| 摘要 |
<p>Biaxially oriented polymer sheet (70) is produced by advancing a workpiece (67) of polymer material in the longitudinal direction between opposed working surfaces (56, 57, 61, 62), causing the material of the workpiece to flow simultaneously in the longitudinal direction (Z) and the sideways direction (Y) whilst decreasing the thickness of the workpiece in the direction (X) by squeezing the workpiece between the opposed working surfaces. The friction between the polymer material and the working surfaces is compensated for by squeezing the workpiece more at the centre than at the edges thereof in the widthwise direction (Y) whereby the material of the workpiece flows bidirectionally to produce the biaxially oriented sheet. In one embodiment, the workpiece is forced through a die affording two opposed surfaces (56, 57) which converge in the longitudinal direction and which carry respective projections (61, 62) which are convex across the width of the workpiece. In an alternative embodiment, the workpiece is drawn between a pair of opposed flexible belts (80, 81) supported by pairs of opposed rollers (87A-N), the spacing of the pairs of rollers and the convexity of the rollers decreasing in the longitudinal direction (Z).</p> |
