How to ensure a strong adhesive bond

Manufacturers rely on adhesives in many demanding applications. They are used to securely hold together parts of airplanes, automobiles and machinery, as well as baby products, mobile phones and more. To achieve optimal performance in these applications, there’s one step in the bonding process that simply cannot be ignored — surface preparation.

Surface energy

The surface in which the adhesive is being applied to is just as important as the adhesive itself. This is where surface energy comes in. For the adhesive to work properly, its surface energy needs to be lower than that of the surface it is being applied to.

Think of water on the hood of a car, for example. A waxed hood has a lower surface energy than water, so the water just rolls off the hood. However, a hood that is not waxed has a higher surface energy, so the water “wets out” on the hood and completely covers it.

With adhesives, “wetting out” creates a strong bond because the adhesive is able to spread across the entire substrate to create a larger contact area.

Increasing surface energy

When surface energy is too low, there are ways to increase it. First, make sure the substrate is clean. This is very important, because even a slight oil film left behind on a substrate can reduce adhesive performance by as much as 60 per cent. Next, make sure the surface is dry to ensure a strong bond. Lastly, adhesives stick better to surfaces that are rough. A light grit blast or sanding should do the trick to increase the bond area where the adhesive interacts with the substrate.

In most cases, a clean, dry and rough surface is generally all you need for a strong bond. However, if the part still has a low surface energy even after it is clean, dry and rough, use a primer. Primers can increase the surface energy of substrates so adhesives bond more effectively. If priming isn’t an option, there are alternate surface preparation methods, including flame treatment, surface roughening and chemical etching.

More information

As a leading provider of adhesive technologies, Henkel has the expertise to help customers select the most appropriate adhesive for the job, ensuring the best performance possible. To learn more, contact Henkel.

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