DIESTER-BASED LUBRICANT COMPOSITION

Description

PRIOR RELATED APPLICATIONS

The present application is a national entry of PCT Application no. PCT/EP2023/069110, filed on Jul. 11, 2023, which claims priority under the Paris Convention to French Application FR FR2207202, filed on Jul. 13, 2022. The entire contents of such prior applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to the field of compositions for lubricating and/or cooling parts of mobile or stationary systems, such as heavy or light vehicles, public works vehicles, or energy storage devices. Same relates more particularly to the use of novel compounds such as diesters in cooling and/or lubricating compositions, in particular used in heavy or light vehicles, public works machinery, or energy storage devices.

PRIOR ART

Lubricating compositions, also known as “lubricants”, are commonly used in the different components of motor vehicles for the main purposes of reducing the friction forces between the different metal parts moving in the components, more particularly the engine, the transmission and the hydraulic circuit. Furthermore, same are effective in preventing premature wear or even damage to such parts, and in particular to the surface thereof. To this end, a lubricating composition is conventionally composed of a base oil, with which are generally associated a plurality of additives dedicated to stimulating the lubricating performance of the base oil, such as e.g. friction modifier additives, and also for obtaining additional performance.

Lubricating compositions for transmissions (for example, gearboxes or axles) must satisfy many requirements, in particular with regard to the strict specifications imposed by car manufacturers. More particularly, same must have satisfactory properties in terms of viscosity, viscosity-temperature resistance, cold performance, etc., suitable for the implementation thereof in a transmission component, in particular in the gearbox or axles, in a vehicle.

Lubricating compositions also called cooling compositions can also be used in energy storage devices, such as data centers.

There is a need to provide lubricating and/or cooling compositions of renewable plant origin with a low impact on the environment.

Furthermore, current environmental concerns, in particular aimed at reducing carbon dioxide emissions, give rise to an urgent need to reduce the fuel consumption of motor vehicles. As such, it is known that lubricating compositions represent an effective means of acting on fuel consumption via the impact thereof on the frictional forces generated between the different components of motor vehicles. Thereby, there is a need to develop lubricants that reduce friction in gearboxes and axle differentials.

Improving the “Fuel Eco” properties of transmission lubricants, while maintaining the high levels of performance required, remains a challenge.

As examples of lubricants for transmissions, mention may be made of document WO 2010/038147 which proposes, in order to save fuel, to formulate lubricating compositions for gearboxes, using at least 30% by weight of one or a plurality of methyl esters of fatty acids of formula RCOOCH3, where R is a paraffinic or olefinic moiety having from 11 to 23 carbon atoms, in combination with one or a plurality of phosphorus, sulfur or phosphorus-sulfur antiwear and/or extreme pressure additives and polyalphaolefins.

Mention may also be made of document US 2017/0145337 which describes lubricating compositions for transmissions, exhibiting a gain in “Fuel Eco”, based on a base oil having a kinematic viscosity at 100° C. ranging from 1.5 mm²/s to 3.5 mm²/s, and comprising from 3% to 10% of an oil of the monoester type with a kinematic viscosity at 100° C. ranging from 2 mm²/s to 10 mm²/s, as well as an ester type providing sulfur.

The present invention aims at proposing a novel lubricating composition having improved properties in terms of reducing friction or cooling properties.

The present invention also aims to propose a novel lubricating composition, exhibiting improved properties in terms of fuel economy (“Fuel Eco” properties), while satisfying the properties required for the implementation thereof for lubricating the transmission components of light or heavy motor vehicles, e.g. gearbox and axles, and more particularly exhibiting good performance in terms of cold properties.

SUMMARY OF THE INVENTION

The subject matter of the present invention thereby primarily relates to a lubricating composition comprising:

• • one or a plurality of diesters, each of said diesters being formed between:
    • a diol selected from 1,2-propanediol, 1,2-decanediol and 1,3-diols having from 3 to 10 carbon atoms, and
    • two monocarboxylic acids, identical or different, having a linear or branched hydrocarbon chain having from 4 to 10 carbon atoms, and
  • at least one base oil distinct from the diester and/or at least one additive distinct from the diester, said additive being selected from friction modifier additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressants (PPD), dispersants, anti-foam agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof.

According to one embodiment, the lubricating composition according to the invention comprises:

• • from 5 to 95% by weight, preferably from 10 to 90% by weight, else preferably from 20 to 80% by weight, even more preferably from 30 to 70% by weight, or even from 40 to 60% by weight of the said diester or diesters,
  • from 1 to 95% by weight, preferably from 10 to 90% by weight, more preferably from 20 to 80% by weight, else more preferentially from 30 to 70% by weight or even from 40 to 60% by weight of one or a plurality of base oils different from said diesters,
  • optionally, from 0.01 to 20% by weight, preferably from 0.05 to 15% by weight, else preferably from 0.1 to 10% by weight, else more preferentially from 0.5 to 7% by weight, or even from 1 to 5% by weight of one or a plurality of additives distinct from the diester and distinct from the base oil(s),
    with respect to the total weight of the composition.

According to one embodiment, the lubricating composition according to the invention comprises:

• • at least 5% by weight, preferably at least 10% by weight, preferably at least 30% by weight, preferably at least 50% by weight, more preferentially at least 70% by weight, or even at least 90% by weight, of one or a plurality of diesters;
  • from 0.01 to 20% by weight, preferably from 0.05 to 15% by weight, more preferably from 0.1 to 10% by weight, else more preferentially from 0.5 to 7% by weight, or even from 1 to 5% by weight, of one or a plurality of additives chosen from friction modifier additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant additives (PPD), dispersants, anti-foam agents, thickeners, corrosion inhibitors, copper thickening agents, and mixtures thereof; and
  • optionally, from 5 to 94% by weight, preferably from 10 to 94% by weight, preferably from 15 to 90% by weight of base oil(s) distinct from the diester according to the invention, with respect to the total weight of the composition.

Preferably, said diester includes 13 to 25 carbon atoms; preferably from 13 to 24 carbon atoms,

Preferably, said diester has a kinematic viscosity at 100° C. ranging from 1 to 6 mm²/s, preferably ranging from 1 to 4 mm²/s.

Preferably, the diol is chosen from 1,2-propanediol, 1,2-decanediol and 1,3-alkanediol having from 3 to 7 carbon atoms, preferably from 1,2-propanediol and 1,3-propanediol, else preferably the diol is 1,2-propanediol.

Preferably, said monocarboxylic acids, either identical or different, include a linear hydrocarbon chain having from 4 to 10 carbon atoms, preferably from 5 to 9 carbon atoms.

Preferably, said diester(s) is (are) chosen from:

• • a diester formed from 1,2-decanediol and two heptanoic acids,
  • a diester formed from 1,2-decanediol and two pentanoic acids,
  • a diester formed from 1,2-propanediol and two heptanoic acids,
  • a diester formed from 1,2-propanediol and two nonanoic acids,
  • a diester formed from 1,3-propanediol and two heptanoic acids,
  • a diester formed from 1,2-propanediol and two octanoic acids,
  • a diester formed from 1,2-propanediol and two decanoic acids,
  • a diester formed from 1,2-propanediol and an octanoic acid and a decanoic acid,
    and mixtures thereof.

Preferably, the lubricating composition according to the invention comprises:

• • One or a plurality of diesters selected from:
    • The diesters formed between:
      • a diol selected from 1,2-decanediol and 1,3-propanediol, and
      • two monocarboxylic acids, identical or different, having a linear or branched hydrocarbon chain having from 4 to 10 carbon atoms, and
    • a diester formed from 1,2-propanediol and two heptanoic acids,
    • a diester formed from 1,2-propanediol and two octanoic acids,
    • a diester formed from 1,2-propanediol and two decanoic acids,
    • a diester formed from 1,2-propanediol and an octanoic acid and a decanoic acid,
  • and mixtures thereof, and
  • at least one base oil distinct from the diester and/or at least one additive distinct from the diester, said additive being selected from friction modifier additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressants (PPD), dispersants, anti-foam agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof.

The invention further relates to the use of at least one diester in a lubricating composition,

• • said diester being formed between:
    • a diol chosen from 1,2-propanediol, 1,2-decanediol and 1,3-diols having from 3 to 10 carbon atoms, and
    • two monocarboxylic acids, identical or different, having a linear or branched hydrocarbon chain having from 4 to 10 carbon atoms, and
  • said lubricating composition further comprising at least one base oil distinct from the diester and/or at least one additive distinct from the diester, s said additive being selected from friction modifier additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressants (PPD), dispersants, anti-foam agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof.

According to one embodiment, said at least one diester is used to lubricate and/or to cool at least one element of a mobile or stationary system, chosen e.g. from a heavy or light vehicle, a public works vehicle, and an energy storage system.

Preferably, the mobile system is a vehicle, the lubricating composition being used to reduce the fuel consumption of a vehicle equipped with a transmission component, in particular of a gearbox and/or of an axle, lubricated by means of the composition.

Preferably, the diester employed in the use according to the invention is as defined within the framework of the lubricating composition according to the invention and/or the lubricating composition employed in the use according to the invention is as defined within the framework of the lubricating composition according to the invention.

According to one embodiment, the invention relates to the use of at least one diester in a lubricating composition for lubricating and/or cooling at least one element of a mobile or stationary system chosen from a public works machinery and an energy storage system,

• • said diester being formed between:
    • a diol selected from 1,2-propanediol, 1,2-decanediol and 1,3-diols having from 3 to carbon atoms, and
    • two monocarboxylic acids, identical or different, having a linear or branched hydrocarbon chain having from 4 to 10 carbon atoms, and
  • said lubricating composition further comprising at least one base oil distinct from the diester and/or at least one additive distinct from the diester, said additive being selected from friction modifier additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressants (PPD), dispersants, anti-foam agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof.

According to one embodiment, the invention relates to the use of at least one diester in a lubricating composition for lubricating and/or cooling at least one element of a mobile system, said mobile system being a vehicle,

• • said diester being formed between:
    • a diol selected from 1,2-propanediol, 1,2-decanediol and 1,3-diols having from 3 to carbon atoms, and
    • two monocarboxylic acids, identical or different, having a linear or branched hydrocarbon chain having from 4 to 10 carbon atoms, and
  • said lubricating composition further comprising at least one base oil distinct from the diester and/or at least one additive distinct from the diester, said additive being selected from friction modifier additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressants (PPD), dispersants, anti-foam agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof, said lubricating composition being used for reducing the consumption of fuel of a vehicle equipped with a transmission component, in particular a gearbox and/or an axle, lubricated using the composition.

Hereinafter in the text, the expressions “comprised between . . . and . . . ”, “ranging from . . . to . . . ” and “varying from . . . to . . . ” are equivalent and mean that the limits are included, unless otherwise stated.

Unless otherwise specified, the expression “comprising a” shall be understood as “comprising at least one”.

DETAILED DESCRIPTION

Firstly, the invention relates to a lubricating composition comprising:

• • at least one diester formed between:
    • a diol selected from 1,2-propanediol, 1,2-decanediol and 1,3-diols having from 3 to 10 carbon atoms, and
    • two monocarboxylic acids, identical or different, having a linear or branched hydrocarbon chain having from 4 to 10 carbon atoms, and
  • at least one ingredient selected from base oils distinct from the diester, additives distinct from the diester, and mixtures thereof, said additive, when present, being selected from friction modifier additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressants (PPD), dispersants, anti-foam agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof.

The lubricating composition according to the invention may comprise one or a plurality of diesters, each of said diesters being formed between:

• • a diol chosen from 1,2-propanediol, 1,2-decanediol and 1,3-diols having from 3 to 10 carbon atoms, and
  • monocarboxylic acids, identical or different, having a linear or branched hydrocarbon chain having from 5 to 10 carbon atoms, and

More particularly, it is possible to prepare a mixture of diesters by reacting a diol and a mixture of monocarboxylic acids.

For example, it is possible to react a diol and three monocarboxylic acids A1, A2 and A3. Thereby, according to such example, the mixture of diesters falling within the scope of the present invention can comprise:

• • a diester formed between the diol and two acids A1,
  • a diester formed between the diol and two acids A2,
  • a diester formed between the diol and two acids A3,
  • a diester formed between the diol and an acid A1 and an acid A2,
  • a diester formed between the diol and an acid A1 and an acid A3,
  • a diester formed between the diol and an acid A2 and an acid A3.

Diester Used According to the Invention

As mentioned hereinabove, the diester(s) used according to the invention is (are) formed between a diol and two monocarboxylic acids.

“Diester formed between a diol and two monocarboxylic acids”, as defined by the present invention, refers to a compound obtained by two esterification reactions, each esterification reaction being carried out between one of the two alcohol functions of the diol and the acid function of one of the two monocarboxylic acids.

According to a preferred embodiment, the diester has 13 to 25 carbon atoms, preferably from 15 to 24 carbon atoms.

The diol used in the invention is among 1,2-propanediol, 1,2-decanediol and 1,3-diols including from 3 to 10 carbon atoms.

“Diol” refers to a compound including (exactly) two hydroxyl functions (—OH).

“1,3-diol including X to Y carbon atoms” means a diol the alcohol functions of which are located in position 1 and in position 3, respectively, of a hydrocarbon chain including X to Y carbon atoms.

“Hydrocarbon chain”, as defined by the invention, refers to a linear or branched, saturated or unsaturated alkyl or alkylene chain. The hydrocarbon chain may optionally be interrupted by one or a plurality of heteroatoms, more particularly by one or a plurality of oxygen atoms. Preferably, the hydrocarbon chain is a linear or branched, saturated or unsaturated alkyl or alkylene chain consisting of carbon and hydrogen atoms.

According to one embodiment, the 1,3-diol having from 3 to 10 carbon atoms is chosen from 1,3-alkanediols having from 3 to 10 carbon atoms

“1,3-alkanediol having X to Y carbon atoms'” means a diol the alcohol functions of which are located in position 1 and in position 3, respectively, of an alkane chain having X to Y carbon atoms.

According to one embodiment, the diol is chosen from 1,2-propanediol, 1,2-decanediol and 1,3-diol having from 3 to 7 carbon atoms, preferably from 1,2-propanediol and 1,3-alkanediol having from 3 to 7 carbon atoms, more preferably from 1,2-propanediol and 1,3-propanediol, advantageously the diol is 1,2-propanediol.

The diol used according to the invention may be available commercially or synthetized according to any method well known to a person skilled in the art.

Preferably, the diol used according to the invention comprises a content of carbon of biological origin of at least 60% by weight, preferably of at least 70% by weight, else preferably of at least 80% by weight, else more preferentially of at least 90% by weight, relative to the total weight of the carbon atoms of the diol.

Within the framework of the present invention, the content of carbon of biological origin can be measured as per the standard ASTM D6866.

The diester used according to the invention is obtained from two identical or different monocarboxylic acids.

“Monocarboxylic acid” means a compound including a single carboxyl function (—COOH).

The hydroxycarboxylic acid used to form a diester of the invention are chosen from monocarboxylic acids having a linear hydrocarbon chain having from 4 to 10 carbon atoms, preferably from 5 to 9 carbon atoms, else preferably from 5 to 8 carbon atoms. Preferably, the linear or branched hydrocarbon chain of monocarboxylic acids is saturated.

According to an embodiment, monocarboxylic acids, either identical or different, include a linear hydrocarbon chain having from 5 to 10 carbon atoms, preferably from 5 to 9 carbon atoms, else preferably from 5 to 8 carbon atoms.

According to an embodiment, monocarboxylic acids, either identical or different, include a saturated linear hydrocarbon chain having from 5 to 10 carbon atoms, preferably from 5 to 9 carbon atoms, else preferably from 5 to 8 carbon atoms.

The monocarboxylic acids used according to the invention may be commercially available or synthesized according to any method known to a person skilled in the art.

Preferably, the monocarboxylic acids used according to the invention comprise a content of carbon of biological origin of at least 60% by weight, preferably of at least 70% by weight, else preferably of at least 80% by weight, else more preferentially of at least 90% by weight, relative to the total weight of the carbon atoms of the diol.

Preferably, the diester used in the invention is saturated.

“Saturated diester”, as defined by the invention, means a diester having saturated hydrocarbon chains. Thereby, preferably, the diol used according to the invention includes a saturated hydrocarbon chain and the monocarboxylic acids used according to the invention each include a saturated hydrocarbon chain. Preferably, said hydrocarbon chain consists of carbon and hydrogen atoms.

According to a particular embodiment, the diester used according to the invention is a branched diester.

“Branched diester”, as defined by the invention, refers to a diester having a branched hydrocarbon chain which can be located between the two ester functions and/or at one or both ends of the diester.

According to a preferred embodiment, the diester used in the invention is saturated and branched.

According to an embodiment, the diester used according to the invention has a kinematic viscosity, measured at 100° C. as per the standard ASTM D445, ranging from 1 to 6 mm²/s, preferably from 1 to 4 mm²/s.

According to an embodiment, the diester according to the invention has a kinematic viscosity, measured at 40° C. as per the standard ASTM D445, ranging from 2 to 20 mm²/s, preferably from 3 to 10 mm²/s.

It is understood that the definitions given above for carboxylic acid and alcohol can be combined, insofar as possible, to define other particular embodiments.

A diester used according to the invention may correspond more particularly to one of the following formulae (I), (II) or (III):

wherein:

• • R¹ represents a linear or branched, saturated or unsaturated, preferably saturated, hydrocarbon-based chain having from 3 to 9 carbon atoms, preferably from 4 to 8 carbon atoms, preferably from 5 to 7 carbon atoms, said hydrocarbon chain being possibly interrupted by one or a plurality heteroatoms, such as oxygen atoms, preferably the hydrocarbon chain consists of carbon atoms and hydrogen atoms; and
  • R² represents a linear or branched, saturated or unsaturated hydrocarbon chain, preferably saturated, having 3 to 9 carbon atoms, preferably from 4 to 8 carbon atoms, preferably from 5 to 7 carbon atoms, said hydrocarbon chain being possibly interrupted by one or a plurality of heteroatoms, such as oxygen atoms, preferably the hydrocarbon chain consists of carbon and hydrogen atoms.

Preferably, the diester(s) corresponding to formula (I), (II) or (III) have from 13 to carbon atoms, preferably from 15 to 24 carbon atoms.

In the diesters of formulae (I), (II) or (III), R¹ and R² may be identical or different.

According to one embodiment, the diester(s) used according to the invention is (are) chosen from:

• • a diester formed from 1,2-decanediol and two heptanoic acids,
  • a diester formed from 1,2-decanediol and two pentanoic acids,
  • a diester formed from 1,2-propanediol and two heptanoic acids,
  • a diester formed from 1,2-propanediol and two nonanoic acids, a diester formed from 1,3-propanediol and two heptanoic acids,
  • a diester formed from 1,2-propanediol and two octanoic acids,
  • a diester formed from 1,2-propanediol and two decanoic acids,
  • a diester formed from 1,2-propanediol and a mixture of acids comprising an octanoic acid and a decanoic acid,
  • and mixtures thereof.

The diesters according to the invention can be prepared according to synthesis methods known to a person skilled in the art. The synthesis methods employ more particularly two esterification reactions, each esterification reaction being carried out between an alcohol function of the diol and the acid function of the monocarboxylic acid.

Of course, it is for a person skilled in the art to adjust the synthesis conditions in order to obtain a diester according to the invention.

It is understood that, within the framework of the present invention, a diester according to the invention may be in the form of a mixture of at least two diesters according to the invention, more particularly diesters as defined hereinabove.

Preferably, the diester used according to the invention comprises a content of carbon of biological origin of at least 60% by weight, preferably of at least 70% by weight, else preferably of at least 80% by weight, else more preferentially of at least 90% by weight, relative to the total weight of the carbon atoms of the diester.

Within the framework of the present invention, the content of carbon of biological origin can be measured as per the standard ASTM D6866.

The diester or the mixture of diesters according to the invention may represent at least 5% by weight of the composition according to the invention, preferably at least 10% by weight, preferably at least 30% by weight, more preferentially at least 50% by weight, else more preferentially at least 70% by weight, more particularly at least 80% by weight, more particularly at least 90% by weight, or even at least 95% by weight, of the total weight of the composition according to the invention.

The diester(s) according to the invention can be used with one or a plurality of ancillary base oils (also called co-bases). According to one embodiment, the composition comprises:

• • from 5 to 95% by weight, preferably from 5 to 50% by weight, more preferably from 10 to 40% by weight, of the diester or diesters according to the invention, and
  • from 5 to 95% by weight, preferably from 50 to 95% by weight, preferably from 60 to 90% by weight, of one or a plurality of different base oils according to the invention,
    with respect to the total weight of the diester(s) and base oils different from the diesters.

According to one embodiment, a lubricating composition according to the invention may comprise at least 30% by weight of a diester or mixture of diesters according to the invention, more particularly between 50% and 99.5% by weight, preferably between 70% and 99% by weight, more preferentially between 80% and 99% by weight, or even between 80% and 95% by weight, with respect to the total weight of said composition.

According to a particular embodiment, a lubricating composition according to the invention may be formed to more than 95% by weight, more particularly to more than 98% by weight, of one or a plurality of diesters according to the invention.

According to a particular embodiment, the composition according to the invention is a composition comprising 100% by weight of a mixture of diester(s) defined in the invention and of additional base oil(s), preferably in a proportion such that the composition comprises:

• • from 5 to 95% by weight, preferably from 5 to 50% by weight, more preferably from 10 to 40% by weight, of the diester or diesters according to the invention, and
  • from 5 to 95% by weight, preferably from 50 to 95% by weight, preferably from 60 to 90% by weight, of one or a plurality of different base oils according to the invention,
  • with respect to the total weight of the composition.

Such embodiment is particularly advantageous when the composition is used for cooling, as a cooling fluid.

Ancillary Base Oil(s) (Co-Base(s))

The lubricating composition according to the invention may comprise, in addition to one or a plurality of diesters according to the invention, one or a plurality of base oils distinct from the diesters according to the invention, referred to as an “ancillary base oil”.

Said base oil or oils optionally present in the lubricating composition according to the invention, are chosen suitably, with regard to the compatibility thereof with said diester or diesters used according to the invention.

There can be a mixture of a plurality of base oils, e.g. a mixture of two, three, or four base oils.

Preferably, the base oil or mixture of ancillary base oils used in the lubricating composition according to the invention may have a kinematic viscosity, measured at 100° C. as per the standard ASTM D445, ranging from 1.5 to 8 mm²/s, in particular from 1.5 to 6.1 mm²/s, more particularly from 1.5 to 4.1 mm²/s, even more particularly from 1.5 to 2.1 mm²/s.

The base oils can be chosen from mineral or synthetic oils belonging to groups I to V as per the classes defined by the API classification (or the equivalents thereof as per the ATIEL classification) and shown in Table 1 hereinafter, or mixtures thereof.

	TABLE 1
	Concentration	Sulfur	Viscosity index
	of saturates	concentration	(VI)

Group I (mineral oils)	<90%	>0.03%	80 ≤ VI < 120
Group II (Hydrocracked oils)	≥90%	≤0.03%	80 ≤ VI < 120
Group III (Hydro-isomerized	≥90%	≤0.03%	≥120
or hydrocracked oils)

Group IV	Polyalphaolefins (PAO)
Group V	Esters and other bases not included in groups I to IV

The mineral base oils include any type of base oil obtained by atmospheric distillation and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, deasphalting, solvent dewaxing, hydrotreatment, hydrocracking, hydroisomerization and hydrofinishing.

Mixtures of synthetic and mineral oils which can be biosourced, can be further used.

The base oils can be further chosen from synthetic oils, such as certain carboxylic acid esters and alcohol esters distinct from the ester defined according to the invention, among polyalphaolefins (PAO), and among polyalkylene glycol (PAG) obtained by polymerization or copolymerization of alkylene oxides comprising from 2 to 8 carbon atoms, more particularly from 2 to 4 carbon atoms.

The PAOs used as base oils are e.g. obtained from monomers comprising from 4 to 32 carbon atoms, e.g. from octene or decene.

The weight-average molecular weight of the PAO can vary quite significantly. Preferentially, the weight-average molecular weight of the PAO is less than 600 Da. The weight-average molecular weight of the PAO can further range from 100 to 600 Da, from 150 to 600 Da, or further from 200 to 600 Da.

For example, the PAOs used in the context of the invention, having a kinematic viscosity, measured at 100° C. as pr the standard ASTM D445, ranging from 1.5 to 8 mm²/s, are sold commercially by Ineos under the trademarks Durasyn® 162, Durasyn® 164, Durasyn® 166 and Durasyn® 168.

Advantageously, the additional base oil or oils are chosen from polyalphaolefins (PAOs).

It is for a person skilled in the art to adjust the content of ancillary base oil(s) to be used in the composition according to the invention.

More particularly, a composition according to the invention may comprise from 5 to 95% by weight, preferably from 50 to 95% by weight, else preferably from 60 to 90% by weight, of one or a plurality of base oils different from the diesters according to the invention, relative to the total weight of said composition.

Additives

The lubricating composition according to the invention may optionally further comprise one or a plurality of additives known to a person skilled in the art in the field of lubrication, more particularly for vehicle transmissions, in particular for transmissions of light or heavy vehicles.

The additives may be chosen in particular from friction modifier additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressants (PPD), dispersants, anti-foam agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof.

Preferably, the lubricating composition according to the invention may further comprise one or a plurality of additives chosen from antioxidants, anti-foams, pour point improvers and anticorrosion agents.

It is understood that the nature and the amount of additives used are chosen so as not to affect the properties of the lubricating composition imparted by the diester according to the invention.

Such additives can be introduced separately and/or as a mixture similar to the additives already available for sale for commercial lubricant formulations for vehicle engines, with a performance level as defined by ACEA (European Automobile Manufacturers Association) and/or API (American Petroleum Institute), well known to a person skilled in the art.

Said additive(s) may be present in the lubricating composition according to the invention in a content of less than or equal to 10% by weight, more particularly less than or equal to 5% by weight, and more particularly ranging from 0.01 to 3% by weight, relative to the total weight of said composition.

A lubricating composition according to the invention can further comprise at least one antioxidant additive.

Thereby the invention relates, according to one of the aspects thereof, to a lubricating composition comprising (i) at least one diester as defined above, and (ii) at least one antioxidant additive.

The antioxidant additive generally makes it possible to delay the degradation of the composition in service. Such degradation most often shows as a deposit formation, in the presence of sludge or in an increase in the viscosity of the composition.

Antioxidant additives in particular act as radical inhibitors or destroyers of hydroperoxides.

The antioxidant additives commonly used include phenolic antioxidants, amine antioxidant additives, phosphosulfur antioxidant additives. Some of such antioxidant additives, e.g. phosphosulfur antioxidant additives, can generate ashes. The phenolic antioxidant additives can be without ashes or in the form of neutral or basic metal salts. The antioxidant additives can in particular be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted with at least one C₁-C₁₂ alkyl moiety, N,N′-dialkyl-aryl-diamines and mixtures thereof. Preferentially, the sterically hindered phenols are chosen from compounds comprising a phenol moiety of which at least one of the neighboring carbon to the carbon atom bearing the alcohol function is substituted by at least one C₁-C₁₀ alkyl moiety, preferentially a C₁-C₆ alkyl moiety, preferentially a C₄ alkyl moiety, preferentially a tert-butyl moiety. Amine compounds are another class of antioxidant additives which can be used optionally in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, e.g. aromatic amines with the formula NR⁵R⁶R⁷ wherein R⁵ represents an aliphatic moiety or a possibly substituted aromatic moiety, R⁶ represents a possibly substituted aromatic moiety, R⁷ represents a hydrogen atom, an alkyl moiety, an aryl moiety or a moiety with the formula R⁸S(O)_zR⁹ wherein R⁸ represents an alkylene or an alkenylene moiety, R⁹ represents an alkyl moiety, an alkenyl moiety or an aryl moiety and z is 0, 1 or 2. Sulfur alkyl phenols or the alkali or alkaline-earth metal salts thereof can be further used as antioxidant additives.

Advantageously, a lubricating composition comprises at least one antioxidant additive without ashes.

Said additive(s) may be used, in a lubricating composition according to the invention, in a proportion of 0.1 to 2% by weight, relative to the total mass of the composition.

The lubricating composition according to the invention can comprise at least one anti-wear additive, one extreme-pressure additive or mixtures thereof.

Anti-wear additives and extreme pressure additives protect surfaces subject to friction by forming a protective film adsorbed on the surfaces.

There is a wide variety of anti-wear additives. Preferably, the anti-wear additives are chosen from phosphorus-sulfur additives such as metal alkylthiophosphates, more particularly zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTP. Preferred compounds have the formula Zn ((SP(S)(OQ²)(OQ³))₂, wherein Q² and Q³—either identical or different—independently represent an alkyl moiety, preferentially an alkyl moiety including from 1 to 18 carbon atoms.

Preferably, the lubricating composition according to the invention is free of esters such as phosphites containing sulfur of formula

wherein R is a C₄ to C₂₀ hydrocarbon moiety and R¹ is hydrogen, a C₄ to C₂₀ hydrocarbon moiety or a C₄ to C₂₀ hydrocarbon moiety containing sulfur.

Amine phosphates as well are anti-wear additives which can be used in the lubricating compositions according to the invention. However, the phosphorus provided by such additives can act as a poison in the catalytic systems of cars since same generate ash. Such effects can be minimized by partially substituting the amine phosphates with additives which do not bring phosphorous, such as e.g. polysulfides, in particular sulfur olefins.

A lubricating composition may comprise from 0.01 to 6% by weight, preferentially from 0.05 to 4% by weight, more preferentially or from 0.1 to 2% by anti-wear additives and extreme-pressure additives, by weight with respect to the total weight of the composition.

A lubricating composition according to the invention can further comprise a anti-foam agent.

The anti-foam agent can be chosen from silicones.

A lubricating composition can comprise from 0.01 to 2% by weight or from 0.01 to 5% by weight, preferentially from 0.1 to 1.5% by weight or from 0.1 to 2% by weight of anti-foam agent, with respect to the total weight of the composition.

A lubricating composition according to the invention can further comprise at least one friction modifier additive.

Friction modifier additives serve to limit friction by forming adsorbed monolayers on the surfaces of the metals in contact thereto. Same can be chosen from compounds providing metallic elements and ashless compounds. The compounds providing metallic elements include transition metal complexes such as Mo and Sb. Sn, Fe, Cu, Zn the ligands of which can be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus atoms. Ashless friction modifier additives are generally of organic origin and can be chosen from fatty acid and polyol esters, distinct from the monoester required according to the invention, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, fatty epoxide borates, amines acid or fatty acid glycerol esters. According to the invention, fatty compounds comprise at least one hydrocarbon moiety comprising from 10 to 24 carbon atoms. More particularly, the molybdenum compounds may be chosen from molybdenum dithiocarbamates (Mo-DTC), molybdenum dithiophosphates (Mo-DTP), and mixtures thereof. A lubricating composition may in particular comprise a content of molybdenum comprised between 1000 and 2500 ppm.

A lubricating composition may comprise from 0.01 to 5% by weight, more particularly from 0.1 to 2% by weight or even more particularly from 0.1 to 1.5% by weight of friction modifier additive, relative to the total mass of the composition.

When used at too high a content, molybdenum compounds can negatively affect the cold properties of the lubricating composition wherein same are used. Thereby, a lubricating composition according to the invention preferably comprises less than 1.5% by weight of molybdenum, more preferentially less than 1% by weight, relative to the total weight of the composition, or is even free of molybdenum.

A lubricating composition according to the invention can comprise at least one detergent additive.

Detergent additives generally reduce the formation of deposits on the surface of metal parts, by dissolving oxidation and combustion by-products.

The detergent additives which can be used in the lubricating compositions are generally known to a person skilled in the art. The detergent additives can be anionic compounds comprising a lipophilic hydrocarbon moiety and a hydrophilic head. The associated cation can be a metal cation of an alkali or alkaline earth metal.

Detergent additives are preferentially chosen from alkali metal salts or alkaline-earth metal salts of carboxylic acid, sulfonates, salicylates, naphthenates, as well as phenate salts. The alkali metals and alkaline earth metals are preferentially calcium, magnesium, sodium or barium.

Such metal salts generally include the metal in a stoichiometric amount or in an excess amount, i.e. in a concentration greater than the stoichiometric amount. Same are then overbased detergents; the metal in excess which gives the overbased character to the detergent additive is generally in the form of an oil-insoluble metal salt, e.g. a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferentially a carbonate.

A lubricating composition can e.g. comprise from 2 to 4% by weight of detergent additive, with respect to the total weight of the composition.

A lubricating composition according to the invention can further comprise at least one pour point depressant (PPD) additive.

By slowing down the formation of paraffin crystals, the pour point depressant additive generally improves the behavior of the composition under cold conditions. Examples of pour point depressant additives include alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalene, alkyls polystyrenes.

A lubricating composition according to the invention can comprise 0.1% to 2%, preferably from 0.2% to 1% pour point depressant additive(s), with respect to the total weight of the composition.

Also, the lubricating composition can comprise at least one dispersing agent.

The dispersing agent can be chosen from Mannich bases, succinimide and derivatives thereof, such as derivatives of polyisobutylene succinic anhydride.

A lubricating composition can comprise e.g. from 0.2 to 10% by weight of dispersant, with respect to the total weight of the composition.

The lubricating composition used according to the invention can comprise at least one viscosity index (VI) improver additive.

Viscosity index improvers, more particularly polymers improving the viscosity index, provide good cold resistance and minimum viscosity at high temperatures.

Examples of polymers improving the viscosity index include polymer esters, hydrogenated or non-hydrogenated homopolymers or copolymers of styrene, of butadiene and of isoprene, homopolymers or copolymers of olefin, such as ethylene or propylene, polyacrylates and polymethacrylates (PMA), preferably homopolymers or copolymers of olefin, such as ethylene or propylene.

More particularly, a lubricating composition according to the invention may comprise from 1 to 15% by weight of additive(s) improving the viscosity index, preferably from 5% to 10% by weight, relative to the total weight of the lubricating composition.

A lubricating composition may also comprise at least one anti-foam additive, e.g. chosen from polar polymers such as polymethylsiloxanes or polyacrylates.

More particularly, a lubricating composition according to the invention can comprise from 0.01 to 3% by weight additive(s) with respect to the total weight of lubricating composition.

Same may also comprise at least one anticorrosion agent or copper passivating agent, e.g. compounds such as polyisobutene succinic anhydrides, thiadiazole sulfonates or mercaptobenzothiazoles. Same are typically present in a lubricating composition according to the invention in contents comprised between 0.01% and 1% by weight, relative to the total weight of the composition.

Advantageously, a lubricating composition according to the invention comprises one or a plurality of additives chosen from viscosity index improvers, pour point depressants, anti-wear agents and antioxidant agents.

According to a particular embodiment, a lubricating composition according to the invention comprises, is even formed (i) by at least one diester according to the invention and (ii) by at least one additive chosen from antioxidants, viscosity index improvers, pour point depressants, anti-wear and/or extreme pressure additives, anti-foam agents detergents, dispersants, and mixtures thereof, preferably from antioxidants, viscosity index improvers, pour point depressants, anti-wear and extreme pressure additives and mixtures thereof.

Advantageously, a lubricating composition according to the invention is formed (i) by at least one diester corresponding to one of the formulae (I), (II) or (III) as defined hereinabove and (ii) at least one antioxidant additive.

Advantageously, a lubricating composition according to the invention is formed (i) by at least one diester corresponding to one of the formulae (I) or (II) as defined hereinabove and (ii) at least one antioxidant additive.

According to a particular embodiment, a composition according to the invention comprises, or even consists of:

• • at least 5% by weight, preferably at least 10% by weight, preferably at least 30% by weight, preferably at least 50% by weight, more preferentially at least 70% by weight, or even at least 90% by weight, of diester(s) corresponding to one of the formulae (I), (II) or (III);
  • from 0.01 to 20% by weight, preferably from 0.05 to 15% by weight, more preferably from 0.1 to 10% by weight, else more preferentially from 0.5 to 7% by weight, or even from 1 to 5% by weight, of one or a plurality of additives chosen from friction modifier additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant additives (PPD), dispersants, anti-foam agents, thickeners, corrosion inhibitors, copper thickening agents, and mixtures thereof; and
  • optionally, from 5 to 94% by weight, preferably from 10 to 94% by weight, preferably from 15 to 90% by weight of base oil(s) distinct from the diester according to the invention,
  • the contents being expressed with respect to the total weight of said composition.

According to a particular embodiment, a composition according to the invention comprises, or even consists of:

• • from 5 to 95% by weight, preferably from 10 to 90% by weight, more preferably from 20 to 80% by weight, even more preferentially from 30 to 70% by weight, or even from 40 to 60% by weight, of diester(s) corresponding to one of the formulae (I), (II) or (III);
  • from 5 to 95% by weight, preferably from 10 to 90% by weight, more preferably from 20 to 80% by weight, else more preferentially from 30 to 70% by weight or even from 40 to 60% by weight of one or a plurality of base oils different from said diesters,
  • optionally, from 0.01 to 20% by weight, preferably from 0.05 to 15% by weight, else preferably from 0.1 to 10% by weight, even more preferentially from 0.5 to 7% by weight, or even from 1 to 5% by weight of one or a plurality of additives distinct from the diester and distinct from the base oil(s), the contents being expressed relative to the total weight of said composition.

According to one particular embodiment, a lubricating composition according to the invention comprises, or even consists of:

• • at least 5% by weight, preferably from 10% to 40%, more preferentially from 15% to 30% by weight, of one or a plurality of diesters according to the invention defined hereinabove, preferably chosen from the diesters corresponding to formula (I);
  • from 50% to 95% by weight of base oil(s) distinct from the diesters defined according to the invention, preferably chosen from group II and/or III base oils according to the API classification;
  • optionally, from 5% to 15% by weight of at least one viscosity index improver additive;
  • optionally, from 0.1% to 1% by weight of at least one pour point depressant additive;
  • optionally, from 0.01% to 6% by weight of at least one anti-wear additive; and
  • optionally, from 0.1% to 2% by weight of at least one antioxidant additive,
    the contents being expressed with respect to the total weight of said composition.

Preferably, the lubricating composition according to the invention comprises, or even consists of:

• • less than 30% by weight, more particularly from 1 and 30% by weight, in particular to 30% by weight, preferably 10 to 30% by weight and more particularly 15 to 30% by weight, of one or a plurality of diesters according to the invention defined hereinabove, preferably chosen from the diesters of formula (I) or (II);
  • from 50% to 85% by weight of base oil(s) distinct from the diesters defined according to the invention, preferably chosen from group II and/or III base oils according to the API classification;
  • optionally, from 5% to 15% by weight of at least one viscosity index improver additive;
  • optionally, from 0.1% to 1% by weight of at least one pour point depressant additive;
  • optionally, from 0.01% to 6% by weight of at least one anti-wear additive; and
  • optionally, from 0.1% to 2% by weight of at least one antioxidant additive,
  • the contents being expressed with respect to the total weight of said composition.

According to a particular embodiment, a composition according to the invention comprises, or even consists of:

• • from 5 to 95% by weight, preferably from 5 to 50% by weight, else preferably from to 40% by weight, of said diester(s) corresponding to the formula (I) or (II);
  • from 5 to 95% by weight, preferably from 50 to 95% by weight, preferably from 60 to 90% by weight, of one or a plurality of different said diesters;
  • optionally, from 0.01 to 20% by weight, preferably from 0.05 to 15% by weight, more preferably from 0.1 to 10% by weight, else more preferentially from 0.5 to 7% by weight, or even from 1 to 5% by weight, of one or a plurality of additives chosen from friction modifier additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant additives (PPD), dispersants, anti-foam agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof; and
  • the contents being expressed with respect to the total weight of said composition.

A composition according to the invention advantageously has a kinematic viscosity, measured at 100° C. as per the standard ASTM D445, ranging from 1 to 20 mm²/s, preferably from 2 to 15 mm²/s.

A composition according to the invention advantageously has a kinematic viscosity, measured at 40° C. as per the standard ASTM D445, ranging from 20 to 50 mm²/s, preferably from 25 to 40 mm²/s.

The composition according to the invention has good lubricating properties.

The composition according to the invention also has good properties in terms of cold resistance.

The composition according to the invention also has good cooling properties.

A further subject matter of present invention relates to the use of a diester in a composition for lubricating and/or cooling at least one part of a mobile or stationary system, said diester being formed between:

• • a diol selected from 1,2-propanediol, 1,2-decanediol and 1,3-diols having from 3 to 10 carbon atoms, and
  • monocarboxylic acids, identical or different, having a linear or branched hydrocarbon chain having from 4 to 10 carbon atoms, and

Preferably, the composition for lubricating and/or cooling further comprises at least one base oil distinct from the diester and/or at least one additive distinct from the diester,

• • said additive being chosen from antioxidants, pour point depressants, anti-foam agents, anticorrosion agents, anti-wear and/or extreme-pressure additives, friction modifiers, detergents, dispersants and mixtures thereof, more particularly from antioxidants, pour point depressants, anti-foam agents and anticorrosion agents.

The characteristic or characteristics of the diester presented in the context of the composition according to the invention are also applicable to the diester used according to the invention.

According to one embodiment of the use according to the invention, the lubricated and/or cooled part is a part of a heavy or light vehicle, of public works machinery, or of an energy storage device (e.g. datacenter).

The diester defined in the present invention serves to reduce the coefficients of friction of the lubricating composition.

The diester defined in the present invention makes it possible to cool the elements of a mobile or stationary system, such as a heavy or light vehicle, public works machinery, an energy storage device.

The composition formulated according to the invention, more particularly as described hereinabove, has excellent tribological properties, in particular in terms of reduction of friction, which makes same particularly well suited to use as a lubricating fluid.

The composition formulated according to the invention, more particularly described hereinabove, has excellent thermal properties, in particular in terms of thermal conductivity, which makes same particularly well suited to use as a cooling fluid.

A composition of the invention is suitable for lubricating transmission components of motor vehicles, in particular transmissions for light or heavy vehicles, e.g. gearboxes and/or axles.

More particularly, same can be used to lubricate the manual gearbox and/or axles of a light or heavy vehicle. Advantageously, a lubricating composition according to the invention has a performance, more particularly in terms of cold properties, which is particularly well suited to the use thereof for the transmission of heavy vehicles, more particularly for lubricating the manual gearbox and/or heavy vehicle axles.

The present invention further relates to a method for lubricating and/or cooling at least one part of a mobile or stationary system, comprising bringing the composition according to the invention into contact with said part.

According to one embodiment, the mobile or stationary system is chosen from a heavy or light vehicle, public works machinery, an energy storage device such as a datacenter.

The present invention further relates to a method for lubricating and/or cooling at least one mechanical part, in particular a motor vehicle transmission member, comprising bringing the lubricating composition according to the invention into contact with said mechanical part, more particularly said motor vehicle transmission component.

The diesters defined in the invention can be added to lubricating compositions used in vehicle transmissions in order to improve the “Fuel-Eco” properties thereof, namely the ability thereof to limit the fuel consumption of motor vehicles, without affecting the performance thereof, in particular in terms of cold properties.

The invention will now be described by means of the following examples, given of course as an illustration of the invention, but not limited to.

Example

Example 1: Preparation of the Compounds Tested

The following compounds were prepared:

• • Diester A: diester formed from 1,2-decanediol and two heptanoic acids
  • Diester B: diester formed from 1,2-decanediol and two pentanoic acids
  • Diester C: diester formed from 1,2-propanediol and two heptanoic acids
  • Diester D: diester formed from 1,2-propanediol and two nonanoic acids
  • Diester E: diester formed from 1,3-propanediol and two heptanoic acids
  • Diester F: mixture of diesters formed from 1,2-propanediol and a bio-based cut of C8-C10 acids
  • a monoester formed from a monocarboxylic acid having a saturated hydrocarbon chain of 3 to 14 carbon atoms; and a mono-alcohol having a saturated hydrocarbon chain of 3 to 14 carbon atoms.

The diesters and the monoester were prepared according to known methods of ester preparation.

The compositions tested hereinafter in the examples comprise 100% of each ester (diester or monoester) defined in the example 1.

Example 2: Viscosity Measurement

The kinematic viscosities at 100° C. (KV100) and at 40° C. (KV40) were determined as per the standard ASTM D445.

The viscosities are shown in Table 2.

	TABLE 2
	KV100 (mm2/s)	KV40 (mm2/s)

	Diester A	2.38	7.916
	Diester B	1.856	5.659
	Diester C	1.55	4.236
	Diester D	1.878	5.503
	Diester E	1.7404	4.7422
	Diester F	2.147	6.61
	Monoester	1.8	5.2

All the diesters used according to the invention have a viscosity of less than 4 mm²/s at 100° C.

Example 3: Measurement of Friction Coefficients

The tribological properties can be evaluated by a test on a ball-disc rotating tribometer (also called ball-plane) such as the linear reciprocating tribometer. The test serves to evaluate the performance of lubricants in terms of friction in mixed/limit conditions according to the load, pressure or speed conditions applied.

The coefficient of friction of the lubricating compositions tested is determined at 40° C. by using a hardened steel ball of about 2 cm in diameter, e.g. 1.905 cm in diameter, on a hardened steel plane.

The tribometer can be a device bringing a steel ball and a steel plane into movement relative to each other in order to determine friction/friction coefficients for a given lubricating composition while varying various properties such as speed, load, and temperature. The hardened steel surface has an AISI 52100 reference with a mirror finish and the ball has also an AISI 52100 reference and is made of hardened steel.

The applied load is 25 N and the driving speed varies from 10 mm/s to 2500 mm/s respectively. More particularly, the coefficient of friction is determined at a speed of rotation of 10 mm/s. The coefficient is determined at a Slide-to-Roll Ratio (% SRR) of 5%.

Approximately 50 ml of lubricating composition tested were added into the device. The ball is engaged face-to-plane, said ball and said plane being actuated independently so as to create a mixed rolling/sliding contact.

The coefficient of friction is measured and recorded by means of a force sensor.

The results with a drive speed of 225 mm²/s are given in Table 3.

The lubricating compositions tested comprise 100% of each ester defined in example 1.

	TABLE 3
	Coefficient of friction - 25N - 40° C. - 5% SRR

	Diester A	0.0053
	Diester B	0.0069
	Diester C	0.0214
	Diester D	0.013
	Diester E	0.019
	Diester F	0.0105
	Monoester	0.0371

The results show that the diesters used according to the invention have very low coefficients of friction, more particularly a coefficient of friction lower than the monoester.

Example 4: Mini Flash Point Measurement

The mini flash point is measured as per the standard ASTM D93Ac (Cleaveland open cup method).

The values are shown in Table 4.

	TABLE 4
	Mini flash point (° C.)

	Diester A	157.6
	Diester B	174.6
	Diester C	144
	Diester D	186.5
	Diester E	174.5
	Diester F	166.6
	Monoester	164.9

As shown by the values in Table 4, the flash point is all the better when the diester is a branched diester. Indeed, the diester formed from a 1,2-propanediol has a lower flash point than the diester formed from 1,3-propanediol, with the same number of carbon atoms in total.

Example 5: Measurement of the Mini Pour Point

The mini pour point is measured as per the standard ASTM D7346.

The values are shown in Table 5.

	TABLE 5
	Mini pour point (° C.)

	Diester A	−69
	Diester B	−87
	Diester C	−90
	Diester D	−48
	Diester F	−69
	Monoester	−34

The results of Table 5 show that the diesters used in the lubricating composition according to the invention have a low pour point, more particularly lower than the monoester.

Example 6: Measurement of the Coefficient of Traction

The coefficient of traction (COT) was measured using PCS Instrument's MTM tribometer. Same serves to evaluate the performance of lubricants in terms of friction in mixed/hydrodynamic conditions. The test consists in moving a steel ball and a steel plane relative to each other, at different speeds, making it possible to define the % SSR (Slide-to-Roll Ratio) which corresponds to the sliding speed/drive speed.

The measurement conditions were 25 N load, a disc velocity of 1.4 m/s for an estimated temperature of 100° C. and an SRR of 20%.

The lower the coefficient of traction for a lubricating composition, the lower the friction between metal parts, resulting in a greater gain in fuel saving.

The results obtained are shown in Table 6.

	TABLE 6
	COT

	Diester A	0.042
	Diester B	0.0028
	Diester D	0.0147
	Diester F	0.0088
	Monoester	0.0205

The results show that the diesters used according to the invention have very low coefficients of traction, more particularly a coefficient of traction lower than the monoester.

Example 7: Measurement of Thermal Conductivity

The thermal conductivity of the compounds described in example 1 was determined as per the standard ASTM D7896-19 at different temperatures.

The results are shown in Table 7.

	TABLE 7
	Thermal conductivity (mW · m−1 · K−1)

	50° C.	90° C.	130° C.

	Diester A	142.67	134.72	126.4
	Diester B	138.82	130.75	122.25
	Diester C	135.98	128.38	119.59
	Diester D	139.79	131.97	123.79
	Diester E	142.88	135.58	126.55
	Diester F	146.51	138.26	129.08
	Monoester	141.1	132.2	123.4

The results show that the diesters defined in the invention have good thermal properties, which makes possible the use thereof as cooling fluid.