Stretch Film Overview
What is Stretch Film?
Stretch films are made from linear low-density polyethylene resins. Since its early introduction in the early 70’s, stretch film has become the most important method of unitizing product loads for transport. There are a number of key features for this including:
- The uniform and relatively high holding force that stretch film applies to a load
- The protection from dust and damage it provides versus other unitizing methods.
- The optics that allow for customers and shippers the ability to identify the product while also keeping it clean.
- It is the most economical method of unitizing
- More details of these and other unitizing features.6
Stretch Film Manufacturing Methods
There are two basic manufacturing methods to create a stretch film. Without needing to get into technical detail they are:
Blown film is created by forcing molten resin through a circular die, creating a tube, which is “blown some 30 feet high”. The bubble is then flattened and cut into strips that when rolled will produce rolls of flat film. Blown film is generally “labeled” as a tough, hazy, and noisy stretch film best suited for “industrial” type applications.
This film is created by molten resin is sent through a large extruder which forces a thin layer of film over a large drum that is cooled. The resulting cooled layer of plastic is then cut and rolled into rolls of stretch film. Today most stretch films are actually multiple layers (co-extrusions) of film each with a specific purpose or feature associated.
The market is roughly 65% cast film and 35% blown film with the majority of the blown film for hand wrap stretch film.
Stretch Film Formulation (getting the right mix)
Like any formulation whether it be for pie crust or stretch film, certain ingredients are added to the formula for certain reasons. In the case of stretch film, certain resins and/or additives are added to provide the puncture resistance, strength, sticky cling, and resistance to ultra violet rays, or to give it anti static properties.
The science of stretch film is ever changing as technology allows us to test the boundaries. It is critical to ensure that you are buying the right stretch film for your specific application. Understand what is needed to getting the specific features you need out of your stretch film is important, and creating up your own specification requirements is a good way to start.
Metallocene in Stretch Film
Metallocene resin is currently the rage in improving the performance of stretch film. Multi layered films are combining lower grade layers for cost with higher grade Metallocene layers to create competitively priced stretch film with higher performance
Stretch Film Application
There are also 2 basic methods of applying stretch film to the load. Hand stretch film rolls are lighter and shorter than machine rolls allowing ease of use for the user. Machine films are the preferred method in high volume accounts where speed and consistency of wrapping are needed.
Hand Wrap Stretch Film
Hand wrap stretch film requires an operator to attach the film to the load and then proceed to unwind the stretch film as he circles the load. The operator also must apply the required tension to the film to ensure enough wrapping force is applied to contain and unitize the load. As the stretch film rolls must be manipulated by the operator, the size and weight must be limited for ease of use. Thus hand wrap is typically shorter in width and length to limit the weight. This method is typically used in only low volume applications.
Machine Wrap Stretch Film
Machine wrap stretch film used in conjunction with a stretch wrapping machine that applies the stretch film to the load using parameters set by the operator. Wrap parameters are set on the stretch wrapper to vary the amount and location of the stretch film to provide maximum load retention. These parameters ensure the load is wrapped exactly the same way each time.
Stretch Film Performance Variables
Here are a few things to consider when determining the stretch film requirement of a particular application. Narrowing these variables down allows you to properly select the type, size and gauge of stretch film that will best suit the load to be wrapped.
Stretch Wrap Machine Performance
You simply cannot ignore stretch wrap machine performance when selecting a film. The marriage between the stretch film and the stretch wrap machine is what decides the overall performance of the stretch film. There is simply no value in purchasing a high performance stretch film because of its properties if your stretch wrap machine can not stretch the film to the point where it extracts those properties.
Either you must ensure the stretch wrap machine is working at optimal performance to take advantage of the high end stretch film (highly suggested) or you should match the stretch film to the existing performance of the stretch wrap machine.
Pallet load configuration
Stretch film and machinery vendors have broken pallet loads into 3 distinct classes. A, B or C:
“A” Profile : These loads are typically cubed with no protrusions and relatively clean. These are the easiest loads to wrap.
“B” Profile : These pallets may have an object protruding or do not have clean vertical sides but rather an irregular sides. The puncture hazard may require a better performance film.
“C” Profile : These pallets have a very irregular load with many corners, sharp edges, or protrusions and are difficult to wrap. A higher performance stretch film will be required to handle this type of difficult load.
Stretch Wrapping Location
Is the wrapping to be done in a cold storage freezer or near a dock door in the winter? The temperature of the film when wrapping can have a tremendous effect on the performance of the film. It is possible that you can use a lower grade of film in the summer months and be required to use a better grade in the winter if the ambient temperature drops too much.