The evidence presented in technical papers on delamination is often compelling,
which leads to the conclusion that the individual theories describe mechanisms for
different situations and that no one theory is exclusive or invalidates the others…
The coating delaminates (disbonds) from the metal when the
high pH breaks coating-polymer bonds and causes a blister to
grow laterally along the coated metal surface. The blister continues
to grow as long as water diffuses into the blister.
Figure 3 provides an example of water hydration of polymermetal
bonds that causes coating delamination. This phenomenon
is often referred to as wet adhesion loss. Water diffuses into and
through polymer coatings and hydrates the polymer-metal bonds,
causing the bonds to break. Bond breakage causes coating delamination
and in some instances substrate metal corrosion.
There are numerous papers supporting the various bonding
and disbonding (delamination) theories. The delamination
in Figures 1–3 appears to be significantly different from each
other. Indeed, the evidence presented in technical papers on
delamination is often compelling, which leads to the conclusion
that the individual theories describe mechanisms for different situations
and that no one theory is exclusive or invalidates the others. In other
words, the actual mechanism for delamination by a given spray
package formula is determined by the chemical composition of
the formula. Spray
June 2018 Spray 27
Figure 3: An example of water hydration of polymer-metal
bonds that causes coating delamination (wet adhesion loss)