Water-based gear oil

Abstract

The present invention relates to a lubricant composition comprising: - from 10 to 75% by weight of water, - from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG1) having a kinematic viscosity at 40°C of at least 10000 cSt, - from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG2) having a kinematic viscosity at 40°C of less than 10000 cSt, based on the total weight of the lubricant composition.

Description

FIELD OF THE INVENTION

[0001] The present invention concerns lubricant compositions based on water and having suitable viscosity for their use in the lubrification of gears, in particular industrial gears. The present invention concerns in particular compositions having a low carbon footprint. In particular, the present invention concerns lubricant compositions based on water and having improved stability and viscosity.TECHNICAL BACKGROUND OF THE INVENTION

[0002] Lubricants are used in industrial applications. Gears are subjected to strong constraints and lubricants used in gears should have particularly good performances.

[0003] Currently along with some performance additives, all industrial gear oils are made with Group-I, Group II, and Group III base oils or with polyalphaolefins (PAO). These base oils are derived from the distillation of crude oils which has a high carbon footprint.

[0004] Lubricant manufacturers try to find solutions with a lower carbon footprint. Water-based lubricants appeared. However, beyond the carbon footprint, lubricant compositions should also have good properties and provide satisfying performances.

[0005] Document US 2012 / 0149616 discloses water-based lubricants comprising one high molecular weight polyalkylene glycol and additive(s) comprising fatty (long) chain(s).

[0006] Gear lubricant compositions for industrial use must have a suitable viscosity and also meet highly specific specifications in terms of performance, in particular in terms of stability.

[0007] There is therefore an advantage in providing lubricant compositions which meet all the specific tests for gear lubricant compositions, that have a low carbon footprint.

[0008] It is one objective of the present invention to provide a lubricant composition having improved viscosity and a low carbon footprint.SUMMARY OF THE INVENTION

[0009] These objectives are reached with a novel gear lubricant composition.

[0010] The invention concerns a lubricant composition comprising: from 10 to 75% by weight of water, from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG1) having a kinematic viscosity at 40°C of at least 10000 cSt, from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG2) having a kinematic viscosity at 40°C of less than 10000 cSt, based on the total weight of the lubricant composition.

[0011] Preferably, the lubricant composition is characterized by one or more of the following features: the ratio between the kinematic viscosity at 40°C of PAG1 and PAG2 is higher than 1.5, preferably higher than 2, more preferably higher than 2.5, even more preferably higher than 3.5, and / or PAG1 has a kinematic viscosity at 40°C ranging from 10000 to 35000 cSt and / or PAG2 has a kinematic viscosity at 40°C ranging from 100 to 5000 cSt, preferably from 100 to 1000 cSt, and / or the PAG1 has an average molecular weight ranging from 8000 g / mol to 50000 g / mol, preferably from 9000 to 40000 g / mol, more preferably from 10000 to 30000 g / mol, even more preferably from 11000 to 20000 g / mol, and / or the PAG2 has an average molecular weight ranging from 500 to 7500 g / mol, preferably from 700 to 6000 g / mol, more preferably from 1000 to 5000 g / mol, even more preferably from 2000 to 4000 g / mol, and / or the lubricant composition comprises: ∘ from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, ∘ from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1, ∘ from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2, based on the total weight of the lubricant composition, and / or PAG1 and PAG2 comprises ethylene oxide units and optionally propylene oxide units. the lubricant composition comprises: ∘ from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, ∘ from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1, ∘ from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2, ∘ from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more functional additive(s) different from polyalkylene glycol, the additive(s) being preferably selected from anti-wear additives, extreme-pressure additives, metal deactivators, corrosion inhibitors, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof. based on the total weight of the lubricant composition, and / or the lubricant composition further comprises at least one functional additive selected from corrosion inhibitors, at least one corrosion inhibitor being preferably selected from carboxylic acids having less than 12 carbon atoms, and / or the lubricant composition has a kinematic viscosity at 40°C ranging from 10 cSt to 1000 cSt, preferably from 10 to 460 cSt, and / or the lubricant composition comprises: ∘ from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, ∘ from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 10000 cSt to 35000 cSt, ∘ from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 100 to 5000 cSt, preferably from 100 to 1000 cSt, ∘ from 0.1 to 10% by weight, preferably from 1 to 5% by weight, of at least one carboxylic acid, wherein the carboxylic acid(s) have less than 12 carbon atoms, ∘ optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more additive(s) selected from anti-wear and / or extreme-pressure additives, metal deactivators, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof, based on the total weight of the lubricant composition.

[0012] The invention also relates to the use of the lubricant composition according to the invention as a lubricant in industrial applications, preferably as industrial gear lubricant.

[0013] The invention also relates to a gear lubricating method comprising applying the lubricant composition according to the invention, to gears.

[0014] The invention also relates to a gear coated with the lubricant composition according to the invention.

[0015] The invention also relates to the use of a mixture of two polyalkylene glycol PAG1 and PAG2 in a lubricant composition in order to improve the viscosity of the lubricant composition, wherein PAG1 has a kinematic viscosity at 40°C of at least 10000 cSt and PAG2 has a kinematic viscosity at 40°C of less than 10000 cSt, wherein the resulting lubricant composition comprises: from 10 to 75% by weight of water, from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG1) having a kinematic viscosity at 40°C of at least 10000 cSt, from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG2) having a kinematic viscosity at 40°C of less than 10000 cSt, preferably of less than 1000 cSt, based on the total weight of the lubricant composition.

[0016] Preferably, within the context of the use of the mixture of two PAG, the resulting lubricant composition is characterized by one or more of the following features: the ratio between the kinematic viscosity at 40°C of PAG1 and PAG2 is higher than 1.5, preferably higher than 2, more preferably higher than 2.5, even more preferably higher than 3.5, and / or PAG1 has a kinematic viscosity at 40°C ranging from 10000 to 35000 cSt and / or PAG2 has a kinematic viscosity at 40°C ranging from 100 to 5000 cSt, preferably from 100 to 1000 cSt, and / or the PAG1 has an average molecular weight ranging from 8000 g / mol to 50000 g / mol, preferably from 9000 to 40000 g / mol, more preferably from 10000 to 30000 g / mol, even more preferably from 11000 to 20000 g / mol, and / or the PAG2 has an average molecular weight ranging from 500 to 7500 g / mol, preferably from 700 to 6000 g / mol, more preferably from 1000 to 5000 g / mol, even more preferably from 2000 to 4000 g / mol, and / or the lubricant composition comprises: ∘ from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, ∘ from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1, ∘ from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2, based on the total weight of the lubricant composition, and / or PAG1 and PAG2 comprises ethylene oxide units and optionally propylene oxide units. the lubricant composition comprises: ∘ from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, ∘ from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1, o from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2, ∘ from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more functional additive(s) different from polyalkylene glycol, the additive(s) being preferably selected from anti-wear additives, extreme-pressure additives, metal deactivators, corrosion inhibitors, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof. based on the total weight of the lubricant composition, and / or the lubricant composition further comprises at least one functional additive selected from corrosion inhibitors, at least one corrosion inhibitor being preferably selected from carboxylic acids having less than 12 carbon atoms, and / or the lubricant composition has a kinematic viscosity at 40°C ranging from 10 cSt to 1000 cSt, preferably from 10 to 460 cSt, and more preferably from 10 to 100 cSt, and / or the lubricant composition comprises: ∘ from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, ∘ from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 10000 cSt to 35000 cSt, ∘ from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 100 to 5000 cSt, preferably from 100 to 1000 cSt, ∘ from 0.1 to 10% by weight, preferably from 1 to 5% by weight, of at least one carboxylic acid, wherein the carboxylic acid(s) have less than 12 carbon atoms, ∘ optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more additive(s) selected from anti-wear and / or extreme-pressure additives, metal deactivators, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof, based on the total weight of the lubricant composition.

[0017] The lubricant compositions of the invention have less carbon footprint than oil-based lubricant compositions.

[0018] The lubricant compositions of the invention have good thermal properties.

[0019] The lubricant compositions of the invention have a very low coefficient of friction, and thus a high energy efficiency.

[0020] The lubricant compositions of the invention have a low pour point and a high viscosity index.

[0021] The lubricant compositions of the invention fulfil the tribology required from gear oil requirements as per ISO 12925-1, notably good load properties.

[0022] The lubricant compositions of the invention have suitable grades of viscosity.

[0023] The lubricant compositions of the invention have improved stability.DETAILED DESCRIPTION OF THE FIGURES

[0024] Figure 1 shows the coefficient of friction of lubricant compositions.DETAILED DESCRIPTION OF THE INVENTION

[0025] The invention first concerns a lubricant composition comprising: from 10 to 75% by weight of water, from 2 to 50% by dry weight of at least one polyalkylene glycol PAG1 having a kinematic viscosity at 40°C of at least 10000 cSt, from 2 to 50% by dry weight of at least one polyalkylene glycol PAG2 having a kinematic viscosity at 40°C of less than 10000 cSt, based on the total weight of the lubricant composition, the ratio between the kinematic viscosity at 40°C of PAG1 and the kinematic viscosity at 40°C of PAG2 being strictly greater than 1.

[0026] Within the present invention, the kinematic viscosity at 40°C of PAG (for example of PAG1 and of PAG2) can be measured according to ASTM D445.

[0027] The average molecular weight of PAG1 and PAG2 can be measured by methods well known for the skilled person, for example by size exclusion chromatography using polystyrene standard.

[0028] Typically, PAG1 and PAG2 used in the present invention are obtained by (co)polymerisation of alkylene glycol(s) comprising from 2 to 4 carbon atoms, for example by random copolymerisation.

[0029] The amount of water allows having both a low evaporation, a good thermal behaviour and low friction coefficient. The lubricant composition of the invention comprises from 10 to 75%wt of water, preferably from 10 to 50%wt, more preferably from 20 to 40%wt of water, based on the total weight of the lubricant composition.

[0030] The inventors found that the combination of PAG1 and PAG2 as defined in the invention allows to reach all grades of viscosities, from 10 to 1000 cSt at 40°C.

[0031] According to an embodiment, the lubricant composition has a kinematic viscosity at 40°C from 10 to 460 cSt.Polyalkylene glycol (PAG1)

[0032] The lubricant composition comprises at least one PAG1 having a kinematic viscosity at 40°C of at least 10000 cSt, preferably from 10000 to 35000 cSt.

[0033] According to an embodiment, the PAG1 has an average molecular weight of at least 7500 g / mol. Preferably, the PAG1 has an average molecular weight ranging from 8000 g / mol to 50000 g / mol, preferably from 9000 to 40000 g / mol, more preferably from 10000 to 30000 g / mol, even more preferably from 11000 to 20000 g / mol.

[0034] PAG1 can be a homopolymer or a copolymer.

[0035] According to an embodiment, PAG1 comprises ethylene oxide units and optionally propylene oxide units. Preferably, PAG1 consists of ethylene oxide units and optionally propylene oxide units.

[0036] According to an embodiment, PAG1 is a copolymer comprising ethylene units and propylene oxide units.

[0037] Within the meaning of the present invention, "ethylene oxide unit" is a unit of formula -CH 2 -CH 2 -O-.

[0038] Within the meaning of the present invention, "propylene oxide unit" is a unit of formula -(CH 3 )CH-CH 2 -O-.

[0039] Preferably, when PAG1 comprises ethylene oxide units and propylene oxide units, the molar ratio ethylene oxide units / propylene oxide units is higher than 1, preferably ranges from higher than 1 to 4, more preferably from higher than 1 to 3.

[0040] PAG1 can be synthetized according to processes known for the skilled person. PAG1 is also commercially available.

[0041] Preferably, PAG1 is selected from biodegradable polyalkylene glycol.

[0042] The lubricant composition comprises from 2 to 50% by dry weight of at least one PAG1. Preferably, the lubricant composition comprises from 2 to 50% by dry weight of one or more PAG1.

[0043] According to an embodiment, the lubricant composition comprises from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one PAG1. Preferably, the lubricant composition comprises from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of one or more PAG1.Polyalkylene glycol (PAG2)

[0044] The lubricant composition comprises at least one PAG2 having a kinematic viscosity at 40°C of less than 10000 cSt, preferably from 100 to 5000 cSt, and more preferably from 100 to 1000 cSt.

[0045] According to an embodiment, the PAG2 has an average molecular weight of less than 7000 g / mol.

[0046] Preferably, the PAG2 has an average molecular weight ranging from 500 to 7500 g / mol, preferably from 700 to 6000 g / mol, more preferably from 1000 to 5000 g / mol, even more preferably from 2000 to 4000 g / mol.

[0047] PAG2 can be a homopolymer or a copolymer.

[0048] According to an embodiment, PAG2 comprises ethylene oxide units and optionally propylene oxide units. Preferably, PAG2 consists of ethylene oxide units and optionally propylene oxide units.

[0049] According to an embodiment, PAG2 is a copolymer comprising ethylene units and propylene oxide units.

[0050] Preferably, when PAG2 comprises ethylene oxide units and propylene oxide units, the molar ratio ethylene oxide units / propylene oxide units is higher than 1, preferably ranges from 1.5 to 5, more preferably from 2 to 4.

[0051] PAG2 can be synthetized according to processes known for the skilled person. PAG2 is also commercially available.

[0052] Preferably, PAG2 is selected from biodegradable polyalkylene glycol.

[0053] The lubricant composition comprises from 2 to 50% by dry weight of at least one PAG2. Preferably, the lubricant composition comprises from 2 to 50% by dry weight of one or more PAG2.

[0054] According to an embodiment, the lubricant composition comprises from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight of at least one PAG2. Preferably, the lubricant composition comprises from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight of one or more PAG2.Lubricant composition

[0055] According to an embodiment of the lubricant composition, the ratio between the kinematic viscosity at 40°C of PAG1 and PAG2 is higher than 1.5, preferably higher than 2, more preferably higher than 2.5, even more preferably higher than 3.5.

[0056] According to an embodiment of the lubricant composition, the ratio between the molecular weight of PAG1 and PAG2 is higher than 1.5, preferably higher than 2, more preferably higher than 2.5, even more preferably higher than 3.5.

[0057] Preferably, the lubricant composition comprises: from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of PAG1, from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of PAG2, based on the total weight of the lubricant composition.

[0058] The lubricant composition preferably comprises at least one additive, different from polyalkylene glycol, the at least one additive being preferably selected from anti-wear additives, extreme-pressure additives, metal deactivators, corrosion inhibitors, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof.

[0059] Typically, the additive(s) of the lubricant composition do not comprise carbon atom chains of more than 12 carbon atoms, the carbon atom chains can be linear or branched, being noted that according to this preferred embodiment, one additive can comprise several carbon atom chains having less than 12 carbon atoms.

[0060] According to an embodiment, the lubricant composition comprises, based on the total weight of the lubricant composition, from 0.1 to 40% by weight, preferably from 10 to 30% by weight, of one or more additive(s), the additive(s) being preferably selected from anti-wear additives, extreme-pressure additives, metal deactivators, corrosion inhibitors, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof.

[0061] According to an embodiment, the lubricant composition comprises at least one anti-wear additives and / or extreme-pressure additives.

[0062] Anti-wear additives and extreme-pressure additives protect surfaces against friction through the forming of a protective film adsorbed on these surfaces. There is a large variety of anti-wear additives. Preferably, some additives are both anti-wear and extreme-pressure additives.

[0063] Preferably, for the lubricant composition of the invention, the anti-wear and / or extreme-pressure additives are selected from among phosphorus-containing additives, sulfurous-containing additives, sulfur-phosphorous containing additives, and mixtures thereof.

[0064] Preferably, the anti-wear and / or extreme-pressure additives are selected from phosphates, phosphites, phosphorothionates, phosphonates, dithiophosphates, thiophosphates, dimercaptothiadiazoles, thiadiazoles, and mixtures thereof, more preferably from phosphates, phosphites, phosphonates, dimercaptothiadiazoles, thiadiazoles, and mixtures thereof. Within the meaning of the present invention, these anti-wear and / or extreme-pressure additives can be substituted by one or more aliphatic groups.

[0065] The anti-wear and / or extreme-pressure additive(s) may represent from 0.1 to 15%wt of the total weight of the lubricant composition, preferably from 0.5 to 10%wt of the total weight of the lubricant composition.

[0066] Within the meaning of the present invention, "aliphatic group" means a group that is not aromatic. The aliphatic group can be cyclic, linear or branched. Preferably, it is linear or branched.

[0067] The aliphatic group can be an alkyl or an alkenyl group. Preferably, the anti-wear and / or extreme-pressure additive(s) does not comprise alkyl group nor alkenyl group having more than 11 carbon atoms.

[0068] The low carbon atom chain length allows to improve the stability of the lubricant composition.

[0069] According to an embodiment, the lubricant composition comprises at least one anticorrosion additive.

[0070] Among anticorrosion additives that can be used in the lubricant composition of the invention, mention can be made of triazine-containing corrosion inhibitors, carboxylic acids comprising carbon atom chains having less than 12 carbon atoms and mixtures thereof.

[0071] The carboxylic acids may be selected from compounds of formula R1-COOH, wherein R1 is a linear or branched alkyl radical comprising less than 12 carbon atoms.

[0072] Preferably, the carboxylic acid(s) of the lubricant composition of the invention comprises from 4 to 10 carbon atoms. Among carboxylic acids, mention may be made of hexanoic acid, octanoic acid or decanoic acid.

[0073] The corrosion inhibitor(s) can represent from 0.1 to 10% by weight, preferably from 0.5 to 5% by weight, of the total weight of the lubricant composition.

[0074] According to an embodiment, the lubricant composition comprises from 0.5 to 10% by weight, preferably from 1 to 5% by weight, of at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0075] According to a specific embodiment, the carboxylic acid(s) of the lubricant composition represent from 1.4% to 4% by weight of the total weight of the lubricant composition.

[0076] The inventors surprisingly found that by adding carboxylic acid(s) having less than 12 carbon atoms in a composition comprising water and PAG(s), the stability of the composition is further improved, in particular the inventors found that the solubility of the ingredients, in particular of the PAG(s) is further improved thanks to the carboxylic acid(s) having less than 12 carbon atoms.

[0077] Among metal-deactivators, mention can be made of tolyltriazole, derivatives of tolyltriazole or dimercaptothiadiazoles. The metal-deactivator particularly allows neutralisation of the catalytic effect of metals such as copper and iron.

[0078] By « derivative of tolyltriazole » it is meant a tolyltriazole compound substituted preferably by one of more alkyl groups optionally comprising one or more heteroatoms.

[0079] The metal deactivator(s) can represent from 0.05 to 5% by weight, preferably from 0.1 to 2% by weight, of the total weight of the lubricant composition.

[0080] Among pH boosters, mention may be made of alkanolamines.

[0081] The pH booster(s) can represent from 0.1 to 15% by weight, preferably from 1 to 10% by weight, of the total weight of the lubricant composition.

[0082] Among anti-freeing agent(s), mention may be made of monoalkylene glycol.

[0083] The anti-freezing agent(s) can represent from 0.1 to 15% by weight, preferably from 1 to 10% by weight, of the total weight of the lubricant composition.

[0084] Among the anti-foam additives that can be used in the lubricant composition of the invention, mention can be made of silicone compounds and polyacrylate compounds.

[0085] The anti-foam agent(s) can represent from 0.001 to 2% by weight, preferably from 0.01 to 1% by weight, of the total weight of the lubricant composition.

[0086] Among lubricity enhancers, mention may be made of esters comprising carbon atom chains having less than 12 carbon atoms.

[0087] According to a preferred embodiment, the lubricant composition has a kinematic viscosity at 40°C ranging from 10 to 1000 cSt, preferably from 20 to 460 cSt, and more preferably from 30 to 100 cSt.

[0088] The kinematic viscosity can be measured according to ASTM D445 standard.

[0089] According to a preferred embodiment, the lubricant composition comprises: from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1 comprising ethylene oxide units and optionally propylene oxide units, from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2 comprising ethylene oxide units and optionally propylene oxide units, optionally from 0.1 to 40% by dry weight, preferably from 1 to 30% by dry weight, of one or more additive(s) selected from anti-wear additives, extreme-pressure additives, metal deactivators, corrosion inhibitors, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof, based on the total weight of the lubricant composition.

[0090] According to a preferred embodiment, the lubricant composition comprises: from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 10000 to 35000 cSt, from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 100 to 5000 cSt, preferably from 100 to 1000 cSt, optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more additive(s) selected from anti-wear additives, extreme-pressure additives, metal deactivators, corrosion inhibitors, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof, based on the total weight of the lubricant composition.

[0091] According to a preferred embodiment, the lubricant composition comprises: from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 10000 to 35000 cSt, from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 100 to 5000 cSt, preferably from 100 to 1000 cSt, from 0.1 to 10% by weight, preferably from 1 to 5% by weight, of at least one carboxylic acid, wherein the carboxylic acid(s) have less than 12 carbon atoms, optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more additive(s) selected from anti-wear and / or extreme-pressure additives, metal deactivators, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof, based on the total weight of the lubricant composition.

[0092] According to a preferred embodiment, the lubricant composition comprises: from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 10000 to 35000 cSt, from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 100 to 5000 cSt, preferably from 100 to 1000 cSt, from 0.1 to 10% by weight, preferably from 1 to 5% by weight, of at least one carboxylic acid, wherein the carboxylic acid(s) have less than 12 carbon atoms, optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more additive(s) selected from anti-wear and / or extreme-pressure additives, metal deactivators, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof, based on the total weight of the lubricant composition, wherein if the functional additive(s) comprise(s) aliphatic carbon chain(s), the aliphatic carbon chains have less than 12 carbon atoms.

[0093] The lubricant composition can be prepared according to processes well known by the skilled person to formulate lubricant compositions, for example by mixing ingredients at a temperature ranging from 20 to 60°C.Applications

[0094] The lubricant composition according to the invention can be used as a gear lubricant.

[0095] Preferably, the lubricant composition is used in industrial applications.

[0096] According to this embodiment, the lubricant composition is used as an industrial gear lubricant, in particular in the manufacturing industry sectors, and for geared equipment likely to come into contact with the environment (water, air, etc.) or with individuals.

[0097] In one embodiment of the invention, the lubricant composition is used in industrial gearing, in particular industrial gearing on offshore installations. Among offshore installations, mention can be made of offshore wind turbines.

[0098] In one embodiment of the invention, the lubricant composition is used on gears intended to come into contact with water.

[0099] In one embodiment of the invention, the lubricant composition is used at temperatures in the range of from 50 to 400°C, preferably in the range of from 100 to 300°C.

[0100] The invention also concerns a gear lubricating method comprising applying the lubricant composition according to the invention to gears.

[0101] The gears can be gears of industrial devices.

[0102] In one embodiment, the lubricant composition used in the lubricating method of the invention has one or more of the characteristics detailed above.

[0103] In one embodiment of the invention, the lubricant composition is used on industrial gears, in particular industrial gears on offshore installations. Among offshore installations, mention can be made of offshore wind turbines.

[0104] In one embodiment of the invention, the temperature of use of the lubricant composition is in the range of from 50 to 400°C, preferably from 100 to 300°C.

[0105] The invention describes a gear coated with the lubricant composition according to the invention.

[0106] The gear can be a gear implemented in an industrial gear.

[0107] In one embodiment, the gear is an industrial gear, in particular an industrial gear for offshore installations. Among offshore installations, mention can be made of wind turbines.

[0108] The invention is also directed to the use of a mixture of two polyalkylene glycol (PAG1 and PAG2) in a lubricant composition in order to improve the viscosity of the lubricant composition, wherein PAG1 has a kinematic viscosity at 40°C of at least 10000 cSt and PAG2 has a kinematic viscosity at 40°C of less than 10000 g / mol, wherein the ratio between the kinematic viscosity at 40°C of PAG1 and the kinematic viscosity at 40°C of PAG2 is strictly greater than 1, and wherein the resulting lubricant composition comprises: from 10 to 75% by weight of water, from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG1) having a kinematic viscosity at 40°C of at least 10000 cSt, from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG2) having a kinematic viscosity at 40°C of less than 10000 cSt, preferably of less than 1000 cSt, based on the total weight of the lubricant composition.

[0109] The resulting lubricant composition is the composition comprising: from 10 to 75% by weight of water, from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG1) having a kinematic viscosity at 40°C of at least 10000 cSt, from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG2) having a kinematic viscosity at 40°C of less than 10000 cSt, preferably of less than 1000 cSt, based on the total weight of the lubricant composition, obtained after adding the mixture of PAG.

[0110] Within the context of the use of the mixture of two PAG, the acid, PAG1 and PAG2 and more generally the lubricant composition may comprise one or more of the characteristics defined for the lubricant composition of the invention.

[0111] The inventors found that the mixture of PAG1 and PAG2 as defined in the present invention allows to improve the viscosity of the composition comprising water.EXAMPLES

[0112] In the remainder of the present description, examples are given for the purpose of illustrating the present invention which are in no way intended to limit the scope thereof.Example 1: Preparation of a lubricant composition

[0113] Lubricant composition CI1 were prepared with the ingredients and amounts listed in Table 1. Table 1: Composition CI1ingredients nature Cl1 Water25% by weightPAG1Polyalkylene glycol having a kinematic viscosity at 40°C of about 17000-19000 cSt and consisting of 75% weight of ethylene oxide units and 25% by weight of propylene oxide units16% by dry weightPAG2Polyalkylene glycol having a kinematic viscosity at 40°C of about 400-500 cSt and consisting of ethylene oxide units and of propylene oxide units33.2% by dry weightCorrosion inhibitorCarboxylic acid having a chain length of less than 12 carbon atoms1.5% by dry weightAdditive packageAnti-wear and / or extreme pressure additives, metal deactivators, corrosion inhibitor, anti-freezing agent, pH booster, anti-foam, lubricity additive28.3% by dry weight

[0114] The viscosity at 40°C of CI1 is of 320 cSt. The combination of a low molecular weight polyalkylene glycol with a medium molecular weight polyalkylene glycol allows to have an improved viscosity for the target applications.Example 2: Coefficient of friction (COF) and lubricity

[0115] The lubricant composition CI1 detailed in example 1 is compared with a commercially available gear lubricant composition based on PAO (CC2).

[0116] The coefficient of friction (COF) is measured for different rolling speed with a MTM method with the following test conditions (ball on disk test): Rolling speed: 10 to 3100 mm / s; Temperature: 40°C; Load:50N; Sliding to roll ratio (SRR): 50%.

[0117] Figure 1 shows that the lubricant composition CI1 (straight line) shows a much lower COF than the comparative composition CC2 based on PAO (line interrupted with A). This lubricity performance also helps to get good energy efficiency.Example 3: FZG test

[0118] The performances of anti-wear and scuffing of the lubricant composition CI1 detailed in example 1 are measured using the FZG 1 as per CEC L-07-95 Mod (A / 8.3 / 60).

[0119] The lubricant composition CI1 passes failer load stage > 12. These results are similar to PAO based gear lubricant compositions. It was also observed a weight loss at the 12 th< stage of 0.001g meaning that the lubricant composition CI1 shows no wear at the FZG test.Example 4: bearing test

[0120] The performances of anti-wear of rolling bearing of the lubricant composition CI1 detailed in example 1 are measured using the FAG FE8 as per DIN 51819-3 mod (D-7.5 / 80-60).

[0121] The lubricant composition CI1 passes the bearing test as per the standard specification for gear oil as per DIN 51819-3 mod (D-7.5 / 80-60). As per the test specification, the roller weight should be less than 30 mg, the pass results of an average of 26 mg pass result was obtained.Example 5: Thermal behavior

[0122] The specific heat capacity (Cp) of the lubricant composition CI1 of example 1 was compared with the specific heat capacity of a PAO based lubricant CC2.

[0123] The results for different temperatures are detailed in table 2. Table 2: specific heat capacity (Cp) expressed in J.g -1< °C -1< Temperature (°C) Cp of CC2 (J.g -1< .°C -1< ) Cp of Cl1 (J.g -1< .°C-1) 102.273.313202.333.2302.413.25402.493.31502.573.39602.643.45682.73.51

[0124] Table 2 shows that the specific heat capacity of the lubricant composition of the invention is higher than the specific heat capacity of PAO based lubricant composition. The lubricant composition of the invention has thus improved thermal properties.Example 6: Physicochemical properties

[0125] Physicochemical properties of the lubricant composition CI1 of the invention were measured and the results are detailed in table 3. Table 3: Physicochemical propertiesTest Parameter Standard Results Viscosity @ 40°CASTM D445332.83Viscosity @ 20°CASTM D4451012.52Viscosity indexASTM 2270163pHASTM D 12879Pour point, °CASTM D97-42Copper corrosion, 80 °C, 7 hASTM D1301aCopper corrosion, 80 °C, 24 hASTM D1301bSteel corrosion, method B, 24 hASTM D665PassWeld load, KgASTM D2783315Scar dia., mm @ 30 °CASTM D41720.728FZG-1CEC L-07-95>12FZG-6CEC L-84-02>12FAG FE8Din 51819-3Pass (26 mg)Foaming Seq 1 25°, mLASTM D89210 / 0Foaming Seq 2 60°C, mL10 / 0Foaming Seq 3 25°C, mL10 / 0ARV at 75°CASTM25.4 minD3427 / ISO9120

[0126] The results of Table 3 show the good performances of the lubricant composition of the invention, in particular in terms of deaeration, anticorrosion, and viscosity. The low pour point shows that the lubricant composition can be operated at low temperature.

[0127] In summary of the examples, the lubricant compositions of the invention have a low carbon footprint, a low coefficient of friction, a low pour point, a high viscosity index, a good thermal conductivity and heat dissipation.

Claims

1. Lubricant composition comprising: - from 10 to 75% by weight of water, - from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG1) having a kinematic viscosity at 40°C of at least 10000 cSt, - from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG2) having a kinematic viscosity at 40°C of less than 10000 cSt, based on the total weight of the lubricant composition.

2. Lubricant composition according to claim 1, wherein the ratio between the kinematic viscosity at 40°C of PAG1 and PAG2 is higher than 1.5, preferably higher than 2, more preferably higher than 2.5, even more preferably higher than 3.5.

3. Lubricant composition according to claim 1 or 2, wherein PAG1 has a kinematic viscosity at 40°C ranging from 10000 to 35000 cSt and / or PAG2 has a kinematic viscosity at 40°C ranging from 100 to 5000 cSt, preferably from 100 to 1000 cSt.

4. Lubricant composition according to any one of claims 1 to 3, wherein the PAG1 has an average molecular weight ranging from 8000 g / mol to 50000 g / mol, preferably from 9000 to 40000 g / mol, more preferably from 10000 to 30000 g / mol, even more preferably from 11000 to 20000 g / mol, and / or the PAG2 has an average molecular weight ranging from 500 to 7500 g / mol, preferably from 700 to 6000 g / mol, more preferably from 1000 to 5000 g / mol, even more preferably from 2000 to 4000 g / mol.

5. Lubricant composition according to any one of claims 1 to 4, comprising: - from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, - from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1, - from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2, based on the total weight of the lubricant composition.

6. Lubricant composition according to any one of claims 1 to 5, wherein PAG1 and PAG2 comprises ethylene oxide units and optionally propylene oxide units.

7. Lubricant composition according to any one of claims 1 to 6, comprising: - from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, - from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1, - from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2, - from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more functional additive(s) different from polyalkylene glycol, the additive(s) being preferably selected from anti-wear additives, extreme-pressure additives, metal deactivators, corrosion inhibitors, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof. based on the total weight of the lubricant composition.

8. Lubricant composition according to claim 7, wherein at least one functional additive is selected from corrosion inhibitors, at least one corrosion inhibitor being preferably selected from carboxylic acids having less than 12 carbon atoms.

9. Lubricant composition according to any one of claims 1 to 8, having a kinematic viscosity at 40°C ranging from 10 cSt to 1000 cSt, preferably from 20 to 460 cSt, more preferably from 30 to 100 cSt.

10. Lubricant composition according to any one of claims 1 to 9, comprising: - from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, - from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight of at least one polyalkylene glycol PAG1 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 10000 cSt to 35000 cSt, - from 10 to 50% by dry weight, preferably from 15 to 40% by dry weight, of at least one polyalkylene glycol PAG2 comprising ethylene oxide units and propylene oxide units and having a kinematic viscosity at 40°C ranging from 100 to 5000 cSt, preferably from 100 to 1000 cSt, - from 0.1 to 10% by weight, preferably from 1 to 5% by weight, of at least one carboxylic acid, wherein the carboxylic acid(s) have less than 12 carbon atoms, - optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more additive(s) selected from anti-wear and / or extreme-pressure additives, metal deactivators, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof, based on the total weight of the lubricant composition.

11. Use of the lubricant composition according to any one of the preceding claims as a lubricant in industrial applications, preferably as industrial gear lubricant.

12. A gear lubricating method comprising applying the lubricant composition according to any one of claims 1 to 10, to gears.

13. Gear coated with the lubricant composition according to any one of claims 1 to 10.

14. Use of a mixture of two polyalkylene glycol PAG1 and PAG2 in a lubricant composition in order to improve the viscosity of the lubricant composition, wherein PAG1 has a kinematic viscosity at 40°C of at least 10000 cSt and PAG2 has a kinematic viscosity at 40°C of less than 10000 cSt, wherein the resulting lubricant composition comprises: - from 10 to 75% by weight of water, - from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG1) having a kinematic viscosity at 40°C of at least 10000 cSt, - from 2 to 50% by dry weight of at least one polyalkylene glycol (PAG2) having a kinematic viscosity at 40°C of less than 10000 cSt, preferably of less than 1000 cSt, based on the total weight of the lubricant composition.

15. Use according to claim 14, wherein the lubricant composition is as defined in any one of claims 2 to 10.

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