Posted by gmharris [71.105.34.147] on Monday, December 01, 2014 at 22:01:20 :
In Reply to: One coat on all of mine- posted by Chris Case [108.247.147.185] on Monday, December 01, 2014 at 21:11:28 :
of substances which stick to and/or seal a surface and no one explanation is going to fit all or even most primers.
The advantage of primer is that the manufacturer does not have to worry about factors such as color, UV resistance, gloss, smoothness and durability. The only significant factors are that the primer sticks to the substrate and the paint sticks to the primer. Thus the manufacturer does not have to worry about the paint adhering to a less adhesive substrate like metal.
The explanation as to why a particular primer sticks better than paint probably has to do with whether strong or weak molecular bonds are formed.
Here is a brief explanation of the adhesive quality of epoxy primer:
The ‘amine' curing agent has a molecular structure which typically consists of four hydrogen ‘arms and legs'. These hydrogens react with the oxirane (epoxy group) ring unit on the ends of the epoxy resin. The result is a new carbon-hydrogen bond, this time using the hydrogen from the curing agent and freeing the epoxy group's hydrogen to unite with the group's oxygen to form an OH (hydroxyl) pendant. This hydroxyl group contributes to the epoxy's outstanding adhesion to many substrates. The aromatic ring unit, which the hydroxyls attach to, helps provide the epoxies positive thermal and corrosion properties.