摘要 |
A process for producing mono-axially oriented polyethylene terephthalate fil m having increased mechanical strength in the machine direction which comprise s the steps of drying substantially homopolymer or copolymer polyethylene terephthalate resin having an intrinsic viscosity in the range of about 0.65 to about 0.85 dg/cc and then blending the dried resin with from about 0.5 to about 4.0 % by weight of anti-block additive; extruding the resin blend to r e- melt the resin and make it homogeneous; casting a film web with the resin blend; orienting the film immediately after casting it to produce a film of uniform thickness, by drawing the film at a ratio of from about 3.5 to about 4.5 times while constraining the web along its edges to prevent shrinkage in the TD direction; allowing the film web to relax to a lower tension, cooling the film web, further relaxing the film web and then quenching it to room temperature; subjecting the film web to a second orientation step under similar conditions to the first step except that the film is drawn at a draw ratio of about 1.025 to about 1.150, and at a draw temperature that is slightly higher than used in the first draw, while constraining the web alon g its edges to prevent shrinkage in the TD direction; allowing the film to rel ax and annealing thefilm to a temperature in the range of from about 100 to about 180 ~C, and then relaxing it further and cooling it to a temperature near room temperature; and trimming and winding the film web into rolls. The film has particular application in the production of tape for all types of purposes, most particularly teartape.
|