Surface Energy & Wetability

Wetability

A “wetable” surface is said to have “high surface energy,” liquid can spread across the substrate without the bunching of droplets. Low surface energy materials which do not “wet out” leave liquid droplets standing proud – imagine a freshly waxed car sprayed with water droplets – the drops bunch up at a steep angle to the paintwork.

Surface energy is normally measured in mJ/m² or Dynes. Generally, to be able to bond a material, it needs to be >36 mN/m. However, this can still be pretty hard to bond to, even with industrial adhesives.

Table showing surface energy values of common engineering materials. Figures in mJ/m².

As you can see, plastics exhibit the lowest surface energy. This makes them challenging for both industrial adhesives and printing inks to adhere to.

Bond Plastics with Low Surface Energy (LSE)

There are three ways to bond.

1. Modify the surface through chemical etching, flame, corona, or plasma treatment. The increase in energy opens up options for a variety of adhesives.
2. Use a primer and cyanoacrylate adhesive. Prime with Permabond POP Polyolefin Primer, then bond with Permabond cyanoacrylate adhesive. This combination also works well on silicone rubber. Check with us to see if this is a good option for your type of plastic.
3. Also available from Permabond are new structural acrylic industrial adhesives that bond untreated “problem” plastics like polypropylene, polyethylene, and even PTFE. They provide high bond strength performance and good resistance to environmental conditions.

For further information or technical advice, please contact Permabond’s helpline team.