EP3237588A1

EP3237588A1 - Lubricating composition with phase-change material

Info

Publication number: EP3237588A1
Application number: EP15813458.5A
Authority: EP
Inventors: Olivier Lerasle; Séverine THEVENET; Julien Guerin; Fanny BRIAND
Original assignee: Total Marketing Services SA
Current assignee: TotalEnergies Marketing Services SA
Priority date: 2014-12-23
Filing date: 2015-12-22
Publication date: 2017-11-01
Also published as: FR3030570A1; CN107207986A; JP2018500434A; FR3030570B1; US20170349850A1; WO2016102529A1

Abstract

The invention concerns the field of lubricants and provides a monophasic lubricating composition comprising a base oil, an oil chosen from the polyalkylene glycols (PAG) and a phase-change material, in particular water. The monophasic lubricating composition according to the invention can be used, in particular, for lubricating a vehicle engine. It has improved thermal performance relative to the lubricant compositions of the prior art. It also helps reduce fouling of the engine parts.

Description

LUBRICATING COMPOSITION WITH PHASE CHANGE MATERIAL

DESCRIPTION

The invention relates to the field of lubricants and provides a monophasic lubricating composition comprising a base oil, an oil selected from polyalkyl glycols (PAG or polyalkylene glycols) and a phase change material, especially water. The monophasic lubricant composition according to the invention is used for the lubrication of a vehicle engine. It has improved thermal performance compared to the lubricant compositions of the state of the art. It also reduces clogging of engine parts.

Engine developments and performance of engine lubricating compositions are inextricably linked. The more the engines have a complex design, the higher the efficiency and the optimization of the consumption, the more the engine lubricating composition is solicited and must improve its performance.

Very high compression in the engine, higher piston temperatures, particularly in the area of the upper piston ring, modern and maintenance-free valve controls with hydraulic lifters, and very high temperatures in the engine space demand increasingly lubricants for modern engines.

The conditions of use of gasoline engines and diesel engines include extremely short journeys as well as long journeys. In fact, 80% of the journeys of Western European cars are less than 12 kilometers while vehicles cover annual mileages of up to 300 000 km.

The emptying intervals are also very variable, from 5,000 km for some small diesel engines to up to 100,000 km on modern commercial diesel engines.

Lubricating compositions and especially lubricating compositions for motor vehicles must therefore have improved properties and performance.

A problem encountered when using known lubricating compositions is the degradation and coking of the oils or additives used. These phenomena of degradation and coking can lead to fouling of the lubricated parts, in particular within a vehicle engine. It is therefore necessary to have lubricating compositions for improving the cleanliness of an engine. Improving the cleanliness of an engine generally involves reducing the formation of deposits, including the formation of high temperature deposits such as varnishes, lacquers or deposits of carbon or coke. Such deposits may be formed on the hot surfaces of the engine parts such as throat bottoms of the pistons or the axes of the turbos. The substances present in the lubricating compositions can oxidize in contact with the hot surfaces of the engine and generate the formation of insoluble products forming deposits. These deposits can foul the engine and cause problems of wear, seizing, scrubbing segments and turbo rotation problems for example. Generally, detergent type additives are used to improve the cleanliness of an engine.

It is therefore necessary to have lubricating compositions for effectively controlling against these phenomena and in particular to have lubricating compositions with improved thermal resistance properties.

It is also necessary to have lubricating compositions for reducing the temperature of the epilamen (film or skin of lubricating composition) present on the lubricated mechanical parts of an engine and in particular on the pistons. Having lubricating compositions making it possible to lower the temperature of the parts in contact, for example within an automobile engine, is therefore particularly advantageous.

Lubricating compositions that make it possible to absorb a portion of the heat produced during the operation of an engine are therefore necessary.

It has now been found that the use of a phase change material in combination with oils can make it possible to absorb some of the heat produced during lubrication, in particular during operation of an engine, and therefore to lower the temperature experienced by the oils and additives used.

Moreover, the stability of the lubricating compositions must also be ensured, in particular when they are used for lubricating an engine. Indeed, in addition to the heat experienced within an engine, the lubricant compositions undergo significant mechanical stresses, including shear stresses.

Without being sufficiently stable, the oils and additives of the lubricating compositions can separate or degrade and lose all or part of their properties. In particular, lubricating compositions comprising different phases, for example emulsions, can be degraded and lead to the separation of oils and additives. During such separations, in particular emulsions included in the lubricating compositions, certain elements or additives may be deposited, for example in the lower parts of the engine. Lubricating compositions thus degraded can lose their properties and lead to accelerated degradation of the oils and additives and lead to increased fouling of the engine parts.

There is therefore a need for engine lubricating compositions which have improved performance and which in particular make it possible to limit or avoid problems of coking and fouling.

Thus, the invention provides a monophasic lubricant composition that provides a solution to all or part of the problems of the lubricant compositions of the state of the art.

The present invention relates to the use of a monophasic lubricating composition comprising a base oil, an oil selected from polyalkylated glycols (PAG or polyalkylene glycols) and from 0.1 to 5% by weight of a phase change material compared to the mass of PAG.

The lubricating composition is monophasic, this is reflected in the composition by a low content of phase change material, especially water, which is 0.1 to 5% by weight relative to the weight of PAG. It therefore comprises a single phase and is different from an emulsion. Thus, the monophasic lubricating composition according to the invention can undergo mechanical stresses, in particular shear stresses, without the risk of undergoing separation of the oils and the phase-change material.

Also preferably, the phase change material and the oil chosen from the PAGs of the composition according to the invention may be in the form of a mixture. More preferably, the phase change material and the oil selected from PAG may be in the form of a solution within the composition according to the invention.

According to the invention, the PAG of the composition according to the invention may be a block polymer or a random polymer. The PAG according to the invention comprises alkyl groups whose length of the hydrocarbon chains may vary. According to the invention, the length of the hydrocarbon chains is defined by a mean value of the number of carbon atoms.

Preferably, the PAG of the composition according to the invention is a block polymer of formula (I) or a random polymer of formula (I)

(I)

in which

^■ R ¹ represents a group CC ₃₀ linear or branched alkyl, preferably a C ₈ -C ₁₂ linear or branched alkyl;

^■ n is a number from 2 to 60, preferably from 5 to 30 or 7 to 15;

^■ R ² and R ^3, identical or different, independently represent a hydrogen atom or a dC ₂ alkyl group.

For the PAG according to the invention, n can represent a number ranging from 2 to 60, preferably ranging from 5 to 30 or from 7 to 15.

In a preferred PAG of the invention, R ¹ is C ₈ -C ₂ linear or branched alkyl, R ² and R ³ are different and independently represent a hydrogen atom or a group -C ₂ -alkyl and n linear represents a number ranging from 7 to 15.

Also preferably, the PAG of the composition according to the invention is a block polymer of formula (IA) or a random polymer of formula (IA)

(IA)

in which

^■ R ¹ represents a group CC ₃₀ linear or branched alkyl, preferably a C ₈ -C ₁₂ linear or branched alkyl; ^■ m is a number from 2 to 60, preferably from 5 to 30 or 7 to 15;

^■ R ⁴ and R ⁵ represent a hydrogen atom; or R ⁴ represents a hydrogen atom and R ⁵ represents a methyl group; or R ⁴ represents a methyl group and R ⁵ represents a hydrogen atom; or R ⁴ and R ⁵ represent a methyl group; or R ⁴ represents an ethyl group and R ⁵ represents a hydrogen atom; or R ⁴ represents a hydrogen atom and R ⁵ represents an ethyl group.

For the PAG according to the invention, m may represent a number ranging from 2 to 60, preferably ranging from 5 to 30 or from 7 to 15.

For a preferred PAG of the invention, R ¹ is C ₈ -C ₂ linear or branched alkyl, R ⁴ and R ⁵ are different and independently represent a hydrogen atom, a methyl group or an ethyl group and m represents a number ranging from 7 to 15.

Also preferably, the PAG of the composition according to the invention is a block polymer of formula (IB) or a random polymer of formula (IB)

(IB)

in which

^■ R ¹ is a C ₃₀ linear alkyl group or branched, preferably a C ₈ -C ₁₂ linear or branched alkyl;

^■ p and q are independently a number ranging from 1 to 30, preferably from 2 to 15 or 2 to 8;

^■ R ⁶ and R ⁷ represent a hydrogen atom; or R ⁶ represents a hydrogen atom and R ⁷ represents a methyl group; or R ⁶ represents a methyl group and R ⁷ represents a hydrogen atom; or R ⁶ and R ⁷ represent a methyl group; or R ⁶ represents an ethyl group and R ⁷ represents a hydrogen atom; or R ⁶ represents a hydrogen atom and R ⁷ represents an ethyl group;

^■ R ⁸ and R ⁹ represent a hydrogen atom; or R ⁸ represents a hydrogen atom and R ⁹ represents a methyl group; or R ⁸ represents a methyl group and R ⁹ represents a hydrogen atom; or R ⁸ and R ⁹ represent a methyl group; or R ⁸ represents an ethyl group and R ⁹ represents a hydrogen atom; or R ⁸ represents a hydrogen atom and R ⁹ represents an ethyl group.

For the PAG according to the invention, p and q may independently represent a number ranging from 1 to 30, preferably from 2 to 15 or from 2 to 8.

As particular PAG according to the invention, mention may be made

^■ PAG for which R ^6, R ^7, R ⁸ and R ⁹ represent a hydrogen atom; or

^■ PAG for which R ⁶ and R ⁸ represent a hydrogen atom and R ⁷ and R ⁹ represent a methyl group; or

^■ PAG for which R ⁶ and R ⁸ represent a hydrogen atom and R ⁷ and R ⁹ are ethyl; or

^■ PAG for which R ⁶ and R ⁸ represent a hydrogen atom, R ⁷ is methyl and R ⁹ is ethyl; or

the PAGs for which R ⁶ and R ⁸ represent a hydrogen atom, R ⁷ represents an ethyl group and R ⁹ represents a methyl group; or

^■ PAG for which R ^6, R ⁷ and R ⁹ represent a hydrogen atom and R ⁸ is methyl; or

^■ PAG for which R ^6, R ⁸ and R ⁹ represent a hydrogen atom and R ⁷ represents a methyl group.

For a preferred PAG according to the invention, R ¹ represents a linear or branched C ₈ -C ₁₂ -alkyl group, R ⁶ , R ⁸ and R ⁹ represent a hydrogen atom and R ⁷ represents a methyl group, p represents a number ranging from 3 to 5, for example 4.5, and q represents a number ranging from 1 to 3, for example 2.

For a more preferred PAG according to the invention, R ¹ represents a linear or branched C ₈ -C ₁₂ -alkyl group, R ⁶ represents a hydrogen atom and R ⁷ represents a methyl group, R ⁸ represents a hydrogen atom and R ⁹ represents an ethyl group, p represents a number ranging from 3 to 8, for example 5, and q represents a number ranging from 3 to 8, for example 4.

More preferably, the PAG of the composition according to the invention is a block polymer of formula (II) or a random polymer of formula (II) in which

^■ R ¹ represents a C ₈ -C ₁₂ linear or branched alkyl

^■ p represents a number from 4 to 5;

^■ q is a number ranging from 2 to 3.

More particularly preferably, the PAG of the composition according to the invention is a block polymer of formula III) or a random polymer of formula (III)

in which

^■ R ¹ represents a C ₂ -C ₈ linear or branched alkyl;

^■ p represents a number from 2 to 6;

^■ q represents a number ranging from 2 to 5.

The PAG used for the composition according to the invention may be prepared by reacting at least one alcohol-type initiator comprising from 1 to 30 carbon atoms with the epoxy bonding of one or more alkylene oxides and then propagation of the reaction. to obtain these polymers. The preferred alkylene oxides are ethylene oxide, propylene oxide and butylene oxide. Methods of preparing PAG are described in International Patent Application WO-2012/070007 or in International Patent Application WO-2013/164449.

In addition to a base oil and a PAG, the monophasic lubricant composition according to the invention comprises a phase change material. Preferably, the phase change material is a liquid-gas phase change material. Also preferably, the phase change material has a vaporization enthalpy or a latent heat of vaporization, measured at 100 ° C and under 0.101 MPa, ranging from 800 to 3500 kJ / kg, preferably from 1000 to 2 500 kJ / kg.

A preferred example of a phase change material has a vaporization enthalpy of 2257 kJ / kg measured at 100 ° C and 0.101 MPa. Also preferably, the phase change material has a boiling point at normal pressure of 50 to 150 ° C, preferably 90 to 120 ° C.

According to the invention, as examples of phase change materials, it is preferred to use a material chosen from water, carboxylic acids, ethers, alcohols, especially short-chain alcohols and particularly C ₁ -C ₈ alcohols. According to the invention, the preferred phase change material is water.

Advantageously, the monophasic lubricating composition according to the invention may comprise from 0.001 to 0.6% by weight of lubricant composition of phase change material. Preferably, the monophasic lubricating composition according to the invention may comprise from 0.01 to 0.3% by weight of lubricant composition of phase change material. Preferably, the monophasic lubricating composition according to the invention can therefore comprise up to 0.6% by weight of water.

Also advantageously, the monophasic lubricating composition according to the invention may comprise from 0.5 to 2% by weight of phase change material relative to the amount of PAG. Also advantageously, the monophasic lubricating composition according to the invention may comprise from 1 to 30% by total weight of lubricant composition of mixture of phase change material and PAG. Preferably, the monophasic lubricating composition according to the invention may comprise from 2 to 20% by total weight of lubricant composition of mixture of phase change material and PAG. More preferably, the monophasic lubricating composition according to the invention may comprise from 5 to 15% by total weight of lubricant composition of mixture of phase change material and PAG.

The monophasic lubricant composition according to the invention comprises a PAG and a phase change material. It also includes a base oil. In general, the monophasic lubricating composition according to the invention may comprise any type of lubricating base oil, mineral, synthetic or natural, animal or plant adapted to its use.

The base oils used in the lubricant compositions according to the invention can therefore be oils of mineral or synthetic origins belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) (Table A) or their mixtures.

Table A The mineral base oils which can be used for the monophasic lubricating composition according to the invention include any type of bases obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, desalphating , solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing. Mixtures of synthetic and mineral oils can also be used.

There is generally no limitation on the use of different lubricating bases to make the lubricating compositions according to the invention, except that they must have properties, in particular viscosity, viscosity index, sulfur content. and oxidation resistance, especially adapted for use for engines or for vehicle transmissions.

The base oils of the lubricating compositions according to the invention may also be chosen from synthetic oils, such as certain carboxylic acid esters and alcohols, as well as from polyalphaolefins. The polyalphaolefins used as base oils are, for example, obtained from monomers comprising from 4 to 32 carbon atoms, for example from octene or decene, and whose viscosity at 100 ° C. is between 1, 5 and 15 mm ² . s ^"1 according to the ASTM D445 standard, their average molecular weight is generally between 250 and 3000 according to the ASTM D5296 standard. Advantageously according to the invention, the base oil can be chosen from Group I II oils, Group IV oils and Group V oils. Preferably, the base oil is a group oil. III or a group V oil. As the preferred group V oil for the monophasic lubricating composition according to the invention, mention may be made of polyalkylated glycols (PAG or polyalkylene glycols) and in particular the oils of formula (IV) which are olymers block or statistical polymers

(IV)

in which

^■ Q is C ₈ -C ₄ linear alkyl;

^■ v represents a number from 2 to 6, preferably 2 to 4;

^■ w represents a number from 2 to 5, preferably 2 to 3.

The monophasic lubricating composition according to the invention may also comprise another base oil. This other base oil can be chosen from Group I II oils, Group IV oils and Group V oils.

Advantageously, the monophasic lubricating composition according to the invention comprises at least 50% by weight of base oils relative to the total mass of the composition. More advantageously, the monophasic lubricating composition according to the invention comprises at least 60% by weight, or even at least 70% by weight, of base oils relative to the total mass of the composition. More particularly advantageously, the monophasic lubricating composition according to the invention comprises from 50, 60 or 70 to 99.9% by weight, or from 50, 60 or 70 to 90% by weight, of one or more base oils. relative to the total mass of the composition.

The monophasic lubricating composition according to the invention may also comprise at least one additive. Many additives can be used for the monophasic lubricating composition according to the invention. The preferred additives for the monophasic lubricating composition according to the invention are chosen from detergent additives, antiwear additives, friction modifying additives, extreme pressure additives, dispersants, pour point improvers, anti-foam agents. , the thickeners and mixtures thereof. Preferably, the monophasic lubricating composition according to the invention comprises at least one antiwear additive, at least one extreme pressure additive or their mixtures. Anti-wear additives and extreme pressure additives protect friction surfaces by forming a protective film adsorbed on these surfaces.

There is a wide variety of anti-wear additives. In a preferred manner for the monophasic lubricating composition according to the invention, the anti-wear additives are chosen from phospho-sulfur-containing additives such as metal alkylthiophosphates, in particular zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTPs. The preferred compounds are of formula Zn ((SP (S) (OR ¹⁰ ) (OR ¹¹ )) ₂ , in which R ¹⁰ and R ¹¹ , which are identical or different, independently represent an alkyl group, preferentially an alkyl group comprising from 1 to at 18 carbon atoms.

Amine phosphates are also anti-wear additives that can be used in the monophasic lubricant composition according to the invention. However, the phosphorus provided by these additives can act as a poison of the catalytic systems of automobiles because these additives are ash generators. These effects can be minimized by partially substituting amine phosphates with non-phosphorus additives, such as, for example, polysulfides, especially sulfur-containing olefins.

Advantageously, the monophasic lubricating composition according to the invention may comprise from 0.01 to 6% by weight, preferably from 0.05 to 4% by weight, more preferably from 0.1 to 2% by weight relative to total mass of lubricating composition, antiwear additives and extreme pressure additives.

Advantageously, the monophasic lubricating composition according to the invention may comprise at least one friction-modifying additive. The friction modifying additive may be chosen from a compound providing metal elements and an ash-free compound. Among the compounds providing metal elements, mention may be made of transition metal complexes such as Mo, Sb, Sn, Fe, Cu and Zn, the ligands of which may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus. The ashless friction modifier additives are generally of organic origin and may be selected from monoesters of fatty acids and polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, borate fatty epoxides; fatty amines or fatty acid glycerol esters. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms.

Advantageously, the monophasic lubricating composition according to the invention may comprise from 0.01 to 2% by weight or from 0.01 to 5% by weight, preferably from 0.1 to 1.5% by weight or from 0, 1 to 2% by weight relative to the total mass of the lubricant composition, friction modifier additives.

Advantageously, the monophasic lubricating composition according to the invention may comprise at least one antioxidant additive. The antioxidant additive generally serves to retard the degradation of the lubricating composition in service. This degradation can notably result in the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricant composition.

Antioxidant additives act in particular as radical inhibitors or destroyers of hydroperoxides. Among the antioxidant additives commonly used, mention may be made of antioxidant additives of phenolic type, antioxidant additives of amine type, antioxidant phosphosulfur additives. Some of these antioxidant additives, for example phosphosulfur antioxidant additives, can be ash generators. Phenolic antioxidant additives may be ash-free or may be in the form of neutral or basic metal salts. The antioxidant additives may in particular be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C ₁₂ -C ₁₂ alkyl group, Ν, Ν ' dialkyl-aryl diamines and mixtures thereof.

Preferably, according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group in which at least one vicinal carbon of the carbon bearing the alcohol function is substituted by at least one C 1 -C 6 alkyl group, preferably an alkyl group. in C ₁ -C ₆ , preferably a C ₄ alkyl group, preferably by the ter-butyl group.

Amino compounds are another class of antioxidant additives that can be used, optionally in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example aromatic amines of formula NR ^a R ^b R ^c wherein R ^a represents an optionally substituted aliphatic or aromatic group, R ^b represents an aromatic group, optionally substituted, R ^c represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R ^d S (O) _z R ^e in wherein R ^d represents an alkylene group or an alkenylene group, R ^e represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.

Sulfurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

Another class of antioxidant additives is copper compounds, for example copper thio- or dithio-phosphates, copper and carboxylic acid salts, dithiocarbamates, sulphonates, phenates, copper acetylacetonates. Copper salts I and II, succinic acid or anhydride salts can also be used.

The monophasic lubricating composition according to the invention may contain all types of antioxidant additives known to those skilled in the art.

Advantageously, the lubricating composition comprises at least one ash-free antioxidant additive.

Also advantageously, the monophasic lubricating composition according to the invention comprises from 0.5 to 2% by weight relative to the total weight of the composition, of at least one antioxidant additive.

The monophasic lubricating composition according to the invention may also comprise at least one detergent additive. The detergent additives generally make it possible to reduce the formation of deposits on the surface of the metal parts by dissolving the secondary oxidation and combustion products.

The detergent additives that may be used in the monophasic lubricating composition according to the invention may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation may be a metal cation of an alkali metal or alkaline earth metal. The detergent additives are preferably chosen from the alkali metal or alkaline earth metal salts of carboxylic acids, the sulphonates, the salicylates, the naphthenates and the phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium. These metal salts generally comprise the metal in stoichiometric amount or in excess, therefore in an amount greater than the stoichiometric amount. It is then overbased detergent additives; the excess metal bringing the overbased character to the detergent additive is then generally in the form of an oil insoluble metal salt, for example a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate . Advantageously, the monophasic lubricating composition according to the invention may comprise from 2 to 4% by weight of detergent additive relative to the total mass of the lubricant composition. Also advantageously, the monophasic lubricating composition according to the invention may also comprise at least one pour point depressant additive.

By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the monophasic lubricating composition according to the invention.

As examples of pour point depressant additives, mention may be made of alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and alkylated polystyrenes. Advantageously, the monophasic lubricating composition according to the invention may also comprise at least one dispersing agent. The dispersing agent may be chosen from Mannich bases, succinimides and their derivatives.

Also advantageously, the monophasic lubricating composition according to the invention may comprise from 0.2 to 10% by weight of dispersing agent relative to the total weight of the lubricating composition.

Advantageously, the lubricating composition may also comprise at least one additional polymer improving the viscosity index. As examples of additional viscosity index improving polymers, there may be mentioned polymeric esters, homopolymers or copolymers, hydrogenated or non-hydrogenated, styrene, butadiene and isoprene, polymethacrylates (PMA).

Also advantageously, the monophasic lubricating composition according to the invention may comprise from 1 to 15% by weight relative to the total weight of the oil-soluble polymer lubricating composition chosen from polyalkylene glycols (PAG) and from this additional polymer improving the viscosity index.

The lubricating composition according to the invention may be prepared according to a process comprising ^■ preparing a mixture or solution comprising an oil selected from polyalkyl glycols (PAG or polyalkylene glycols) and a phase change material;

^■ the addition of this mixture or this solution to a base oil.

The particular, advantageous or preferred characteristics of the base oil, the PAG or the phase change material of the monophasic lubricating composition according to the invention define processes according to the invention. By analogy, these methods constitute particular, advantageous or preferred methods according to the invention.

The monophasic lubricating composition according to the invention and the monophasic lubricating composition prepared according to the preparation method according to the invention are particularly advantageous for the lubrication of mechanical parts undergoing a significant heating in the engine. Thus, the lubricating monophasic composition according to the invention is advantageously used in compressor fluids, in hydraulic fluids, in greases, in turbine fluids, in gear lubricants or in lubricants. for automobile engine. It can in particular be used for the lubrication of automotive engines. Preferably, the monophasic lubricating composition according to the invention is used for the lubrication of an automobile engine. During its use, the monophasic lubricating composition according to the invention is therefore brought into contact with at least one of the engine parts.

In a particularly advantageous manner, the use of a monophasic lubricating composition according to the invention makes it possible to reduce the fouling of the engine. It can also reduce the amount of coking products within the engine. This use of a monophasic lubricating composition according to the invention is therefore particularly advantageous for improving the cleanliness of the engine, in particular for improving the cleanliness of the engine pistons.

The invention also relates to the use of a phase change material defined according to the invention as a thermal agent in a monophasic lubricant composition for an engine. The use as thermal agent in a monophasic lubricant composition according to the invention of a phase change material is also part of the invention. The invention also relates to the use of a mixture or a solution of an oil chosen from polyalkyl glycols (PAG or polyalkylene glycols), defined according to the invention, and a phase-change material, defined according to the invention, as a thermal agent in a monophasic lubricant composition for an engine or as a thermal agent in a monophasic lubricating composition defined according to the invention.

The various aspects of the invention can be illustrated by the following examples.

Example 1 Preparation of a Lubricating Composition (CL-1) According to the Invention Comprising Water and a PAG (PAG-1)

PAG-1: R ¹ = linear alkyl chain resulting from an alcohol in C p = 5.1 q = 3.9

A monophasic lubricating composition (CL-1) according to the invention is prepared from a mixture of water and a polyalkylene glycol (PAG-1: commercial product Ucon OSP 32 from Dow) by mixing 1 g of water in 99 g of PAG-1. PAG-1 is prepared according to the method of Example 1 of International Patent Application WO-2013/164449 and comprises about 57% by weight of propylene oxide units and about 43% by weight of butylene oxide units. Its average molecular weight (measured according to ASTM D4274) is about 760 g. mol ^"1 , its viscosity measured at 40 ° C (according to ASTM D445) is 32 mm ² s ^-1 , its viscosity measured at 100 ° C (according to ASTM D445) is 6.1 mm ² . s ^"1 and its viscosity number (measured according to ASTM D2270) is 149.

Then, 15 g of a mixture of water and PAG-1 are introduced into a formulated motor oil comprising: 13.3% of additive package sold under the name P6660 of the company Infineum, 5.3% of hydrogenated polydiene polymer marketed under the name of Infineum SV261, 0.3% of PPD (pour point depressant) sold under the name LZ7748 at Lubrizol and 81.1% of Group III base oils marketed under the name Nexbase 3043 (78%) and Nexbase 3050 (3.1%) at Neste.

Example 2 Preparation of a Lubricating Composition (CL-2) According to the Invention Comprising Water and a PAG (PAG-2)

PAG-2: R ¹ = linear alkyl chain resulting from an alcohol in C _{11> 9} p = 4.4 q = 2.2

A monophasic lubricating composition (CL-2) according to the invention is prepared from a mixture of water and a polyalkylene glycol (PAG-2: Dow Dow's commercial product 20A42EB) by mixing 1 g of water. in 99 g of PAG-2. PAG-2 comprises about 66% by weight of propylene oxide units and about 34% by weight of ethylene oxide units. Its average molecular weight (measured according to ASTM D4274) is about 535 g. mol ^"1 , its viscosity measured at 40 ° C. (according to ASTM D445) is 32 mm ² s ^-1 , its viscosity measured at 100 ° C. (according to ASTM D445) is 7 mm ² . s ^"1 and its viscosity index (measured according to ASTM D2270) is 189. Then, 14 g of water mixture and PAG-2 are introduced into a formulated motor oil comprising: 13.3% of package of additives marketed under the name P6660 of the company Infineum, 5.3% of hydrogenated polydiene polymer sold under the name of SV261 from Infineum, 0.3% of PPD (pour point depressant) sold under the name LZ7748 at Lubrizol and 81, 1% of Group III base oils marketed under the name Nexbase 3043 (78%) and Nexbase 3050 (3.1%) at Neste.

Example 3 Preparation of a Comparative Lubricating Composition (CC-1) Comprising a PAG (PAG-1)

A comparative lubricating composition (CC-1) is prepared comprising: 13.3% of additive package marketed under the name P6660 from Infineum, 5.3% of hydrogenated polydiene polymer marketed under the name SV261 from the company Infineum , 0.3% of PPD (pour point depressant) sold under the name LZ7748 at Lubrizol and 81.1% of Group III base oils marketed under the name Nexbase 3043 (78%) and Nexbase 3050 (3 , 1%) at Neste. Then, PAG-1 is introduced in an amount of 15% by weight in the lubricating composition.

Example 4: Preparation of a Comparative Lubricating Composition (CC-2) Comprising a PAG (PAG-2)

A comparative lubricating composition (CC-2) comprising: 13.3% of additive package marketed under the name P6660 from the company Infineum, 5.3% of hydrogenated polydiene polymer marketed under the name of SV261 from the company Infinuem, 0.3% of PPD (pour point depressant) sold under the name LZ7748 at Lubrizol and 81.1% of Group III base oils marketed under Nexbase 3043 (78%) and Nexbase 3050 (3.1%) at Neste. Then, PAG-2 is introduced in an amount of 14% by weight in the lubricating composition.

EXAMPLE 5 Evaluation of the Properties of the Lubricating Compositions (CL-1) and CL-2) According to the Invention, Properties of a Reference Lubricating Composition (CR-1) and Comparative Lubricating Compositions (CC-1 and CC-1) 2)

The reference lubricating composition (CR-1) consists of 13.3% of additive package marketed under the name P6660 of the company Infineum, 5.3% of hydrogenated polydiene polymer sold under the name of SV261 from the company Infineum. , 0.3% of PPD (pour point depressant) sold under the name LZ7748 at Lubrizol and 81.1% of Group III base oils marketed under the name Nexbase 3043 (78%) and Nexbase 3050 (3 , 1%) at Neste.

Each lubricating composition (10 kg) is evaluated during a cleanliness test of a diesel engine with a common rail for cars. The engine has a displacement of 1, 4 L for 4 cylinders. Its power is 80 kW. The cycle time of the test is 96 hours alternating idle speed and 4 000 rpm. The temperature of the lubricating composition is 145 ° C. and the temperature of the water of the cooling system is 100 ° C. No emptying or extra makeup composition is performed during the test. EN 590 fuel is used. The test is carried out in two phases for a total duration of 106 hours and in a first rinsing and lapping step for 10 hours and then in a second step with the evaluated composition (4 kg), finally according to an endurance stage lasting 96 hours with the evaluated composition (4 kg).

During the test, the physicochemical parameters of the lubricant are evaluated. Then, the lubricant consumption during the break-in and during the test is evaluated. The deposits on the engine pistons are also evaluated. The results obtained are summarized in Table 1.

composition evaluated merit rating piston after test (%)

CL-1 79.6

CC-1 70.4

CL-68.1

CC-2 65

CR-1 63

Table 1: Piston merit cost after test It is found that the lubricant compositions according to the invention (CL-1 and CL-2) allow a significant gain in the cleanliness of the engine compared to comparative lubricating compositions (CC-1 and CC-2). The lubricant compositions according to the invention also allow a rating of the piston after test merit which is much higher than the quotation of the reference lubricating composition (CR-1).

It is also found that the lubricant compositions according to the invention are stable.

Claims

1. Use of a monophasic lubricating composition comprising a base oil, an oil selected from polyalkylated glycols (PAG or polyalkylene glycols) and from 0.1 to 5% by weight of phase change material relative to the amount of PAG for lubrication of an engine.

2. Use according to claim 1, wherein the composition comprises

^■ a base oil and a mixture of an oil selected from the PAG and a phase change material; or

^■ a base oil and a solution of an oil selected from the PAG and a phase change material.

3. Use according to one of claims 1 and 2 for which the PAG is a block polymer of formula (I) or a random polymer of formula (I)

in which

^■ R ¹ is a C ₃₀ linear alkyl group or branched, preferably a C ₈ -C ₂ alkyl linear or branched;

^■ n is a number from 2 to 60, preferably from 5 to 30 or 7 to 15;

^■ R ² and R ^3, identical or different, independently represent a hydrogen atom or a C ₂ alkyl group.

4. Use according to one of claims 1 to 3 wherein the PAG is selected from o a block polymer of formula (IA) or a random polymer of formula (IA)

(IA)

in which ^■ R ¹ represents a group CC ₃₀ linear or branched alkyl, preferably a C ₈ -C ₁₂ linear or branched alkyl;

^■ m is a number from 2 to 60, preferably from 5 to 30 or 7 to

15;

^■ R ⁴ and R ⁵ represent a hydrogen atom; or R ⁴ represents a hydrogen atom and R ⁵ represents a methyl group; or R ⁴ represents a methyl group and R ⁵ represents a hydrogen atom; or R ⁴ and R ⁵ represent a methyl group; or R ⁴ represents an ethyl group and R ⁵ represents a hydrogen atom; or R ⁴ represents a hydrogen atom and R ⁵ represents an ethyl group;

a block polymer of formula (IB) or a random polymer of formula (IB)

(IB)

in which

5. Use according to one of claims 1 to 4 wherein the PAG is selected from - a block polymer of formula II) or a random polymer of formula (II)

(II)

in which

^■ R ¹ represents a C ₈ -C ₁₂ linear or branched alkyl;

^■ p represents a number from 4 to 5;

^■ q is a number from 2 to 3; or

a block polymer of formula III) or a random polymer of formula (III)

in which

^■ R ¹ represents a C ₂ -C ₈ linear or branched alkyl;

^■ p represents a number from 2 to 6;

^■ q represents a number ranging from 2 to 5.

6. Use according to one of claims 1 to 5 for which the phase change material is liquid-gas phase change.

7. Use according to one of claims 1 to 6 for which the phase change material has a vaporization enthalpy or a latent heat of vaporization, measured at 100 ° C and under 0.101 MPa ranging from 800 to 3500 kJ / kg preferably from 1000 to 2500 kJ / kg.

8. Use according to one of claims 1 to 7 wherein the phase change material has a boiling point at normal pressure ranging from 50 to 150 ° C, preferably from 90 to 120 ° C.

9. Use according to one of claims 1 to 8 for which the phase change material is selected from water, carboxylic acids, ethers, alcohols, short-chain alcohols, C ₁ -C ₈ alcohols.

10. Use according to one of claims 1 to 9 wherein the composition comprises from 0.5 to 2% by weight of phase change material relative to the amount of PAG.

1 1. Use according to one of claims 1 to 10 for which the composition comprises from 1 to 30% by weight, preferably from 2 to 20% by weight or from 5 to 15% by weight, of phase change material and PAG. relative to the total amount of lubricating composition.

12. Use according to one of claims 1 to 1 1, wherein the composition is prepared according to a process comprising

^■ preparing a mixture or solution comprising an oil selected from polyalkyl glycols (PAG or polyalkylene glycols) and a phase change material;

^■ the addition of this mixture or this solution to a base oil.

13. Use according to one of claims 1 to 12 for the lubrication of an automobile engine.