Patent ID: 6299821
Filing Date: 2001-10-09
Classification: B29C,B29L,Y10T

Abstract:
A melt extrusion process for a film layer of a thermoplastic polyolefin, the process comprising:(a) selecting a thermoplastic polyolefin having a characteristic time (.lambda..sub.c) determined by fitting a curve of dynamic viscosity (.eta.*) vs. frequency of oscillation (.omega.) such that.eta.*(.omega.)=.eta..sub.0 /1+(.lambda..sub.c.omega.).sup.m,where .eta..sub.0 is the zero shear viscosity and m is a power law index, and said .lambda..sub.c is a value of from 0.001 to 0.6 s;(b) setting the aspect ratio (A) of the air gap length (X) to one-half an extrusion die orifice width (L.sub.0) to lower than 0.8, where X is defined as the distance from said die orifice of a melt extruder to the location on a chill roll where extrudate of said polyolefin is solidified;(c) extruding the film through said extrusion die orifice onto said chill roll while maintaining a ratio (Dr) of film velocity at said chill roll (u.sub.f) to film velocity at said die orifice (u.sub.o) of at least 30; andd) maintaining the product (De) of said .lambda..sub.c times the ratio of said film velocity at the die orifice (u.sub.o) to said air gap length (X) at a value greater than 0.005.