Document Type
Article
Publication Date
9-1-2024
Abstract
Coating performance is influenced by factors inherent to formulation design and processing conditions. Understanding the complex interplay of these attributes enables for mitigating defects, such as sag, which is a gravity-driven phenomenon that impacts the aesthetic and functionality of a coating. The work herein investigates the impact of resin molecular weight and solvent choice on the drying kinetics and sag velocity in polymer films. These films, ranging in thickness from ~60 μm to ~120 μm were formulated with 45 % by weight polymer resin in one of two solvent packages with different relative evaporation rates (RER). Gravimetry was initially used to track drying rate 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 rate 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° 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.
Keywords
coating defects, non-invasive imaging, drying
Language
English
Publication Title
Progress in Organic Coatings
Grant
1931636
Rights
© The Author(s) 2024.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/), which permits non-commercial copying and redistribution of the material in any medium or format, provided the original work is not changed in any way and is properly cited.
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Issa, Marola W. and Wirth, Christpher L., "Impact of Resin Molecular Weight on Drying Kinetics and Sag of Coatings" (2024). Faculty Scholarship. 1101.
https://commons.case.edu/facultyworks/1101
Manuscript Version
Final Publisher Version