FAQ - frequently asked questions
What is stretch film?
Stretch Film is a very particular plastic material, highly flexible with exceptional elongation characteristics, as it can stretch 3 to 4 times its length without breaking. It is either transparent or colored and may contain different additives to make it stickier or more slippery. It is used by hand or with semi or fully automatic machines on a number of very wide applications, from stabilizing loads on a pallet to protect from dust and humidity, in various conditions, from the lightest pallets (e.g. tissue products) to the heaviest (e.g. concrete blocks).
It is part of a large family of plastic materials, produced using Linear Low-Density Polyethylene, in short LLDPE. While other applications are available, LLDPE is used predominantly in film applications due to its toughness, flexibility and relative transparency.
The first stretch films for palletization arrived on the market at the end of the 1970’s and were extremely successful due to their ease of use. This alongside the parallel launch of film-wrapping machines enhanced end of line palletization enormously.
The last thirty years has seen enormous technological advances in terms of extrusion machine technology and the quality of plastic resins, this has allowed considerable reduction in film thickness from 30µm down to 8µm further enhanced by improved mechanical properties of films in terms of elongation and overall strength.
It is a significant market, consuming more than 1 million tons in Europe alone, with manufacturers or converters present in most countries.
Why to use stretch film?
Stretch film is basically used to protect and secure packages on pallets. Main advantages include:
- Low supply cost
- Protection from moisture, dirt, and abrasion
- Reliable performance
- Scan-through optics
- Ease of removal
- Elimination or reduction of other packaging materials
Is there a specific way to wrap the pallet with stretch film?
Stretch film can be applied by hand (manually) or with support of a machine, semi-automatic or fully automatic.
Stretch film has normally one side that is stickier than the other, usually the inside of the film on the roll. This sticky side must be positioned against the pallet, while the less sticky side facing on the outside of the pallet. There are additives to strengthen the sticky side or make a side slippery, these are possible options for each film quality.
What is the film pre-stretch and how it works?
Pre-stretch is the process that allows the stretch film to be stretched before being applied to a pallet. The process is extremely simple, the film passes between two or more rollers which rotate at different speeds, the difference in speed and/or in diameter of the rollers causes a forced elongation between them. For example, if the rolls have the same diameter, if one roll makes one turn and the second makes three, 1m of film becomes 3m and the elongation is 200%.
Initially, pre-stretching was applied essentially to reduce the quantities of films used, because the gain is immediate and significant by reducing the quantities consumed by a minimum of two.
It then also makes it possible to optimize the stability of the pallet by bringing the film into its blocking zone with a strong elastic return to correctly hold the package being wrapped.
Please note, the percentage of pre-stretch given by the machine does not mean that it is the percentage of pre-stretch actually applied on the load. In fact, depending on the types of machine and the quality of maintenance, slipping of the film in the carriage can be small or significant.
What is the difference between film tension and pre-stretch?
Pre-stretch is generated in the pre-stretch carriage of the wrapping machine and is linked to the elongation.
Tension (or post-stretch, lay-on force) is generated between the carriage and the pallet. This tension can generally be adjusted by a sensor at the output of the carriage (mechanical by spring or strain gauge), electrically connected to the electrical card of the machine in the case of a motorized pre-stretching, this sensor will feel a greater tension. strong at each corner of the pallet and will automatically request a brief acceleration of the pre-stretch motor in order to release a little more film at each corner of the pallet, this helps to avoid any crushing of the goods on the corners.
The latest generations of automatic double-motorized machines allow much more precise management of the tension, taking into account the perimeter of the pallet. Tension is important because it adjusts the force that the film is applied to the load, to avoid crushing while maintaining the stability of the unit.
What is the difference between cast and blown stretch film?
This has to do with the production process. Blown films are produced by pumping melted resin through a heated circular slotted rotating die to form a tube. The tube is filled with air which assisted in determining the gauge. The flow of air cools the film before it reaches the nip rollers. The collapsed tube is then slit into various widths and roll lengths.
Cast co-extrusion manufacturing method consists of melted resin pumped through several extruders through a straight slotted die creating a layered sheet of film. The film is then quickly cooled by a water filled roller and slit to size.
The cast process usually produces superior quality stretch film with more uniform gauge and more consistent cling. Cast films traditionally offer better tear strength which results in the prevention of tear propagation.
What is the pallet stability, how to measure it and how to improve it?
The stability of the pallet is in its ability to resist acceleration / deceleration and remain intact and secure. This can be replicated with a deformation frame which measures anomalies potentially affecting the presentation and integrity of the pallet.
There is a European regulatory framework to standardize this stability, EN 12195 and EUMOS. The EUMOS 40509 test is dynamic testing method that evaluates the rigidity and stability of a unit load that is subjected to horizontal accelerations and decelerations that are typical of road transportation on board industrial vehicles. This EUMOS standard is outlined in directive 2014/47/EU, ANNEX no. 3 – Principles of cargo securing and went into effect within EU in MAY 2018.
It must be also noted that pallet stability and load securing is no longer responsibility of the truck driver, but the load’s dispatcher.
Pallet load stability is measured on test benches present in many laboratories, these are either independent or at film manufacturers. It is also possible to measure the stability by tests of inclinations or vibration, but these tests do not allow certification.
A lot of parameters come into play to guarantee stability, the film is only the last link in a long chain of elements starting with the primary packaging of the product. If we had to summarize them before the application of the film:
- Strength and weight of the primary packaging
- Height and weight of the pallet
- Number of layers of product
- Consistency of the palletization plan
- Centering of products on the pallet
- Slip factor for secondary or tertiary packaging
- Edgeboards and/or anti-slip sheets between layers
Finally, for stretch film it is more its application than these characteristics which will favorably or unfavorably impact pallet stability. Indeed, before determining what type of film to use, it is very important to ensure:
- in case of manual use that the operators are well trained
- in the event of machine use that all the settings and capabilities of the machine allow:
- A minimum 5cm (especially when there is no roping) overlap to cover the wooden pallet on the bottom
- The application of roping, if possible, to be applied also on the wooden pallet
- A real pre-stretch application suited to the film's capabilities
- To adapt the wrapping pattern, that means the distribution of the film on the pallet.
Are Sigma Stretch Film products recyclable? Is recycled content used?
Our Stretch Film is 100% recyclable.
In case of stretch film, there are available products with 30% post-consumer recycled content, also able to cover more demanding applications.
Sigma Stretch Film continues to innovate in the field of environmental sustainability, offering product solutions and services that are helping to decrease carbon footprint and drive circular economy forward. Through a series of products with high percentage of post-consumer recycled content, bio-based stretch films certified by ISCC, and extensive recycling projects, we provide the means to reach sustainability goals and contribute to a better world for the next generations.