|
Home > MacroLetter > 13.1 - Autumn 2009
MacroLetter 13.1 - Autumn 2009
Taking Control of Blown Film Gauge
Contents:
The blown extrusion process is used to make single and multilayer films that act as starting materials for printing, lamination and converting (PLC). Today's PLC industry demands blown film processors to make both exceptionally flat films that can be converted at high speeds, and large diameter rolls for minimized changeovers. These requirements call for tight control of the gauge distribution over the total thickness of the film. When blown film is used for specific applications, such as barriers for meat packaging, the control of individual layer thickness for the specialty layer is also critical and should be held to tight tolerances. Examples of these specialty layers include a sealant layer which has EZ-peel and antifog properties in a 3-layer PE based film and barrier layers (nylon or EVOH) in multilayer coextrusion films. With tight gauge control a more uniform performance of the film is achieved in the field.
Aside from the benefits of increased product performance, there is also a significant cost saving to having good gauge. Amidst rising polymer costs and highly competitive markets a processors ability to produce film with uniform thickness has become a necessity. It's no secret that processors spend more than 50% of their operating costs strictly on resin, masterbatches and special additives, and excessive use of these materials, particularly costly barrier and tie resins or additives, reduces the profitability of the business.
Unfortunately, no matter how good your blown film system is there will always be some variation in gauge. These gauge variations can be created by a number of processes and/or equipment, such as temperature variations in the die, and uneven cooling by the air ring or IBC.
To reduce the amount of gauge irregularities in the film a gauge control system is often employed. These control systems vary in configuration and sensing technologies, typically to match certain applications; however, they all share several common elements:
– Sensing device
– Scanning device
– Method of correction
|
