- Author
-
Rosen, H. N.
|
Martin, J. W.
- Title
- Sorption of Moisture on Epoxy and Alkyd Free Films and Coated Steel Panels.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Journal
-
Journal of Coatings Technology,
Vol. 63,
No. 792,
85-93,
January 1991
- Keywords
-
films
|
steel panels
|
coatings
|
sorption
|
moisture
|
epoxy resins
|
equilibrium
- Abstract
- Sorption isotherm curves at 23 deg C were determined for alkyd and epoxy free films and coated steel panels as well as for alkyd "pocket" panels, consisting of an unadhered free film surrounding and enclosing the steel panel. The isotherms consist of an increasing linear portion to about 75% relative humidity (RH), followed by a rapidly rising nonlinear portion to 100% RH. A model assuming weak bonding forces between the paint film and water with microvoid condensation at high RH gave an excellent fit to the data. Transient sorption data on the approach to equilibrium conditions showed differences between alkyd and epoxy coatings. For alkyd films, surface boundary layer resistance was significant and sorption followed a Fickian model. For the epoxy coating, surface resistance was not significant and moisture movement was non-Fickian.