Patent ID: 6589463
Filing Date: 2003-07-08
Classification: B29C,B29K

Abstract:
A process for producing mono-axially oriented polyethylene terephthalate film having increased mechanical strength in the machine direction which comprises the steps ofdrying 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 re-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 along its edges to prevent shrinkage in the TD direction; allowing the film to relax and annealing the film to a temperature in the range of from about 100 to about 180Â° C., and then relaxing it further and cooling it to a temperature near room temperature; and trimming and winding the film web into rolls.