Determining Equipment Size for Blown Barrier Film Extrusion, 1990 Polymers, Laminations & Coatings Conference Proceedings

Three to seven layer blown film coextrusion lines are being used to manufacture films for packaging snack foods, cereals, baked goods, meats, milk, medical devices and many other items. The reason for using coextrusion is to allow the incorporation of one or more barrier polymers which will prevent contamination or degradation of the package contents or will prevent loss of Something from the contents such as flavor, aroma, or moisture.

The barrier and adhesive resins used in these film structures are expensive and generally do not heat seal well. Some are good gas barriers but not good moisture barriers or do not retain their gas barrier if they take on water. Therefore it is necessary to coextrude them with other resins, usually polyolefins to provide heat sealability, printability and moisture resistance.

Some of these resins are less heat stable and some are stiffer than the standard polyolefin resins used in single layer blown film. In some instances particular attention must be given to screw size and design, die size, collapsing and winding techniques. Of particular concern is melt temperature, melt residence time, layer orientation (which polymer is on outside and inside of the blown bubble), collapsing geometry, drag characteristics and winding tension.

It is the purpose of this presentation to review these and other aspects of blown film coextrusion in order to determine such things as how many extruders are required; what size should they be; how much Hp drive should they have; what size of die and take-off should be used and what type of collapsing and winding should be employed. All of these and other aspects will be discussed with the main objective of maximizing the profitability of the extrusion operation.