Industrial Manufacturing and Engineering Blog

This blog includes insights from LOCTITE experts on a wide range of technologies that can improve industrial manufacturing, such as: instant bonding, structural bonding, machinery adhesives, and functional coatings/surface treatments, as well as equipment solutions. We will also cover more specific topics including: electric motors, speakers, cables and components, low pressure molding, specialty vehicles, fluid power equipment, liquid optically clear adhesives (LOCA), and more!

Why Proper Surface Preparation is Important to Ensure a Strong Adhesive Bond

    May 12, 2016

Adhesives can be seriously strong. They’re used in the manufacture of anything from airplanes, automobiles and massive machinery to baby products, golf clubs and mobile phones. These are demanding applications.

But if you’re hoping to achieve optimal performance, there’s a job that must be completed before an adhesive is applied: surface preparation.

The Importance of Surface Energy

To ensure a strong bond, the surface you’re applying an adhesive to is equally as important as the adhesive itself. Surface energy is the main measurement that you need to understand. An adhesive’s surface energy needs to be lower than that of the surface you’re applying it to in order for it to work correctly. 

Think of water on the hood of a car: a waxed hood has a lower surface energy than water, so the water beads up and rolls off the hood. An unwaxed hood has a higher surface energy, so the water “wets out” on the hood and completely covers it. 

wetting out

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.

Three Ways to Increase Surface Energy

If you find that your substrate’s surface energy is too low, there are ways to increase it. To start, it should be: 

1. Clean – If a substrate is dirty, your bond is only as strong as the adhesion of the contaminant to the part, not the adhesive to the part.

Contaminants can come from machining, protecting, handling, manufacturing, facility surroundings, and even from cleaners used previously that have left a film. Just a slight oil film left behind on a substrate can reduce adhesive performance by as much as 60 percent.

surface energy contaminant

2. Dry – A wet surface poses the same problems as a dirty one. Moisture between an adhesive and a substrate should be treated as a contaminant and removed to ensure a strong bond. 

3. Rough – A surface is best when made rough. A light grit blast or sanding will increase the bond area where the adhesive interacts with the substrate because a surface with peaks and valleys has more surface area than a completely flat surface. The roughness will also provide a slight mechanical grip for the adhesive to hold onto. 

Using Primers

Once the part is clean, dry and rough, it might still have a low surface energy. Some materials are just notoriously hard to bond. When that’s the case, primers can increase the surface energy of substrates so adhesives bond more effectively. 

As with choosing a cleaner, it’s best to consult with your supplier or local sales representative to discuss the proper product selection. In addition, you can contact our team directly.

Alternate Surface Preparation Methods 

When chemically priming a surface isn’t an option, there are alternate surface preparation methods ranging from flame treatment to surface roughening to chemical etching. What you choose will depend substrate materials, adhesive types and surface conditions.

That said, in most scenarios, a clean, dry and rough surface is generally all you need for a strong bond. 

Resources for Working with Different Materials

For more information on surface preparation, you can check out the following resources: 

Over to You

Do you have any questions about surface preparation? Let us know in the comments!

About the Author, Michael Pomykala

Mike is an Application Engineer for Henkel North America, based in Rocky Hill, CT. He is responsible for specialized technical support of the Electrical and Optical market and Defense market for North America. Mike also provides general technical support for the North Central region of the United States. Mike has been with Henkel for two years. He spent his first year in the Prism Program – a rotational program that provides training in various business roles throughout the General Industry segment at Henkel. Mike also holds Bachelors and Masters degrees in Chemical Engineering from the University of Connecticut.

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