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Stretch Film 101

Tuesday, December 11, 2018

Stretch film is a staple in the packaging industry. Since the early 1970’s, it has been used to stabilize loads. In this article, we will go over some common terms you may come across when dealing with stretch film.

Let’s start with the process of making the various films and the different types and go over the glossary of terms for these:

 

  • Extruder: The piece of equipment which uses both mechanical and thermal components to change solid polymer into molten polymer.

  • Extrusion: The process that takes material form one or more extruders which results in the manufacturing of stretch film.

  • Co-Extrusion: The process of taking in the material from other extruders and merging them to create a multi-layer stretch film.

  • Blown film: A type of stretch film that is made by the blown film extrusion process. Typically, they have higher puncture resistance but are less aesthetically pleasing than the cast films.

  • Cast Film: A type of stretch film made by the cast film extrusion process. Typically, they have a higher tear resistance, higher aesthetically pleasing and are quiet on the unwind.

  • Hand Film: A stretch film that is manually applied and is designed for this type of application. They are usually lighter & smaller for ease of use for applicator.

  • Machine Film: A type of stretch film for automated application of the film. A stretch wrapper applies the film.

  • LDPE: Low Density Polyethylene Stretch Film

  • LLDPE: Linear Low Density Polyethylene Stretch Film

  • Metallocene: A new type of polyethylene resin which uses metallocene. This resin increases puncture resistance and clarity.

 

After the film has been made, there are different characteristics that are used to describe the film. Below are common terms in regards to stretch film’s characteristics:

  • Cling: This refers to the sticking to self but not to the product. Films can be designed with single or two-sided cling. This is done during the co-extrusion process.

  • Dart Drop: A technique used to measure the impact strength or sturdiness of a stretch film. Usually, a crescent shape weight is dropped onto the film to measure its strength.

  • Elastic Recovery: The ability for a film to recover and return to its original form after its been stretched.

  • Elmendorf Tear: A test where a tear is put in the sample material, then measure the amount of force needed to tear the sample apart.

  • Film Memory: The memory of the stretch film trying to return to its original unstretched form. This process makes the load tighter and more secure.

  • Gauge: A measurement used to measure the thickness or caliper of a stretch film.

  • Gloss: The shine or sparkle in the surface of a stretch film. High gloss are typically found in cast films.

  • Haze: The inability to see through a stretch film or lack of clarity. Typical in blown stretch films.

  • Impact Strength: The ability of a stretch film to defy applied destructive forces.

  • Microns: A metric measurement used to measure the thickness of the stretch film.

  • Tackifiers: Additives that are used to increase the tack or cling of a film.

  • Tensile Strength: A measurement of the maximum amount of force the material can take without breaking.

 

The final terminology section deals with the application of the stretch film.

  • Banding: The process of applying multiple wraps of film to reinforce a specific section of a pallet.

  • Bottom Wraps: Wrapping the bottom portion of a pallet with more than one layer of stretch film. This is usually done to increase pallet stability.

  • Film Feed: Refers to when the film is being applied by a stretch wrapper and refers to the rate at which the film is supplied to the load.

  • Film Force: The amount of tension the film is applied with when applying with a stretch wrapper.

  • Film Tail: Refers to the start and end pieces that are applied in the beginning and then later cut off from a pallet when applying film.

  • Neckdown: When a film losses is roll width and narrows due to it being stretched.

  • Overwrap: Refers to the amount of film applied over the top of the load. Usually used to secure a pallet top sheet or corrugated top.

  • Poststretch: The stretching of a film by using the load to pull the film out at the same time as it is applied.

  • Prestretch: The stretching of a fim prior to application.

  • Roping: The bunching of the stretch films full width to create a rope.

 

We hope you’ve learned a little bit more than you use to know about stretch film. At Murphy Packaging we believe knowledge is power and can equate to cost savings to your bottom line. Not all stretch films are created equal and we hope this glossary of terms help you differentiate the various types of films and their values.