Primers
are used when the adherence of the coating to the substrate is weak. Primer is an intermediate layer between the substrate and the coating having a strong adhesion to the both.Primers are commonly low viscosity liquids easily wetting the substrate surface and filling its the microscopic pores.
Primer and the topcoat (paint, adhesive, sealant) are usually made of the same polymer base.
The surface energy of a substrate coated with a primer is higher that increases the wettability and provides strong bonding of the topcoat to the substrate.
Besides enhancing adhesion primers also protect the substrate from oxidation and corrosion.
