| 摘要 |
The thickness profile of a monoaxially drawn thermoplastics sheet is improved in the region where the sheet, after extrusion from a fishtail die and heating, is longitudinally drawn over a relatively long bath between rolls before passing around a cooled roll. At or just before the line of contact where the sheet first touches the cooled roll, the sheet is held, laterally extended, at a width exceeding the width of the cooled roll. The lateral edges of the sheet are supported in this position, pref. so that the initial width is maintained, and are also pref. cooled, esp. to the same temperatures are the part of the sheet resting on the cooled roll. A considerably greater degree of uniformity of the thickness, right across the sheet, is obtd. than with the conventional procedure in which the sheet is allowed to shrink laterally in the space between the hot roll and cool roll. |
