Method for lubricating surfaces

Abstract

A method of lubricating the contact between a first surface coated with a hydrogenous carbon film or coating of type a-C:H, ta-C:H, a-C:H:Me or a-C:H:X, as classified by VDI-Standard VDI 2840 and a second ferrous, preferably steel surface. The method comprises supplying to said contact a lubricating oil composition comprising a major amount of an oil of lubricating viscosity and (a) an oil-soluble or oil-dispersible molybdenum compound in an amount such as to provide between 150 and 1000 ppm by weight of molybdenum to the lubricating oil composition, and (b) between 0.1 and 5% by weight with respect to the weight of the lubricating oil composition of a polymeric organic friction modifier, the organic friction modifier being the reaction product of (i) a functionalised polyolefin, (ii) a polyether, (iii) a polyol and (iv) a monocarboxylic acid chain terminating group.

Claims

1. A method of lubricating the frictional contact between a first surface coated with a hydrogenous carbon film or coating of type a-C:H, ta-C:H, a-C:H:Me or a-C:H:X, as classified by VDI-Standard VDI 2840; and a second, ferrous surface, which method comprises supplying to said frictional contact a lubricating oil composition comprising a major amount of an oil of lubricating viscosity and (a) an oil-soluble or oil-dispersible molybdenum compound in an amount such as to provide between 150 and 1000 ppm by weight of molybdenum to the lubricating, oil composition, and (b) between 0.1 and 5% by weight with respect to the weight of the lubricating oil composition of a polymeric organic friction modifier, the organic friction modifier being a reaction product of (i) a functionalised polyolefin, (ii) a polyether, (iii) a polyol and (iv) a monocarboxylic acid chain terminating group.

2. The method of claim 1 wherein the oil-soluble molybdenum compound (a) is present in an amount to provide between 300 and 1000 ppm by weight of molybdenum to the lubricating oil composition.

3. The method of claim 1 wherein the oil-soluble molybdenum compound (a) comprises one or more molybdenum dithiocarbamates.

4. The method of claim 3 wherein the oil-soluble molybdenum compound (a) comprises one or more di-nuclear molybdenum dithiocarbamates or one or more tri nuclear molybdenum dithiocarbamates.

5. The method of claim 4 wherein the oil-soluble molybdenum compound (a) comprises a mixture of one or more di-nuclear molybdenum compounds and one or more tri-nuclear molybdenum compounds.

6. The method of claim 1 wherein the functionalised polyolefin (i) is derived from a polymer of a mono-olefin having from 2 to 6 carbon atoms.

7. The method of claim 1 wherein the functionalised polyolefin (i) comprises a diacid or anhydride functional group from reaction of the polyolefin with an unsaturated diacid or anhydride.

8. The method of claim 1 wherein the functionalised polyolefin (i) is a polyisobutylene polymer that has been reacted with maleic anhydride to form polyisobutylene succinic anhydride (PIBSA).

9. The method of claim 1 wherein the polyether (ii) comprises a polyglycerol or a polyalkylene glycol.

10. The method of claim 1 wherein the polyether (ii) comprises a polyethylene glycol (PEG), a mixed poly(ethylene-propylene) glycol or a mixed polyethylene-butylene)glycol.

11. The method of claim 1 wherein the polyol (iii) comprises a diol, triol, tetraol or related dimers, trimers or larger oligomers of such compounds.

12. The method of claim 1 wherein the polyol (iii) comprises one or more of glycerol, neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, pentaerythritol, dipentaerythritol, tripentaerythritol and sorbitol.

13. The method of claim 1 wherein the carboxylic acid (iv) comprises a C.sub.2-C.sub.36 carboxylic acid, which acid is linear or branched, saturated or unsaturated.

14. The method of claim 1 wherein the carboxylic acid (iv) comprises one or more of lauric acid, erucic acid, isostearic acid, palmitic acid, oleic acid and linoleic acid.

15. The method of claim 1 wherein the polymeric friction modifier (b) comprises the reaction product of (i) maleated polyisobutylene (PIBSA), (ii) polyethylene glycol (PEG), (iii) glycerol and (iv) tall oil fatty acid.

16. The method of claim 1 wherein the polymeric friction modifier (b) is present in the lubricating oil composition in an amount of between 0.1 and 3% by weight with respect to the weight of the lubricating oil composition.

17. The method of claim 1 wherein the lubricating oil composition further comprises one or more additional additives selected from the group consisting of ashless dispersants, metal detergents, corrosion inhibitors, metal dihydrocarbyl dithiophosphates, antioxidants, pour point depressants, anti-foaming agents, additional friction modifiers, antiwear agents and viscosity modifiers.

18. An internal combustion engine having one or more component parts coated with a hydrogenous carbon film or coating of type a-C:1-1, ta-C:H, a-C:H:Me or a-C:H:X, as classified by VDI-Standard VDI 2840, which parts during operation of the engine, are in frictional contact with a ferrous surface and, contained in a reservoir in the engine, a lubricating oil composition comprising a major amount of an oil of lubricating viscosity and (a) an oil-soluble or oil-dispersible molybdenum compound in an amount such as to provide between 150 and 1000 ppm by weight of molybdenum to the lubricating oil composition, and (b) between 0.1 and 5% by weight with respect to the weight of the lubricating oil composition of a polymeric organic friction modifier, the organic friction modifier being a reaction product of (i) a functionalised polyolefin, (ii) a polyether, (iii) a polyol and (iv) a monocarboxylic acid chain terminating group.

19. The internal combustion engine of claim 18 wherein the lubricating oil composition further comprises one or more additional additives selected from the group consisting of ashless dispersants, metal detergents, corrosion inhibitors, metal dihydrocarbyl dithiophosphates, antioxidants, pour point depressants, anti-foaming agents, additional friction modifiers, antiwear agents and viscosity modifiers.

20. The method of claim 1, wherein the ferrous surface is a steel surface.

21. The internal combustion engine of claim 18 wherein the ferrous surface is a steel surface.

22. The method of claim 20, wherein the steel surface is present in the cam shaft, pistons, cylinder liners and/or valves.

23. The internal combustion engine of claim 21, wherein the steel surface is present in the cam shaft, pistons, cylinder liners and/or valves.

Description

EXAMPLES

(1) A base lubricating oil composition was prepared. The base oil contained a succinimide dispersant, a calcium sulphonate detergent, zinc dialkyldithiophosphate (ZDDP), a combination of anti-oxidants comprising a hindered phenol, a diphenylamine and a sulphurised ester, a silicon-containing antifoamant, a pour point depressant and a viscosity modifier. These components were blended into an API Group II base-stock to produce the base lubricating oil composition.

(2) Test oils were then prepared. One test oil comprised the base lubricating oil as prepared above without further components added and seven test oils were prepared by adding additional components to the base lubricating oil. Details of the test oils are given in the table below where the concentration of molybdenum in the test oil is expressed in parts per million (ppm) by weight, relative to the weight of the test oil as measured by ASTM D5185, and the amount of friction modifier added is given in weight %, again relative to weight of the test oil:

(3) TABLE-US-00003 Friction Test [Mo] in oil/ modifier/ Oil Added component(s) ppm wt %  1(c) None 0 0  2(c) Tri-nuclear molybdenum dithiocarbamate 600 0  3(c) Mixture of di-nuclear molybdenum 600 0 dithiocarbamate and tri-nuclear molybdenum dithiocarbamate  4(c) Polymeric organic friction modifier 0 1  5(c) Glycerol mono-oleate friction modifier 0 1  6(c) Mixture of di-nuclear molybdenum 600 1 dithiocarbamate and tri-nuclear molybdenum dithiocarbamate + glycerol mono-oleate friction modifier  7 Tri-nuclear molybdenum dithiocarbamate + 600 1 polymeric organic friction modifier  8 Mixture of di-nuclear molybdenum 600 1 dithiocarbamate and tri-nuclear molybdenum (300 from dithiocarbamate + polymeric organic friction each Mo modifier compound)  9 Di-nuclear molybdenum dithiocarbamate + 600 1 polymeric organic friction modifier 10(c) Tri-nuclear molybdenum dithiocarbamate 300 0 11 Tri-nuclear molybdenum dithiocarbamate + 300 1 polymeric organic friction modifier (c)comparative example

(4) Oils 1 to 6 and 10 are comparative examples and oils 7, 8, 9 and 11 are examples in accordance with the present invention. The polymeric organic friction modifier used was the reaction product of (i) maleated polyisobutylene (PIBSA) where the polyisobutylene group had an average molecular weight of around 950 amu, and an approximate saponification value of 98 mg KOH/g (ii) polyethylene glycol (PEG) having a hydroxyl value of 190 mg KOH/g, (iii) glycerol and (iv) tall oil fatty acid. It was prepared as described hereinabove. Glycerol mono-oleate was chosen as it is a conventional friction modifier commonly used in lubricating oil compositions.

(5) Each oil was tested using a Mini-Traction Machine with reciprocating function (MTM-R) available from PCS Instruments, London, UK. This machine employs a inch (19 mm) diameter ball as an upper specimen which is reciprocated under an applied load against a lower specimen in the form of a disc. The ball was made from AISI52100 grade steel and was uncoated. The disc was made of steel which had been coated with DLC (Balinit® DLC-Star: a-C:H type)) to a depth of around 2 μm. The contact between the ball and the disc was thus between a ferrous (steel) surface and a surface coated with a diamond-like carbon coating. The test conditions are given in the table below:

(6) TABLE-US-00004 Oil temperature 100° C. Disc frequency 10 Hz Ball speed 200 mms.sup.−1 Stroke length 4000 μm Applied load 50 N Contact pressure 1.2 GPa Test duration 2 hours

(7) The wear scars formed on the lower disc specimens (DLC coated) were analysed using a Zemetrics ZeScope 3D optical profilometer using non-contact interferometric focal scanning. This permitted a measurement of the amount of wear by determining the material lost from the disc during the test. This was reported as a wear scar volume (WSV) in units of μm.sup.3. Additionally, the co-efficient of friction of the contact was recorded at the end of each test. Results are shown in the table below where each value is the average of two tests using each test oil.

(8) TABLE-US-00005 Test Oil WSV/μm.sup.3 Friction co-efficient  1(c) 40755 0.1069  2(c) 143390 0.0633  3(c) 93563 0.0462  4(c) 22682 0.1021  5(c) 13034 0.0929  6(c) 70145 0.0476  7 59222 0.0769  8 13430 0.0783  9 37810 0.0885 10(c) 85133 0.0665 11 42396 0.0510 (c)comparative example

(9) By comparing Oils 1, 2, 3 and 10 it can be seen clearly that the presence of the molybdenum compound alone leads to significantly increased wear on the DLC surface. This confirms the observations reported by I Sugimoto referred to above in, Transactions of the Japan Society of Mechanical Engineers, Series A, Vol. 78, No. 786, pp. 213-222. The friction modifiers alone, either the polymeric organic friction modifier (b) or the conventional glycerol mono-oleate friction modifier, were effective to reduce wear on the DLC surface but did not provide any significant reduction in friction co-efficient (compare Oil 1 with Oils 4 and 5). The combination of molybdenum compounds with the conventional glycerol mono-oleate friction modifier provided good friction performance but poor wear protection (compare Oil 1 with Oil 6). Contrastingly, the examples according to the invention (using Oil 7, Oil 8 and Oil 9) provided both good wear protection and low friction co-efficients. Oil 7 differs from Oil 2 only in the presence of the polymeric organic friction modifier (b) but this leads to a nearly 60% fall in recorded WSV while maintaining a low friction co-efficient. Similarly, Oil 8 differs from Oil 3 only in the presence of the polymeric organic friction modifier (b) but this leads to an 85% fall in recorded WSV while maintaining a low friction co-efficient. Oil 9 also showed good wear protection and a low friction co-efficient Oil 10 shows that a lower amount of molybdenum compound alone also leads to a significant increase in wear (c.f. Oil 1). Addition of the polymeric organic friction modifier (b) restores the wear protection while also providing a low co-efficient of friction (Oil 11).

(10) The results show that the combination of a molybdenum compound with the particular type of polymeric organic friction modifier (b), in accordance with the present invention, is able to provide a lubricating oil which when used to lubricate the contact between a DLC surface and a ferrous (steel) surface, protects the DLC surface from wear while also maintaining a low friction contact. This behaviour is not seen with a common type of friction modifier. The combination of a di-nuclear molybdenum compound and a tri-nuclear molybdenum compound (Oil 8) provided the best overall performance in terms of good wear protection and low friction co-efficient. The present invention thus enables the lubricant formulator to exploit the beneficial properties provided by molybdenum compounds in systems where DLC surfaces are in contact with ferrous surfaces.

(11) Further test oils were prepared using a base lubricating oil containing a succinimide dispersant, a calcium sulphonate detergent, zinc dialkyldithiophosphate (ZDDP), a combination of anti-oxidants comprising a hindered phenol, a diphenylamine and a sulphurised ester, a silicon-containing antifoamant, a pour point depressant and a viscosity modifier. As above, the base-stock used was an API Group II base-stock. The table below details the test oils.

(12) TABLE-US-00006 [Mo] Friction Test in oil/ modifier/ Oil Added component(s) ppm wt % 12(c) None 0 0 13(c) Tri-nuclear molybdenum dithiocarbamate 600 0 14(c) Tri-nuclear molybdenum dithiocarbamate + 600 1 Perfad ™ 3006 (c)comparative example

(13) It is believed that Perfad™ 3006 is polymeric organic friction modifier formed from the reaction of sorbitol, ethylene oxide and poly (12-hydroxystearic acid) as described in WO 2015/065801. Perfad™ 3006 is thus chemically distinct from the polymeric organic friction modifier used in the present invention. MTM-R testing as described above was carried out on Test Oils 12-14 giving the following results.

(14) TABLE-US-00007 Test Oil WSV/μm.sup.3 Friction co-efficient 12(c) 47173 0.0896 13(c) 133155 0.0580 14(c) 99559 0.0509

(15) As before, the presence of the molybdenum compound alone lead to significantly increased wear on the DLC surface (compare Oils 12 and 13). However, although the combination of Perfad™ 3006 and the molybdenum compound gave good friction performance, the wear protection afforded to the DLC surface was much less pronounced. Comparing Oils 13 and 14 shows that with respect to the presence of the molybdenum compound alone, the additional presence of Perfad™ 3006 gave only a 25% reduction in WSV. This can be contrasted with the results for Oils 2 and 7 where the presence of the polymeric organic friction modifier gave a 60% reduction in WSV. It is thus clear that the polymeric organic friction modifiers used in the present invention are significantly more effective at preventing wear in a steel-DLC contact than is Perfad™ 3006.