Impact of Resin Molecular Weight on Drying Kinetics and Sag of Coatings
arxiv(2024)
摘要
The work herein investigates the impact of resin molecular weight and solvent
choice on drying kinetics and sag velocity in polymer films. These films,
ranging in thickness from 60 micrometer to 120 micrometer were formulated
with 45
relative evaporation rates (RER). Gravimetry was initially used to track drying
kinetics and a one-dimensional diffusion model was utilized to compute the
apparent solvent diffusivity. In addition, the film thickness was tracked with
optical profilometry. Results from these measurements showed that for fixed
molecular weight the drying kinetics increased by approximately two-fold for
the high RER solvent, whereas the apparent diffusivity tended to increase with
increasing polymer molecular weight. Films formulated from higher molecular
weight resins had greater initial viscosities and thicknesses for identical
draw down blade clearance. By extension, the higher apparent diffusivities at
greater molecular weights were attributed to effects of prolonged evaporation
times for the thicker films. The sag velocity was measured through the
thickness of the film for these systems at a 5 degree incline using the
Variable Angle Inspection Microscope (VAIM). Measurements showed an increase in
sag velocity for thinner and less viscous films, which was somewhat surprising
both because a thinner film will experience lower gravitational stress and
quicker drying times as compared to a thicker film. From these data we conclude
that formulating a coating with higher molecular weight resin, although likely
to increase drying time, will tend to deter sag because of the large impact of
viscosity on these phenomena.
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