The draw ratio–Deborah number diagram: A useful tool for coating applications

The understanding of the basic physical effects of viscoelasticity on drawing performances in the coating process leads to a useful approach to link the rupture of the polymer melt to critical processing conditions. In particular, we show that when solving the drawing problem in the air gap with a simple constitutive equation—like the upper convected Maxwell model—a mathematical inconsistency appears for some drawing parameters. This mathematical instability may be experimentally correlated to the occurrence of melt‐rupture, giving rise to a discussion on the effect of viscoelastic properties on drawing performances. Results are given in terms of a diagram representing the maximum drawing ratio Dr with respect to the Deborah number De. A master curve, obtained form experimental results, accounts for the temperature, melt‐index, air‐gap height, and extrusion output dependences. The limitations of the “universality” of the concept are discussed later. POLYM. ENG. SCI. 46:372–380, 2006. © 2006 Society of Plastics Engineers