High drawdown extrusion process with greater resistance to draw resonance

In a process for extrusion coating a substrate or for making a cast film with a thermoplastic composition, comprising the steps of:

• (i) feeding a thermoplastic composition into at least one extruder,
• (ii) melting and mixing the thermoplastic composition to form at least one uniform molten polymer stream, and
• (iii) extruding the molten polymer stream through a die to form a primary web,
• the improvement comprising:
• (i) operating said extruder at line speeds greater than 152 meters/minute, and either
• (a) drawing down said web onto said substrate to thereby coat said substrate with at least one layer of said thermoplastic composition, or
• (b) cooling and drawing down said web onto a take-off device to make said film with at least one layer of said thermoplastic composition,
• (ii) conveying or collecting said coated substrate or said film for subsequent use, and
• (iii) using as said thermoplastic composition:
• (I) from about 10 to 100 percent by weight of at least one substantially linear ethylene polymer characterized as having:
• (a) a melt flow ratio, I.sub.10 /I.sub.2,.gtoreq.5.63,
• (b) a molecular weight distribution, M.sub.w /M.sub.n, defined by the equation:
• M.sub.w /M.sub.n .ltoreq.(I.sub.10 /I.sub.2)-4.63,
• (c) a critical shear rate at the onset of surface melt fracture of at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a linear olefin polymer having about the same I.sub.2 and M.sub.w /M.sub.n, and
• (d) a single melting peak as determined using differential scanning calorimetry;
• and
• (II) from 0 to about 90 percent by weight of at least one polymer selected from the group consisting of a heterogeneous linear ethylene polymer and high pressure ethylene polymer.