Core Principles of Adhesion Considered
When trying to choose the right adhesive in any given situation, it is necessary to carefully consider the requirements of aesthetic appearance, the surrounding environment and the nature of the surface itself. We have laid out the basic principles of adhesion below to aid these considerations.
What Is Adhesion?
Adhesion is the attractive force, on a molecular level, between two dissimilar materials. An adhesive bond is stronger or weaker depending on the surface energy of the material in question. Greater levels of surface energy mean stronger molecular attraction – and this, in turn, results in increased levels of contact between the adhesive and the substrate (the material to which the adhesive is being stuck).
In other words, on a material with high surface energy, the adhesive is allowed to flow more, creating more contact across the surface and thus a stronger bond. In recent years, adhesives have been developed using modified acrylic or synthetic rubber to allow for better flow over substrates with low levels of surface energy.
Metal that has been painted with acrylic or enamel tends to have high surface energy, making adhesion easier to achieve. Treating metal with wax, however, leads to a low surface energy substrate. The most commonly used metal bonding adhesive tends to be epoxy-based, but companies such as http://www.ct1ltd.com/en also offer silicone- and polyurethane-based adhesives for use on metal surfaces, among others.
Contact between the surface and the adhesive is key to the creation of a strong bond. To ensure maximum adhesive contact, the surface should be clean and dry. Strong pressure is necessary to maximise contact between the adhesive and the substrate material, and longer periods and time and higher temperatures tend to increase both the amount of surface contact and the strength of the bond.
From this, we can deduce the problems that are faced when trying to create a strong adhesive bond. In environments subject to vibrations, such as work sites near a main road, the small but constant movements make it difficult for pressure to be consistently applied over the surface. Specialised adhesives have been developed to solve this. Likewise, in situations where the temperature is likely to fluctuate, such as outdoors in line of sight with the sun, normal adhesives may fail. Again, temperature-resistant adhesives are available for these circumstances.