Polymer grease manufacturing process

Abstract

A process for the manufacture of a lubricating grease composition, the process comprising steps of: (a) providing an essentially homogeneous liquid composition comprising a lubricating oil and a thickening polymer, and (b) flowing the liquid composition through a shear-mixing device to mix and cool the liquid composition to form a lubricating grease composition.

Claims

1. A process for a manufacture of a lubricating grease composition, the process comprising steps of: providing an essentially homogeneous liquid composition comprising a lubricating oil and a thickening polymer; flowing the essentially homogeneous liquid composition through a shear-mixing device to mix and cool the essentially homogeneous liquid composition to form the lubricating grease composition, wherein the thickening polymer forms from 5 to 20 wt % of the essentially homogeneous liquid composition, wherein the liquid composition flows through the shear-mixing device along a flow-path provided with one or more temperature-controlled portions to each at least one of heat and cool the liquid composition, wherein the shear-mixing device comprises at least one pair of heat-transfer plates between which the liquid composition is flowed, wherein the surface of at least one plate is provided with surface features in a flow path of the liquid composition which act as baffles for the flow of the liquid composition, causing shear-mixing.

2. The process according to claim 1, wherein the essentially homogeneous liquid composition is provided at a temperature of from 150 to 350° C. before flowing the essentially homogeneous liquid composition through the shear-mixing device.

3. The process according to claim 1, wherein the lubricating oil comprises one or more oils selected from mineral oils, synthetic hydrocarbons, ester oils, vegetable oils and mixtures of two or more thereof.

4. The process according to claim 1, wherein the thickening polymer comprises a polymer selected from polyamides, polyesters, polyethylene oxides, polyethylene, polypropylene, polylactides, cellulose or cellulose derivatives, including copolymers thereof, and mixtures of two or more thereof.

5. The process according to claim 1, wherein the shear-mixing device is a shear-mixing conduit.

6. The process according to claim 1, wherein the shear-mixing device is a closed gas-tight system.

7. The process according to claim 1, wherein the liquid composition flows through the shear-mixing device along a flow-path provided with at least one static mixing element.

8. The process according to claim 7, wherein the liquid composition flows through the shear-mixing device along a flow-path provided with a plurality of static mixing elements arranged to provide regions of increased shear mixing.

9. The process according to claim 1, wherein the one or more temperature-controlled portions comprise a first temperature-controlled portion and a second temperature-controlled portion disposed downstream of the first temperature-controlled portion in the flow-path, the second temperature-controlled portion being at a higher temperature than the first temperature-controlled portion.

10. The process according to claim 1, wherein the lubricating grease composition is continuously extruded.

11. The process according to claim 1, wherein the shear-mixing is controlled by altering a flow rate of the liquid composition.

12. The process according to claim 1, wherein at least one additive is added to the liquid composition in the shear-mixing device.

13. The process according to claim 1, wherein the essentially homogeneous liquid composition is provided at a temperature of from 200 to 250° C. before flowing the essentially homogeneous liquid composition through the shear-mixing device.

14. The process according to claim 1, wherein the shear-mixing device is a shear-mixing conduit having a cross-sectional area that varies along the flow-path.

15. A method of manufacturing a lubricating grease composition, comprising: providing an essentially homogeneous liquid composition comprising a lubricating oil and a thickening polymer constituting 5 to 20 wt % of the essentially homogeneous liquid composition; and forcing the essentially homogeneous liquid composition to flow through a shear-mixing device defining a flow path having at least a first temperature-controlled portion and a second temperature-controlled portion such that the essentially homogeneous liquid composition is mixed and cooled in the first and second temperature-controlled portions to form the lubricating grease composition, wherein the second temperature-controlled portion is at a different temperature than the first temperature-controlled portion, the first and second temperature-controlled portions of the shear-mixing device each comprise at least one pair of heat-transfer plates between which the liquid composition flows, a baffle is defined on a surface of at least one of the heat-transfer plates and the baffle is arranged to deflect the flow of the liquid composition along the flow path such that the liquid composition undergoes shear in at least one of the first and second temperature-controlled portions.

16. The process according to claim 15, wherein baffles are defined on both of the heat-transfer plates of the first temperature-controlled portion and on both of the heat-transfer plates of the second temperature-controlled portion.

17. The process according to claim 16, wherein: the baffles on the heat-transfer plates of the second temperature-controlled portion cause more shear to be generated in the liquid composition than the baffles on the heat-transfer plates of the first temperature-controlled portion; and the heat-transfer plates of the first temperature-controlled portion are held at a higher temperature than the heat-transfer plates of the second temperature-controlled portion.

18. The process according to claim 17, wherein: the essentially homogeneous liquid composition is provided at a temperature of from 150 to 350° C. before being supplied to the first-temperature controlled portion.

19. The process according to claim 18, wherein: the essentially homogeneous liquid composition is provided in a reservoir that is fluidly connected to the first and second temperature-controlled portions in a gas-tight manner; and the essentially homogeneous liquid composition is pushed through the first and second temperature-controlled portions by pressurized gas.

20. The process according to claim 19, wherein the lubricating oil comprises a synthetic hydrocarbon/ester mixture and the thickening polymer comprises a propylene polymer or co-polymer having a weight average molecular weight of from 50,000 to 100,000.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described further, by way of example, in relation to the following non-limiting figures, in which:

(2) FIG. 1 shows the microstructure of a grease composition during manufacture;

(3) FIG. 2 shows a schematic of an apparatus for use in the present invention;

(4) FIG. 3 shows a cross-section of the flow-path used in a method of the present invention; and

(5) FIG. 4 shows a cooling and shear profile for the Example of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) As shown in FIG. 1, the formation of a grease can occur in several steps. The four slides, A-D, show the microstructures of the grease during its formation. In slide A, the hot liquid composition (or “solution”) is essentially homogeneous. In slide B, following quenching, there is a liquid-liquid separation. In slide C, there is some solidification as the thickener structure forms. With on-going working of the grease, a more stable structure is formed in slide D.

(7) FIG. 2 shows an example of an apparatus for executing the method of the invention. A reservoir is provided for the hot solution comprising the oil and the thickener as a substantially homogeneous liquid composition. The reservoir has an outlet in fluid communication with a plurality of pairs of cooling/shearing plates. The reservoir is gas-tight and in contact with a source of pressurised gas, by which the solution can be driven through the cooling/shearing plates.

(8) As shown in FIG. 2, the apparatus has three pairs of cooling/shearing plates. These each can be used to hold the liquid composition at a different temperature (see the temperature profile in Example 1 and in FIG. 4). The internal structure between the pairs of plates will determine the flow speed and the amount of shear-mixing that occurs. As shown in FIG. 2, after the sequential treatment between the plates, the grease is continually extruded to fill containers for transport and sale.

(9) As shown in FIG. 3, the flow-path between pairs of parallel plates allows for working of the liquid composition. The internal surface texture of the plates acts as baffles for the flow of the liquid composition, causing shear-mixing.

(10) Means may be provided to heat and/or cool one or more of the sets of plates. Cooling may be achieved by water-cooling. Heating may be achieved by the uses of electrical heating elements. One set of plates may comprise both cooling means and heating means.

(11) FIG. 4 shows a graph over time of the temperature (degrees Celsius) and the shear (Pa) applied in the formation of the grease in Example 1. The liquid composition of the base oil and thickener are held at a high temperature and then cooled step-wise. The shear level is controlled so that is peaks during a second quenching step. As can be seen, the shear changes stepwise as the composition moves from each set of parallel plates, but the rate of temperature change is more finely controlled, with a fast rate of cooling in the first quenching step and a slower rate at the grease is equilibrated.

EXAMPLE 1

(12) The invention will now be described in relation to the following non-limiting example.

(13) A homogeneous mixture was formed comprising a synthetic hydrocarbon/ester mixture as the base oil and the thickening polymer comprising a propylene polymer or co-polymer having a weight average molecular weight of from 50,000 to 100,000. This was passed through a processing unit having the following temperature and shear profile:

(14) TABLE-US-00001 Zone Shear Step temperature intensity Process step 1 190° C. Homogeneous polymer/base oil solution 2 120° C. Low shear 1.sup.st Quenching step: generation of thickener structure, determination of fiber size 3  80° C. High shear 2.sup.nd Quenching step: homogenisation of thickener structure 4  25° C. Low shear Equilibration

(15) The final grease had exemplary performance characteristics and was capable of continuous production.

(16) The process as described herein is capable of improving the controllability of polymer grease synthesis. The process can be exploited to investigate the use of new polymers and/or lubricants. Furthermore, the use of a closed system allows the process to be applied beyond what is possible with current batch-production and laboratory-scale synthesis. Use of polymer types with high melting points means that temperatures for the starting mixture can be higher than temperatures currently used, which tend to be limited to a maximum of about 250° C. This allows for the development of greases with a higher temperature-limit compared to current polymer greases.

(17) Although preferred embodiments of the invention have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the scope of the invention or of the appended claims.