Modern plastics can be a challenge for self-adhesive vinyls. Even if you have a highly-conformable face film, sticking self-adhesive graphics to many plastic substrates means you really need to think about choosing and specifying a special adhesive: new Avery MPI 2006 AP is a good example.
We asked Horst Rothenberger, to explain the science...
Taking a look at adhesive flow characteristics
‘It’s all a question of getting the adhesive to move across the application surface to create a nice, smooth, sticky layer on the application surface’, says Horst Rothenberger. ‘That’s easy to achieve on smooth surfaces like glass, metals, and ABS (acrylonitrile butadiene styrene), where the adhesive can flow like water across the surface. We call these high-energy surfaces for that reason.’
Horst continues: ‘Low-surface-energy substrates like PE don’t have that characteristic. Modern plastics are a good case in point. They often have low surface energy, and positively discourage adhesive from flowing across them. They’re often described as apolar – hence the ‘AP’ in the name of new Avery MPI 2006 AP. If you can’t achieve good adhesive flow over the application surface, the vinyl you’re applying simply won’t stick properly. Most modern plastics come into this low-surface-energy category – good examples are the polypropylenes (PP) and the polyethylenes (PE), with HDPE and LDPE the most frequently-encountered problem substrates for self-adhesive graphics.
‘Finally, you know very well that the lowest-suitable application temperature for a self-adhesive vinyl is always specified on our datasheets. That’s to do with adhesive flow too. The colder the temperature, the less able to “wet out” the application surface the adhesive becomes. Always pay attention to this aspect, particularly when you’re applying graphics out of doors or in an unheated workshop.’
What’s the answer?
‘Even for short-life applications’, says Horst, ‘it’s important to analyse the nature of the application substrate before deciding on film specification. Choosing the right adhesive is just as important as choosing the right face film if you want a satisfactory result. Fortunately, our Avery Dennison product range features a great choice of specialist adhesive formulations – developed across the corporation’s unmatched experience in a broad range of self-adhesive markets – to meet specific, technical application needs.’
Specify the right adhesive
Horst explains: ‘For applications on low-surface-energy surfaces, there are special adhesive “recipes” that include ingredients (especially what we call tackifiers) that not only enhance the flow characteristics of the mixture, but also deliver high initial tack, so that, as soon as the self-adhesive vinyl is applied, it immediately sticks fast where it touches the substrate, flowing across the rest of the application surface afterwards to deliver smooth, all-over adhesion.
‘So while they can present a real challenge,’ Horst concludes, ‘there’s no need for a low-surface-energy, apolar substrate to be a reason for adhesive failure. We have the answer in our standard product range – but if you need help in choosing, don’t hesitate to ask us!’