Method and apparatus for the production of high tenacity polyolefin sheet

1. A process for the production of high tenacity, highly oriented polyolefin sheet having a high heat of fusion comprising:

a) feeding a metered amount of polyolefin powder into the nip between two counter rotating heated calender rolls;

b) rolling the powder through the gap under these conditions until a coherent sheet of polyolefin is produced:

c) once a coherent sheet of polyolefin exits the gap increasing the gap to a desired operating level above the thickness of the largest powder particle; and

d) drawing the coherent sheet under controlled tension to produce a high tenacity, highly oriented polyolefin sheet having a high heat of fusion.

2. The process of claim 1 wherein the two counter rotating heated calender rolls are stacked vertically.

3. The process of claim 1 wherein

the polyolefin powder comprises an ultra high molecular weight polyethylene (UHMWPE) powder; and

the UHMWPE powder exhibits high crystallinity, a heat of fusion equal to or greater than 220 joules/gram, and low levels of entanglement.

4. The process of claim 1 wherein

said calender rolls are initially set at a gap smaller than the size of the smallest polyolefin powder particle; and

once a coherent sheet of polyolefin exits the nip increasing the gap to a desired level above the thickness of the largest powder particle.

5. The process of claim 4 wherein the gap at the operating level is set to between 100 and 230μ and the operating temperature of the calender rolls is set to a temperature below the melting point of the polyolefin powder.

6. The process of claim 1 wherein the counter rotating heated calender rolls rotate at a rate of between 1.9 and 12 meters/minute.

7. The process of claim 1 wherein drawing is performed in-line and continuously with the formation of the coherent sheet.

8. The process of claim 5 wherein

the initial temperature of the calender rolls is set to 3° C. above the melting point of the polyolefin powder; and

the operating temperature of the calender rolls is maintained between 136 and 144° C.

9. A process for the production of a coherent virtually full density polyolefin sheet suitable for further processing by drawing to produce a high tenacity, highly oriented film, tape, fiber or sheet from a polyolefin powder comprising:

a) feeding a metered amount of polyolefin powder into the nip between two counter rotating heated calender rolls initially set at an initial gap smaller than the size of the smallest polyolefin powder particle;

b) rolling the powder through the nip under these conditions until a coherent polyolefin sheet is produced; and

c) once a coherent sheet of polyolefin exits the nip increasing the gap to a desired operating level above the thickness of the largest powder particle.

10. The process of claim 9 wherein the polyolefin powder comprises an ultra high molecular weight polyethylene (UHMWPE) powder.

11. The process of claim 10 wherein the UHMWPE exhibits high crystallinity, a heat of fusion equal to or greater than 220 joules/gram, and low levels of entanglement.

12. The process of claim 9 wherein the initial gap is set below 50μ and the initial temperature of the calender rolls are set to a temperature above the melting point of the polyolefin powder.

13. The process of claim 12 wherein the gap at the operating level is set to between 100 and 230μ and the operating temperature of the calender rolls is set to a temperature below the melting point of the polyolefin powder.

14. The process of claim 13 wherein

the initial temperature of the calender rolls is set to 3° C. above the melting point of the polyolefin powder; and

the operating temperature of the calender rolls is maintained between 136 and 144° C.

15. The process of claim 9 wherein the counter rotating calender rolls rotate at a rate of between 1.9 and 12 meters/minute.