Buses, watercraft and even airplanes can be wrapped with self-adhesive films.
Adhesives
The two primary types of adhesive are pressure-sensitive and pressure-activated.
A pressure-sensitive adhesive (PSA) will stick to the surface upon contact, whereas a pressure-activated adhesive (PAA) can slide along the surface and be repositioned until the installer applies firm pressure to it, thanks to tiny ‘posts’ that extend from the adhesive toward the surface. A PSA is suitable for a flat surfaces and simple curves, is usually applied ‘wet’ and requires greater skill on the installer’s part. A PAA is preferable when tackling compound curves, is usually applied ‘dry’ and can be used by installers of all skill levels.
For certain applications, such as fleet graphics for box trucks, some installers do not want the slideability of a PAA, but instead prefer the opportunity to tack the film right where they want it to be upon first contact. Their margin for error is very limited, but as expert installers, they prefer this challenge over the way a slideable adhesive behaves.
In most other cases, installers enjoy the extra freedom offered by slideability. And when they are tackling the complex curves and deep channels of most vehicles, it is necessary.
Different surface materials will also exhibit different levels of affinity for an adhesive. ‘Peel’ combines the effects of this surface affinity and the level of energy dissipation dictated by the adhesive’s rheology (i.e. flow). Hence, the same film will peel differently from glass than it will from a polytetrafluoroethylene (PTFE) surface like Teflon.
A heat gun helps stretch the film across compound curves.
To achieve a strong installation, it is best to choose an adhesive and a surface based on their mutual compatibility. The adhesive should have a lower surface energy than that of the material to which it will be applied. And if the material is modified by cleaning and roughing it, it will provide for stronger bonding at its surface.
Of course, the highest level of adhesion is not always desirable. A permanent adhesive is not intended for removal, so if there is a need to change out the graphic later on, it may be very difficult, even with heat, chemicals and tool. In some instances, more than 30 per cent of the adhesive could be left behind as residue.
A removable adhesive, on the other hand, may provide a medium to high level of tack, may be easily removable with heat and/or chemicals and may leave behind less than 30 per cent residue. And a changeable or ‘ultra-removable’ adhesive could prove even easier, providing medium tack, requiring little to no heat for removal and leaving behind little to no residue.
It is also important to note adhesion builds over time and with exposure to the elements. For this reason, an adhesive film left on a surface for longer than its warranted durability may become extremely difficult to remove.
Typically, graphic film manufacturers test their products for durability and weatherability across different climates and for varying periods of exposure. So, in general, signmakers should not need to test the materials in the same ways themselves. That said, surface adhesion test kits are available for checking the compatibility of a film and adhesive with a given surface.
