If it is challenging to adhere to a material due to its low surface energy, it is very critical to choose the correct adhesive to bond that material. There are various ways to increase the surface energy of a material, improving the ability to bond. Here are several different ways to modify surface energy.
Priming
The ability of a liquid to chemically interact at the surface can be improved with primers or adhesion promoters. Primers work by adding a monolayer or thin coating of a functional material to the surface. Primers are chemically designed so that one end of the molecules bond very well to low-surface-energy materials while the free end bonds very well to adhesives.
Plasma Treating
Plasma treatments expose the surface of a material to an ionized gas which changes the chemical reactivity of the surface atoms. There are several different varieties of plasma treating, and there many different companies specializing in plasma-treatment services.
Flame Treating
Flame treatment takes advantage of the combustion chemistry of a “flame” to chemically alter the surface atoms of a substrate. As with plasma treatments, there are a variety of companies specializing in flame treatment for different materials.
Surface cleanliness
Although we just spent a great deal of time understanding the intricacies of surface energy of materials, in reality, a material to be bonded will arrive with a surface that has been contaminated. This can include dust, oil, grease, fingerprints or any other debris capable of winding up on a surface.
Contamination can result in:
- Reduced contact between adhesive and substrate, preventing a bond
- De-tackified adhesive, preventing effective wet out
- Reduced bond strength
Therefore, it is important to make sure the surface is clean before bonding
Abrading – When Cleaning isn’t enough
There are times when cleaning alone is not capable of removing the contaminants on the surface of a material. Injection-molded plastics may contain traces of mold release agents that are designed to resist many solvents. Oxide layers of metals (e.g. rusted iron) are “bonded” to the surface and cannot be removed by solvent cleaning alone. Some industrial oils are resistant to solvents and chemicals with the goal of keeping a metal surface safe from harm during transit.
Surface Preparation Process Using Abrading
To prepare a surface adequately for bonding, it may be necessary to add an abrasion step to the process.
1. Clean first – a first round of cleaning can remove much of the contamination present and will prevent debris from smearing during abrasion.
2. Abrade – abrasion with standard abrasive paper or non-woven abrasive pads can remove the contaminated surface and provide roughness.
3. Clean – final cleaning removes any debris left over from abrasion and provides the new, clean surface for bonding.