What Is The Role of The Car Primer?

It is well known that the construction of automotive refinish lacquer is made up of a number of lacquered layers: phosphating primer + plaster + primer + topcoat (single component) + varnish (two component); What is the role of the primer in whole paint layer?

Car primer is a paint under the topcoat, the main role is to increase the adhesion between the paint layer and the paint layer, can be filled in the gap between the plaster layer and the primer layer, provide a smooth construction surface for the subsequent spray paint, so that the decorative effect of the paint is more obvious.