Air Ring Considerations for Optimizing Blown Film Properties, 1996 Polymers, Laminations & Coatings Conference Proceedings

The physical properties of blown film can be influenced by a great number of factors in the fabrication process. These factors can range from choice of raw material or base resin, various additives available, processing temperature, extrusion rates, die gap/draw down ratio, blow up ratio, bubble geometry, frost line height, and others too numerous to mention here. This paper will attempt to focus on the properties which can be directly affected by the external cooling - air ring performance. These are the properties generally influenced by polymer chain orientation and rate of crystallization, specifically, clarity and mechanical properties. The use of a specialized dual lip air ring for long stalk extrusion of HMW-LDPE producing high clarity film with evenly balanced MD and TD elongation and shrink characteristics at commercially viable rates will be discussed. Additionally, the use of a modified Model D94 dual lip air ring producing LLDPE at a large blow up ratio will be discussed. This process utilizes rapid quenching essential for optimal MD tear properties while maintaining excellent bubble stability at above average extrusion rates.