Good adhesion is generally required whenever a coating is applied to a surface. In addition to a common case of painting, for example, adhesion is important in many industrial processes as well. Many products are composed of layers of different materials that all have specific function in a final product. For example, a milk carton is composed of layers of paper and polymer films and electronic sensor is a complex device with altering conductive and insulation layers. In order to these products fulfill their function, good adhesion between different layers is required. So, what are the requirements for good adhesion?
Good adhesion requires a clean surface
The most common reasons for adhesion failure are contamination. Any type of grease, oil or other impurities on the surface can cause the loss of adhesion. Making sure that the cleaning protocols are in place in your process is one of the most important things to ensure successful manufacturing. One way to determine the cleanliness of the surface is through contact angle measurements. As the contamination is often non-polar by nature, the contact angle of water on the unclean surface is higher than on a clean surface.
Drop of water on (left) Clean glass surface (right) dirty glass surface
Surface treatments should be applied to increase the wettability of the substrate
Apart from cleaning the surface, some type of surface treatment may also be required to ensure good bonding between the two layers. One of the most used surface treatments is plasma treatment. In addition to providing an extra cleaning step for the surface, it will also improve the wettability of the substrate through the introduction of hydroxyl-, carboxyl and/or amine groups. Good surface wettability is prerequisite to good adhesion.
Water contact angle measurements can again be used to evaluate the impact of selected surface treatment method. To read more how contact angle measurements have been utilized in industrial processes, please download the review below.