초록 ▼

UHMWPE panels of large width may be prepared by a continuous ram extrusion process by employing a slit die which preferably narrows from both sides in a direction transverse to the machine direction, and/or which employs a plurality of transversely positioned cooling zones located on the top and the

UHMWPE panels of large width may be prepared by a continuous ram extrusion process by employing a slit die which preferably narrows from both sides in a direction transverse to the machine direction, and/or which employs a plurality of transversely positioned cooling zones located on the top and the bottom of the die, proximate the exit thereof. The panel exits the die at a temperature lower than the crystalline melt temperature.

대표청구항 ▼

What is claimed is: 1. A ram extrusion process for preparing UHMWPE panels of widths greater than 0.6 m as extruded, comprising: providing a slit die having a width of greater than 0.6 m which has a substantially rectangular cross-section under ram extrusion operating pressure, the die having a top

What is claimed is: 1. A ram extrusion process for preparing UHMWPE panels of widths greater than 0.6 m as extruded, comprising: providing a slit die having a width of greater than 0.6 m which has a substantially rectangular cross-section under ram extrusion operating pressure, the die having a top portion and a bottom portion and an inlet face and an exit face, and having at least three independently controllable cooling zones in each of the top portion and bottom portion, said cooling zones located proximate the exit face of the die, and positioned along the width of the die, such that the temperature of each respective cooling zone may be adjusted to vary the temperature of respective portions of the die transverse to the exit face; incrementally introducing UHMWPE resin particles into the die under pressure from a ram; heating the UHMWPE particles to a temperature above the crystalline melt temperature of UHMWPE to form a substantially continuous molten thermoplastic; cooling the UHMWPE to a temperature below the crystalline melt temperature while within the die and while maintaining contact with the walls of the die; and obtaining a solidified UHMWPE panel product which has exited the die. 2. The process of claim 1 wherein the UHMWPE is cooled to a temperature in the range of 40° C. to 100° C. prior to exiting the die. 3. The process of claim 1, wherein the UHMWPE is cooled to a temperature below 85° C. prior to exiting the die. 4. The process of claim 1 wherein a back pressure device located external to and downstream from the die exerts a pressure against UHMWPE panels exiting the die, increasing contact of the UHMWPE with the walls of the die. 5. The process of claim 1, wherein said die has a substantially rectangular cavity therein to receive UHMWPE powder and to process it to a consolidated HMWPE panel, the substantially rectangular cavity comprising: a) an entrance cavity; b) an exit slit; the height of the entrance cavity being greater than the average height of the exit slit; c) a consolidation cavity positioned between the entrance cavity and the exit slit and having a heated zone downstream from the entrance cavity and a cooling zone proximate the exit slit; and d) a vertical taper transitioning between the entrance cavity and the consolidation cavity, which is optionally heated. 6. The process of claim 5, wherein the height of the die at the center of the exit slit is lower than the height at the edges of the exit slit. 7. The process of claim 6, wherein the cross-sectional shape of the exit slit of at least one half of the die is a conic section, a combination of two or more conic sections, or a combination of one or more conic sections and one or more straight sections. 8. The process of claim 7, wherein said conic section is selected from the group consisting of a circle, a parabola, a hyperbola, an oblate ellipse, and a prolate ellipse. 9. The process of claim 6 wherein the exit slit, viewed facing the slit, comprises left and right portions proximate the left and right edges, respectively of the die, said left and right portions extending slopingly inwards towards a centerline of the exit slit to form tapered zones whose height at the end of the tapered zone nearest the centerline is less than the height at the edges of the exit slit, and a central surface extending between said tapered zones, the curvature of said central surface being different from the curvature of said tapered zones. 10. The process of claim 9, wherein said tapered zones are flat or have a very low curvature with a radius greater than about 1000 m, and said central surface has a radius greater than about 1000 m/2W where W is the width of the exit slit in meters, and the curvature of the central surface is greater than the curvature of the tapered zones. 11. The process of claim 10, wherein the exit slit has a width of 1.0 to 1.5 m, the tapered zones are flat and at an angle of .02° to 0.1° from a plane parallel to the width of the die and extend towards the centerline of the die for a length of about 10 to 40 cm, and the central surface has a radius of from 250 m to about 1000 m. 12. A process for producing an UHMWPE panel of greater than 0.6 m width, comprising ram extruding UHMWPE through a slit die contained within a support structure, the exit slit of the slit die not having a substantially rectangular shape as manufactured, but the die coacting with the support structure to distort to a substantially rectangular shape under ram extrusion pressure. 13. The process of claim 12, wherein said support structure comprises at least one window frame support structure. 14. The process of claim 12, wherein the exit slit of said slit die has a height at its center which is lower than the height at an edge. 15. The process of claim 14, wherein the shape of both the top and bottom surfaces of the exit slit are convex surfaces. 16. The process of claim 14, wherein the slit die has top and bottom surfaces each having an edge region and a central region, the shape of the edge regions and the central region being different. 17. The process of claim 13, wherein top and bottom surfaces of the exit slit of the slit die are plane parallel, and the window frame support structure has a thickness such that a panel having a thickness variation of not more than ±1.27 mm is extruded. 18. The process of claim 12, further comprising exerting a back pressure against a panel exiting the slit die. 19. A process for extruding UHMWPE panels of greater than 0.4 m width, comprising ram extruding UHMWPE through a slit die at a temperature higher than the crystalline melt temperature of the UHMWPE and cooling the UHMWPE to a temperature below the crystalline melt temperature while still within the slit die, said cooling effected by a plurality of independently controllable cooling zones located above and below the slit proximate an exit face of the slit die, and the respective plurality of independently controllable cooling zones positioned across the width of the die. 20. The process of claim 19, further comprising adjusting the temperature of one or more of said cooling zones during said extruding to maintain or improve product characteristics. 21. The process of claim 19, wherein the average temperature of cooling zones in the bottom die half are lower than the average temperature of cooling zones in the top die half. 22. The process of claim 19, further comprising monitoring the thickness of the panel at locations across its width; determining whether the thickness at any of said locations is less than others; and adjusting the temperature zone corresponding to the location of the lower thickness to increase the thickness at that location.