Process for manufacturing polyolefin films

Abstract

A process for manufacturing a film of ultra-high molecular weight polyolefin includes (a) feeding an ultra-high molecular weight polyethylene with a weight average molecular weight of at least 500,000 gram/mole as a powder having a bulk density below 0.5 g/cm 3 to a compaction zone of an isobaric double belt press; (b) subjecting the ultra-high molecular weight polyethylene powder in the compaction zone to an isobaric pressure to form a single layer sheet of compacted polyethylene at a temperature that is below the melting point of the polyethylene under process conditions and that is maintained within a temperature window of 2° C.; and (c) subjecting the sheet of compacted polyethylene to a rolling step and at least one stretching step at a temperature below the melting point of the polyethylene under process conditions.

What is claimed is: 
     
         1 . A process for manufacturing a film of ultra-high molecular weight polyethylene comprising:
 feeding an ultra-high molecular weight polyethylene with a weight average molecular weight of at least 500,000 gram/mole as a powder having a bulk density below 0.5 g/cm 3 , to a compaction zone of an isobaric double belt press;   subjecting the ultra-high molecular weight polyethylene powder in the compaction zone to an isobaric pressure to form a single layer sheet of compacted polyethylene at a temperature that is below the melting point of the polyethylene under process conditions and that is maintained within a temperature window of 2° C.; and   subjecting the sheet of compacted polyethylene to a rolling step and at least one stretching step at a temperature below the melting point of the polyethylene under process conditions.   
     
     
         2 . A process for manufacturing a film of ultra-high molecular weight polyethylene comprising:
 feeding a powder of an ultra-high molecular weight polyethylene with a weight average molecular weight Mw of at least 500,000 gram/mole and an Mw/Mn ratio of at most 8 to a compaction zone of a double belt press;   subjecting the ultra-high molecular weight polyethylene powder in the compaction zone to a pressure to form a single layer sheet of compacted polyethylene at a temperature that is below the melting point of the polyethylene under process conditions and that is maintained within a temperature window of 2° C.; and   subjecting the sheet of compacted ultra-high molecular weight polyethylene to a rolling step and at least one stretching step at a temperature below the melting point of the polyethylene under process conditions.   
     
     
         3 . A process for manufacturing a film of ultra-high molecular weight polyethylene comprising:
 feeding a powder of an ultra-high molecular weight polyethylene with a weight average molecular weight Mw of at least 500,000 gram/mole to a compaction zone of a double belt press;   subjecting the ultra-high molecular weight polyethylene powder in the compaction zone to a pressure to form a single layer sheet of compacted polyethylene at a temperature that is below the melting point of the polyethylene under process conditions and that is maintained within a temperature window of 2° C., to form a sheet of compacted polyolefin; and   subjecting the sheet of compacted ultra-high molecular weight polyethylene to a rolling step and at least one stretching step at a temperature below the melting point of the polyethylene under process conditions to form a film having a 200/110 uniplanar orientation parameter Φ of at least 3.   
     
     
         4 . A process for manufacturing a film of ultra-high molecular weight polyethylene comprising:
 feeding a powder of an ultra-high molecular weight polyethylene with a weight average molecular weight Mw of at least 500,000 grain/mole and with an elastic shear modulus G 0   N  determined directly after melting at 160° C. of at most 1.4 MPa into a compaction zone of a double belt press;   subjecting the ultra-high molecular weight polyethylene powder in the compaction zone to a pressure to form a single layer sheet of compacted polyethylene at a temperature below the melting point of the polyethylene under process conditions; and   subjecting the sheet of compacted ultra-high molecular weight polyethylene to a rolling step and at least one stretching step at a temperature below the melting point of the polyethylene under process conditions.   
     
     
         5 . A process for manufacturing a film of ultra-high molecular weight polyolefin comprising:
 feeding an ultra-high molecular weight polyolefin with a weight average molecular weight of at least 500,000 gram/mole in powder form to a compaction zone of an isobaric double belt press comprising a lower belt, an upper belt on top of the lower belt and pressure cushions comprising a liquid or gaseous pressure medium;   subjecting the ultra-high molecular weight polyolefin powder in the compaction zone to a pressure using the isobaric press, wherein the liquid or gaseous pressure medium in the pressure cushions is heated to heat the powder in the compaction zone to a temperature that is at least 1° C. below an unconstrained melting point of the polyolefin and that is maintained within a temperature window of 2° C.; and   subjecting the sheet of compacted polyolefin to a rolling step and at least one stretching step at a temperature of at least 1° C. below the melting point of the polyolefin under process conditions.