Influence of Surface Characteristics on the Degradation of Epoxyphenolic Coatings on Electrolytic Tinplates

E. Zumelzu¹ and F. Rull²

¹Instituto de Materiales y Procesos Termomecánicos, Universidad Austral de Chile, Casilla 567 – Valdivia, Chile.
Phone: 56-63-221863; Fax: 56-63-221033;
E-mail: ezumelzu@uach.cl

²Departamento de Física de la Materia Condensada,

Cristalografía y Mineralogía

Universidad de Valladolid, 47006, Valladolid, España.
E-mail: rull@fmc.uva.es

ABSTRACT

The surface characteristics, presence of contaminants, and lacquer composition of tinplates and protecting epoxyphenolic coatings were studied by X-ray photoelectron spectroscopy (XPS) techniques. The surface topography of coatings was analyzed by high- and low-resolution 3-D images obtained by atomic force microscopy (AFM). The degradation of the epoxyphenolic coating, or sanitary lacquer continuity, was measured by electrolytic porosity tests; surface defects were evident by the current level measured at the metal substrate-lacquer interface, indicating the existence of unprotected areas on the tinplate. The migration of metal ions to the solution was measured by atomic absorption methods, which provided information on the degradation of the tested tinplate.

The former analyses were supported both by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations, and EDAX chemical microanalysis.

During this study, relationships between the oxidation state of tinplate substrates and degradation by the solution, and between the existence of pores and surface discontinuities at the physico-chemical interactions and the microstructure of the various substrates at the coating bonding, were found.

Keywords: Tinplate, epoxyphenolic, surface, adherence, and degradation.