A METHOD FOR CONTINUOUSLY MANUFACTURING UHMWPE PRODUCTS

Abstract

The present invention relates to a method for continuously manufacturing UHMWPE products comprising:—providing a counter-rotating twin-screw extruder;—feeding UHMWPE powder into a hopper of said counter-rotating twin-screw extruder;—transporting said UHMWPE powder from said hopper through said counter-rotating twin-screw extruder to an outlet of said counter-rotating twin-screw extruder;—further transporting said UHMWPE powder from said outlet of said counter-rotating twin-screw extruder to an entrance of a heat-controlled tooling system for defining the shape of UHMWPE products;—withdrawing said UHMWPE products from an outlet of said heat-controlled tooling system.

Claims

1. A method for continuously manufacturing UHMWPE products comprising: providing a counter-rotating twin-screw extruder; feeding UHMWPE powder into a hopper of said counter-rotating twin-screw extruder; transporting said UHMWPE powder from said hopper through said counter-rotating twin-screw extruder to an outlet of said counter-rotating twin-screw extruder; further transporting said UHMWPE powder from said outlet of said counter-rotating twin-screw extruder to an entrance of a heat-controlled tooling system for defining the shape of UHMWPE products; withdrawing said UHMWPE products from an outlet of said heat-controlled tooling system.

2. The method according to claim 1, wherein the temperature management of said counter-rotating twin-screw extruder during the transportation of said UHMWPE powder through said counter-rotating twin-screw extruder is such that said UHMWPE powder is in a transition-temperature region between solid and melt; wherein the temperature of the UHMWPE powder at the outlet of said counter-rotating twin-screw extruder is optionally<=T.sub.m.

3. (canceled)

4. The method according to claim 1, wherein the temperature at the outlet of the counter-rotating twin-screw extruder is lower than the temperature at the entrance of the heat-controlled tooling system.

5. The method according to claim 1, wherein the temperature management of said heat-controlled tooling system is such that said UHMWPE is>T.sub.m.

6. The method according to claim 5, wherein the temperature of UHMWPE is in a range of 150 degrees centigrade and 180 degrees centigrade.

7. The method according to any claim 1, wherein said UHMWPE powder further comprises one or more additives chosen from the group of lubricants, pigments, antioxidants, process stabilizers, or a combination thereof; wherein the total amount of additives is optionally 0.1 to 2.5 wt. %, based on the total weight of the UHMWPE powder.

8. (canceled)

9. The method according to claim 1, wherein said entrance of said heat-controlled tooling system comprises increasing conical or trapezoid lands.

10. The method according to claim 1, wherein said heat-controlled tooling system comprises different temperature zones along the length of said heat-controlled tooling system.

11. The method according to claim 1, wherein said step of withdrawing said UHMWPE products from said heat-controlled tooling system further comprises a synchronized haul-off; wherein said haul-off is optionally chosen from the group of motor driven caterpillar, belt, traction or roller type, or a combination thereof.

12. (canceled)

13. The method according to claim 1, wherein the shape of said UHMWPE products is chosen from the group of profiles, rods, sheets and panels.

14. A profile, rod, sheet or panel made of UHMWPE, wherein the outer surface of said profile, rod, sheet or panel is free of shot marks, wherein the total amount of additives is 0.1 to 2.5 wt. %, based on the total weight of the product.

15. The profile, rod, sheet or panel made of UHMWPE according to claim 14, wherein throughout the bulk of the UHMWPE material no shot marks are present.

16. The profile, rod, sheet or panel made of UHMWPE according to claim 14, wherein said rod, sheet or panel did not undergo additional processing for removing any shot marks.

17. The profile, rod, sheet or panel made of UHMWPE according to a method according to claim 14, wherein the outer surface of said profile, rod, sheet or panel is free of shot marks.

18. The profile, rod, sheet or panel made of UHMWPE according to claim 17, wherein throughout the bulk of the UHMWPE material no shot marks are present; and/or wherein said rod, sheet or panel did not undergo additional processing for removing any shot marks.

19. (canceled)

20. An apparatus for continuously manufacturing UHMWPE products comprising a counter-rotating twin-screw extruder, said counter-rotating twin-screw extruder being provided with a hopper for feeding UHMWPE powder into said extruder and an outlet for discharging processed UHMWPE, a heat-controlled tooling system for defining the shape of UHMWPE products, said heat-controlled tooling system being provided with an entrance for processed UHMWPE and an outlet for shaped UHMWPE products, wherein said outlet of said counter-rotating twin-screw extruder is in communication with said entrance of said heat-controlled tooling system.

21. The apparatus according to claim 20, wherein said outlet of heat-controlled tooling system is in communication with a haul-off system for withdrawing UHMWPE product from said outlet.

22. The apparatus according to claim 21, wherein said haul-off system for withdrawing UHMWPE product from said outlet is chosen from the group of motor driven caterpillar, belt, traction or roller type, or a combination thereof.

23. The apparatus according to claim 20, wherein said entrance of said heat-controlled tooling system comprises increasing conical or trapezoid lands.

24. The apparatus according to claim 20, wherein said heat-controlled tooling system comprises different temperature zones along the length of said heat-controlled tooling system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] FIG. 1 illustrates schematically in a side view the present method for continuously manufacturing UHMWPE products with the downstream haul-off.

[0057] FIG. 2 illustrates schematically a top view of sheet extrusion.

[0058] FIG. 3 illustrates schematically in a side view the present method for continuously manufacturing UHMWPE profiles.

[0059] FIG. 4 illustrates schematically cross-sections of typical profiles types.

[0060] FIG. 1 illustrates schematically in a side view the apparatus 10 for continuously manufacturing UHMWPE products with a downstream haul-off. Counter-rotating twin-screw extruder 2 is provided with a hopper 1 for feeding UHMWPE powder (not shown) into hopper 1 of counter-rotating twin-screw extruder 2. Rotating twin screws 3 transport UHMWPE powder from hopper 1 through counter-rotating twin-screw extruder 2 to outlet 6 of counter-rotating twin-screw extruder 2. UHMWPE powder is further transported from outlet 6 of counter-rotating twin-screw extruder 2 to entrance 4 of a heat-controlled tooling system 5 for defining the shape of UHMWPE products. The UHMWPE products 7 are withdrawn from outlet 12 of heat-controlled tooling system 5 via a downstream haul-off system 8, 9, comprising rollers 8 and a driven belt 9.

[0061] FIG. 2 illustrates schematically a top view of an apparatus 20 for sheet extrusion. Counter-rotating twin-screw extruder 2 is provided with a hopper 1 for feeding UHMWPE powder (not shown) into hopper 1 of counter-rotating twin-screw extruder 2. Rotating twin screws 3 transport UHMWPE powder from hopper 1 through counter-rotating twin-screw extruder 2 to outlet 6 of counter-rotating twin-screw extruder 2. UHMWPE powder is further transported from outlet 6 of counter-rotating twin-screw extruder 2 to entrance 4 of a heat-controlled tooling system 5 for defining the shape of UHMWPE products. Heat-controlled tooling system 5 comprises increasing conical lands 9. The UHMWPE products 7 are withdrawn from heat-controlled tooling system 5 via a downstream haul-off system (not shown here).

[0062] FIG. 3 illustrates schematically in a side view the apparatus 30 for continuously manufacturing UHMWPE profiles with a downstream haul-off. Counter-rotating twin-screw extruder 2 is provided with a hopper 1 for feeding UHMWPE powder (not shown) into hopper 1 of counter-rotating twin-screw extruder 2. Rotating twin screws 3 transport UHMWPE powder from hopper 1 through counter-rotating twin-screw extruder 2 to outlet 6 of counter-rotating twin-screw extruder 2. UHMWPE powder is further transported from outlet 6 of counter-rotating twin-screw extruder 2 to entrance 4 of a heat-controlled tooling system 5 for defining the shape of UHMWPE products. The UHMWPE profiles 11 are withdrawn from outlet 12 of heat-controlled tooling system 5 via a downstream haul-off system (not shown here).

[0063] FIG. 4 illustrates schematically examples of cross-sections of typical profiles types that can be made with the present method for continuously manufacturing UHMWPE products. In practice, some of the dimensions would require re-defining.

EXAMPLE 1

[0064] A conical counter-rotating twin screw extruder (manufacturer Battenfeld, Cincinnati (USA)) is continuously fed via a hopper with a mix of 99.5% UHMWPE 4120 from Celanese, 0.15% Irganox B225 from BASF, 0.35% Ligastar, Peter Greven Gmbh. The extruder is run at 7 rpm having a temperature profile from the entrance throat to the exit of 80° C., 110 ° C., 125° C., 143° C. Extrusion pressure of about 140 bar was measured at the extruder outlet and vacuum was applied to the mid-section of the extruder. The extruder is directly connected to a 300 mm×15 mm sheet temperature controlled tooling system with an extended trapezoidal with an ellipsoid distribution section, where temperature-controlled zones rise from 150° C. −175° C. and then several subsequent zones reduced the temperature to 80° C. The extruded sheet is then passed over several appropriate rollers to a driven roller haul-off (manufacturer Anton Breyer KG) that is synchronized to the extruder giving a line speed of 4 m/hr. The extruded sheet thus produced has no shot marks at all.

EXAMPLE 2

[0065] A conical counter-rotating twin screw extruder (manufacturer Weber) is continuously fed via a hopper with a mix of 98.5% UHMWPE 3040 from Braskem, 0.15% Irganox B225 from BASF, 0.5% zinc stearate, 0.85% Lupolen 3621 M rt Lyondell Basel. The extruder is run at 4 rpm having a temperature profile from the entrance throat to the exit of 80° C., 110° C., 125° C., 140° C. Extrusion pressure of about 160 bar was measured at the extruder outlet and vacuum was applied to the mid-section of the extruder. The extruder is directly connected to a 22 mm×22mm H profile mould with an extended trapezoidal entrance, where temperature-controlled zones rise from 150° C. −170° C. and then several subsequent zones reduced the temperature to 80° C. The extruded profile is then passed over an appropriate heated form table to a driven belt haul-off (manufacturer Weber) that is synchronized to the extruder giving a line speed of 12 m/hr. The extruded profile thus produced has no shot marks at all.

[0066] This rail type profile was produced for testing in a mechanical transport system such as found in depots and warehousing. The produced rail profile has runners traveling along and suspended from it. This method produced a reduction in surface friction and is noticeably quieter in use in a warehousing setup when compared with an equivalent compression moulded and machined profile.

EXAMPLE 3

[0067] A conical-counter-rotating twin-screw extruder (manufacturer Battenfeld Cincinnati, USA) is continuously fed via a hopper with a mix of 98.5% UHMWPE 4120 from Celanese, 0.25% Irganox B225 from BASF, 1.25% Ligastar, Peter Greven Gmbh. The counter-rotating twin screw extruder is run at 11 rpm having a temperature profile from the entrance throat to the exit of 80° C., 110° C., 125° C., 143° C. Extrusion pressure of about 140 bar was measured at the extruder outlet and vacuum was applied to the mid-section of the extruder. The extruder is directly connected to a 130 mm diameter mould (tooling system) with an extended conical entrance land, where temperature-controlled zones rise from 145° C.-170° C. and then several subsequent zones reduced the temperature to 80° C. The extruded rod is then passed over several appropriate rollers to a driven belt haul-off (manufacturer Battenfeld, Cincinnati (USA)) that is synchronized to the extruder giving a line speed of 2.2 m/hr. resulting as product. The extruded rod thus produced has no shot marks at all.

Comparative Example 1

[0068] A hydraulic ram-extruder for producing 130 mm diameter rod comprising a hydraulic pump which powers a reciprocating piston moving back and forth at the feed section of a heated tubular barrel is fed by the backwards motion of the piston allowing a measure, or a shot of UHMWPE material from a hopper to enter a 130 mm barrel at a suitably placed inlet. The material is then transported through the forwards motion of the piston and heated to 160° C.-200° C., the piston holds position for approximately 270 seconds before retracting allowing more material to enter the barrel and repeating the process. This alternating back and forth movement that allows a measure of material to enter the barrel causes shot-marks in this case every 40 mm-50 mm that are visible on the extruded rod. A line speed of 0.6 m/hr. of resulting product with visible shot marks was obtained. This comparative example of ram extrusion leads to a bar with shot marks.

Comparative Example 2

[0069] A conical counter-rotating twin screw extruder (manufacturer Battenfeld, Cincinnati (USA)) is continuously fed via a hopper with as supplied UHMWPE UTEC 3040 from the company Braskem. The extruder is run at speed settings between 3-9 rpm having a temperature profile from the entrance throat to the exit of 80° C., 110° C., 125° C., 143° C. Extrusion pressure was unstable at all rpms ranging between 100-380 bar measured at the extruder outlet, vacuum was applied to the mid-section of the extruder. The extruder is directly connected to a 130 mm diameter temperature-controlled tooling system with an extended conical entrance land where temperature-controlled zones rise from 150° C.-175° C. and then several subsequent zones reduced the temperature to 80° C. The extruded rod is then passed over several appropriate rollers to a driven belt haul-off (manufacturer Battenfeld Cincinnati (USA)) that is synchronized to the extruder. No stable line speed could be satisfactorily attained without frequent operator intervention, the extruded rod thus produced had dimensional and surface defects.

[0070] Lower properties result when an amount of additive greater than 2.5 wt. % is used, and can be seen when standard tests used for UHMWPE namely ISO 15527 (the sand slurry test which is used to quantify abrasive resistance), also in the impact strength/Charpy test ISO 11542 are applied. The reference material GUR® 4120 (PE-UHMW, Average molecular weight 4.7E6 g/mol Margolies' Equation, Density: 930 kg/m3, ISO 1183) is a UHMWPE polymer made by Celanese that meets the requirements for the reference material required in the ISO standardized tests. It is a comparative test with samples being run simultaneously.

TABLE-US-00001 Abrasion Test Impact Strength (acc. ISO (Double Notch Percentage - Additive (%) 15527) acc. ISO 11542) 3.0 182 110 1.5 90 170 0.5 87 178 Reference (GUR4120) 100 183