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What is Pre-Stretch Film?

Posted March 28, 2012

What is pre-stretch stretch film?

Don was telling me a story the other day about a visit he made to a customer that was evaluating their stretch film. It turns out that this particular customer was using the wrong machine stretch film, and in turn, using too much film per pallet. After it was explained to me, there was a personal ah ha moment that I thought would be interesting to share.

There are a few different types of stretch film, including: blown, cast, high performance, and pre-stretch. For the purpose of this entry, we are going to discuss pre-stretch film only, as this relates to my personal ah ha moment.

Think of an ordinary balloon. To start, it fits in the palm of your hand, but you have to put some effort into blowing it up. Most kids I know like to try and blow up the balloon as large as they can without popping it. They want to see how far it will stretch...see where I am going with this yet? It would not be as much fun if all the balloons were already inflated, but with having pre-stretch film, a lot of valuable resources can be saved.

So what is pre-stretch film? Well, it is stretch film that has been stretched before being wound onto its core. The film is processed through two rollers at different speeds. The second roller rotates faster than the first which actually stretches the film.

Just like stretch film, not all balloons will stretch to the same size. This should not be a problem for the next birthday party, but with stretch film, you could be losing valuable benefits. The stretching of the film is actually what helps keep the load upright while in transit. The farther you stretch film, without passing the point permanent deformation, the stronger the film becomes. 

What happens when you let all the air out of the balloon? Of course, it deflates back to its original size, or close to it. Stretch film works the same way: stretch film has a memory. After wrapping a load the stretch film, both pre-stretched and non-pre-stretched, the film wants to shrink back to its initial form securing the load. Film memory is actually what differentiates stretch film from any other type of unitization. However, the more you stretch the film, the less memory it has.

If you wrap a pallet with film that has not been stretched to capacity while the pallet is moving, there is still room for the stretch film to continue to stretch. This leaves the stretch film with a looser grip on the materials it is trying to hold together, allowing the load to sway even further. But if the film is stretched properly, the load will continue to its destination with much less movement. This was actually my ah ha moment. Let me explain it to you as it was explained to me. Take about 10 pencils, group them together, and wrap a rubber band twice around them. Your pencils are now grouped together and the rubber band is responsible. But if you start to toss the pencils around, say play a game of office catch, which I do not endorse with sharp objects…you could lose an eye…the pencils will start to shift. Now if you take that same rubber band and wrap it around the pencils two more times, the results are much different. The rubber band is now stretched as far as it can without breaking and the pencils are not shifting. Non-pre-stretch film can be elongated to 100-150%, which is a lot of force for a person to continually exude. Pre-stretch film is applied with minimal force allowing the user to actually walk forward safely rather than backwards while fighting with the stretch film.

There are other benefits to pre-stretch film. Since the film is already stretched to its optimal performance, you know that each pallet is being wrapped without waste. When using non-pre-stretched film, machines and humans can change the force in which they stretch the film while in use. Operators can get tired or machines may not be set to the proper settings. So the film may not always be stretched as far as it can go, actually increasing the amount of stretch film that is used per load. Pre-stretch film also tends to be lighter making the rolls easier for the operator to change out the rolls. Pre-stretch film also offers good film clarity and excellent film cling. 

All of these reasons blown up into one big balloon point to the last benefit of pre-stretch film: cost. Using pre-stretched film can decrease stretch film cost up to 40% when used properly and under the right circumstances. Now of course you may not see these kinds of savings if you are using a non-pre-stretched film under the right circumstances. If you have any questions or would like an evaluation of your current film, please do not hesitate to contact us.


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