1 to 7 show excellent wear resistance, displaying low friction properties, with a frictional coefficient of approx. 0.056 to 0.083 in the Falex test, the maximum surface roughness of the test sample being approx. 5.9 to 10.1 μm.

In contrast, as is clear from Table 3 and Table 4, the products of Comparative Examples 1 to 8 show in each case results that are unsatisfactory as regards both the coefficient of friction and wear resistance properties. Specifically, the products of Comparative Examples 1, 2, 5, 7 and 8 have a high coefficient of friction and show large values of the maximum surface roughness of the test sample. The products of Comparative Examples 3 and 4 show comparatively low values of the coefficient of friction, but display large values of the maximum surface roughness of the test sample; it is inferred that in these cases the low coefficient of friction is displayed due to lowering of the contact area pressure due to increased wear. In the case of the product of Comparative Example 6, the maximum surface roughness of the test sample is comparatively close to that of the practical examples, but this product shows a high value of the coefficient of friction. Also, as can be seen by comparing the Examples and Comparative Examples 7, 8, in the case of molybdenum disulphide or graphite, which are substances of the same layer lattice structure as the tungsten disulphide used in the present invention, results satisfying both the requirement to provide an excellent low coefficient of friction and good wear resistance as in the case of the

practical examples are not obtained even when these are used together with for example Mo-DTC, Mo-DTP or Zn-DTP. Thus, with the grease composition according to the present invention, an excellent lubricating effect can be obtained without using molybdenum compounds such as molybdenum dialkyl dithiocarbamate sulphide, or a reduction in the amount of use of such molybdenum compounds can be achieved.