WO2025051849A1

WO2025051849A1 - Gear lubricant compositions

Info

Publication number: WO2025051849A1
Application number: PCT/EP2024/074818
Authority: WO
Inventors: Jayram DAWKHAR; Ashok-Kumar GOYAL
Original assignee: Totalenergies Onetech
Priority date: 2023-09-05
Filing date: 2024-09-05
Publication date: 2025-03-13

Abstract

The present invention relates to the use of at least one polyisobutylene succinic anhydride compound as a friction modifier in a lubricating composition intended for the lubrication of gears or equipment comprising gears, said composition comprising more than 70% by weight, in particular more than 80% by weight, and more particularly 90% by weight, of at least one polyol ester of a C₃ to C₁₀ linear or branched aliphatic polyalcohol compound and of a linear or branched, saturated or unsaturated, C₆-C₃₀ monocarboxylic acid.

Description

Gear lubricant compositions

The present invention relates to gear lubricant compositions and a process for lubricating gearing or equipment that comprises gears. Said compositions according to the invention are biodegradable, do not accumulate in organisms and do not represent toxicity to the environment, especially the aquatic environment.

Since December 2013, US regulations have been amended to require all vessels operating in US waters to use Environmentally Acceptable lubricant (EAL) products, and since 1992 in Europe, an Ecolabel has been used to identify products that respect the environment in the field of lubricants. The components of these products may be derived from the LuSC list (Lubricant Substance Classification) and meet, in particular the strict requirements of biodegradability, bioaccumulation and aquatic toxicity. Ecolabel lubricants are considered to be lubricants that meet the environmental specifications of EAL lubricants.

Moreover, gear lubricant compositions for marine use must meet very specific performance, particularly in terms of tribological performance and seal compatibility. Specifically lubricant compositions for marine clutch application have to pass the so-called “Ortlinghaus friction test”. The Ortlinghaus test is a specific test used for the wet running multi plate marine clutches using specific reference sintered material to determine the static and dynamic coefficients of friction of a lubricant composition. These coefficients of friction need to reach specific values to be able to engage the clutch during operation. In brief, lubricant compositions need to reach a specific minimum value of the static friction coefficient and dynamic friction coefficient in order to be considered as suitable to be used on marine engine.

There is therefore an interest in providing high performance marine gear oil that meets the specific and required static and dynamic coefficient of friction as defined according to the Ortlinghaus friction test for the suitability of lubricants to use in wet running multi-plate clutches.

There is also an interest in providing biodegradable lubricant compositions, not exhibiting bioaccumulation in the organisms, exhibiting no toxicity for the environment, more particularly the aquatic environment.

SUMMARY OF THE INVENTION

The present invention aims precisely to provide a lubricating composition which has the specific properties required for gear lubricants, particularly in terms of tribological properties, more specifically which meets the requirements of the Ortlinghaus friction test, while at the same time having good biodegradability properties, in particular which does not exhibit bioaccumulation in organisms and exhibits no toxicity for the environment, more particularly the aquatic environment.

The present invention therefore relates to the use of at least one polyisobutylene succinic anhydride compound as a friction modifier in a lubricating composition intended for the lubrication of gears or equipment comprising gears, said composition comprising more than 70% by weight, in particular more than 80% by weight, and more particularly than 90% by weight of at least one polyol ester of a C3 to C10, in particular C4-C6, linear or branched aliphatic polyalcohol compound and of a linear or branched, saturated or unsaturated, C&- C30, preferably C8-C26, and more preferably C8-C22, monocarboxylic acid.

In the remainder of the text, and unless indicated otherwise, the term “ester-based lubricating composition” will denote a lubricating composition as defined above that comprises a major amount of one or more polyol ester(s) as defined hereabove.

By “friction modifier”, it is meant a molecule added to lubricants in order to adjust the level of friction in machine components, and to modify, even improve the tribological performance.

The present invention also relates to a lubricating composition for gears or equipment comprising gears, comprising:

- more than 70% by weight, in particular more than 80% by weight, and more particularly more than 90% by weight of at least one polyol ester of a C3 to C10 , in particular C4 to Ce, linear or branched aliphatic polyalcohol compound and of a linear or branched, saturated or unsaturated C6-C30 monocarboxylic acid; and

- at least one polyisobutylene succinic anhydride compound.

As will become apparent from the following examples, the introduction of a polyisobutylene succinic anhydride in an ester-based lubricating composition as defined above makes it possible to obtain a lubricating composition which has improved tribological performance while respecting the biodegradability criteria.

Advantageously, the use of a polyisobutylene succinic anhydride in an ester-based lubricating composition makes it possible to obtain a lubricating composition for gears which meets the specifications required by the test and evaluation, well recognized regarding lubricants of marine gearboxes, carried out by the multi-disk clutch manufacturer Ortlinghaus.

The so-called “Ortlinghaus friction test” aims at testing the suitability though the measurement of static and dynamic friction coefficients of the lubricant for use in wet running multi-plate marine clutches.

A lubricating composition according to the invention that incorporates at least one polyisobutylene succinic anhydride compound thus complies with the required static friction coefficient and dynamic friction coefficient, as defined according to the Ortlinghaus friction test for the requirements for the operation in wet running clutching as detailed in the example that follows. The test more particularly requires, for a lubricant to be suitable for use in wet running multi-plate marine clutches, that it complies with a minimum value of static friction coefficient (p₀) of 0.12 and minimum value of dynamic friction coefficient (pd) according to the run-in process of 0.080.

Thus, the present invention also describes the use of at least one polyisobutylene succinic anhydride compound as a friction modifier in an ester-based lubricating composition intended for the lubrication of gears or equipment comprising gears, as defined above, to pass the Ortlinghaus friction test.

In particular, the polyisobutylene succinic anhydride compound(s) may be used in an ester-based lubricant according to the invention in an amount of at least 0.5% by weight, in particular ranging from 1% to 5% by weight, relative to the total weight of the lubricant for gears.

Further, the lubricating composition does not exhibit bioaccumulation in organisms and exhibits no toxicity for the environment, more particularly the aquatic environment.

The non-toxicity on biotic systems can be assessed as described in the examples below according to the OECD Guidelines, for example Test No. 202 that assesses effects of chemicals towards daphnids and Test No. 203 that assesses effects on the fish exposed to the tested substance; biodegradability can be assessed according to the OECD 301 B aerobic biodegradation test.

A lubricating composition according to the invention is particularly useful for lubricating equipment comprising gears, in particular in the marine field.

Thus, the present invention also describes the use of a lubricating composition according to the invention for gear lubrication, in particular in the marine field, and in equipment having gearing that may be in contact with the environment (water, air, etc,) or humans.

For example, a lubricating composition according to the invention may be useful for the lubricating of equipment comprising gears, in particular for the stern tube.

The stern tube is the system for passing through the hull to the propeller shaft while maintaining maximum sealing.

Therefore, the present invention also relates to the use of a lubricating composition as defined above for the lubrication of gears or equipment comprising gears, for example for the lubrication of the stern tube. The present invention likewise describes a method for lubricating gears or equipment comprising gearing, in particular the stern tube, comprising the implementation of a lubricating composition according to the invention. Said method more particularly comprises at least one step in which said gear or equipment comprising gears, in particular the inner walls of the equipment comprising gears, for example the inner walls of the stern tube, is brought into contact with a lubricating composition according to the invention.

Other characteristics, variants and advantages of the use of a polyisobutylene succinic anhydride compound in an ester-based lubricating composition and of the resulting lubricating compositions according to the invention will become more clearly apparent on reading the description and examples which follow and are given by way of illustration and do not limit the invention.

In the remainder of the text, the expressions “between ... and ...”, “ranging from ... to ...” and “varying from ... to ...” are equivalent and are intended to mean that the limits are included, unless otherwise stated.

Unless otherwise indicated, the expression “comprising a” should be understood as “comprising at least on”.

DETAILED DESCRIPTION

Polyisobutylene succinic anhydride

As specified above, the present invention is based on the use of at least one polyisobutylene succinic anhydride compound, hereafter referred as “PIBSA”.

By “polyisobutylene succinic anhydride compound”, it is meant a chemical compound selected from the group consisting of polyisobutylene-substituted succinimides. More specifically, the compound consists in succinic anhydride substituted by a polyisobutylene chain in which the polyisobutylene substituent is bonded to at least one of the carbons located in position alpha to the carbonyl groups of the succinic anhydride.

Preferably, the polyisobutylene succinic anhydride compound comes from the reaction between polyisobutylene and maleic anhydride.

Preferably, the polyisobutylene chain substituting succinic acid anhydride or succinic anhydride has a number-average molecular weight from 500 g/mol to 5 000 g/mol, preferably from 500 g/mol to 2 000 g/mol, more preferably from 800 g/mol to 2 000 g/mol and even more preferably from 900 g/mol to 1 600 g/mol.

The number average molecular weight is determined by gel permeation chromatography (GPC) or so-called steric exclusion chromatography. According to an embodiment, the polyisobutylene succinic anhydride compound has a molecular weight comprised from 500 to 5,000 g/mol, preferably from 800 to 2,000 g/mol.

The molecular weight of said polyisobutylene succinic anhydride compound is determined by GPC.

The preparation of polyisobutylene succinic anhydride is widely described in the literature. Documents US 3,361 ,673 and US 3,018,250 describe, for example, their preparation by the high-temperature reaction between a polyisobutene and maleic anhydride or by the reaction between a halogenated, in particular chlorinated, polyisobutene and maleic anhydride.

According to one embodiment, the polyisobutylene succinic anhydride compound used in a lubricating composition according to the invention has a degree of polymerization n comprised from 10 to 90, preferably from 10 to 50, and more preferably from 15 to 35.

Advantageously, a polyisobutylene succinic anhydride compound may be formulated in a lubricating composition according to the invention in a proportion of at least 0.5% by weight, relative to the total weight of the composition, in particular at least 1% by weight, preferably from 1% to 5% by weight, more particularly from 1% to 3% by weight, for example of 1 .5% by weight, relative to the total weight of the lubricating composition.

Ester-based lubricating composition

As mentioned above, the PIBSA compound(s) is(are) used as friction modifier in an ester-based lubricating composition intended for the lubrication of gears or equipment comprising gears, also referred to as an ester-based gear oil.

The ester-based lubricating composition according to the invention comprises more than 70% by weight, in particular more than 80% by weight and more particularly more than 90% by weight, preferably from 90% to 98% by weight, of at least one polyol ester of a C3 to C , in particular C4 to C&, linear or branched aliphatic polyalcohol compound and of a linear or branched, saturated or unsaturated C6-C30 monocarboxylic acid.

By “polyol ester” according to the invention, it is meant any ester obtained by esterification of an aliphatic polyalcohol compound as defined above with at least one, linear or branched, saturated or unsaturated C6-C30 monocarboxylic acid.

By “aliphatic polyalcohol” also called “aliphatic polyol”, it is meant a linear or ramified alkyl group comprising at least two hydroxyl groups, preferably at least three hydroxyl groups or four hydroxyl groups. The aliphatic polyalcohol does not comprise any aromatic moieties, nitrogen atoms or sulphur atoms. The term “C3 to C10 polyalcohol” is understood to denote a polyalcohol, the alkyl-type hydrocarbon-based chain of which has 3 to 10 carbon atoms.

In an embodiment of the invention, the aliphatic polyalcohol comprises at least three hydroxyl groups, more preferably between three and six hydroxyl groups.

In a more preferred embodiment of the invention, the aliphatic polyalcohol comprises three or four hydroxyl groups.

In a preferred embodiment of the invention, the aliphatic polyalcohol comprises from 3 to 8 carbon atoms, and more preferably from 4 to 6 carbon atoms.

Examples of aliphatic polyalcohols according to the invention include glycerol, trimethylolpropane, pentaerythritol or dipentaerythritol.

Advantageously, the polyol ester(s) according to the invention can for example be obtained from trimethylolpropane or from pentarerythritol.

By “monocarboxylic acid” according to the invention is meant a compound formed of a hydrocarbon-based, linear or branched, chain, bearing a carboxylic function at one of its ends. Preferably, the hydrocarbon-based chain consists of carbon and hydrogen, in other words is of alkyl or alkenyl type. In other words, the monocarboxylic acid according to the invention preferably does not comprise any heteroatom other than those of the carboxylic function.

The term “C& to C30 monocarboxylic acid” is understood to denote a monocarboxylic acid the alkyl- or alkenyl-type hydrocarbon-based chain of which comprises from 6 to 30 carbon atoms. The monocarboxylic acid may thus be chosen from among:

- saturated and linear monocarboxylic acids;

- unsaturated and linear monocarboxylic acids;

- saturated and branched monocarboxylic acids; and

- unsaturated and branched monocarboxylic acids.

According to an embodiment, the monocarboxylic acid comprises from 8 to 30 carbon atoms, preferably from 8 to 26 carbon atoms.

In a particular embodiment of the invention, the monocarboxylic acid comprises from 8 to 22 carbon atoms.

Thus, the monocarboxylic acid may be chosen from among:

- saturated and linear monocarboxylic acids comprising from 6 to 30 carbon atoms, preferably from 8 to 30 carbon atoms, in particular from 8 to 26 carbon atoms, more preferably from 8 to 22 carbon atoms; - unsaturated and linear monocarboxylic acids comprising from 6 to 30 carbon atoms, preferably from 8 to 30 carbon atoms, in particular from 8 to 26 carbon atoms, more preferably from 8 to 22 carbon atoms;

- saturated and branched monocarboxylic acids comprising from 6 to 30 carbon atoms, preferably from 8 to 30 carbon atoms, in particular from 8 to 26 carbon atoms, more preferably from 8 to 22 carbon atoms; and

- unsaturated and branched monocarboxylic acids comprising from 6 to 30 carbon atoms, preferably from 8 to 30 carbon atoms, in particular from 8 to 26 carbon atoms, more preferably from 8 to 22 carbon atoms.

Examples of carboxylic acids according to the invention include, caproic acid, capric acid, caprylic acid, lauric acid, pelargonic acid, stearic acid, isostearic acid or oleic acid.

It is understood that the definitions given above for the monocarboxylic acid and for the polyalcohol can be combined, as far as possible, to define particular polyol esters suitable for the invention.

According to a preferred embodiment, the polyol esters of a lubricating composition according to the invention are selected from the group consisting of: triesters of a C4-C6 aliphatic polyalcohol and of a C6-C30, preferably C8-C30, and even more preferably Cs-C , monocarboxylic acid, tetraesters of a C4-C6 aliphatic polyalcohol and of a C6-C30, preferably C8-C30, and even more preferably C16-C22, monocarboxylic acid, and mixtures thereof.

The polyol esters of a lubricating composition according to the invention may be commercially available or prepared according to synthesis methods known to those skilled in the art. These synthesis methods more particularly carry out an esterification reaction between an aliphatic polyalcohol and at least one monocarboxylic acid as defined hereabove.

It is understood that, in the context of the present invention, the lubricating composition can be based on a mixture of at least two different polyol esters, as defined above.

Preferably, the polyol ester or mixture of polyol esters according to the invention has a kinematic viscosity, measured at 40°C according to the standard ASTM D445, ranging from 90 to 165 mm². s^-1, preferably from 95 to 160 mm².s'¹, more preferably from 135 to 165 mm². s^-1.

Preferably, the lubricating composition according to the invention comprises a mixture of several polyol esters as defined hereabove.

More precisely, the lubricating composition used according to the invention may comprise a mixture of at least one first polyol ester as defined hereabove and at least one second polyol ester as defined above and different from the first ester. Advantageously, a lubricating composition according to the invention comprises a mixture of at least two different polyol esters which differ each other by their kinematic viscosity, and more particularly a mixture of at least one polyol ester, hereafter referred as to “polyol ester (a)” of low kinematic viscosity, and of at least one polyol ester, hereafter referred as to “polyol ester (b)” of high kinematic viscosity.

According to an embodiment, the lubricating composition according to the invention comprises a mixture of:

- at least one polyol ester (a) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 16 to 25 mm².s'¹; and

- at least one polyol ester (b) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 140 to160mm².s'¹.

The respective proportions of said polyol esters (a) and (b) in the lubricating composition according to the invention are preferably such that the mixture of polyol esters has the desired kinematic viscosity, in particular a kinematic viscosity, measured at 40°C according to the standard ASTM D445, ranging from 90 to 165 mm².s'¹, preferably from 95 to 160 mm² s’¹, more preferably from 135 to 165 mm² s’¹.

According to one embodiment, the lubricating composition according to the invention comprises a mixture of polyol esters consisting of:

- from 1 % to 30% by weight, in particular from 1 % to 25% by weight, more particularly from 1 .5% to 20% by weight, of at least one polyol ester (a) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 16 to 25 mm². s^-1 ; and

- from 70 % to 99% by weight, in particular from 75% to 99% by weight, more particularly from 80% to 99% by weight, of at least one polyol ester (b) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 140 to 160 mm².s'¹.

- from 1% to 7% by weight of at least one polyol ester (a) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 16 to 25 mm².s'¹ ; and

- from 90% to 98% by weight of at least one polyol ester (b) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 140 to 160 mm².s'¹. According to one embodiment, the polyol ester (a) of low kinematic viscosity is selected from triesters of a C4-C6 aliphatic tri-alcohol with a C6-C30, preferably C8-C22, and even more preferably Cs-C , monocarboxylic acid, in particular as defined hereafter.

According to one embodiment, the polyol ester (b) of high kinematic viscosity is selected from tetraesters of a C4-C6 aliphatic tetra-alcohol with a C6-C30, preferably C8-C30, and even more preferably C16-C22, monocarboxylic acid, in particular as defined hereafter.

According to a particular embodiment, the lubricating composition according to the invention comprises a mixture of at least one triester of a C4-C6 aliphatic polyalcohol and a C6-C30 monocarboxylic acid, and of at least one tetraester of a C4-C6 aliphatic polyalcohol and a C6-C30 monocarboxylic acid.

Thus, in a more particular embodiment, a lubricating composition according to the invention comprises a mixture of:

- at least one triester of a C4-C6 aliphatic tri-alcohol with a C6-C30, preferably C8-C22, and even more preferably Cs-C , monocarboxylic acid, and

- at least one tetraester of a C4-C6 aliphatic tetra-alcohol with a C6-C30, preferably Cs- C30, and even more preferably C16-C22, monocarboxylic acid.

Preferably, the triester is a triester of a branched C4-C6 aliphatic tri-alcohol and a C&- C30, preferably C8-C22, and more preferably Cs-C , unsaturated or saturated, linear or branched, monocarboxylic acid.

In a preferred embodiment, the lubricating composition according to the invention comprises at least one trimethylolpropane triester.

By “trimethylolpropane triester” it is meant a triester obtained from trimethylolpropane (TMP) and linear or branched, saturated or unsaturated, monocarboxylic acids having from 6 to 30 carbon atoms.

Preferably, the triester is a triester of trimethylolpropane with a linear or branched Cs- C22, more preferably Cs-C , saturated or unsaturated monocarboxylic acid as defined above.

Preferably, the trimethylolpropane triester comes from the reaction between trimethylolpropane and at least one linear or branched, saturated or unsaturated, monocarboxylic acid having from 8 to 30, more preferably from 8 to 16 carbon atoms.

Preferably, the trimethylolpropane triester is a triester of trimethylolpropane (TMP) and linear or branched, saturated or unsaturated, C8-C22, preferably Cs-C , monocarboxylic acids.

Preferably, the trimethylolpropane triester is a triester of TMP with a branched saturated C8-C22, preferably Cs-C , monocarboxylic acid. According to one embodiment, a lubricating composition used according to the invention comprises at least 1.0% by weight, in particular from 1.0% to 30% by weight and more particularly from 1.0% to 25% by weight, preferably from 1.5 to 20% by weight, in relation to the total weight of said composition, of at least one polyol ester (a) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 16 to 25 mm².s'¹.

In particular, a lubricating composition according to the invention can comprise at least 1 .0% by weight, in particular from 1 .0% to 30% by weight and more particularly from 1 .0% to 25% by weight, preferably from 1.5 to 20% by weight of at least one trimethylolpropane triester, in particular as defined hereabove, in relation to the total weight of said composition.

According to one embodiment, a lubricating composition used according to the invention comprises from 1.0% to 7% by weight, in relation to the total weight of said composition, of at least one polyol ester (a) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 16 to 25 mm².s'¹.

According to an embodiment, a lubricating composition according to the invention comprises from 1 .0% to 7% by weight of at least one trimethylolpropane triester, in particular as defined hereabove, in relation to the total weight of said composition.

Preferably, the tetraester is a tetraester of a branched C4-C6 aliphatic tetra-alcohol and a C6-C30, preferably C8-C30, and more preferably C12-C22, unsaturated or saturated, linear or branched, monocarboxylic acid.

In a preferred embodiment, the lubricating composition according to the invention comprises at least one pentaerythritol tetraester.

By “pentaerythritol tetraester” it is meant a tetraester obtained from pentaerythritol and linear or branched, saturated or unsaturated, monocarboxylic acids having from 6 to 30, carbon atoms.

Preferably, the pentaerythritol tetraester is a tetraester of pentaerythritol and a linear C12-C30 saturated monocarboxylic acid.

More preferably, the pentaerythritol tetraester is a tetraester of pentaerythritol and a linear C16-C22 saturated monocarboxylic acid.

Advantageously, the pentaerythritol tetraester is a tetraester of pentaerythritol with a linear C18 saturated monocarboxylic acid.

According to one embodiment, a lubricating composition used according to the invention comprises at least 60% by weight, in particular from 60% to 98% by weight and more particularly at least 70% by weight, preferably at least 75% by weight, relative to the total weight of the composition, of at least one polyol ester (b) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 140 to 160mm². s^-1.

In particular, a lubricating composition according to the invention can comprise at least 60% by weight, in particular from 60% to 98% by weight and more particularly at least 70% by weight, preferably at least 75% by weight, relative to the total weight of the composition, of at least one pentaerythritol tetraester, in particular as defined hereabove.

According to one embodiment, a lubricating composition used according to the invention comprises from 90% to 98% by weight, relative to the total weight of the composition, of at least one polyol ester (b) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 140 to 160mm².s'¹.

According to one embodiment, a lubricating composition used according to the invention comprises from 90% to 98% by weight, relative to the total weight of the composition, of at least one pentaerythritol tetraester, in particular as defined hereabove.

According to a particular embodiment, the mixture of polyol esters of a lubricating composition according to the invention comprises, or in particular consists of:

- at least one trimethylolpropane triester, in particular as defined above, more particularly in a content ranging from 1 % to 30% by weight, in particular 1 % to 25% by weight, preferably from 1 .5% to 20% by weight,

- at least one pentaerythritol tetraester, in particular as defined above, more particularly in a content ranging from 70% to 99% by weight, in particular from 75% to 99% by weight, more particularly from 80% to 98.5% by weight, relative to the total weight of the mixture of polyol esters.

- at least one trimethylolpropane triester, in particular as defined above, more particularly in a content ranging from 1% to 7% by weight,

- at least one pentaerythritol tetraester, in particular as defined above, more particularly in a content ranging from 90% to 98% by weight, relative to the total weight of the mixture of polyol esters.

It is understood that the different embodiments given above for the PIBSA and polyol ester(s) used in a lubricating composition according to the invention can be combined, as far as possible, to define embodiment variants of a lubricating composition according to the invention.

Thus, according to a particular embodiment, a lubricating composition according to the invention comprises:

- at least 0.5% by weight, in particular at least 1% by weight, preferably from 1% to 5% by weight, more particularly from 1% to 3% by weight, of at least one polyisobutylene succinic anhydride compound; and

- at least 70% by weight, in particular at least 80% by weight, preferably at least 90% by weight and more particularly from 90% to 98% by weight, of one or more polyol ester(s) as defined according to the invention, preferably of a mixture of at least one polyol ester (a) of low kinematic viscosity, in particular as defined above, and of at least one polyol ester (b) of high kinematic viscosity, in particular as defined above, the contents being expressed relative to the total weight of said lubricating composition.

Said mixture of polyol esters is in particular as defined according to any particular embodiments above.

According to a more preferred embodiment, a lubricating composition according to the invention comprises:

- at least 0.5% by weight, in particular at least 1% by weight, preferably from 1% to 5% by weight, more particularly from 1 % to 3% by weight, of at least one polyisobutylene succinic anhydride compound;

- at least 60% by weight, in particular from 60% to 98% by weight and more particularly at least 70% by weight, preferably at least 75% by weight of at least one polyol ester (b) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 140 to 160 mm².s^-1 ; said polyol ester (b) being in particular a pentaerythritol tetraester, preferably as defined above; and

- at least 1 .0% by weight, in particular from 1 .0% to 30% by weight and more particularly from 1 .0% to 25% by weight, preferably from 1 .5 to 20% by weight of at least one polyol ester (a) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 16 to 25 mm².s'¹; said polyol ester (a) being in particular a trimethylolpropane triester, preferably as defined above; the contents being expressed relative to the total weight of said lubricating composition. According to a more preferred embodiment, a lubricating composition according to the invention comprises:

- from 1% to 3% by weight, of at least one polyisobutylene succinic anhydride compound;

- from 90% to 98% by weight of at least one polyol ester (b) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 140 to 160 mm².s'¹; said polyol ester (b) being in particular a pentaerythritol tetraester, preferably as defined above; and

- from 1 .0% to 7% by weight of at least one polyol ester (a) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 16 to 25 mm².s'¹; said polyol ester (a) being in particular a trimethylolpropane triester, preferably as defined above; the contents being expressed relative to the total weight of said lubricating composition.

In particular, a lubricating composition according to the invention comprises:

- from 1 .0% to 20% by weight of at least one trimethylolpropane triester, in particular as defined above;

- from 75% to 98% by weight of at least one pentaerythritol tetraester, in particular as defined above, and

- from 1% to 3% by weight of at least one polyisobutylene succinic anhydride compound; the contents being expressed relative to the total weight of said lubricating composition.

In particular, a lubricating composition according to the invention comprises:

- from 1 .0% to 7% by weight of at least one trimethylolpropane triester, in particular as defined above;

- from 90% to 98% by weight of at least one pentaerythritol tetraester, in particular as defined above, and

Additives

A lubricating composition according to the invention may further comprise any types of additives suitable for use in a lubricant for gears or gear equipment with which the lubricating composition is intended to be used. These additives can in particular be selected in the group consisting of anti-wear additives, extreme pressure additives, antioxidants, anticorrosive additives, metal deactivator additives, defoamers, and mixtures thereof.

The additives that may be used in the compositions according to the invention are additives from the Lubricant Substance Classification list (LuSC-list) or additives that make it possible to obtain a biodegradable formula that meets the Ecolabel standard or the American EAL specifications.

Anti-wear additives and extreme pressure additives protect the friction surfaces by forming a protective film adsorbed on these surfaces. There is a wide variety of anti-wear additives. In a preferred manner, certain additives are both anti-wear and extreme pressure additives.

In a preferred manner for compositions according to the invention, the anti-wear and extreme pressure additives are chosen from among phosphorus and/or sulfur based ashless additives such as, for example, phosphates, phosphorothionates, phosphonates, dithiophosphates and thio phosphates such as dialkyl dithiophosphates.

As an anti-wear additive, mention may also be made of triaryl thiophosphate, carbamates and thiocarbamates.

Also preferably, certain additives may be simultaneously anti-wear, extreme pressure and anti-corrosion additives. Among these additives, mention may be made of amine phosphates which may be used in the composition according to the invention.

Advantageously, the composition according to the invention comprises at least one anti-corrosion additive such as an N-acyl sarcosine compound.

Advantageously, the composition according to the invention comprises at least one metal-deactivating additive such as a tolutriazole or di-mercapto thiadiazole derivative.

Advantageously, the composition according to the invention comprises at least one anti-foam additive such as a silicone compound or a polyacrylate compound.

Advantageously, the composition according to the invention comprises at least one antioxidant additive.

The antioxidant additive generally serves to retard the degradation of the composition in service. Antioxidant additives act, in particular, as radical inhibitors or destroyers of hydro peroxides. Among antioxidant additives commonly used, mention may be made of antioxidant additives of the phenolic type, antioxidant additives of the amine type.

The phenolic antioxidant additives may, in particular, be chosen from among sterically- hindered phenols, sterically-hindered phenol esters and sterically-hindered phenols comprising a thioether bridge. Preferably, according to the invention, the sterically-hindered phenols are chosen from among 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 C1 - C10 alkyl group, preferably a C1 -C6 alkyl group, preferably a C4 alkyl group, preferably by the tert-butyl group.

The antioxidant amine additives may be chosen from diphenylamines, diphenylamines substituted with at least one C1 -C12 alkyl group, N,N'-dialkyl-aryl-diamines, octylphenyl naphthylamine and mixtures thereof.

Examples of amine compounds are aromatic amines, for example aromatic amines of formula NR⁴R⁵R⁶ in which R⁴ represents an optionally substituted aliphatic or aromatic group, R⁵ represents an optionally substituted aromatic group, R⁶ represents a hydrogen atom, an alkyl group, an aryl group.

Antioxidant amine additives may be used in combination with phenolic antioxidant additives.

Preferably, the amine phosphate is selected from amine alkyl phosphate.

Preferably, the phenolic antioxidant is preferably chosen from among sterically- hindered phenols, chosen among compounds comprising a phenol group in which at least one vicinal carbon of the carbon carrying the alcohol function is substituted by at least one C1 -C10 alkyl group, preferably a C1 -C6 alkyl group, preferably a C4 alkyl group, preferably by the tert-butyl group. Preferably, the phenol is chosen from among phenolic compounds in which the two vicinal carbons of the carbon carrying the alcohol function are substituted by at least one C1 -C10 alkyl group, preferably a C1 -C6 alkyl group, preferably a C4 alkyl group, preferably by the ter-butyl group, while another carbon is substituted by an alkyl ester group.

According to one embodiment, the composition comprises from 0.1 % to 10% by weight, in particular from 1% to 5% by weight, preferably from 1 to 3% of one or more additive(s), in relation to the total weight of said composition.

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

- at least 80% by weight, preferably at least 90% by weight and more particularly from 90% to 98% by weight, of one or more polyol ester(s) as defined according to the invention, preferably of a mixture of polyol esters (a) and (b) as defined according to any particular embodiments above; and

- at least 1 % by weight, preferably from 1% to 10% by weight and more particularly from 1% to 5% by weight, of one or more additives, in particular chosen from anti-wear additives, extreme pressure additives, antioxidants, anticorrosive additives, metal deactivator additives, defoamers, and mixtures thereof; the contents being expressed relative to the total weight of said lubricating composition.

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

- at least 70% by weight, in particular from 70% to 98% by weight and more particularly at least 75% by weight of at least one polyol ester (b) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 140 to 160mm².s^-1 ; said polyol ester (b) being in particular a pentaerythritol tetraester, preferably as defined above;

- at least 1 .0% by weight, in particular from 1 .0% to 30% by weight and more particularly from 1 .0% to 25% by weight, preferably from 1 .5 to 20% by weight of at least one polyol ester (a) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 16 to 25 mm².s'¹; said polyol ester (a) being in particular a trimethylolpropane triester, preferably as defined above; and

- at least 1 % by weight, pr from 1 % to 10% by weight and more particularly from 1 % to 5% by weight, of one or more additives, in particular chosen from anti-wear additives, extreme pressure additives, antioxidants, anticorrosive additives, metal deactivator additives, defoamers, and mixtures thereof; the contents being expressed relative to the total weight of said lubricating composition.

- from 1% to 3% by weight of at least one polyisobutylene succinic anhydride compound;

- from 90% to 98% by weight of at least one polyol ester (b) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 140 to 160mm².s^-1 ; said polyol ester (b) being in particular a pentaerythritol tetraester, preferably as defined above;

- from 1 .0% to 7% by weight of at least one polyol ester (a) having a kinematic viscosity, measured at 40°C in accordance with the standard ASTM D445, ranging from 16 to 25 mm².s'¹; said polyol ester (a) being in particular a trimethylolpropane triester, preferably as defined above; and

- from 75% to 98% by weight of at least one pentaerythritol tetraester, in particular as defined above;

- from 1% to 3% by weight of at least one polyisobutylene succinic anhydride compound; and

- from 1 % to 3% by weight of one or more additives, in particular chosen from anti-wear additives, extreme pressure additives, antioxidants, anticorrosive additives, metal deactivator additives, defoamers, and mixtures thereof; the contents being expressed relative to the total weight of said lubricating composition.

- from 90% to 98% by weight of at least one pentaerythritol tetraester, in particular as defined above,

It is understood that the particular, advantageous or preferred features given above for the PIBSA compound, the polyol ester(s) and for the lubricating composition applies to the uses and processes according to the invention, as well as to the lubricating composition according to the invention.

The present invention will now be described with the aid of the following examples, given by way of illustration and without limiting the invention. EXAMPLES

1. Preparation of compositions according to the invention

The composition in Table 1 is prepared by mixing at 50-55°C the trimethylolpropane triester and the pentaerythritol tetraester. Then, the PIBSA and additive package are added, to give the proportions in Table 1. The percentages shown are based on 100 % weight of the composition

Table 1

* Additive package comprises detergents, dispersants, antioxidants, Antiwear agents, defoamer and metal deactivator.

2. Ortlinghaus test

The test is a specific test used for the wet running multi plate marine clutches using specific reference sintered material. The measurement of static and dynamic coefficient is carried out on actual materials. Passing of the test meaning oil helps to offer high operating efficiency with high torque, low moment of inertia, high engagement frequencies and minimum need of maintenance.

The Ortlinghaus test was carried out under the following conditions, which represent typical values of load in marine clutches. The test conditions are listed in the following table 2. Table 2

- Measurement of the dynamic friction coefficient, U

The hydraulically test brake is used to stop the rotation of the flywheel. The underlying engagement work results from the rotational speed and the inertia of the flywheel. Based on the measured and recorded signals of rotational speed, engagement force and torque as well as the geometry of the plates, the temporal progress of the friction coefficient value for every 10^th engagement is determined. Afterwards each recorded measurement is evaluated to calculate the arithmetical average of the friction coefficient of an engagement, which is plotted over the number of engagements.

- Measurement of static friction coefficient, uo

In order to measure the static friction coefficient, the brake is closed and subjected to increasing torque, developed with a lever, until the plates slide. At each test, a rotation of approximately 30 degrees is made. The recorded values of torque and engagement force are used to calculate the friction coefficient at the start of the sliding process. The friction coefficient is recorded and plotted over the number of engagements.

To pass the Ortlinghaus test, the measured values of the static friction coefficient and dynamic friction coefficient have to be greater than defined minimum values, which are poS 0.120 ± 3% and pd s 0.080 ± 3%. The test was reproduced two times on two separate compositions with the same parameters. Table 3 gives the average results for the composition LC1 .

Table 3

The results show that the composition according to the invention meets the requirements for the operation in wet running clutches.

3. Toxicity and Biodegradability test

The composition according to the invention has been submitted to the Daphnia Toxicity test as per OECD 202. The daphnia did not show any abnormal behavior in the experimental conditions and no external apparent impact was detected. The composition gives no acute toxicity towards daphnia.

The composition according to the invention has been submitted to the fish acute toxicity as per OECD 203. The fish did not show any abnormal behavior in the experimental conditions and no external apparent impact was detected. The composition gives no acute toxicity towards fish.

The composition according to the invention has been submitted to the biodegradability test as per OECD 301 B. The oil is 75.5% biodegradable in 28 days compared to reference standard.

Claims

1. Use of at least one polyisobutylene succinic anhydride compound as a friction modifier in a lubricating composition intended for the lubrication of gears or equipment comprising gears, said composition comprising more than 70% by weight, in particular more than 80% by weight, and more particularly 90% by weight, of at least one polyol ester of a C3 to C10 linear or branched aliphatic polyalcohol compound and of a linear or branched, saturated or unsaturated, C6-C30, preferably C8-C30, and more preferably C16- C22, monocarboxylic acid.

2. The use according to claim 1 , wherein the polyol ester has a viscosity from 90 to 165 mm². s^-1, preferably from 95 to 160 mm² s^-1 at 40°C.

3. The use according to any one of the preceding claims, wherein the composition comprises a mixture of several polyol esters, said composition comprising preferably:

- from 1% to 30% by weight of at least one polyol ester (a) having a viscosity from 16 to 25 mm² s^-1 at 40°C; and

- from 70% to 99% by weight of at least one polyol ester (b) having a viscosity from 140 to 160 mm² s^-1 at 40°C.

4. The use according to any one of claims 1 to 3, wherein the polyol ester is selected from the group consisting of: triesters of a C4-C6 aliphatic polyalcohol and of a C&- C30, preferably C8-C26, and even more preferably Cs-C , monocarboxylic acid, tetraesters of a C4-C6 aliphatic polyalcohol and of a C6-C30, preferably C8-C30, and even more preferably C16-C22, monocarboxylic acid, and mixtures thereof.

5. The use according to any one of claims 1 to 4, wherein the composition comprises a mixture of at least one triester of a C4-C6 aliphatic polyalcohol and a C6-C30 monocarboxylic acid, and of at least one tetraester of a C4-C6 aliphatic polyalcohol and a C&- C30 monocarboxylic acid.

6. The use according to claim 5, wherein the triester is a triester of a branched C4-C6 aliphatic tri-alcohol and a C6-C30, preferably C8-C26, and more preferably Cs-C , unsaturated or saturated, linear or branched, monocarboxylic acid, said triester being preferably a triester of trimethylolpropane with a linear or branched C8-C30, and more preferably Cs-C , saturated or unsaturated monocarboxylic acid .

7. The use according to claim 5 or 6, wherein the tetraester is a tetraester of a branched C4-C6 aliphatic tetra-alcohol and a C6-C30, preferably C8-C30 and more preferably C16-C22, unsaturated or saturated monocarboxylic acid, said tetraester being preferably a tetraester of pentaerythritol with a linear or branched C12-C30, preferably C16-C22, saturated or unsaturated monocarboxylic acid.

8. The use according to any one of the preceding claims, wherein the polyisobutylene succinic anhydride compound has a molecular weight comprised from 500 g/mol to 5,000 g/mol, preferably from 800 g/mol to 2,000 g/mol.

9. The use according to any one of the preceding claims, wherein the polyisobutylene succinic anhydride compound has a degree of polymerization n comprised from 10 to 90, preferably from 15 to 35.

10. A composition comprising:

- more than 70% by weight, in particular more than 80% by weight, and more particularly more than 90% by weight, of at least one polyol ester of a C3 to C10 linear or branched aliphatic polyalcohol compound and of a linear or branched, saturated or unsaturated C6-C30 monocarboxylic acid; and

- at least one polyisobutylene succinic anhydride compound.

11. The composition according to claim 10, wherein the polyol ester is as defined in any one of claims 1 to 7.

12. The composition according to claim 10 or 11 , further comprising at least one additive selected from the group consisting of anti-wear additives, extreme pressure additives, antioxidants, anticorrosive additives, metal deactivator additives, defoamers, and mixtures thereof.

13. The use of a composition according to any one of the claims 10 to 12 for the lubrication of gears or equipment comprising gears, in particular the stern tube.

14. A method of lubricating gearing or equipment comprising gearing, in particular stern tube, comprising the implementation of the composition according to any one of claims 10 to 12.