Water-based industrial gear oil

Abstract

The present invention relates to a lubricant composition having a kinematic viscosity at 40°C of at least 150 cSt, the lubricant composition comprising: - from 10 to 75% by weight of water, - from 2 to 80% by dry weight of at least one polyalkylene glycol (PAG), - from 0.1 to 20% by weight of at least one carboxylic acid having less than 12 carbon atoms, 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 stability and 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.TECHNICAL BACKGROUND OF THE INVENTION

[0002] 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.

[0003] 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.

[0004] 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.

[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] 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.

[0007] It is one objective of the present invention to provide a lubricant composition having improved viscosity and stability as well as a low carbon footprint.SUMMARY OF THE INVENTION

[0008] These objectives are reached with a novel gear lubricant composition.

[0009] The invention concerns a lubricant composition having a kinematic viscosity at 40°C of at least 150 cSt, the lubricant composition comprising: from 10 to 75% by weight of water, from 2 to 80% by dry weight of at least one polyalkylene glycol (PAG), from 0.1 to 20% by weight of at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0010] Preferably, the lubricant composition is characterized by one or more of the following features: the carboxylic acid(s) comprises from 4 to 10 carbon atoms, and / or the lubricant composition further comprises at least one anti-wear and / or extreme-pressure additive, preferably selected from phosphorus compounds, sulfurous compounds, sulfur-phosphorous compounds, and mixtures thereof, preferably from phosphorus compounds, sulfurous compounds, and mixtures thereof, and / or the at least one polyalkylene glycol (PAG) comprises ethylene oxide units and optionally propylene oxide units, and / or the at least one polyalkylene glycol (PAG) has a kinematic viscosity at 40°C ranging from 5000 to 60000 cSt, preferably from 10000 to 35000 cSt, and / or the at least one polyalkylene glycol (PAG) has an average molecular weight ranging from 8000 to 50000 g / mol, preferably from 11000 g / mol to 20000 g / mol, and / or the at least one polyalkylene glycol (PAG) comprises a mixture of two polyalkylene glycol PAG1 and PAG2, PAG1 having 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, PAG2 having 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 having a kinematic viscosity at 40°C of at least 10000 cSt, ∘ from 10 to 50% by dry weight, preferably from 15 to 40% 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 1 000 cSt, ∘ 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, ∘ optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more functional 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, wherein at least one of the functional additive(s) is an anti-wear and / or extreme-pressure additive. based on the total weight of the lubricant composition, and / or the lubricant composition has a kinematic viscosity at 40°C ranging from 150 cSt to 750 cSt.

[0011] The invention also relates to the use of the lubricant composition according to the invention as a gear lubricant, preferably an industrial gear lubricant.

[0012] The invention also relates to a gear lubricating method comprising applying the lubricant composition according to the invention, to gears.

[0013] The invention also relates to a gear coated with the lubricant composition according to the invention.

[0014] The invention also relates to the use of at least one carboxylic acid having less than 12 carbon atoms in a lubricant composition to improve the stability of the lubricant composition having a kinematic viscosity at 40°C of at least 150 cSt, wherein the resulting lubricant composition comprises: from 10 to 75% by weight of water, from 2 to 80% by dry weight of the at least one polyalkylene glycol (PAG), from 0.1 to 20% by weight of the at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0015] Preferably, within the context of the use of the carboxylic acid having less than 12 carbon atoms, the resulting lubricant composition is characterized by one or more of the following features: the carboxylic acid(s) comprises from 4 to 10 carbon atoms, and / or the lubricant composition further comprises at least one anti-wear and / or extreme-pressure additive, preferably selected from phosphorus compounds, sulfurous compounds, sulfur-phosphorous compounds, and mixtures thereof, preferably from phosphorus compounds, sulfurous compounds, and mixtures thereof, and / or the at least one polyalkylene glycol (PAG) comprises ethylene oxide units and optionally propylene oxide units, and / or the at least one polyalkylene glycol (PAG) has a kinematic viscosity at 40°C ranging from 5000 to 60000 cSt, preferably from 10000 to 35000 cSt, and / or the at least one polyalkylene glycol (PAG) has an average molecular weight ranging from 8000 to 50000 g / mol, preferably from 11000 g / mol to 20000 g / mol, and / or the at least one polyalkylene glycol (PAG) comprises a mixture of two polyalkylene glycol PAG1 and PAG2, PAG1 having 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, PAG2 having 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: o from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, o from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight, of at least one polyalkylene glycol PAG1 having a kinematic viscosity at 40°C of at least 10000 cSt, ∘ from 10 to 50% by dry weight, preferably from 15 to 40% 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, ∘ 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, ∘ optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more functional 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, wherein at least one of the functional additive(s) is an anti-wear and / or extreme-pressure additive. based on the total weight of the lubricant composition, and / or the lubricant composition has a kinematic viscosity at 40°C ranging from 150 cSt to 750 cSt.

[0016] According to an embodiment, the carboxylic acid having less than 12 carbon atoms is used to improve the solubility of the at least one polyalkylene glycol (PAG) in 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 composition comprising: from 10 to 75% by weight, preferably from 10 to 50%wt, of water, from 2 to 80% by dry weight, preferably from 10 to 70% by dry weight, more preferably from 20 to 60% by dry weight, of at least one polyalkylene glycol (PAG), from 0.1 to 20% by weight, preferably from 0.5 to 10%wt, more preferably from 1 to 5%wt, of at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0026] The inventors found that the low carbon atom chain length of the carboxylic acid allows to improve the stability of the lubricant composition, as well as that the molecular weight of the PAG allows to further improve the stability of the composition since the viscosity is better controlled, in particular during evaporation of water.

[0027] 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.Polyalkylene glycol (PAG)

[0028] The lubricant composition of the invention comprises from 2 to 80% by dry weight of at least one polyalkylene glycol (PAG), preferably from 10 to 70% by dry weight of at least one polyalkylene glycol (PAG), more preferably from 20 to 60% by dry weight of at least one polyalkylene glycol (PAG), based on the total weight of the lubricant composition.

[0029] PAG can be a homopolymer or a copolymer.

[0030] According to an embodiment, PAG has a kinematic viscosity at 40°C ranging from 5000 to 60000 cSt, preferably from 10000 to 35000 cSt. The inventors found that when the composition comprising at least one PAG having a kinematic viscosity at 40°C from 10000 to 35000 cSt, the viscosity of the resulting composition is improved, in particular for the target applications.

[0031] Within the present invention, the kinematic viscosity at 40°C of PAG can be measured according to ASTM D445.

[0032] According to an embodiment, PAG has an average molecular weight of less than 20000 g / mol, preferably an average molecular weight ranging from 500 g / mol to 20000 g / mol, preferably from 1000 to 18000 g / mol, more preferably from 2000 to 15000 g / mol.

[0033] The average molecular weight of PAG can be measured by methods well known for the skilled person, for example by size exclusion chromatography using polystyrene standard.

[0034] According to an embodiment, PAG comprises ethylene oxide units and optionally propylene oxide units. Preferably, PAG consists of ethylene oxide units and optionally propylene oxide units.

[0035] According to an embodiment, PAG is a copolymer comprising ethylene units and propylene oxide units.

[0036] Within the meaning of the present invention, "ethylene oxide unit" is a unit of formula -CH 2 -CH 2 -O-.

[0037] Within the meaning of the present invention, "propylene oxide unit" is a unit of formula -(CH 3 )CH-CH 2 -O-.

[0038] Preferably, when PAG comprises ethylene oxide units and propylene oxide units, the molar ratio ethylene oxide units / propylene oxide units is higher than 1, preferably from higher than 1 to 5, more preferably from higher than 1 to 4.

[0039] Typically, PAG used in the present invention is obtained by (co)polymerisation of alkylene glycol(s) comprising from 2 to 4 carbon atoms, for example by random copolymerisation.

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

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

[0042] PAG can be a mixture of two polyalkylene glycol PAG1 and PAG2. PAG1 and PAG2 can differ for example by their kinematic viscosity at 40°C.

[0043] According to an embodiment, the lubricant composition of the invention comprises: PAG1 having a kinematic viscosity at 40°C of at least 10000 cSt, preferably ranging from 10000 to 35000 cSt, and PAG2 having a kinematic viscosity at 40°C of less than 10000 cSt, preferably ranging from 100 to 5000 cSt, and more preferably from 100 to 1 000 cSt. Polyalkylene glycol (PAG1)

[0044] Preferably, the PAG1 has a kinematic viscosity at 40°C of at least 10000 cSt, preferably from 10000 to 35000 cSt.

[0045] According to an embodiment, the PAG1 has an average molecular weight ranging from 8000 g / mol to 30000 g / mol, preferably from 9000 to 25000 g / mol, more preferably from 10000 to 20000 g / mol, even more preferably from 11000 to 15000 g / mol.

[0046] PAG1 can be a homopolymer or a copolymer.

[0047] 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.

[0048] According to an embodiment, PAG1 is a copolymer comprising ethylene units and propylene oxide units.

[0049] 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 from higher than 1 to 4, more preferably from higher than 1 to 3.

[0050] PAG1 can be synthetized according to processes known for the skilled person. PAG1 is also commercially available.

[0051] Preferably, PAG1 is selected from biodegradable polyalkylene glycol.

[0052] According to an embodiment, 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.

[0053] 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)

[0054] Preferably, the PAG2 has 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.

[0055] Preferably, 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.

[0056] PAG2 can be a homopolymer or a copolymer.

[0057] 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.

[0058] According to an embodiment, PAG2 is a copolymer comprising ethylene units and propylene oxide units.

[0059] 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 higher than 1 to 4, more preferably from higher than 1 to 3.

[0060] PAG2 can be synthetized according to processes known for the skilled person. PAG2 is also commercially available.

[0061] Preferably, PAG2 is selected from biodegradable polyalkylene glycol.

[0062] According to an embodiment, 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 weight of one or more PAG2.

[0063] 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.

[0064] The inventors found that the combination of PAG1 and PAG2 as defined in the invention allows to reach all grades of viscosities, from 150 to 1000 cSt.

[0065] 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.

[0066] 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, 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.

[0067] Preferably, if only one PAG is present in the lubricant composition, the PAG is selected from PAG1, and it can have one or more of the features described above for PAG1.Carboxylic acid(s)

[0068] The lubricant composition of the invention comprises at least one carboxylic acid having less than 12 carbon atoms. Typically, all the carboxylic acids of the lubricant composition of the invention have less than 12 carbon atoms.

[0069] The carboxylic acid(s) can be selected from monocarboxylic acids and dicarboxylic acids.

[0070] The carboxylic acids may be selected from compounds of formula R1-COOH or HOOC-R1-COOH, wherein R1 is selected from saturated or unsaturated, linear, branched or cyclic, aliphatic groups comprising less than 12 carbon atoms, preferably from linear or branched alkyl radical comprising less than 12 carbon atoms.

[0071] Preferably, the carboxylic acid(s) of the lubricant composition of the invention comprises from 4 to 10 carbon atoms.

[0072] Among carboxylic acids, mention may be made of hexanoic acid, octanoic acid or decanoic acid.

[0073] Preferably, the lubricant composition comprises from 0.5 to 10% by weight, preferably from 1 to 5% by weight, of carboxylic acid(s) having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0074] 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.

[0075] Within the lubricant composition of the invention, the carboxylic acids may have a role of anticorrosion additive.

[0076] Furthermore, 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 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) as defined in the invention.Lubricant composition

[0077] The lubricant composition of the invention may further comprise one or more functional additives, different from the carboxylic acids and different from the PAG(s).

[0078] The functional additive(s) may be selected from anti-wear and / or extreme-pressure additives, metal deactivators, corrosion inhibitors (different from carboxylic acids), pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof.

[0079] Preferably, if the functional additive(s) comprise(s) aliphatic group(s), the aliphatic group(s) have less than 12 carbon atoms.

[0080] 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.

[0081] 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.

[0082] The low carbon atom number allows to improve the stability of the lubricant composition.

[0083] 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 functional additive(s), preferably selected from anti-wear and / or extreme-pressure additives, metal deactivators, corrosion inhibitors, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof.

[0084] According to an embodiment, the lubricant composition of the invention comprises anti-wear and / or extreme-pressure additive(s).

[0085] 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.

[0086] 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, preferably from phosphorus compounds, sulfurous compounds, and mixtures thereof.

[0087] According to an embodiment, the anti-wear and / or extreme-pressure additives are selected from phosphates, phosphites, phosphonates, dimercaptothiadiazoles, thiadiazoles, and mixtures thereof.

[0088] 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.

[0089] The lubricant composition of the invention may also optionally comprise one or more anticorrosion additives (different from the carboxylic acids).

[0090] Among anticorrosion additives that can be used in the lubricant composition of the invention, mention can be made of triazine-containing corrosion inhibitors.

[0091] 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.

[0092] 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.

[0093] By « derivative of tolyltriazole » it is meant a tolyltriazole compound substituted preferably by one of more alkyl groups optionally comprising one or more heteroatoms.

[0094] 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.

[0095] Among pH boosters, mention may be made of alkanolamines.

[0096] 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.

[0097] Among anti-freeing agent(s), mention may be made of monoalkylene glycol.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Among lubricity enhancers that can be used in the lubricant composition, mention can be made of esters, typically esters comprising aliphatic chain(s) of less than 12 carbon atoms.

[0102] The lubricity enhancer(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.

[0103] The carboxylic acid and functional additive(s) can be added separately or in the form of an additive package comprising several additives into the lubricant composition of the invention.

[0104] According to a preferred embodiment, the lubricant composition has a kinematic viscosity at 40°C of at least 150 cSt, preferably from 150 to 750 cSt.

[0105] The kinematic viscosity can be measured according to ASTM D445 standard.

[0106] 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 15 to 80% by dry weight, preferably from 25 to 65% by dry weight of at least one polyalkylene glycol PAG comprising ethylene oxide units and optionally propylene oxide units, 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.

[0107] 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 cSt to 35000 cSt, from 10 to 50% by weight, preferably from 15 to 40% by 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.

[0108] 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

[0109] The lubricant composition according to the invention can be used as a gear lubricant, preferably an industrial gear lubricant, and for geared equipment likely to come into contact with the environment (water, air, etc.) or with individuals.

[0110] 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.

[0111] In one embodiment of the invention, the lubricant composition is used on gears intended to come into contact with water.

[0112] 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.

[0113] The invention also concerns a gear lubricating method comprising applying the lubricant composition according to the invention to gears.

[0114] In one embodiment, the lubricant composition used in the lubricating method of the invention has one or more of the characteristics detailed above with regard to the use of the invention.

[0115] 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.

[0116] 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.

[0117] The invention describes a gear coated with the lubricant composition according to the invention.

[0118] 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.

[0119] The invention is also directed to the use of at least one carboxylic acid having less than 12 carbon atoms in a lubricant composition to improve the stability of the lubricant composition, wherein the resulting lubricant composition comprises: from 10 to 75% by weight of water, from 2 to 80% by dry weight of the at least one polyalkylene glycol (PAG), from 0.1 to 20% by weight of the at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0120] The resulting lubricant composition is the composition comprising: from 10 to 75% by weight of water, from 2 to 80% by dry weight of the at least one polyalkylene glycol (PAG), from 0.1 to 20% by weight of the at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0121] According to a preferred embodiment, the resulting lubricant composition has a kinematic viscosity at 40°C of at least 150 cSt, preferably ranging from 150 to 750 cSt.

[0122] Within the context of the use of the acid, the acid, the PAG and more generally the lubricant composition may comprise one or more of the characteristics defined for the lubricant composition of the invention.

[0123] The inventors found that the carboxylic acid as defined in the present invention allows to improve the stability of the composition comprising water and PAG. In particular, the inventors found that the carboxylic acid as defined in the present invention allows to improve the solubility of the ingredients of the lubricant composition, in particular of the PAG(s) in the water-containing composition.EXAMPLES

[0124] 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

[0125] Lubricant compositions were prepared with the ingredients and amounts listed in Table 1, according to a process well-known for the skilled person. Table 1: Compositions Cl1 and CI2ingredients nature Cl1 Cl2 Water25% by weight25% 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 weight37% 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 weight1.5% by dry weightAdditivesAnti-wear and / or extreme pressure additives, metal deactivators, corrosion inhibitor, anti-freezing agent, pH booster, anti-foam, lubricity additive28.3% by dry weight*36.5% by dry weight** the amount of the additives in each composition Cl1 and CI2 are the same, unless for the anti-freezing agent. Compositions CI2 comprises 12.2%wt more anti-freezing agent than compositions Cl1.

[0126] The viscosity at 40°C of CI1 is of 320 cSt and the viscosity of Cl2 is of 510 cSt.

[0127] The inventors also prepared the same composition as composition CI2 but by replacing the carboxylic acid having less than 12 carbon atoms with a carboxylic acid having more than 12 carbon atoms and the inventors observed a lower neat state stability at low temperatures, such as temperatures lower than 15°C.

[0128] The low carbon atom chain length of the carboxylic acid allows to improve the stability of the lubricant composition, in particular of the solubility of the PAG(s) in the water-containing composition, both at room temperatures and at low temperatures such as 15°C.Example 2: Coefficient of friction (COF) and lubricity

[0129] The lubricant composition Cl1 detailed in example 1 is compared with a commercially available gear lubricant composition based on PAO (CC2).

[0130] 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%.

[0131] Figure 1 shows that the lubricant composition Cl1 (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

[0132] 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).

[0133] The lubricant composition Cl1 passes failer load stage > 12. These results are similar to PAO based gear lubricant compositions. It was also observed a weight loss at the 12th stage of 0.001 g meaning that the lubricant composition Cl1 shows no wear at the FZG test.Example 4: bearing test

[0134] 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).

[0135] 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

[0136] The specific heat capacity (Cp) of the lubricant composition Cl1 of example 1 was compared with the specific heat capacity of a PAO based lubricant CC2.

[0137] The results for different temperatures are detailed in table 2. Table 2 soecific heat capacity (Cp) exoressed in J.a -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

[0138] 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

[0139] Physicochemical properties of the lubricant composition Cl1 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>12 stageFZG-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°CASTM D3427 / ISO 912025.4 min

[0140] 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.

[0141] 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.Example 7: Effect of the kinematic viscosity of PAGs

[0142] In this example, two PAG were compared: PAG-HMW = PAG consisting of ethylene oxide (EO) and propylene oxide (PO) units with a ratio EO / PO of 3 / 1, obtained from random co-polymerisation and having a kinematic viscosity at 40°C of about 45000-47000 cSt, PAG-MMW = PAG consisting of ethylene oxide (EO) and propylene oxide (PO) units with a ratio EO / PO of 3 / 1, obtained from random co-polymerisation and having a kinematic viscosity at 40°C of about 20000-22000 cSt.

[0143] The viscosity at 40°C of a composition comprising 50% water and 50% of either PAG-HMW or PAG-MMW was measured and shown in Table 4. Table 4Ex. 7AEx. 7BWater50%50%PAG-HMW50%PAG-MMW50%Viscosity at 40°C947,98 cSt403

[0144] The results of Table 4 show an improved viscosity with the PAG having a medium kinematic viscosity at 40°C than with the PAG having a higher kinematic viscosity at 40°C.

Examples

example 1

Preparation of a lubricant composition

[0125]Lubricant compositions were prepared with the ingredients and amounts listed in Table 1, according to a process well-known for the skilled person.

Table 1: Compositions Cl1 and CI2

ingredients nature Cl1 Cl2

Water25% by weight25% by weight

PAG1Polyalkylene 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 weight37% by dry weight

PAG2Polyalkylene 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 weight

Corrosion inhibitorCarboxylic acid having a chain length of less than 12 carbon atoms1.5% by dry weight1.5% by dry weight

AdditivesAnti-wear and / or extreme pressure additives, metal deactivators, corrosion inhibitor, anti-freezing agent, pH booster, anti-foam, lubricity additive28.3% by dry weight*36.5% by dry weight*

* the amount ...

example 2

Coefficient of friction (COF) and lubricity

[0129]The lubricant composition Cl1 detailed in example 1 is compared with a commercially available gear lubricant composition based on PAO (CC2).

[0130]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%.

[0131]Figure 1 shows that the lubricant composition Cl1 (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

[0132]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).

[0133]The lubricant composition Cl1 passes failer load stage > 12. These results are similar to PAO based gear lubricant compositions. It was also observed a weight loss at the 12th stage of 0.001 g meaning that the lubricant composition Cl1 shows no wear at the FZG test.

FIELD OF THE INVENTION

[0001] The present invention concerns lubricant compositions based on water and having suitable stability and 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.TECHNICAL BACKGROUND OF THE INVENTION

[0002] 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.

[0003] 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.

[0004] 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.

[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] 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.

[0007] It is one objective of the present invention to provide a lubricant composition having improved viscosity and stability as well as a low carbon footprint.SUMMARY OF THE INVENTION

[0008] These objectives are reached with a novel gear lubricant composition.

[0009] The invention concerns a lubricant composition having a kinematic viscosity at 40°C of at least 150 cSt, the lubricant composition comprising: from 10 to 75% by weight of water, from 2 to 80% by dry weight of at least one polyalkylene glycol (PAG), from 0.1 to 20% by weight of at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0010] Preferably, the lubricant composition is characterized by one or more of the following features: the carboxylic acid(s) comprises from 4 to 10 carbon atoms, and / or the lubricant composition further comprises at least one anti-wear and / or extreme-pressure additive, preferably selected from phosphorus compounds, sulfurous compounds, sulfur-phosphorous compounds, and mixtures thereof, preferably from phosphorus compounds, sulfurous compounds, and mixtures thereof, and / or the at least one polyalkylene glycol (PAG) comprises ethylene oxide units and optionally propylene oxide units, and / or the at least one polyalkylene glycol (PAG) has a kinematic viscosity at 40°C ranging from 5000 to 60000 cSt, preferably from 10000 to 35000 cSt, and / or the at least one polyalkylene glycol (PAG) has an average molecular weight ranging from 8000 to 50000 g / mol, preferably from 11000 g / mol to 20000 g / mol, and / or the at least one polyalkylene glycol (PAG) comprises a mixture of two polyalkylene glycol PAG1 and PAG2, PAG1 having 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, PAG2 having 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 having a kinematic viscosity at 40°C of at least 10000 cSt, ∘ from 10 to 50% by dry weight, preferably from 15 to 40% 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 1 000 cSt, ∘ 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, ∘ optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more functional 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, wherein at least one of the functional additive(s) is an anti-wear and / or extreme-pressure additive. based on the total weight of the lubricant composition, and / or the lubricant composition has a kinematic viscosity at 40°C ranging from 150 cSt to 750 cSt.

[0011] The invention also relates to the use of the lubricant composition according to the invention as a gear lubricant, preferably an industrial gear lubricant.

[0012] The invention also relates to a gear lubricating method comprising applying the lubricant composition according to the invention, to gears.

[0013] The invention also relates to a gear coated with the lubricant composition according to the invention.

[0014] The invention also relates to the use of at least one carboxylic acid having less than 12 carbon atoms in a lubricant composition to improve the stability of the lubricant composition having a kinematic viscosity at 40°C of at least 150 cSt, wherein the resulting lubricant composition comprises: from 10 to 75% by weight of water, from 2 to 80% by dry weight of the at least one polyalkylene glycol (PAG), from 0.1 to 20% by weight of the at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0015] Preferably, within the context of the use of the carboxylic acid having less than 12 carbon atoms, the resulting lubricant composition is characterized by one or more of the following features: the carboxylic acid(s) comprises from 4 to 10 carbon atoms, and / or the lubricant composition further comprises at least one anti-wear and / or extreme-pressure additive, preferably selected from phosphorus compounds, sulfurous compounds, sulfur-phosphorous compounds, and mixtures thereof, preferably from phosphorus compounds, sulfurous compounds, and mixtures thereof, and / or the at least one polyalkylene glycol (PAG) comprises ethylene oxide units and optionally propylene oxide units, and / or the at least one polyalkylene glycol (PAG) has a kinematic viscosity at 40°C ranging from 5000 to 60000 cSt, preferably from 10000 to 35000 cSt, and / or the at least one polyalkylene glycol (PAG) has an average molecular weight ranging from 8000 to 50000 g / mol, preferably from 11000 g / mol to 20000 g / mol, and / or the at least one polyalkylene glycol (PAG) comprises a mixture of two polyalkylene glycol PAG1 and PAG2, PAG1 having 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, PAG2 having 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: o from 10 to 50% by weight, preferably from 20 to 40% by weight, of water, o from 5 to 30% by dry weight, preferably from 10 to 25% by dry weight, of at least one polyalkylene glycol PAG1 having a kinematic viscosity at 40°C of at least 10000 cSt, ∘ from 10 to 50% by dry weight, preferably from 15 to 40% 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, ∘ 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, ∘ optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more functional 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, wherein at least one of the functional additive(s) is an anti-wear and / or extreme-pressure additive. based on the total weight of the lubricant composition, and / or the lubricant composition has a kinematic viscosity at 40°C ranging from 150 cSt to 750 cSt.

[0016] According to an embodiment, the carboxylic acid having less than 12 carbon atoms is used to improve the solubility of the at least one polyalkylene glycol (PAG) in 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 composition comprising: from 10 to 75% by weight, preferably from 10 to 50%wt, of water, from 2 to 80% by dry weight, preferably from 10 to 70% by dry weight, more preferably from 20 to 60% by dry weight, of at least one polyalkylene glycol (PAG), from 0.1 to 20% by weight, preferably from 0.5 to 10%wt, more preferably from 1 to 5%wt, of at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0026] The inventors found that the low carbon atom chain length of the carboxylic acid allows to improve the stability of the lubricant composition, as well as that the molecular weight of the PAG allows to further improve the stability of the composition since the viscosity is better controlled, in particular during evaporation of water.

[0027] 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.Polyalkylene glycol (PAG)

[0028] The lubricant composition of the invention comprises from 2 to 80% by dry weight of at least one polyalkylene glycol (PAG), preferably from 10 to 70% by dry weight of at least one polyalkylene glycol (PAG), more preferably from 20 to 60% by dry weight of at least one polyalkylene glycol (PAG), based on the total weight of the lubricant composition.

[0029] PAG can be a homopolymer or a copolymer.

[0030] According to an embodiment, PAG has a kinematic viscosity at 40°C ranging from 5000 to 60000 cSt, preferably from 10000 to 35000 cSt. The inventors found that when the composition comprising at least one PAG having a kinematic viscosity at 40°C from 10000 to 35000 cSt, the viscosity of the resulting composition is improved, in particular for the target applications.

[0031] Within the present invention, the kinematic viscosity at 40°C of PAG can be measured according to ASTM D445.

[0032] According to an embodiment, PAG has an average molecular weight of less than 20000 g / mol, preferably an average molecular weight ranging from 500 g / mol to 20000 g / mol, preferably from 1000 to 18000 g / mol, more preferably from 2000 to 15000 g / mol.

[0033] The average molecular weight of PAG can be measured by methods well known for the skilled person, for example by size exclusion chromatography using polystyrene standard.

[0034] According to an embodiment, PAG comprises ethylene oxide units and optionally propylene oxide units. Preferably, PAG consists of ethylene oxide units and optionally propylene oxide units.

[0035] According to an embodiment, PAG is a copolymer comprising ethylene units and propylene oxide units.

[0036] Within the meaning of the present invention, "ethylene oxide unit" is a unit of formula -CH 2 -CH 2 -O-.

[0037] Within the meaning of the present invention, "propylene oxide unit" is a unit of formula -(CH 3 )CH-CH 2 -O-.

[0038] Preferably, when PAG comprises ethylene oxide units and propylene oxide units, the molar ratio ethylene oxide units / propylene oxide units is higher than 1, preferably from higher than 1 to 5, more preferably from higher than 1 to 4.

[0039] Typically, PAG used in the present invention is obtained by (co)polymerisation of alkylene glycol(s) comprising from 2 to 4 carbon atoms, for example by random copolymerisation.

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

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

[0042] PAG can be a mixture of two polyalkylene glycol PAG1 and PAG2. PAG1 and PAG2 can differ for example by their kinematic viscosity at 40°C.

[0043] According to an embodiment, the lubricant composition of the invention comprises: PAG1 having a kinematic viscosity at 40°C of at least 10000 cSt, preferably ranging from 10000 to 35000 cSt, and PAG2 having a kinematic viscosity at 40°C of less than 10000 cSt, preferably ranging from 100 to 5000 cSt, and more preferably from 100 to 1 000 cSt. Polyalkylene glycol (PAG1)

[0044] Preferably, the PAG1 has a kinematic viscosity at 40°C of at least 10000 cSt, preferably from 10000 to 35000 cSt.

[0045] According to an embodiment, the PAG1 has an average molecular weight ranging from 8000 g / mol to 30000 g / mol, preferably from 9000 to 25000 g / mol, more preferably from 10000 to 20000 g / mol, even more preferably from 11000 to 15000 g / mol.

[0046] PAG1 can be a homopolymer or a copolymer.

[0047] 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.

[0048] According to an embodiment, PAG1 is a copolymer comprising ethylene units and propylene oxide units.

[0049] 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 from higher than 1 to 4, more preferably from higher than 1 to 3.

[0050] PAG1 can be synthetized according to processes known for the skilled person. PAG1 is also commercially available.

[0051] Preferably, PAG1 is selected from biodegradable polyalkylene glycol.

[0052] According to an embodiment, 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.

[0053] 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)

[0054] Preferably, the PAG2 has 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.

[0055] Preferably, 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.

[0056] PAG2 can be a homopolymer or a copolymer.

[0057] 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.

[0058] According to an embodiment, PAG2 is a copolymer comprising ethylene units and propylene oxide units.

[0059] 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 higher than 1 to 4, more preferably from higher than 1 to 3.

[0060] PAG2 can be synthetized according to processes known for the skilled person. PAG2 is also commercially available.

[0061] Preferably, PAG2 is selected from biodegradable polyalkylene glycol.

[0062] According to an embodiment, 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 weight of one or more PAG2.

[0063] 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.

[0064] The inventors found that the combination of PAG1 and PAG2 as defined in the invention allows to reach all grades of viscosities, from 150 to 1000 cSt.

[0065] 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.

[0066] 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, 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.

[0067] Preferably, if only one PAG is present in the lubricant composition, the PAG is selected from PAG1, and it can have one or more of the features described above for PAG1.Carboxylic acid(s)

[0068] The lubricant composition of the invention comprises at least one carboxylic acid having less than 12 carbon atoms. Typically, all the carboxylic acids of the lubricant composition of the invention have less than 12 carbon atoms.

[0069] The carboxylic acid(s) can be selected from monocarboxylic acids and dicarboxylic acids.

[0070] The carboxylic acids may be selected from compounds of formula R1-COOH or HOOC-R1-COOH, wherein R1 is selected from saturated or unsaturated, linear, branched or cyclic, aliphatic groups comprising less than 12 carbon atoms, preferably from linear or branched alkyl radical comprising less than 12 carbon atoms.

[0071] Preferably, the carboxylic acid(s) of the lubricant composition of the invention comprises from 4 to 10 carbon atoms.

[0072] Among carboxylic acids, mention may be made of hexanoic acid, octanoic acid or decanoic acid.

[0073] Preferably, the lubricant composition comprises from 0.5 to 10% by weight, preferably from 1 to 5% by weight, of carboxylic acid(s) having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0074] 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.

[0075] Within the lubricant composition of the invention, the carboxylic acids may have a role of anticorrosion additive.

[0076] Furthermore, 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 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) as defined in the invention.Lubricant composition

[0077] The lubricant composition of the invention may further comprise one or more functional additives, different from the carboxylic acids and different from the PAG(s).

[0078] The functional additive(s) may be selected from anti-wear and / or extreme-pressure additives, metal deactivators, corrosion inhibitors (different from carboxylic acids), pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof.

[0079] Preferably, if the functional additive(s) comprise(s) aliphatic group(s), the aliphatic group(s) have less than 12 carbon atoms.

[0080] 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.

[0081] 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.

[0082] The low carbon atom number allows to improve the stability of the lubricant composition.

[0083] 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 functional additive(s), preferably selected from anti-wear and / or extreme-pressure additives, metal deactivators, corrosion inhibitors, pH boosters, anti-freezing agents, anti-foam agents, lubricity enhancers, and mixtures thereof.

[0084] According to an embodiment, the lubricant composition of the invention comprises anti-wear and / or extreme-pressure additive(s).

[0085] 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.

[0086] 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, preferably from phosphorus compounds, sulfurous compounds, and mixtures thereof.

[0087] According to an embodiment, the anti-wear and / or extreme-pressure additives are selected from phosphates, phosphites, phosphonates, dimercaptothiadiazoles, thiadiazoles, and mixtures thereof.

[0088] 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.

[0089] The lubricant composition of the invention may also optionally comprise one or more anticorrosion additives (different from the carboxylic acids).

[0090] Among anticorrosion additives that can be used in the lubricant composition of the invention, mention can be made of triazine-containing corrosion inhibitors.

[0091] 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.

[0092] 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.

[0093] By « derivative of tolyltriazole » it is meant a tolyltriazole compound substituted preferably by one of more alkyl groups optionally comprising one or more heteroatoms.

[0094] 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.

[0095] Among pH boosters, mention may be made of alkanolamines.

[0096] 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.

[0097] Among anti-freeing agent(s), mention may be made of monoalkylene glycol.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Among lubricity enhancers that can be used in the lubricant composition, mention can be made of esters, typically esters comprising aliphatic chain(s) of less than 12 carbon atoms.

[0102] The lubricity enhancer(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.

[0103] The carboxylic acid and functional additive(s) can be added separately or in the form of an additive package comprising several additives into the lubricant composition of the invention.

[0104] According to a preferred embodiment, the lubricant composition has a kinematic viscosity at 40°C of at least 150 cSt, preferably from 150 to 750 cSt.

[0105] The kinematic viscosity can be measured according to ASTM D445 standard.

[0106] 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 15 to 80% by dry weight, preferably from 25 to 65% by dry weight of at least one polyalkylene glycol PAG comprising ethylene oxide units and optionally propylene oxide units, 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.

[0107] 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 cSt to 35000 cSt, from 10 to 50% by weight, preferably from 15 to 40% by 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.

[0108] 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

[0109] The lubricant composition according to the invention can be used as a gear lubricant, preferably an industrial gear lubricant, and for geared equipment likely to come into contact with the environment (water, air, etc.) or with individuals.

[0110] 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.

[0111] In one embodiment of the invention, the lubricant composition is used on gears intended to come into contact with water.

[0112] 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.

[0113] The invention also concerns a gear lubricating method comprising applying the lubricant composition according to the invention to gears.

[0114] In one embodiment, the lubricant composition used in the lubricating method of the invention has one or more of the characteristics detailed above with regard to the use of the invention.

[0115] 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.

[0116] 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.

[0117] The invention describes a gear coated with the lubricant composition according to the invention.

[0118] 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.

[0119] The invention is also directed to the use of at least one carboxylic acid having less than 12 carbon atoms in a lubricant composition to improve the stability of the lubricant composition, wherein the resulting lubricant composition comprises: from 10 to 75% by weight of water, from 2 to 80% by dry weight of the at least one polyalkylene glycol (PAG), from 0.1 to 20% by weight of the at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0120] The resulting lubricant composition is the composition comprising: from 10 to 75% by weight of water, from 2 to 80% by dry weight of the at least one polyalkylene glycol (PAG), from 0.1 to 20% by weight of the at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

[0121] According to a preferred embodiment, the resulting lubricant composition has a kinematic viscosity at 40°C of at least 150 cSt, preferably ranging from 150 to 750 cSt.

[0122] Within the context of the use of the acid, the acid, the PAG and more generally the lubricant composition may comprise one or more of the characteristics defined for the lubricant composition of the invention.

[0123] The inventors found that the carboxylic acid as defined in the present invention allows to improve the stability of the composition comprising water and PAG. In particular, the inventors found that the carboxylic acid as defined in the present invention allows to improve the solubility of the ingredients of the lubricant composition, in particular of the PAG(s) in the water-containing composition.EXAMPLES

[0124] 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

[0125] Lubricant compositions were prepared with the ingredients and amounts listed in Table 1, according to a process well-known for the skilled person. Table 1: Compositions Cl1 and CI2ingredients nature Cl1 Cl2 Water25% by weight25% 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 weight37% 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 weight1.5% by dry weightAdditivesAnti-wear and / or extreme pressure additives, metal deactivators, corrosion inhibitor, anti-freezing agent, pH booster, anti-foam, lubricity additive28.3% by dry weight*36.5% by dry weight** the amount of the additives in each composition Cl1 and CI2 are the same, unless for the anti-freezing agent. Compositions CI2 comprises 12.2%wt more anti-freezing agent than compositions Cl1.

[0126] The viscosity at 40°C of CI1 is of 320 cSt and the viscosity of Cl2 is of 510 cSt.

[0127] The inventors also prepared the same composition as composition CI2 but by replacing the carboxylic acid having less than 12 carbon atoms with a carboxylic acid having more than 12 carbon atoms and the inventors observed a lower neat state stability at low temperatures, such as temperatures lower than 15°C.

[0128] The low carbon atom chain length of the carboxylic acid allows to improve the stability of the lubricant composition, in particular of the solubility of the PAG(s) in the water-containing composition, both at room temperatures and at low temperatures such as 15°C.Example 2: Coefficient of friction (COF) and lubricity

[0129] The lubricant composition Cl1 detailed in example 1 is compared with a commercially available gear lubricant composition based on PAO (CC2).

[0130] 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%.

[0131] Figure 1 shows that the lubricant composition Cl1 (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

[0132] 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).

[0133] The lubricant composition Cl1 passes failer load stage > 12. These results are similar to PAO based gear lubricant compositions. It was also observed a weight loss at the 12th stage of 0.001 g meaning that the lubricant composition Cl1 shows no wear at the FZG test.Example 4: bearing test

[0134] 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).

[0135] 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

[0136] The specific heat capacity (Cp) of the lubricant composition Cl1 of example 1 was compared with the specific heat capacity of a PAO based lubricant CC2.

[0137] The results for different temperatures are detailed in table 2. Table 2 soecific heat capacity (Cp) exoressed in J.a -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

[0138] 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

[0139] Physicochemical properties of the lubricant composition Cl1 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>12 stageFZG-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°CASTM D3427 / ISO 912025.4 min

[0140] 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.

[0141] 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.Example 7: Effect of the kinematic viscosity of PAGs

[0142] In this example, two PAG were compared: PAG-HMW = PAG consisting of ethylene oxide (EO) and propylene oxide (PO) units with a ratio EO / PO of 3 / 1, obtained from random co-polymerisation and having a kinematic viscosity at 40°C of about 45000-47000 cSt, PAG-MMW = PAG consisting of ethylene oxide (EO) and propylene oxide (PO) units with a ratio EO / PO of 3 / 1, obtained from random co-polymerisation and having a kinematic viscosity at 40°C of about 20000-22000 cSt.

[0143] The viscosity at 40°C of a composition comprising 50% water and 50% of either PAG-HMW or PAG-MMW was measured and shown in Table 4. Table 4Ex. 7AEx. 7BWater50%50%PAG-HMW50%PAG-MMW50%Viscosity at 40°C947,98 cSt403

[0144] The results of Table 4 show an improved viscosity with the PAG having a medium kinematic viscosity at 40°C than with the PAG having a higher kinematic viscosity at 40°C.

Examples

example 1

Preparation of a lubricant composition

[0125]Lubricant compositions were prepared with the ingredients and amounts listed in Table 1, according to a process well-known for the skilled person.

Table 1: Compositions Cl1 and CI2

ingredients nature Cl1 Cl2

Water25% by weight25% by weight

PAG1Polyalkylene 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 weight37% by dry weight

PAG2Polyalkylene 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 weight

Corrosion inhibitorCarboxylic acid having a chain length of less than 12 carbon atoms1.5% by dry weight1.5% by dry weight

AdditivesAnti-wear and / or extreme pressure additives, metal deactivators, corrosion inhibitor, anti-freezing agent, pH booster, anti-foam, lubricity additive28.3% by dry weight*36.5% by dry weight*

* the amount ...

example 2

Coefficient of friction (COF) and lubricity

[0129]The lubricant composition Cl1 detailed in example 1 is compared with a commercially available gear lubricant composition based on PAO (CC2).

[0130]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%.

[0131]Figure 1 shows that the lubricant composition Cl1 (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

[0132]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).

[0133]The lubricant composition Cl1 passes failer load stage > 12. These results are similar to PAO based gear lubricant compositions. It was also observed a weight loss at the 12th stage of 0.001 g meaning that the lubricant composition Cl1 shows no wear at the FZG test.

Claims

1. Lubricant composition having a kinematic viscosity at 40°C of at least 150 cSt, the lubricant composition comprising: - from 10 to 75% by weight of water, - from 2 to 80% by dry weight of at least one polyalkylene glycol (PAG), - from 0.1 to 20% by weight of at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

2. Lubricant composition according to claim 1, wherein the carboxylic acid(s) comprises from 4 to 10 carbon atoms.

3. Lubricant composition according to any one of claims 1 to 2, further comprising at least one anti-wear and / or extreme-pressure additive, preferably selected from phosphorus compounds, sulfurous compounds, sulfur-phosphorous compounds, and mixtures thereof, preferably from phosphorus compounds, sulfurous compounds, and mixtures thereof.

4. Lubricant composition according to any one of claims 1 to 3, wherein the at least one polyalkylene glycol (PAG) comprises ethylene oxide units and optionally propylene oxide units.

5. Lubricant composition according to any one of claims 1 to 4, wherein the at least one polyalkylene glycol (PAG) has a kinematic viscosity at 40°C ranging from 5000 to 60000 cSt, preferably from 10000 to 35000 cSt.

6. Lubricant composition according to any one of claims 1 to 5, wherein the at least one polyalkylene glycol (PAG) has an average molecular weight ranging from 8000 to 50000 g / mol, preferably from 11000 g / mol to 20000 g / mol.

7. Lubricant composition according to any one of claims 1 to 5, wherein the at least one polyalkylene glycol (PAG) comprises a mixture of two polyalkylene glycol PAG1 and PAG2, PAG1 having 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, PAG2 having 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.

8. Lubricant composition according to any one of claims 1 to 7, 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 having a kinematic viscosity at 40°C of at least 10000 cSt, - from 10 to 50% by dry weight, preferably from 15 to 40% 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, - 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, - optionally from 0.1 to 40% by weight, preferably from 1 to 30% by weight, of one or more functional 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, wherein at least one of the functional additive(s) is an anti-wear and / or extreme-pressure additive. based on the total weight of the lubricant composition.

9. Lubricant composition according to any one of claims 1 to 8, having a kinematic viscosity at 40°C ranging from 150 cSt to 750 cSt.

10. Use of the lubricant composition according to any one of the preceding claims as a gear lubricant, preferably an industrial gear lubricant.

11. A gear lubricating method comprising applying the lubricant composition according to any one of claims 1 to 9, to gears.

12. Gear coated with the lubricant composition according to any one of claims 1 to 9.

13. Use of at least one carboxylic acid having less than 12 carbon atoms in a lubricant composition to improve the stability of the lubricant composition having a kinematic viscosity at 40°C of at least 150 cSt, wherein the resulting lubricant composition comprises: - from 10 to 75% by weight of water, - from 2 to 80% by dry weight of the at least one polyalkylene glycol (PAG), - from 0.1 to 20% by weight of the at least one carboxylic acid having less than 12 carbon atoms, based on the total weight of the lubricant composition.

14. Use according to claim 13, wherein the lubricant composition is as defined in any one of claims 2 to 9.

15. Use according to claim 13 or 14, to improve the solubility of the at least one polyalkylene glycol (PAG) in the lubricant composition.

Images