Grease compositions and method for making the same

Abstract

A grease composition contains a mixture of a lubricating base oil, an ester-terminated polyamide and at least one polyolefin. The ester-terminated polyamide has the formula:
R1-O—CO—R2-CO—[NH—R3-NH—CO—R2-CO]n-O—R1.
R1 contains 4-22 carbon atoms, R2 contains 4-42 carbon atoms, R3 contains 2-9 carbon atoms and n is an integer in the range of 1-20. The grease composition can be used for lubricating a mechanical component having a metal surface and/or for protecting a mechanical component having a metal surface against corrosion, wear and/or fretting.

Claims

1. A grease composition comprising a mixture of: a lubricating base oil, an ester-terminated polyamide, and at least one polyolefin thickener, wherein: the ester-terminated polyamide has the formula: R1-O-CO-R2-CO-[NH-R3-NH-CO-R2-CO].sub.n-O-R1, wherein: each R1 is independently a linear or branched, saturated or unsaturated, substituted or unsubstituted hydrocarbon group containing 4-22 carbon atoms, each R2 is independently a linear or branched, saturated or unsaturated, substituted or unsubstituted hydrocarbon group containing 4-42 carbon atoms, each R3 is independently a linear or branched, saturated or unsaturated, substituted or unsubstituted hydrocarbon group containing 2-9 carbon atoms, n is an integer in the range of 1-20.

2. The grease composition according to claim 1 comprising: (a) 75 to 90 wt.% of the lubricating base oil; (b) 1 to 19 wt.% of the ester-terminated polyamide; and (c) 1 to 19 wt.% of the at least one polyolefin thickener, all weights being based on the total weight of the grease composition.

3. The grease composition according to claim 1 comprising: (a) 76-84 wt.% of the lubricating base oil; (b) 11-15 wt.% of the ester-terminated polyamide; and (c) 5-9 wt.% of the at least one polyolefin thickener, wherein all weights are based on the total weight of the grease composition.

4. The grease composition according to claim 1, wherein n is 2-14.

5. The grease composition according to claim 1, wherein the at least one polyolefin thickener comprises one of: polyethylene, polypropylene, polyisoprene or polybutadiene.

6. The grease composition according to claim 1, wherein the at least one polyolefin thickener comprises a mixture of: a (co- or homo-) polymer of polyolefin having a weight average molecular weight of more than 200,000; and a (co- or homo-) polymer of polyolefin having a weight average molecular weight of less than 100,000.

7. The grease composition according to claim 6, wherein the (co- or homo-) polymer of propylene having a weight average molecular weight of less than 100,000 is a polypropylene homopolymer.

8. The grease composition according to claim 6, wherein the (co- or homo-) polymer of propylene having a weight average molecular weight of more than 200,000 is one of: a polypropylene homopolymer or a propylene/ethylene-copolymer.

9. The grease composition according to claim 6, comprising: (a) 76 -84 wt.% of the lubricating base oil; (b) 11-15 wt.% of the ester-terminated polyamide; and (c) 5-9 wt.% of the mixture of the polyolefins, wherein all weights are based on the total weight of the grease composition.

10. The grease composition according to claim 9, wherein n is 2-14.

11. The grease composition according to claim 10, wherein: the (co- or homo-) polymer of propylene having a weight average molecular weight of less than 100,000 is a polypropylene homopolymer; and the (co- or homo-) polymer of propylene having a weight average molecular weight of more than 200,000 is a propylene/ethylene-copolymer.

12. The grease composition according to claim 11, wherein: the polypropylene homopolymer has a weight average molecular weight of 50,000-100,000; and the propylene/ethylene-copolymer has a weight average molecular weight of 200,000-350,000.

13. The grease composition according to claim 12, wherein the polypropylene homopolymer and the propylene/ethylene-copolymer are present in a weight ratio in the range of 1:25-1:15.

14. The grease composition according to claim 13, wherein the propylene/ethylene-copolymer has a melt flow rate of 1.5-7 as measured according to ASTM D-1238.

15. The grease composition according to claim 14, wherein: the -NH-R3-NH- group is derived from one of an ethylene diamine or a hexamethylene diamine; the -CO-R2-CO- group is derived from a mixture of a dimer acid composed of two molecules of unsaturated fatty acids and a diacid selected from the group consisting of an adipic acid, an azelaic acid or a sebacic acid; and R1 is derived from one of stearyl alcohol or oleyl alcohol.

16. The grease composition according to claim 15, wherein: at least 50% of the R2 groups have 30-42 carbon atoms; and less than 30% of the R2 groups have 4-12 carbon atoms.

17. The grease composition according to claim 16, wherein: R1 is an unsubstituted, saturated, linear hydrocarbon having 18 carbons, R3 is an unsubstituted, saturated, linear hydrocarbon having 2 carbons, less than 30% of the R2 groups are an unsubstituted, saturated, linear hydrocarbon having 7 carbons.

18. A method for manufacturing the grease composition according to claim 1, comprising: mixing the ester-terminated polyamide, the at least one polyolefin thickener and the lubricating base oil in any order and holding the mixture at a temperature above the melting point of the ester-terminated polyamide, and cooling the resulting mixture to 0-120° C. in less than 3 minutes.

19. The method according to claim 18, wherein the mixture is held at a temperature of 190-210° C. and then the resulting mixture is cooled to a temperature of 15-35° C. within 5-15 seconds.

20. The method according to claim 19, wherein, prior to the mixing step, the ester-terminated polyamide is prepared by mixing a dimer acid, a diacid, a diamine and a monoalcohol and allowing them to react.

Description

EXAMPLES

Example 1 (According to the Invention)

(1) An ester-terminated polyamide was prepared by reacting 61 gram of a dimer and 7.4 gram of azealic acid with 5.9 gram of ethylene diamine. The acids were mixed under heating at a temperature of 95° C. until the mixture was homogeneous. Ethylene diamine was added slowly to the mixture dropwise with constant stirring under dry nitrogen supply. 25.7 gram of stearyl alcohol was added to the reaction vessel. After the completion of monoalcohol addition, the temperature of reaction mixture was raised to 180° C. and maintained for 3 hours. The temperature of the reaction mixture was raised to 205° C. and kept under constant dry nitrogen supply and constant stirring for 30 minutes. The mixture was discharged onto a metal plate and cooled to room temperature. In a reaction vessel, 13 gram of the ester-terminated oligomer polyamide was heated to its melting point of around 160° C. in the presence of dry nitrogen and under continuous stirring. 80 gram of a lubricating ester base oil Priolube 1426 (available from Croda) was added slowly and the temperature was not allowed to cool down to below 145° C. The temperature was raised to 160° C., after which 6.65 gram of a low molecular weight homo-polymer of polypropylene was added, and 0.35 gram of a high molecular weight co-polymer of a polypropylene were added. The low molecular weight homo-polymer of polypropylene was Borflow HL508 FB, obtained from Borealis. The high molecular weight co-polymer of polypropylene was Moplen EP300K, a poly(ethylene-co-propylene) block co-polymer, obtained from Lyondell Basell. The temperature of the mixture was then raised to 180° C. and kept under dry nitrogen and continuous stirring for 60 minutes. The temperature was then further raised to 205° C. and kept under dry nitrogen, whilst the mixture was continuously stirred for 30 minutes. The mixture so obtained was then cooled to room temperature within 10 seconds by means of quenching, executed by discharging the mixture in a thin layer onto a solid metal plate at room temperature. The properties of the grease obtained are listed in Table 1.

Example 2 (According to the Invention)

(2) In accordance with the procedure described in Example 1, a grease composition was prepared wherein the lubricating base oil was a mineral base oil (Cirkan C68, available from Total Lubricants). The properties of the grease obtained are listed in Table 1.

(3) Solubility in Oil: Completely Soluble (Visual Appearance)

Example 3

(4) In accordance with the procedure in Example 2, a homogeneous, heated mixture of ester-terminated polyamide and lubricating mineral oil was prepared, and kept under stirring and nitrogen at 205° C. In the final step, the mixture was removed from the heating source and allowed to cool to room temperature without any quenching and any time limit, in more than 30 minutes.

(5) A grease structure was not formed. At the early stage there was little formation of gel structure and at later stage gel was separated into oil and oligomer. This example shows that cooling by quenching during the preparation of a grease composition in step (b) of the method of the present invention is of essential importance.

Example 4

(6) In a reaction vessel, 20 gram of the ester-terminated polyamide used in Example 1 was heated to its melting point of around 160° C. in the presence of dry nitrogen and under continuous stirring. 80 gram of lubricating ester base oil Priolube 1851 (available from Croda) was added slowly and the temperature was not allowed to cool down to below 145° C. The temperature of the reaction mixture was then raised to 180° C. and kept under dry nitrogen and continuous stirring for 60 minutes. The temperature was then further raised to 205° C. and kept under dry nitrogen, whilst the mixture was continuously stirred for 30 minutes. The mixture so obtained was then cooled to room temperature within 10 seconds by means of quenching, executed by discharging the mixture in a thin layer onto a solid metal plate at room temperature. The properties of the grease obtained are listed in Table 1.

(7) Solubility in Oil: Completely Soluble (Visual Appearance)

Example 5

(8) In a reaction vessel, 435 gram of a lubricating mineral oil (Cirkan C68 from Total Lubricants) was mixed with 61.75 gram of the low molecular weight homo-polymer of polypropylene as used in Example 1, and 3.25 gram of the high molecular weight co-polymer of propylene as used in Example 1. The temperature of the mixture was then raised to 180° C. and kept under dry nitrogen and continuous stirring for 60 minutes. The temperature was then further raised to 205° C. and kept under dry nitrogen, whilst the mixture was continuously stirred for 30 minutes. The mixture so obtained was then cooled to room temperature within 10 seconds by means of quenching, executed by discharging the mixture in a thin layer onto a solid metal plate at room temperature. The properties of the grease obtained are listed in Table 1.

(9) TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Oligomer content 13 13 13 20 0 (wt. %) Polymer content 7 7 7 0 13 (wt. %) Lubricating base Ester Mineral Mineral Mineral Mineral oil type Base oil viscosity 65 68 (cSt at 40° C.) Cooling method Quenching Quenching Slow Quenching Quenching cooling Physical Clear Clear Turbid Clear Opaque appearance Semi-solid Semi-solid Semi-liquid Semi-solid Semi-solid homogeneous homogeneous Separated Homogeneous Homogeneous Penetration 207 215 N.A. 283 270 (mm/10) Consistency 3-4 3-4 N.A. 2 2 (NLGI grade) Oil separation 1.6 1.1 N.A. 11.5 7.5 (%) Dropping point 179 145 N.A. 128 145 (° C.)

(10) Examples 1 and 2 represent greases in accordance with the present invention, wherein the thickener comprises an ester-terminated oligomer and a polymer (polypropylene in the given examples). Example 4 represents a grease wherein the thickener comprises only an ester-terminated oligomer; Example 5 is a polypropylene-thickened grease containing no ester-terminated oligomer. Example 3 failed to produce a grease structure, due to the slow cooling rate during preparation, and tests could not be performed.

(11) The remaining examples were subjected to an oil separation test according to DIN 51817, to determine oil bleeding. Consistency was measured using a standard cone penetration method (DIN 51804) and the dropping point of the grease was measured according to DIN 51801.

(12) The results of the oil separation test are particularly interesting. The polypropylene-thickened grease of Example 5 has better oil-bleeding characteristics than the oligomer-thickened grease of Example 4, and it might have been expected that a grease having a “hybrid” thickener comprising both components would exhibit an oil bleeding rate of between 7.5% and 11.5%. Surprisingly, the greases of Examples 1 and 2 exhibit considerably lower oil bleeding, having lost only 1.6% and 1.1% by weight of oil after conclusion of the test. The advantageous oil bleeding characteristics of the “hybrid” greases according to the invention are thus clear.