Stretch Film – Cast vs. Blown
Stretch films from both production methods are available in a variety of grades which perform equally well on all types of stretch machinery and through many types of stretch mechanisms. However, there are a few areas where cast and blown films are not totally interchangeable.
Occasionally there is a specific requirement that determines the choice of stretch film. Otherwise the choice is determined by the customers or manufacturers preference. The customer may be happier with the look or feel of a particular type or just be reluctant to change. The supplier may prefer to sell the type that is most readily available. Although both cast and blown films are generally interchangeable, there are some specific difference between them:
|Clarity||The rapid cooling of the cast process gives a very clear film. This can be important for scanning labels or bar codes.||Blown film is cooled slowly giving a film with slightly lighter haze or see through than cast film.|
|Stickiness||Cast film relies on its smooth surface and resin type to achieve cling.||Added tackifier or the co-extrusion tack in blown film makes it very sticky on one surface.|
|Noise||Cast film is quiet in use.||The tackifier in conventional blown film makes it noisy when unwinding. Low noise blown films are also available.|
|Telescoping||Cast film cannot telescope.||NPP’s blown film has a specially formulated tack layer to prevent telescoping.|
|Thickness||Thickness variation can be controlled to smaller tolerances on cast film, typically +/- 10% spot to spot.||Typical spot-to-spot thickness variation is +/- 20%.|