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Cast vs. Blown Films


Before 2011, Flair Flexible Packaging produced film through a co-extruded blown film process. This process vertically extrudes molten resin pellets in a tubular shape that cools, collapses and winds up as a thin film. In comparison, co-extruded cast film production improves on many important physical properties of the film, especially as they are applied to thermoforming and high barrier efficacy. As of May 2011, Flair Flexible Packaging has entirely shifted its film production method to cast co-extrusion. H.I. Lee, VP of Technology for Flair, recently explained some of the benefits of cast coextruded film.

Better Formability

Blown films are pre-stretched by virtue of their manufacturing process, which is somewhat more challenging to thermoform (stretch and mold) than cast films. Because cast film does not have significant orientation in MD (machine direction) and TD (transverse direction), cast films arrive at customers’ converting and packaging lines minimally stretched. Therefore, the depth of thermoforming, especially deep drawing (for a large cheese block or multiple layers of stacked hot dogs, for example), is significantly improved when using cast film instead of blown film.

This is especially obvious when a customer is deep drawing the thermoforming films around the bottom four corners of the aforementioned cheese block. These are the most critical points on the cheese block for hermetic packaging due to the weight of the cheese and the exposure to environmental stresses, including transport and handling. Thicker, more even distribution of the cast film’s structure makes this a better, more quality choice for deep draw thermoforming applications.

Higher Barrier Efficiency for Gases, Moisture, and Aromas

When high barrier films are required to prevent the transmission of gases, moisture and aromas, co-extruded cast films effectively extend product shelf life. Overall cast film thickness and the more evenly distributed layers of the polyolefins in cast film structures make them an optimal choice.

EVOH (ethylene vinyl alcohol copolymer) is the chemical resin that contributes these high gas barrier characteristics. EVOH is shown to be more effective when co-extruded in a cast versus blown film extrusion process. The resin, while used in both cast and blown films, benefits from shorter periods of cooling and crystallinity formation when cast, thus increasing its effectiveness.

Positive Customer Feedback

According to H.I. Lee, feedback from customer trials of the cast film line has been very positive. “Customers appreciate the easier thermoforming, the enhanced contact clarity and better resistance to pinholes and punctures. We continue to seek resins and film manufacturing processes that result in the best cast coextruded film performance. Quality and performance are our most important goals, not just at the beginning, but as a continuous process.”