17 Nov Buying Shrink Wrap Film – What Every Contractor Should Know
Much shrink wrap sheeting sold around the world is simply standard plastic shrink wrap sheeting that is being marketed and sold as ‘scaffold shrink wrap’. It is often produced by film manufacturers, who have little idea of the final use and the challenges faced by those that shrink wrap scaffolds day to day. Before you next buy shrink wrap sheeting, read this short guide and find out the 5 essential areas that affect the quality and appearance of your next shrink wrap job.
It may seem obvious, but an important factor in how well a shrink wrap sheeting will encapsulate a scaffolding is how well it shrinks. If a shrink wrap sheet shrinks well, it will fit tightly and it will not flap or ‘chafe’ in high winds. It will be strong.
WHAT AFFECTS THE SHRINK RATIO?
If you look at the specification sheet of a shrink wrap film you should see that the shrinkage, sometimes known as the ‘shrink ratio’, is described in two ways; Machine Direction (MD) and Transverse Direction (TD). A shrink wrap film should have balanced shrinkage, which means that the shrinkage in both the MD and TD should be similar. However, while most shrink-wrap films have a good shrink ratio % in the Machine Direction (MD) very few have good shrinkage in the Transverse Direction (TD). As well as making the installation process difficult for the shrink wrap installer / end user, a poor shrink ratio may also cause the shrink wrap film to loosen or become slack in the first few days after installation. So what affects the shrink ratio? It is mostly due to the size of the die from which the shrink wrap film is extruded.
To make Rhino shrink wrap film we use a very small die from which the melted plastic polymers are blown into a large bubble of shrink film. This difference between the size of the die and size of bubble, (sometimes called the ‘blow up ratio’), is critical in achieving a powerful shrinkage because when the film is heat shrunk by the end user, around a scaffolding for example, the shrink wrap has a ‘memory’ and will try and return to it’s original size at the point of extrusion.
However, to speed up the manufacturing process most shrink wrap manufacturers use a die that is much larger than we do to manufacture their shrink wrap film. (A larger die has a higher production rate / hour). Typically, a die will be 1800mm to 2000mm wide. This larger die, although making a machine more profitable for the manufacturer, will produce a shrink wrap film with a much poorer shrink ratio, particularly in the transverse direction (TD). So, although our film is a little bit slower to manufacture, by using a smaller die we ensure that our customers get a shrink wrap film that has a shrinkage of 45% in the transverse direction (compared with a typical figure of 10-15% for competitor films). The end result of this is that Verisafe® is much easier for our customers to install properly, even in tough weather conditions, and once fixed in place is much more resistant to high winds.
Looking at the specification sheet should also tell you whether the shrink wrap film you are buying is a mono (1 layer) film or a multi layer film. In a similar way to ‘die size’above, it is generally more convenient for manufacturers (but not better for the end user) to supply a multi layered film as it is faster to manufacture and multi layered machines can produce a wide variety of products. However, it can enable unscrupulous manufacturers to ‘hide’ poor quality but cheaper regenerated plastic material within layers. At Verisafe we only produce a mono layer film. This is slower to manufacture but it means that any additives, such as flame retardancy, are contained throughout the whole film, and not just the outside layers, and it means we can only use premium resins.
3. DART DROP
This is a very important measure of the basic mechanical strength of the film. It is a standard test procedure outlined in ISO7765-1/2. Compare between alternative films and try and buy a shrink wrap film with the best performance in this area.
4. SEAL RANGE
Seal Range The seal range of Verisafe shrink wrap film is in the range of 95 to 125 Degrees Celsius. This is an important value because the lower temperature a film requires to seal, the easier it will be to heat weld by the end user. Again, the reason why some shrink wrap films are difficult to heat weld properly is that they have a much higher seal range and this is because many shrink wrap manufacturers add HDPE to their LDPE films, to speed up the production process and make each machine more profitable. However, an film with HDPE added will have a higher weld temperature and so be more difficult for the end user to weld, especially when weather conditions are challenging.
5. FLAME RETARDANCY
There are many flame retardant standards in different countries. In the United Kingdom we tend to use the European EN13501 standard and the LPS1207/1215 scheme. For the purpose of this article you should ensure that you get a copy of the standards that apply to your country and be aware of the difference between a simple flame retardant ‘test’ (such as EN13501) and a more extensive third party verification ‘scheme’ (such as LPS1207). Once again, manufacturers have a vested interest that is different from the end user. As flame retardant is a highly expensive additive they want to use as little as possible and so it is up to the end user to check that they are meeting their health and safety requirements.
5. UV STABILITY
Verisafe is specified as having a UV stability of 12 months in Northern Europe. You should be aware that films that if a flame retardant shrink wrap film claims to have a UV stability beyond this it is unlikely to also have enough flame retardancy added as these two additives ‘compete’ with each other.
Some Final Thoughts
Using a shrink wrap film for encapsulating scaffolding and large industrial projects is a demanding application which requires high performance shrink wrap sheeting. Most shrink wrap plastic film is made in a way that is most convenient for the manufacturer, even if makes life more difficult for the end user on site.
We think it makes more sense to start with the end user and work backwards to make sure the whole manufacturing process is designed to create a film with the desired performance.
Always ask your supplier for a specification sheet / data sheet and look closely at the figures for shrink ratio, dart drop and seal range. Ask your supplier to prove to you that the product they supply matches the specification sheet that they have given you. If you are buying a flame retardant film consider using a film that is part of a certification scheme such as LPS1207 and LPS1215 that includes an annual independent / third party audit of the product as this is the only way to prove that a product meets the required standard. In addition, always try and purchase from an ISO accredited supplier, as they will have the necessary quality controls in place to ensure consistency between batches.
For further advice on shrink wrapping scaffolding and large industrial products call or email us on +44 (0)1477 532222 or email email@example.com