LUBRICANT COMPOSITION

The present invention is in the field of lubricants. More particularly, it relates to a lubricating composition for a combustion engine.

Lubricants are commonly used in combustion engines. In order to improve their durability, they generally include an antioxidant additive. The usual antioxidant additive composition is a mixture of phenolic antioxidant and amine antioxidant.

The need to improve the resistance of lubricating compositions to heat degradation has existed since the advent of combustion engines. However, the compositions of antioxidant packages for lubricant formulations and their performance have changed very little in the last 20 years.

Document WO2014134506 discloses lubricating compositions comprising antioxidants. However, the results obtained in terms of durability are not satisfactory. Furthermore, this document proposes a combination of phenol and amine as an antioxidant, and alternatively proposes a list of products, however without giving any technical effect associated with each proposed product, nor any indication to the person skilled in the art about the advantages of one or the other product.

One object of the present invention is to provide a lubricating composition having good thermal stability against oxidation degradation.

Another object of the present invention is to provide a lubricating composition whose environmental impact is reduced.

It is an object of the present invention to at least partially meet the above objects by providing a lubricating composition with an improved antioxidant additive. To this end, it proposes a lubricating composition comprising a base oil and an antioxidant additive, said antioxidant additive comprising a phenolic antioxidant, an amine antioxidant, and a tocopherol supplement comprising at least one element from the list consisting of: beta-tocopherol, delta-tocopherol and gamma-tocopherol.

Thanks to these provisions, the composition according to the invention has a better thermal stability against oxidation degradation, compared to compositions of the state of the art, while allowing a reduction in the proportion of amine-type antioxidant, which is an advantage because of the toxicity of this product.

According to other characteristics:

• • the sum of the contents by weight of beta-tocopherol, delta-tocopherol and gamma-tocopherol in the tocopherol supplement may be greater than 50%, preferably greater than 70%, improving the thermal stability against oxidation degradation of the lubricating composition,
  • the tocopherol supplement may consist of a mixture of several types of tocopherols, namely between 0 and 20% of alpha-tocopherol, between 0 and 5% of beta-tocopherol, between 50 to 65% of gamma-tocopherol and between 20 and 35% of delta-tocopherol, which is a product showing good results,
  • the tocopherol supplement may comprise delta-tocopherol, which allows an improved durability of the lubricating composition,
  • the tocopherol supplement may have a content by weight of delta-tocopherol greater than 50%, which further improves the thermal stability against oxidation degradation of the lubricating composition,
  • the content by weight of the antioxidant additive may be between 0.5 and 1.5%, which is an effective embodiment of the invention,
  • the antioxidant additive may have a content by weight of tocopherol supplement between 5 and 30%, which is an effective embodiment of the invention,
  • the antioxidant additive may have a ratio of the contents by weight of the amine antioxidant to the phenolic antioxidant of less than 0.9, preferably less than 0.8, thereby improving the toxicological profile of the lubricating composition,
  • the base oil may have a weight content of sulfur of less than 0.03% and a viscosity index greater than 120, which is an effective embodiment of the invention.

The present invention also relates to a use of a lubricating composition according to the invention, in a combustion engine.

Thanks to these provisions, the combustion engine benefits from a composition which has improved durability compared with compositions of the state of the art thanks to better thermal stability against oxidation degradation, while allowing a reduction in the proportion of amine-type antioxidant, which is an advantage because of the toxicological risk that this product may represent.

The present invention will be better understood from the detailed description that follows, with reference to the appended figures in which:

FIG. 1 is a graph showing the results of a series of comparative tests of a composition according to the invention,

FIG. 2 is a graph showing a second aspect of the results of the series of comparative tests shown in FIG. 1.

The lubricating composition according to the invention comprises a base oil and an antioxidant additive. The lubricating composition may have a content by weight of antioxidant additive between 0.5 and 1.5%.

The base oil is preferably a Group III oil, but may also be a Group I, Group II, Group III+, Group IV or Group V oil.

The antioxidant additive comprises a phenolic antioxidant, an amine antioxidant, and a tocopherol supplement.

The antioxidant additive may have a content by weight of tocopherol supplement between 5 and 30%, preferably between 5 and 20%.

The phenolic antioxidant may be any phenolic compound, i.e., a compound that has a free OH group attached to a phenyl ring, suitable for being an antioxidant. As used herein, the term “phenolic antioxidant” also includes compounds where the OH group is attached to a phenyl ring, wherein the phenyl ring is part of a fused ring structure, e.g., the phenyl ring is part of a benzothiophene ring, a naphthalene ring, an indole ring, a benzofuran ring or similar. Preferred phenolic antioxidants are hindered phenols (e.g., with at least one of the two ortho positions of the phenolic OH group substituted with, for example, an alkyl group such as methyl, ethyl, propyl, cyclopropyl, isopropyl, butyl, isobutyl or tert-butyl) and dimeric phenols.

Thus, the phenolic antioxidant may consist of a hindered phenol or a mixture of a plurality of hindered phenols selected from 2,6-di-tert-butyl-4-methylphenol, 2-butyl-4,6-dimethylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butyl-4-n-butylphenol, 2,6-di-tert-butyl-4-isobutylphenol, 2,6-dicyclopentyl-4-methylphenol, 2-(α-methylcyclohexyl)-4,6-dimethylphenol 2,4,6-tricyclohexylphenol, 2,6-di-tert-butyl-4-methoxymethylphenol, 2,6-dinonyl-4-methylphenol, 2,4-dimethyl-6-(1′-methyl-undec-1′-yl)-phenol, 2,4-dimethyl-6-(1′-methylheptadec-1′-yl)-phenol, 2, 4-dim ethyl-6-(1′-methyltridec-1′-yl)-phenol, 2,4-diotylthiomethyl-6-tert-butylphenol, 2,4-diotylthiomethyl-6-methylphenol, 2,4-diotylthiomethyl-6-ethylphenol, and 2,6-didodecylthiomethyl-4-nonylphenol.

The amine antioxidant can be an aliphatic or aromatic amine.

The aromatic amine is a compound that has an amine group, either a free amine group (e.g., NH2), or a substituted amine group (e.g., NR¹R², where R¹ and R² are independently hydrogen, alkyl, arylalkyl, heteroarylalkyl, cycloalkylalkyl, heterocyclocycloalkyl, arylcycloalkyl, heteroarylcycloalkyl, arylheterocycloalkyl heteroarylheterocycloalkyl, heteroarylheterocycloalkyl, cycloalkyl, arylcycloalkyl, heteroarylcycloalkyl, heterocycloalkyl, arylheterocycloalkyl, alkenyl, arylalkenyl, cycloalkenyl, arylcycloalkene, heteroarylcycloalkenyl, heterocycloalkenyl, arylheterocycloalkenyl, heteroarylheterocycloalkenyl alkynyl, arylalkynyl, aryl, cycloalkylaryl, heterocycloalkylaryl, cycloalkenylaryl, heterocycloalkenyl, heteroaryl, cycloalkylheteroaryl, heteroalkylheteroaryl, cycloalkenylheteroaryl or heterocycloalkenylheteroaryl), directly attached to an aromatic ring, such as a monocyclic aromatic ring (e.g. a phenyl ring, or a monocyclic heteroaromatic ring such as a thiophene ring, a pyridine ring, a pyrimidine ring, a furan ring, a pyrazine ring, a pyridazine ring, a triazine ring), or a polycyclic aromatic ring (e.g. a bicyclic aromatic ring such as a naphthalene ring, or a bicyclic heteroaromatic ring such as an indole ring, a benzofuran ring, a benzoimidazole ring or a benzothiophene ring, etc. or a tricyclic aromatic ring such as a carbazole).

The amine antioxidant may be an aromatic amine, wherein the amine group is bonded to two aromatic rings, such as two monocyclic aromatic rings (e.g., as described herein) that are the same or different, two polycyclic aromatic rings (e.g., as described herein) that are the same or different, or one monocyclic aromatic ring (e.g., as described herein) and one polycyclic aromatic ring (e.g., as described herein). The amine antioxidant may be a diphenylamine. Alternatively, the amine antioxidant may be an aromatic amine having the amine group attached to a monocyclic aromatic ring (e.g., a phenyl ring) and a polycyclic aromatic ring (e.g., a naphthalene ring). The amine antioxidant may be selected from the group consisting of dinonyl diphenylamine, butylated, octylated diphenylamine, dioctyl diphenylamine, N,N′-diisopropyl-p-phenylenediamine, N,N′-di-sec-butyl-p-phenylenediamine, N,N′-bis(1,4-dimethylpentyl)-p-phenylenediamine, N,N′-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, N,N′-bis(1-methylheptyl)-p-phenylenediamine, N,N′-dicyclohexyl-p-phenylenediamine, N,N′-diphenyl-p-phenylenediamine, N, N′-di(naphth-2-yl)-p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, N-(1-methylheptyl)-N′-phenyl-p-phenylenediamine 4-(p-toluenesulfonamido)-diphenylamine, N,N′-dimethyl-N,N′-di-sec-butyl-p-phenylenediamine, diphenylamine, diphenyl amine styrene (CAS No. 68442-68-2), N-allyldiphenylamine, 4-isopropoxydiphenylamine, di(4-methoxyphenyl)amine 2,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, N,N,N′,N′-tetramethyl-4,4′-diaminodiphenylmethane, 1,2-di[(2-methylphenyl)amino]-ethane, 1,2-di(phenylamino)propane, (o-tolyl)biguanide, di[4-(1′,3′-dimethylbutyl)phenyl]amine, tert-octylated N-phenyl-1-naphthylamine, phenyl-1-naphthylamine amine p,p′-dioctyldiphenyl, mixture of tert-butylated/tert-octylated mono- and di-alkylated diphenylamines, mixture of mono- and di-alkylated nonyldiphenylamines mixture of mono- and di-alkylated dodecyldiphenylamines, mixture of mono- and di-alkylated isopropyl/isohexyldiphenylamines, mixtures of mono- and di-alkylated tert-butyldiphenylamines, 2,3-dihydro-3,3-dimethyl-4H-1,4-benzothiazine phenothiazine, mixtures of mono- and di-alkylated tert-butyl/tert-octyl-phenothiazines, mixtures of mono- and di-alkylated tert-octyl-phenothiazines, N-allylphenothiazine, and N,N,N′,N′-tetraphenyl-1,4-diaminobut-2-ene.

The tocopherol supplement comprises at least one element among beta-tocopherol, delta-tocopherol and gamma-tocopherol.

The sum of the contents by weight of beta-tocopherol, gamma-tocopherol and delta-tocopherol in the tocopherol supplement may be greater than 50%, preferably greater than 70%.

Example of the composition of the tocopherol supplement according to the invention:

• • 0 to 20% alpha-tocopherol,
  • 0 to 5% beta-tocopherol,
  • 50 to 65% gamma-tocopherol,
  • 20 to 35% delta-tocopherol.

In a preferred embodiment of the invention, the tocopherol supplement comprises delta-tocopherol, preferably the delta-tocopherol content by weight in the tocopherol supplement is greater than 50%.

The antioxidant additive may have a ratio of the contents by weight of the amine antioxidant to the phenolic antioxidant between 0.6 and 1.2.

In a preferred embodiment, the ratio of the contents by weight of the amine antioxidant to the phenolic antioxidant is less than 0.9, preferably less than 0.8. The amine antioxidant may represent a toxicological risk, which is why it is advantageous to reduce its proportion in the antioxidant additive. This reduction is possible by the presence of the tocopherol supplement, which makes it possible to obtain good antioxidant performance while reducing the proportion of amine antioxidant.

In a preferred embodiment of the invention, the base oil is a Group III oil, i.e., it has a weight content of sulfur of less than 0.03% and a viscosity index of more than 120.

The lubricating composition according to the invention may further comprise one or more additional products selected from the group consisting of an anti-wear agent, a detergent, a metal deactivating additive, a phosphite, a lactone, a dispersant, a diluent, an emulsifier, an anti-foaming agent, a corrosion/rust inhibitor, an extreme pression agent, a pour point depressant, a viscosity index improver, and a friction modifier.

EXAMPLE

A composition according to the invention was tested using a Group III HC6 oil, to compare its performance with comparative compositions. A thermal ageing test at 150° C. for 216 hours was carried out according to CEC (“Coordinating European Council”) procedure L-109-14.

The evolution of the viscosity KV100 (mm²/s) according to ASTM D445/446 standard as well as the resistance to oxidation (A/cm) according to DIN 51453 standard were measured at regular intervals of the aging at 150° C.: t=0 hours (initial), t=72 hours, t=144 hours, t=168 hours, t=216 hours.

The antioxidants tested were AO 1135, AO 5057, alpha-tocopherol, and a tocopherol supplement under the reference VB T70.

AO 1135 is a phenolic antioxidant of composition: benzopropanoic acid, 3,5-bis(1,1-dimethyl-1,1-dimethylethyl)-4-hydroxy-, C7-9 branched alkyl esters.

AO 5057 is an amine-type antioxidant, composition: benzenamine, N-phenyl-, reaction products with 2,4,4-trimethylpentene.

VB T70 is a Mixture of Antioxidants and Sunflower Oil, Composition:

• • 30% sunflower oil
  • 70% of tocopherols, among which are:

    • 9 to 20% of alpha-tocopherol
    • 1 to 4% of beta-tocopherol
    • 50 to 65% of gamma-tocopherol
    • 20 to 35% of delta-tocopherol.

Comparative Compositions:

• • Composition A:

    • base oil HC6

  • Composition B:

    • 99% HC6 base oil
    • 1% AO 1135

  • Composition C:

    • 99% base oil HC6
    • 0,7% AO 1135
    • 0.3% VB170 (which corresponds to about 0.21% of tocopherol supplement, due to the presence of sunflower oil in VB170)

  • Composition D (state of the art):

    • 99% HC-6 base oil
    • 0.5% AO 1135
    • 0.5% AO 5057

  • Composition E:

    • 99% base oil HC-6
    • 0.4% AO 1135
    • 0.4% AO 5057
    • 0.2% alpha-tocopherol

Example of a Lubricating Composition According to the Invention:

Composition F:

• • 98.9% base oil HC6
  • 0.45% AO 1135
  • 0.45% AO 5057
  • 0.2% VB 170 (which corresponds to about 0.14% of tocopherol supplement)

The test results are shown in Tables 1 and 2 below, as well as in FIGS. 1 and 2.

• • Table 1: Viscosity KV100 according to ASTM D445/446 standards (mm²/s)
  • Table 2: Oxidation (A/cm) according to DIN 51543 standard

TABLE 1

Aging time at

150° C. (hours)

0

72

144

168

216

Composition A

6.365

8.258

11.54

13.45

19.87

Composition B

6.348

7.475

9.956

11.14

14.57

Composition C

6.351

7.503

10.04

11.37

15.21

Composition D

6.348

6.962

9.357

10.43

13.59

Composition E

6.358

7.531

10.46

12

17.06

Composition F

6.354

7.198

8.867

9.595

11.4

TABLE 2

Aging time at

150° C. (hours)

0

72

144

168

216

Composition A

0

79.3

128.6

144.6

173.9

Composition B

0

47.1

104.6

118.5

144.2

Composition C

0

48.2

110.6

126.1

156.9

Composition D

0

29.5

102.4

120.9

157

Composition E

0

50.4

119.3

138.2

174.6

Composition F

0

36.5

87

99.5

123.2

The graph in FIG. 1 and Table 1 show the evolution of the viscosity of the oil during thermal aging, measured according to ASTM D445/D446 protocols. The unit on the ordinate is mm²/s. The unit of time on the abscissa is the duration of thermal aging at 150° C., expressed in hours. This test is particularly relevant for evaluating the performance of a lubricating composition and its durability.

The graph in FIG. 2 and Table 2 show the evolution of oxidation, measured according to the DIN 51453 protocol. The unit on the ordinate is A/cm. The unit of time on the abscissa is the duration of thermal aging at 150° C., expressed in hours.

In FIGS. 1 and 2, it can be seen that the performance is lowest for composition A, which does not contain an antioxidant additive.

Composition D, which is the reference antioxidant formulation used on a large scale in the lubricant market, is the composition of the state of the art that achieves the best performance in terms of viscosity (FIG. 1). Composition F, made according to the invention, is similar to composition D with part of the antioxidants replaced by a mixture of alpha, beta, gamma and delta type tocopherols.

The results of composition F are better in terms of viscosity (FIG. 1) and oxidation (FIG. 2) than those of composition D. The comparison of compositions D and F leads to the conclusion of improved performance obtained by the presence of tocopherols.

Composition E is also similar to composition D, but this time with the presence of exclusively alpha type tocopherols.

The performance of composition E shown in FIGS. 1 and 2 is worse than composition F, and even worse than composition D. The previously observed performance-enhancing effect is therefore not present with exclusively alpha type tocopherols, which shows the importance of beta, gamma and delta type tocopherols.

Composition B includes only a phenolic antioxidant, and composition C is similar to composition B with a portion of the phenolic antioxidant replaced by the mixture of alpha, beta, gamma and delta tocopherols.

The performance of composition C shown in FIGS. 1 and 2 is worse than composition B. The previously observed performance enhancing effect of tocopherols is therefore not present in the absence of an amine antioxidant. This reveals a regeneration effect of the amine-type antioxidant by the tocopherols, which explains why the tocopherols make it possible to improve performance in composition F.

Therefore, in the compositions according to the invention, it is possible to reduce the amount of amine-type antioxidant compared to the state of the art by adding some beta, gamma or delta tocopherol, which is an advantage because of the toxicity of amine-type antioxidants. For example, an antioxidant with 50% phenol antioxidant, 40% amine antioxidant, and 10% tocopherol supplement can be provided, or 45% phenol antioxidant, 40% amine antioxidant, and 15% tocopherol supplement.

Although the above description is based on particular embodiments, it is by no means limiting the scope of the invention, and modifications may be made, in particular by substitution of technical equivalents or by different combination of all or part of the features developed above.