FIELD OF THE INVENTION

The present invention relates to grease compositions, methods for manufacturing the grease compositions, and the use of the grease compositions for lubricating bearings, gears and couplings.

BACKGROUND OF THE INVENTION

Grease compositions are widely used for lubricating bearings and other structural components. A grease is an essential product to reduce, for example, wear, friction, running temperatures and energy losses. Greases are materials which comprise a base oil that is thickened with a metal soap, and they are usually prepared by reacting a metal hydroxide with a fatty acid in the presence of the base oil. Conventional metal soap greases require an energy intensive grease cooking and milling process in order to achieve proper thermo-mechanical stability. Conventional metal soap greases can still be sensitive to poor thermo-mechanical stability and can require additional treatments. It is known to improve further the stability, and thus the lubricating capacity, of conventional greases by adding solid additives during the thickening process. Examples of such solid additives are, for example, molybdenum disulfide, graphite, zinc oxide and/or a silica gel. The process of grease cooking and milling and additional treatments is relatively expensive because it is carried out at an elevated temperature and over a relatively long period of time. Moreover, the greases so prepared are still unsuitable for a variety of applications, and not all conventional greases are suitable for food and beverage processing applications. Consequently, there is a need for greases which can easily be manufactured at low costs, which are stable and show highly attractive lubricating properties in terms of low friction performance. In addition, there is a need for greases that are biodegradable, environmentally benign and food compatible. SUMMARY OF THE INVENTION

Object of the present invention is to provide grease compositions which show excellent lubricating properties such as grease life performance, corrosion wear and thermo and mechanical stability, and which can easily be manufactured at low costs and/or are more environmental friendly. Surprisingly, it has now been found that this can be established when use is made of a base oil and a particular thickener which comprises hydrophilic metal oxide particles and one or more metal salts of fatty acids.

Accordingly, the present invention relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles and one or more metal salts of fatty acids, wherein at least one of the metal salts of fatty acids contains two or more unsaturated C-C bonds, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μιη, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease

composition.

Suitably, the grease composition comprises in addition one or more metal salts such as metal sulphonates, metal sulphates, metal phosphates and/or metal phosphonates.

The grease compositions according to the present invention show an attractive low friction performance, whereas at the same time they can easily be manufactured at low costs and/or are more environmental friendly. DETAILED DESCRIPTION OF THE INVENTION

The thickener to be used in the present grease composition comprises one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds.

It will be understood that fatty acids are aliphatic monocarboxylic acids derived from, or contained in esterified form in an animal or vegetable fat, oil or wax. In accordance with the present invention use can be made of natural and synthetic fatty acids. The one or more metal salts of fatty acids to be used in accordance with the present invention have a relative polarity which is introduced by means of two or more unsaturated C-C bonds along the fatty acid chain. Preferably, the metal salts of the fatty acids to contain in addition at least one OH group. For example an OH-group can be introduced on a secondary position in the fatty acid chain. In this way an improved low friction performance could be realized. Preferably, the fatty acid chain contains two or more unsaturated C-C bonds. Preferably, the fatty acid chain of the metal salt contains two or more unsaturated C-C bonds and two or more OH groups. The introduction of two or more unsaturated C-C bonds and at least two OH groups has the advantage that the relative polarity is even further increased along the fatty acid chain.

In accordance with the invention use can be of a mixture of metal salts of different fatty acids that each contains two or more unsaturated C-C bonds. Suitably, the different fatty acids may comprise a different number of carbon atoms. Suitably, the grease composition comprises two metal salts of fatty acids. The one or more metal salts of fatty acids to be used in accordance with the invention may be metal salts of different fatty acids. When use is made of two metal salts of different acids the first metal and the second metal may be the same metal or they may differ from each other. In another embodiment, use can be made of two different metal salts of fatty acids, the fatty acid of the first metal salt and the fatty acid of the second metal salt may be the same fatty acid. When two different metal salts of fatty acids are used, the at least first and second metals will not be the same metal when the fatty acid of the first metal salt and the fatty acid of the second metal salt are the same fatty acids, and vice versa. In one embodiment, a first metal salt of a fatty acid may contain two or more unsaturated C-C bonds and a second metal salt of a fatty acid may contain one unsaturated C-C bond

In another embodiment, a first metal salt of a fatty acid may contain two or more unsaturated C-C bonds and a second metal salt of a saturated fatty acid. Preferably, the second metal salt is derived stearic acid, oleic acid andl2-hydroxy stearic acid. Such grease compositions are particularly attractive in a diversity of industrial and automotive applications such as in mining, steel, fans, electrical motors, wheel bearings, agricultural, conveyors, bakery equipment and food processing.

Preferably, the amount of such a first metal salt of a fatty acid is 0.01-15% by weight and the amount of a second metal salt of a fatty acid is 0.01-15% by weight, based on the total weight of the grease composition. More preferably, the amount of such a first metal salt of a fatty acid is 0.5-8% by weight and the amount of such a second metal salt of a fatty acid is 0.5-8% by weight, based on the total weight of the grease composition. In another embodiment of the present invention, the grease composition comprises three types of metal salts of different fatty acids, wherein at least one of the fatty acids contain two or more unsaturated C-C bonds.

In a preferred embodiment of the present invention, the grease composition comprises in addition one or more fatty acids.

Accordingly, the present invention also relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more metal salts of fatty acids and one or more fatty acids, wherein at least one of the metal salts of fatty acids contains two or more unsaturated C-C bonds, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μιη, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

The additional fatty acid may suitably be selected from the group consisting of caprylic acid, pelargonic acid, capric acid, lauric acid, linderic acid, rayristic acid, tsuzuic acid, physetoleic acid, myristoleic acid, pentadecylic acid, palmitic acid, palmitoleic acid, margaric acid, stearic acid, 12-hydroxystearic acid, petroselinic acid, oleic acid, elaidic acid, vaccenic acid, linolic acid, linolenic acid, elaeostearic acid, tuberculostearic acid, arachidic acid, eicosadienic acid, eicosatrienic acid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid, hexadocosanic acid, octadocosanic acid and erucic acid.

Suitably, the second fatty acid to be used in addition to the first fatty acid that contains one or more unsaturated C-C bonds and at least one OH group may be selected from the group consisting of palmitoleic acid, petroselinic acid, linolic acid, linolenic acid, eicosadienic acid and erucic acid.

Examples of unsaturated fatty acids are: vaccenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, nervonic acid, , eicosatrienic acid, eicosadienic acid, elaeostearic acid, myristoleic acid, physetoleic acid, linderic acid, rayristic acid, tsuzuic acid, docosadienoic acid, gondoic acid, mead acid, paullinic acid, arachidonic acid, dihomo-y-linolenic acid, y- linolenic acid, pinolenic acid, crotonic acid, eleostearic acid, stearidonic acid, adrenic acid, pentaunsaturated fatty acids, sardine acid, and hexa-unsaturated fatty acids.

Examples of natural unsaturated fatty acids are: Jojoba oil, nut oils, seed oils, pecan oil, olive oil, penola oil, castrol oil, and fish oil.

Examples of hydroxy fatty acids include 15-hydroxy hexadecanoic acid, 12-hydroxy stearic acid, and 17 -hydroxy- octadecanoic acids. Beeswax is a natural hydroxy fatty acid.

In chemistry, a fatty acid is a carboxylic acid with a long aliphatic tail (chain), which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 12 to 28. Fatty acids are usually derived from triglycerides or phospholipids. Hydrogenation will form from unsaturated fatty acids saturated fatty acids.

Fats first can hydrolyse into free fatty acids and then combine with the alkali in saponification to form the metal salts of the fatty acids. Metal hydroxides as alkali are examples of being used in the saponification process. Preferably, the fatty acid chain of the additional one or more fatty acids contains one or more unsaturated C-C bonds and/or at least one OH group, preferably the additional one or more fatty acids contains one or more unsaturated C-C bonds and at least one OH group. More preferably, the additional one or more fatty acids contain two or more unsaturated C-C bonds and at least one OH group, preferably at least two OH groups. The introduction of at least one OH group has the advantage that the relative polarity is even further increased along the fatty acid chain. An example of such a fatty acid is ricinoleic acid having an unsaturated C-C in the ninth position and an OH group in the twelfth position. Further, also metal salts of rapseed oil and castor oil can be used.

The metal in the metal salts is preferably an alkali metal or an alkaline earth metal of Groups 1 and 2 of the Periodic System of Elements, and bismuth. Suitable examples of metals include lithium, potassium, sodium, calcium, aluminium, rubidium, cesium, francium, beryllium, strontium, barium, radium, bismuth and magnesium. In addition it is noted that the metal in the metal salt to be used can be a semi-metal such as borium. According to a preferred embodiment according to the present invention, the metal is an alkaline earth metal, most preferably calcium.

In a particular attractive embodiment the thickener to be used in accordance with the present invention contains one or more glycerides such as saturated or unsaturated triglycerides, wherein the three fatty acid chains may each comprise one or more unsaturated C-C bonds. Especially attractive are usaturated glycerides. Suitable glycerides include castor oil, linseed oil, rapeseed oil, glyceryl trioleate and glyceryl tristearate. Further, also metal salts of rapseed oil and castor oil can be used.

Suitably, the thickener comprises in addition one or more metal salts such as metal sulphonates, metal sulphates, metal phosphates and/or metal phosphonates.

The grease compositions according to the present invention are preferably non-hydroxide grease compositions. Non-hydroxide grease compositions in accordance with the present invention do not contain impurities such as excess amounts of hydroxide which are normally present in greases that are prepared in conventional lime soap manufacturing processes. The non-hydroxide grease compositions according to the present invention are suitably substantially free of free hydroxide ions and/or metal hydroxide. Preferably, the present non- hydroxide grease compositions contain less than 0.2% by weight, and more preferably less than 0.1% by weight of free hydroxide ions and/or metal hydroxide, based on the total weight of the grease composition. Preferably, the present non-hydroxide grease compositions are substantially free of free hydroxide ions and/or metal hydroxide. Preferably, the present grease compositions contain less than 0.2% by weight, and more preferably less than 0.1% by weight of metal hydroxide, based on the total weight of the grease composition. Most preferably, the present non-hydroxide grease compositions are completely free of metal hydroxide. It will be understood that OH-groups present on the hydrophilic metal oxide particles or in an fatty acid such as 12-hydroxy stearate or the metal salt of such an fatty acid are not to be considered free hydroxide ions since they are bonded to silicon atoms or to a carbon atom of the fatty acid. The thickener to be used in accordance with the present invention is suitably a non- saponified thickener.

The grease composition in accordance with the present invention is preferably a non- hydroxide grease composition wherein the thickener comprises hydrophilic metal oxide particles, preferably silicon oxide particles, and one or more metal salts of fatty acids, wherein at least one of the metal salts of fatty acids contains two or more unsaturated C-C bonds, wherein the hydrophilic silicon oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the hydrophilic silicon oxide particles have a mean particle size of 5 nm to 900 μιη, and wherein the amount of the thickener is 0.1-40% by weight, based on the total weight of the grease composition.

The present invention further provides a grease composition comprising a base oil and a thickener which comprises hydrophilic silicon oxide particles and one or more metal salts of different fatty acids that contain two or more unsaturated C-C bonds, wherein the hydrophilic silicon oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the hydrophilic silicon oxide particles have a mean particle size of 5 nm to 900 μιη, and wherein the amount of the thickener is 0.1-40% by weight, based on the total weight of the grease composition.

The present invention further provides a grease composition comprising a base oil and a thickener which comprises hydrophilic titanium oxide particles and/or hydrophilic aluminium oxide particles and one or more metal salts of different fatty acids that contain two or more unsaturated C-C bonds, wherein the hydrophilic titanium oxide particles and/or hydrophilic aluminium oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the hydrophilic titanium oxide particles and/or hydrophilic aluminium oxide particles have a mean particle size of 5 nm to 900 μιη, and wherein the amount of the thickener is 0.1- 40% by weight, based on the total weight of the grease composition.

In a preferred embodiment, the present invention relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more metal salts of fatty acids and one or more esters, wherein at least one of the metal salts of fatty acids contains two or more unsaturated C-C bonds, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μιη, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition. Suitably, the thickener comprises in addition one or more metal salts such as metal sulphonates, metal sulphates, metal phosphates and/or metal phosphonates.

The esters to be used in accordance with the present invention include branched and unbranched esters.

The esters to be used suitably contain one or more unsaturated C-C bonds and/or at least one OH group. Suitable esters include unsaturated esters such as methyl oleate ester and ethyl linoleate ester; saturated diesters such as dioctyl sebacate ester, diisooctylsebacate ester and dioctyl adipate ester; and OH-group containing esters such methyl- 12-hydroxystearate ester 9-Octadecenoic acid, 12 hydroxy methyl ester and hydroxy palmitic ester. The diesters to be used may also contain one or more unsaturated C-C bonds. Other suitable esters include unbranched and branched alkylated carboxylate esters, as well as triglycerides, in particularly unsaturated triglycerides. The esters may also include an amine and/or amide group.

Further, the present invention preferably provides a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more metal salts of fatty acids, wherein at least one of the metal salts of fatty acids contains two or more unsaturated C-C bonds, and in addition one or more esterified fatty acids that contain one or more unsaturated C-C bonds and/or at least one OH group, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the hydrophilic metal oxide particles have a mean particle size of 5 nm to 900 μιη, and wherein the amount of the thickener is 0.1-40% by weight, based on the total weight of the grease composition.

The present invention preferably relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more metal salts of fatty acids and in addition one or more amides that contain one or more unsaturated C-C bonds and/or at least one OH group, wherein at least one of the metal salts of fatty acids contains two or more unsaturated C-C bonds, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the hydrophilic metal oxide particles have a mean particle size of 5 nm to 900 μιη, and wherein the amount of the metal salt(s) is 0.1-40% by weight, based on the total weight of the grease composition.

In an attractive embodiment the one or more amides contain one or more unsaturated C-C bonds and at least one OH group. In another attractive embodiment, the one or more amides contain two or more unsaturated C-C bonds.

Suitable amides that contain one or more unsaturated C-C bonds include unsaturated amides such as oleamide and linoleamide; diamides such as ethylene bis stearamide, hydroxy ethyl ethylene bis oleamide, ethylene bis-12-hydroxystearamide and bishydroxethyl oleylamine; and OH-group containing amides such as hydroxy ethyl ethylene bis oleamide, ethylene bis- 12-hydroxy stearamide . Preferably, the unsaturated amides are unsaturated fatty acid amides, more preferably the amides are metal salts of unsaturated fatty acid amides. The amides to be used in accordance with the present invention include branched and unbranched amides. The amides may contain an ester group.

The present invention preferably relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more metal salts of fatty acids and in addition one or more amines that contain one or more unsaturated C-C bonds and/or at least one OH group, wherein at least one of the metal salts of fatty acids contains two or more unsaturated C-C, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the hydrophilic metal oxide particles have a mean particle size of 5 nm to 900 μιη, and wherein the amount of the thickener is 0.1-40% by weight, based on the total weight of the grease composition.

Suitably, the unsaturated amines further include at least one OH-group. Suitable examples of such amines are ethyl hydroxy stearamine and bishydroxyethyl oleylamine, and diamines such as bishydroxyethyl oleylamine. Suitably, the one or more amines are fatty acid amines. The one or more unsaturated amines may suitably in addition contain at least one OH group, suitably at least two OH groups. Suitably, the one or more amines contain two or more unsaturated C-C bonds and at least one OH group. Suitably, the one or more amines are metal salts. The amines to be used in accordance with the present invention include branched and unbranched amines. The amines may contain an ester group.

Preferably, the present invention relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more metal sulphonates, metal sulphates, metal phosphates and/or metal phosphonates, and one or more fatty acids, wherein at least one of the fatty acids contains one or more unsaturated C-C bonds and/or at least one OH group, wherein the metal oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the metal oxide particles have a mean particle size of 5 nm to 900 μιη, and wherein the amount of the metal salt(s) is 0.1-40% by weight, based on the total weight of the grease. The present invention preferably provides a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more metal salts of fatty acids, and in addition one or more fatty acids, one or more esters, one or more amides and/or one or more amines, wherein at least one of the metal salts of fatty acids contains two or more unsaturated C-C bonds, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m /g and at least 80% of the hydrophilic metal oxide particles have a mean particle size of 5 nm to 900 μιη, and wherein the amount of the thickener is 0.1-40% by weight, based on the total weight of the grease composition.

Suitably, the additional one or more fatty acids, one or more esters, one or more amides and/or one or more amines contain one or more unsaturated C-C bonds and/or at least one OH group. Preferably, the additional one or more fatty acids, one or more esters, one or more amides and/or one or more amines contain one or more unsaturated C-C bonds and at least one OH group. The one or more metal salts of fatty acids, one or more fatty acids, one or more esters, one or more amides and/or one or more amines may be any of the fatty acids, fatty acids, esters and amines as described hereinabove.

The nature of the base oil to be used in accordance with the present invention is not essential. The base oil may be selected from the group consisting of mineral base oils and synthetic base oils. Mineral base oils are derived from crude oils and are either formulated on the basis of aromatic, paraffinic and/or naphthenic base oils. Further, a wide range of synthetic base oils is known and they include esters, poly-alpha-olefins, polysiloxanes and the like.

The base oil to be used in accordance with the present invention may comprise a base oil blend. Suitably, blends of mineral base oils and synthetic base oils may be used. The base oil in this invention is one which may ordinarily be used as the base oil of a lubricating oil or as the base oil of a grease, and there are no special restrictions. As examples mention may be made of mineral oils, synthetic oils, animal and plant oils, and mixtures thereof. 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 a suitable combination of refining processes such as solvent refining, hydrorefining, and dewaxing in respect of lubricating oil - o fractions obtained by atmospheric distillation of crude oil. Group II base oils include, for example, paraffinic mineral oils obtained by 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 not more than 5% and so are suitable for this invention. Group III base oils and Group 11+ base oils include paraffinic mineral oils manufactured by a high degree of hydrorefining in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil, base oils refined by the Isodewax process which dewaxes and substitutes the wax produced by the dewaxing process with isoparaffins, and base oils refined by the Mobil wax isomerisation process. These too are suitable for use in this invention. Concrete examples of synthetic oils include polyolefins, polyoxyalkylene glycols such as polyethylene glycol or polypropylene glycol, esters such as di-2- ethylhexyl sebacate or di-2-ethylhexyl adipate, polyol esters such as trimethylolpropane esters or pentaerythritol esters, perfluoroalkyl ethers, silicone oils, polyphenyl ethers, and so on.

The aforementioned polyolefins include polymers of various olefins or hydrides thereof. Any olefin may be used, and as examples mention may be made of ethylene, propylene, butene and [alpha] -olefins with five or more carbons. In the manufacture of polyolefins, one of the aforementioned olefins may be used singly or two or more may be used in combination.

Particularly suitable are the polyolefins called poly- [alpha] -olefins (PAO). These are base oils of Group IV. GTL (gas to liquid) 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. As typical examples of animal and plant oils mention may be made of castor oil and rape-seed oil. The various aforementioned oils may be used singly or in mixtures for the base oil. The aforementioned examples are listed singly but the invention is not limited thereby.

Preferably, the base oil or the base oil blend to be used in accordance with the present invention has a kinematic viscosity in the range of 1 to 60 000 cSt at a temperature of 40 °C according to DIN 51562/1. Suitable base oils include ISO VG 68, ISO VG 46, ISO VG 32, ISO VG 22, ISO VG 15 and ISO VG 10 oils.

The hydrophilic metal oxide particles to be used in accordance with the present invention can be derived from titanium oxide, aluminium oxide and silicon oxide. Preferably, the hydrophilic metal oxide particles are hydrophilic silicon oxide particles. The hydrophilic metal oxide particles may be crystalline metal oxide particles or amorphous metal oxide particles. Preferably, the hydrophilic silicon oxide particles are amorphous hydrophilic silicon oxide particles. The amorphous hydrophilic silicon oxide may contain various amounts of water, implying that it may comprise silicic acid. In this respect it is noted that silicic acid is a general name for a group of chemical compounds, oligomers and polymers consisting of silicon, hydrogen, and oxygen. Preferably, the amorphous hydrophilic silicon oxide particles are derived from an amorphous fumed silicon oxide. Fumed silicon oxide is an exceptionally pure form of silicon oxide made from silica tetrachloride as a starting material, as is well known in the art. Suitable sources for the fumed silicon oxide are Aerosil(R) which is commercially available from Evonik Industries (formerly known as Degussa) or Cap-o-Sil(R) which is commercially available from Cabbot Corporation. Preferably, silicon oxide particles have an average size in the range of from 5-100 microns and have a BET specific surface area in the range of from 5-100 m /g.

In accordance with the present invention also mixtures of different hydrophilic metal oxide particles can be used. For example a mixture of hydrophilic titanium oxide particles and hydrophilic aluminium oxide particles can be used. Suitably, the hydrophilic metal oxide particles have a BET specific surface area of at least 50 m 2 /g, more preferably at least 75 m 2 /g, yet even more preferably at least 100 m2/g, even yet more preferably at least 125 m 2 /g and most preferably at least 150 m 2 /g Although is it preferred that the BET specific surface area is as high as possible, it will usually not be higher than 500 m /g Methods for determining the BET specific surface area are well known in the art.

In some embodiments of the present invention, the hydrophilic metal oxide particles have a BET specific surface area of less than 50 m ² /g.

According to the present invention at least 80% of the hydrophilic metal oxide particles have a particle size of 5 nm to 900 μιη. In some embodiments at least 80% of the hydrophilic metal oxide particles have a particle size of 5-50 nm, preferably of 5-40 nm, more preferably of 10- 40 nm and most preferably of 20-40 nm. The total particle size distribution of the amorphous silicon oxide particles is preferably in the range of 1-50 nm. The grease compositions according to the invention may additionally comprise other thickening components, e.g. polymers or other fatty compounds that contain one or more OH- groups and/or one or more unsaturated bonds and/or one or more ester groups and/or one or more aromatic groups. Such thickening components can suitably be present in an amount of less than 3% by weight, preferably less than 2% by weight, based on the total weight of the grease composition.

The grease compositions according to the present invention may comprise other additives to tailor its suitability to a certain use as is well known in the art. Such additives include anti- wear agents, anti-corrosion agents, rust inhibitors, friction modifiers, anti-oxidants, VI- improvers and the like as is well known by the person skilled in the art. As suitable examples of such additives sulphonates, sulphates, phosphates and/or phosphonates can be mentioned. Suitable sulphonates include for instance methyl ester sulphonate, sodium methyl ester sulphonate and calium sulphonate. Suitable sulphates include for example calcium sulphate, sodium dodecyl sulphate and sodium lauryl sulphate. Suitable phosphates include for instance calcium hydrogen phosphate and amine phosphate. Suitable phosphonates include for example calcium phosphonate ester and other phosphonate esters.

Other suitable additives include silanes, (alkylated) siloxanes, metal hydroxide silicates, silanols, hydrosilicates, metal bonded silicon compound such as Mg ₃ (Si205)(OH) ₂ . Examples of such additives are for instance polydimethyl siloxane oil, hexomethyldisiloxane, magnesium hydrosilicate and other phyllosilicates. As well as polymethylsilesquioxane, hydrated (metal) silicates, amorphous silica, and sythetic silica gels, which additives are all used to improve polymer performance. Such other additives can suitably be present in an amount in the range of from 1-40% by weight, preferably 2-20% by weight, based on the total weight of the grease composition. In case the grease composition contains a high amount of such other additives, e.g. 20-40% by weight, based on total weight of the grease composition, the grease composition will display paste-type properties. Hence, the grease composition in accordance with the present invention also includes pastes. The other additives may also include small amounts (less than 3% by weight, preferably less than 2% by weight, based on the total weight of the grease composition) of further metal salts of fatty acids, but such metal salts will not substantially contribute to the formation of the grease thickener. In that case the grease composition will contain more than four metal salts of different fatty acids. A number of grease compositions according to the present invention are hydroxide grease compositions. The present grease compositions may in addition also contain a small amount of metal hydroxide. Suitable metal hydroxides include potassium hydroxide, aluminium hydroxide, calcium hydroxide, lithium hydroxide, sodium hydroxide, magnesium hydroxide barium hydroxide and bismuth hydroxide. Other suitable additives include polypropylene, polyethylene, urea, bentonite, and other greases such as (complex) greases and PTFE/PFPE greases.

A common disadvantage of conventionally manufacturing methods is that it requires a multiple number of hours for blending the various components, gelling and cooling of the grease composition. At a batch scale of about 1-5 metric tons, the total cooking (gelling) and cooling can take about four hours or more, whereas grease milling can require two or more hours. Usually, the total manufacturing time takes about eight hours. However, the grease compositions according to the present invention can be prepared in a very short manufacturing process, wherein blending, gelling and cooling is preferably performed within one hour, more preferably within half an hour period. The mechanical treatment, preferably grease milling, in accordance with the present invention for a 5 metric ton volume can require about two or two and a half hours. In addition, it is observed that conventional grease manufacturing processes are carried out at high temperatures, typically in the range of from 170-220 °C, whereas the present grease composition can suitably be prepared at a temperature below 90 °C, including room temperature. The present invention also provides methods for preparing the present grease compositions. In accordance with the present invention the components of the present grease compositions can be mixed in any possible order of sequence. Preferably, the hydrophilic metal oxide particles and the one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds are subjected to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment. Hence, (a) a mixture of the hydrophilic metal oxide particles, one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds is subjected to a mechanical treatment and/or thermal treatment; (b) a mixture of the hydrophilic metal oxide particles and one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds is subjected to a mechanical treatment and/or thermal treatment; or (c) a mixture of the base oil, the hydrophilic metal oxide particles and one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds is subjected to a mechanical treatment and/or thermal treatment. Preferably, the hydrophilic metal oxide particles and the one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds are before or after mixing with the other component(s) subjected to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment.

In accordance with the present invention the entire amount of base oil to be used or parts of the base oil can, for example, be added at one or more stages of the process. Suitable embodiments of the present invention include: Subjecting a mixture of hydrophilic metal oxide particles and one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds to a mechanical and/or thermal treatment, followed by adding to the mixture so obtained the base oil and optionally any further additives, and subjecting the grease composition so obtained to a mechanical and/or thermal treatment.

Subjecting a mixture of hydrophilic metal oxide particles and one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds, and optionally any of the hereinbefore described one or more fatty acids, esters, amides and/or amines, and a part of the base oil to a mechanical and/or thermal treatment, followed by adding to the mixture so obtained the remaining part of the base oil and optionally any further additives, and subjecting the grease composition so obtained to a mechanical and/or thermal treatment.

Subjecting a mixture of hydrophilic metal oxide particles, the one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds, and optionally any of the hereinbefore described one or more fatty acids, esters, amides and/or amines, and the base oil to a mechanical and/or thermal treatment, followed by adding to the mixture so obtained any further additives, and subjecting the grease composition so obtained to a mechanical and/or thermal treatment.

Subjecting a mixture of the base oil, the hydrophilic metal oxide particles and one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds, and optionally any of the hereinbefore described one or more fatty acids, esters, amides and/or amines, and optionally any further additives, to a mechanical and/or thermal treatment.

Subjecting the hydrophilic metal oxide particles to a mechanical and/or thermal treatment of, followed by adding one or more one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds, and optionally any of the hereinbefore described one or more fatty acids, esters, amides and/or amines, to the hydrophilic metal oxide particles so obtained and subjecting the mixture so obtained subsequently to a mechanical and/or thermal treatment. The base oil and optionally any further additives are then added to the mechanically and/or thermally treated mixture and the grease composition so obtained is then subjected to a mechanical and/or thermal treatment.

Subjecting the hydrophilic metal oxide particles to a mechanical and/or thermal treatment, followed by adding the base oil, one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds, and optionally any of the hereinbefore described one or more fatty acids, esters, amides and/or amines, and optionally any further additives, to the mechanically and/or thermally treated hydrophilic metal oxide particles, and subjecting the grease composition so obtained to a mechanical and/or thermal treatment.

Subjecting one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds to a mechanical and/or thermal treatment, and optionally any of the hereinbefore described one or more fatty acids, esters, amides and/or amines, followed by adding the base oil, the hydrophilic metal oxide particles and optionally any further additives to the at least one metal salt so obtained, and subjecting the grease composition so obtained to a mechanical and/or thermal treatment.

Subjecting one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds to a mechanical and/or thermal treatment of, and optionally any of the hereinbefore described one or more fatty acids, esters, amides and/or amines, followed by adding the hydrophilic metal oxide particles to the mechanically and/or thermally treated metal salt(s) and subjecting the mixture so obtained subsequently to a mechanical and/or thermal treatment. The base oil and optionally any further additives are then added to the mechanically and/or thermally treated mixture and the grease composition so obtained is then subjected to a mechanical and/or thermal treatment. As indicated above, the grease composition may comprise any further additives. Such further additives can be added to one or more of the components at any stage of the preparation process of the grease composition.

In the process according to the present invention each of the components or any mixture of the components can be subjected to a mechanical and/or thermal treatment in any possible order of sequence. For example, all components can be added together after which the mechanical and/or thermal treatment is applied. One of the components (e.g. the hydrophilic metal oxide particles) can first be subjected to a mechanical and/or thermal treatment after which one other component(s) (e.g. a metal salt of a fatty acid) or two or more other components (i.e. one or more of the fatty acids, and optionally a metal salt of fatty acid, and the base oil) can be added to the mechanically and/or thermally treated component, followed by subjecting the grease composition so obtained to a mechanical and/or thermal treatment. Alternatively, one of the components (e.g. the hydrophilic metal oxide particles) can first be subjected to a mechanical and/or thermal treatment after which one other component (e.g. a metal salt of a fatty acid) can be added to the mechanically and/or thermally treated component, subjecting the mixture so obtained to a further mechanical and/or thermal treatment, followed by adding yet one or more other components (e.g. the base oil and an optionally another metal salt of a fatty acid) to the mechanically and/or thermally treated mixture so obtained, and subjecting the grease composition thus obtained to a mechanical and/or thermal treatment. According to one embodiment of the present invention, the hydrophilic metal oxide particles are first subjected to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment. Subsequently, the hydrophilic metal oxide particles so obtained are mixed with the base oil and the one or more metal salts fatty acids that contain two or more unsaturated C-C bonds to form a grease composition. Hence, the present invention also relates to a method for manufacturing a grease composition according to the present invention, which method comprises the following sequential steps:

(a) subjecting the hydrophilic metal oxide particles to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment; and

(b) mixing the hydrophilic metal oxide particles so obtained with the base oil and one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds to form a grease composition.

Any of the hereinbefore described one or more fatty acids, esters, amides and/or amines can be part of the mixture in step (a).

In case use is made of a plurality of metal salts of different fatty acids, the metal salts of the fatty acids may optionally be processed together with the hydrophilic metal oxide particles in step (a). According to another embodiment of the present invention, the hydrophilic metal oxide particles are first mixed with the base oil and the one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds to form a grease composition, whereafter the grease composition so formed is subjected to the mechanical treatment, the thermal treatment or to both the mechanical treatment and the thermal treatment. Accordingly, the present invention also relates to a method for manufacturing a grease according to the present invention, which method comprises the following sequential steps: (a) mixing the hydrophilic metal oxide particles with the base oil and one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds to form a grease composition; and (b) subjecting the grease composition so formed to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment. The mechanical treatment is preferably a milling step which can be performed in any suitable milling apparatus, e.g. a high pressure homogeniser, a colloid mill, a three-roller mill (e.g. a three- roller mill) or a worm gear mill. Preferably, the milling apparatus is a worm gear milling apparatus. The milling step can be performed under inert conditions, i.e. in the absence of air or oxygen and/or in the absence of water (vapour). The thermal treatment is preferably a heating step. The heating step preferably involves heating at a temperature in the range of 30- 120 °C, more preferably 40-110 °C and in particular 45- 90 °C. In this heating step, the water content of the amorphous hydrophilic metal oxide particles is reduced, preferably to a water content of the metal oxide particles of less than 5% by weight, more preferably less than 1% by weight, even more preferably less than 0.5% by weight, yet even more preferably less than 0.25% by weight, based on the total weight of the metal oxide particles. The water content of the metal oxide particles is usually more than 0.01% by weight, based on the total weight of the metal oxide particles. Most preferably, the grease composition is manufactured by optionally subjecting hydrophilic metal oxide particles to a thermal treatment, preferably a heating step, to reduce the water content of the metal oxide particles, followed by mixing the hydrophilic metal oxide particles with the base oil and the one or more metal salts of fatty acids that contain two or more unsaturated C-C bonds to form a grease composition, whereafter the grease composition so formed is subjected to a mechanical treatment, preferably a milling step. As disclosed above, the grease composition according to the present invention comprises a base oil, hydrophilic metal oxide particles, in particular hydrophilic silicon oxide particles, and one or more metal salts fatty acids which contain two or more unsaturated C-C bonds, wherein the amount of the thickener is 0.1-40% by weight, based on the total weight of the grease composition.

Suitably, the amount of the hydrophilic metal oxide particles will be 0.1-20% by weight, preferably 1-5% by weight, based on the total weight of the thickener. The skilled person will understand how such amounts can be realised starting from the respective starting materials.

According to a preferred embodiment of the present invention, the total amount of the metal salts of fatty acids is within a range of 0.1-30% by weight, preferably within the range of 0.1- 20% by weight, based on the total amount of the thickener. The grease composition according to the present invention can be used in many applications. However, it is in particular useful for lubricating a bearing, preferably a rolling element bearing, e g. a spherical roller bearing, a taper roller bearing, a cylindrical roller bearing, a needle roller bearing, a ball bearing, and may also be used to lubricate a sliding or plain bearing It is furthermore very useful in coupling and gearing applications.

The grease compositions according to the present invention encompass NLGI (National Lubricating Grease Institute) grades ranging from NLGI grade 000 to NLGI grade 6.

Preferably, the grease compositions according to the present invention have a dropping point of at least 70 °C up to about 200 °C according to ASTM D-2265.

When used in low loading gearings, the grease composition has preferably a NLGI grade of 000 to 1. When used in high loading gearings, the grease composition has preferably a NLGI grade of 0 to 2. When used in bearings, the grease composition has preferably a NLGI grade of 1 to 4, more preferably a NLGI grade of 2 or 3 and most preferably a NLGI grade of 2.