Adhesion - What is adhesion?
The tendency of dissimilar particles or surfaces to hold together; a state in which two different substances are held together by interfacial forces.
These forces may include chemical bonds (the surface atoms of the two materials bond together), covalent bonds (the surface atoms share electrons), electrostatic forces (positively and negatively charged surfaces are attracted to each other), mechanical interlocking (surface particles physically interlock), polymeric diffusion (molecules from one polymer penetrate into another polymer, while remaining bound to their original source), van der Waals forces (interaction between surface molecules based on regions of slight positive and negative charge within each molecule that are attracted to an oppositely charged region of a neighbouring molecule), or any combination of these.
In labelling, the primary interfacial forces that create adhesion (and cohesion) are van der Waals forces. Adhesion is important in the application of a label to a substrate and in the construction of a label from a number of layers; the adhesive and the substrate must have good adhesion to ensure the label remains on the substrate and the layers within the construction must have good adhesion to ensure the label doesn't delaminate.