The most obvious job of a primer is to enhance adhesion. Since the early days of high-performance coatings such as PTFE, primers have been needed to help topcoats stick to a substrate. But today, primers have evolved to offer their own properties, giving design engineers more options when it comes to achieving the ideal surface properties.
One of the key properties that primers can offer enhance corrosion protection. This is important when the coating with the ideal surface properties won’t fully protect your substrate from environmental conditions.
Primers for Corrosion Protection from External Elements
The use of primers as added corrosion protection is common in the automotive industry, where corrosion from outdoor elements is vital. Most often, automotive companies will use a phosphate or zinc phosphate wash primer. The primer not only helps etch the topcoat into the metal, but it provides an extra layer of protection against weather elements that cause corrosion.
Primers for Corrosion Protection from Chemical Exposure
When the concern is protection from chemical corrosion, pure polyamide primers can provide the ideal solution. Whitford Worldwide makes a primer for its Xylan series called P92. P92 is a pure polyamide that will go on pinhole free, creating a strong barrier against chemical corrosion while providing an ideal layer for topcoats to adhere to. (P92 can be used effectively as a primer for many types of coatings, beyond the Xylan line.)
Many of the new PTFE products are self-priming or have resin systems designed to ensure excellent adhesion. But often, it is worth considering a unique primer and topcoat combination in which the primer provides more than just adhesion enhancement.
Primers for Edge Coverage and Increased Coating Strength
Another thing primers can do beyond simple adhesion is to help with edge coverage. Particularly in powder coating, primers can be used as fillers to smooth over sharp points and edges. (With any part, sharp edges often represent the weakest point of the coating.) If sharp edges have been causing coating failures, a simple primer (rather than any design changes) may be the ideal solution.