| 摘要 |
<p>A method and apparatus for carrying out the method are for forming a sheet or film of thermoplastic polymer alloy by extruding an intimate blend of incompatible polymer materials, such as polypropylene dispersed in LLDPE, through an extrusion die and stretching after extrusion. In the die upstream from the exit is a grid chamber comprising one or more grids, the grid or grids having at least 4 (in the longitudinal sections perpendicular to the main surfaces of the flow) closely spaced lamellae (303) having walls extending several millimetres in the direction of the flow, which are interconnected (306) at intervals such that viewed in sections perpendicular to the direction of flow they form a network, the intervals being essentially longer than the distance between each pair of lamellae and between the lamellae apertures of a size selected to reduce the average size of the dispersed phase of P1 or P2 in the blend, the grid or grids being located at a position in the chamber where the gap is wider than the said exit gap, the grip chamber further comprising a gap reduction portion between the screen and the die exit wherein the gap through which the blend flows is reduced at least part way to the gap of the die exit. There may be two grids with parallel lamellae arranged so that the lamellae of the downstream grid are located mid-way between the lamellae of the upstream grid.</p> |
