Aqueous lubricant composition comprising a gallic acid ester

Abstract

The invention relates to an aqueous lubricant composition comprising at least: - water; - at least one polyalkylene glycol; - at least one antifreeze compound selected from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; - at least one gallic acid ester; and - at least one pH-regulating additive, making it possible to maintain the pH of said lubricant composition between (8) and (15). It also relates to the use of such an aqueous lubricant composition, for lubricating and / or cooling the moving parts in a mechanical system or as a hydraulic fluid. The invention also relates to the use of at least one gallic acid ester as an additive for improving the tribological properties of an aqueous lubricant composition.

Description

[0001] Description

[0002] Title: Aqueous lubricating composition comprising a gallic acid ester

[0003] Technical field

[0004] The present invention relates to the field of lubricating compositions. These lubricating compositions can be used for various applications, in particular as hydraulic fluids, for the lubrication and / or cooling of various mechanical systems, such as bearings, gears, bearings or engines.

[0005] More particularly, the present invention aims to provide a novel aqueous-based lubricating composition

[0006] Prior art

[0007] Lubricating compositions, also called "lubricants", are commonly used in mechanical systems to reduce friction between parts and thus protect them against wear. In addition to wear phenomena, friction can oppose the relative movement of the parts in contact and induce energy losses that are detrimental to optimal operation of the mechanical system.

[0008] Lubricants are used for many applications, for example in metalworking, especially for metal deformation operations, for gas or steam turbines in the aeronautics, naval, rail transport and electricity production sectors, for motor vehicle propulsion systems, for example for the lubrication of bearings, gears, an engine, etc.

[0009] For example, in the field of lubricants for motor vehicle engines or transmissions, the formulation of lubricants represents an important issue insofar as they make it possible to act on fuel consumption and, consequently, on carbon dioxide emissions, via their impact on the friction forces generated between the different components of motor vehicles.

[0010] Regardless of the intended application, the most common lubricants are hydrocarbon-based lubricants, typically composed of one or more base oils, to which are generally associated additives dedicated to boosting the lubricating performance of the base oils, such as friction modifier additives. On the other hand, friction between moving parts generates heat, and it may be necessary to provide, in conjunction with lubrication, cooling of mechanical systems or machined parts. This cooling is typically provided by a cooling fluid, distinct from the hydrocarbon lubricant, such as air, an aqueous fluid, such as water, or a mixture of water and a glycol.

[0011] Today, the development of new lubricants must take into account new constraints aimed at freeing themselves from the use of toxic or potentially toxic solvents, or at reducing their impact on the environment and carbon dioxide emissions. As such, water-based formulations are of growing interest.

[0012] Although water is an excellent cooling fluid, it does not, however, have the tribological properties required for a lubricant, particularly in terms of reducing friction and protecting parts against wear.

[0013] Water-based lubricating compositions, supplemented with various additives, have already been studied. Generally speaking, these aqueous lubricants are thus composed of an aqueous fraction and an organic fraction.

[0014] For example, US 2012 / 0149616 proposes an aqueous lubricant comprising, in addition to water, water-soluble polyalkylene glycols, emulsifiers, antifreeze additives of the alkylene glycol or glycerol type, anticorrosion additives, antifoam additives and friction reducing additives.

[0015] Also citeable is document EP 3 042 946 which proposes an oil- and emulsifier-free metalworking fluid comprising a cellulose-type polymer.

[0016] However, the use of organic compounds proposed so far for aqueous lubricants (polyalkylene glycols, organic surfactants, biocomponents) does not provide sufficient lubricating properties under severe conditions (high temperature and / or pressure conditions, severe mechanical contacts, high shear, etc.), also known as "limit regime" lubrication conditions (defined for example in the Manuel des Techniques de l'ingénieur, Introduction à la tribologie, Partie 2.1, Jean Frêne and Hamid Zaïdi, publication date September 10, 2017). These aqueous lubricants are thus likely to lead to the formation of carbon deposits on mechanical parts when used in limit regimes.

[0017] The use of these aqueous lubricants therefore involves specific running-in conditions and materials or part design, which represents a barrier to their widespread use as a replacement for conventional hydrocarbon lubrications.

[0018] It has also already been proposed to implement solid lubricant nanoparticles (nanodiamond, M0S2, WS3, graphite, etc.) suspended in an aqueous fluid in aqueous formulations. Unfortunately, the use of these solid particles is not without problems of stability, lubricant implementation and safety from a toxicological point of view.

[0019] As a result, the aqueous lubricants offered to date cannot compete with hydrocarbon lubricants.

[0020] Thus, there remains a need to be able to develop new additive systems making it possible to give the aqueous fluid satisfactory lubrication performance, particularly under severe conditions and, at the very least, performance equivalent to that obtained with conventional hydrocarbon lubricants.

[0021] For example, a new water-based lubricant formulation comprising glycerol and hypericin was proposed in application WO 2021 / 1259851. Mention may also be made of application WO 2021 / 259853, which proposes an aqueous lubricating composition comprising a polyalkylene glycol, an antifreeze compound and a phosphorus compound.

[0022] Statement of the invention

[0023] The present invention aims precisely to propose a new aqueous lubricant, having particularly advantageous tribological properties, in particular good friction reduction and wear resistance properties, allowing its implementation in applications imposing severe lubrication constraints, in particular under conditions of high pressure and shear stress.

[0024] More particularly, the present invention relates, according to a first of its aspects, to an aqueous lubricating composition, comprising at least:

[0025] - water;

[0026] - at least one polyalkylene glycol;

[0027] - at least one antifreeze compound chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof;

[0028] - at least one ester of gallic acid; and

[0029] - at least one pH regulating additive, making it possible to maintain the pH of said lubricating composition between 8 and 15.

[0030] For the purposes of the present invention, the term "aqueous composition" is intended to denote a composition comprising water as a base fluid, in other words as the major solvent. In particular, water preferably represents more than 35% by mass of the total mass of the lubricating composition.

[0031] In the remainder of the text, the term “aqueous lubricating composition” or “aqueous lubricant” will refer to a lubricating composition according to the invention as defined above.

[0032] Gallic acid is found naturally in various plants and is known for its antioxidant, antitumor, and antibacterial properties. Furthermore, some gallic acid esters have already been proposed as antioxidant additives in the food industry (propyl gallate is known as the antioxidant "E310") or in vegetable oils (Lida A. Quinchia et al., Journal of Agricultural and Food Chemistry, 2011, 29, 12917-12924).

[0033] On the other hand, to the inventors' knowledge, it has never been proposed to use gallic acid esters in aqueous lubricants, and even less so with the aim of improving their tribological performance.

[0034] Against all expectations, the inventors have discovered that it is possible, by implementing the specific association of at least one antifreeze compound chosen from glycols, at least one gallic acid ester and at least one polyalkylene glycol, to achieve an aqueous formulation with excellent tribological properties.

[0035] In particular, as illustrated in the examples which follow, it is possible, by supplementing an aqueous formulation, containing a mixture of water, at least one polyalkylene glycol, at least one pH regulating additive maintaining the pH of said formulation between 8 and 15, and at least one glycol-type antifreeze compound, with a gallic acid ester, such as octyl or lauryl gallate, to obtain a lubricating fluid having improved tribological properties. Advantageously, an aqueous lubricant according to the invention thus has good performance in terms of friction reduction, in particular under severe operating conditions.

[0036] The invention thus relates to the use of at least one gallic acid ester as an additive for improving the tribological properties, in particular in terms of friction reduction, of an aqueous composition further comprising at least: water, at least one polyalkylene glycol, at least one antifreeze compound chosen from glycols, and at least one pH regulating additive maintaining the pH of said composition between 8 and 15.

[0037] In particular, the aqueous lubricating compositions formulated according to the invention allow a reduction in wear and friction such that they can be considered "super-lubricating", namely that the friction phenomena can be considered insignificant, or even harmful, even under severe lubrication conditions. This phenomenon of extreme reduction in wear and friction between moving mechanical parts is known by the term "superlubricity" in English.

[0038] The good tribological properties of the aqueous lubricating compositions according to the invention, even under severe lubrication conditions, thus allow their widespread use. They are thus suitable for use as lubricants for multiple applications, in particular as hydraulic fluids, for the lubrication and / or cooling of various mechanical systems, in particular under severe lubrication conditions. They can thus be used in all systems and for all applications, as a substitute for conventionally used lubricants, in particular hydrocarbon lubricants. Examples of application are given in the rest of the text.

[0039] The invention thus relates, according to another of its aspects, to the use of an aqueous lubricating composition according to the invention, for the lubrication and / or cooling of moving parts in a mechanical system, for example for the lubrication and / or cooling of mobile or stationary motorization systems, or as a hydraulic fluid. The present application also relates to the use of an aqueous lubricating composition according to the invention, for reducing friction between moving parts in a mechanical system, as well as the use of an aqueous lubricating composition according to the invention for reducing wear of parts in a mechanical system.

[0040] By way of example, an aqueous lubricant according to the invention can be used to reduce friction and / or wear of moving parts in a mobile or stationary motorization system, for example in the transmission part of a vehicle propulsion system.

[0041] An aqueous lubricant according to the invention can also be used to reduce friction and / or wear of the various components, particularly metallic ones, in a hydraulic system.

[0042] Advantageously, a composition according to the invention combines good cooling properties linked to the presence of water, and good tribological properties, in particular friction reduction and wear resistance. Thus, an aqueous composition according to the invention can advantageously ensure the dual function of lubrication and cooling.

[0043] It is thus possible to take advantage of an aqueous composition according to the invention to avoid the use of two separate fluids, on one side a cooling fluid, on the other, a lubricating fluid.

[0044] Also, a composition according to the invention has the advantage of being easy to formulate. Advantageously, it also has good anti-corrosion properties.

[0045] Finally, the gallic acid esters used in a composition according to the invention can advantageously be biosourced. By "biosourced" is meant any component of plant or animal origin, preferably plant.

[0046] A lubricating composition according to the invention, formed mainly of water, and comprising at least one bio-sourced additive, thus meets expectations in terms of reducing the use of substances harmful to the environment, while achieving lubrication performance equivalent to that of conventional oil-based lubricants.

[0047] Finally, an aqueous lubricating composition according to the present invention advantageously has a very good capacity to solubilize the various compounds that it comprises, in particular said antifreeze compound(s), said gallic acid ester(s) and said polyalkylene glycol(s).

[0048] Other characteristics, variants and advantages of an aqueous lubricating composition according to the invention will become more apparent upon reading the description and examples which follow, given by way of illustration and not limitation of the invention.

[0049] The expressions "between ... and ...", "ranging from ... to ...", "formed from ... to ...", and "varying from ... to ...", must be understood inclusively, unless otherwise stated.

[0050] In the description and examples, unless otherwise indicated, percentages are by weight. The percentages are therefore expressed by mass relative to the total mass of the composition.

[0051] Detailed description

[0052] AQUEOUS COMPOSITION

[0053] As mentioned above, an aqueous lubricating composition according to the invention, also called an aqueous lubricant, is a formulation comprising water as the major solvent.

[0054] For the purposes of the invention, the term "majority solvent" is understood to mean that water is present in a greater quantity than any other solvent possibly present in the composition. Preferably, an aqueous lubricating composition according to the invention comprises at least 20% by mass of water, in particular deionized water, preferably at least 30% by mass, in particular between 35% and 90% by mass, more preferably between 40% and 75% by mass, relative to the total mass of the composition.

[0055] By its role as a solvent, water allows, at the desired pH of said composition, to solubilize the polyalkylene glycol(s), the glycol-type antifreeze compound(s) and the gallic acid ester(s), as well as any additive optionally present in the composition, in particular chosen from those detailed in the rest of the text. Advantageously, in addition to its role as a solvent, water allows access to a lubricating composition having good cooling properties, and which can be used as a cooling fluid for moving parts in a mechanical system.

[0056] According to a particular embodiment, the water used in an aqueous lubricating composition according to the invention is osmosed or demineralized water, more preferably deionized water.

[0057] For the purposes of the present invention, the term “osmosed water” is intended to denote water that has undergone purification, in particular by a reverse osmosis process, in order to reduce the content of organic and / or mineral compounds, for example to a content of less than 5.0% by weight, preferably less than 1.0% by weight. In the remainder of the text, the expressions “demineralized water” or “ultrapure water” will be considered equivalent or synonymous with the expression “osmosed water”. In particular, osmosed water may be “deionized water”, in other words water that has undergone purification in order to reduce the content of ions, such as Ca ions. 2+ and HCO3' generally present in water. Preferably deionized water does not contain ions.

[0058] The use of deionized water is therefore particularly advantageous in the context of the use of the aqueous lubricant according to the invention for applications requiring a fluid that conducts little, or even not at all, electricity, such as for example for the use of the aqueous lubricant for the lubrication and cooling of mechanical systems comprising an electrical circuit, for example electric or hybrid motors, in particular in electric or hybrid vehicles.

[0059] An aqueous lubricating composition according to the invention therefore differs from lubricants conventionally used in mechanical systems, which comprise a majority proportion of one or more base oils which are not soluble in water.

[0060] "Water-insoluble oil" means, in particular, an oil that does not dissolve substantially in water at room temperature (at about 25°C). In particular, a water-insoluble oil has a solubility in water of less than 0.2 g / L at room temperature.

[0061] These include lubricating base oils belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) and mixtures thereof. Preferably, an aqueous lubricating composition according to the present invention comprises less than 5% by mass of oil(s) not soluble in water, preferably less than 2% by mass, more preferably less than 1% by mass, relative to the total mass of the composition.

[0062] Advantageously, an aqueous lubricating composition according to the invention is completely free of oil which is not soluble in water.

[0063] POLYALKYLENE GLYCOL

[0064] As indicated previously, an aqueous lubricating composition according to the invention comprises at least one polyalkylene glycol.

[0065] Polyalkylene glycols (denoted “PAG”) are chosen from water-soluble polyalkylene glycols.

[0066] By "water soluble" is meant a polyalkylene glycol having a water solubility of at least 10 g / L, preferably at least 500 g / L, in water at room temperature (about 25°C).

[0067] The polyalkylene glycols may be more particularly formed from C1-C4, preferably C1-C3, more particularly C2-C3, alkylene oxide units.

[0068] Advantageously, a polyalkylene glycol used in an aqueous lubricating composition according to the invention comprises at least 50% by mass, in particular at least 80% by mass, more preferably at least 90% by mass of propylene oxide and / or ethylene oxide units. It may be a copolymer, optionally random, of ethylene oxide / propylene oxide.

[0069] Preferably, a polyalkylene glycol used in an aqueous lubricating composition according to the invention has a weight-average molecular mass (Mw) of between 100 and 50,000 g. mol 1 , preferably between 5,000 and 25,000 g.mol 1 .

[0070] Weight average molecular mass can be measured by gel permeation chromatography (GPC).

[0071] Preferably, a polyalkylene glycol used in an aqueous lubricating composition according to the invention has a kinematic viscosity measured at 100°C (KV100), according to standard ASTM D445, of between 100 and 25,000 mm 2 / s, especially between 150 and 10,000 mm 2 / s. Preferably, a polyalkylene glycol used in an aqueous lubricating composition according to the invention has a kinematic viscosity measured at 40°C (KV40), according to standard ASTM D445, of between 500 and 100,000 mm 2 / s, more particularly between

[0072] I 000 and 95 000 mm 2 / s.

[0073] The flash point of a polyalkylene glycol used in an aqueous lubricating composition according to the invention is preferably greater than or equal to 160°C, in particular greater than or equal to 220°C. The flash point can be measured by the ISO 2592 or ASTM D92 standard.

[0074] Preferably, a polyalkylene glycol used in an aqueous lubricating composition according to the invention has a viscosity index measured according to standard ASTM D2270, between 100 and 800, preferably between 250 and 550.

[0075] In particular, said polyalkylene glycol compound(s) may be used in an aqueous lubricating composition according to the invention in a content of at least 5.0% by mass, preferably between 5.0% and 50% by mass, more preferably between 10% and 40% by mass, in particular between 10% and 20% by mass, relative to the total mass of the composition.

[0076] It is understood that an aqueous lubricating composition according to the invention may comprise a single polyalkylene glycol or a mixture of several different polyalkylene glycols.

[0077] In particular, an aqueous lubricating composition according to the invention may comprise a mixture of at least two distinct polyalkylene glycols, more particularly at least one polyalkylene glycol of low weight average molecular mass and at least one polyalkylene glycol of high weight average molecular mass.

[0078] It is within the general skills of the person skilled in the art to adjust the nature and content of low and high average molecular weight polyalkylene glycols in the polyalkylene glycol mixture, particularly with regard to the viscosity targeted for the final lubricating composition.

[0079] The combination of at least one polyalkylene glycol of low average molecular mass by weight and at least one polyalkylene glycol of high average molecular mass by weight is particularly advantageous in order to obtain good solubilization of the different compounds introduced into the aqueous lubricating composition. ANTIFREEZE COMPOUND

[0080] As indicated previously, an aqueous lubricating composition according to the invention comprises at least one antifreeze compound chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof.

[0081] These compounds are known for their antifreeze action, in other words for reducing the freezing temperature of the composition.

[0082] Glycols are diols in which the two hydroxyl groups are carried by different carbon atoms, preferably by vicinal carbon atoms.

[0083] Preferably, the glycols are alkylene glycols, in particular having from 2 to 10 carbon atoms, in particular from 2 to 6 carbon atoms. Examples that may be mentioned are monoethylene glycol, diethylene glycol and propylene glycol.

[0084] The antifreeze compound may further be chosen from glycerol, diglycerol, triglycerol and mixtures thereof.

[0085] Preferably, the antifreeze compound used according to the invention is chosen from monoethylene glycol, diethylene glycol, propylene glycol, glycerol and mixtures thereof. Preferably, the antifreeze compound is diethylene glycol.

[0086] In particular, said antifreeze compound(s) may be used in an aqueous lubricating composition according to the invention in a content of at least 5.0% by mass, preferably between 5.0% and 45% by mass, more preferably between 10% and 35% by mass, in particular between 20% and 35% by mass, relative to the total mass of the composition.

[0087] GALLIC ACID ESTER

[0088] An aqueous lubricating composition according to the invention comprises at least one gallic acid ester.

[0089] Said gallic acid ester(s) are advantageously used in a form which is soluble or emulsifiable in water, in particular in the form of ionic salts.

[0090] It is understood that a lubricating composition according to the invention may comprise a single gallic acid ester or a mixture of at least two distinct gallic acid esters. For the purposes of the invention, a gallic acid ester means an ester formed between gallic acid and at least one alcohol.

[0091] A gallic acid ester may comprise several ester functions resulting from the reaction of the carboxylic acid function of gallic acid and several hydroxyl functions of a polyol.

[0092] A gallic acid ester can thus be a monoester or polyester, in particular a diester or a triester of gallic acid.

[0093] In particular, a gallic acid ester may be formed between gallic acid and at least one monoalcohol or polyol, for example a monoalcohol or diol.

[0094] For the purposes of the invention, the term "monoalcohol" means a compound formed from a hydrocarbon chain, of the alkyl or alkenyl type, carrying a single alcohol function, unlike a "polyol" comprising at least two alcohol functions.

[0095] It may preferably be an ester formed between gallic acid and one or more monoalcohols.

[0096] Said monoalcohol(s), identical or different, preferably comprise between 1 and 24 carbon atoms, preferably between 3 and 20 carbon atoms, in particular between 3 and 18 carbon atoms, more preferably between 6 and 16 carbon atoms, for example between 8 and 14 carbon atoms.

[0097] Preferably, said monoalcohol(s) are linear monoalcohols, in particular saturated.

[0098] A gallic acid ester suitable for the present invention may more particularly correspond to the following formula (I): in which R represents a linear or branched, saturated, mono- or polyunsaturated hydrocarbon chain, preferably a linear and saturated hydrocarbon chain, in C1-C24, preferably in C3-C20, more preferably in C3-C18, in particular in C6-C10, for example in C8-C14- In a particular embodiment, an ester of gallic acid according to the invention is obtained from gallic acid and a monoalcohol chosen from propan-1-ol, butan-1-ol, octan-1-ol and dodecan-1-ol, in particular chosen from octan-1-ol and dodecan-1-ol.

[0099] Advantageously, a gallic acid ester according to the invention is chosen from octyl gallate, lauryl gallate, and mixtures thereof.

[0100] According to a particular embodiment, an aqueous lubricating composition according to the invention comprises, as ester(s) of gallic acid, at least lauryl gallate.

[0101] According to a particular embodiment, an aqueous lubricating composition according to the invention comprises, as gallic acid ester(s), at least octyl gallate.

[0102] In a particular embodiment, an aqueous lubricating composition according to the invention may use a single ester of gallic acid, in particular lauryl gallate or octyl gallate, preferably lauryl gallate.

[0103] The gallic acid ester(s) used according to the invention may be commercially available or prepared according to synthesis methods known to those skilled in the art. These synthesis methods more particularly implement an esterification reaction between at least one hydroxyl function of an alcohol and the carboxylic acid function of gallic acid.

[0104] The ester(s) of gallic acid can advantageously be biosourced, i.e. they can be obtained from biomass.

[0105] An aqueous lubricating composition according to the invention may comprise between 0.001% and 10% by mass of gallic acid ester(s), in particular as defined above, preferably between 0.01% and 5% by mass, more preferably between 0.1% and 2% by mass, relative to the total mass of the composition.

[0106] PH REGULATING ADDITIVE

[0107] An aqueous lubricating composition according to the invention comprises at least one pH regulating additive, more particularly an “alkaline buffer”, making it possible to maintain the alkaline pH of the lubricating composition. The said pH regulating additive(s) more particularly make it possible to maintain the pH of the said lubricating composition between 8 and 15.

[0108] The said pH regulator(s), by ensuring that the pH of the aqueous lubricating composition is maintained between 8 and 15, makes it possible in particular to prevent corrosion of the metal surfaces, but also to promote the solubilization of the various compounds in the lubricating composition, in particular the polyalkylene glycol(s), the antifreeze compound(s) and the gallic acid ester(s), in particular as defined above.

[0109] Advantageously, the pH regulating additive(s) make it possible to maintain the pH of the aqueous lubricating composition between 8.5 and 14, more particularly between 9 and 13, or for example between 8 and 11.

[0110] In particular, the pH regulating additive(s) are chosen from amines, more particularly from alkanolamines and amino alcohols.

[0111] Examples of pH regulating additives that may be mentioned are alkanolamines, such as dimethylethanolamine (DMEA), ethanolamines, such as monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), isopropanolamines, such as monoisopropanolamine (MIPA), diisopropanolamine (DIPA) and triisopropanolamine (TIPA); diglycolamine (DGA); ethylene amines, such as ethylene diamine (EDA), diethylene triamine (DETA), triethylene tetramine (TETA) and tetraethylene pentamine (TEPA); cyclamines, such as cyclohexylamine; 2-amino-2-ethyl-1,3-propanediol; 2-amino-2-methyl-1-propanol; and mixtures thereof.

[0112] Preferably, the pH regulating additive(s) are chosen from alkanolamines, in particular ethanolamines, and more particularly from dimethylethanolamine (DMEA), triethanolamine (TEA) and their mixture, more particularly is dimethylethanolamine.

[0113] It is understood that the composition may comprise one or more pH regulating additives for maintaining the desired pH of the aqueous lubricating composition.

[0114] According to a particular embodiment, an aqueous lubricating composition according to the invention comprises at least one alkanolamine, in particular dimethylethanolamine (DMEA) and / or triethanolamine (TEA), as a pH regulating additive. According to another embodiment, an aqueous lubricating composition according to the invention comprises an ethanolamine, in particular triethanolamine (TEA) as a pH regulating additive.

[0115] An aqueous lubricating composition according to the invention may in particular comprise from 0.1% to 10% by mass of pH regulating additive(s) making it possible to maintain the pH of the composition between 8 and 15, in particular as defined previously, in particular chosen from alkanolamines, preferably from 0.5% to 5% by mass, relative to the total mass of the composition.

[0116] An aqueous lubricating composition according to the invention may optionally comprise, in addition to at least one pH regulating additive making it possible to maintain the pH of the lubricating composition between 8 and 15, in particular as defined above, one or more separate pH regulating additive(s), called “additional pH regulating additive(s)”.

[0117] In this case, it is understood that the nature and content of the additional pH regulating additive(s) are chosen so as not to affect the overall pH of the aqueous lubricating composition, maintained by the presence of the said pH regulating additive(s) as described above between 8 and 15.

[0118] According to a particular embodiment, an aqueous lubricating composition according to the invention may comprise at least:

[0119] - at least 35% by mass of water, in particular deionized water;

[0120] - from 5.0% to 50% by mass of at least one polyalkylene glycol, in particular as defined above;

[0121] - from 5.0% to 35% of at least one antifreeze compound, chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; preferably diethylene glycol;

[0122] - from 0.001% to 10% by mass of at least one ester of gallic acid, in particular as described above, in particular lauryl gallate; and

[0123] - from 0.1% to 10% by mass of at least one pH regulating additive, making it possible to maintain the pH of the lubricating composition between 8 and 15, in particular as defined above, notably chosen from alkanolamines. OTHER ADDITIVES

[0124] An aqueous lubricating composition according to the invention may further comprise various other additives.

[0125] It is understood that the said additive(s) are compatible with their implementation in an aqueous medium. Advantageously, the additives are implemented in a form that is soluble or emulsifiable in water, for example in the form of salts or ionic liquids.

[0126] The said additive(s) are of course chosen with regard to the intended application for the aqueous lubricant.

[0127] Of course, the person skilled in the art will take care to choose the possible additives and / or their quantity in such a way that the advantageous properties of the aqueous lubricating composition according to the invention, in particular the tribological properties, in particular the reduction of friction and protection of parts against wear, and the cooling properties, are not impaired by the envisaged addition.

[0128] Such additives may be more particularly chosen from anti-foaming agents, biocides, corrosion inhibitors, anti-wear and / or extreme pressure additives, sequestering agents, metal passivating agents, colorants, dispersants, emulsifying agents, and mixtures thereof.

[0129] Advantageously, an aqueous lubricating composition according to the invention may comprise one or more additives chosen from anti-foaming agents, corrosion inhibitors, metal passivating agents, colorants, and mixtures thereof.

[0130] An aqueous lubricating composition according to the invention may more particularly comprise from 0.1 to 10% by mass of additives, in particular from 1.0 to 8.0% by mass of additives, relative to the total mass of the composition.

[0131] Corrosion inhibitor

[0132] An aqueous lubricating composition according to the invention may comprise at least one corrosion inhibiting agent. Corrosion inhibitors advantageously make it possible to reduce or even prevent the corrosion of metal parts. The nature of said corrosion inhibitor(s) may be chosen with regard to the metal to be protected against corrosion, such as aluminum, steel, galvanized steel, yellow metals, for example copper or brass. Among the inorganic corrosion inhibitors that may be mentioned are nitrites, sulfites, silicates, borates, sodium, potassium, calcium or magnesium phosphates, alkali metal phosphates, hydroxides, molybdates, zinc, magnesium or nickel sulfates.

[0133] Among the organic corrosion inhibitors that may be mentioned are alkanolamines, such as triethanolamine, aliphatic monocarboxylic acids, in particular having from 4 to 15 carbon atoms, for example octanoic acid, aliphatic dicarboxylic acids having from 4 to 15 carbon atoms, for example decanedioic acid, undecanedioic acid, dodecanedioic acid or mixtures thereof, polycarboxylic acids optionally neutralized by triethanolamine, such as 1,3,5-triazine-2,4,6-tri-(6-aminocaproic acid), alkanoylamidocarboxylic acids, in particular isononanoylamidocaproic acid, and mixtures thereof. Borated amides, products of the reaction of amines or amino alcohols with boric acid, may also be used.

[0134] Preferably, the corrosion inhibitor(s) are distinct from the pH regulating additive(s) making it possible to maintain the pH of the lubricating composition between 8 and 15, and defined previously.

[0135] An aqueous lubricating composition according to the invention may in particular comprise from 0.1% to 5% by mass of corrosion inhibitor(s), preferably from 0.5% to 4% by mass, more preferably from 1% to 2.5% by mass, relative to the total mass of the composition.

[0136] In a particular embodiment, an aqueous lubricating composition according to the invention comprises at least:

[0137] - water;

[0138] - at least one polyalkylene glycol;

[0139] - at least one antifreeze compound chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof;

[0140] - at least one ester of gallic acid, in particular as defined above;

[0141] - at least one pH regulating additive, making it possible to maintain the pH of the lubricating composition between 8 and 15, in particular as defined above, notably chosen from alkanolamines; and

[0142] - at least one corrosion inhibitor, in particular at least one organic corrosion inhibitor, more particularly chosen from aliphatic monocarboxylic acids. Anti-wear / extreme pressure additive

[0143] An aqueous lubricating composition according to the invention may comprise at least one anti-wear and / or extreme pressure additive. Their function is to reduce wear and the coefficient of friction, or to prevent metal-metal contact by forming a protective film adsorbed on these surfaces.

[0144] There is a wide variety of anti-wear additives, among which can be mentioned those chosen from phosphosulfur additives such as metal alkylthiophosphates or their salts.

[0145] Additives that do not provide phosphorus may also be suitable, such as, for example, polysulfides, particularly sulfur-containing olefins.

[0146] According to a particular embodiment, an aqueous lubricating composition according to the invention comprises at least one extreme pressure additive chosen from sulfur-containing fatty acids and dimercaptothiadiazoles, preferably used in their neutralized, emulsifiable or water-soluble form. Advantageously, an aqueous lubricating composition according to the invention comprises at least one extreme pressure additive of sulfur-containing fatty acid type, preferably in a neutralized form, in particular by inorganic alkalizing agents or alkanolamines.

[0147] Sulfur-containing fatty acids may comprise from 8 to 22 carbon atoms, preferably

[0148] 12 to 18 carbon atoms.

[0149] The quantity of sulfur according to ASTM D2622 standard provided by said sulfur-containing fatty acid(s) may be between 5% and 30% by mass, in particular between 10% and 20% by mass.

[0150] Preferably, the quantity of active sulfur at 150°C according to standard ASTM D 1662 provided by said sulfur-containing fatty acid(s) in the aqueous lubricating composition according to the invention is greater than or equal to 2% by mass, in particular between 5 and 10% by mass, relative to the total mass of the lubricating composition.

[0151] For the purposes of the present invention, the term "active sulfur" means the sulfur that a chemical compound is capable of yielding or releasing when this compound is placed under the conditions of ASTM D1662. ASTM D-1662 defines an active sulfur level of a compound at a given temperature as a difference expressed as a weight percentage of sulfur content before and after reaction of a sample of this sulfur compound with a given quantity of copper for a fixed time.

[0152] The amount of active sulfur at 150°C (ASTM DI 662 standard) in the aqueous lubricating composition of the invention can influence its extreme pressure performance. This amount of active sulfur at 150°C (ASTM D1662) in the lubricating composition must not be too low, otherwise satisfactory extreme pressure behavior cannot be obtained. It must not be too high, to avoid a risk of corrosion, in particular with respect to metals and metal alloys, in particular with respect to copper.

[0153] As mentioned above, said sulfur-containing fatty acid(s) are preferably used in an aqueous lubricating composition according to the invention in their form neutralized by an alkalizing agent, such as sodium hydroxide, potassium hydroxide, or an alkanolamine, such as monoethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine and triisopropanolamine.

[0154] An aqueous lubricating composition according to the invention may comprise between 0.01% and 10% by mass of anti-wear and / or extreme pressure additive(s), in particular sulfur-containing fatty acid(s), as defined above, preferably between 0.2% and 5% by mass, relative to the total mass of the composition.

[0155] Anti-foam

[0156] An aqueous lubricating composition according to the invention may comprise at least one anti-foam additive. Anti-foams make it possible to prevent foaming of the lubricating fluid.

[0157] It may be, for example, an anti-foaming agent based on polysiloxanes or acrylate polymers. Preferably, the anti-foaming agent is chosen from three-dimensional siloxanes.

[0158] Also, antifoam agents can be polar polymers such as polymethylsiloxanes or polyacrylates.

[0159] In particular, an aqueous lubricating composition according to the invention may comprise from 0.001% to 3.0% by mass of anti-foam additive(s), preferably from 0.005% to 1.5% by mass, more preferably from 0.01% to 1.0% by mass, relative to the total mass of the lubricating composition. In a particular embodiment, an aqueous lubricating composition according to the invention comprises at least:

[0160] - water;

[0161] - at least one polyalkylene glycol;

[0162] - at least one antifreeze compound chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof;

[0163] - at least one ester of gallic acid, in particular as defined above;

[0164] - at least one pH regulating additive, making it possible to maintain the pH of the lubricating composition between 8 and 15, in particular as defined above, notably chosen from alkanolamines; and

[0165] - at least one anti-foam additive, in particular chosen from three-dimensional siloxanes.

[0166] Metal passivating agents

[0167] An aqueous lubricating composition according to the invention may comprise at least one metal passivating agent. Metal passivating agents make it possible to protect metal parts by promoting the formation of metal oxide on their surface.

[0168] The metal passivating agents may be, for example, selected from triazole derivatives, such as tetrahydrobenzotriazole (THBTZ), tolyltriazole (TTZ), benzotriazole (BTZ), amines substituted with a triazole group, such as N,N-bis(2-ethylhexyl)-1,2,4-triazol-1-yl methanamine, N'-bis(2 ethylhexyl)-4-methyl-1H-benzotriazol-1-methyl-amine, N,N-bis(heptyl)-ar-methyl-1H-benzotriazole-1-methanamine, N,N-bis(nonyl)-ar-methyl-1H-benzotriazole-1-methanamine, N,N-bis(decyl)-ar-methyl-1H-benzotriazole-1-methanamine, N,N-bis(undecyl)-ar-methyl-1H- benzotriazole-1 -methanamine, N,N-bis(dodecyl)-ar-methyl-lH-benzotriazole-l-methanamine, N,N-bis(2-ethylhexyl)-ar-methyl-lH-benzotriazole-l-methanamine, 1,2,4-triazoles, benzimidazoles, 2-alkyldithiobenzimidazoles, 2-alkyldithiobenzo thiazoles, 2-(N,N-dialkyldithiocarbamoyl)benzothiazoles, 2,5-bis(alkyldithio)-l,3,4-thiadiazoles, such as 2,5-bis(tert-octyldithio)-l,3,4-thiadiazole,THE,

[0169] 2.5-bis(tert-nonyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-decyldithio)-1,3,4-thiadiazole,

[0170] 2.5-bis(tert-undecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-dodecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-tridecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-tetradecyldithio)- 1,3,4-thiadiazole, 2,5-bis(tert-pentadecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-hexadecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-heptadecyldithio)-1,3,4-thiadiazole, 2, 5-bis(tert-octadecyldithio)- 1,3,4-thiadiazole, 2, 5-bis(tert-nonadecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-eicosyldithio)-l,3,4-thiadiazole, 2,5-bis(N,N-dialkyldithiocarbamoyl)-l,3,4-thiadiazoles, 2-alkyldithio-5-mercaptothiadiazoles, and mixtures thereof.

[0171] Preferably, the metal passivating agents are chosen from tetrahydrobenzotriazole (THBTZ), tolyltriazole (TTZ), benzotriazole (BTZ), and their salts, taken alone or in mixtures.

[0172] An aqueous lubricating composition according to the invention may in particular comprise from 0.01% to 2.0% by mass of metal passivating agent(s), preferably from 0.1% to 1.0% by mass, more preferably from 0.2% to 0.8% by mass, relative to the total mass of the composition.

[0173] In a particular embodiment, an aqueous lubricating composition according to the invention comprises at least:

[0174] - water;

[0175] - at least one polyalkylene glycol;

[0176] - at least one antifreeze compound chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof;

[0177] - at least one ester of gallic acid, in particular as defined above;

[0178] - at least one pH regulating additive, making it possible to maintain the pH of the lubricating composition between 8 and 15, in particular as defined above, notably chosen from alkanolamines; and

[0179] - at least one metal passivating agent, in particular chosen from triazole derivatives, more particularly chosen from tetrahydrobenzotriazole, tolyltriazole, benzotriazole, and their salts, taken alone or in mixtures.

[0180] Dyes

[0181] An aqueous lubricating composition according to the invention may comprise one or more colorants. The colorants may be natural or synthetic, generally organic. The colorants that may be used in an aqueous lubricating composition may be more particularly chosen from natural or synthetic water-soluble colorants, for example the colorants FDC Red 4, DC Red 6, DC Red 22, DC Red 28, DC Red 30, DC Red 33, DC Orange 4, DC Yellow 5, DC Yellow 6, DC Yellow 8, FDC Green 3, DC Green 5, FDC Blue 1, betanin (beetroot), carmine, a chlorophyllin, methylene blue, anthocyanins (enocyanin, black carrot and hibiscus), xanthenes, caramel and riboflavin.

[0182] An aqueous lubricating composition according to the invention may comprise between 0.01% and 2.0% by mass of colorant(s), preferably between 0.01% and 1.5% by mass, more preferably between 0.02% and 1.0% by mass, relative to the total mass of the composition.

[0183] In a particular embodiment, an aqueous lubricating composition according to the invention comprises at least:

[0184] - water;

[0185] - at least one polyalkylene glycol;

[0186] - at least one antifreeze compound chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof;

[0187] - at least one ester of gallic acid, in particular as defined above;

[0188] - at least one pH regulating additive, making it possible to maintain the pH of the lubricating composition between 8 and 15, in particular as defined above, notably chosen from alkanolamines; and

[0189] - at least one colorant, in particular chosen from xanthenes.

[0190] Emulsifying agents

[0191] An aqueous lubricating composition according to the invention may comprise one or more emulsifying agents, also called emulsifiers. Their function is to generate stable emulsions in water.

[0192] The emulsifying agents may be more particularly non-ionic, such as for example ethoxylated fatty alcohols, ethoxylated fatty acids, ethoxylated fatty amides; anionic, for example KOH, NaOH soaps; sulphonates; cationic, such as quaternary ammonium compounds; or even carboxylic acid esters soluble or emulsifiable in water.

[0193] In particular, an aqueous lubricating composition according to the invention may comprise from 0.01% to 10% by mass of emulsifying agent(s), preferably from 0.1% to 5.0% by mass, relative to the total mass of the lubricating composition.

[0194] Sequestering agents

[0195] An aqueous lubricating composition according to the invention may comprise at least one sequestering agent. Sequestering agents, also called chelating agents, make it possible to limit the encrustation of metal ions in the composition.

[0196] Examples of sequestering agents include those derived from phosphonic acids and phosphonates, such as diethylenetriaminepentamethylphosphonic acid (DTPMPA), aminotri(methylenephosphonic acid) (ATMP), hydroxyethanediphosphonic acid (HEDP), 1,1-hydroxyethylidene diphosphonate, 2-hydroxyethylamine di(methylenephosphonic acid) (HEAMBP), diethylenetriaminopenta(methylenephosphonic acid) (DTMP), multifunctional organic acids and hydroxy acids, such as ethylenediaminetetraacetic acid (EDTA), pteroyl-L-glutamic acid (PGLU), organic polyacids, such as maleic acid and polyaspartic acid, polysaccharides and carbohydrates, such as inulin, carboxymethylinulin and carboxymethylchitosan.

[0197] An aqueous lubricating composition according to the invention may comprise from 0.001% to 2.0% by mass of sequestering agent(s), preferably from 0.01% to 1.0% by mass, relative to the total mass of the composition.

[0198] Biocides and fungicides

[0199] An aqueous lubricating composition according to the invention may comprise at least one biocidal and / or fungicidal agent. The biocides and fungicides may be used to improve the biological stability of the composition by limiting the proliferation of bacteria, fungi and yeasts in the lubricating fluid.

[0200] Such biocides may be selected from parabens, aldehydes, reactive acetylacetone compounds, isothiazolinones, phenolic compounds, acid salts, halogenated compounds, quaternary ammoniums, certain alcohols and mixtures thereof. Preferably, the biocides may be selected from optionally substituted benzisothiazolinones (BIT), such as N-butyl-1,2-benzisothiazolin-3-one, methylisothiazolinones (MIT), mixtures of methylisothiazolinone and chloromethylisothiazolinone (MIT / CMIT), orthophenyl-phenol (OPP) or its sodium salt, 3-iodo-2-propynylbutylcarbamate (IPBC), chloro-cresol and N,N-methylene-bis-morpholine (MBM); sorbic acid; preferably from orthophenyl-phenol (OPP) or its sodium salt, 3-iodo-2-propynylbutylcarbamate, chloro-cresol, benzisothiazolinones and N,N-methylene-isomorpholine.

[0201] An aqueous lubricating composition according to the invention may in particular comprise between 0.01% and 10% by mass of biocide(s) and / or fungicide(s), preferably between 0.5% and 5.0% by mass, relative to the total mass of the composition.

[0202] According to a particular embodiment, an aqueous lubricating composition according to the invention comprises at least:

[0203] - water, especially deionized water;

[0204] - at least one polyalkylene glycol, in particular as defined above;

[0205] - at least one antifreeze compound chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; preferably diethylene glycol;

[0206] - at least one ester of gallic acid, in particular as described above, in particular lauryl gallate;

[0207] - at least one pH regulating additive, making it possible to maintain the pH of the lubricating composition between 8 and 15, in particular as defined above, notably chosen from alkanolamines; and

[0208] - one or more other additives chosen from anti-foaming agents, corrosion inhibitors, metal passivating agents, colorants, in particular as defined above.

[0209] In particular, an aqueous lubricating composition according to the invention may comprise:

[0210] - at least 35% by mass of water, in particular deionized water;

[0211] - from 5.0% to 50% by mass of at least one polyalkylene glycol, in particular as defined above; - from 5.0% to 35% of at least one antifreeze compound, chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; preferably diethylene glycol;

[0212] - from 0.001% to 10% by mass of at least one ester of gallic acid, in particular as described above, in particular lauryl gallate;

[0213] - from 0.1% to 10% by mass of at least one pH regulating additive, making it possible to maintain the pH of the lubricating composition between 8 and 15, in particular as defined above, in particular chosen from alkanolamines; and

[0214] - optionally from 0.1% to 10% by mass of one or more other additives chosen from anti-foaming agents, corrosion inhibitors, metal passivating agents, colorants, in particular as defined above.

[0215] More particularly, an aqueous lubricating composition according to the invention may consist of:

[0216] - from 5.0% to 50% by mass of at least one polyalkylene glycol, in particular as defined above;

[0217] - from 5.0% to 35% of at least one antifreeze compound, chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; preferably diethylene glycol;

[0218] - from 0.01% to 5% by mass of at least one ester of gallic acid, in particular as described above, in particular lauryl gallate;

[0219] - from 0.1% to 10% by mass of at least one pH regulating additive, making it possible to maintain the pH of the lubricating composition between 8 and 15, in particular as defined above, in particular chosen from alkanolamines; and

[0220] - optionally from 0.1% to 10% by mass of one or more other additives chosen from anti-foaming agents, corrosion inhibitors, metal passivating agents, colorants, in particular as defined above; the contents being expressed relative to the total mass of the lubricating composition, the remainder consisting of water, in particular deionized water. It is understood that the various particular embodiments described above may be combined, as far as possible, to define other particular embodiments.

[0221] In particular, each of the additives specifically described above may be introduced alone, or in combination with at least one other of the additives specifically described, which defines different variant embodiments of an aqueous lubricating composition according to the invention. In other words, particular embodiments of the invention are defined by an aqueous lubricating composition according to the invention, comprising at least water, one or more polyalkylene glycol(s); one or more antifreeze compounds, one or more gallic acid esters, in particular as defined above, one or more pH regulating additives in particular as defined above, preferably in the proportions indicated above, and further comprising one or more of the other additives detailed specifically in the text.

[0222] Advantageously, a lubricating composition according to the invention has a kinematic viscosity, measured at 40°C (KV40), according to standard ASTM D445 (ISO 3104) of between 10 and 1000 mm 2 / s, especially between 20 and 300 mm 2 / s and more particularly between 25 and 80 mm 2 / s.

[0223] The kinematic viscosity, measured at 100°C (KV100), according to standard ASTM D445 (ISO 3104), of a lubricating composition according to the invention may advantageously be between 3 and 50 mm 2 / s, especially between 4 and 25 mm 2 / s and more particularly between 5 and 10 mm 2 / s.

[0224] Advantageously, a lubricating composition according to the invention has a kinematic viscosity, measured at -10°C (KV-10), according to standard ASTM D445 (ISO 3104) of between 200 and 600 mm 2 / s, especially between 250 and 500 mm 2 / s and more particularly between 275 and 400 mm 2 / s.

[0225] APPLICATION

[0226] As mentioned above, an aqueous lubricating composition formulated according to the invention, in particular as described above, has excellent tribological properties, in particular in terms of friction reduction and wear resistance, which makes it particularly well suited for use as a lubricating fluid. The aqueous lubricating compositions can find various applications. In general, they can be used as a lubricating fluid for systems and applications, as a substitute for conventional hydrocarbon lubricants. The invention is thus not limited to a particular application of the aqueous lubricants according to the invention, the following development being given solely for illustrative and non-limiting purposes.

[0227] The mechanical parts lubricated using a lubricating composition according to the invention can be made of any material conventionally used in the fields concerned, in particular metal, such as steel, galvanized steel, stainless steel, yellow metals, but also ceramic or polymer material.

[0228] It is understood that the surface of these different materials can be coated, for example with a DLC coating (for “Diamond Like Carbon” in English).

[0229] As an illustration of a possible application, an aqueous lubricating composition according to the invention may be intended to lubricate moving parts in a mechanical system, and more particularly intended to lubricate a mobile or stationary motorization system.

[0230] An aqueous lubricating composition according to the invention can thus be used for the lubrication and / or cooling of gears, rolling bearings, bearings, such as rolling or sliding bearings or even motors.

[0231] By "motorization system" within the meaning of the present invention, is meant a system comprising all the mechanical parts necessary for the intended mobile or stationary application and including at least one engine. It may be a combustion, gas, in particular hydrogen, ammonia, electric or hybrid engine system, depending on the nature of the engine(s) included in the motorization system: combustion, gas, in particular hydrogen, ammonia and / or electric engine.

[0232] A "stationary" motorization system within the meaning of the invention is a motorization system including a stationary engine. It may, for example, find applications in electrical energy production devices. It may in particular be a gas motorization system, in particular a stationary gas engine. A "mobile" motorization system is more particularly a motorization system implemented in vehicles, including light vehicles, heavy goods vehicles, so-called "off-road" mobile machines, or even marine vehicles.

[0233] A mobile motorization system can thus be a propulsion system of a vehicle, in particular an electric or hybrid vehicle.

[0234] For the purposes of the present invention, the term "propulsion system" is intended to denote a system comprising the mechanical parts necessary for the propulsion of a vehicle. The propulsion system more particularly encompasses a motor, for example an electric motor comprising the rotor-stator assembly of the power electronics (dedicated to speed regulation), a transmission and possibly a battery. The battery itself is generally made up of a set of electrical accumulators, called cells. An aqueous lubricating composition according to the invention advantageously makes it possible to act effectively on fuel consumption via its impact on the friction forces generated between the various components of motor vehicles. In particular, an aqueous lubricating composition proves to be particularly advantageous for reducing friction in gearboxes, in axle differentials and / or in the cylinder head.

[0235] By thus reducing friction between moving parts in the vehicle's propulsion system, a lubricating composition according to the invention not only reduces wear, but also limits energy losses responsible for excess fuel consumption.

[0236] An aqueous lubricating composition according to the invention thus advantageously has good properties in terms of reducing the fuel consumption of motor vehicles, also known as “Fuel Eco” properties, and, in fact, contributes to the reduction of CO2 emissions.

[0237] An aqueous lubricating composition according to the invention may find an interesting application for the lubrication and / or cooling of an electric or hybrid vehicle propulsion system, and more particularly of the engine, power electronics, transmission and / or battery.

[0238] An aqueous composition according to the invention can be used both as a cooling fluid and as a lubricant, for example in a propulsion system of an electric or hybrid vehicle. Advantageously, a composition according to the invention makes it possible to jointly achieve good properties in terms of cooling and lubrication of the parts of the propulsion system of an electric or hybrid vehicle, such as an electric motor of an electric or hybrid vehicle. It proves to be particularly effective for cooling the power electronics and / or the rotor and / or the stator of an electric motor. It also ensures the lubrication of the bearings located between the rotor and the stator of an electric motor of an electric or hybrid vehicle.

[0239] Also, a composition according to the invention advantageously makes it possible to effectively cool the battery present in an electric or hybrid vehicle.

[0240] Thus, advantageously, it is for example possible, by implementing a single composition according to the invention, to ensure both the cooling of the battery and the lubrication of the transmission, in particular the reducer, in an electric or hybrid vehicle.

[0241] An aqueous lubricating composition according to the invention can be used as a running-in lubricant, for example for running-in mobile or stationary motorization systems.

[0242] Indeed, new or refurbished mechanical systems may require, during the first start-ups, appropriate lubrication in order to avoid initial damage to the surface of the parts until the mechanical system reaches its optimal functioning.

[0243] As mentioned above, an aqueous lubricating composition according to the invention can also find applications as a hydraulic fluid, in particular in hydraulic actuators (cylinders / motors) or machine assemblies on demand. In particular, hydraulic fluids are subjected to constant mechanical stresses and high shear due to their constant passage in a pump in order to maintain an appropriate pressure in the hydraulic system.

[0244] An aqueous lubricating composition according to the invention advantageously makes it possible to reduce friction forces and wear under severe operating conditions, such as those encountered in hydraulic systems.

[0245] Thus, an aqueous lubricating composition according to the invention can be used for the lubrication of the various moving parts in a hydraulic system. It can also ensure heat transfer between the various components of a hydraulic system. All of the applications detailed above illustrate certain advantageous implementations of an aqueous lubricating composition according to the invention.

[0246] According to the invention, the particular, advantageous or preferred characteristics of the composition according to the invention make it possible to define uses according to the invention which are also particular, advantageous or preferred.

[0247] Example

[0248] The invention will now be described by means of the following examples, given by way of illustration and not limitation of the invention.

[0249] Evaluation of tribological properties

[0250] Tribological properties can be assessed using a rotating ball-disc tribometer test (also called a ball-plate tribometer) of the Linear Reciprocating Tribometer type. This test is used to assess the performance of lubricants in terms of friction in mixed / limit conditions depending on the load, pressure or speed conditions applied.

[0251] The coefficient of friction of the tested lubricating compositions is determined at 40°C by using a hardened steel ball of approximately 2 cm in diameter, for example 1.905 cm in diameter, on a hardened steel plane.

[0252] The tribometer can be a device from the Laboratory of Dynamic Tribology of Systems (LTDS). This device allows a steel ball and a steel plane to be put into relative motion in order to determine the friction coefficients for a given lubricant composition, while varying various properties such as speed, load, and temperature. The hardened steel plane is of AISI 52100 reference with a mirror finish and the ball is also of AISI 52100 reference made of hardened steel.

[0253] The applied load is 10 N and the rotation speed varies from 1 mm / s to 2,500 mm / s. The coefficient of friction is determined in particular at a rotation speed of 3 mm / s.

[0254] Approximately 50 ml of the tested lubricating composition was introduced into the device. The ball is engaged face against plane, said ball and said plane being actuated independently so as to create a mixed rolling / sliding contact.

[0255] The coefficient of friction is measured and recorded using a force sensor. Solubilization tests

[0256] The solubilization of all the ingredients in the lubricant composition is assessed visually at the end of the formulation. Solubilization is considered satisfactory if the composition is transparent. Conversely, solubilization is considered insufficient if the composition is cloudy or precipitated.

[0257] pH measurement

[0258] The pH of the compositions is measured at the end of formulation using a pH meter.

[0259] EXAMPLE 1

[0260] Preparation of lubricating compositions

[0261] A reference aqueous lubricant composition, not comprising gallic acid ester, was formulated by simple mixing at room temperature of the following components, in the mass percentages indicated in Table 1 below. The percentages are therefore expressed by mass relative to the total mass of the composition. The pH regulator is an alkanolamine such as dimethylethanolamine, and makes it possible to maintain the pH of the composition between 8 and 15.

[0262] [Table 1]

[0263] ** ) Mixture of additives comprising one or more anti-corrosion additives, one or more passivators, one or more anti-foam additives and / or one or more colorants.

[0264] Four aqueous lubricating compositions (II, 12, 13 and 14) according to the invention are formulated by adding, at room temperature, a gallic acid ester to the reference composition, in the mass proportions detailed in Table 2 below. [Table 2]

[0265] Four other aqueous lubricating compositions according to the invention (15, 16, 17 and 18) are formulated according to the following protocol.

[0266] Polyalkylene glycol and diethylene glycol are added to deionized water in the following proportions: Deionized water 3 / 7, diethylene glycol 3 / 7 and polyalkylene glycol 1 / 7. The solution is stirred for 15 minutes at a temperature of approximately 60 °C in the presence of a magnetic stirrer.

[0267] The gallic acid ester is then added.

[0268] Finally, the pH regulating additive (Triethanolamine (TEA) or dimethylethanolamine (DMEA)) is added to the formulation.

[0269] The mass proportions of compositions 15 to 18 are detailed in table 3 below.

[0270] [Table 3]

[0271] EXAMPLE 2

[0272] Characterization of compositions

[0273] The coefficient of friction is determined for the reference composition and the compositions (II, 12, 13 and 14) according to the invention. These are gathered in the following Table 4. [Table 4]

[0274] It is clear from these examples that the compositions in accordance with the invention (II, 12, 13 and 14) have a significantly reduced coefficient of friction compared to the reference composition, not using gallic acid ester.

[0275] Consequently, the aqueous lubricating compositions according to the invention exhibit particularly advantageous friction reduction performances, in particular under severe lubrication conditions.

[0276] The compositions according to the invention (15, 16, 17 and 18) are transparent, reflecting good solubilization of the various ingredients that they contain. Consequently, the aqueous lubricating compositions according to the invention have a very good ability to solubilize the various compounds that they comprise, in particular the antifreeze compound(s), the gallic acid ester(s) and the polyalkylene glycol(s).

Claims

Demands 1. Aqueous lubricating composition comprising at least: - water; - at least one polyalkylene glycol; - at least one antifreeze compound selected from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; - at least one ester of gallic acid; and - at least one pH regulating additive, allowing the pH of said lubricating composition to be maintained between 8 and 15.

2. Aqueous lubricating composition according to claim 1, characterized in that the water is osmosis water, in particular deionized water.

3. Aqueous lubricating composition according to claim 1 or 2, comprising at least 20% by mass of water, in particular deionized water, preferably at least 30% by mass, in particular between 35% and 90% by mass, more preferably between 40% and 75% by mass, relative to the total mass of said composition.

4. Aqueous lubricating composition according to any one of the preceding claims, characterized in that the pH regulating additive(s) are selected from alkanolamines, in particular ethanolamines, and more particularly from dimethylethanolamine, triethanolamine, and their mixture, more particularly dimethylethanolamine.

5. Aqueous lubricating composition according to any one of the preceding claims, characterized in that the content of pH regulating additive(s) is between 0.1% and 10% by mass, preferably between 0.5% and 5% by mass, relative to the total mass of the composition 6. Aqueous lubricating composition according to any one of the preceding claims, characterized in that said polyalkylene glycol(s) comprises at least 50% by mass, in particular at least 80% by mass, more preferably at least 90% by mass of propylene oxide and / or ethylene oxide units, in particular said polyalkylene glycol(s) is an ethylene oxide / propylene oxide copolymer.

7. Aqueous lubricating composition according to any one of the preceding claims, characterized in that said polyalkylene glycol(s) has / are a Kinematic viscosity measured at 100 °C (KV100), according to ASTM D445, ranging from 100 to 25,000 mm 2 / s, particularly between 150 and 10000 mm 2 / s.

8. Aqueous lubricating composition according to any one of the preceding claims, comprising at least 5.0% by mass of polyalkylene glycol(s), preferably between 5.0% and 50% by mass, more preferably between 10% and 40% by mass, in particular between 10% and 20% by mass, relative to the total mass of the composition.

9. Aqueous lubricating composition according to any one of the preceding claims, characterized in that said antifreeze compound is selected from monoethylene glycol, diethylene glycol, propylene glycol, glycerol and mixtures thereof, in particular diethylene glycol.

10. Aqueous lubricating composition according to any one of the preceding claims, comprising at least 5.0% by mass of antifreeze compound(s), preferably between 5.0% and 45% by mass, more preferably between 10% and 35% by mass, in particular between 20% and 35% by mass, relative to the total mass of said composition.

11. Aqueous lubricating composition according to any one of the preceding claims, characterized in that said gallic acid ester is obtained from a monoalcohol comprising between 1 and 24 carbon atoms, preferably between 3 and 20 carbon atoms, in particular between 3 and 18 carbon atoms, more preferably between 6 and 16 carbon atoms, for example between 8 and 14 carbon atoms, in particular selected from octan-l-ol and dodecan-l-ol.

12. Aqueous lubricating composition according to any one of the preceding claims, characterized in that said gallic acid ester has formula (I): in which R represents a linear or branched, saturated, mono- or polyunsaturated hydrocarbon chain, preferably a linear saturated hydrocarbon chain, in C1-C24, preferably in C3-C20, more preferably in C3-C18, in particular in C0-C10, for example in Cs-C14, preferably said gallic acid ester is lauryl gallate.

13. Aqueous lubricating composition according to any one of the preceding claims, comprising between 0.001% and 10% by mass of gallic acid ester(s), in particularly between 0.01% and 5% by mass, more particularly between 0.1% and 2% by mass relative to the total mass of the composition.

14. Aqueous lubricating composition according to any one of the preceding claims, further comprising at least one additive selected from antifoaming agents, biocides, corrosion inhibitors, anti-wear and / or extreme-pressure additives, sequestering agents, metal passivating agents, colorants, dispersants, emulsifying agents, and mixtures thereof, preferably selected from antifoaming agents, corrosion inhibitors, metal passivating agents, colorants, and mixtures thereof.

15. Aqueous lubricating composition according to any one of the preceding claims, comprising less than 5% by mass of water-insoluble oil(s), preferably less than 2% by mass, more preferably less than 1% by mass, relative to the total mass of said composition, said composition being more particularly free of water-insoluble oil.

16. Use of an aqueous lubricating composition as defined according to any one of the preceding claims, for the lubrication and / or cooling of moving parts in a mechanical system, for example for the lubrication and / or cooling of mobile or stationary drive systems, or as a hydraulic fluid.

17. Use of at least one gallic acid ester, in particular as defined according to claim 11 or 12, as an additive to improve the tribological properties, in particular in terms of friction reduction, of an aqueous composition otherwise comprising at least: water, at least one polyalkylene glycol and at least one antifreeze compound selected from glycols, and at least one pH regulating additive maintaining the pH of said composition between 8 and 15.

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