Polymer thickened grease composition and method for making the same

Abstract

A method for preparing a final grease product comprising steps of: (a) mixing a polymeric thickener, which comprises a polymer of propylene, and a lubricating base oil at a temperature above the melting point of the polymeric thickener, wherein the polymeric thickener is present in an amount of 11.5-15.5 wt %, based on the total weight of the mixture so obtained; (b) cooling the mixture as obtained in step (a); (c) subjecting the cooled mixture as obtained in step (b) to a first mechanical treatment, to obtain an intermediate grease; (d) subjecting the intermediate grease as obtained in step (c) to a second mechanical treatment, carried out at a temperature in the range of from 50-90 C., to obtain the final grease product. The method can be applied to manufacturing of a grease.

Claims

1. A manufactured grease obtainable by a method comprising steps of: (a) mixing a polymeric thickener and a lubricating base oil at a temperature above the melting point of the polymeric thickener, wherein the polymeric thickener is present in an amount of 11.5-15.5 wt. %, based on the total weight of the mixture so obtained; (b) cooling the mixture as obtained in step (a) to room temperature in less than 30 seconds; (c) subjecting the cooled mixture as obtained in step (b) to a first mechanical treatment, to obtain an intermediate grease; and (d) subjecting the intermediate grease as obtained in step (c) to a second mechanical treatment, carried out at a temperature in the range of from 50-90 C., to obtain the manufactured grease, wherein the polymeric thickener comprises: a low molecular weight polypropylene having an average molecular weight in the range of 20,000-100,000 Da and a melt flow rate (ASTM D-1238) in the range of 750-1250; and a high molecular weight polypropylene having an average molecular weight in the range of 200,000-350,000 Da and a melt flow rate (ASTM D-1238) in the range of 1.5-7; and wherein the high molecular weight component and the low molecular weight component are present in a weight ratio of between 1:25 and 1:15; and the manufactured grease has a cone penetration depth in the range of 260-29510.sup.1 mm according to ASTM D217.

2. The manufactured grease according to claim 1, which additionally comprises at least one additive component which is selected from the group consisting of antioxidants, corrosion inhibitors, anti-wear agents and pressure tolerance-increasing additives, and wherein the total content of the additive component(s) is in the range between 1 and 8% by weight, based on the total weight of the grease composition.

3. The manufactured grease according to claim 1, wherein the weight ratio between the high molecular weight component and the low molecular weight component is 1:20-1:18.

4. A method, comprising: (a) mixing a polymeric thickener, which comprises at least one polymer of propylene, and a lubricating base oil at a temperature of 150-250 C. to form a mixture, wherein the polymeric thickener is present in an amount of 11.5-15.5 wt. % based on the total weight of the mixture; (b) quenching the mixture obtained in step (a) to room temperature in between 1 second and 3 minutes; (c) subjecting the cooled mixture obtained in step (b) to milling at room temperature, to obtain an intermediate grease; and (d) further mixing the intermediate grease obtained in step (c) in a planetary mixer for 1-20 hours at the temperature in the range of from 50-90 C., to obtain a final grease product having a cone penetration depth in the range of 260-29510.sup.1 mm according to ASTM D217.

5. The method according to claim 4, wherein the polymeric thickener comprises: a low molecular weight polypropylene having an average molecular weight in the range of 20,000-100,000 Da and a melt flow rate (ASTM D-1238) in the range of 750-1250; and a high molecular weight polypropylene having an average molecular weight in the range of 200,000-350,000 Da and a melt flow rate (ASTM D-1238) in the range of 1.5-7; and wherein the high molecular weight component and the low molecular weight component are present in a weight ratio of between 1:25 and 1:15.

6. The method according to claim 4, wherein the polymeric thickener is present in an amount of 12-15 wt. %, based on the total weight of the mixture so obtained.

7. The method according to claim 4, wherein the polymeric thickener is present in an amount of 12.5-13.5 wt. %, based on the total weight of the mixture so obtained.

8. The method according to claim 4, wherein the temperature in step (d) is in the range of from 70-90 C.

9. The method according to claim 4, wherein the at least one polymer of propylene of the polymeric thickener comprises a first component which comprises a first polymer of propylene and a second component which comprises a second polymer of propylene, the first component having a higher weight average molecular weight than the second component.

10. The method according to claim 9, wherein the first component is a (co- or homo-)polymer of propylene having a weight average molecular weight of more than 200,000 and the second component is a (co- or homo-)polymer of propylene having a weight average molecular weight of less than 200,000.

11. The method according to claim 10, wherein the weight ratio between the first component and the second component is 1:40-1:5.

12. The method according to claim 10, wherein the second component is a polypropylene homopolymer.

13. The method according to claim 10, wherein the second component has an average molecular weight between 20,000 and 100,000 and a melt flow rate (ASTM D-1238) of 500-1500.

14. The method according to claim 10, wherein the first component is one of a polypropylene homopolymer or a propylene/ethylene-copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention provides a method for preparing polymer thickened grease products. The method for preparing a final grease product comprises the following steps: (a) mixing a polymeric thickener, comprising a polymer of propylene, and a lubricating base oil at a temperature above the melting point of the polymeric thickener, wherein the polymeric thickener is present in an amount of 11.5-15.5 wt %, based on the total weight of the mixture so obtained; (b) cooling the mixture as obtained in step (a); (c) subjecting the cooled mixture as obtained in step (b) to a first mechanical treatment, to obtain an intermediate grease; (d) subjecting the intermediate grease composition as obtained in step (c) to a second mechanical treatment, carried out at a temperature in the range of from 50-90 C., to obtain the final grease product.

(2) In a preferred embodiment of the present method, the polymeric thickener is present in step (a) in an amount of 12-15 wt %, based on the total weight of the mixture so obtained, and step (a) is carried out at a temperature of 150-250 C.; the cooling in step (b) is carried out in less than 30 sec; and the mechanical treatment in step (d) is carried out at a temperature in the range of from 70-90 C.

(3) In a more preferred embodiment of the present invention, the polymeric thickener is present in step (a) in an amount of 12.5-14.5 wt %, based on the total weight of the mixture so obtained, and step (a) is carried out at a temperature of 190-210 C.; the cooling in step (b) is carried out between 10 and 25 seconds; and the mechanical treatment in step (d) is carried out at a temperature in the range of from 70-90 C.

(4) It will be understood that the properties of the final grease product are of course also dependent on the properties of the lubricating oil and additives used, as is well known to a man skilled in the art.

(5) The polymeric thickener to be used in accordance with the present invention comprises a polymer of propylene. Suitably, the polymeric thickener comprises a first component which comprises a polymer of propylene and a second component which comprises a polymer of propylene, with the first component having a higher weight average molecular weight than the second component.

(6) Preferably, the polymeric thickener comprises a high molecular weight component and a low molecular weight component, characterized in that the thickener comprises a mixture of (1) a (co- or homo-)polymer of propylene with a weight average molecular weight of more than 200.000 (Da) and (2) a (co- or homo-)polymer of propylene with a weight average molecular weight of less than 200.000 (Da).

(7) Preferably, the weight ratio between the high molecular weight component and the low molecular weight component is 1:40-1:5, preferably 1:25-1:15, more preferably 1:18-1:20.

(8) In accordance with the present invention the low molecular weight component is preferably a polypropylene homopolymer. Preferably, the low molecular weight component has an average molecular weight in the range of from 20.000 and 100.000 (Da) and a melt flow rate (ASTM D-1238) in the range of from 500-1500, preferably 750-1250.

(9) Suitably, the high molecular weight component is a polypropylene homopolymer or a propylene/ethylene-copolymer. Preferably, the high molecular weight component has an average molecular weight in the range of from 200.000-350.000 (Da) and a melt flow rate (ASTM D-1238) in the range of from 1.5-15, preferably 1.5-7.

(10) Preferably, the polymeric thickener to be used in accordance with the invention comprises a mixture of (1) a (co- or homo-)polymer of propylene with an average molecular weight of more than 200.000 (Da) and (2) a (co- or homo-) polymer of propylene with an average molecular weight of less than 100.000 (Da).

(11) The polymeric thickener according to the present invention may contain a high molecular weight component comprising a (co- or homo-)polymer of propylene with a weight average molecular weight of more than 200.000 (Da), preferably in the range of from 200.000-500.000 (Da) and a low molecular weight component comprising a (co- or homo-) polymer of propylene with a weight average molecular weight of less than 100.000 (Da), preferably in the range of from 50.000-100.000 (Da).

(12) The weight ratio between the high molecular weight component and the low molecular weight component in the polymeric thickener is preferably in the range of from 1:40-1:5, more preferably in the range of from 1:25-1:15, and most preferably in the range of from 1:20-1:18.

(13) Outside this preferred range for the weight ratio between the high and low molecular weight components the final lubricating grease composition may not have the desired application properties, in particular mechanical stability and consistency, i.e. be too rubbery/elastic and/or too buttery. However, as the properties of the final composition are also dependent on the lubricant base oil and additives incorporated in grease compositions, as well as on the way the composition is prepared, other ratios may also be used for obtaining the desired properties of the final composition, as is well known to a man skilled in the art.

(14) The low molecular weight component of the polymeric thickener is preferably a polypropylene homopolymer, more preferably a polypropylene homopolymer with a melt flow rate of 500-1000 dg/min., especially 750-850 dg/min. as determined by test ASTM D 1238 L.

(15) The high molecular weight component of the polymeric thickener preferably has a melt flow rate (ASTM D-1238) of 1.5-15, more preferably 1.5-7, especially about 3.5.

(16) As the lubricating base oil any lubricating oil known per se may be used, such as mineral oils, synthetic hydrocarbons, ester oils, vegetable (biodegradable) oils and mixtures thereof, of different viscosity. The type of base oil and viscosity can be selected to suit specific applications.

(17) The mechanical stability of the polymer-thickened grease is dependent on the content of the polymer thickener and is further influenced by the thickener used, the lubricating base oil used, as well as the additives used.

(18) The mechanical stability of the grease can be ascertained by means of tests known in the art, such as the Shell roll stability test according to ASTM D1831. Preferably, the final grease product will have a drop in penetration after the Shell roll stability test (24 hrs at 82 C., 165 rpm), of maximum 50 preferably less than 40, when consistency is measured in 10.sup.1 mm via the cone penetration test of ASTM D217.

(19) The consistency of greases can be further classified by means of the NLGI-class. According to the present invention, the grease can be prepared to a NLGI-class range of 2-3 or a consistency in the range of from 220-300, preferably in the range of from 260-295, (in 10.sup.1 mm).

(20) Apart from the polymeric thickener according to the invention, the lubricant grease composition may also contain conventional thickeners for lubricant grease compositions, such as metal soaps, in amounts of less than 75 wt. %, preferably less than 25 wt. %, as well as other polymeric thickeners.

(21) Preferably, the lubricant grease compositions according to the invention contain only polymeric thickeners, most preferably the polymeric thickener mixture as described hereinabove.

(22) The polymer thickened grease according to the present invention can be used for all conventional applications for lubricant grease compositions, so long as these are compatible with the components of the lubricant grease composition.

(23) The greases prepared in accordance with the invention are especially suited for low temperature applications, for instance windmills. Also, on account of the long(er) relubrication intervals compared to conventional greases, the compositions according to the invention can advantageously be used in applications for which frequent relubrication is unpractical or undesired.

(24) Further uses of the lubricant greases according to the present invention are e.g. agricultural machinery, bearings in dam-gates, low noise electric motors, large size electric motors, fans for cooling units, machine tool spindles, screw conveyors.

(25) The present invention further relates to a lubricating grease obtainable by the method according to the present invention. The polymeric thickener is present in an amount of 11.5-15.5 wt %, based on the total weight of the mixture so obtained, and the lubricating grease has a consistency in the range of from 220-300 (in 10.sup.1 mm). The polymeric thickener is preferably present in an amount of 12-14.5 wt %, more preferably 12.5-14.5 wt %, and most preferably 12.5-13.5 wt %, based on the total weight of the mixture so obtained.

(26) Further, the lubricating grease suitably has a softness which corresponds to at least 80%, preferably at least 90% of the maximum softness of the grease composition.

(27) The lubricating grease of the invention may additionally comprise at least one additive component which is selected from the group consisting of antioxidants, corrosion inhibitors, anti-wear agents and pressure tolerance-increasing additives, and wherein the total content of the additive component(s) is in the range between 0.1 and 15% by weight, and preferably between 1 and 8% by weight, based on the total weight of the grease composition.

(28) The invention will now be further illustrated by the following Examples, which do not limit the invention in any way.

Examples

(29) Two grease compositions A and B were prepared by mixing particular amounts of a high molecular weight polypropylene (average mw. 230,000), a low molecular weight polypropylene (average mw. 82,000), and a base-oil (Poly-Alpha Olefin (PAO) having viscosity 68 mm.sup.2/s), and heating the mixture under nitrogen to 195 C. until complete dissolution of polypropylenes has taken place. The weight ratio of the low molecular weight polypropylene and high molecular propylene was in each case 19/1. The grease compositions so obtained were then rapidly cooled to room temperature in 30 seconds by pouring the mixture onto a metal plate.

(30) Grease composition A comprises the following constituents: 13 wt % polypropylene in PAO200 (polyalphaolefin base oil), with no additives. Grease composition B comprises the following constituents: 13 wt % polypropylene in base oil of mineral oil 68, with the following additives: 0.5 wt % anti-oxidant; 2.5 wt % anti-corrosion and 2.5 wt % anti-wear additives.

(31) The grease compositions A and B were then homogenized in a planetary mixer at ambient temperature, to obtain intermediate grease samples A.sub.S1 and B.sub.S1. The samples A.sub.S1 and B.sub.S1 are representative of conventional polymer-thickened greases prepared in a conventional manner. Further samples A.sub.S2 and B.sub.S2 were then prepared according to the method of the invention, by mechanically shearing the intermediate greases for approximately 3 hours at a temperature of 80 C. in a planetary mixer.

(32) The initial consistency of the grease samples A.sub.S1, B.sub.S1, A.sub.S2, B.sub.S2 was measured via the cone penetration test in accordance with ASTM D217. Each sample was then subjected to a mechanical stability test in which the grease samples were mechanically sheared at a temperature of 80 C. for several hours. The consistency of each sample was measured after 24 hours of the mechanical stability test and again after 50 hours. The results are shown in table 1.

(33) TABLE-US-00001 TABLE 1 Penetration (10.sup.1 Initial mm) after Penetration(10.sup.1 mm) Grease penetration mechanical stability after mechanical Samples (10.sup.1 mm) test 24 h/80 C. stability test 50 h/80 C. A.sub.S1 231 290 285 B.sub.S1 229 294 277 A.sub.S2 271 289 297 B.sub.S2 265 299 305

(34) The grease compositions A and B are designed for rolling bearing applications in which the desired consistency of the grease is between 260 and 29510.sup.1 mm.

(35) The intermediate grease samples A.sub.S1 and B.sub.S1 have a stiffness of around 23010.sup.1 mm, which is too high for the intended bearing application. The relatively stiff grease would generate a high amount of friction. Furthermore, the intermediate greases become considerably softer when subjected to the mechanical stability test. Penetration increases by more than 5010.sup.1 mm, which is considered by bearing manufacturers as an unacceptable level of mechanical stability.

(36) By contrast, the grease samples A.sub.S2 and B.sub.S2 prepared according to the method of the invention have an initial consistency which is desirable for the intended bearing application. Furthermore, the samples A.sub.S2 and B.sub.S2 display an acceptable level of mechanical stability, with an increase in penetration of max. 4010.sup.1 mm. The inventive sample of composition A displays an increase of only 2610.sup.1 mm.

(37) The mechanical stability of grease products prepared using the method steps of the invention depends on the polymer content. The effect of polymer content on mechanical stability was investigated by preparing five grease products as follows.

(38) Five grease compositions G1, G2, G3, G4 and G5 were prepared by mixing particular amounts of a high molecular weight polypropylene (average mw. 230,000), a low molecular weight polypropylene (average mw. 82,000), and a base-oil (Poly-Alpha Olefin (PAO) having viscosity 68 mm.sup.2/s), and heating the mixture under nitrogen to 195 C. until complete dissolution of polypropylenes has taken place. The weight ratio of the low molecular weight polypropylene and high molecular propylene was in each case 19/1. The five grease compositions had a total polypropylene content of 9 wt % (G1), 11 wt % (G2), 13 wt % (G3), 15 wt % (G4) and 17 wt % (G5) respectively. The grease compositions so obtained were then rapidly cooled to room temperature in 30 seconds by pouring the mixture onto a metal plate.

(39) A reference sample of each grease composition G1.sub.ref, G2.sub.ref, G3.sub.ref, G4.sub.ref, G5.sub.ref was then prepared by carrying out steps (c) and (d) of the inventive method. Specifically, the grease compositions were sheared in a three-roll mill at ambient temperature and then subjected to mechanical shearing in a planetary mixer at a temperature of 80 C. for 1-6 hours until a desired consistency, suitable for bearing applications, was obtained. The duration of the thermo-mechanical treatment depends on the polypropylene content of the grease composition. A consistency of around NLGI class 2-3 (corresponding to a cone penetration depth of approx. 225-29510.sup.1 mm) is desirable for bearing applications. NB it is to be noted that for the grease composition with 17 wt % polypropylene content, a reference sample of desired consistency could not be produced.

(40) The consistency of each reference sample was measured using the cone penetration method as defined in ASTM D217. Next, each reference sample was subjected to further mechanical shearing at a temperature of 80 C. The consistency of each reference sample was measured again after 24 hours of this treatment and then after 50 hours. The results are shown in the bar chart of FIG. 1, whereby for each reference sample, the left-hand bar shows the initial measured consistency of the reference sample, the middle bar shows the measured consistency after 24 hours of shearing at 80 C. and the right-hand bar shows the measured consistency after 50 hours of shearing at 80 C.

(41) Looking at the 9% composition, it can be seen that mechanical shearing of the reference sample G1.sub.ref at a temperature of 80 C. leads to considerable softening (a drop of around 7010.sup.1 mm occurs). In other words, the 9% composition exhibits unacceptable mechanical stability. The reference sample of the 11% composition G2.sub.ref displays better mechanical stability, although still exhibits significant softening.

(42) Looking now at the reference sample of the 13% composition G3.sub.ref, it can be seen that very little softening occurs after 24 hours and then after 50 hours, while for the 15% composition, the consistency of the reference sample G4.sub.ref remains essentially constant under the aforementioned thermo-mechanical treatment. The consistency of the 17% composition also remains quite constant, and even becomes somewhat stiffer, which is undesirable.

(43) Thus, a grease product prepared according to the method of the invention has a polymer content of greater than 11 wt % and less than 15.5 wt %, such that a mechanically stable grease of desired consistency is obtained.