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66
Jan/Fev 2012
PAINT & PINTURA
2K Waterborne Epoxy: Implementing Resin Changes
New Generation Epoxy Resin Dispersion
The NewGen epoxy dispersion is based on a Type 1 resin that
has three distinctive polymer segments that bring benefits
to the final coating. First, it is based on Bisphenol A aroma-
tic segments that form planar crystalline hard films. Then
there is an aliphatic, hydrocarbon group that wets pigments
and non-polar substrates. The third segment is a polyether
segment that provides easy dispersibility and additive/filler
compatibility.
The hydrophobic segment imparts many of the performance
characteristics needed for corrosion protection. In water, the
epoxy groups on the hydrophobic Bis-A segments concentrate
toward the micelle’s hydrophobic center, whereas the more
hydrophilic portions of the polymer migrate toward the wa-
ter phase. The epoxy resin backbone is designed so that the
PEO segments will be surrounded by the hydrophobic polymer
segments in the cured film.
1
New Generation Curing Agent Dispersion
A NewGen curing agent dispersion was
developed to be compatible with the epoxy
resin dispersion. This improved compatibility
promotes the optimum particle coalescence
and high gloss early in pot life at low VOC.
Since the curing agent has mostly secondary
amine functionality, the risk of amine blush
formation is reduced.
Furthermore, the curing agent has a lower
T
g
than the epoxy resin to facilitate film
formation. This lower minimum film forming
temperature (MFFT) enables coatings with
very low VOCs. The higher molecular weights
of the epoxy and curing agent facilitate fas-
ter lacquer dry. This enables faster back-to-
-service times.
Formulation and Application
Development Using Waterborne Epoxy
Systems
A corrosion-resistant white primer and gray
enamel based on the NewGen waterbor-
ne epoxy system have been evaluated and
compared to a standard solvent-borne epoxy
polyamide system.
2,3
The waterborne epoxy
primer dries harder and has faster hardness
development (Table 1). The salt fog resis-
tance of the waterborne epoxy primer after
7-days cure is superior. The water immersion
resistance of the waterborne epoxy enamel
after 14-days cure is comparable to that
of the solvent-borne standard, but the salt
fog resistance of the waterborne coating is
significantly better. The enamel test results
also show improved water and salt spray
resistance versus the solvent-borne enamel
(Table 2).
Figure 1. Sandwich Nature of Cross-linked,
Epoxy-Polyamidoamine