Grease formulations

Abstract

A grease formulation containing a thickener and a Fischer-Tropsch derived base oil, in particular a heavy or extra heavy base oil. The use of a Fischer-Tropsch oil results in an increase in thickener concentration and in improved properties such as anti-wear and copper corrosion performance. Also provided is the use of a Fischer-Tropsch derived base oil in a grease formulation, for the purpose of improving its anti-wear and/or copper corrosion performance, and/or for reducing the concentration of an additive in the formulation.

Claims

1. A grease formulation comprising: a thickener that comprises a soap, wherein the soap is a metal salt of a C.sub.6-C.sub.20 fatty acid or a derivative thereof, wherein the metal is selected from the group consisting of lithium, sodium, magnesium, calcium, aluminum and a combination thereof, and the thickener is present in the grease formulation in an amount of from 5 to 20 wt %; and a base oil comprising a Fischer-Tropsch derived base oil, wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100 C. of from 8 to 25 mm.sup.2/s and is present in the base oil in an amount of more than 90 wt %, and wherein the base oil is present in the grease formulation in an amount of from 60 to 95 wt %.

2. A grease formulation according to claim 1, wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100 C. of from 10 to 25 mm.sup.2/s.

3. A method, comprising: applying a grease formulation to the surfaces of two relatively moving components, wherein the grease formulation comprises: a thickener that comprises a soap, wherein the soap is a metal salt of a C.sub.6-C.sub.20 fatty acid or a derivative thereof, wherein the metal is selected from the group consisting of lithium, sodium, magnesium, calcium, aluminum and a combination thereof, and the thickener is present in the grease formulation in an amount of from 5 to 20 wt %; and a base oil comprising a Fischer-Tropsch derived base oil, wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100 C. of from 8 to 25 mm.sup.2/s and is present in the base oil in an amount of more than 90 wt %, and wherein the base oil is present in the grease formulation in an amount of from 60 to 95 wt %.

4. A method according to claim 3, wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100 C. of from 8 to 20 mm.sup.2/s.

5. A method according to claim 3, wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100 C. of from 10 to 25 mm.sup.2/s.

6. A method according to claim 3, wherein the Fischer-Tropsch derived base oil is present in the base oil in an amount of 100 wt %.

7. A grease formulation according to claim 1, wherein the Fischer-Tropsch derived base oil is present in the base oil in an amount of 100 wt %.

8. A grease formulation according to claim 1, wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100 C. of from 10 to 25 mm.sup.2/s.

9. A grease formulation according to claim 1, wherein the thickener is present in the grease formulation in an amount of from 10 to 20 wt %.

10. A grease formulation comprising: a thickener that comprises a soap, wherein the soap is a metal salt of a C.sub.6-C.sub.20 fatty acid, wherein the metal is selected from the group consisting of lithium, sodium, calcium, aluminum and a combination thereof, and the thickener is present in the grease formulation in an amount of from 5 to 20 wt %; and a base oil comprising a Fischer-Tropsch derived base oil, wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100 C. of from 8 to 25 mm.sup.2/s and is present in the base oil in an amount of more than 90 wt. %, and wherein the base oil is present in the grease formulation in an amount of from 60 to 95 wt %.

11. A grease formulation according to claim 10, wherein the Fischer-Tropsch derived base oil is present in the grease formulation in an amount of from 70 to 95 wt %.

12. A grease formulation according to claim 10, wherein the Fischer-Tropsch derived base oil is present in the grease formulation in an amount of from 80 to 95 wt %.

13. A grease formulation according to claim 10, wherein the Fischer-Tropsch derived base oil is present in the grease formulation in an amount of from 90 to 95 wt %.

14. A grease formulation comprising: a thickener that comprises a soap, wherein the soap is a metal salt of a C.sub.6-C.sub.20 fatty acid or a derivative thereof, wherein the metal is selected from the group consisting of lithium, sodium, calcium, aluminum and a combination thereof, and the thickener is present in the grease formulation in an amount of from 5 to 20 wt %; and a base oil comprising a non-Fischer-Tropsch derived base oil and a Fischer-Tropsch derived base oil, wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100 C. of from 8 to 25 mm.sup.2/s, and wherein the non-Fischer-Tropsch derived base oil is present in the base oil in an amount less than 10 wt %, and wherein the base oil is present in the grease formulation in an amount of from 60 to 95 wt %.

15. A grease formulation according to claim 14, wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100 C. of from 10 to 25 mm.sup.2/s.

16. A grease formulation according to claim 14, wherein the thickener is present in the grease formulation in an amount of from 10 to 20 wt %.

17. A grease formulation according to claim 1, wherein the metal is selected from the group consisting of lithium, sodium and a combination thereof.

18. A method according to claim 3, wherein the metal is selected from the group consisting of lithium, sodium and a combination thereof.

Description

EXAMPLES

(1) Lithium grease formulations according to the invention were prepared, and their properties tested and compared with those of standard commercially available mineral oil-based greases.

(2) Each of the formulations contained a major proportion of a Fischer-Tropsch derived base oil. The two base oils used, BO-1 and BO-2, had the properties shown in Table 1 below. They had been prepared using Fischer-Tropsch processes analogous to those described above.

(3) TABLE-US-00002 TABLE 1 Test Property method Units BO-1 BO-2 Kinematic ASTM mm.sup.2/s 132 43.88 viscosity at D-445 40 C. Kinematic ASTM mm.sup.2/s 19 7.77 viscosity at D-445 100 C. Viscosity index ASTM 163 148 D-2270 Digital density @ IP kg/m.sup.3 834.1 827.5 15 C. 365/97 NOACK evaporation CEC L- Wt % 2.3 40-A-93 Flash point D-92 ASTM C. 284 274 D-92 Flash point D-93 ASTM C. 247.5 238.5 D-93 Pour point ASTM C. 30 24 D-5950 Colour ASTM L0.5 L1.0 D-1500 Appearance Hazy Clear & pale bright; yellow pale brown

(4) It can be seen that the Fischer-Tropsch derived base oils have high viscosity indices, low pour points (in the case of the heavy base oil BO-1, for instance, about 10 or 20 C. lower than a typical mineral derived Group I base oil), high flash points and low evaporation rates (potentially beneficial for stability under higher temperature operating conditions). Although the heaviest oil BO-1 is slightly cloudy in appearance, due to the presence of a small number of residual wax crystals which are not removed during its production, this is not a problem in grease formulations and is not believed to affect the properties of the final product. Because of this cloudiness, however, the viscosity of BO-1 could not be measured accurately at 40 C.; the value quoted in Table 1 is therefore calculated from values taken at 100 and 70 C.

Example 1

(5) A lithium grease formulation GF-1, containing the base oil BO-1, was prepared using a standard Pretzsch kettle procedure.

(6) 1100 g of the base oil, 330 g of hydrogenated castor oil and 46.2 g lithium hydroxide were placed in a Pretzsch kettle with 50 g of water. This mixture was heated in the sealed kettle, under stirring, to approximately 150 C. The steam was vented off and heating continued to approximately 220 C. The reaction mass was then cooled.

(7) From 200 to 165 C., cooling took place at a rate of 1 C. per minute. At a charge temperature of 163 C., 723.8 g of the base oil was added over 10 minutes. The oil cooler was then switched on. Once the grease had cooled to room temperature it was homogenised, for instance by being passed once through a three-roll mill.

(8) The finished formulation GF-1 was a light beige grease containing 82.9 wt % of the base oil, 15 wt % of hydrogenated castor oil and 2.1 wt % of lithium hydroxide. The overall soap content was close to that predicted to be necessary to produce a grease with penetration around 280, based on polarity and viscosity data for the oil.

(9) GF-1 did not contain any performance enhancing additives.

(10) A number of relevant properties of the grease formulation GF-1 were measured using standard test methods as well as a number of additional test procedures. The same properties were also measured for a commercially available mineral oil-based grease formulation GF-A (ex-Shell). The results are shown in Table 2 below.

(11) TABLE-US-00003 TABLE 2 Test Test Property conditions method GF-1 GF-A Base fluid BO-1 SN500 mineral oil Thickener 15 9 content (wt %) Penetration Undisturbed ASTM 275 273 D-217 60 strokes ASTM 286 279 D-217 Difference 11 6 100,000 ASTM 290 307 strokes D-217 Difference 4 28 Dropping Mettler IP 396 199.3 189 point ( C.) automatic Roll 18 hrs, 65 C. ASTM 313 358 stability D-1831 (difference Difference 27 79 in 50 hrs, 80 C. ASTM 327 penetration) D-1831 Difference 41 100 hrs, 100 C. ASTM 341 409 D-1831 Difference 55 130 Oil 40 C., 18 hrs IP 121 1.3 2.1 separation 40 C., 7 days IP 121 2.47 6 (% m/m) 80 C., 18 hrs IP 121 2.9 80 C., 7 days IP 121 6.84 Water ASTM 3.7 washout, 79 C. D-1264 (% m/m) 4-ball wear Wear, 40 kg, IP 239 0.41 0.42 test (mm) 1 hour Copper 100 C. ASTM 1a 1a corrosion, D-130 24 hr 125 C. ASTM 1a (rating) D-130 150 C. ASTM 1a D-130 Emcor rust Distilled IP 220 0 0 test water (rating) Oxidation 100 hrs ASTM 17.5 17 to 28 stability D-942 (kPa) 400 hrs ASTM 47.5 41 to 52 D-942 Wheel 130 C. for ASTM 1.05 g bearing 6 hrs D-1263 leakage

(12) The yield for GF-1 (i.e. the amount of thickener needed to achieve a certain consistency or penetration value) was significantly lower than for the conventional mineral oil grease, which confirmed predictions based on the lower polarity of the Fischer-Tropsch base oil. Fischer-Tropsch derived oils are known to require up to 75% more thickener than typical mineral-derived Group I base oils.

(13) A higher thickener content is also known to lead to improved mechanical stability and lower oil separation. This is confirmed by the Table 2 data, which show the stability and oil separation of GF-1 to far exceed those of the conventional mineral oil-based grease. Indeed, the oil separation for GF-1 at 80 C. is approximately equivalent to that of a conventional lithium grease at 40 C. These stability and oil separation benefits are reflected in the result of the wheel bearing leakage test at 130 C., the performance of GF-1 being as would normally be expected from a good complex grease. These results are better than expected due to the use of a Fischer-Tropsch derived base oil rather than the mineral base oil on which GF-A is based.

(14) More surprising is the result of the four ball wear test. The performance of the grease formulation of the invention was outstanding, especially considering that it contained no recognised anti-wear additives. GF-1 gave a higher anti-wear effect than that provided by base greases containing lower thickener contents.

(15) GF-1 also gave an excellent result in the Emcor rust test with distilled water. This too is surprising for an unadditivated grease.

(16) Also outstanding, even up to 150 C., were the copper corrosion test results for GF-1.

(17) The results of the oxidation test were also well within normal specifications for standard grease formulations, despite the absence of antioxidants.

(18) Overall, the properties and performance of the grease formulation according to the invention are well within, and in many respects exceed, specifications for typical premium quality greases. Its stability, for example, is more in line with that of a lithium complex grease rather than a typical lithium hydroxide grease. Its performance in the four ball anti-wear test is comparable with that of high quality anti-wear additive-containing greases. This is despite the fact that GF-1 itself contains no additives.

Example 2

(19) A second lithium grease formulation according to the invention, GF-2, was prepared using the base oil BO-2. The preparation method was as described in Example 1.

(20) The finished formulation GF-2 was a light beige, almost white, grease containing 84.9 wt % of the base oil, 13.2 wt % of hydrogenated castor oil and 1.9 wt % of lithium hydroxide.

(21) A number of relevant properties of the grease formulation GF-2 were measured using standard test methods. The same properties were also measured for a commercially available mineral oil-based grease formulation GF-B (ex-Shell). The results are shown in Table 3 below.

(22) Neither GF-2 nor GF-B contained any performance enhancing additives.

(23) TABLE-US-00004 TABLE 3 Test Test Property conditions method GF-1 GF-B Base fluid BO-2 SN150 mineral oil Thickener 13.2 9.0 content (wt %) Penetration Undisturbed ASTM 308 311 D-217 60 strokes ASTM 310 312 D-217 Difference 2 1 4-ball wear Wear, 40 IP 239 0.60 0.88 test (mm) kg, 1 hour

(24) The data in Table 3 confirm that the Fischer-Tropsch base oil BO-2 needs significantly more thickener (in this case 47% more) than does a conventional mineral oil, in order to make a grease with a specific consistency. This demonstrates that the effect is generally applicable to Fischer-Tropsch derived oils and not only to the specific high viscosity grade represented by BO-1.

(25) Furthermore Table 3 confirms that the enhanced thickener content, brought about by the use of the Fischer-Tropsch derived base oil, leads to better anti-wear performance than the equivalent grease made in a conventional mineral base oil.

(26) Thus the present invention can be seen to provide grease formulations with enhanced performance, and/or to make possible the preparation of greases with lower additive levels than might previously have been necessary in order to meet performance specifications. Lower additive levels can in turn reduce the cost and time required for manufacture, as well as the effort required in monitoring additive levels and qualities, for example to comply with legislative requirements, to meet consumer expectations and/or to safeguard users.

Example 3

(27) A lithium complex grease formulation GF-3 was prepared according to the invention, and its properties tested and compared with those of a standard commercially available mineral oil-based grease GF-C.

(28) The formulation GF-3 contained a major proportion of the Fischer-Tropsch derived base oil BO-1 described in Table 1 above. It was prepared using the following method, which was based on a standard Pretzsch kettle procedure.

(29) Slurries of LiOH.H2O, boric acid, salicylic acid and water were added, in the proportions of 1 part solid to 5 parts water, to hydrogenated castor oil fatty acid in cold base oil. The mixture was heated in a sealed autoclave to 170 C. The steam was vented off and heating continued to 220 C. before the reaction mass was cooled and the product homogenised. The finished formulation GF-3 contained 76.2 wt % of the base oil and 12.6 wt % of hydrogenated castor oil; it did not contain any performance enhancing additives and was light beige in appearance.

(30) A number of relevant properties of the grease formulation GF-3 were measured using standard test methods. The same properties were also measured for a commercially available mineral oil-based lithium complex EP (extreme pressure) grease formulation GF-C (ex-Shell). The results are shown in Table 4 below.

(31) TABLE-US-00005 TABLE 4 Test Test Property conditions method GF-3 GF-C Base fluid BO-1 SN500 mineral oil Thickener content 12.6 9 (wt %) Penetration Undisturbed ASTM 278 276 D-217 Penetration 60 strokes ASTM 285 279 D-217 Dropping point ( C.) Mettler IP 396 >300 269 automatic Roll stability 18 hrs, 65 C. ASTM 311 302 (Difference in D-1831 penetration) Difference 26 23 Oil separation 40 C., 7 days IP 121 2.7 2.7 (% m/m) 4-ball weld load ASTM 250 250 (kg) D-2596 Fafnir fretting ASTM 7.2 10.1 test (mg) D-4170 Oxidation stability 100 hrs ASTM 15.0 14.0 (kPa) D-942 400 hrs ASTM 30.0 59.0 D-942 FAG FE-9 bearing 150 C. DIN 120 131 life test (L50 hrs) 51821

(32) Again the yield for GF-3 was significantly lower than for the conventional mineral oil grease, which confirmed predictions based on the lower polarity of the Fischer-Tropsch base oil.

(33) The Table 4 data show that the stability and oil separation of GF-3 are in line with those of the conventional mineral-based grease formulation GF-C.

(34) The dropping point of GF-3 is higher than that of GF-C, which is a consequence of the additive-free nature of GF-3. Many additives are known to reduce or depress the dropping point of a grease, and the absence of any additives removes the risk of this happening.

(35) More surprising is the result of the four ball weld test. The performance of the additive-free grease formulation of the invention (GF-3) was identical to that of GF-C, which contains EP additives for the express purpose of improving the extreme pressure grease properties, including its performance in the four-ball weld test. The performance of GF-3 in the Fafnir fretting test, another indication of EP/wear properties, was also better than that of the additive-containing, mineral oil-based grease GF-C.

(36) Equally surprisingly, the result of the oxidation test for GF-3 was in line with that of the mineral-oil benchmark GF-C after the standard test time of 100 hours, but was significantly better than GF-C after 400 hours. This indicates an inherent resistance to oxidation in GF-3, even with no oxidation inhibiting additives such as are included in GF-C.

(37) The FAG FE-9 bearing life test at 150 C. provides further outstanding evidence of the efficacy of the high thickener content grease-forming properties of the Fischer-Tropsch base oils. The grease of the invention, GF-3, exceeded the 100 hour running time required of a fully-additivated, high performance lithium complex grease, despite its complete freedom from chemical additives of the type discussed above.