Abstract
Phase segregation and stratification of coil coatings is of great interest to the paint
and coatings industry, both due to cost savings and increased efficiency. This work
looks at several coil coating formulations and uses different methods to explore the
reasons for phase segregation and ultimately stratification.
Polyester-polyester blends made up of a combination of linear and branched resins,
have shown to produce a three-layered structure with the low molecular weight
branched polyester being found at both the surface and the substrate. In this work,
increasing the curing time of the coating has shown to be ineffective at altering the
structure produced. This segregation of short, branched polyesters is understood as
being entropically favored, with the shorter branched chains able to fit into the
constraints of the surface interface, losing less energy than the longer chains found in
the bulk of the coating.
Immiscibility in a resin blend is commonly seen as a requirement for phase
segregation. Here the monomers that make up both the linear and branched polyester
have been examined using Molecular Dynamics. Those with a similar backbone such
as aromatic with aromatic or aliphatic-aliphatic have showed increased miscibility, in
comparison to hetero blends.
Differences in surface tension of resins in a polymer blend, have been historically seen
to explain the segregation of resins to the surface. In this work, an elastomeric system
has been explored, made up of an acrylic with a fluorinated resin, producing a coating
with the acrylic component at the surface. This is an unexpected result, as due to its
low surface tension, fluorinated resins normally dominate the surface of a blend.
Further understanding of the linear-branched polyester blend has been examined,
using the pendant drop technique, to measure the surface tension of various resins.
The pendant drop method is a cheap and easy technique available to the paints and
coatings industry. Both the linear and branched polyesters have shown to exhibit a
similar surface tension.
The use of Secondary Ion Mass Spectrometry with microtomy and multivariate analysis
has been extended in this work, identifying both the flow aid and the dispersant in the
formulated coating.