BASE STOCK

[0001] Disclosed herein are new lubricant compositions, specifically lubricant grease compositions derived from high viscosity polydimethylsiloxane base stock oils which can be utilised for a variety of applications given the physical properties thereof. Methods of making these compositions and their uses are also described.

[0002] The primary purpose of lubrication is the separation of solid surfaces moving relative to one another, to minimise friction and wear. The materials most frequently used lubricants are oils and greases with typically the choice of lubricant being largely determined by the particular application.

[0003] Lubricating greases are generally employed where:

(i) heavy pressures exist;

(ii) where oil drip from the solid surfaces such as bearings is undesirable; or

(iii) where the motion of the contacting surfaces is discontinuous so that it is

difficult to maintain a separating film between them.

[0004] There are a wide variety of lubricating greases which have been developed to lubricate interactions between e.g., metal-metal metal-plastic parts and plastic-plastic parts. Because of design simplicity, decreased sealing requirements and less need for maintenance, greases are almost universally given first consideration for lubricating bearings in electric motors, household appliances, automotive wheel bearings, machine tools or aircraft accessories. Greases are also used for the lubrication of small gear drives and for many slow speed sliding applications. For example lubricating greases are typically used to lubricate bearings for constant velocity joints, ball joints, wheel bearings, alternators, cooling fans, ball screws, chucks, linear guides for machine tools, bearings and gears, each having individual requirements for a lubricant given the forces and duress they are under and the functions they are designed to perform. As performance requirements of such joints, bearings and gears become more demanding there is likewise a continued demand for lubricants with improved physical properties to help achieve such performance requirements. [0005] Currently, in the automotive industry there is a determined effort to reduce the weight of vehicles and thereby make them more economical to operate by reducing the energy/power required. The use of new lighter materials for certain vehicle parts has achieved this need, to an extent, but additional means and ways of achieving this goal are constantly being sought. For example, large (heavy) electrical motors are required to be used to commence movement of a vehicle from a stationary position. The power needed is partially due to the necessity to overcome large differences in the static and dynamic coefficients of friction of the vehicle before movement can commence. The provision of a suitable lubricant which can provide a very low difference in static and dynamic coefficients of friction in such systems will result in a reduction in the forces/power needed to commence motion from a static position. This reduction in the required power will in turn mean that smaller and therefore lighter in weight electric engines can be utilised.

[0006] There is also an ongoing need to provide dampening in for example HiFi systems and also lubricants which are able to lubricate in extreme temperature conditions e.g., temperatures below -30°C e.g., low temperature bearings and gears.

[0007] It is the aim herein to provide silicone grease compositions which both

(i) maintain lubricity with reduced differences between static and dynamic

coefficients of friction and

(ii) have good dampening capabilities at elevated temperatures and/or reduced temperatures (below -30°C).

[0008] There is provided herein a lubricating grease composition comprising

(a) 60 to 89.9 % by weight of a silicone base stock oil having a kinematic viscosity of from 20,000 to 100,000 mm ² /s at 25°C;

(b) 10 to 35% by weight of a metal salt of a fatty acid wherein the metal is selected from the group of lithium, calcium, aluminum, barium, titanium, zinc, magnesium and/or sodium; and (c) 0.1 to 2% by weight of a suitable anti-wear and/or anti-corrosion additive, wherein the total composition is present in an amount of 100% by weight.

[0009] Base stock oils are classified by the American Petroleum Institute (API) in five Groups, namely Groups I, II, III, IV and V. They include natural lubricating oils, synthetic lubricating oils, and mixtures thereof. Groups I to III relate to base stock oils derived from petroleum based oils, while Groups IV and V relate to synthetic base stock oils.

[0010] Silicone base stock oils are generally in Group V. They may be used in lubricant compositions in both (metal-to-metal) applications and critical (plastic-to-plastic) applications mainly due to their good low and high temperature behavior. They show chemical resistance, lubricity, thermal stability and oxidative stability. However in respect of lubrication under high loads, silicones, with the exception of halogenated silicones, are generally both inferior to organic base oil as described above and are typically more costly than organic base stock oils.

[0011] A silicone base stock oil is to be understood to be mainly a siloxane based material having a polymeric backbone largely consisting of silicon-oxygen atom bonds -[Si-O-]- . Silicone base stock oils include, but are not limited to silicone polymer fluids, which may be linear, branched and/or cyclic silicone polymers, liquid silicone resins and/or silicone waxes. Silicone base stock oil (a) of the composition herein has a kinematic viscosity of from 20,000 to 100,000 mm ² /s at 25°C following the general method described in ISO 3104 : l994(en). The terms silicone and siloxane may be used interchangeably to designate silicone base stock oils such as trialkylsilyl terminated polydialkylsiloxane, trialkylsilyl terminated polyalkylalkylsiloxane and trialkylsilyl terminated

polyalkylarylsiloxanes.

[0012] Siloxanes generally conform to a polymeric backbone consisting of units of the formula RmSi04-m/2 in which m is zero, 1, 2 or 3 and where m has an average value of from 1.98 to 2.5 per molecule and has a degree of polymerisation > 2. Each R may be the same or different and denotes, hydrogen or an organic group. [0013] When R is an organic group R may be selected from hydrocarbon groups having from 1 to 45 carbon atoms, alternatively from 1 to 20 carbon atoms, alternatively 1 to 15 carbon atoms, alternatively 1 to 6 carbon atoms. Examples of R may include as alkyl groups (methyl, ethyl, propyl, isopropyl, butyl, octyl, nonyl, tetradecyl, octadecyl);

cycloalkyl groups (cyclohexyl, cycloheptyl); alkenyl groups having from 2 to 45 carbon atoms, (vinyl, hexenyl); aryl groups having from 6 to 45 carbon atoms (phenyl, diphenyl, naphthyl); alkaryl groups having from 7 to 45 carbon atoms(tolyl, xylyl, ethylphenyl); aralkyl groups having from 7 to 45 carbon atoms (phenylethyl).

[0014] Alternatively when R is an organic group R may be any of the above hydrocarbon groups wherein one or more hydrogen atoms have been replaced with another substituent. Examples of such substituents include, but are not limited to halogen atom containing groups such as haloalkyl groups (chloromethyl, perfluorobutyl, trifluoroethyl and nonafluorohexyl) and haloaryl groups (monochlorophenyl, dibromophenyl,

tetrachlorophenyl, monofluorophenyl); oxygen atom containing groups such as carboxyl, carbinol, ester, ether, acrylic groups and polyoxyalkylene groups (polyoxyethylene, polyoxypropylene, polyoxybutylene); nitrogen atom containing groups such as nitrile, amino, amido, cyano, cyanoalkyl and urethane groups; sulphur atoms; sulphur atom containing groups such as sulphide, sulphone, sulphate, sulphonate and mercapto groups; phosphorus atoms; phosphorus atom containing groups such as phosphate, phosphate and phosphonate groups.

[0015] A silicone base stock oil in the present composition may be a cyclic, linear or branched silicone polymer.

[0016] Cyclic siloxanes have the general formula (R2SiO)x where R is as described above, and x is 3 to 20 and the total number of carbon atoms in the R groups is between 20 and 1000 [0017] Examples of cyclic siloxanes include hexamethylcyclotrisiloxane (solid at 25°C), octamethylcyclotetrasiloxane, tetraphenyltetramethylcyclotetrasiloxane,

octaethylcyclotetrasiloxane, tetramethyltetraoctylcyclotetrasiloxane,

pentamethylpentaoctylcyclopentasiloxane and

pentamethylpentadodecylcyclopentasiloxane.

[0018] Linear siloxanes conform to the general formula R(SiR20)rSiR3, where R is as described above and r is 1 to 5000 or higher such that the kinematic viscosity is within the range of 20,000 to 100,000 mm ² /s at 25°C following the general method described in ISO 3104 : l994(en). Linear siloxanes include polydimethylsiloxane when R is methyl and polydiethylsiloxane when R is ethyl. Such compounds may have a wide variety of terminal groups which typically include, for the sake of example methyl, ethyl phenyl groups. The siloxanes herein may have a kinematic viscosity in the range of 20,000 to 100,000 mm ² /s at 25° following the general method described in ISO 3104 : l994(en).

[0019] In one alternative linear silicone base oil (a) may have the following formula:

in which Me is a methyl group and each R ¹ , each R ² and each R ³ is individually selected from groups R as described above, each R ⁵ is individually selected from a hydrocarbon group containing from 1 to 18 carbon atoms e.g., linear or branched alkyl groups, phenyl groups and/or alkylaryl groups, alternatively alkyl groups having from 1 to 10 carbon atoms, alternatively alkyl groups having from 1 to 6 carbon atoms; and each R ⁴ group is a hydrocarbon groups having from 2 to 45 carbon atoms, alternatively from 2 to 25 carbon atoms. As indicated above the kinematic viscosity of the silicone base oil (a) is within the range of 20,000 to 100,000 mm ² /s and wherein n is zero or an integer, v is zero or an integer and t is zero or an integer.

[0020] In one alternative, each R ¹ , each R ² , and each R ³ may be independently selected from alkyl groups, of 1 to 45, alternatively of 1 to 30 and further alternatively 1 to 16 carbon atoms or phenyl groups containing 6 to 16 carbon atoms and each R ⁴ is

independently an alkyl group having from 2 to 16 carbon atoms.

[0021] Examples of linear siloxanes include polyalkylalkylsiloxane polymers such as polymethyloctylsiloxane; polyalkylarylsiloxanes such as polymethylphenylsiloxane;

having a kinematic viscosity at 25°C of from 20,000 to 100,000 mm ² /s, alternatively of from 20,000 to 80,000 mm ² /s following the general method described in ISO 3104 :

l994(en).

[0022] As well as determining the kinematic viscosity e.g., following the general method described in ISO 3104 : l994(en) if the kinematic viscosity and material density are known dynamic viscosity may be determined by the following equation

Kinematic viscosity (mm ² /s) = dynamic viscosity (mPa.s)

material density

[0023] The density may be measured using glass pycnometer according to DIN 51757 - 2011-01 (Procedure V2). Ideal mixing is assumed for blends of materials, meaning that the density of the blend can be calculated from the respective values of the ingredients.

The values of dynamic viscosities were subsequently used to calculate kinematic viscosities using the material densities tabulated below.

[0024] The silicone base stock oil may, for example, be selected from polydiethylsiloxane, polydimethylsiloxane, polydimethylmethylalkylsiloxane and polymethylalkylsiloxane wherein the alkyl groups are . The alkyl groups attached to the siloxane polymer backbone as part of the methylalkylsiloxane units typically have from 2 to 20 carbon atoms and may be linear or branched. Examples may include ethyl, propyl, isopropyl, butyl, octyl, nonyl, tetradecyl and/or octadecyl groups. [0025] The silicone base stock oil may, for example, be selected from trialkyl terminated polydiethylsiloxane, trialkyl silyl terminated polydimethylsiloxane, trialkyl silyl terminated polydimethylmethylalkylsiloxane, or trialkyl silyl terminated

polymethylalkylsiloxane. Generally the terminal alkyls in the trialkyl silyl terminated will contain from 1 to 6 carbons, alternatively are methyl and/or ethyl, alternatively methyls. Again, for the avoidance of doubt, the alkyl groups attached to the siloxane polymer backbone as part of the methylalkylsiloxane units typically have from 2 to 20 carbon atoms and may be linear or branched. Examples may include ethyl, propyl, isopropyl, butyl, octyl, nonyl, tetradecyl and/or octadecyl groups.

[0026] Liquid silicone resins which may be utilized as the component (a) include, for the sake of example, silicone resins having two or more of the following groups (R^SiOi^a (R ² 2SiO 2/2)>b (R ³ SiC>3/2) c and (S1O4/2) d with R ¹ , R ² and R ³ as hereinbefore described. In the silicone resins each R ¹ , R ² and R ³ may alternatively represent an alkyl group containing from 1 to 8 carbon atoms, an aryl group, a carbinol group, an alkoxy group (preferably methoxy or ethoxy) or an amino group, 0,05 < a < 0,5; 0 < b < 0,3; c > 0; 0,05 < d < 0,6, and a+b+c+d=l (with a, b, c and d being mole fractions).

[0027] The silicone base stock oil can be a blend of multiple silicone oils described above.

[0028] The silicone base stock oil is present in an amount of from 65 to 89.9 % by weight of a silicone base stock oil having a kinematic viscosity of from 20,000 to 100,000 mm ² /s at 25°C following the general method described in ISO 3104 : l994(en); alternatively in an amount of from 65 to 85 % by weight of a silicone base stock oil based on the total weight of the composition.

[0029] One advantage of having high viscosity polymers in the composition described herein as the silicone base stock oil is that such a material is generally tacky to the articles being lubricated because of the natural viscosity thereof. This avoids the need for the addition of tackifying additives which are commonly required in grease formulations at least partially because of the low viscosity of the base oils used. [0030] In accordance with the composition as described above component (b) is a metal salt of a fatty acid wherein the metal is selected from the group of lithium, calcium, aluminum, barium titanium, zinc, magnesium and/or sodium. Such materials function as thickeners in the composition as hereinbefore described. Examples include any one or more of the lithium monocarboxylic fatty acids or lithium hydroxymonocarboxylic fatty acids, calcium monocarboxylic fatty acids or calcium hydroxymonocarboxylic fatty acids, aluminum monocarboxylic fatty acids or aluminum hydroxymonocarboxylic fatty acids barium monocarboxylic fatty acids or barium hydroxymonocarboxylic fatty acids and titanium monocarboxylic fatty acids or titanium hydroxymonocarboxylic fatty acids zinc monocarboxylic fatty acids or zinc hydroxymonocarboxylic fatty acids, magnesium monocarboxylic fatty acids or magnesium hydroxymonocarboxylic fatty acids and/or sodium monocarboxylic fatty acids. Component (b) may also comprise lithium, calcium, aluminum, barium and titanium, zinc, magnesium and/or sodium salts of fatty acids derived from animal oils or from vegetable oils, e.g., a seed oil used in the production of metal soaps.

[0031] Preferable are the salts of monocarboxylic fatty acids or hydroxymonocarboxylic fatty acids having 8 to 22 carbon atoms, for example metal salts wherein the metal is selected from the group of lithium, calcium, aluminum, barium titanium, zinc, magnesium and/or sodium, of a lauric acid (dodecanoic acid), myristic acid (l-tetradecanoic acid), palmitic acid (hexadecanoic acid), stearic acid (octadecanoic acid, behenic acid

(docosanoic acid), myristoleic acid (9-tetradecenoic acid), palmitoleic acid (hexadec-9- enoic acid), oleic acid (9Z)-Octadec-9-enoic acid, or a linoleic acid (cis-9,l2- octadecadienoic acid).

[0032] In one alternative the metal salts may include metal salts of 12-hydroxy stearic acid, 14-hydroxy stearic acid, 16-hydroxy stearic acid, 6-hydroxystearic acid, or 9,10- hydroxystearic acid wherein the metals are selected from lithium, calcium, aluminum, barium and titanium, zinc, magnesium and sodium in particular lithium. Any suitable mixture of the above may be utilised. Particularly preferred are the lithium soaps are derived from Cl 0-24, preferably Cl 5-18, saturated or unsaturated fatty acids or derivatives thereof. One particular derivative is hydrogenated castor oil, which is the glyceride of 12- hydroxystearic acid. 12-hydroxy stearic acid is a particularly preferred fatty acid for example 12-Hydroxy Lithium stearate.

[0033] Component (b) is present in an amount of from 10 to 35% by weight of the total composition.

[0034] Component c) of the composition is an anti-wear and/or anti-corrosion additive in an amount of from 0.1 to 2% by weight of the composition. Any suitable anti-wear and/or anti-corrosion additive may be utilised. These may include zinc dithiophosphate, organosulphur and organo-phosphorus compounds, such as organic polysulphides among which alkylpolysulphides; phosphates among which trihydrocarbyl phosphate, dibutyl hydrogen phosphate, amine salt of sulphurized dibutyl hydrogen phosphate,

dithiophosphates e.g., zinc dithiophosphate ; dialkyldithiophosphates, e.g., zinc dialkyldithiophosphates, dithiocarbamates dihydrocarbyl phosphate; tricresyl phosphate sulphurized olefins, such as sulphurized isobutylene, and sulphurized fatty acid esters.

[0035] Optionally the composition herein may contain dry lubricant in an amount of up to 5% by weight of the composition, alternatively up to 3% by weight of the composition. Any suitable dry lubricant may be utilised when present. Examples might include one or more selected from the list of graphite, molybdenum disulphide, boron nitride, talc, polytetrafluoroethylene (PTFE), calcium fluoride, cerium fluoride, and tungsten disulfide.

[0036] The composition of the present invention may contain one or more grease additives in amounts normally used in this field of application, to impart desirable characteristics to the grease, such as oxidation stability and extreme pressure properties. In particular additional thickeners and thickener complexing agents may be introduced into the composition in addition to component (b).

[0037] In addition to component (b) of the composition one or more complex thickeners may be introduced. These are typically low to medium molecular weight monobasic acids or dibasic acids or salts thereof. In this instance the acids are not fatty acids. Examples include benzoic acid, boric acid or a lithium borate.

[0038] Examples of additional thickeners to be used in conjunction with component (b) might include silica, expanded graphite, polyurea and/or clays such as hectorite or bentonite. ETrea compounds may alternatively be introduced as additional thickeners.

Such thickeners in greases include the urea group (-NHCONH-) in their molecular structure. These compounds may be mono-, di- or polyurea compounds. Such additional thickeners may be used at a level of from 5 to 25%wt based on the total weight of the composition.

[0039] As previously indicated various other conventional grease additives may be incorporated into the lubricating greases, in amounts normally used in this field of application, to impart certain desirable characteristics to the grease. These might include friction modifiers, extreme pressure additives, seal swelling agents, rust and corrosion inhibitors, Viscosity Index improvers, pour point depressants, anti-oxidants, free-radical scavengers, hydroperoxide decomposers, metal passivators, surface active agents such as detergents, emulsifiers, demulsifiers, defoamants, compatibilizers, dispersants, and mixtures thereof.

[0040] Further additives include deposit control additives, film forming additives, tackifiers, antimicrobials, additives for biodegradable lubricants, haze inhibitors, chromophores, and limited slip additives.

[0041] Examples of friction modifiers include molybdenum compounds, aliphatic amines or ethoxylated aliphatic amines, ether amines, alkoxylated ether amines, acylated amines, tertiary amines, aliphatic fatty acid amides, aliphatic carboxylic acids, aliphatic carboxylic esters, polyol esters, aliphatic carboxylic ester-amides, imidazolines, aliphatic

phosphonates, aliphatic phosphates, aliphatic thiophosphonates and aliphatic

thiophosphates. [0042] Examples of extreme pressure additives include organosulphur and organo- phosphorus compounds, such as organic polysulphides among which alkylpolysulphides; phosphates among which trihydrocarbyl phosphate, dibutyl hydrogen phosphate, amine salt of sulphurized dibutyl hydrogen phosphate, dithiophosphates; dithiocarbamates dihydrocarbyl phosphate; sulphurized olefins, such as sulphurized isobutylene, and sulphurized fatty acid esters.

[0043] Examples of seal swell agents include esters, adipates, sebacates, azeealates, phthalates, sulphones such as 3-alkoxytetraalkylene sulphone, substituted sulpholanes, aliphatic alcohols of 8 to 13 carbon atoms such as tridecyl alcohol, alkylbenzenes, aromatics, naphthalene depleted aromatic compounds and mineral oils.

[0044] Examples of rust and corrosion inhibitors include monocarboxylic acids such as octanoic acid, decanoic acid and dodecanoic acid; polycarboxylic acids such as dimer and trimer acids from tall oil fatty acids, oleic acid, linoleic acid; thiazoles; triazoles such as benzotri azole, decyltriazole, 2-mercapto benzothiazole; thiadiazoles such as 2,5- dimercapto-l,3,4-thiadiazole, 2-mercapto-5- hydrocarbyldithio- l,3,4-thiadiazole; metal dithiophosphates; ether amines; acid phosphates; amines; polyethoxylated compounds such as ethoxylated amines; ethoxylated phenols; ethoxylated alcohols; imidazolines and aminosuccinic acids.

[0045] Examples of Viscosity Index improvers include polymethacrylates, olefin copolymers, polyisoalkylene such as polyisobutylene, styrene-diene copolymers, and styrene-ester copolymers such as styrene-maleic ester.

[0046] Examples of pour point depressants include wax-alkylated naphthalenes and phenols, polymethacrylates and styrene-ester copolymers.

[0047] Examples of anti-oxidants include phenolic antioxidants such as 2,6-di-tert- butylphenol, tertiary butylated phenols such as 2,6-di-tert-butyl-4-methylphenol, 4,4'- methylenebis(2,6-di-tert-butylphenol),2,2'-methylenebis(4-me thyl-6-ter t-butylphenol), 4,4'-thiobis(2-methyl-6-tert-butylphenol); mixed methylene-bridged polyalkyl phenols; aromatic amine antioxidants; sulphurized phenolic antioxidants; organic phosphites; amine derivatives such as p-, p'-dioctyldiphenylamine, N,N'-di-sec-butylphenylenediamine, 4- isopropylaminodiphenylamine, phenyl-. alpha. -naphthyl amine, phenyl-. alpha. -naphthyl amine, ring-alkylated diphenylamines; bisphenols and cinnamic acid derivatives.

[0048] Examples of free-radical scavengers include zinc dialkyl dithiophosphates, hindered phenols, and alkylated arylamines.

[0049] Examples of hydroperoxide decomposers include organo-sulphur compounds and organo-phosphorus compounds.

[0050] Examples of metal passivators include poly-functional (polydentate) compounds, such as ethylenediaminetetraacetic acid (EDTA) and salicylaldoxime.

[0051] Examples of surface active agents such as detergents, dispersants, emulsifiers, demulsifiers include alkali metal or alkaline earth metal salts of organic acids such as magnesium sulphonate, zinc sulphonate, magnesium phenate, zinc phenate, lithium sulphonate, lithium carboxylate, lithium salicylate, lithium phenate, sulphurized lithium phenate, magnesium sulphonate, magnesium carboxylate, magnesium salicylate, magnesium phenate, sulphurized magnesium phenate, potassium sulphonate, potassium carboxylate, potassium salicylate, potassium phenate, sulphurized potassium phenate; common acids such as alkylbenzenesulphonic acids, alkylphenols, fatty carboxylic acids, polyamine, polyhydric alcohol derived polyisobutylene derivatives.

[0052] Examples of defoamants include polysiloxanes, polyacrylates and styrene ester polymers.

[0053] Examples of dispersants include alkenylsuccinimide such as polyisobutylene succinimide, N-substituted polyisobutenyl succinimides such as polyisobutenyl succinimide-polyethylenepolyamine, succinates, succinate esters, alkyl methacrylate-vinyl pyrrolidinone copolymers, alkyl methacrylate-dialkylaminoethyl methacrylate copolymers, alkylmethacrylate-polyethylene glycol methacrylate copolymers, polystearamides, high molecular weight amines, phosphoric acid derivatives such as bis- hydroxypropyl phosphorate.

[0054] Some additives may possess multiple properties and provide for a multiplicity of affects. For example, graphite and molybdenum disulphide may both be used as friction modifiers and extreme pressure additives or functionalized soaps may be used to thicken but also provide extreme pressure and antiwear performances to greases.

[0055] When present in the lubricant composition of the invention, the one or more additive(s) may be used at a level of from 0.01 to 10 wt% based on the total weight of the composition, alternatively 0.1 to 5 wt%, based on the total weight of the composition.

[0056] The composition is produced by mixing components (a), (b) and (c) and any optional additives present, by conventional mixing means, optionally with heating.

[0057] Lubricating compositions may be used in a variety of applications where friction occurs between rubbing surfaces. The surfaces may be plastic or metal.

[0058] Types of friction include sliding, rolling, static, kinetic, stick-slip, solid (dry), boundary, mixed, wear, erosion, elasto-hydrodynamic frictions.

[0059] The present invention includes a method to lubricate interacting parts (e.g., metal- metal surfaces, metal-plastic surfaces and/or plastic to plastic surface, alternatively metal to metal surfaces) comprising:

i. obtaining a lubricant composition comprising the composition as hereinbefore described and;

ii lubricating the interacting parts with said lubricant composition.

[0060] The composition herein may be utilised to lubricate interactions between e.g., metal-metal and metal-plastic parts for example bearings, e.g., lubricating bearings in electric motors, wheel bearings, bearings in household appliances, machine tools or aircraft accessories. Greases are also used for the lubrication of small gear drives and for many slow speed sliding applications. They are often utilised in constant velocity joints, ball joints, alternators, cooling fans, ball screws, chucks, linear guides for machine tools, and gears, each having individual requirements for a lubricant given the forces, duress they are under and the functions they are designed to perform. Surprisingly despite the significantly greater viscosity of the silicone base oils herein compared to those previously used our composition functions well. As will be seen below it was unexpectedly identified that the composition herein was found to have a low difference in value between the static and dynamic friction which renders our composition suitable for use in joints used by electrical motors to commence movement of a vehicle from a stationary position. The provision of our composition provides a very low difference in static and dynamic coefficients of friction resulting in a reduction in the forces/power needed to commence motion from a static position. This reduction in the required power will in turn mean that smaller and therefore lighter in weight electric engines can be utilised. Furthermore, given the viscosity of component (a) of our composition our composition is of a tacky nature, resulting in tackifying agents not being required for excellent contact of the grease to the metal and/or plastic surfaces being lubricated.

[0061] Joints used in automobiles applications such as constant velocity joints and ball joints especially in the metal/plastic context and the like require both a low coefficient of friction and as little wear as possible between the different parts of the respective joints. Under a load, the lubricant composition herein has been found to adhere strongly to the essential moving parts of the joint and will form a lubricant (grease) layer with

approximately constant thickness. The present composition has excellent

adhesion/tackiness properties not least because of the high viscosity of component (a) the silicone base stock oil. A lubricant composition for such joints is also needed to flow smoothly when the interacting parts (sometimes referred to as gliding parts) change from a stationary condition to a moving condition, and the lubricant (grease) layer needs to be maintained without change even after repeated movement so that a stable lubricating function is maintained. Surprisingly the compositions as herein provided are also able to meet these requirements.

[0062] The composition herein is also suitable for the provision of dampening in, for example, HiFi systems and also lubricants which are able to lubricate in extreme temperature conditions e.g., temperatures below -30°C, e.g., low temperature bearings and gears/ This because the composition, when utilised to lubricate, will:

(i) maintain lubricity with reduced differences between static and dynamic

coefficients of friction,

(ii) (ii) have good dampening capabilities at elevated temperatures and/or reduced temperatures (below -30°C),

(Hi) adhere strongly to the surfaces being lubricated to form a“lubricating layer” between them with a relatively constant thickness.

(iv) flow smoothly at the gliding part when the adjacent surfaces meet.

Furthermore, the lubricating layer created is successfully maintained without the need to re-lubricate after repeated movement resulting in a stable lubricating function.

[0063] The present lubricant composition may be used in any system that includes machine elements that contain gears of any kind and roller bearings. Examples of such systems include electricity generating systems, industrial manufacturing equipment such as paper, steel and cement mills hydraulic systems, automotive drive trains, aircraft propulsion systems, etc. Hence, they may be used to lubricate bearings for constant velocity joints, ball joints, wheel bearings, alternators, cooling fans, ball screws, chucks, linear guides for machine tools, bearings and gears.

[0064] Further systems include crankcases, 2-stroke engines, 4-stroke engines, diesel engines, internal combustion engines, gears for manual or differential transmissions, industrial lubricants, hydraulic, compressor, turbine, metal working and metal forming.

[0065] Further systems also include traction and torque systems.

[0066] Operating temperatures for the use of the lubricant composition, meaning the temperatures at which the lubricant composition may be used for prolonged times (also called service temperatures), range of from -55°C to +200°C. Short term peak

temperatures may be higher.

[0067] The ingredients may be pre-prepared and mixed in their pre-prepared form but alternatively they may be prepared in situ.

Examples

[0068] The following formulation identified as Example l is a composition in accordance with composition herein and which was used throughout the following examples.

Table 1 : Composition of Example 1 (Ex.l)

[0069] The following table shows the test results of common industrial standard tests for greases, which tests were undertaken on the composition identified as Example 1 above and depict .describe grease properties in general for said Example 1. The ingredients were mixed together. Table. 2 Physical Properties of Ex. 1 grease composition

[0070] The difference between the static and dynamic coefficients of friction of Example 1 (high viscosity) were then compared with those of a variety of comparative lubricant grease compositions all of which contained much lower viscosity silicone base stock oils (<1000 mm ² /s) at 25°C following the general method described in ISO 3104 : l994(en) having their compositions identified in Tables 3 to 7. Table. 3 composition of Comparative. 1 (Comp. 1)

Table. 4 composition of Comparative. 2 (Comp. 2)

Table. 5 composition of Comparative. 3 (Comp. 3) Table. 6 composition of Comparative. 4 (Comp. 4)

Table. 7 composition of Comparative. 5 (Comp.5)

[0071] Example. 1 and the above comparatives were analysed to determine the difference between their respective dynamic and static coefficients of friction using a stick-slip tester from AKE-technologies GmbH called Anti-Knarz (noise) Machine.

[0072] The Anti-Knarz (noise) Machine is sensitive enough to measure the static and dynamic friction coefficient by way of a ball plate tribometer- system. The tester was used for internal pre-test selection of the grease candidate with lowest friction level of static and dynamic friction coefficient and the smallest difference of both. The tests were run using the parameters:

Specimen: 12.7 mm POM Ball / S-36 Q-Panel

Speed: 0.5 mm/sec

Load: 30 Newton

Cycles: 1000 (measured every 10 cycles)

Running distance: 5 mm

Duration of measurement: 20sec

The results are depicted in Table 8 below. Table 8 comparisons of Coefficients of friction and their respective differences.

[0073] Optimal greases have as low static and dynamic coefficients of friction as possible and as small a difference between said static and dynamic values. It was unexpectedly identified that Example 1 produced better or no worse results than each of the comparatives, despite using a silicone base stock oil having a significantly greater viscosity. The differences between the static and dynamic viscosity coefficients can also be seen to be good for Example. 1. [0074] In a further series of experiments the rubber compatibility of different rubbers with Example 1 in terms of shore hardness change and weight change by comparing a blank rubber sample to a grease treated rubber sample using the following methods.

1. Rubber compatibility test - Weight loss (DIN 53521 -1987 - 11).

Rubber tensile bars of shape“S2” were cleaned lightly with a lintless textile or tissue (if needed isopropyl alcohol was used as a cleaning fluid). The resulting cleaned test bars were then coated completely in Example. 1 grease composition. The resulting samples were then stored at 70°C for 96 hours the un-treaded and treaded test pieces were cleaned and balanced again. The weight differences were calculated and the value reported in g and % weight difference

Table 9a Rubber compatibility test - Weight loss (DIN 53521 -1987 - 11). Blank sample without grease treatment

[0075] All blank samples showing after storing at 70°c for 96 h a weight loss between 0.16 and 0.66 weight %

Table 9b Rubber compatibility test - Weight loss (DIN 53521 -1987 - 11) after silicone grease had been applied

[0076] All rubber samples showing a very good (< 5%) to acceptable (>5 - <10%) weight loss after storing at 70°c for 96 h.

2. Rubber compatibility test - Shore A hardness

A Shore hardness tester (Digi test II) (durometer) was used to measure the depth of an indentation in the rubber material created by a given force on a standardized presser foot following the standard method in DIN ISO 7619-1 :20l2 02. Tests were made using blank Samples (i.e., not previously treated with lubricant) and after treating with lubricant. The results are depicted in Table 10 below.

Table 10 Rubber Compatibility Test - Shore A Hardness

[0077] All rubber samples showing a very good (D < +/-5) to acceptable (D >+/-5 - <+/- 10) shore hardness change after storing at 70°c for 96 h.