DISPERSANTS FOR LUBRICATING OIL COMPOSITIONS

Abstract

A lubricating oil composition comprises a major amount of an oil of lubricating viscosity and a minor amount of an unsymmetrical bis-succinimide, or a mixture of unsymmetrical bis-succinimides, of the structure (I):

##STR00001##

wherein one of R.sub.1 and R.sub.2 is a polyisobutylene group having a weight average molecular weight of 400 to 5,000, as determined by GPC with reference to linear polystyrene standards, and the other of R.sub.1 and R.sub.2 is a hydrocarbon group made by the metallocene-catalysed polymerisation of an -olefin feedstock; and x is from 1 to 10 and is the same for all molecules of structure (I), or an average of all molecules of structure (I) in a mixture of molecules of structure (I).

Claims

1. A lubricating oil composition comprising a major amount of an oil of lubricating viscosity and a minor amount of an unsymmetrical bis-succinimide dispersant, or a mixture of unsymmetrical bis-succinimide dispersants, of the structure (I): ##STR00013## wherein one of R.sub.1 and R.sub.2 is a polyisobutylene group having a number average molecular weight of 400 to 5,000, as determined by GPC with reference to linear polystyrene standards, and the other of R.sub.1 and R.sub.2 is a hydrocarbon group made by the metallocene-catalysed polymerisation of an -olefin feedstock, and wherein x is from 1 to 10 and is the same for all molecules of structure (I) or an average of all molecules of structure (1) in a mixture of molecules of structure (I).

2. A lubricating oil composition according to claim 1, wherein the -olefin feedstock comprises 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene and 1-octadecene and any mixtures of two or more of these -olefins.

3. A lubricating oil composition according to claim 2, wherein the -olefin feedstock consists essentially of 1-octene, 1-decene, 1-dodecene or any mixture thereof.

4. A lubricating oil composition according to claim 1, wherein the hydrocarbon group made by the metallocene-catalysed polymerisation of an -olefin feedstock has a number average molecular weight of 300 to 20,000, as determined by GPC with reference to linear polystyrene standards.

5. A lubricating oil composition according to claim 1, wherein x is from 1 to 8.

6. A lubricating oil composition according to claim 1, wherein the unsymmetrical bis-succinimide dispersant of the structure (I) is present in the lubricating oil composition in an amount of from 0.01 to 20% by mass, based on the mass of the composition.

7. A lubricating oil composition according to claim 1, which is an automatic transmission fluid.

8. A lubricating oil composition according to claim 7, further comprising as a friction modifier the product of an isomerized alkenyl-substituted succinic anhydride and a polyamine, the product having structure (II): ##STR00014## wherein x and y are independently zero or integers from 1 to 30, where x+y is from 1 to 30, and z is zero or an integer from 1 to 10.

9. A lubricating oil composition according to claim 1, further comprising one or more co-additives in addition to the unsymmetrical bis-succinimide dispersant of the structure (I).

10. A lubricating oil composition according to claim 8, further comprising one or more co-additives in addition to the unsymmetrical bis-succinimide dispersant of the structure (I) and the friction modifier product of an isomerized alkenyl-substituted succinic anhydride and a polyamine having structure (II).

11. A method of making an unsymmetrical bis-succinimide dispersant, or a mixture of unsymmetrical bis-succinimide dispersants, of the structure (I): ##STR00015## wherein one of R.sub.1 and R.sub.2 is a polyisobutylene group having a number average molecular weight of 400 to 5,000, as determined by GPC with reference to linear polystyrene standards, and the other of R.sub.1 and R.sub.2 is a hydrocarbon group made by the metallocene-catalysed polymerisation of an -olefin feedstock, and wherein x is from 1 to 10 and is the same for all molecules of structure (I) or an average of all molecules of structure (I) in a mixture of molecules of structure (I); the method comprising: (a) forming or otherwise providing a mixture of (i) a polyisobutenyl-substituted succinic anhydride, the polyisobutylene group having a number average molecular weight of 400 to 5,000, as determined by GPC with reference to linear polystyrene standards, and (ii) a hydrocarbyl-substituted succinic anhydride where the hydrocarbyl substituent is a hydrocarbon group made by the metallocene-catalysed polymerisation of an -olefin feedstock; and (b) reacting the mixture from step (a) with a polyethylene polyamine or a mixture of polyethylene polyamines.

12. A method according to claim 11, wherein the -olefin feedstock comprises 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene and 1-octadecene and any mixtures of two or more of these -olefins.

13. A method according to claim 11, wherein the -olefin feedstock consists essentially of 1-octene, 1-decene, 1-dodecene or any mixture thereof.

14. A method according to claim 11, wherein in step (a), the mixture of component (i) and component (ii) contains equal molar quantities of (i) and (ii).

15. A method according to claim 11, wherein the polyalkylene polyamine used in step (b) is diethylene triamine, triethylene tetrarnine, tetraethylene pentamine, pentaethylene hexamine or any mixture thereof, or the polyalkylene polyamine used in step (b) is a mixture of polyethylene polyamines where the average number of nitrogen atoms of the molecules forming the mixture is from 5 to 8.

16. A method of increasing the fatigue lifetime between two or more contacting surfaces moving relative to one another, the method comprising lubricating the contacting surfaces with a lubricating oil composition according to claim 1.

Description

EXAMPLE 1

Synthesis of an Unsymmetrical Bis-Succinimide of Structure (I)

[0118] A one liter round-bottomed, 4-necked flask was fitted with a thermometer, mechanical stirrer, nitrogen sweep, Dean-Starke trap, and a water-cooled condenser. The flask was charged with a 50:50 molar mixture of (i) a polyisobutenyl-substituted succinic anhydride where the polyisobutenyl group had a number average molecular weight of 950 and (ii) a hydrocarbyl-substituted succinic anhydride where the hydrocarbyl group had a number average molecular weight of 2,300 and was made by the metallocene-catalysed polymerisation of a mixture of 1-octene, 1-decene and 1-dodecene. The flask was heated to 130 C. under stirring. A commercial mixture of polyethylene polyamines having an average of six nitrogen atoms per molecule was then added slowly to the flask via an addition funnel in an amount equivalent to provide one mole of primary amine per mole of anhydride groups. The temperature of the reaction mixture was raised to 165 C. and held there for 3 hours. This stage was followed by a one hour nitrogen sparge to remove residual water. After cooling, the reaction yielded a product having a nitrogen content of 2.2% by mass.

EXAMPLE 2

Symmetrical Bis-Succinimide Made Using Polyisobutylene (PIB)

[0119] Example 1 was repeated using the same mixture of polyethylene polyamines but only reactant (i): the polyisobutenyl-substituted succinic anhydride where the polyisobutenyl group had a number average molecular weight of 950. The product obtained had a nitrogen content of 3.46% by mass.

EXAMPLE 3

Synthesis of a Symmetrical Bis-Succinimide Made Using mPAO

[0120] Example 1 was repeated using the same mixture of polyethylene polyamines but only reactant (ii): the hydrocarbyl-substituted succinic anhydride where the hydrocarbyl group had a number average molecular weight of 2,300 and was made by the metallocene-catalysed polymerisation of a mixture of 1-octene, 1-decene and 1-dodecene. The product obtained had a nitrogen content of 1.56% by mass.

[0121] Four automatic transmission fluid compositions were prepared as detailed in Table 1. Three compositions were comparative examples: Comp. 1 did not contain any of the bis-succinimides of Examples 1-3; Comp. 2 contained only the symmetrical bis-succinimide of Example 2, made using polyisobutylene (PIB); and Comp. 3 contained a combination of both the symmetrical bis-succinimides of Examples 2 and 3. Ex. 4 is an example of the present invention as it contains only the un-symmetrical bis-succinimide of Example 1.

TABLE-US-00001 TABLE 1 Component/wt % Comp. 1 Comp. 2 Comp. 3 Ex. 4 Example 1 2.0 Example 2 2.0 1.52 Example 3 1.40 Additive package.sup.1 10.0 8.0 7.1 8.0 Base Oil.sup.2 90.0 90.0 90.0 90.0 Properties Kv 100.sup.3 (cSt) 3.50 3.49 3.54 3.54 Kv 40.sup.3 (cSt) 14.30 14.90 15.05 14.93 .sup.1The Additive Package was a conventional additive package typically found in automatic transmission fluid compositions. The same package was used in all examples. It contained a conventional borated dispersant, an oil-soluble phosphorus anti-wear compound, a calcium sulphonate detergent, anti-oxidants, corrosion inhibitors and friction modifiers. .sup.2The base oil was Yubase 3 which is an API Group III mineral oil. .sup.3Kinematic viscosity was determined according to ASTM D445.

Friction Performance Data

[0122] Friction measurements were made on each fluid from Table 1 on an SAE No. 2 test machine using method JASO M348. The test clutch assembly used steel plates and NW461E fibre plates. Static friction (S) and dynamic friction (D) were measured after 5000 cycles. Results are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Friction Comp. 1 Comp. 2 Comp. 3 Ex. 4 S 0.0806 0.1251 0.1159 0.1152 D 0.1264 0.1383 0.1398 0.1392

[0123] For optimum performance in a fluid used in an automatic transmission, S should be between 0.100 and 0.115 and D should be above 0.130. Comp. 1, which did not contain any of the bis-succinimides of Examples 1-3, had both static and dynamic friction which were too low. For Comp. 2, which contained the conventional symmetrical bis-succinimide made using PIB, dynamic friction was good but static friction was too high. The fluid according to the present invention, Ex. 4, had both good static friction and good dynamic friction. Comp. 3 also had both good static friction and good dynamic friction but importantly, as shown in Table 1, Comp. 3 contained a total of 2.92 mass % of dispersant (combination of Examples 2 and 3) whereas Ex. 4 contained only 2 mass %.

Fatigue Testing

[0124] A modified 4-ball test rig was used. AXK1105 needle bearings were run against two FTRE-2542 races at the conditions shown in the table below. Fresh bearings and races were used for each test and each test fluid was run until pitting occurred. The number of cycles before pitting was recorded with better fatigue lifetimes being evidenced by a greater number of cycles before pitting.

TABLE-US-00003 Roller Race Test Pieces No. of needle bearings 18 Radius mm 1 Surface roughness m 0.05 0.2 Test conditions Contact pressure Gpa 1.94 Contact length mm 4.71 Shaft revolutions rpm 2095 Entrainment speed ms.sup.1 1.84 Sliding speed ms.sup.1 0.20 Slide-to-roll ratio % 11 Oil temperature C. 120 Oil volume cm.sup.3 50 Contact cycles hr.sup.1 2.11 10.sup.6 1.13 10.sup.6

[0125] Fluid Comp 2 from the table above (containing only the conventional symmetrical bis-succinimide made using PIB) ran for an average of 16.8 million cycles before pitting was observed. Contrastingly, the oil containing the unsymmetrical bis-succinimide of the present invention (fluid Ex 4 from the table above) ran for an average of 28.0 million cycles prior to pitting. This was nearly double the wear lifetime of fluid Comp 2, illustrating a significant advantage for the fluid according to the present invention.