Fluoropolymers represent a special situation. Sodium naphthenate and potassium hydroxide etches are effective, and some methods for direct priming have been developed using molten materials to chemically modify the surface. Interestingly, copolymers of fluoropolymer with other materials allow surface preparation specific to either species. For example, a copolymer of fluoropolymer and polyethylene can be treated either at the fluorinated sites or the polyethylene sites using a chosen method such as naphthenate etch or flame treatment, respectively. Surface Preparation of Metals.
Metals are acid-etched or anodized using sulfuric, phosphoric, or chromic acids.
Stainless steels, nickel, platinum, and titanium all require some type of surface etch or anodization for proper bonding. This may be followed by application of a primer. Etching acts almost as a deep cleaning, but does not give a high surface profile. Anodization produces a deeper profile, but is most effective with low-viscosity primers and adhesives. Otherwise, the deep profile remains unfilled and the mechanical advantage is lost.