Differences Between Blown and Cast Stretch Wrap/Film

Differences Between Blown and Cast Stretch Wrap/Film

When you ask the experts of packaging material supplier, they will tell you how blown and cast stretch wrap is different; although many of us laymen might not understand it at first look. There are two alternative ways to make stretch film (blown or cast), blown film is the favoured method for producing a higher-quality product.

 

Manufacturing

 

The terms “cast” and “blown” allude to how the film is made or made. Blown stretch film is extruded in the same way that regular PE films are. The resin is heated and pressed through a circular die before being blown into a bubble vertically. As it is turned into rolls of stretch film, the bubble is cooled by the surrounding air as the packaging solutions.

Cast stretch film is made by heating resin in the same way that blown stretch film is made, but instead of going through a circular die, it goes through a narrow slotted die. Instead of a bubble, a “sheet” of film is created (as with blown). The film is then chilled and solidified on a rolling path before being turned into rolls.

 

Clarity

 

By casting molten resin over a frozen roller and reducing crystallisation, the Cast Film technique reaches higher levels of clarity. Slow cooling of blown film increases crystallisation and reduces clarity. Shrink wrap packaging solutions use the modern technology resins which has substantially improved the clarity to the point where bar code scanning is quite trustworthy.

 

Gloss

 

The gloss of blown film is lower. Under warehouse lighting, this decreases reflection, making product identification and scanning easier. The gloss levels on Cast Film are greater. This is usually due to the resin employed and the speed with which the film was cooled. High gloss is not an advantage in ordinary warehouse stretch wrapping operations since it is difficult to see or scan through the film under warehouse lighting.

 

Memory 

 

Stretching LLDPE (Linear Low Density Polyethylene) film causes the molecules to excite, causing the film to retract. Blown film has a far higher degree of memory than regular film. The molecular chains’ composite orientation results in a film that contracts in both the MD (machine direction) and CD (cross direction) directions. Cast Film’s single orientation, along with its “softer” qualities, results in a film with less memory.

 

Tear Resistance 

 

Blown films are more tear resistant than cast stretch. This is owing to the different types of manufacturing process which decides the orientation of the molecular structures as well as the cooling rates of these wraps. 

 

Holding Power 

The Blown Film’s higher mechanical properties will provide more load retention and holding power. Stretching the Blown Film takes a little more effort, and the improved mechanical qualities make re-stretching the film once it’s been applied extremely difficult = More Holding Power. Cast Films will readily break yield (stretch). The disadvantage is that it easily breaks yield (re-stretches) once it has been applied. This makes it easy for your product to shift in shipment, resulting in costly damages.

 

Cost 

 

When determining which form of stretch film is best for your application, it’s important to understand how the two varieties differ in terms of their qualities. However, there’s also the matter of cost to consider. If your application does not necessitate the strength and film memory of blown stretch film, cast stretch can save you money.

The cast manufacturing process allows for more film to be made per man hour, making it a more cost-effective option for most. Not to add, cast has several advantages over blown stretch, such as better film quality and quieter operation. However, you may need the strength and puncture resistance that blown stretch provides on occasion. In such instances, the additional expenditure may be justified.

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