Bubbles/Voids in Extrusion Coated Films, 1990 Polymers, Laminations & Coatings Conference Proceedings

In extrusion coating, bubbles and/or voids lead to mechanical and optical problems causing rejection. Extrusion coaters need to be concerned with two interfaces (substrate/melt, melt/cylinder) and numerous process variables ranging from melt curtain position to nip pressure. Review of these process and mechanical variables enables one to formulate process conditions to eliminate these problems.

Bubbles, as defined herein, are interface problems, while internal defects are defined as voids. Textured chill rolls or rough substrates can pull more air than usual causing bubbles. Control of variables affecting adhesion are shown to be critical to bubble elimination. Voids are a more complex subject, especially in thicker coatings (1.5 mils and up). Voids can be formed from entrained moisture or outgases in extrusion. However, rapid cooling or improper flow can also cause voids.

A historical review coupled with designed experiments show how to set die conditions for one structure. Other variables are discussed both from an experimental and theoretical basis.