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Understanding Surface Energy

Surface energy…what is it? When talking about labels, you’ll hear people sometimes things like, “That material has low surface area.” or “This adhesive only works on high surface energy applications.” What are they talking about and how important is it?

When it comes to labels, surface energy is all about how well the adhesive is going to stick to a given application surface. In other words, how receptive to adhesive is the thing you are sticking labels to. The higher the surface energy of a material, the easier things stick; the lower, the harder it is. Consider a freshly waxed car. When it rains, water beads up into small droplets. In a rough approximation, this is the equivalent of adhesive on a low surface energy material. Now as the wax is removed over time, water starts to flatten out and pool up into larger clumps. This is more like adhesive on a high surface energy material.

Why do you care about this? Well, adhesives bond better when they are able to spread out over the full surface. So when objects with low surface energy (plastics for example) interact with adhesive, it is more difficult to get a complete bond. To counteract this, depending on where your label is going, you may need different formulations to achieve the desired performance results you are looking for.

To give you a feel for relative surface energy , here is a breakdown of some common materials. Bigger numbers have higher surface energy. Smaller numbers have lower.

Application Surface
Copper
Stainless Steel
Aluminum
Zinc
Tin
Glass
Lead
Phenolic
Nylon
Polyester
Epoxy Paint
Polyurethane Paint
ABS
Polycarbonate
Rigid PVC
Acrylic
PVA
Polystyrene
EVA
Polyethylene
Polypropylene
Polyvinyl
PTFE Flouropolymer

mJ/m^2
1103
1100-700
840
753
526
500-250
458
47
45
43
43
43
42
42
39
38
37
36
33
31
29
28
18