Method and apparatus for the production of high tenacity polyolefin sheet
View Patent ↗A process for the production of virtually full density polyolefin suitable for further processing by drawing to form a high tenacity, highly oriented polyolefin sheet comprising: a) feeding a metered amount of polyolefin powder into the nip between two heated calender rolls; b) rolling the powder through the nip under these conditions until a coherent sheet of polyolefin is produced. According to a highly preferred embodiment, initially, the nip is set at a gap smaller than the size of the smallest polyolefin powder particle and at a temperature above the melting point of the powder and once a coherent sheet of polyolefin exits the nip the temperature in the nip is lowered to a temperature below the melting point of the polyolefin powder and the gap increased to a desired level above the thickness of the largest powder particle.
1. A process for the production of high tenacity, highly oriented polyolefin sheet having a high heat of fusion comprising:
a) providing a pair of horizontally aligned counter rotating calender rolls separated by a nip, a doctor blade in alignment with a first of said calender rolls, and a gap between said doctor blade and said first calender roll;
b) feeding a metered amount of polyolefin powder into said nip between said counter rotating heated calender rolls;
c) controlling the amount of polyolefin powder at said nip by adjusting said gap between said doctor blade and said first calender roll;
d) rolling the powder through the nip until a coherent fully dense sheet of polyolefin is produced: and
e) drawing the coherent fully dense sheet of polyolefin under controlled tension at a temperature of between 140° C. and 158° C. to produce a high tenacity, highly oriented polyolefin sheet having a high heat of fusion.
2. The process of claim 1 wherein the polyolefin powder comprises an ultra high molecular weight polyethylene powder.
3. The process of claim 2 wherein the ultra high molecular weight polyethylene powder exhibits high crystallinity, a molecular weight above 1 million, a heat of fusion equal to or greater than 190 joules/gram and low levels of entanglement.
4. The process of claim 3 wherein the fully dense coherent sheet has a density above 0.945 g/cc.
5. The process of claim 4 wherein
said nip includes an operating gap;
said operating gap is between 0.015 mm and 0.35 mm; and
said counter rotating calender rolls include surface temperatures between 136.5° C. and 142° C.
6. The process of claim 5 wherein the counter rotating calender rolls rotate at a rate of between 1 and 12 meters/minute.
7. The process of claim 6 wherein drawing is performed in-line and continuously with the formation of the coherent fully dense sheet.
8. A process for the production of a coherent virtually fully dense polyolefin sheet suitable for further processing by drawing to produce a high tenacity, highly oriented film, tape, fiber, ribbon or sheet from a polyolefin powder comprising:
a) providing a pair of horizontally aligned counter rotating calender rolls separated by a nip, a doctor blade in alignment with a first of said calender rolls, and a gap between said doctor blade and said first calender roll;
b) feeding a metered amount of polyolefin powder into said nip between said counter rotating heated calender rolls;
c) controlling the amount of polyolefin powder at said nip by adjusting said gap between said doctor blade and said first calender roll; and
d) rolling the powder through the nip under these conditions until a coherent fully dense polyolefin sheet is produced.
9. The process of claim 8 wherein the polyolefin powder comprises an ultra high molecular weight polyethylene powder.
10. The process of claim 9 wherein the ultra high molecular weight polyethylene exhibits high crystallinity, a molecular weight above 1 million, a heat of fusion equal to or greater than 190 joules/gram and low levels of entanglement.
11. The process of claim 10 wherein the coherent fully dense sheet has a density above 0.945 g/cc.
12. The process of claim 11 wherein the operating gap is between about 0.015 mm and 0.35 mm and the operating temperature is between 136.5° C. and 142° C.
13. The process of claim 12 wherein the counter rotating heated calender rolls are aligned horizontally and rotate at a rate of between 1 and 12 meters/minute.