These studies were undertaken to examine holy particle size of epoxy phenol
novolac (EPN) powder coatings may affect adhesion to metal substrates. Par
ticle sizes of 21 and 83 mu m diameter were utilized. DSC analysis shows th
at the activation energies of crosslinking for the 21 mu m particle size is
41 kJ/mol and 58 kJ/mol for 83 mu m particle size which is attributed to t
he effect of particle size, and time-temperature-particle size (TTPS) param
eters are used to describe powder-liquid-solid from transformation process.
Although, the TTSP term represents a combination of intrinsic and extrinsi
c properties. We believe that this is the TTPS term that adequately describ
es the processes in which, in order for crosslinking reactions to occur, pa
rticles must initiate the flow. Quantitative attenuated total reflectance (
ATR) Fourier transform infrared (FTIR) spectroscopic analysis was used to f
ollow crosslinking processes by monitoring the decrease of oxirane concentr
ation, and showed that for thermal cure at 185 degrees C for 20 min, the ox
irane concentration decreases at a similar rate for 21 mu m and 83 mu m par
ticle sizes. The results of pull-off adhesion measurements from an Al subst
uate show that when the 21 mu m particle size is crosslinked for 10 min at
110, 140, and 170 degrees C, adhesion is consistently higher than for the s
ame coating system at 83 mu m particle size. This difference is attributed
to the finite time required for powder particles to reach a proper melt vis
cosity, followed by reactions of functional groups leading to crosslinking.
Extended cure times to 120 min for the 83 mu m particle resulted in adhesi
on similar to the 21 mu m particle size.