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Choosing an Adhesive - Sticking to Low Surface Energy Plastics

Every once in a while you run across a plastic to which stickers just wont stick. Why is that? Do they have grease on them? Well, unless they are a recently used butter container, the answer is probably no.

Several plastics are "non stick" by their very molecular structure. Think "Teflon". That is a plastic surface applied to cookware, which can resist heat, but which also has the handy characteristic of not having things stick to it. Whether it is overcooked scrambled eggs or an adhesive label, neither is likely to stick well to a smooth Teflon surface. Plastics like this are known as Low Surface Energy, or LSE plastics. Besides Teflon, other LSE plastics are polypropylene and polyethylene.

Surface energy as you may recall from school is what holds a soap bubble together. It's what makes calm water feel "hard" when you slap at it with your open palm. It is essentially the other surface molecules holding onto each other. But surface energy is a relative thing, and this is what determines how well (or badly) an adhesive will stick to a LSE plastic.

It turns out that if you pour a lower surface energy liquid onto a material that has a higher surface energy, the liquid will "wet out". That is, the liquid will not bead up, but rather completely smoothly cover the other surface. Think of water on an unwaxed car. But if you pour that same liquid onto a surface which has a lower surface energy that the liquid, then the liquid will bead up. Wax that same car and pour water on it; it beads up.

In fact, this is how you can tell if you have an LSE plastic surface. Simply spray or pour some water on it. If it beads up, it is either an LSE plastic, or someone may have waxed it, or recently eaten butter off of it.

So think of a pressure sensitive adhesive as a thick liquid. If you put it onto a surface with a higher surface energy than itself, it will "wet out" and cover the surface. This provides a strong bond because the adhesive is able to form links between the underlying surface, and the surface of the label all over the surface of the label.

But if you place that same pressure sensitive adhesive onto a surface that has a lower surface energy, the "liquid" adhesive will tend to bead up. It will not spread itself out completely to bond to the surface below it. That is what happens with an LSE plastic.

Choose a LSE laminating adhesive. This is a special 2 mil laminating adhesive designed by 3M to adhere to LSE plastics and be sure to choose one with 2 mil polyesters. These are formulated with an adhesive that has superior performance on LSE plastics. But you have to be advised that no adhesive will work as well on as LSE plastic as it will on a non LSE plastic.

Article Source: http://www.articleadventure.com

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