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What is Viscoelasticity, and Why Should I Care?

Viscoelasticity is one of the most important characteristics of a pressure sensitive adhesive (PSA) - but do you know what it means? By definition a viscoelastic material exhibits the characteristics of both a liquid and a solid - think silly putty.

If you roll silly putty into a ball, it will hold its shape for a time, like a solid, but will eventually begin to wet-out onto a surface forming a flat plane, like a liquid.

So how does this influence PSA selection and performance? Let's say you have two uneven, rough surfaces you are tying to bond. If you choose a thin, hard adhesive, the tape's viscoelasticity will not come into play as there is not enough adhesive to flow into the inconsistencies of the substrate - likely leading to adhesive failure. If you choose a high coat weight soft adhesive, the adhesive is more likely to flow into surface imperfections and fully wet-out - creating the strong stable bond you're trying to achieve.

It is important to keep in mind, however, that viscoelastic materials are also characterized by their dependence on both time and temperature. Unless they've been specially formulated for low- or high- temperature application, most PSAs require temperatures above 50ºF, and don't reach full adhesion immediately. A very general rule is that an adhesive will reach 50% total adhesion in 20 minutes, 80% within 24 hours, and 100% in 72 hours.

For more information on other factors to consider when selecting a PSA for your application, contact one of adhesive tape experts.