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Askthe Expert: Shrink, Stretch, Strapping

What is the difference between Cast stretch film and Blown stretch film? Most manufacturers produce both blown and cast films as they both have separate positive attributes. The largest difference between these two films is the way in which the resins are cooled after production. Cast film is wound onto a “ chill” roll cooling the film rather quickly. This creates a strong bi-directional molecular structure. Cast film tends to have a quiet unwind and greater clarity when compared with a blown film.

Blown film is produced when the resin is melted and “ blown” upwards over a circular die. This creates a bubble of resin that is cooled by air. This process is significantly slower and requires more manpower than creating a cast film which usually results in a higher price for blown stretch film. Blown film is typically softer than cast film and has a greater stretch and increased tear resentence. Blown stretch film is usually tackier than cast films which tend to make them much louder coming off the roll. Blown film tends to have better cling for cold temperature applications.

Stretch films are often referred to in reference to the gauge. The gauge refers to the thickness of the film. Generally, the larger the number: the stronger the film. Today, many manufacturers have started to identify the strength as a micron rather than a gauge. Below is a chart comparing the most common gauge to micron conversions.

Gauge Microns
47 12
50 12.7
53 13.5
60 15.2
63 16.0
65 16.5
70 17.8
75 19.0
80 20.3
90 22.9

What is high performance stretch film?
Many manufacturers have started manufacturing high performance stretch film to increase strength and lower costs. Many stretch film users have started using high performance films for these reasons. High performance films tend to work on all load types including those that are extremely irregular with sharp corners. These rolls tend to be lighter with increased strength.

Is shrink film different from stretch film?
It is common for users of stretch film to refer to the product as shrink film, however they are very different products. Stretch film is typically used for wrapping pallets or banding small groups of products. Shrink film on the other hand is typically used to wrap individual products often creating an airtight seal. Shrink film comes in many forms including rolls, bags, and tubing. Open ends can be sealed with heat creating an airtight seal. This is useful when dealing with food packaging or the need to wrap individual toys for example. You can also use shrink wrap when wrapping a gift basket. You can tie the open top with a bow and call it complete or you can use a heat source to shrink the material down for a closer fit. As with stretch film, shrink film comes in a variety of gauges to fit your specific application. For more information please contact us directly.

What is the difference between Polypropylene and Polyester strapping?
There are three basic kinds of strapping: steel, polypropylene and polyester. Steel strapping  is obviously the strongest available on the market. Then there are polypropylene strapping and polyester strapping which most people have a difficult time differentiating. Polypropylene is the most economical type of strapping. This strapping is used for bundling and light palletizing applications. Polyester on the other hand is made to handle large and heavy loads once thought only to be handled by steel strapping. Polyester strapping retains tension longer than polypropylene and has a larger elastic effect allowing it to slightly give to keep shrinking and shifting packages tighter. Polyester strapping does not work well for small loads it is best used for palletizing on heavy loads.

How do I measure the core?
The core of the strapping role is important as many strapping dispensers will only accept certain sizes. The core is determined by measuring the inside diameter of the core and the face width of the core.

How can I tell if I am using Polyester or Polypropylene strapping?
There are three ways that you can differentiate these. First, polyester strapping tends to be smooth and glossy while polypropylene strapping is embossed. Next, polyester strapping will never split lengthwise whereas polypropylene strapping is very easy to split. Finally, polyester strapping will sink in water where as polypropylene will not. It is best to test this last method with a piece of strapping that is approximately 2 inches as an entire roll of strapping will sink regardless of the materials.